mediabunny/src/source.ts

/*!
 * Copyright (c) 2026-present, Vanilagy and contributors
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at https://mozilla.org/MPL/2.0/.
 */

import type { FileHandle } from 'node:fs/promises';
import {
	assert,
	binarySearchLessOrEqual,
	clamp,
	closedIntervalsOverlap,
	FilePath,
	isNumber,
	isThenable,
	isWebKit,
	MaybePromise,
	mergeRequestInit,
	normalizeHeaders,
	polyfillSymbolDispose,
	promiseWithResolvers,
	retriedFetch,
	toDataView,
	toUint8Array,
	wait,
	EventEmitter,
} from './misc';
import * as nodeAlias from './node';
import { InputDisposedError } from './input';
import { Logging } from './logging';

polyfillSymbolDispose();

const node = typeof nodeAlias !== 'undefined'
	? nodeAlias // Aliasing it prevents some bundler warnings
	: undefined!;

export type ReadResult = {
	bytes: Uint8Array;
	view: DataView;
	/** The offset of the bytes in the file. */
	offset: number;
};

export const DEFAULT_MIN_READ_POSITION = 0;
export const DEFAULT_MAX_READ_POSITION = Infinity;

/**
 * The events emitted by a {@link Source}, with each key being an event name and its value being the event data.
 * @group Input sources
 * @public
 */
export type SourceEvents = {
	/** Emitted each time data is retrieved from the source. */
	read: {
		/** The start of the retrieved range, inclusive. */
		start: number;
		/** The end of the retrieved range, exclusive. */
		end: number;
	};
};

let sourceFinalizationRegistry: FinalizationRegistry<() => unknown> | null = null;
if (typeof FinalizationRegistry !== 'undefined') {
	sourceFinalizationRegistry = new FinalizationRegistry((cleanup) => {
		cleanup();
	});
}

/**
 * The source base class, representing a resource from which bytes can be read.
 * @group Input sources
 * @public
 */
export abstract class Source extends EventEmitter<SourceEvents> {
	/** @internal */
	abstract _getFileSize(): number | null | undefined;
	/** @internal */
	abstract _read(
		start: number,
		end: number,
		minReadPosition: number,
		maxReadPosition: number,
	): MaybePromise<ReadResult | null>;
	/** @internal */
	abstract _dispose(): void;
	/** @internal */
	_disposed = false;
	/** @internal */
	_refCount = 0;
	/**
	 * Used internally to mark if a source stems from an HLS reading operation. Used to suppress certain warnings.
	 * @internal
	 */
	_usedForHls = false;
	/**
	 * FinalizationRegistry for rogue refs to this source that didn't get freed. It lives on the Source itself so that
	 * in case the Source transitively points back to itself and forms a cycle (for example through a custom
	 * CustomSource callback) that we're not leaking memory.
	 * @internal
	 */
	_refFinalizationRegistry: FinalizationRegistry<Source> | null = null;

	/** @internal */
	private _sizePromise: Promise<number | null> | null = null;

	constructor() {
		super();

		if (typeof FinalizationRegistry !== 'undefined') {
			this._refFinalizationRegistry = new FinalizationRegistry((source) => {
				source._decrementRefCount();
			});
		}
	}

	/**
	 * Resolves with the total size of the file in bytes. This function is memoized, meaning only the first call
	 * will retrieve the size.
	 *
	 * Returns null if the source is unsized.
	 */
	async getSizeOrNull() {
		if (this._disposed) {
			throw new InputDisposedError();
		}

		return this._sizePromise ??= (async () => {
			let size = this._getFileSize();
			if (size !== undefined) {
				return size;
			}

			await this._read(0, 1, DEFAULT_MIN_READ_POSITION, DEFAULT_MAX_READ_POSITION);
			size = this._getFileSize();
			assert(size !== undefined);

			return size;
		})();
	}

	/**
	 * Resolves with the total size of the file in bytes. This function is memoized, meaning only the first call
	 * will retrieve the size.
	 *
	 * Throws an error if the source is unsized.
	 */
	async getSize() {
		if (this._disposed) {
			throw new InputDisposedError();
		}

		const result = await this.getSizeOrNull();
		if (result === null) {
			throw new Error('Cannot determine the size of an unsized source.');
		}

		return result;
	}

	/**
	 * Returns a new {@link RangedSource} that maps data onto this source using the given offset and length. If a length
	 * is not provided, the ranged source spans until the end of this source's data.
	 *
	 * Useful for reading files that are embedded within larger files.
	 */
	slice(offset: number, length?: number) {
		if (!Number.isInteger(offset) || offset < 0) {
			throw new TypeError('offset must be a non-negative integer.');
		}
		if (length !== undefined && (!Number.isInteger(length) || length < 0)) {
			throw new TypeError('length, when provided, must be a non-negative integer.');
		}

		return new RangedSource(this, offset, length);
	}

	/**
	 * Called each time data is retrieved from the source. Will be called with the retrieved range (end exclusive).
	 *
	 * @deprecated Use `source.on('read', ({ start, end }) => ...)` instead.
	 */
	onread: ((start: number, end: number) => unknown) | null = null;

	/** @internal */
	_dispatchRead(start: number, end: number) {
		// eslint-disable-next-line @typescript-eslint/no-deprecated
		this.onread?.(start, end);
		this._emit('read', { start, end });
	}

	/**
	 * Creates a new `SourceRef` pointing to this source. You are expected to call `.free()` on said `SourceRef` when
	 * you're done with it.
	 */
	ref() {
		return new SourceRef(this);
	}

	/** @internal */
	_incrementRefCount() {
		this._refCount++;
	}

	/** @internal */
	_decrementRefCount() {
		this._refCount--;

		if (this._refCount === 0) {
			this._dispose();
			this._disposed = true;
		}
	}
}

/**
 * A reference to a {@link Source}, used to manage a source's lifecycle. Creating a `SourceRef` via {@link Source.ref}
 * increases that source's internal reference count. As long as a source has a non-zero reference count, it is assumed
 * to still be in use. Once all references are freed via {@link SourceRef.free}, the source gets disposed.
 *
 * @group Input sources
 * @public
 */
export class SourceRef<S extends Source = Source> implements Disposable {
	/** @internal */
	private _source: S | null;
	/** @internal */
	private _freed = false;

	/** @internal */
	constructor(source: S) {
		if (source._disposed) {
			throw new Error('Cannot ref a disposed source.');
		}

		source._incrementRefCount();
		source._refFinalizationRegistry?.register(this, source, this);

		this._source = source;
	}

	/** The {@link Source} this ref references. Accessing this field throws an error after having freed the ref. */
	get source() {
		if (!this._source) {
			throw new Error('Can\'t get source; ref has already been freed.');
		}

		return this._source;
	}

	/** Whether or not this reference has been freed via {@link SourceRef.free}. */
	get freed() {
		return this._freed;
	}

	/**
	 * Frees the ref, decrementing the source's internal reference count. If the source's internal reference count
	 * reaches zero, it gets disposed. To catch bugs, this method throws if the ref is already freed.
	 */
	free() {
		if (this._freed) {
			throw new Error('Illegal operation: double free on SourceRef.');
		}

		const source = this.source;
		assert(source._refCount > 0);

		source._decrementRefCount();
		source._refFinalizationRegistry?.unregister(this);

		this._freed = true;
		this._source = null;
	}

	/**
	 * Calls {@link SourceRef.free}.
	 */
	[Symbol.dispose]() {
		if (!this.freed) {
			this.free();
		}
	}
}

/**
 * A source which can create new sources from file paths. Required for multi-file inputs such as HLS playlists.
 * @public
 * @group Input sources
 */
export abstract class PathedSource extends Source {
	constructor(
		/**
		 * The path that points to the root file; the entry file of the media.
		 *
		 * This path may be modified by the source to indicate a redirect: an updated path to perform new requests
		 * relative to.
		 */
		public rootPath: FilePath,
		/** The callback that is called for each requested file; must return a {@link Source} or {@link SourceRef}. */
		public readonly requestHandler: (request: SourceRequest) => MaybePromise<Source | SourceRef>,
	) {
		if (typeof rootPath !== 'string') {
			throw new TypeError('rootPath must be a string.');
		}
		if (typeof requestHandler !== 'function') {
			throw new TypeError('requestHandler must be a function.');
		}

		super();
	}

	/** @internal */
	_resolveRequest(request: SourceRequest): MaybePromise<SourceRef> {
		const result = this.requestHandler(request);

		const handle = (result: Source | SourceRef) => {
			if (!(result instanceof Source || result instanceof SourceRef)) {
				throw new TypeError('requestHandler must return or resolve to a Source or SourceRef.');
			}

			const ref = result instanceof Source
				? result.ref()
				: result;

			ref.source._usedForHls ||= this._usedForHls;

			return ref;
		};

		if (isThenable(result)) {
			return result.then(handle);
		} else {
			return handle(result);
		}
	}
}

/**
 * A request for a {@link Source} at the given path.
 * @group Input sources
 * @public
 */
export type SourceRequest = {
	/** The requested file path. */
	path: FilePath;
	/** Whether the requested file is the root file. */
	isRoot: boolean;
};

export const sourceRequestsAreEqual = (a: SourceRequest, b: SourceRequest) => {
	return a.path === b.path;
};

/**
 * A custom multi-file source where each file is uniquely identified by a {@link FilePath} and can be resolved to
 * an arbitrary {@link Source}.
 *
 * @public
 * @group Input sources
 */
export class CustomPathedSource extends PathedSource {
	/** @internal */
	_root: SourceRef | null = null;
	/** @internal */
	_rootRequest: Promise<SourceRef> | null = null;

	/** @internal */
	override _read(
		start: number,
		end: number,
		minReadPosition: number,
		maxReadPosition: number,
	): MaybePromise<ReadResult | null> {
		if (!this._root) {
			if (!this._rootRequest) {
				const result = this._resolveRequest({ path: this.rootPath, isRoot: true });

				const handle = (result: Source | SourceRef) => {
					const ref = result instanceof Source
						? result.ref()
						: result;

					this._root = ref;
					this._rootRequest = null;

					return ref;
				};

				if (isThenable(result)) {
					this._rootRequest = result.then(handle);
				} else {
					handle(result);
					assert(this._root);
				}
			}

			if (this._rootRequest) {
				return this._rootRequest.then(ref => ref.source._read(start, end, minReadPosition, maxReadPosition));
			}
		}

		return this._root!.source._read(start, end, minReadPosition, maxReadPosition);
	}

	/** @internal */
	override _getFileSize(): number | null | undefined {
		if (this._root) {
			return this._root.source._getFileSize();
		}

		return undefined;
	}

	/** @internal */
	override _dispose(): void {
		if (this._root) {
			this._root.free();
		} else if (this._rootRequest) {
			void this._rootRequest
				.then(ref => ref.free());
		}
	}
}

/**
 * A source backed by an ArrayBuffer or ArrayBufferView, with the entire file held in memory.
 * @group Input sources
 * @public
 */
export class BufferSource extends Source {
	/** @internal */
	_bytes: Uint8Array;
	/** @internal */
	_view: DataView;
	/** @internal */
	_onreadCalled = false;

	/**
	 * Creates a new {@link BufferSource} backed by the specified `ArrayBuffer`, `SharedArrayBuffer`,
	 * or `ArrayBufferView`.
	 */
	constructor(buffer: AllowSharedBufferSource) {
		if (
			!(buffer instanceof ArrayBuffer)
			&& !(typeof SharedArrayBuffer !== 'undefined' && buffer instanceof SharedArrayBuffer)
			&& !ArrayBuffer.isView(buffer)
		) {
			throw new TypeError('buffer must be an ArrayBuffer, SharedArrayBuffer, or ArrayBufferView.');
		}

		super();

		this._bytes = toUint8Array(buffer);
		this._view = toDataView(buffer);
	}

	/** @internal */
	_getFileSize(): number {
		return this._bytes.byteLength;
	}

	/** @internal */
	_read(): ReadResult {
		if (!this._onreadCalled) {
			// We just say the first read retrieves all bytes from the source (which, I mean, it does)
			this._dispatchRead(0, this._bytes.byteLength);
			this._onreadCalled = true;
		}

		return {
			bytes: this._bytes,
			view: this._view,
			offset: 0,
		};
	}

	/** @internal */
	_dispose() {}
}

/**
 * Options for {@link BlobSource}.
 * @group Input sources
 * @public
 */
export type BlobSourceOptions = {
	/** The maximum number of bytes the cache is allowed to hold in memory. Defaults to 8 MiB. */
	maxCacheSize?: number;
	/**
	 * Defaults to `true`. When `true`, Mediabunny will acquire a `ReadableStream` reader internally to efficiently read
	 * data from the blob. Since this can lead to errors in some (very) rare cases due to browser bugs, you can set this
	 * field to `false` to try a slower but more stable reading method.
	 */
	useStreamReader?: boolean;
};

/**
 * A source backed by a [`Blob`](https://developer.mozilla.org/en-US/docs/Web/API/Blob). Since a
 * [`File`](https://developer.mozilla.org/en-US/docs/Web/API/File) is also a `Blob`, this is the source to use when
 * reading files off the disk.
 * @group Input sources
 * @public
 */
export class BlobSource extends Source {
	/** @internal */
	_blob: Blob;
	/** @internal */
	_options: BlobSourceOptions;
	/** @internal */
	_orchestrator: ReadOrchestrator;

	/**
	 * Creates a new {@link BlobSource} backed by the specified
	 * [`Blob`](https://developer.mozilla.org/en-US/docs/Web/API/Blob).
	 */
	constructor(blob: Blob, options: BlobSourceOptions = {}) {
		if (!(blob instanceof Blob)) {
			throw new TypeError('blob must be a Blob.');
		}
		if (!options || typeof options !== 'object') {
			throw new TypeError('options must be an object.');
		}
		if (
			options.maxCacheSize !== undefined
			&& (!isNumber(options.maxCacheSize) || options.maxCacheSize < 0)
		) {
			throw new TypeError('options.maxCacheSize, when provided, must be a non-negative number.');
		}
		if (options.useStreamReader !== undefined && typeof options.useStreamReader !== 'boolean') {
			throw new TypeError('options.useStreamReader, when provided, must be a boolean.');
		}

		super();

		this._blob = blob;
		this._options = options;

		this._orchestrator = new ReadOrchestrator({
			maxCacheSize: options.maxCacheSize ?? (8 * 2 ** 20 /* 8 MiB */),
			maxWorkerCount: 4,
			runWorker: this._runWorker.bind(this),
			prefetchProfile: PREFETCH_PROFILES.fileSystem,
		});

		this._orchestrator.fileSize = blob.size;
	}

	/** @internal */
	_getFileSize(): number {
		return this._orchestrator.fileSize!; // Faster than blob.size
	}

	/** @internal */
	_read(
		start: number,
		end: number,
		minReadPosition: number,
		maxReadPosition: number,
	): MaybePromise<ReadResult | null> {
		return this._orchestrator.read(start, end, minReadPosition, maxReadPosition);
	}

	/** @internal */
	_readers = new WeakMap<ReadWorker, ReadableStreamDefaultReader<Uint8Array> | null>();

	/** @internal */
	private async _runWorker(worker: ReadWorker) {
		assert(worker.strictTarget);

		let reader = this._readers.get(worker);
		if (reader === undefined) {
			// https://github.com/Vanilagy/mediabunny/issues/184
			// WebKit has critical bugs with blob.stream():
			// - WebKitBlobResource error 1 when streaming large files
			// - Memory buildup and reload loops on iOS (network process crashes)
			// - ReadableStream stalls under backpressure (especially video)
			// Affects Safari and all iOS browsers (Chrome, Firefox, etc.).
			// Use arrayBuffer() fallback for WebKit browsers.
			if ('stream' in this._blob && !isWebKit() && this._options.useStreamReader !== false) {
				// Get a reader of the blob starting at the required offset, and then keep it around
				const slice = this._blob.slice(worker.currentPos);
				reader = slice.stream().getReader();
			} else {
				// We'll need to use more primitive ways
				reader = null;
			}

			this._readers.set(worker, reader);
		}

		while (worker.currentPos < worker.targetPos && !worker.aborted) {
			if (reader) {
				const { done, value } = await reader.read();
				if (done) {
					this._orchestrator.onWorkerFinished(worker);
					throw new Error('Blob reader stopped unexpectedly before all requested data was read.');
				}

				if (worker.aborted) {
					break;
				}

				this._dispatchRead(worker.currentPos, worker.currentPos + value.length);
				this._orchestrator.supplyWorkerData(worker, value);
			} else {
				const data = await this._blob.slice(worker.currentPos, worker.targetPos).arrayBuffer();

				if (worker.aborted) {
					break;
				}

				this._dispatchRead(worker.currentPos, worker.currentPos + data.byteLength);
				this._orchestrator.supplyWorkerData(worker, new Uint8Array(data));
			}
		}

		this._orchestrator.signalWorkerStoppedRunning(worker);

		if (worker.aborted) {
			// MDN: "Calling this method signals a loss of interest in the stream by a consumer."
			await reader?.cancel();
		}
	}

	/** @internal */
	_dispose() {
		this._orchestrator.dispose();
	}
}

const URL_SOURCE_MIN_LOAD_AMOUNT = 0.5 * 2 ** 20; // 0.5 MiB
const DEFAULT_RETRY_DELAY
	= ((previousAttempts, error, src) => {
		// Check if this could be a CORS error. If so, we cannot recover from it and
		// should not attempt to retry.
		// CORS errors are intentionally not opaque, so we need to rely on heuristics.
		const couldBeCorsError = error instanceof Error
			&& (
				error.message.includes('Failed to fetch') // Chrome
				|| error.message.includes('Load failed') // Safari
				|| error.message.includes('NetworkError when attempting to fetch resource') // Firefox
			)
			&& typeof window !== 'undefined'; // CORS only happens in browser environments

		if (couldBeCorsError) {
			let originOfSrc: string | null = null;
			// Checking if the origin is different, because only then a CORS error could originate
			try {
				if (typeof window !== 'undefined' && typeof window.location !== 'undefined') {
					originOfSrc = new URL(src instanceof Request ? src.url : src, window.location.href).origin;
				}
			} catch {
				// URL parse failed
			}

			// If user is offline, it is probably not a CORS error.
			const isOnline
			= typeof navigator !== 'undefined' && typeof navigator.onLine === 'boolean' ? navigator.onLine : true;

			if (isOnline && originOfSrc !== null && originOfSrc !== window.location.origin) {
				Logging._warn(
					`Request will not be retried because a CORS error was suspected due to different origins. You can`
					+ ` modify this behavior by providing your own function for the 'getRetryDelay' option.`,
				);
				return null;
			}
		}

		return Math.min(2 ** (previousAttempts - 2), 16);
	}) satisfies UrlSourceOptions['getRetryDelay'];

const warnedOrigins = new Set<string>();

/**
 * Options for {@link UrlSource}.
 * @group Input sources
 * @public
 */
export type UrlSourceOptions = {
	/**
	 * The [`RequestInit`](https://developer.mozilla.org/en-US/docs/Web/API/RequestInit) used by the Fetch API. Can be
	 * used to further control the requests, such as setting custom headers.
	 *
	 * The `signal` field is not available, as Mediabunny controls request cancellation internally. If you want to
	 * cancel ongoing requests, use {@link Input.dispose}.
	 */
	requestInit?: Omit<RequestInit, 'signal'>;

	/**
	 * A function that returns the delay (in seconds) before retrying a failed request. The function is called
	 * with the number of previous, unsuccessful attempts, as well as with the error with which the previous request
	 * failed. If the function returns `null`, no more retries will be made.
	 *
	 * By default, it uses an exponential backoff algorithm that never gives up unless
	 * a CORS error is suspected (`fetch()` did reject, `navigator.onLine` is true and origin is different).
	 */
	getRetryDelay?: (previousAttempts: number, error: unknown, url: string | URL | Request) => number | null;

	/** The maximum number of bytes the cache is allowed to hold in memory. Defaults to 64 MiB. */
	maxCacheSize?: number;

	/** The maximum number of parallel requests to use for fetching. Defaults to 2. */
	parallelism?: number;

	/**
	 * A WHATWG-compatible fetch function. You can use this field to polyfill the `fetch` function, add missing
	 * features, or use a custom implementation.
	 */
	fetchFn?: typeof fetch;
};

/**
 * A source backed by a URL. This is useful for reading data from the network. Requests will be made using an optimized
 * reading and prefetching pattern to minimize request count and latency. Works best with servers that support HTTP
 * range requests; otherwise, resources must be streamed and read sequentially.
 * @group Input sources
 * @public
 */
export class UrlSource extends PathedSource {
	/** @internal */
	_url: string | URL | Request;
	/** @internal */
	_getRetryDelay: (previousAttempts: number, error: unknown, url: string | URL | Request) => number | null;
	/** @internal */
	_options: UrlSourceOptions;
	/** @internal */
	_requestInit: RequestInit;
	/** @internal */
	_offset = 0;
	/** @internal */
	_length: number | null = null;
	/** @internal */
	_orchestrator: ReadOrchestrator;
	/**
	 * Note that this value being true does NOT mean the file size can't change anymore; it just signals that we have at
	 * least checked if we know the file size or not.
	 * @internal
	 */
	_fileSizeDetermined = false;
	/**
	 * When the server doesn't support range requests, we abandon the orchestrator and instead defer to an internal
	 * ReadableStreamSource wrapping the response body, which pulls new data only when reads demand it.
	 * @internal
	 */
	_sequentialBacking: ReadableStreamSource | null = null;

	/**
	 * Creates a new {@link UrlSource} backed by the resource at the specified URL.
	 *
	 * When passing a `Request` instance, note that its `signal` will be overridden by Mediabunny; if you want to cancel
	 * ongoing requests, use {@link Input.dispose}.
	 */
	constructor(
		url: string | URL | Request,
		options: UrlSourceOptions = {},
	) {
		if (
			typeof url !== 'string'
			&& !(url instanceof URL)
			&& !(typeof Request !== 'undefined' && url instanceof Request)
		) {
			throw new TypeError('url must be a string, URL or Request.');
		}
		if (!options || typeof options !== 'object') {
			throw new TypeError('options must be an object.');
		}
		if (options.requestInit !== undefined && (!options.requestInit || typeof options.requestInit !== 'object')) {
			throw new TypeError('options.requestInit, when provided, must be an object.');
		}
		if (options.getRetryDelay !== undefined && typeof options.getRetryDelay !== 'function') {
			throw new TypeError('options.getRetryDelay, when provided, must be a function.');
		}
		if (
			options.maxCacheSize !== undefined
			&& (!isNumber(options.maxCacheSize) || options.maxCacheSize < 0)
		) {
			throw new TypeError('options.maxCacheSize, when provided, must be a non-negative number.');
		}
		if (options.parallelism !== undefined && (!Number.isInteger(options.parallelism) || options.parallelism < 1)) {
			throw new TypeError('options.parallelism, when provided, must be a positive number.');
		}
		if (options.fetchFn !== undefined && typeof options.fetchFn !== 'function') {
			throw new TypeError('options.fetchFn, when provided, must be a function.');
			// Won't bother validating this function beyond this
		}

		const urlString = url instanceof Request
			? url.url
			: url instanceof URL
				? url.href
				: url;

		super(
			urlString,
			request => new UrlSource(request.path, this._options),
		);

		this._url = url;
		this._options = options;
		this._getRetryDelay = options.getRetryDelay ?? DEFAULT_RETRY_DELAY;

		// A user-supplied Range header is interpreted as a byte offset (and optional length) into the resource. We
		// pull it out of the request and remember it for subsequent requests.
		this._requestInit = { ...options.requestInit };

		let rangeHeaderValue: string | null = null;

		if (options.requestInit?.headers) {
			const headers = { ...normalizeHeaders(options.requestInit.headers) };
			const rangeKey = Object.keys(headers).find(key => key.toLowerCase() === 'range');
			if (rangeKey !== undefined) {
				rangeHeaderValue = headers[rangeKey]!;
				delete headers[rangeKey];
				this._requestInit.headers = headers;
			}
		}

		if (url instanceof Request) {
			const requestRange = url.headers.get('Range');
			if (requestRange !== null) {
				rangeHeaderValue ??= requestRange;

				// Clone the request so we don't mutate the user's object, then strip the Range header
				const strippedRequest = new Request(url);
				strippedRequest.headers.delete('Range');
				this._url = strippedRequest;
			}
		}

		if (rangeHeaderValue !== null) {
			const parsed = parseByteRangeHeader(rangeHeaderValue);
			if (parsed) {
				this._offset = parsed.offset;
				this._length = parsed.length;
			}
		}

		// Most files in the real-world have a single sequential access pattern, but having two in parallel can
		// also happen
		const DEFAULT_PARALLELISM = 2;

		this._orchestrator = new ReadOrchestrator({
			maxCacheSize: options.maxCacheSize ?? (64 * 2 ** 20 /* 64 MiB */),
			maxWorkerCount: options.parallelism ?? DEFAULT_PARALLELISM,
			runWorker: this._runWorker.bind(this),
			prefetchProfile: PREFETCH_PROFILES.network,
		});
	}

	/** @internal */
	_getFileSize(): number | null | undefined {
		if (!this._fileSizeDetermined) {
			return this._length !== null ? this._length : undefined;
		}

		const baseSize = this._sequentialBacking
			? this._sequentialBacking._endIndex
			: this._orchestrator.fileSize;
		if (baseSize === null) {
			return this._length !== null ? this._length : null;
		}

		return clamp(baseSize - this._offset, 0, this._length ?? Infinity);
	}

	/** @internal */
	_read(
		start: number,
		end: number,
		minReadPosition: number,
		maxReadPosition: number,
	): MaybePromise<ReadResult | null> {
		if (this._length !== null && end > this._length) {
			return null;
		}

		const offset = this._offset;
		const result = this._sequentialBacking
			? this._sequentialBacking._read(offset + start, offset + end)
			: this._orchestrator.read(
					offset + start,
					offset + end,
					Math.max(offset + minReadPosition, offset),
					offset + Math.min(maxReadPosition, this._length ?? Infinity),
				);

		const processResult = (result: ReadResult | null) => {
			if (!result) {
				return null;
			}

			result.offset -= this._offset;
			return result;
		};

		if (isThenable(result)) {
			return result.then(processResult);
		} else {
			return processResult(result);
		}
	}

	/** @internal */
	private async _runWorker(worker: ReadWorker) {
		// The outer loop is for resuming a request if it dies mid-response
		while (true) {
			const abortController = new AbortController();
			const response = await retriedFetch(
				this._options.fetchFn ?? fetch,
				this._url,
				mergeRequestInit(this._requestInit, {
					headers: {
						// Always sending a range request is a good way to probe if the server supports them
						Range: `bytes=${worker.currentPos}-`,
					},
					signal: abortController.signal,
				}),
				this._getRetryDelay,
				() => this._disposed,
			);

			if (!response.ok) {
				// eslint-disable-next-line @typescript-eslint/no-base-to-string
				throw new Error(`Error fetching ${String(this._url)}: ${response.status} ${response.statusText}`);
			}

			if (response.redirected) {
				// Modify our own root path so that future subrequests get made relative to the redirected URL
				this.rootPath = response.url;
			}

			outer:
			if (this._orchestrator.fileSize === null) {
				// See if we can deduce the file size from the response

				const contentRange = response.headers.get('Content-Range');
				if (contentRange) {
					const match = /\/(\d+)/.exec(contentRange);
					if (match) {
						this._orchestrator.supplyFileSize(Number(match[1]));
						break outer;
					}
				}

				const contentLength = response.headers.get('Content-Length');
				if (contentLength) {
					// Note: For range requests, this is _technically_ not correct, as the range response could contain
					// less data than was requested. In practice, it seems most servers don't do this though, and the
					// Content-Length header actually contains the length until the end of the file.
					// A non-206 response always spans the entire resource, no matter what range we asked for.
					const basePos = response.status === 206 ? worker.currentPos : 0;
					this._orchestrator.supplyFileSize(basePos + Number(contentLength));
				}
			}

			this._fileSizeDetermined = true; // Yes, this is correct even if file size is still null

			if (!response.body) {
				throw new Error(
					'Missing HTTP response body stream. The used fetch function must provide the response body as a'
					+ ' ReadableStream.',
				);
			}

			if (response.status !== 206) {
				if (this._sequentialBacking) {
					// Another worker already discovered the missing range request support and initiated the
					// transition into sequential mode; this response is of no use anymore
					void response.body.cancel();
					return;
				}

				if (!this._usedForHls) {
					const url = new URL(
						this._url instanceof Request ? this._url.url : this._url,
						typeof window !== 'undefined' ? window.location.href : undefined,
					);

					if (
						url.origin !== 'null'
						// Don't show the warning for M3U8 playlist files, it's irrelevant for those
						&& !(url.pathname.endsWith('.m3u8') || url.pathname.endsWith('.m3u'))
					) {
						if (!warnedOrigins.has(url.origin)) {
							Logging._warn(
								`HTTP server (origin ${url.origin}) did not respond to a range request with 206 Partial`
								+ ' Content, meaning the resource will now be streamed sequentially, with old data'
								+ ' being evicted from the cache. Reads into evicted regions will throw. To enable'
								+ ' efficient media file streaming across a network, please make sure your server'
								+ ' supports range requests. Alternatively, set maxCacheSize to Infinity in the'
								+ ' UrlSource options to keep the entire resource in memory.',
							);
							warnedOrigins.add(url.origin);
						}
					}
				}

				this._transitionToSequentialMode(response.body);
				return;
			}

			const reader = response.body.getReader();

			while (true) {
				if (worker.currentPos >= worker.targetPos || worker.aborted) {
					abortController.abort();
					this._orchestrator.signalWorkerStoppedRunning(worker);

					return;
				}

				let readResult: ReadableStreamReadResult<Uint8Array>;

				try {
					readResult = await reader.read();
				} catch (error) {
					if (this._disposed) {
						// No need to try to retry
						throw error;
					}

					const retryDelayInSeconds = this._getRetryDelay(1, error, this._url);
					if (retryDelayInSeconds !== null) {
						Logging._error('Error while reading response stream. Attempting to resume.', error);
						await wait(1000 * retryDelayInSeconds);

						break;
					} else {
						throw error;
					}
				}

				if (worker.aborted) {
					continue; // Cleanup happens in next iteration
				}

				const { done, value } = readResult;

				if (done) {
					if (worker.currentPos >= worker.targetPos) {
						// All data was delivered, we're good
						this._orchestrator.onWorkerFinished(worker);
						return;
					}

					if (worker.strictTarget) {
						// The response stopped early, before the target. This can happen if server decides to cap range
						// requests arbitrarily, even if the request had an uncapped end. In this case, let's fetch the
						// rest of the data using a new request.
						break;
					} else {
						// Assume we have simply reached the end of the resource
						this._orchestrator.onWorkerFinished(worker);
						return;
					}
				}

				this._dispatchRead(worker.currentPos, worker.currentPos + value.length);
				this._orchestrator.supplyWorkerData(worker, value);
			}
		}

		// The previous UrlSource had logic for circumventing https://issues.chromium.org/issues/436025873; I haven't
		// been able to observe this bug with the new UrlSource (maybe because we're using response streaming), so the
		// logic for that has vanished for now. Leaving a comment here if this becomes relevant again.
	}

	/** @internal */
	private _transitionToSequentialMode(body: ReadableStream<Uint8Array>) {
		// The server ignored our range request and is sending the entire resource from byte 0. Instead of downloading
		// and caching the whole thing, we hand the response over to an internal ReadableStreamSource, which pulls new
		// data only when reads demand it and evicts old data as usual. The response body is wrapped in a stream that
		// transparently resumes when the connection dies.

		let currentReader = body.getReader();
		let streamPosition = 0;
		let skipRemaining = 0;

		const wrappedStream = new ReadableStream<Uint8Array>({
			pull: async (controller) => {
				while (true) {
					let readResult: ReadableStreamReadResult<Uint8Array>;

					try {
						readResult = await currentReader.read();
					} catch (error) {
						if (this._disposed) {
							throw error;
						}

						const retryDelayInSeconds = this._getRetryDelay(1, error, this._url);
						if (retryDelayInSeconds === null) {
							throw error;
						}

						Logging._error('Error while reading response stream. Attempting to resume.', error);
						await wait(1000 * retryDelayInSeconds);

						const newResponse = await retriedFetch(
							this._options.fetchFn ?? fetch,
							this._url,
							mergeRequestInit(this._requestInit, {
								headers: {
									// Who knows, maybe the server honors range requests this time
									Range: `bytes=${streamPosition}-`,
								},
							}),
							this._getRetryDelay,
							() => this._disposed,
						);

						if (!newResponse.ok) {
							throw new Error(
								// eslint-disable-next-line @typescript-eslint/no-base-to-string
								`Error fetching ${String(this._url)}:`
								+ ` ${newResponse.status} ${newResponse.statusText}`,
							);
						}

						if (!newResponse.body) {
							throw new Error(
								'Missing HTTP response body stream. The used fetch function must provide the'
								+ ' response body as a ReadableStream.',
							);
						}

						currentReader = newResponse.body.getReader();
						// If the server still doesn't do ranges, the new response starts at byte 0 again and
						// we need to skip over everything we already delivered. Cursed!
						skipRemaining = newResponse.status === 206 ? 0 : streamPosition;

						continue;
					}

					if (readResult.done) {
						controller.close();
						return;
					}

					let chunk = readResult.value;

					if (skipRemaining > 0) {
						const skippedAmount = Math.min(skipRemaining, chunk.length);
						skipRemaining -= skippedAmount;
						chunk = chunk.subarray(skippedAmount);
					}

					if (chunk.length === 0) {
						continue;
					}

					streamPosition += chunk.length;
					controller.enqueue(chunk);

					return;
				}
			},
			cancel: () => currentReader.cancel(),
		});

		const backing = new ReadableStreamSource(wrappedStream, {
			maxCacheSize: this._orchestrator.options.maxCacheSize,
		});
		backing._endIndex = this._orchestrator.fileSize; // Might still be null
		backing._cacheMissErrorMessage = 'Attempted to read data from an already-evicted part of the cache. Because the'
			+ ' HTTP server did not honor the range request, data can only be read sequentially, with old data being'
			+ ' evicted from the cache. To fix this issue, either ensure your server responds to range requests with'
			+ ' 206 Partial Content, or set maxCacheSize to Infinity in the UrlSource options. Note that the latter'
			+ ' will store the entire file in the cache if needed, no matter how large.';
		backing.on('read', ({ start, end }) => this._dispatchRead(start, end));

		this._sequentialBacking = backing;

		// Everything still pending in the orchestrator must now be served by the backing instead. Gather all
		// pending slices, then retire the orchestrator's workers and queued reads for good; _read will only
		// consult the backing from now on.
		const uniqueSlices = new Set<PendingSlice>();

		for (const otherWorker of this._orchestrator.workers) {
			for (const slice of otherWorker.pendingSlices) {
				uniqueSlices.add(slice);
			}

			otherWorker.aborted = true;
			otherWorker.pendingSlices.length = 0;
		}

		for (const queuedRead of this._orchestrator.queuedReads) {
			for (const slice of queuedRead.pendingSlices) {
				uniqueSlices.add(slice);
			}
		}

		this._orchestrator.workers.length = 0;
		this._orchestrator.queuedReads.length = 0;

		for (const slice of uniqueSlices) {
			const result = backing._read(slice.start, slice.start + slice.bytes.length);

			if (isThenable(result)) {
				result.then((readResult) => {
					if (readResult) {
						// The backing's cache is empty at this point, so the read is guaranteed to produce
						// exactly the requested range
						assert(readResult.offset === slice.start);
						slice.resolve(readResult.bytes);
					} else {
						slice.resolve(null);
					}
				}, (error: unknown) => slice.reject(error));
			} else {
				// Can only happen synchronously when the slice lies beyond the known file size
				assert(result === null);
				slice.resolve(null);
			}
		}
	}

	/** @internal */
	_dispose() {
		this._orchestrator.dispose();

		if (this._sequentialBacking) {
			this._sequentialBacking._disposed = true;
			this._sequentialBacking._dispose();
		}
	}
}

const BYTE_RANGE_REGEX = /^bytes=(\d+)-(\d*)$/;
const parseByteRangeHeader = (value: string) => {
	const match = BYTE_RANGE_REGEX.exec(value.trim());
	if (!match) {
		return null;
	}

	const offset = Number(match[1]);
	const end = match[2] === '' ? null : Number(match[2]);

	if (end !== null && end < offset) {
		return null;
	}

	return {
		offset,
		length: end !== null ? end - offset + 1 : null,
	};
};

/**
 * Options for {@link FilePathSource}.
 * @group Input sources
 * @public
 */
export type FilePathSourceOptions = {
	/** The maximum number of bytes the cache is allowed to hold in memory. Defaults to 8 MiB. */
	maxCacheSize?: number;
};

/**
 * A source backed by a path to a file. Intended for server-side usage in Node, Bun, or Deno.
 *
 * Make sure to call `.dispose()` on the corresponding {@link Input} when done to explicitly free the internal file
 * handle acquired by this source.
 * @group Input sources
 * @public
 */
export class FilePathSource extends PathedSource {
	/** @internal */
	_customSource: CustomSource;
	/** @internal */
	_fileHandle: FileHandle | null = null;

	/** Creates a new {@link FilePathSource} backed by the file at the specified file path. */
	constructor(filePath: string, options: FilePathSourceOptions = {}) {
		if (typeof filePath !== 'string') {
			throw new TypeError('filePath must be a string.');
		}
		if (!options || typeof options !== 'object') {
			throw new TypeError('options must be an object.');
		}
		if (
			options.maxCacheSize !== undefined
			&& (!isNumber(options.maxCacheSize) || options.maxCacheSize < 0)
		) {
			throw new TypeError('options.maxCacheSize, when provided, must be a non-negative number.');
		}

		if (!node.fs) {
			throw new Error(
				'FilePathSource is only available in server-side environments (Node.js, Bun, Deno).',
			);
		}

		super(filePath, request => new FilePathSource(request.path, options));

		// Let's back this source with a CustomSource, makes the implementation very simple
		this._customSource = new CustomSource({
			getSize: async () => {
				const fileHandle = await node.fs.open(filePath, 'r');
				this._fileHandle = fileHandle;

				sourceFinalizationRegistry?.register(this, () => {
					// If it's not closed, Node prints annoying warnings
					void fileHandle.close();
				}, this);

				const stats = await fileHandle.stat();
				return stats.size;
			},
			read: async (start, end) => {
				assert(this._fileHandle);

				const buffer = new Uint8Array(end - start);
				await this._fileHandle.read(buffer, 0, end - start, start);

				return buffer;
			},
			maxCacheSize: options.maxCacheSize,
			prefetchProfile: 'fileSystem',
		});
	}

	/** @internal */
	_read(
		start: number,
		end: number,
		minReadPosition: number,
		maxReadPosition: number,
	): MaybePromise<ReadResult | null> {
		return this._customSource._read(start, end, minReadPosition, maxReadPosition);
	}

	/** @internal */
	_getFileSize(): number | null | undefined {
		return this._customSource._getFileSize();
	}

	/** @internal */
	_dispose() {
		this._customSource._dispose();

		if (this._fileHandle) {
			void this._fileHandle.close();
			this._fileHandle = null;
			sourceFinalizationRegistry?.unregister(this);
		}
	}
}

/**
 * Options for defining a {@link CustomSource}.
 * @group Input sources
 * @public
 */
export type CustomSourceOptions = {
	/**
	 * Called when the size of the entire file is requested. Must return or resolve to the size in bytes. This function
	 * is guaranteed to be called before `read`.
	 */
	getSize: () => MaybePromise<number>;

	/**
	 * Called when data is requested. Must return or resolve to the bytes from the specified byte range, or a stream
	 * that yields these bytes.
	 *
	 * You are guaranteed that `0 <= start < end < fileSize`.
	 */
	read: (start: number, end: number) => MaybePromise<Uint8Array | ReadableStream<Uint8Array>>;

	/**
	 * Called when the {@link Input} driven by this source is disposed.
	 */
	dispose?: () => unknown;

	/** The maximum number of bytes the cache is allowed to hold in memory. Defaults to 8 MiB. */
	maxCacheSize?: number;

	/**
	 * Specifies the prefetch profile that the reader should use with this source. A prefetch profile specifies the
	 * pattern with which bytes outside of the requested range are preloaded to reduce latency for future reads.
	 *
	 * - `'none'` (default): No prefetching; only the data needed in the moment is requested.
	 * - `'fileSystem'`: File system-optimized prefetching: a small amount of data is prefetched bidirectionally,
	 * aligned with page boundaries.
	 * - `'network'`: Network-optimized prefetching, or more generally, prefetching optimized for any high-latency
	 * environment: tries to minimize the amount of read calls and aggressively prefetches data when sequential access
	 * patterns are detected.
	 */
	prefetchProfile?: 'none' | 'fileSystem' | 'network';
};

/**
 * A general-purpose, callback-driven source that can get its data from anywhere. Use this source to implement your own
 * custom source if the other sources don't cover your case.
 * @group Input sources
 * @public
 */
export class CustomSource extends Source {
	/** @internal */
	_options: CustomSourceOptions;
	/** @internal */
	_orchestrator: ReadOrchestrator;

	/** Creates a new {@link CustomSource} whose behavior is specified by `options`.  */
	constructor(options: CustomSourceOptions) {
		if (!options || typeof options !== 'object') {
			throw new TypeError('options must be an object.');
		}
		if (typeof options.getSize !== 'function') {
			throw new TypeError('options.getSize must be a function.');
		}
		if (typeof options.read !== 'function') {
			throw new TypeError('options.read must be a function.');
		}
		if (options.dispose !== undefined && typeof options.dispose !== 'function') {
			throw new TypeError('options.dispose, when provided, must be a function.');
		}
		if (
			options.maxCacheSize !== undefined
			&& (!isNumber(options.maxCacheSize) || options.maxCacheSize < 0)
		) {
			throw new TypeError('options.maxCacheSize, when provided, must be a non-negative number.');
		}
		if (options.prefetchProfile && !['none', 'fileSystem', 'network'].includes(options.prefetchProfile)) {
			throw new TypeError(
				'options.prefetchProfile, when provided, must be one of \'none\', \'fileSystem\' or \'network\'.',
			);
		}

		super();

		this._options = options;

		this._orchestrator = new ReadOrchestrator({
			maxCacheSize: options.maxCacheSize ?? (8 * 2 ** 20 /* 8 MiB */),
			maxWorkerCount: 2, // Fixed for now, *should* be fine
			prefetchProfile: PREFETCH_PROFILES[options.prefetchProfile ?? 'none'],
			runWorker: this._runWorker.bind(this),
		});
	}

	/** @internal */
	_getFileSize(): number | null | undefined {
		return this._orchestrator.fileSize ?? undefined;
	}

	/** @internal */
	_read(
		start: number,
		end: number,
		minReadPosition: number,
		maxReadPosition: number,
	): MaybePromise<ReadResult | null> {
		if (this._orchestrator.fileSize !== null) {
			return this._orchestrator.read(start, end, minReadPosition, maxReadPosition);
		}

		const result = this._options.getSize();

		if (isThenable(result)) {
			return result.then((size) => {
				if (!Number.isInteger(size) || size < 0) {
					throw new TypeError('options.getSize must return or resolve to a non-negative integer.');
				}

				this._orchestrator.fileSize = size;
				return this._orchestrator.read(start, end, minReadPosition, maxReadPosition);
			});
		} else {
			if (!Number.isInteger(result) || result < 0) {
				throw new TypeError('options.getSize must return or resolve to a non-negative integer.');
			}

			this._orchestrator.fileSize = result;
			return this._orchestrator.read(start, end, minReadPosition, maxReadPosition);
		}
	}

	/** @internal */
	private async _runWorker(worker: ReadWorker) {
		while (worker.currentPos < worker.targetPos && !worker.aborted) {
			const originalCurrentPos = worker.currentPos;
			const originalTargetPos = worker.targetPos;

			let data = this._options.read(worker.currentPos, originalTargetPos);
			if (isThenable(data)) data = await data;

			if (worker.aborted) {
				break;
			}

			if (data instanceof Uint8Array) {
				data = toUint8Array(data); // Normalize things like Node.js Buffer to Uint8Array

				if (data.length !== originalTargetPos - worker.currentPos) {
					// Yes, we're that strict
					throw new Error(
						`options.read returned a Uint8Array with unexpected length: Requested ${
							originalTargetPos - worker.currentPos
						} bytes, but got ${data.length}.`,
					);
				}

				this._dispatchRead(worker.currentPos, worker.currentPos + data.length);
				this._orchestrator.supplyWorkerData(worker, data);
			} else if (data instanceof ReadableStream) {
				const reader = data.getReader();

				while (worker.currentPos < originalTargetPos && !worker.aborted) {
					const { done, value } = await reader.read();
					if (done) {
						if (worker.currentPos < originalTargetPos) {
							// Yes, we're *that* strict
							throw new Error(
								`ReadableStream returned by options.read ended before supplying enough data.`
								+ ` Requested ${originalTargetPos - originalCurrentPos} bytes, but got ${
									worker.currentPos - originalCurrentPos
								}`,
							);
						}

						break;
					}

					if (!(value instanceof Uint8Array)) {
						throw new TypeError('ReadableStream returned by options.read must yield Uint8Array chunks.');
					}

					if (worker.aborted) {
						break;
					}

					const data = toUint8Array(value); // Normalize things like Node.js Buffer to Uint8Array

					this._dispatchRead(worker.currentPos, worker.currentPos + data.length);
					this._orchestrator.supplyWorkerData(worker, data);
				}
			} else {
				throw new TypeError('options.read must return or resolve to a Uint8Array or a ReadableStream.');
			}
		}

		this._orchestrator.signalWorkerStoppedRunning(worker);
	}

	/** @internal */
	_dispose() {
		this._orchestrator.dispose();
		this._options.dispose?.();
	}
}

/**
 * An alias for {@link CustomSource}.
 * @deprecated This name is misleading and will be removed in a future release. Please use {@link CustomSource} instead.
 *
 * @group Input sources
 * @public
 */
export const StreamSource = CustomSource;

/**
 * An alias for {@link CustomSourceOptions}.
 * @deprecated This name is misleading and will be removed in a future release. Please use
 * {@link CustomSourceOptions} instead.
 *
 * @group Input sources
 * @public
 */
export type StreamSourceOptions = CustomSourceOptions;

type ReadableStreamSourcePendingSlice = {
	start: number;
	end: number;
	bytes: Uint8Array;
	resolve: (bytes: ReadResult | null) => void;
	reject: (error: unknown) => void;
};

/**
 * Options for {@link ReadableStreamSource}.
 * @group Input sources
 * @public
 */
export type ReadableStreamSourceOptions = {
	/** The maximum number of bytes the cache is allowed to hold in memory. Defaults to 32 MiB. */
	maxCacheSize?: number;
};

/**
 * A source backed by a [`ReadableStream`](https://developer.mozilla.org/en-US/docs/Web/API/ReadableStream) of
 * `Uint8Array`, representing an append-only byte stream of unknown length. This is the source to use for incrementally
 * streaming in input files that are still being constructed and whose size we don't yet know, like for example the
 * output chunks of [MediaRecorder](https://developer.mozilla.org/en-US/docs/Web/API/MediaRecorder).
 *
 * This source is *unsized*, meaning calls to `.getSize()` will throw and readers are more limited due to the
 * lack of random file access. You should only use this source with sequential access patterns, such as reading all
 * packets from start to end. This source does not work well with random access patterns unless you increase its
 * max cache size.
 *
 * @group Input sources
 * @public
 */
export class ReadableStreamSource extends Source {
	/** @internal */
	_stream: ReadableStream<Uint8Array>;
	/** @internal */
	_reader: ReadableStreamDefaultReader<Uint8Array> | null = null;
	/** @internal */
	_cache: CacheEntry[] = [];
	/** @internal */
	_maxCacheSize: number;
	/** @internal */
	_pendingSlices: ReadableStreamSourcePendingSlice[] = [];
	/** @internal */
	_currentIndex = 0;
	/** @internal */
	_targetIndex = 0;
	/** @internal */
	_maxRequestedIndex = 0;
	/** @internal */
	_endIndex: number | null = null;
	/** @internal */
	_pulling = false;
	/**
	 * Overridable for internal use.
	 * @internal
	 */
	_cacheMissErrorMessage = 'Attempted to read data from an already-evicted part of the cache. With'
		+ ' ReadableStreamSource, you must access the data more sequentially or increase the size of its cache.';

	/** Creates a new {@link ReadableStreamSource} backed by the specified `ReadableStream<Uint8Array>`. */
	constructor(stream: ReadableStream<Uint8Array>, options: ReadableStreamSourceOptions = {}) {
		if (!(stream instanceof ReadableStream)) {
			throw new TypeError('stream must be a ReadableStream.');
		}
		if (!options || typeof options !== 'object') {
			throw new TypeError('options must be an object.');
		}
		if (
			options.maxCacheSize !== undefined
			&& (!isNumber(options.maxCacheSize) || options.maxCacheSize < 0)
		) {
			throw new TypeError('options.maxCacheSize, when provided, must be a non-negative number.');
		}

		super();

		this._stream = stream;
		this._maxCacheSize = options.maxCacheSize ?? (32 * 2 ** 20 /* 32 MiB */);
	}

	/** @internal */
	_getFileSize(): number | null {
		return this._endIndex; // Starts out as null, meaning this source is unsized
	}

	/** @internal */
	_read(start: number, end: number): MaybePromise<ReadResult | null> {
		if (this._endIndex !== null && end > this._endIndex) {
			return null;
		}

		this._maxRequestedIndex = Math.max(this._maxRequestedIndex, end);

		const cacheStartIndex = binarySearchLessOrEqual(this._cache, start, x => x.start);
		const cacheStartEntry = cacheStartIndex !== -1 ? this._cache[cacheStartIndex]! : null;

		if (cacheStartEntry && cacheStartEntry.start <= start && end <= cacheStartEntry.end) {
			// The request can be satisfied with a single cache entry
			return {
				bytes: cacheStartEntry.bytes,
				view: cacheStartEntry.view,
				offset: cacheStartEntry.start,
			};
		}

		let lastEnd = start;
		const bytes = new Uint8Array(end - start);

		if (cacheStartIndex !== -1) {
			// Walk over the cache to see if we can satisfy the request using multiple cache entries
			for (let i = cacheStartIndex; i < this._cache.length; i++) {
				const cacheEntry = this._cache[i]!;
				if (cacheEntry.start >= end) {
					break;
				}

				const cappedStart = Math.max(start, cacheEntry.start);
				if (cappedStart > lastEnd) {
					// We're too far behind
					this._throwDueToCacheMiss();
				}

				const cappedEnd = Math.min(end, cacheEntry.end);

				if (cappedStart < cappedEnd) {
					bytes.set(
						cacheEntry.bytes.subarray(cappedStart - cacheEntry.start, cappedEnd - cacheEntry.start),
						cappedStart - start,
					);

					lastEnd = cappedEnd;
				}
			}
		}

		if (lastEnd === end) {
			return {
				bytes,
				view: toDataView(bytes),
				offset: start,
			};
		}

		// We need to pull more data

		if (this._currentIndex > lastEnd) {
			// We're too far behind
			this._throwDueToCacheMiss();
		}

		const { promise, resolve, reject } = promiseWithResolvers<ReadResult | null>();

		this._pendingSlices.push({
			start,
			end,
			bytes,
			resolve,
			reject,
		});

		this._targetIndex = Math.max(this._targetIndex, end);

		// Start pulling from the stream if we're not already doing it
		if (!this._pulling) {
			this._pulling = true;
			void this._pull()
				.catch((error) => {
					this._pulling = false;

					if (this._pendingSlices.length > 0) {
						this._pendingSlices.forEach(x => x.reject(error)); // Make sure to propagate any errors
						this._pendingSlices.length = 0;
					} else {
						throw error; // So it doesn't get swallowed
					}
				});
		}

		return promise;
	}

	/** @internal */
	_throwDueToCacheMiss() {
		throw new Error(this._cacheMissErrorMessage);
	}

	/** @internal */
	async _pull() {
		this._reader ??= this._stream.getReader();

		// This is the loop that keeps pulling data from the stream until a target index is reached, filling requests
		// in the process
		while (this._currentIndex < this._targetIndex && !this._disposed) {
			const { done, value } = await this._reader.read();
			if (done) {
				for (const pendingSlice of this._pendingSlices) {
					pendingSlice.resolve(null);
				}
				this._pendingSlices.length = 0;
				this._endIndex = this._currentIndex; // We know how long the file is now!

				break;
			}

			const startIndex = this._currentIndex;
			const endIndex = this._currentIndex + value.byteLength;

			this._dispatchRead(startIndex, endIndex);

			// Fill the pending slices with the data
			for (let i = 0; i < this._pendingSlices.length; i++) {
				const pendingSlice = this._pendingSlices[i]!;

				const cappedStart = Math.max(startIndex, pendingSlice.start);
				const cappedEnd = Math.min(endIndex, pendingSlice.end);

				if (cappedStart < cappedEnd) {
					pendingSlice.bytes.set(
						value.subarray(cappedStart - startIndex, cappedEnd - startIndex),
						cappedStart - pendingSlice.start,
					);
					if (cappedEnd === pendingSlice.end) {
						// Pending slice fully filled
						pendingSlice.resolve({
							bytes: pendingSlice.bytes,
							view: toDataView(pendingSlice.bytes),
							offset: pendingSlice.start,
						});
						this._pendingSlices.splice(i, 1);
						i--;
					}
				}
			}

			this._cache.push({
				start: startIndex,
				end: endIndex,
				bytes: value,
				view: toDataView(value),
				age: 0, // Unused
			});

			// Do cache eviction, based on the distance from the last-requested index. It's important that we do it like
			// this and not based on how far we've pulled the stream, because if the stream supplies data faster than it
			// is being requested, we'd unnecessarily evict data that we still might need.
			while (this._cache.length > 0) {
				const firstEntry = this._cache[0]!;
				const distance = this._maxRequestedIndex - firstEntry.end;

				if (distance <= this._maxCacheSize) {
					break;
				}

				this._cache.shift();
			}

			this._currentIndex += value.byteLength;
		}

		this._pulling = false;
	}

	/** @internal */
	_dispose() {
		for (const pendingSlice of this._pendingSlices) {
			pendingSlice.reject(new InputDisposedError());
		}

		this._pendingSlices.length = 0;
		this._cache.length = 0;
		void this._reader?.cancel();
	}
}

type PrefetchProfile = (start: number, end: number, workers: ReadWorker[]) => {
	start: number;
	end: number;
};

const PREFETCH_PROFILES = {
	none: (start, end) => ({ start, end }),
	fileSystem: (start, end) => {
		const padding = 2 ** 16;

		start = Math.floor((start - padding) / padding) * padding;
		end = Math.ceil((end + padding) / padding) * padding;

		return { start, end };
	},
	network: (start, end, workers) => {
		// Add a slight bit of start padding because backwards reading is painful
		const paddingStart = 2 ** 16;
		start = Math.max(0, Math.floor((start - paddingStart) / paddingStart) * paddingStart);

		// Remote resources have extreme latency (relatively speaking), so the benefit from intelligent
		// prefetching is great. The network prefetch strategy is as follows: When we notice
		// successive reads to a worker's read region, we prefetch more data at the end of that region,
		// growing exponentially (up to a cap). This performs well for real-world use cases: Either we read a
		// small part of the file once and then never need it again, in which case the requested about of data
		// is small. Or, we're repeatedly doing a sequential access pattern (common in media files), in which
		// case we can become more and more confident to prefetch more and more data.
		for (const worker of workers) {
			const maxExtensionAmount = 8 * 2 ** 20; // 8 MiB

			// When the read region cross the threshold point, we trigger a prefetch. This point is typically
			// in the middle of the worker's read region, or a fixed offset from the end if the region has grown
			// really large.
			const thresholdPoint = Math.max(
				(worker.startPos + worker.targetPos) / 2,
				worker.targetPos - maxExtensionAmount,
			);

			if (closedIntervalsOverlap(
				start, end,
				thresholdPoint, worker.targetPos,
			)) {
				const size = worker.targetPos - worker.startPos;

				// If we extend by maxExtensionAmount
				const a = Math.ceil((size + 1) / maxExtensionAmount) * maxExtensionAmount;
				// If we extend to the next power of 2
				const b = 2 ** Math.ceil(Math.log2(size + 1));

				const extent = Math.min(b, a);
				end = Math.max(end, worker.startPos + extent);
			}
		}

		end = Math.max(end, start + URL_SOURCE_MIN_LOAD_AMOUNT);

		return {
			start,
			end,
		};
	},
} satisfies Record<string, PrefetchProfile>;

type PendingSlice = {
	start: number;
	bytes: Uint8Array;
	holes: Hole[];
	resolve: (bytes: Uint8Array | null) => void;
	reject: (error: unknown) => void;
};

type Hole = {
	start: number;
	end: number;
};

type CacheEntry = {
	start: number;
	end: number;
	bytes: Uint8Array;
	view: DataView;
	age: number;
};

type ReadWorker = {
	startPos: number;
	currentPos: number;
	targetPos: number;
	/** The target is considered _strict_ when it is an error for the worker to terminate before reaching the target. */
	strictTarget: boolean;
	running: boolean;
	aborted: boolean;
	pendingSlices: PendingSlice[];
	age: number;
};

/**
 * Godclass for orchestrating complex, cached read operations. The reading model is as follows: Any reading task is
 * delegated to a *worker*, which is a sequential reader positioned somewhere along the file. All workers run in
 * parallel and can be stopped and resumed in their forward movement. When read requests come in, this orchestrator will
 * first try to satisfy the request with only the cached data. If this isn't possible, workers are spun up for all
 * missing parts (or existing workers are repurposed), and these workers will then fill the holes in the data as they
 * march along the file.
 */
class ReadOrchestrator {
	fileSize: number | null = null;
	nextAge = 0; // Used for multiple things
	workers: ReadWorker[] = [];
	cache: CacheEntry[] = [];
	currentCacheSize = 0;
	disposed = false;
	queuedReads: {
		hole: Hole;
		strictTarget: boolean;
		pendingSlices: PendingSlice[];
		age: number;
	}[] = [];

	constructor(public options: {
		maxCacheSize: number;
		runWorker: (worker: ReadWorker) => Promise<void>;
		prefetchProfile: PrefetchProfile;
		maxWorkerCount: number;
	}) {}

	read(
		innerStart: number,
		innerEnd: number,
		minReadPosition: number,
		maxReadPosition: number,
	): MaybePromise<ReadResult | null> {
		assert(!this.disposed);

		const prefetchRange = this.options.prefetchProfile(innerStart, innerEnd, this.workers);
		const outerStart = Math.max(prefetchRange.start, minReadPosition);
		const outerEnd = Math.min(prefetchRange.end, this.fileSize ?? Infinity, maxReadPosition);
		assert(outerStart <= innerStart && innerEnd <= outerEnd);

		let result: MaybePromise<ReadResult | null> | null = null;

		const innerCacheStartIndex = binarySearchLessOrEqual(this.cache, innerStart, x => x.start);
		const innerStartEntry = innerCacheStartIndex !== -1 ? this.cache[innerCacheStartIndex] : null;

		// See if the read request can be satisfied by a single cache entry
		if (innerStartEntry && innerStartEntry.start <= innerStart && innerEnd <= innerStartEntry.end) {
			innerStartEntry.age = this.nextAge++;

			result = {
				bytes: innerStartEntry.bytes,
				view: innerStartEntry.view,
				offset: innerStartEntry.start,
			};
			// Can't return yet though, still need to check if the prefetch range might lie outside the cached area
		}

		const outerCacheStartIndex = binarySearchLessOrEqual(this.cache, outerStart, x => x.start);

		const bytes = result ? null : new Uint8Array(innerEnd - innerStart);
		let contiguousBytesWriteEnd = 0; // Used to track if the cache is able to completely cover the bytes

		let lastEnd = outerStart;
		// The "holes" in the cache (the parts we need to load)
		const outerHoles: Hole[] = [];

		// Loop over the cache and build up the list of holes
		if (outerCacheStartIndex !== -1) {
			for (let i = outerCacheStartIndex; i < this.cache.length; i++) {
				const entry = this.cache[i]!;
				if (entry.start >= outerEnd) {
					break;
				}
				if (entry.end <= outerStart) {
					continue;
				}

				const cappedOuterStart = Math.max(outerStart, entry.start);
				const cappedOuterEnd = Math.min(outerEnd, entry.end);
				assert(cappedOuterStart <= cappedOuterEnd);

				if (lastEnd < cappedOuterStart) {
					outerHoles.push({ start: lastEnd, end: cappedOuterStart });
				}
				lastEnd = cappedOuterEnd;

				if (bytes) {
					const cappedInnerStart = Math.max(innerStart, entry.start);
					const cappedInnerEnd = Math.min(innerEnd, entry.end);

					if (cappedInnerStart < cappedInnerEnd) {
						const relativeOffset = cappedInnerStart - innerStart;

						// Fill the relevant section of the bytes with the cached data
						bytes.set(
							entry.bytes.subarray(cappedInnerStart - entry.start, cappedInnerEnd - entry.start),
							relativeOffset,
						);

						if (relativeOffset === contiguousBytesWriteEnd) {
							contiguousBytesWriteEnd = cappedInnerEnd - innerStart;
						}
					}
				}
				entry.age = this.nextAge++;
			}

			if (lastEnd < outerEnd) {
				outerHoles.push({ start: lastEnd, end: outerEnd });
			}
		} else {
			outerHoles.push({ start: outerStart, end: outerEnd });
		}

		if (bytes && contiguousBytesWriteEnd >= bytes.length) {
			// Multiple cache entries were able to completely cover the requested bytes!
			result = {
				bytes,
				view: toDataView(bytes),
				offset: innerStart,
			};
		}

		if (outerHoles.length === 0) {
			assert(result);
			return result;
		}

		// We need to read more data, so now we're in async land
		const { promise, resolve, reject } = promiseWithResolvers<Uint8Array | null>();

		const innerHoles: typeof outerHoles = [];
		for (const outerHole of outerHoles) {
			const cappedStart = Math.max(innerStart, outerHole.start);
			const cappedEnd = Math.min(innerEnd, outerHole.end);

			if (cappedStart === outerHole.start && cappedEnd === outerHole.end) {
				innerHoles.push(outerHole); // Can reuse without allocating a new object
			} else if (cappedStart < cappedEnd) {
				innerHoles.push({ start: cappedStart, end: cappedEnd });
			}
		}

		const pendingSlice: PendingSlice | null = bytes && {
			start: innerStart,
			bytes,
			holes: innerHoles,
			resolve,
			reject,
		};

		// Fire off workers to take care of patching the holes
		outer:
		for (const outerHole of outerHoles) {
			for (const worker of this.workers) {
				const addedToWorker = this.checkHoleAgainstWorker(
					worker,
					outerHole,
					pendingSlice ? [pendingSlice] : [],
				);

				if (addedToWorker) {
					this.checkQueuedReadsAgainstWorker(worker);
					continue outer;
				}
			}

			// We need to spawn a new worker
			const strictTarget = outerHole.end < outerEnd || this.fileSize !== null;
			const newWorker = this.createWorker(outerHole.start, outerHole.end, strictTarget);

			if (newWorker) {
				if (pendingSlice) {
					newWorker.pendingSlices = [pendingSlice];
				}

				this.runWorker(newWorker);
			} else {
				// Max worker count has been reached, let's queue a read for later

				let index = binarySearchLessOrEqual(this.queuedReads, outerHole.start, x => x.hole.start);
				let entry = index !== -1
					? this.queuedReads[index]!
					: null;

				if (entry && outerHole.start <= entry.hole.end) {
					entry.hole.end = Math.max(entry.hole.end, outerHole.end);
					entry.strictTarget &&= strictTarget;

					if (pendingSlice) {
						entry.pendingSlices.push(pendingSlice);
					}
				} else {
					index++;
					entry = {
						hole: {
							// Clone the hole because it might be mutated later
							start: outerHole.start,
							end: outerHole.end,
						},
						strictTarget,
						pendingSlices: pendingSlice ? [pendingSlice] : [],
						age: this.nextAge++,
					};
					this.queuedReads.splice(index, 0, entry);
				}

				// Merge with any subsequent entries that overlap
				while (index + 1 < this.queuedReads.length) {
					const nextEntry = this.queuedReads[index + 1]!;
					if (nextEntry.hole.start > entry.hole.end) {
						break;
					}

					entry.hole.end = Math.max(entry.hole.end, nextEntry.hole.end);
					entry.pendingSlices.push(...nextEntry.pendingSlices);
					entry.strictTarget &&= nextEntry.strictTarget;
					entry.age = Math.min(entry.age, nextEntry.age);
					this.queuedReads.splice(index + 1, 1);
				}
			}
		}

		if (!result) {
			assert(bytes);

			result = promise.then(bytes => bytes && ({
				bytes,
				view: toDataView(bytes),
				offset: innerStart,
			} satisfies ReadResult));
		} else {
			// The requested region was satisfied by the cache, but the entire prefetch region was not
			promise.catch((error) => {
				if (this.disposed) {
					return; // Swallow the error
				}

				// Nobody's awaiting this result but an errored read is still notable
				throw error;
			});
		}

		return result;
	}

	checkHoleAgainstWorker(worker: ReadWorker, hole: Hole, pendingSlices: PendingSlice[]) {
		// A small tolerance in the case that the requested region is *just* after the target position of an
		// existing worker. In that case, it's probably more efficient to repurpose that worker than to spawn
		// another one so close to it
		const gapTolerance = 2 ** 17;

		// This check also implies worker.currentPos <= hole.start, a critical condition
		if (closedIntervalsOverlap(
			hole.start - gapTolerance, hole.start,
			worker.currentPos, worker.targetPos,
		)) {
			worker.targetPos = Math.max(worker.targetPos, hole.end); // Update the worker's target position

			for (let i = 0; i < pendingSlices.length; i++) {
				const pendingSlice = pendingSlices[i]!;
				if (!worker.pendingSlices.includes(pendingSlice)) {
					worker.pendingSlices.push(pendingSlice);
				}
			}

			if (!worker.running) {
				// Kick it off if it's idle
				this.runWorker(worker);
			}

			return true;
		}

		return false;
	}

	checkQueuedReadsAgainstWorker(worker: ReadWorker) {
		let wasTrueOnce = false;

		for (let i = 0; i < this.queuedReads.length; i++) {
			const queuedRead = this.queuedReads[i]!;
			const result = this.checkHoleAgainstWorker(worker, queuedRead.hole, queuedRead.pendingSlices);

			if (result) {
				this.queuedReads.splice(i, 1);
				i--;
				wasTrueOnce = true;
			} else if (wasTrueOnce) {
				// We can stop since the holes are sorted
				break;
			}
		}
	}

	createWorker(startPos: number, targetPos: number, strictTarget: boolean) {
		if (this.workers.length >= this.options.maxWorkerCount) {
			let oldestWorker: ReadWorker | null = null;
			let oldestIndex: number | null = null;

			for (let i = 0; i < this.workers.length; i++) {
				const worker = this.workers[i]!;

				if (
					!worker.running
					&& worker.pendingSlices.length === 0
					&& (!oldestWorker || worker.age < oldestWorker.age)
				) {
					oldestIndex = i;
					oldestWorker = worker;
				}
			}

			if (oldestWorker) {
				// LRU eviction
				assert(oldestIndex !== null);
				assert(oldestWorker.pendingSlices.length === 0);
				this.workers.splice(oldestIndex, 1);
			} else {
				return null; // All workers are still running, we can't create a new one
			}
		}

		const worker: ReadWorker = {
			startPos,
			currentPos: startPos,
			targetPos,
			strictTarget,
			running: false,
			// Due to async shenanigans, it can happen that workers are started after disposal. In this case, instead of
			// simply not creating the worker, we allow it to run but immediately label it as aborted, so it can then
			// shut itself down.
			aborted: this.disposed,
			pendingSlices: [],
			age: this.nextAge++,
		};
		this.workers.push(worker);

		return worker;
	}

	runWorker(worker: ReadWorker) {
		assert(!worker.running);
		assert(worker.currentPos < worker.targetPos);

		worker.running = true;
		worker.age = this.nextAge++;

		void this.options.runWorker(worker)
			.catch((error) => {
				worker.running = false;

				if (worker.pendingSlices.length > 0) {
					worker.pendingSlices.forEach(x => x.reject(error)); // Make sure to propagate any errors
					worker.pendingSlices.length = 0;
				} else if (!worker.aborted && !this.disposed) {
					throw error; // So it doesn't get swallowed
				}
			})
			.finally(() => {
				if (worker.running) {
					// Rare, but can happen with multiple concurrent reads. In this case, don't do anything.
					return;
				}

				if (this.queuedReads.length > 0) {
					let oldestIndex = 0;
					for (let i = 1; i < this.queuedReads.length; i++) {
						const queuedRead = this.queuedReads[i]!;
						if (queuedRead.age < this.queuedReads[oldestIndex]!.age) {
							oldestIndex = i;
						}
					}

					const queuedRead = this.queuedReads[oldestIndex]!;

					const newWorker = this.createWorker(
						queuedRead.hole.start,
						queuedRead.hole.end,
						queuedRead.strictTarget,
					);
					if (!newWorker) {
						// In high-contention cases, it could be that we've already reached max worker count, so in this
						// case we don't do anything.
						return;
					}

					this.queuedReads.splice(oldestIndex, 1);
					newWorker.pendingSlices = queuedRead.pendingSlices;
					this.runWorker(newWorker);
				}
			});
	}

	/** Called by a worker when it has read some data. */
	supplyWorkerData(worker: ReadWorker, bytes: Uint8Array) {
		assert(!worker.aborted);

		const start = worker.currentPos;
		const end = start + bytes.length;

		this.insertIntoCache({
			start,
			end,
			bytes,
			view: toDataView(bytes),
			age: this.nextAge++,
		});
		worker.currentPos += bytes.length;

		if (worker.currentPos > worker.targetPos) {
			// In case it overshoots
			worker.targetPos = worker.currentPos;
			this.checkQueuedReadsAgainstWorker(worker);
		}

		// Now, let's see if we can use the read bytes to fill any pending slice
		for (let i = 0; i < worker.pendingSlices.length; i++) {
			const pendingSlice = worker.pendingSlices[i]!;

			const clampedStart = Math.max(start, pendingSlice.start);
			const clampedEnd = Math.min(end, pendingSlice.start + pendingSlice.bytes.length);

			if (clampedStart < clampedEnd) {
				pendingSlice.bytes.set(
					bytes.subarray(clampedStart - start, clampedEnd - start),
					clampedStart - pendingSlice.start,
				);
			}

			for (let j = 0; j < pendingSlice.holes.length; j++) {
				// The hole is intentionally not modified here if the read section starts somewhere in the middle of
				// the hole. We don't need to do "hole splitting", since the workers are spawned *by* the holes,
				// meaning there's always a worker which will consume the hole left to right.
				const hole = pendingSlice.holes[j]!;
				if (start <= hole.start && end > hole.start) {
					hole.start = end;
				}

				if (hole.end <= hole.start) {
					pendingSlice.holes.splice(j, 1);
					j--;
				}
			}

			if (pendingSlice.holes.length === 0) {
				// The slice has been fulfilled, everything has been read. Let's resolve the promise
				pendingSlice.resolve(pendingSlice.bytes);
				worker.pendingSlices.splice(i, 1);
				i--;
			}
		}

		// Remove other idle workers if we "ate" into their territory
		for (let i = 0; i < this.workers.length; i++) {
			const otherWorker = this.workers[i]!;
			if (worker === otherWorker || otherWorker.running) {
				continue;
			}

			if (closedIntervalsOverlap(
				start, end,
				otherWorker.currentPos, otherWorker.targetPos, // These should typically be equal when the worker's idle
			)) {
				this.workers.splice(i, 1);
				i--;
			}
		}
	}

	supplyFileSize(size: number) {
		assert(this.fileSize === null);

		this.fileSize = size;

		// Trim the workers with this new information
		for (const worker of this.workers) {
			worker.targetPos = Math.min(worker.targetPos, size);
			worker.strictTarget = true;

			for (let i = 0; i < worker.pendingSlices.length; i++) {
				const pendingSlice = worker.pendingSlices[i]!;

				for (const hole of pendingSlice.holes) {
					if (hole.end > size) {
						// Can't satisfy this slice anymore
						pendingSlice.resolve(null);
						worker.pendingSlices.splice(i, 1);
						i--;

						break;
					}
				}
			}
		}

		// Trim the queued reads as well
		for (let i = 0; i < this.queuedReads.length; i++) {
			const queuedRead = this.queuedReads[i]!;
			if (queuedRead.hole.start >= size) {
				// Entirely out of bounds
				for (const slice of queuedRead.pendingSlices) slice.resolve(null);
				this.queuedReads.splice(i, 1);
				i--;
			} else if (queuedRead.hole.end > size) {
				// Partially out of bounds
				queuedRead.hole.end = size;
				queuedRead.strictTarget = true;

				for (let j = 0; j < queuedRead.pendingSlices.length; j++) {
					const slice = queuedRead.pendingSlices[j]!;
					// If the slice itself is out of bounds, resolve it
					if (slice.start >= size) {
						slice.resolve(null);
						queuedRead.pendingSlices.splice(j, 1);
						j--;
					}
				}
			}
		}
	}

	signalWorkerStoppedRunning(worker: ReadWorker) {
		worker.running = false;

		if (!worker.aborted) {
			// When a worker stops running, that means it has hit its targetPos. It might still have pendingSlices
			// assigned, but this is because those pending slices cover data that other workers are assigned to fill.
			// Since targetPos has been reached, we can confidently say that this worker has completed its share of work
			// on the pending slices and must no longer care about them.
			worker.pendingSlices.length = 0;
		}
	}

	/** Called when a worker reaches the end of the underlying data and must be cleaned up. */
	onWorkerFinished(worker: ReadWorker) {
		const index = this.workers.indexOf(worker);
		assert(index !== -1);

		worker.running = false;
		this.workers.splice(index, 1);

		if (this.fileSize === null) {
			// We can now deduce the file size!
			this.supplyFileSize(worker.currentPos);
		}

		for (const pendingSlice of worker.pendingSlices) {
			pendingSlice.resolve(null);
		}
	}

	insertIntoCache(entry: CacheEntry) {
		if (this.options.maxCacheSize === 0) {
			return; // No caching
		}

		let insertionIndex = binarySearchLessOrEqual(this.cache, entry.start, x => x.start) + 1;

		if (insertionIndex > 0) {
			const previous = this.cache[insertionIndex - 1]!;
			if (previous.end >= entry.end) {
				// Previous entry swallows the one to be inserted; we don't need to do anything
				return;
			}

			if (previous.end > entry.start) {
				// Partial overlap with the previous entry, let's join
				const joined = new Uint8Array(entry.end - previous.start);
				joined.set(previous.bytes, 0);
				joined.set(entry.bytes, entry.start - previous.start);

				this.currentCacheSize += entry.end - previous.end;

				previous.bytes = joined;
				previous.view = toDataView(joined);
				previous.end = entry.end;

				// Do the rest of the logic with the previous entry instead
				insertionIndex--;
				entry = previous;
			} else {
				this.cache.splice(insertionIndex, 0, entry);
				this.currentCacheSize += entry.bytes.length;
			}
		} else {
			this.cache.splice(insertionIndex, 0, entry);
			this.currentCacheSize += entry.bytes.length;
		}

		for (let i = insertionIndex + 1; i < this.cache.length; i++) {
			const next = this.cache[i]!;
			if (entry.end <= next.start) {
				// Even if they touch, we don't wanna merge them, no need
				break;
			}

			if (entry.end >= next.end) {
				// The inserted entry completely swallows the next entry
				this.cache.splice(i, 1);
				this.currentCacheSize -= next.bytes.length;
				i--;
				continue;
			}

			// Partial overlap, let's join
			const joined = new Uint8Array(next.end - entry.start);
			joined.set(entry.bytes, 0);
			joined.set(next.bytes, next.start - entry.start);

			this.currentCacheSize -= entry.end - next.start; // Subtract the overlap

			entry.bytes = joined;
			entry.view = toDataView(joined);
			entry.end = next.end;
			this.cache.splice(i, 1);

			break; // After the join case, we're done: the next entry cannot possibly overlap with the inserted one.
		}

		// LRU eviction of cache entries
		while (this.currentCacheSize > this.options.maxCacheSize) {
			let oldestIndex = 0;
			let oldestEntry = this.cache[0]!;

			for (let i = 1; i < this.cache.length; i++) {
				const entry = this.cache[i]!;

				if (entry.age < oldestEntry.age) {
					oldestIndex = i;
					oldestEntry = entry;
				}
			}

			if (this.currentCacheSize - oldestEntry.bytes.length <= this.options.maxCacheSize) {
				// Don't evict if it would shrink the cache below the max size
				break;
			}

			this.cache.splice(oldestIndex, 1);
			this.currentCacheSize -= oldestEntry.bytes.length;
		}
	}

	dispose() {
		for (const worker of this.workers) {
			for (const slice of worker.pendingSlices) {
				slice.reject(new InputDisposedError());
			}

			worker.pendingSlices.length = 0;
			worker.aborted = true;
		}

		for (const queuedRead of this.queuedReads) {
			for (const slice of queuedRead.pendingSlices) {
				slice.reject(new InputDisposedError());
			}
		}

		this.workers.length = 0;
		this.cache.length = 0;
		this.queuedReads.length = 0;
		this.disposed = true;
	}
}

/**
 * A dummy source from which no data can be read. Can be used in conjunction with input formats that get their data
 * from another source.
 */
export class NullSource extends Source {
	override _getFileSize(): number | null {
		return null;
	}

	override _read(): MaybePromise<ReadResult | null> {
		return null;
	}

	override _dispose(): void {
		// Do nothing
	}
}

/**
 * A source that covers a range (offset + length) of another source. Useful for reading files that are embedded within
 * larger files.
 *
 * @group Input sources
 * @public
 */
export class RangedSource extends Source {
	/** @internal */
	_baseSource: Source;
	/** @internal */
	_ref: SourceRef | null = null;
	/** @internal */
	_offset: number;
	/** @internal */
	_length: number | null;

	/** @internal */
	constructor(baseSource: Source, offset: number, length?: number) {
		super();

		if (baseSource._disposed) {
			throw new Error('Cannot create a slice of a disposed source.');
		}

		this._baseSource = baseSource;
		this._offset = offset;
		this._length = length ?? null;
	}

	/** @internal */
	override _getFileSize(): number | null | undefined {
		const baseSize = this._baseSource._getFileSize();
		if (baseSize === undefined) {
			return this._length !== null
				? this._length
				: undefined;
		}

		if (baseSize === null) {
			if (this._length !== null) {
				return this._length;
			} else {
				return null;
			}
		}

		return clamp(baseSize - this._offset, 0, this._length ?? Infinity);
	}

	/** @internal */
	override _read(
		start: number,
		end: number,
		minReadPosition: number,
		maxReadPosition: number,
	): MaybePromise<ReadResult | null> {
		if (this._length !== null && end > this._length) {
			return null;
		}

		const result = this._baseSource._read(
			this._offset + start,
			this._offset + end,
			this._offset + minReadPosition,
			this._offset + maxReadPosition,
		);

		const processResult = (result: ReadResult | null) => {
			if (!result) {
				return null;
			}

			result.offset -= this._offset;
			return result;
		};

		if (isThenable(result)) {
			return result.then(processResult);
		} else {
			return processResult(result);
		}
	}

	/** @internal */
	override _dispose(): void {
		this._ref?.free();
	}

	override ref() {
		this._ref ??= this._baseSource.ref();
		return super.ref();
	}
}