package library

import (
	"fmt"

	"yellowjacket/backend/events"
)

// scanQueueEntry holds the metadata needed to scan a single library.
type scanQueueEntry struct {
	libraryID   int64
	libraryName string
	libraryPath string
}

// ScanLibrary queues a scan for the library with the given database ID.
// If no scan is active the library is scanned immediately; otherwise it
// is appended to the queue. Duplicate requests (same library already
// scanning or already queued) are silently ignored.
func (l *Library) ScanLibrary(id int64) error {
	lib, err := l.db.Queries.GetLibrary(l.ctx, id)
	if err != nil {
		return fmt.Errorf("could not get library %d: %w", id, err)
	}

	l.mu.Lock()

	// Silent dedup: already scanning this library.
	if l.currentScanLibraryID == id {
		l.mu.Unlock()

		return nil
	}

	// Silent dedup: already queued.
	for _, entry := range l.scanQueue {
		if entry.libraryID == id {
			l.mu.Unlock()

			return nil
		}
	}

	entry := scanQueueEntry{
		libraryID:   lib.ID,
		libraryName: lib.Name,
		libraryPath: lib.Path,
	}

	if !l.scanActive {
		l.scanActive = true
		l.currentScanLibraryID = entry.libraryID
		l.currentScanLibraryName = entry.libraryName
		l.mu.Unlock()

		go l.startScan(entry)

		return nil
	}

	// A scan is already running — queue this library.
	l.scanQueue = append(l.scanQueue, entry)
	queueLength := len(l.scanQueue)
	l.mu.Unlock()

	l.emit(events.LibraryScanQueued, map[string]any{
		"libraryId":   lib.ID,
		"libraryName": lib.Name,
		"queueLength": queueLength,
	})

	// Registering the queued job takes l.mu again, so it must happen
	// after the unlock above.
	l.registerQueuedScanJob(entry)

	return nil
}

// ScanAllLibraries queries all libraries from the database and queues
// each one for scanning. Existing dedup logic ensures no duplicates.
func (l *Library) ScanAllLibraries() error {
	libs, err := l.db.Queries.GetAllLibraries(l.ctx)
	if err != nil {
		return fmt.Errorf("could not get all libraries: %w", err)
	}

	for _, lib := range libs {
		if err := l.ScanLibrary(lib.ID); err != nil {
			l.logger.Warn(
				"could not queue library for scan",
				"libraryID", lib.ID,
				"libraryName", lib.Name,
				"err", err,
			)
		}
	}

	return nil
}

// SoftScanAllLibraries performs a lightweight launch-time scan.
// First it claims any orphaned tracks (library_id=0) left over from
// the pre-multi-library schema. Then for each library it compares
// the number of audio files on disk against the track count in the
// database. Only libraries where the counts differ (files added or
// removed since last scan) are queued for a full scan. Libraries
// that are unchanged are silently skipped — no progress bar, no
// scan events.
func (l *Library) SoftScanAllLibraries() error {
	libs, err := l.db.Queries.GetAllLibraries(l.ctx)
	if err != nil {
		return fmt.Errorf("could not get all libraries: %w", err)
	}

	// Claim orphaned tracks from the pre-multi-library schema.
	// Tracks with library_id=0 exist from before the migration and
	// need to be assigned to the library whose path matches.
	// SAFETY: Hand-crafted UPDATE — path-prefix LIKE matching with
	// dynamic library_id unsupported by sqlc. No user input.
	for _, lib := range libs {
		result, claimErr := l.db.ExecContext(
			`UPDATE audio_files SET library_id = ?`+
				` WHERE library_id = 0`+
				` AND file_path LIKE ? || '%'`,
			lib.ID, lib.Path+"/",
		)
		if claimErr != nil {
			l.logger.Warn("soft scan: could not claim orphaned tracks",
				"libraryID", lib.ID, "err", claimErr)
		} else if claimed, _ := result.RowsAffected(); claimed > 0 {
			l.logger.Info("soft scan: claimed orphaned tracks",
				"libraryID", lib.ID, "libraryName", lib.Name,
				"claimed", claimed)
		}
	}

	for _, lib := range libs {
		// A scan the user paused stays paused across restarts — the
		// soft scan must not quietly start it again behind their back.
		// RestorePausedScans has already surfaced it in the jobs panel
		// with a resume button.
		if l.isScanPausedPersistently(lib.ID) {
			l.logger.Info(
				"soft scan: library scan is paused, skipping",
				"libraryID", lib.ID,
				"libraryName", lib.Name,
			)

			continue
		}

		dbCount, countErr := l.db.Queries.CountAudioFiles(
			l.ctx, lib.ID,
		)
		if countErr != nil {
			l.logger.Warn(
				"soft scan: could not count DB tracks, queueing full scan",
				"libraryID", lib.ID,
				"libraryName", lib.Name,
				"err", countErr,
			)

			_ = l.ScanLibrary(lib.ID)

			continue
		}

		dbModTime, modErr := l.db.Queries.GetLibraryMaxModifiedAt(
			l.ctx, lib.ID,
		)
		if modErr != nil {
			l.logger.Warn(
				"soft scan: could not read newest mtime, queueing full scan",
				"libraryID", lib.ID,
				"libraryName", lib.Name,
				"err", modErr,
			)

			_ = l.ScanLibrary(lib.ID)

			continue
		}

		// Excluded paths are on disk and deliberately not in the
		// database, so the survey must skip them or the two counts
		// disagree forever and every launch queues a full scan.
		diskCount, diskModTime := surveyAudioFiles(
			lib.Path, l.excludedPathSet(lib.ID),
		)

		// A newer file on disk than anything on record means something
		// was edited in place since the last scan.  An older newest-mtime
		// is not evidence of a change: deleting the newest file lowers it
		// while the count check already covers that case.
		staleTags := diskModTime > dbModTime

		if diskCount == dbCount && !staleTags {
			l.logger.Info(
				"soft scan: library unchanged, skipping",
				"libraryID", lib.ID,
				"libraryName", lib.Name,
				"tracks", dbCount,
			)

			continue
		}

		l.logger.Info(
			"soft scan: library changed, queueing scan",
			"libraryID", lib.ID,
			"libraryName", lib.Name,
			"diskFiles", diskCount,
			"dbTracks", dbCount,
			"diskModTime", diskModTime,
			"dbModTime", dbModTime,
			"reason", softScanReason(diskCount != dbCount, staleTags),
		)

		if err := l.ScanLibrary(lib.ID); err != nil {
			l.logger.Warn(
				"soft scan: could not queue library",
				"libraryID", lib.ID,
				"libraryName", lib.Name,
				"err", err,
			)
		}
	}

	return nil
}

// softScanReason labels why the soft scan queued a library, for the log.
func softScanReason(countChanged, staleTags bool) string {
	switch {
	case countChanged && staleTags:
		return "file count mismatch and modified files"
	case countChanged:
		return "file count mismatch"
	default:
		return "modified files"
	}
}

// CancelCurrentScan cancels only the currently scanning library.
// The next queued library (if any) starts automatically when the
// current scan's goroutine completes.
func (l *Library) CancelCurrentScan() {
	l.mu.Lock()
	cancel := l.scanCancel
	l.mu.Unlock()

	if cancel != nil {
		cancel()
	}
}

// CancelAllScans cancels the current scan and clears the entire
// queue so no further libraries are scanned.
func (l *Library) CancelAllScans() {
	l.mu.Lock()
	l.scanQueue = nil
	cancel := l.scanCancel
	l.mu.Unlock()

	if cancel != nil {
		cancel()
	}
}

// GetScanQueueLength returns the number of libraries waiting in the
// scan queue (excludes the currently scanning library).
func (l *Library) GetScanQueueLength() int {
	l.mu.Lock()
	defer l.mu.Unlock()

	return len(l.scanQueue)
}

// QueuedLibraryNames returns the display names of libraries waiting
// in the scan queue, in FIFO order.
func (l *Library) QueuedLibraryNames() []string {
	l.mu.Lock()
	defer l.mu.Unlock()

	names := make([]string, len(l.scanQueue))
	for i, entry := range l.scanQueue {
		names[i] = entry.libraryName
	}

	return names
}

// startScan runs the scan for a single library entry and then drains
// the queue. It is always called in a new goroutine.
func (l *Library) startScan(entry scanQueueEntry) {
	l.scanInternal(entry.libraryID, entry.libraryName, entry.libraryPath)
	l.drainQueue()
}

// drainQueue is called after each scan completes. If the queue is
// non-empty the next entry is popped and scanned; otherwise the
// scan pipeline is marked idle.
func (l *Library) drainQueue() {
	l.mu.Lock()

	if len(l.scanQueue) > 0 {
		next := l.scanQueue[0]
		l.scanQueue = l.scanQueue[1:]
		l.currentScanLibraryID = next.libraryID
		l.currentScanLibraryName = next.libraryName
		l.mu.Unlock()

		go l.startScan(next)

		return
	}

	l.currentScanLibraryID = 0
	l.currentScanLibraryName = ""
	l.scanActive = false
	hooks := l.scanHooks
	l.mu.Unlock()

	l.emit(events.LibraryScanQueueDrained)

	if hooks.OnAllScansComplete != nil {
		hooks.OnAllScansComplete()
	}
}
