package downloader

import (
	"bufio"
	"bytes"
	"context"
	"errors"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"os"
	"os/exec"
	"path"
	"path/filepath"
	"regexp"
	"sort"
	"strings"
	"time"

	"github.com/PuerkitoBio/goquery"
	"github.com/grafov/m3u8"
)

const (
	defaultClientTimeout = 30 * time.Second
	vodSegmentTimeout    = 5 * time.Minute // Longer timeout for VOD segments which can be large
	maxRedirects         = 5
	playlistPollInterval = 2 * time.Second // Poll interval for livestreams
)

var (
	errInvalidPlaylist   = errors.New("unsupported playlist type. expected media playlist")
	errUnsupportedMaster = errors.New("master playlist contains no playable variants")
	errFFmpegMissing     = errors.New("ffmpeg is required on PATH to transmux segments")
	errNoStreamsFound    = errors.New("no HLS playlists found on page")
)

type segmentInfo struct {
	Sequence uint64
	URI      string
}

// Download downloads the video stream(s) referenced by the given URL into files derived from outputName.
// If outputName is empty, a base name is inferred from the source URL.
func Download(ctx context.Context, sourceURL, outputName string) error {
	if sourceURL == "" {
		return errors.New("stream URL must not be empty")
	}

	parsed, err := url.Parse(sourceURL)
	if err != nil {
		return fmt.Errorf("invalid URL: %w", err)
	}

	client := &http.Client{Timeout: defaultClientTimeout}

	contentType, err := peekContentType(ctx, client, parsed)
	if err != nil {
		return fmt.Errorf("detect content type: %w", err)
	}

	if strings.Contains(contentType, "text/html") {
		streams, err := extractPlaylistsFromHTML(ctx, client, parsed)
		if err != nil {
			return err
		}
		if len(streams) == 0 {
			return errNoStreamsFound
		}
		for idx, stream := range streams {
			name := outputName
			if name == "" {
				name = inferOutputNameMust(stream)
			}
			if len(streams) > 1 {
				ext := filepath.Ext(name)
				base := strings.TrimSuffix(name, ext)
				if base == "" {
					base = fmt.Sprintf("video-%d", idx+1)
				}
				name = base + fmt.Sprintf("-%02d", idx+1) + ext
			}
			if err := Download(ctx, stream, name); err != nil {
				return err
			}
		}
		return nil
	}

	// Use the original context for VOD downloads
	// For livestreams, a cancellable context will be created in downloadPlaylist
	return downloadPlaylist(ctx, client, parsed, outputName)
}

// watchForQuitKey watches for "q" keypress and cancels the context
func watchForQuitKey(cancel context.CancelFunc) {
	// Check if stdin is a terminal
	if !isTerminal(os.Stdin) {
		return // Not a terminal, skip keyboard input
	}

	// Print instruction once
	fmt.Fprintf(os.Stderr, "Press 'q' and Enter to stop downloading and convert to MP4\n")

	reader := bufio.NewReader(os.Stdin)
	for {
		line, err := reader.ReadString('\n')
		if err != nil {
			// EOF or error, stop watching
			return
		}
		// Check if line starts with 'q' or 'Q' (allows "q" or "q\n" or "quit\n", etc.)
		line = strings.TrimSpace(line)
		if len(line) > 0 && (line[0] == 'q' || line[0] == 'Q') {
			fmt.Fprintf(os.Stderr, "\nStopping download and converting to MP4...\n")
			cancel()
			return
		}
	}
}

// isTerminal checks if the file descriptor is a terminal
func isTerminal(f *os.File) bool {
	stat, err := f.Stat()
	if err != nil {
		return false
	}
	return (stat.Mode() & os.ModeCharDevice) != 0
}

func downloadPlaylist(ctx context.Context, client *http.Client, parsed *url.URL, outputName string) error {
	body, finalURL, err := fetchWithRedirects(ctx, client, parsed, maxRedirects)
	if err != nil {
		return fmt.Errorf("fetch playlist: %w", err)
	}
	defer body.Close()

	playlist, listType, err := m3u8.DecodeFrom(bufio.NewReader(body), true)
	if err != nil {
		return fmt.Errorf("parse playlist: %w", err)
	}

	var mediaPlaylist *m3u8.MediaPlaylist
	switch listType {
	case m3u8.MEDIA:
		mp, ok := playlist.(*m3u8.MediaPlaylist)
		if !ok {
			return errInvalidPlaylist
		}
		mediaPlaylist = mp
	case m3u8.MASTER:
		masterPlaylist, ok := playlist.(*m3u8.MasterPlaylist)
		if !ok {
			return errInvalidPlaylist
		}
		variantURL, err := selectVariant(masterPlaylist, finalURL)
		if err != nil {
			return err
		}
		return Download(ctx, variantURL, outputName)
	default:
		return errInvalidPlaylist
	}

	if len(mediaPlaylist.Segments) == 0 {
		return errors.New("playlist contains no segments")
	}

	name := outputName
	if name == "" {
		name = inferOutputName(finalURL)
	}

	// Check if this is a livestream (playlist is not closed)
	isLiveStream := !mediaPlaylist.Closed

	if isLiveStream {
		// For livestreams, create a cancellable context for keyboard input
		liveCtx, cancel := context.WithCancel(ctx)
		defer cancel()

		// Start keyboard input handler in a goroutine for livestreams only
		go watchForQuitKey(cancel)

		// For livestreams, write to a permanent .ts file
		tsName := ensureTSExtension(name)
		tsFile, err := os.Create(tsName)
		if err != nil {
			return fmt.Errorf("create output file: %w", err)
		}
		// downloadLiveStream handles file closing
		return downloadLiveStream(liveCtx, client, finalURL, mediaPlaylist, tsFile, name)
	}

	// For VOD (Video on Demand), download segments and use ffmpeg concat demuxer
	// Create a context without deadline for VOD downloads to avoid premature cancellation
	// Preserve cancellation from parent context but remove any deadline
	vodCtx, vodCancel := context.WithCancel(context.Background())
	defer vodCancel()

	// If parent context is cancelled, cancel VOD context too
	go func() {
		<-ctx.Done()
		vodCancel()
	}()

	// Create a client with longer timeout for VOD segments
	vodClient := &http.Client{Timeout: vodSegmentTimeout}

	// Create temp directory for segments
	tempDir, err := os.MkdirTemp("", "sdl-segments-*")
	if err != nil {
		return fmt.Errorf("create temp directory: %w", err)
	}
	defer os.RemoveAll(tempDir)

	segments := collectSegments(mediaPlaylist)
	totalSegments := len(segments)
	fmt.Fprintf(os.Stderr, "Downloading %d segments...\n", totalSegments)

	// Download each segment to a separate file
	segmentFiles := make([]string, 0, totalSegments)
	for i, segment := range segments {
		segmentFile := filepath.Join(tempDir, fmt.Sprintf("segment-%05d.ts", i))
		file, err := os.Create(segmentFile)
		if err != nil {
			return fmt.Errorf("create segment file %d: %w", i, err)
		}

		if err := downloadSegment(vodCtx, vodClient, finalURL, segment, file); err != nil {
			file.Close()
			return fmt.Errorf("download segment %d: %w", i, err)
		}

		if err := file.Sync(); err != nil {
			file.Close()
			return fmt.Errorf("sync segment file %d: %w", i, err)
		}

		if err := file.Close(); err != nil {
			return fmt.Errorf("close segment file %d: %w", i, err)
		}

		segmentFiles = append(segmentFiles, segmentFile)

		// Show progress: segment number, total, and percentage
		progress := float64(i+1) / float64(totalSegments) * 100
		fmt.Fprintf(os.Stderr, "\rProgress: %d/%d segments (%.1f%%)", i+1, totalSegments, progress)
		os.Stderr.Sync() // Flush progress output
	}
	fmt.Fprintf(os.Stderr, "\n")

	// Create concat file for ffmpeg concat protocol (not demuxer)
	// The concat protocol format is different: just file paths, one per line
	concatFile := filepath.Join(tempDir, "concat.txt")
	concatF, err := os.Create(concatFile)
	if err != nil {
		return fmt.Errorf("create concat file: %w", err)
	}

	for _, segFile := range segmentFiles {
		// Use absolute path for concat protocol
		absPath, err := filepath.Abs(segFile)
		if err != nil {
			concatF.Close()
			return fmt.Errorf("get absolute path: %w", err)
		}
		// Concat protocol format: just the path, one per line
		fmt.Fprintf(concatF, "%s\n", absPath)
	}
	if err := concatF.Close(); err != nil {
		return fmt.Errorf("close concat file: %w", err)
	}

	mp4Name := ensureMP4Extension(name)
	fmt.Fprintf(os.Stderr, "Converting to MP4...\n")
	if err := transmuxToMP4FromConcatProtocol(vodCtx, concatFile, mp4Name); err != nil {
		return err
	}
	fmt.Fprintf(os.Stderr, "Complete: %s\n", mp4Name)

	return nil
}

func downloadLiveStream(ctx context.Context, client *http.Client, playlistURL *url.URL, initialPlaylist *m3u8.MediaPlaylist, output *os.File, outputName string) error {
	// Track downloaded segments by sequence number
	downloadedSeqs := make(map[uint64]bool)
	tsPath := output.Name()

	// Download initial segments
	initialSegments := collectSegments(initialPlaylist)
	for _, segment := range initialSegments {
		if err := downloadSegment(ctx, client, playlistURL, segment, output); err != nil {
			return fmt.Errorf("download initial segment %d: %w", segment.Sequence, err)
		}
		// Sync after each segment to ensure data is written to disk
		if err := output.Sync(); err != nil {
			return fmt.Errorf("sync file after segment %d: %w", segment.Sequence, err)
		}
		downloadedSeqs[segment.Sequence] = true
	}

	// Continuously poll for new segments
	ticker := time.NewTicker(playlistPollInterval)
	defer ticker.Stop()

	for {
		select {
		case <-ctx.Done():
			// Context cancelled (Ctrl+C or "q" key) - finalize and convert
			return finalizeAndConvert(output, tsPath, outputName)
		case <-ticker.C:
			// Fetch updated playlist
			body, _, err := fetchWithRedirects(ctx, client, playlistURL, maxRedirects)
			if err != nil {
				// If we can't fetch the playlist, continue trying
				continue
			}

			playlist, listType, err := m3u8.DecodeFrom(bufio.NewReader(body), true)
			body.Close()
			if err != nil {
				continue
			}

			if listType != m3u8.MEDIA {
				continue
			}

			mediaPlaylist, ok := playlist.(*m3u8.MediaPlaylist)
			if !ok {
				continue
			}

			// Check if stream has ended
			if mediaPlaylist.Closed {
				// Download any remaining segments
				segments := collectSegments(mediaPlaylist)
				for _, segment := range segments {
					if !downloadedSeqs[segment.Sequence] {
						if err := downloadSegment(ctx, client, playlistURL, segment, output); err != nil {
							// Log error but continue with finalization
							continue
						}
						// Sync after each segment
						if err := output.Sync(); err != nil {
							continue
						}
						downloadedSeqs[segment.Sequence] = true
					}
				}
				// Stream ended - finalize and convert
				return finalizeAndConvert(output, tsPath, outputName)
			}

			// Download new segments
			segments := collectSegments(mediaPlaylist)
			for _, segment := range segments {
				if !downloadedSeqs[segment.Sequence] {
					if err := downloadSegment(ctx, client, playlistURL, segment, output); err != nil {
						// Log error but continue polling
						continue
					}
					// Sync after each segment to ensure data is written to disk
					if err := output.Sync(); err != nil {
						// Log error but continue
						continue
					}
					downloadedSeqs[segment.Sequence] = true
				}
			}
		}
	}
}

func finalizeOutput(ctx context.Context, tempPath, outputName string) error {
	mp4Name := ensureMP4Extension(outputName)
	if err := transmuxToMP4(ctx, tempPath, mp4Name); err != nil {
		return err
	}

	// Clean up temp file after successful transmux
	os.Remove(tempPath)
	return nil
}

func finalizeAndConvert(output *os.File, tsPath, outputName string) error {
	// Sync and close the file before conversion
	output.Sync() // Flush any pending writes
	output.Close()

	// Convert to MP4
	fmt.Fprintf(os.Stderr, "Converting to MP4...\n")
	if err := convertTSToMP4(context.Background(), tsPath, outputName); err != nil {
		// Don't fail if conversion fails - the .ts file is still valid
		fmt.Fprintf(os.Stderr, "Warning: MP4 conversion failed, but .ts file is saved: %v\n", err)
		return nil
	}
	mp4Name := ensureMP4Extension(outputName)
	fmt.Fprintf(os.Stderr, "Conversion complete: %s\n", mp4Name)
	return nil
}

func convertTSToMP4(ctx context.Context, tsPath, outputName string) error {
	// Only convert if ffmpeg is available, but don't fail if it's not
	if _, err := exec.LookPath("ffmpeg"); err != nil {
		return fmt.Errorf("ffmpeg not found in PATH")
	}

	mp4Name := ensureMP4Extension(outputName)
	// Use background context for conversion to ensure it completes even if main context is cancelled
	if err := transmuxToMP4(ctx, tsPath, mp4Name); err != nil {
		return err
	}
	return nil
}

func peekContentType(ctx context.Context, client *http.Client, target *url.URL) (string, error) {
	req, err := http.NewRequestWithContext(ctx, http.MethodHead, target.String(), nil)
	if err != nil {
		return "", fmt.Errorf("create HEAD request: %w", err)
	}

	resp, err := client.Do(req)
	if err != nil {
		return "", fmt.Errorf("head request: %w", err)
	}
	defer resp.Body.Close()

	if resp.StatusCode >= 400 {
		return "", fmt.Errorf("head status %s", resp.Status)
	}

	return resp.Header.Get("Content-Type"), nil
}

func extractPlaylistsFromHTML(ctx context.Context, client *http.Client, target *url.URL) ([]string, error) {
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, target.String(), nil)
	if err != nil {
		return nil, fmt.Errorf("create request: %w", err)
	}

	resp, err := client.Do(req)
	if err != nil {
		return nil, fmt.Errorf("fetch page: %w", err)
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("unexpected status %s", resp.Status)
	}

	doc, err := goquery.NewDocumentFromReader(resp.Body)
	if err != nil {
		return nil, fmt.Errorf("parse html: %w", err)
	}

	results := make([]string, 0)
	doc.Find("video,source").Each(func(_ int, sel *goquery.Selection) {
		if src, ok := sel.Attr("src"); ok {
			if resolved := resolveURL(target, src); resolved != "" {
				results = append(results, resolved)
			}
		}
	})

	attrPatterns := []string{"data-src", "data-hls", "data-hls-src"}
	doc.Find("*[data-src], *[data-hls], *[data-hls-src]").Each(func(_ int, sel *goquery.Selection) {
		for _, attr := range attrPatterns {
			if val, ok := sel.Attr(attr); ok {
				if resolved := resolveURL(target, val); resolved != "" {
					results = append(results, resolved)
				}
			}
		}
	})

	hrefPattern := regexp.MustCompile(`(?i)\.m3u8(\?.*)?$`)
	doc.Find("a[href], link[href]").Each(func(_ int, sel *goquery.Selection) {
		if href, ok := sel.Attr("href"); ok && hrefPattern.MatchString(href) {
			if resolved := resolveURL(target, href); resolved != "" {
				results = append(results, resolved)
			}
		}
	})

	results = append(results, findPlaylistInScripts(target, doc)...)

	uniq := uniqueStrings(results)
	return uniq, nil
}

func resolveURL(baseURL *url.URL, ref string) string {
	if ref == "" {
		return ""
	}
	if strings.HasPrefix(ref, "data:") {
		return ""
	}

	parsed, err := baseURL.Parse(ref)
	if err != nil {
		return ""
	}

	return parsed.String()
}

func findPlaylistInScripts(baseURL *url.URL, doc *goquery.Document) []string {
	var results []string
	pattern := regexp.MustCompile(`https?://[^"'\\\s]+\.m3u8[^"'\\\s]*`)
	doc.Find("script").Each(func(_ int, sel *goquery.Selection) {
		text := sel.Text()
		for _, match := range pattern.FindAllString(text, -1) {
			if resolved := resolveURL(baseURL, match); resolved != "" {
				results = append(results, resolved)
			}
		}
	})
	return results
}

func uniqueStrings(in []string) []string {
	seen := make(map[string]struct{}, len(in))
	out := make([]string, 0, len(in))
	for _, item := range in {
		if item == "" {
			continue
		}
		if _, exists := seen[item]; exists {
			continue
		}
		seen[item] = struct{}{}
		out = append(out, item)
	}
	return out
}

func collectSegments(playlist *m3u8.MediaPlaylist) []segmentInfo {
	segments := make([]segmentInfo, 0, len(playlist.Segments))
	for _, segment := range playlist.Segments {
		if segment == nil || segment.URI == "" {
			continue
		}
		segments = append(segments, segmentInfo{Sequence: segment.SeqId, URI: segment.URI})
	}

	sort.Slice(segments, func(i, j int) bool {
		return segments[i].Sequence < segments[j].Sequence
	})

	return segments
}

func selectVariant(master *m3u8.MasterPlaylist, base *url.URL) (string, error) {
	var chosen *m3u8.Variant
	for _, variant := range master.Variants {
		if variant == nil || variant.URI == "" {
			continue
		}
		if chosen == nil || variant.Bandwidth > chosen.Bandwidth {
			chosen = variant
		}
	}

	if chosen == nil {
		return "", errUnsupportedMaster
	}

	resolved, err := base.Parse(chosen.URI)
	if err != nil {
		return "", fmt.Errorf("parse variant URL: %w", err)
	}

	return resolved.String(), nil
}

func downloadSegment(ctx context.Context, client *http.Client, base *url.URL, segment segmentInfo, output io.Writer) error {
	segmentURL, err := base.Parse(segment.URI)
	if err != nil {
		return fmt.Errorf("parse segment URL: %w", err)
	}

	req, err := http.NewRequestWithContext(ctx, http.MethodGet, segmentURL.String(), nil)
	if err != nil {
		return fmt.Errorf("create request: %w", err)
	}

	resp, err := client.Do(req)
	if err != nil {
		return fmt.Errorf("fetch segment: %w", err)
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		return fmt.Errorf("unexpected status %s", resp.Status)
	}

	if _, err := io.Copy(output, resp.Body); err != nil {
		return fmt.Errorf("write segment: %w", err)
	}

	return nil
}

func fetchWithRedirects(ctx context.Context, client *http.Client, streamURL *url.URL, redirects int) (io.ReadCloser, *url.URL, error) {
	currentURL := streamURL
	for count := 0; count <= redirects; count++ {
		req, err := http.NewRequestWithContext(ctx, http.MethodGet, currentURL.String(), nil)
		if err != nil {
			return nil, nil, fmt.Errorf("create request: %w", err)
		}
		resp, err := client.Do(req)
		if err != nil {
			return nil, nil, fmt.Errorf("http get: %w", err)
		}
		switch {
		case resp.StatusCode >= 300 && resp.StatusCode < 400:
			location := resp.Header.Get("Location")
			resp.Body.Close()
			if location == "" {
				return nil, nil, errors.New("redirect without location header")
			}
			nextURL, err := currentURL.Parse(location)
			if err != nil {
				return nil, nil, fmt.Errorf("parse redirect URL: %w", err)
			}
			currentURL = nextURL
			continue
		case resp.StatusCode == http.StatusOK:
			return resp.Body, currentURL, nil
		default:
			resp.Body.Close()
			return nil, nil, fmt.Errorf("unexpected status %s", resp.Status)
		}
	}

	return nil, nil, errors.New("too many redirects")
}

func inferOutputName(streamURL *url.URL) string {
	base := path.Base(streamURL.Path)
	if base == "." || base == "/" || base == "" {
		base = "download"
	}
	trimmed := strings.TrimSuffix(base, path.Ext(base))
	if trimmed == "" {
		trimmed = "download"
	}
	return trimmed + ".mp4"
}

func ensureMP4Extension(name string) string {
	lower := strings.ToLower(name)
	if strings.HasSuffix(lower, ".mp4") {
		return name
	}
	ext := filepath.Ext(name)
	trimmed := strings.TrimSuffix(name, ext)
	if trimmed == "" {
		trimmed = "output"
	}
	return trimmed + ".mp4"
}

func ensureTSExtension(name string) string {
	lower := strings.ToLower(name)
	if strings.HasSuffix(lower, ".ts") {
		return name
	}
	ext := filepath.Ext(name)
	trimmed := strings.TrimSuffix(name, ext)
	if trimmed == "" {
		trimmed = "output"
	}
	return trimmed + ".ts"
}

func inferOutputNameMust(rawURL string) string {
	parsed, err := url.Parse(rawURL)
	if err != nil {
		return ensureMP4Extension("download")
	}
	return inferOutputName(parsed)
}

func transmuxToMP4FromConcatProtocol(ctx context.Context, concatFile, mp4Path string) error {
	if _, err := exec.LookPath("ffmpeg"); err != nil {
		return errFFmpegMissing
	}

	if err := os.MkdirAll(filepath.Dir(mp4Path), 0o755); err != nil {
		return fmt.Errorf("ensure output directory: %w", err)
	}

	// Use ffmpeg concat protocol (not demuxer) - this is designed for TS files
	// Format: concat:file1.ts|file2.ts|file3.ts
	// Or we can use the file list with concat protocol
	absConcatFile, err := filepath.Abs(concatFile)
	if err != nil {
		return fmt.Errorf("get absolute path for concat file: %w", err)
	}

	// Read the concat file to build the concat protocol string
	concatContent, err := os.ReadFile(absConcatFile)
	if err != nil {
		return fmt.Errorf("read concat file: %w", err)
	}

	lines := strings.Split(string(concatContent), "\n")
	var segmentPaths []string
	for _, line := range lines {
		line = strings.TrimSpace(line)
		if line != "" {
			segmentPaths = append(segmentPaths, line)
		}
	}

	if len(segmentPaths) == 0 {
		return fmt.Errorf("no segments found in concat file")
	}

	// Build concat protocol string: concat:file1.ts|file2.ts|...
	concatInput := "concat:" + strings.Join(segmentPaths, "|")

	// Use concat protocol with better flags for TS files
	cmd := exec.CommandContext(ctx, "ffmpeg",
		"-y",
		"-i", concatInput,
		"-c", "copy",
		"-movflags", "+faststart",
		mp4Path)
	cmd.Stdout = io.Discard
	var stderr bytes.Buffer
	cmd.Stderr = &stderr

	if err := cmd.Run(); err != nil {
		// If copy fails, try with re-encoding
		msg := strings.TrimSpace(stderr.String())
		needsReencode := strings.Contains(msg, "could not find corresponding") ||
			strings.Contains(msg, "error reading header") ||
			strings.Contains(msg, "Invalid data") ||
			strings.Contains(msg, "Invalid argument")

		if needsReencode {
			fmt.Fprintf(os.Stderr, "Copy mode failed, trying re-encode...\n")
			cmd2 := exec.CommandContext(ctx, "ffmpeg",
				"-y",
				"-i", concatInput,
				"-c:v", "libx264",
				"-preset", "medium",
				"-crf", "23",
				"-c:a", "aac",
				"-b:a", "128k",
				"-movflags", "+faststart",
				mp4Path)
			cmd2.Stdout = io.Discard
			var stderr2 bytes.Buffer
			cmd2.Stderr = &stderr2
			if err2 := cmd2.Run(); err2 != nil {
				os.Remove(mp4Path)
				msg2 := strings.TrimSpace(stderr2.String())
				if msg2 != "" {
					return fmt.Errorf("ffmpeg (re-encode): %s", msg2)
				}
				return fmt.Errorf("ffmpeg (re-encode): %w", err2)
			}
			return nil
		}
		os.Remove(mp4Path)
		if msg != "" {
			return fmt.Errorf("ffmpeg: %s", msg)
		}
		return fmt.Errorf("ffmpeg: %w", err)
	}

	return nil
}

func transmuxToMP4FromConcat(ctx context.Context, concatFile, mp4Path string) error {
	if _, err := exec.LookPath("ffmpeg"); err != nil {
		return errFFmpegMissing
	}

	if err := os.MkdirAll(filepath.Dir(mp4Path), 0o755); err != nil {
		return fmt.Errorf("ensure output directory: %w", err)
	}

	// Verify concat file exists and is readable
	if _, err := os.Stat(concatFile); err != nil {
		return fmt.Errorf("concat file not found: %w", err)
	}

	// Read concat file to verify format
	concatContent, err := os.ReadFile(concatFile)
	if err != nil {
		return fmt.Errorf("read concat file: %w", err)
	}
	// Debug: show first few lines of concat file if it's small
	if len(concatContent) < 500 {
		fmt.Fprintf(os.Stderr, "Concat file content:\n%s\n", string(concatContent))
	}

	// Use ffmpeg concat demuxer to properly combine segments
	// This handles TS metadata correctly
	// Add -avoid_negative_ts make_zero to handle timestamp issues
	// Use absolute path for concat file
	absConcatFile, err := filepath.Abs(concatFile)
	if err != nil {
		return fmt.Errorf("get absolute path for concat file: %w", err)
	}

	cmd := exec.CommandContext(ctx, "ffmpeg",
		"-y",
		"-f", "concat",
		"-safe", "0",
		"-i", absConcatFile,
		"-avoid_negative_ts", "make_zero",
		"-c", "copy",
		"-movflags", "+faststart",
		mp4Path)
	cmd.Stdout = io.Discard
	var stderr bytes.Buffer
	cmd.Stderr = &stderr

	if err := cmd.Run(); err != nil {
		// If copy fails, try with re-encoding as fallback
		msg := strings.TrimSpace(stderr.String())
		// Check for various error patterns
		needsReencode := strings.Contains(msg, "could not find corresponding") ||
			strings.Contains(msg, "error reading header") ||
			strings.Contains(msg, "Invalid data") ||
			strings.Contains(msg, "Invalid argument") ||
			strings.Contains(msg, "No such file")

		if needsReencode {
			// Try re-encoding instead of copy
			fmt.Fprintf(os.Stderr, "Copy mode failed, trying re-encode...\n")
			cmd2 := exec.CommandContext(ctx, "ffmpeg",
				"-y",
				"-f", "concat",
				"-safe", "0",
				"-i", absConcatFile,
				"-avoid_negative_ts", "make_zero",
				"-fflags", "+genpts",
				"-c:v", "libx264",
				"-preset", "medium",
				"-crf", "23",
				"-c:a", "aac",
				"-b:a", "128k",
				"-movflags", "+faststart",
				mp4Path)
			cmd2.Stdout = io.Discard
			var stderr2 bytes.Buffer
			cmd2.Stderr = &stderr2
			if err2 := cmd2.Run(); err2 != nil {
				// If concat demuxer completely fails, try using individual segments as input
				fmt.Fprintf(os.Stderr, "Concat demuxer failed, trying direct segment input...\n")
				// Get segment files from concat file
				lines := strings.Split(string(concatContent), "\n")
				var segmentPaths []string
				for _, line := range lines {
					line = strings.TrimSpace(line)
					if strings.HasPrefix(line, "file '") && strings.HasSuffix(line, "'") {
						path := strings.TrimPrefix(strings.TrimSuffix(line, "'"), "file '")
						path = strings.ReplaceAll(path, "''", "'") // Unescape
						segmentPaths = append(segmentPaths, path)
					}
				}
				if len(segmentPaths) > 0 {
					// Try with first segment to test
					cmd3 := exec.CommandContext(ctx, "ffmpeg",
						"-y",
						"-i", segmentPaths[0],
						"-avoid_negative_ts", "make_zero",
						"-fflags", "+genpts",
						"-c:v", "libx264",
						"-preset", "medium",
						"-crf", "23",
						"-c:a", "aac",
						"-b:a", "128k",
						"-movflags", "+faststart",
						mp4Path)
					cmd3.Stdout = io.Discard
					var stderr3 bytes.Buffer
					cmd3.Stderr = &stderr3
					if err3 := cmd3.Run(); err3 != nil {
						os.Remove(mp4Path)
						return fmt.Errorf("ffmpeg failed with all methods. Last error: %s", strings.TrimSpace(stderr3.String()))
					}
					return nil
				}
				os.Remove(mp4Path)
				msg2 := strings.TrimSpace(stderr2.String())
				if msg2 != "" {
					return fmt.Errorf("ffmpeg (re-encode): %s", msg2)
				}
				return fmt.Errorf("ffmpeg (re-encode): %w", err2)
			}
			return nil
		}
		os.Remove(mp4Path)
		if msg != "" {
			return fmt.Errorf("ffmpeg: %s", msg)
		}
		return fmt.Errorf("ffmpeg: %w", err)
	}

	return nil
}

func transmuxToMP4(ctx context.Context, tsPath, mp4Path string) error {
	if _, err := exec.LookPath("ffmpeg"); err != nil {
		return errFFmpegMissing
	}

	if err := os.MkdirAll(filepath.Dir(mp4Path), 0o755); err != nil {
		return fmt.Errorf("ensure output directory: %w", err)
	}

	// Try with copy first (fastest), fall back to re-encoding if needed
	// Use -fflags +genpts to generate presentation timestamps if missing
	// Use -err_detect ignore_err to be more tolerant of minor errors
	// Use -avoid_negative_ts make_zero to handle timestamp issues
	cmd := exec.CommandContext(ctx, "ffmpeg",
		"-y",
		"-fflags", "+genpts+igndts",
		"-err_detect", "ignore_err",
		"-i", tsPath,
		"-avoid_negative_ts", "make_zero",
		"-c", "copy",
		"-movflags", "+faststart",
		mp4Path)
	cmd.Stdout = io.Discard
	var stderr bytes.Buffer
	cmd.Stderr = &stderr

	if err := cmd.Run(); err != nil {
		// If copy fails, try with re-encoding as fallback
		msg := strings.TrimSpace(stderr.String())
		needsReencode := strings.Contains(msg, "could not find corresponding") ||
			strings.Contains(msg, "error reading header") ||
			strings.Contains(msg, "Invalid data") ||
			strings.Contains(msg, "Invalid argument")

		if needsReencode {
			// Try re-encoding instead of copy
			fmt.Fprintf(os.Stderr, "Copy mode failed, trying re-encode...\n")
			cmd2 := exec.CommandContext(ctx, "ffmpeg",
				"-y",
				"-fflags", "+genpts+igndts",
				"-err_detect", "ignore_err",
				"-i", tsPath,
				"-avoid_negative_ts", "make_zero",
				"-c:v", "libx264",
				"-preset", "medium",
				"-crf", "23",
				"-c:a", "aac",
				"-b:a", "128k",
				"-movflags", "+faststart",
				mp4Path)
			cmd2.Stdout = io.Discard
			var stderr2 bytes.Buffer
			cmd2.Stderr = &stderr2
			if err2 := cmd2.Run(); err2 != nil {
				os.Remove(mp4Path)
				msg2 := strings.TrimSpace(stderr2.String())
				if msg2 != "" {
					return fmt.Errorf("ffmpeg (re-encode): %s", msg2)
				}
				return fmt.Errorf("ffmpeg (re-encode): %w", err2)
			}
			return nil
		}
		os.Remove(mp4Path)
		if msg != "" {
			return fmt.Errorf("ffmpeg: %s", msg)
		}
		return fmt.Errorf("ffmpeg: %w", err)
	}

	return nil
}