// Package scanner walks configured music folders, detects new/changed/
// deleted/renamed files, and indexes them into the library via a bounded
// worker pool.
package scanner

import (
	"context"
	"database/sql"
	"fmt"
	"io/fs"
	"log/slog"
	"os"
	"path/filepath"
	"strings"
	"sync"
	"time"

	"git.noroutes.net/NoRoutes/vibetunes/internal/coverart"
	"git.noroutes.net/NoRoutes/vibetunes/internal/database"
	"git.noroutes.net/NoRoutes/vibetunes/internal/library"
	"git.noroutes.net/NoRoutes/vibetunes/internal/metadata"
	"git.noroutes.net/NoRoutes/vibetunes/internal/streaming"
)

// recognizedExtensions are the file extensions VibeSonic attempts to
// probe as media. Anything else (art, .nfo, playlists, ...) is skipped
// during a scan rather than passed to ffprobe.
var recognizedExtensions = map[string]bool{
	".mp3": true, ".flac": true, ".ogg": true, ".oga": true, ".opus": true,
	".aac": true, ".m4a": true, ".m4b": true, ".alac": true,
	".wav": true, ".aiff": true, ".aif": true, ".wma": true, ".mp4": true,
}

const maxWorkers = 4

// Scanner indexes one or more music folders into the database.
type Scanner struct {
	DB     *sql.DB
	Prober *metadata.Prober
	Log    *slog.Logger

	mu       sync.Mutex
	scanning map[string]bool // music_folder_id -> in progress
}

func New(db *sql.DB, prober *metadata.Prober, log *slog.Logger) *Scanner {
	return &Scanner{DB: db, Prober: prober, Log: log, scanning: make(map[string]bool)}
}

// ScanFolder walks a single music folder and indexes it incrementally:
// unchanged files (same size+mtime) are only marked seen, changed files
// are reprobed, moved files are matched by content hash and just get
// their path updated, and files no longer found on disk are marked
// missing rather than deleted outright.
func (s *Scanner) ScanFolder(ctx context.Context, folderID string) error {
	if !s.beginScan(folderID) {
		return fmt.Errorf("scan already in progress for folder %s", folderID)
	}
	defer s.endScan(folderID)

	folder, err := database.GetMusicFolder(s.DB, folderID)
	if err != nil {
		return err
	}

	startedAt := time.Now()
	if err := database.StartScan(s.DB, folderID); err != nil {
		return err
	}

	var seen, added, updated int
	var mu sync.Mutex
	sem := make(chan struct{}, maxWorkers)
	var wg sync.WaitGroup
	var firstErr error

	walkErr := filepath.WalkDir(folder.Path, func(path string, d fs.DirEntry, err error) error {
		if err != nil {
			s.Log.Warn("scan: walk error", "path", path, "err", err)
			return nil // keep scanning the rest of the tree
		}
		if ctx.Err() != nil {
			return ctx.Err()
		}
		if d.IsDir() {
			return nil
		}
		if !recognizedExtensions[strings.ToLower(filepath.Ext(path))] {
			return nil
		}
		rel, err := filepath.Rel(folder.Path, path)
		if err != nil {
			return nil
		}
		rel = filepath.ToSlash(rel)

		wg.Add(1)
		sem <- struct{}{}
		go func() {
			defer wg.Done()
			defer func() { <-sem }()

			wasAdded, wasUpdated, err := s.indexOne(ctx, folder.ID, path, rel)
			mu.Lock()
			defer mu.Unlock()
			seen++
			if err != nil {
				s.Log.Warn("scan: index failed", "path", rel, "err", err)
			} else {
				if wasAdded {
					added++
				} else if wasUpdated {
					updated++
				}
			}
			if seen%25 == 0 {
				_ = database.UpdateScanProgress(s.DB, folder.ID, seen, added, updated)
			}
		}()
		return nil
	})
	wg.Wait()
	if walkErr != nil && firstErr == nil {
		firstErr = walkErr
	}

	_ = database.UpdateScanProgress(s.DB, folder.ID, seen, added, updated)

	removed, err := database.MarkFolderFilesMissingExcept(s.DB, folder.ID, startedAt)
	if err != nil && firstErr == nil {
		firstErr = err
	}

	errMsg := ""
	if firstErr != nil {
		errMsg = firstErr.Error()
	}
	if err := database.FinishScan(s.DB, folder.ID, int(removed), errMsg); err != nil {
		return err
	}
	return firstErr
}

// indexOne probes and indexes a single file, returning whether it was
// newly added or updated so the caller can track progress.
func (s *Scanner) indexOne(ctx context.Context, folderID, absPath, relPath string) (added, updated bool, err error) {
	info, err := os.Stat(absPath)
	if err != nil {
		return false, false, err
	}
	size := info.Size()
	mtime := info.ModTime().Unix()
	hash := fingerprint(size, mtime)

	existing, err := database.FindMediaFileByPath(s.DB, folderID, relPath)
	if err == nil {
		if existing.SizeBytes == size && existing.MtimeUnix == mtime {
			return false, false, database.TouchMediaFileScanned(s.DB, existing.ID)
		}
		// Changed: reprobe and update in place; the media_file (and
		// therefore song) ID stays the same.
		tags, perr := s.Prober.Probe(ctx, absPath)
		if perr != nil {
			return false, false, perr
		}
		if err := database.UpdateMediaFileScanned(s.DB, existing.ID, size, mtime, hash, tags.Format, tags.Kind, tags.DurationSeconds, tags.BitrateKbps, tags.SampleRateHz, tags.Channels); err != nil {
			return false, false, err
		}
		mf, err := database.GetMediaFile(s.DB, existing.ID)
		if err != nil {
			return false, false, err
		}
		song, err := library.IndexFile(s.DB, mf, absPath, tags)
		if err != nil {
			return false, false, err
		}
		s.indexCoverArt(absPath, song, tags)
		return false, true, nil
	}
	if err != database.ErrNotFound {
		return false, false, err
	}

	// Not found by path. Check whether this is a rename/move of a file we
	// already indexed (same content fingerprint, different path).
	if renamed, rerr := database.FindMediaFileByHash(s.DB, folderID, hash); rerr == nil {
		if err := database.RenameMediaFile(s.DB, renamed.ID, relPath); err != nil {
			return false, false, err
		}
		return false, true, nil
	}

	// Genuinely new file.
	tags, err := s.Prober.Probe(ctx, absPath)
	if err != nil {
		return false, false, err
	}
	mf, err := database.CreateMediaFile(s.DB, folderID, relPath, size, mtime, hash, tags.Format, tags.Kind, tags.DurationSeconds, tags.BitrateKbps, tags.SampleRateHz, tags.Channels)
	if err != nil {
		return false, false, err
	}
	song, err := library.IndexFile(s.DB, mf, absPath, tags)
	if err != nil {
		return false, false, err
	}
	s.indexCoverArt(absPath, song, tags)
	return true, false, nil
}

// indexCoverArt records where an album's cover art can be found: a
// folder image next to the file if one exists, otherwise the file's own
// embedded artwork (extracted lazily by the web layer on request, not
// here). Failures are non-fatal to the scan.
func (s *Scanner) indexCoverArt(absPath string, song *database.Song, tags *metadata.Tags) {
	if !song.AlbumID.Valid {
		return
	}
	dir := filepath.Dir(absPath)
	if folderImage := coverart.FindFolderImage(dir); folderImage != "" {
		hash, err := coverart.ContentHashOf(folderImage)
		if err != nil {
			return
		}
		_, _ = database.UpsertAlbumCoverArt(s.DB, song.AlbumID.String, "folder", folderImage, "", streaming.MimeType(folderImage), hash, 0, 0)
		return
	}
	if tags.HasEmbeddedArt {
		_, _ = database.UpsertAlbumCoverArt(s.DB, song.AlbumID.String, "embedded", "", song.MediaFileID, "image/jpeg", song.MediaFileID, 0, 0)
	}
}

// fingerprint is a cheap, fast rename/change detector based on size and
// mtime rather than hashing file content (which would mean reading every
// byte of every file on every scan).
func fingerprint(size, mtime int64) string {
	return fmt.Sprintf("%d-%d", size, mtime)
}

func (s *Scanner) beginScan(folderID string) bool {
	s.mu.Lock()
	defer s.mu.Unlock()
	if s.scanning[folderID] {
		return false
	}
	s.scanning[folderID] = true
	return true
}

func (s *Scanner) endScan(folderID string) {
	s.mu.Lock()
	defer s.mu.Unlock()
	delete(s.scanning, folderID)
}

// IsScanning reports whether a scan of folderID is currently running.
func (s *Scanner) IsScanning(folderID string) bool {
	s.mu.Lock()
	defer s.mu.Unlock()
	return s.scanning[folderID]
}

// IsAnyScanning reports whether any folder is currently being scanned.
func (s *Scanner) IsAnyScanning() bool {
	s.mu.Lock()
	defer s.mu.Unlock()
	return len(s.scanning) > 0
}

// ScanAllEnabled scans every enabled music folder sequentially (folders
// run one at a time; files within a folder run concurrently via the
// worker pool above).
func (s *Scanner) ScanAllEnabled(ctx context.Context) error {
	folders, err := database.ListMusicFolders(s.DB)
	if err != nil {
		return err
	}
	var firstErr error
	for _, f := range folders {
		if !f.Enabled {
			continue
		}
		if err := s.ScanFolder(ctx, f.ID); err != nil && firstErr == nil {
			firstErr = err
		}
	}
	return firstErr
}

// RunScheduled runs ScanAllEnabled once at startup and then on the given
// interval, until ctx is cancelled. interval <= 0 disables the periodic
// rescan (startup scan still runs).
func (s *Scanner) RunScheduled(ctx context.Context, interval time.Duration) {
	if err := s.ScanAllEnabled(ctx); err != nil {
		s.Log.Warn("startup scan finished with errors", "err", err)
	}
	if interval <= 0 {
		return
	}
	ticker := time.NewTicker(interval)
	defer ticker.Stop()
	for {
		select {
		case <-ctx.Done():
			return
		case <-ticker.C:
			if err := s.ScanAllEnabled(ctx); err != nil {
				s.Log.Warn("scheduled scan finished with errors", "err", err)
			}
		}
	}
}