// Phase 2b — durable async job queue (Postgres). Idempotent on (bot_slug, update_id).
// Voir ~/.claude/plans/pour-les-notifications-on-inherited-seal.md § Phase 2.
package main

import (
	"context"
	"database/sql"
	"errors"
	"fmt"
	"time"
)

// Job is a unit of async work : a Telegram Update routed to a particular bot,
// to be processed by that bot's handler.
type Job struct {
	ID          int64
	BotSlug     string
	HandlerType string
	UpdateID    int64
	Payload     []byte
	Attempts    int
	NextRetryAt time.Time
	Status      string
	LastError   string
}

type Queue interface {
	// Enqueue inserts a job ; on UNIQUE conflict (Telegram redelivery) it
	// returns nil without touching the existing row.
	Enqueue(ctx context.Context, j Job) error
	// Pop atomically claims the oldest pending job whose next_retry_at has
	// passed (FOR UPDATE SKIP LOCKED, status → 'running', attempts++).
	// Returns (nil, nil) when there is nothing to claim.
	Pop(ctx context.Context) (*Job, error)
	// MarkDone marks a job 'done'.
	MarkDone(ctx context.Context, id int64) error
	// MarkFailed schedules a retry (status back to 'pending', next_retry_at
	// in the future). After maxAttempts the row is set to 'dead'.
	MarkFailed(ctx context.Context, id int64, attempt int, err error, maxAttempts int) error
	// PurgeDone removes rows with status='done' older than `olderThan`.
	// Returns the number of rows deleted. Used by the Janitor goroutine.
	PurgeDone(ctx context.Context, olderThan time.Duration) (int64, error)
	// RecoverStuck reverts rows stuck in status='running' for more than
	// `stuckFor` back to 'pending' so a worker can retry. Handles the case
	// of a pod dying mid-job. Returns the number of rows reverted.
	RecoverStuck(ctx context.Context, stuckFor time.Duration) (int64, error)
}

type PostgresQueue struct {
	db *sql.DB
}

func NewPostgresQueue(db *sql.DB) *PostgresQueue { return &PostgresQueue{db: db} }

const (
	enqueueSQL = `
INSERT INTO gateway_jobs (bot_slug, handler_type, update_id, payload)
VALUES ($1, $2, $3, $4)
ON CONFLICT (bot_slug, update_id) DO NOTHING
`
	popSQL = `
UPDATE gateway_jobs
   SET status = 'running', attempts = attempts + 1, updated_at = NOW()
 WHERE id = (
   SELECT id FROM gateway_jobs
    WHERE status = 'pending' AND next_retry_at <= NOW()
    ORDER BY next_retry_at ASC
    FOR UPDATE SKIP LOCKED
    LIMIT 1
 )
RETURNING id, bot_slug, handler_type, update_id, payload, attempts, next_retry_at, status, COALESCE(last_error, '')
`
	markDoneSQL = `
UPDATE gateway_jobs SET status = 'done', updated_at = NOW(), last_error = NULL WHERE id = $1
`
	markRetrySQL = `
UPDATE gateway_jobs
   SET status = 'pending',
       next_retry_at = $2,
       last_error = $3,
       updated_at = NOW()
 WHERE id = $1
`
	markDeadSQL = `
UPDATE gateway_jobs
   SET status = 'dead',
       last_error = $2,
       updated_at = NOW()
 WHERE id = $1
`
	purgeDoneSQL = `
DELETE FROM gateway_jobs
 WHERE status = 'done'
   AND updated_at < NOW() - make_interval(secs => $1::int)
`
	recoverStuckSQL = `
UPDATE gateway_jobs
   SET status = 'pending', updated_at = NOW()
 WHERE status = 'running'
   AND updated_at < NOW() - make_interval(secs => $1::int)
`
)

func (q *PostgresQueue) Enqueue(ctx context.Context, j Job) error {
	_, err := q.db.ExecContext(ctx, enqueueSQL, j.BotSlug, j.HandlerType, j.UpdateID, j.Payload)
	return err
}

func (q *PostgresQueue) Pop(ctx context.Context) (*Job, error) {
	var j Job
	err := q.db.QueryRowContext(ctx, popSQL).Scan(
		&j.ID, &j.BotSlug, &j.HandlerType, &j.UpdateID, &j.Payload,
		&j.Attempts, &j.NextRetryAt, &j.Status, &j.LastError,
	)
	if errors.Is(err, sql.ErrNoRows) {
		return nil, nil
	}
	if err != nil {
		return nil, err
	}
	return &j, nil
}

func (q *PostgresQueue) MarkDone(ctx context.Context, id int64) error {
	_, err := q.db.ExecContext(ctx, markDoneSQL, id)
	return err
}

func (q *PostgresQueue) MarkFailed(ctx context.Context, id int64, attempt int, jobErr error, maxAttempts int) error {
	msg := ""
	if jobErr != nil {
		msg = truncate(jobErr.Error(), 4096)
	}
	if attempt >= maxAttempts {
		_, err := q.db.ExecContext(ctx, markDeadSQL, id, msg)
		return err
	}
	retryIn := Backoff(attempt)
	next := time.Now().Add(retryIn)
	_, err := q.db.ExecContext(ctx, markRetrySQL, id, next, msg)
	return err
}

func (q *PostgresQueue) PurgeDone(ctx context.Context, olderThan time.Duration) (int64, error) {
	res, err := q.db.ExecContext(ctx, purgeDoneSQL, int(olderThan.Seconds()))
	if err != nil {
		return 0, err
	}
	return res.RowsAffected()
}

func (q *PostgresQueue) RecoverStuck(ctx context.Context, stuckFor time.Duration) (int64, error) {
	res, err := q.db.ExecContext(ctx, recoverStuckSQL, int(stuckFor.Seconds()))
	if err != nil {
		return 0, err
	}
	return res.RowsAffected()
}

// Backoff returns the delay before the next attempt of a failed job.
// 30s, 2m, 10m, 1h (capped). Spans roughly one night by attempt 5.
func Backoff(attempt int) time.Duration {
	base := 30 * time.Second
	switch attempt {
	case 1:
		return base // 30s
	case 2:
		return 2 * time.Minute
	case 3:
		return 10 * time.Minute
	default:
		return 1 * time.Hour
	}
}

// EnqueueWithDefaults is a convenience used by the webhook handler — wraps
// Enqueue with sensible defaults and returns a contextful error message.
func EnqueueWithDefaults(ctx context.Context, q Queue, slug, handlerType string, updateID int64, payload []byte) error {
	if q == nil {
		return fmt.Errorf("queue not initialized (DATABASE_URL unset ?)")
	}
	return q.Enqueue(ctx, Job{
		BotSlug:     slug,
		HandlerType: handlerType,
		UpdateID:    updateID,
		Payload:     payload,
	})
}