package config

import (
	"context"
	"os"
	"path/filepath"
	"testing"
	"time"

	"github.com/spf13/viper"
	"github.com/stretchr/testify/assert"
	"github.com/stretchr/testify/require"
)

// loadFromFile is a helper that mimics LoadConfig() for a specific file path
// without going through the env-prefix and singleton machinery — keeps the
// test hermetic.
func loadFromFile(t *testing.T, path string) *Config {
	t.Helper()
	v := viper.New()
	v.SetConfigFile(path)
	v.SetConfigType("yaml")
	v.SetDefault("logging.level", "info")
	v.SetDefault("auth.jwt.ttl", time.Hour)
	require.NoError(t, v.ReadInConfig())

	c := &Config{viper: v}
	require.NoError(t, v.Unmarshal(c))
	return c
}

// TestWatchAndApply_LoggingLevel proves the hot-reload pipe end-to-end:
// write a new logging.level to the watched file, the OnConfigChange handler
// re-unmarshals, and the in-memory Config reflects the new value.
func TestWatchAndApply_LoggingLevel(t *testing.T) {
	dir := t.TempDir()
	path := filepath.Join(dir, "config.yaml")
	require.NoError(t, os.WriteFile(path, []byte("logging:\n  level: info\n"), 0644))

	c := loadFromFile(t, path)
	assert.Equal(t, "info", c.GetLogLevel())

	ctx, cancel := context.WithCancel(context.Background())
	defer cancel()
	c.WatchAndApply(ctx)

	// Mutate the file. fsnotify needs a real write event; rewrite atomically.
	require.NoError(t, os.WriteFile(path, []byte("logging:\n  level: debug\n"), 0644))

	// Poll for up to 2s waiting for the in-memory level to flip.
	deadline := time.Now().Add(2 * time.Second)
	for time.Now().Before(deadline) {
		c.reloadMu.RLock()
		level := c.GetLogLevel()
		c.reloadMu.RUnlock()
		if level == "debug" {
			return
		}
		time.Sleep(20 * time.Millisecond)
	}
	c.reloadMu.RLock()
	defer c.reloadMu.RUnlock()
	t.Fatalf("logging level did not hot-reload to debug: still %q", c.GetLogLevel())
}

// TestWatchAndApply_NoFileNoOp confirms the watcher is a safe no-op when no
// config file is in use (env-only / defaults) — important so production
// containers without a mounted config.yaml don't crash.
func TestWatchAndApply_NoFileNoOp(t *testing.T) {
	c := &Config{viper: viper.New()}
	ctx, cancel := context.WithCancel(context.Background())
	defer cancel()
	c.WatchAndApply(ctx) // should return without panicking
}

// TestWatchAndApply_NilViperNoOp confirms the watcher tolerates a Config
// constructed without the viper field (e.g. tests that build a Config{}
// manually — same defensive code path as production but exercised explicitly).
func TestWatchAndApply_NilViperNoOp(t *testing.T) {
	c := &Config{}
	ctx, cancel := context.WithCancel(context.Background())
	defer cancel()
	c.WatchAndApply(ctx)
}

// TestWatchAndApply_JWTTTL proves Phase 2 of ADR-0023: the JWT TTL is
// re-read on every token generation via the GetJWTTTL method value, so
// after a config-file change the new TTL takes effect without restart.
func TestWatchAndApply_JWTTTL(t *testing.T) {
	dir := t.TempDir()
	path := filepath.Join(dir, "config.yaml")
	require.NoError(t, os.WriteFile(path, []byte("auth:\n  jwt:\n    ttl: 1h\n"), 0644))

	c := loadFromFile(t, path)
	assert.Equal(t, time.Hour, c.GetJWTTTL())

	ctx, cancel := context.WithCancel(context.Background())
	defer cancel()
	c.WatchAndApply(ctx)

	require.NoError(t, os.WriteFile(path, []byte("auth:\n  jwt:\n    ttl: 30m\n"), 0644))

	deadline := time.Now().Add(2 * time.Second)
	for time.Now().Before(deadline) {
		c.reloadMu.RLock()
		ttl := c.GetJWTTTL()
		c.reloadMu.RUnlock()
		if ttl == 30*time.Minute {
			return
		}
		time.Sleep(20 * time.Millisecond)
	}
	c.reloadMu.RLock()
	defer c.reloadMu.RUnlock()
	t.Fatalf("auth.jwt.ttl did not hot-reload to 30m: still %s", c.GetJWTTTL())
}