// Package database wires up GORM against SQLite (WAL mode) and exposes the
// auto-migration entry point used at startup.
package database

import (
	"context"
	"fmt"
	"path/filepath"

	"github.com/glebarez/sqlite"
	"go.uber.org/zap"
	"gorm.io/gorm"
	"gorm.io/gorm/logger"

	"github.com/ShukeBta/MediaStationGo/internal/config"
	"github.com/ShukeBta/MediaStationGo/internal/model"
)

// Open initialises the SQLite database file applying WAL pragmas for
// better concurrent read performance — same defaults as nowen-video.
func Open(cfg *config.Config, log *zap.Logger) (*gorm.DB, error) {
	dsn := buildDSN(cfg)

	gormLogger := logger.New(
		zapStdLogger{log: log},
		logger.Config{
			SlowThreshold:             0,
			LogLevel:                  logger.Warn,
			IgnoreRecordNotFoundError: true,
			Colorful:                  false,
		},
	)

	db, err := gorm.Open(sqlite.Open(dsn), &gorm.Config{
		Logger:                                   gormLogger,
		PrepareStmt:                              true,
		DisableForeignKeyConstraintWhenMigrating: false,
	})
	if err != nil {
		return nil, fmt.Errorf("gorm open: %w", err)
	}
	installSQLiteWriteGate(db)
	sqlDB, err := db.DB()
	if err != nil {
		return nil, fmt.Errorf("gorm sqldb: %w", err)
	}
	if cfg.Database.MaxOpenConns > 0 {
		sqlDB.SetMaxOpenConns(cfg.Database.MaxOpenConns)
	}
	if cfg.Database.MaxIdleConns > 0 {
		sqlDB.SetMaxIdleConns(cfg.Database.MaxIdleConns)
	}
	return db, nil
}

func installSQLiteWriteGate(db *gorm.DB) {
	if db == nil {
		return
	}
	const lockedKey = "mediastation:sqlite_write_locked"
	gate := newSQLiteWriteGate()
	lock := func(tx *gorm.DB) {
		ctx := context.Background()
		if tx.Statement != nil && tx.Statement.Context != nil {
			ctx = tx.Statement.Context
		}
		if err := gate.Lock(ctx); err != nil {
			_ = tx.AddError(err)
			return
		}
		tx.InstanceSet(lockedKey, struct{}{})
	}
	unlock := func(tx *gorm.DB) {
		if _, ok := tx.InstanceGet(lockedKey); ok {
			gate.Unlock()
		}
	}
	_ = db.Callback().Create().Before("gorm:create").Register("mediastation:sqlite_write_lock", lock)
	_ = db.Callback().Create().After("gorm:create").Register("mediastation:sqlite_write_unlock", unlock)
	_ = db.Callback().Update().Before("gorm:update").Register("mediastation:sqlite_write_lock", lock)
	_ = db.Callback().Update().After("gorm:update").Register("mediastation:sqlite_write_unlock", unlock)
	_ = db.Callback().Delete().Before("gorm:delete").Register("mediastation:sqlite_write_lock", lock)
	_ = db.Callback().Delete().After("gorm:delete").Register("mediastation:sqlite_write_unlock", unlock)
	_ = db.Callback().Raw().Before("gorm:raw").Register("mediastation:sqlite_write_lock", lock)
	_ = db.Callback().Raw().After("gorm:raw").Register("mediastation:sqlite_write_unlock", unlock)
}

// sqliteWriteGate 串行化进程内的 SQLite 写操作，避免多连接写竞争触发
// SQLITE_BUSY。Lock 尊重语句自身的 context：此前用 sync.Mutex 时，一条
// 长写语句（如 FTS 回填批次）会让登录等关键写操作无限期排队——客户端
// 早已超时断开，goroutine 还挂在互斥锁上。现在等待方可随 context 取消
// 及时失败，不再把整个进程的写路径拖死。
type sqliteWriteGate struct {
	ch chan struct{}
}

func newSQLiteWriteGate() *sqliteWriteGate {
	return &sqliteWriteGate{ch: make(chan struct{}, 1)}
}

func (g *sqliteWriteGate) Lock(ctx context.Context) error {
	select {
	case g.ch <- struct{}{}:
		return nil
	default:
	}
	if ctx == nil {
		ctx = context.Background()
	}
	select {
	case g.ch <- struct{}{}:
		return nil
	case <-ctx.Done():
		return ctx.Err()
	}
}

func (g *sqliteWriteGate) Unlock() {
	select {
	case <-g.ch:
	default:
	}
}

func buildDSN(cfg *config.Config) string {
	dbPath := cfg.Database.DBPath
	if !filepath.IsAbs(dbPath) {
		// keep as-is to respect user-provided relative paths.
		dbPath = filepath.Clean(dbPath)
	}
	dsn := dbPath + "?_pragma=foreign_keys(1)"
	if cfg.Database.WALMode {
		dsn += "&_pragma=journal_mode(WAL)"
	}
	if cfg.Database.BusyTimeout > 0 {
		dsn += fmt.Sprintf("&_pragma=busy_timeout(%d)", cfg.Database.BusyTimeout)
	}
	if cfg.Database.CacheSize != 0 {
		dsn += fmt.Sprintf("&_pragma=cache_size(%d)", cfg.Database.CacheSize)
	}
	return dsn
}

// AutoMigrate creates tables for every model registered in the model package.
func AutoMigrate(db *gorm.DB) error {
	if err := db.AutoMigrate(model.AllModels()...); err != nil {
		return err
	}
	if err := enforceTelegramBindingOneToOne(db); err != nil {
		return err
	}
	if err := ensurePerformanceIndexes(db); err != nil {
		return err
	}
	return ensureMediaSearchIndex(db)
}

func ensurePerformanceIndexes(db *gorm.DB) error {
	statements := []string{
		`CREATE INDEX IF NOT EXISTS idx_media_library_created_active ON media(library_id, created_at DESC) WHERE deleted_at IS NULL`,
		`CREATE INDEX IF NOT EXISTS idx_media_library_episode_active ON media(library_id, season_num, episode_num, created_at DESC) WHERE deleted_at IS NULL`,
		`CREATE INDEX IF NOT EXISTS idx_media_series_active ON media(series_id, season_num, episode_num) WHERE deleted_at IS NULL`,
		`CREATE INDEX IF NOT EXISTS idx_media_title_active ON media(title COLLATE NOCASE) WHERE deleted_at IS NULL`,
		`CREATE INDEX IF NOT EXISTS idx_media_original_name_active ON media(original_name COLLATE NOCASE) WHERE deleted_at IS NULL`,
		`CREATE INDEX IF NOT EXISTS idx_favorites_user_media_active ON favorites(user_id, media_id) WHERE deleted_at IS NULL`,
		`CREATE INDEX IF NOT EXISTS idx_playback_histories_user_media_active ON playback_histories(user_id, media_id, watched_at DESC) WHERE deleted_at IS NULL`,
		`CREATE INDEX IF NOT EXISTS idx_playback_histories_resume_active ON playback_histories(user_id, completed, watched_at DESC) WHERE deleted_at IS NULL`,
		`CREATE INDEX IF NOT EXISTS idx_play_profiles_user_created_active ON play_profiles(user_id, created_at DESC) WHERE deleted_at IS NULL`,
	}
	for _, stmt := range statements {
		if err := db.Exec(stmt).Error; err != nil {
			return err
		}
	}
	return nil
}

// mediaSearchIndexSchemaVersion 标识 FTS 索引的物理布局版本。
// v2：FTS 行的 rowid 与 media.rowid 对齐，并由触发器实时维护。
const mediaSearchIndexSchemaVersion = 2

func ensureMediaSearchIndex(db *gorm.DB) error {
	if err := db.Exec(`CREATE TABLE IF NOT EXISTS media_search_meta (id INTEGER PRIMARY KEY CHECK (id = 1), version INTEGER NOT NULL)`).Error; err != nil {
		return nil
	}
	var version int
	_ = db.Raw(`SELECT version FROM media_search_meta WHERE id = 1`).Scan(&version).Error
	if version != mediaSearchIndexSchemaVersion {
		// 旧版（v1）FTS 表按 UNINDEXED 的 media_id 寻址。FTS5 的普通列
		// 不支持索引查找，按 media_id 的 DELETE / NOT EXISTS 都是整表
		// 扫描：十几万行的库每次启动回填要做上百亿次行访问，纯 Go
		// sqlite 直接把 CPU 钉满数小时，并隔着全局写锁拖死登录。
		// v2 起 FTS 行的 rowid 与 media.rowid 对齐，所有寻址走 rowid
		// 点查，索引一致性交给下方触发器维护。
		for _, stmt := range []string{
			`DROP TRIGGER IF EXISTS media_search_fts_ai`,
			`DROP TRIGGER IF EXISTS media_search_fts_au`,
			`DROP TRIGGER IF EXISTS media_search_fts_ad`,
			`DROP TABLE IF EXISTS media_search_fts`,
		} {
			_ = db.Exec(stmt).Error
		}
	}
	if err := db.Exec(`CREATE VIRTUAL TABLE IF NOT EXISTS media_search_fts USING fts5(media_id UNINDEXED, title, original_name, path, genres, tokenize='trigram')`).Error; err != nil {
		if fallbackErr := db.Exec(`CREATE VIRTUAL TABLE IF NOT EXISTS media_search_fts USING fts5(media_id UNINDEXED, title, original_name, path, genres, tokenize='unicode61')`).Error; fallbackErr != nil {
			// FTS is an acceleration path. Some embedded SQLite builds may omit
			// FTS5; keep startup working and let repository queries fall back to
			// LIKE-based Chinese fuzzy search.
			return nil
		}
	}
	// 触发器让 FTS 与 media 行保持同步（新增/标题刮削改写/软删/恢复/
	// 硬删全覆盖），应用层不再需要按 media_id 手工刷新索引——也顺带
	// 修复了刮削直写 Updates() 后新标题搜不到的问题。
	for _, stmt := range []string{
		`CREATE TRIGGER IF NOT EXISTS media_search_fts_ai AFTER INSERT ON media WHEN new.deleted_at IS NULL BEGIN
			DELETE FROM media_search_fts WHERE rowid = new.rowid;
			INSERT INTO media_search_fts(rowid, media_id, title, original_name, path, genres)
			VALUES (new.rowid, new.id, COALESCE(new.title, ''), COALESCE(new.original_name, ''), COALESCE(new.path, ''), COALESCE(new.genres, ''));
		END`,
		`CREATE TRIGGER IF NOT EXISTS media_search_fts_au AFTER UPDATE OF title, original_name, path, genres, deleted_at ON media BEGIN
			DELETE FROM media_search_fts WHERE rowid = old.rowid;
			INSERT INTO media_search_fts(rowid, media_id, title, original_name, path, genres)
			SELECT new.rowid, new.id, COALESCE(new.title, ''), COALESCE(new.original_name, ''), COALESCE(new.path, ''), COALESCE(new.genres, '')
			WHERE new.deleted_at IS NULL;
		END`,
		`CREATE TRIGGER IF NOT EXISTS media_search_fts_ad AFTER DELETE ON media BEGIN
			DELETE FROM media_search_fts WHERE rowid = old.rowid;
		END`,
	} {
		if err := db.Exec(stmt).Error; err != nil {
			return err
		}
	}
	if version != mediaSearchIndexSchemaVersion {
		if err := db.Exec(`INSERT INTO media_search_meta(id, version) VALUES (1, ?) ON CONFLICT(id) DO UPDATE SET version = excluded.version`, mediaSearchIndexSchemaVersion).Error; err != nil {
			return err
		}
	}
	return nil
}

func enforceTelegramBindingOneToOne(db *gorm.DB) error {
	if !db.Migrator().HasTable(&model.TelegramBinding{}) {
		return nil
	}
	return db.Transaction(func(tx *gorm.DB) error {
		if err := tx.Exec(`
DELETE FROM telegram_bindings
WHERE deleted_at IS NULL
  AND user_id IN (
    SELECT user_id
    FROM telegram_bindings
    WHERE deleted_at IS NULL
    GROUP BY user_id
    HAVING COUNT(*) > 1
  )
  AND id NOT IN (
    SELECT id
    FROM (
      SELECT id,
             ROW_NUMBER() OVER (PARTITION BY user_id ORDER BY created_at ASC, id ASC) AS rn
      FROM telegram_bindings
      WHERE deleted_at IS NULL
    )
    WHERE rn = 1
  )
`).Error; err != nil {
			return err
		}
		return tx.Exec(`
CREATE UNIQUE INDEX IF NOT EXISTS idx_telegram_bindings_user_id_active
ON telegram_bindings(user_id)
WHERE deleted_at IS NULL
`).Error
	})
}

// zapStdLogger adapts a *zap.Logger to GORM's tiny logger interface.
type zapStdLogger struct{ log *zap.Logger }

func (z zapStdLogger) Printf(format string, args ...interface{}) {
	z.log.Sugar().Infof(format, args...)
}