package service

import (
	"bufio"
	"bytes"
	"context"
	"database/sql"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"log"
	"os"
	"os/exec"
	"path/filepath"
	"sort"
	"strconv"
	"strings"
	"sync"
	"syscall"
	"time"

	"github.com/gabriel-vasile/mimetype"

	"vidarchive/internal/config"
	"vidarchive/internal/models"
	"vidarchive/internal/repository"
	"vidarchive/internal/util"
)

type DownloadService struct {
	repo            *repository.DownloadRepository
	librarySvc      *LibraryService
	presetSvc       *PresetService
	settingsSvc     *SettingsService
	subscriptionSvc *SubscriptionService
	cfg             *config.Config
	cache           *ProgressCache
	activeMu        sync.Mutex
	active          map[int64]context.CancelFunc
}

func NewDownloadService(repo *repository.DownloadRepository, librarySvc *LibraryService, presetSvc *PresetService, settingsSvc *SettingsService, subscriptionSvc *SubscriptionService, cfg *config.Config) *DownloadService {
	return &DownloadService{
		repo:            repo,
		librarySvc:      librarySvc,
		presetSvc:       presetSvc,
		settingsSvc:     settingsSvc,
		subscriptionSvc: subscriptionSvc,
		cfg:             cfg,
		cache:           NewProgressCache(),
		active:          make(map[int64]context.CancelFunc),
	}
}

func (s *DownloadService) Create(url string, presetID *int64, formatOverride, customFlags, outputDir string) (*models.Download, error) {
	d := &models.Download{
		URL:            url,
		Status:         "queued",
		FormatOverride: formatOverride,
		CustomFlags:    customFlags,
		OutputDir:      sql.NullString{String: outputDir, Valid: outputDir != ""},
	}

	if presetID != nil {
		d.PresetID = sqlNullInt64(*presetID)
	}

	if err := s.repo.Create(d); err != nil {
		return nil, err
	}
	return d, nil
}

// CreateForSubscription queues a download for a subscription run, copying its
// download options and tagging it with the subscription id so ExecuteDownload
// applies the right refresh mode and pruning.
func (s *DownloadService) CreateForSubscription(sub *models.Subscription) (*models.Download, error) {
	d := &models.Download{
		URL:            sub.URL,
		Status:         "queued",
		FormatOverride: sub.FormatOverride,
		CustomFlags:    sub.CustomFlags,
		OutputDir:      sql.NullString{String: sub.OutputDir, Valid: sub.OutputDir != ""},
		PresetID:       sub.PresetID,
		SubscriptionID: sqlNullInt64(sub.ID),
	}
	if err := s.repo.Create(d); err != nil {
		return nil, err
	}
	return d, nil
}

func (s *DownloadService) GetByID(id int64) (*models.Download, error) {
	d, err := s.repo.GetByID(id)
	if err != nil {
		return nil, err
	}
	if logs := s.cache.Snapshot(id); logs != "" {
		d.Logs = sql.NullString{String: logs, Valid: true}
	}
	return d, nil
}

func (s *DownloadService) GetAll(status, sortBy string) ([]*models.Download, error) {
	downloads, err := s.repo.GetAll(status, sortBy)
	if err != nil {
		return nil, err
	}

	for _, d := range downloads {
		if logs := s.cache.Snapshot(d.ID); logs != "" {
			d.Logs = sql.NullString{String: logs, Valid: true}
		}
	}

	return downloads, nil
}

func (s *DownloadService) GetQueued(limit int) ([]*models.Download, error) {
	return s.repo.GetQueued(limit)
}

// HasActiveForSubscription reports whether the subscription already has a queued
// or in-progress download, so the scheduler can skip stacking another run.
func (s *DownloadService) HasActiveForSubscription(subID int64) (bool, error) {
	return s.repo.HasActiveForSubscription(subID)
}

func (s *DownloadService) Delete(id int64) error {
	s.cancelDownload(id)
	s.cache.Delete(id)
	return s.repo.Delete(id)
}

// registerActive records the cancel func for a claimed download and returns a
// release func. Registration happens at claim time rather than after the process
// spawns, so a delete arriving during setup, between yt-dlp and the import, or
// mid-import still stops the work instead of silently letting it finish.
func (s *DownloadService) registerActive(id int64, cancel context.CancelFunc) func() {
	s.activeMu.Lock()
	s.active[id] = cancel
	s.activeMu.Unlock()

	return func() {
		s.activeMu.Lock()
		delete(s.active, id)
		s.activeMu.Unlock()
	}
}

func (s *DownloadService) cancelDownload(id int64) {
	s.activeMu.Lock()
	cancel, ok := s.active[id]
	delete(s.active, id)
	s.activeMu.Unlock()

	if ok {
		cancel()
	}
}

// CancelAll stops every download currently in flight. Used on shutdown and when
// clearing the queue, so no yt-dlp child outlives the rows that described it.
func (s *DownloadService) CancelAll() {
	s.activeMu.Lock()
	cancels := make([]context.CancelFunc, 0, len(s.active))
	for id, cancel := range s.active {
		cancels = append(cancels, cancel)
		delete(s.active, id)
	}
	s.activeMu.Unlock()

	for _, cancel := range cancels {
		cancel()
	}
}

func (s *DownloadService) DeleteAll() error {
	// Clearing the queue must also stop what is running; otherwise yt-dlp keeps
	// going and imports into the library after its row is gone.
	s.CancelAll()
	return s.repo.DeleteAll()
}

func (s *DownloadService) CountByStatus(ctx context.Context) (map[string]int, error) {
	return s.repo.CountByStatus(ctx)
}

// ResetStalledDownloads re-queues downloads left mid-flight by a previous run and
// discards their temp directories. Without the cleanup the re-run imports into a
// fresh uniqueDir and the library ends up with a duplicate of the same item.
func (s *DownloadService) ResetStalledDownloads() error {
	ids, err := s.repo.IDsByStatus("downloading")
	if err != nil {
		return err
	}

	for _, id := range ids {
		for _, dir := range s.tempDirsFor(id) {
			if err := os.RemoveAll(dir); err != nil {
				log.Printf("warning: failed to remove stale temp dir %s: %v", dir, err)
			}
		}
	}

	return s.repo.UpdateStatusWhere("downloading", "queued")
}

// tempDirFor returns the scratch directory a download writes into.
func (s *DownloadService) tempDirFor(id int64) string {
	return filepath.Join(s.cfg.TempDir, strconv.FormatInt(id, 10))
}

// tempNewDirFor returns the second-pass scratch directory used by metadata mode.
func (s *DownloadService) tempNewDirFor(id int64) string {
	return s.tempDirFor(id) + "-new"
}

// tempDirsFor returns every scratch directory a download owns. ResetStalledDownloads
// clears these, so the two builders above must stay the only places that name them.
func (s *DownloadService) tempDirsFor(id int64) []string {
	return []string{s.tempDirFor(id), s.tempNewDirFor(id)}
}

func (s *DownloadService) ListFormats(url string) ([]*models.FormatInfo, error) {
	// Use machine-readable JSON (-J) rather than scraping the human "-F" table,
	// whose columns/separators shift between yt-dlp versions. stderr is captured
	// separately so warnings can't corrupt the JSON on stdout.
	cmd := exec.Command(s.cfg.YTDLPPath, "-J", "--no-warnings", url)
	var stderr bytes.Buffer
	cmd.Stderr = &stderr
	output, err := cmd.Output()
	if err != nil {
		return nil, fmt.Errorf("yt-dlp -J failed: %w\n%s", err, stderr.String())
	}

	return parseFormatJSON(output)
}

// ExecuteDownload runs the download for d. The bool reports whether this call
// actually processed it: false means another worker already claimed it (Submit
// and the queue checker can both enqueue the same row within the 2s poll window),
// so the caller should not log it as completed. A cancelled run returns
// ErrCancelled.
//
// parent belongs to the worker pool: deriving from it means a shutdown cancels
// the download even if it lands before this call registers its own cancel func.
func (s *DownloadService) ExecuteDownload(parent context.Context, d *models.Download) (bool, error) {
	claimed, err := s.repo.MarkStarted(d.ID)
	if err != nil {
		return false, err
	}
	if !claimed {
		return false, nil
	}

	// Registered before any work starts so Delete/CancelAll can interrupt every
	// phase, not just the window where yt-dlp happens to be running.
	ctx, cancel := context.WithCancel(parent)
	defer cancel()
	defer s.registerActive(d.ID, cancel)()

	s.cache.Set(d.ID, &LiveDownload{LastUpdate: time.Now()})
	defer s.cache.Delete(d.ID)

	var preset *models.Preset
	if d.PresetID.Valid {
		preset, err = s.presetSvc.GetByID(d.PresetID.Int64)
		if err != nil {
			log.Printf("download %d: preset %d lookup failed (%v); falling back to default", d.ID, d.PresetID.Int64, err)
			preset = nil
		}
	}
	if preset == nil {
		var derr error
		if preset, derr = s.presetSvc.GetDefault(); derr != nil {
			log.Printf("download %d: no default preset available (%v); using built-in defaults", d.ID, derr)
			preset = &models.Preset{}
		}
	}

	var sub *models.Subscription
	if d.SubscriptionID.Valid && s.subscriptionSvc != nil {
		var serr error
		if sub, serr = s.subscriptionSvc.GetByID(d.SubscriptionID.Int64); serr != nil {
			log.Printf("download %d: subscription %d lookup failed: %v", d.ID, d.SubscriptionID.Int64, serr)
		}
	}

	// Reject custom flags that clash with options VidArchive sets itself, before
	// spending any work — the download fails with a message naming the offender.
	isSubscription := d.SubscriptionID.Valid
	for _, flags := range []string{d.CustomFlags, preset.CustomFlags} {
		if err := checkReservedFlags(flags, isSubscription); err != nil {
			s.finalizeError(d.ID, err)
			return false, err
		}
	}

	tempDownloadDir := s.tempDirFor(d.ID)
	if err := os.MkdirAll(tempDownloadDir, 0755); err != nil {
		return false, fmt.Errorf("create temp download dir: %w", err)
	}
	// Own the temp dir's lifetime here, where it's created, so it's removed on
	// every exit path — including a failed yt-dlp run or an early return that
	// crashes mid-import. The import helpers below no longer clean it up.
	defer os.RemoveAll(tempDownloadDir)

	args := s.presetSvc.BuildArgs(preset, d.FormatOverride, d.CustomFlags)

	// Record the meaningful flags (format/audio/subs/custom) that shaped this
	// download, before the internal plumbing (cookies, -P/-o, URL) is appended,
	// so each imported item can show how it was fetched.
	ytdlpFlags := strings.Join(args, " ")

	var cookieCleanup func()
	args, cookieCleanup = s.appendCookies(args)
	defer cookieCleanup()

	if sub != nil {
		// Always write info.json so the import step can read the stable identity
		// (yt-dlp's video id) used to match/replace existing items.
		args = append(args, "--write-info-json")
		switch sub.RefreshMode {
		case "skip":
			// Let yt-dlp skip entries already recorded — no re-download.
			archive := s.subscriptionSvc.ArchivePath(sub.ID)
			if err := os.MkdirAll(filepath.Dir(archive), 0755); err == nil {
				args = append(args, "--download-archive", archive)
			}
		case "metadata":
			// Refresh metadata only; don't fetch media.
			args = append(args, "--skip-download")
		}
	}

	args = append(args, "-P", tempDownloadDir)
	args = append(args, "-o", "item-%(autonumber)05d/%(title)s.%(ext)s")
	args = append(args, d.URL)

	runErr := s.runYTDLP(ctx, d, args)

	// Cancellation wins over both the run error and the import: a cancel that
	// lands just after yt-dlp exited 0 leaves runErr nil, and the item must not
	// reach the library after the user removed it.
	if ctx.Err() != nil {
		return false, s.finalizeCancelled(parent, d.ID)
	}
	if runErr != nil {
		s.finalizeError(d.ID, runErr)
		return false, runErr
	}

	mode := ""
	if sub != nil {
		mode = sub.RefreshMode
	}

	// Post-process before marking completed, so the download stays "downloading"
	// until everything is really done — including metadata mode's second pass,
	// which downloads any genuinely new entries as full items.
	var postErr error
	if mode == "metadata" {
		// The main pass ran with --skip-download, so the temp dir holds only
		// info.json files: refresh existing items in place and fetch new ones.
		postErr = s.refreshAndAddNew(ctx, d, preset, tempDownloadDir, ytdlpFlags)
	} else {
		imported, err := s.importDownloadedItems(ctx, d, tempDownloadDir, mode, ytdlpFlags)
		switch {
		case err != nil:
			postErr = err
		// A plain (non-subscription) download that yields nothing is a failure, not
		// a silent "completed". Subscription modes legitimately import zero (skip
		// mode, or a metadata refresh with no new entries), so only enforce this for
		// plain runs.
		case sub == nil && imported == 0:
			postErr = fmt.Errorf("yt-dlp finished but no media files were downloaded")
		}
	}

	if postErr == nil && sub != nil && sub.PruneRemoved {
		s.pruneSubscription(ctx, d, sub)
	}

	// Same cancellation check as above: a stop during post-processing must not
	// be recorded as "completed".
	if ctx.Err() != nil {
		return false, s.finalizeCancelled(parent, d.ID)
	}
	if postErr != nil {
		s.finalizeError(d.ID, postErr)
		return false, postErr
	}

	if err := s.repo.MarkCompleted(d.ID, "completed"); err != nil {
		return false, err
	}

	return true, nil
}

// runYTDLP executes yt-dlp with args, streaming combined output into the live
// progress cache and periodically flushing it to the download's persisted log.
// Cancelling ctx kills the whole process group and makes this return.
func (s *DownloadService) runYTDLP(ctx context.Context, d *models.Download, args []string) error {
	// --newline forces yt-dlp to emit each progress update on its own line. Without
	// it, progress is rewritten in place with carriage returns, so a long download
	// becomes one ever-growing line that overflows the reader's buffer and stalls
	// the pipe — hanging the download. See the hardened scanner below.
	fullArgs := append([]string{"--newline"}, args...)
	cmd := exec.CommandContext(ctx, s.cfg.YTDLPPath, fullArgs...)
	cmd.SysProcAttr = &syscall.SysProcAttr{Setpgid: true}
	// yt-dlp spawns helpers (ffmpeg, external downloaders). Kill the whole group
	// rather than just the parent, which would leave those orphaned.
	cmd.Cancel = func() error {
		return syscall.Kill(-cmd.Process.Pid, syscall.SIGKILL)
	}

	stdout, err := cmd.StdoutPipe()
	if err != nil {
		return err
	}
	cmd.Stderr = cmd.Stdout

	if err := cmd.Start(); err != nil {
		return err
	}

	ticker := time.NewTicker(10 * time.Second)
	defer ticker.Stop()
	done := make(chan struct{})
	go func() {
		for {
			select {
			case <-ticker.C:
				s.flushLogs(d.ID)
			case <-done:
				return
			}
		}
	}()

	scanner := bufio.NewScanner(stdout)
	// Allow long lines (a single yt-dlp message can exceed the 64 KiB default)
	// rather than letting the scanner abort and leave the pipe unread.
	scanner.Buffer(make([]byte, 0, 64*1024), 1024*1024)
	for scanner.Scan() {
		s.cache.AppendLog(d.ID, scanner.Text())
	}
	if err := scanner.Err(); err != nil {
		log.Printf("download %d: error reading yt-dlp output: %v", d.ID, err)
	}
	close(done)

	s.flushLogs(d.ID)

	return cmd.Wait()
}

// appendCookies writes the saved cookies (if any) to a temp file and appends a
// --cookies flag. The returned cleanup removes the temp file and is always safe
// to call, even when no cookies were configured.
func (s *DownloadService) appendCookies(args []string) ([]string, func()) {
	cookies, err := s.settingsSvc.GetCookies()
	if err != nil || strings.TrimSpace(cookies) == "" {
		return args, func() {}
	}
	path, err := s.writeCookiesFile(cookies)
	if err != nil {
		return args, func() {}
	}
	return append(args, "--cookies", path), func() { os.Remove(path) }
}

// writeCookiesFile writes cookies to a temp file in the app's own temp dir (the
// same volume the rest of the run uses). On any failure the partial file is
// removed — a truncated cookies file must not be handed to yt-dlp.
func (s *DownloadService) writeCookiesFile(cookies string) (string, error) {
	if err := os.MkdirAll(s.cfg.TempDir, 0755); err != nil {
		return "", err
	}
	tmpFile, err := os.CreateTemp(s.cfg.TempDir, "cookies-*.txt")
	if err != nil {
		return "", err
	}
	if _, err := tmpFile.WriteString(cookies); err != nil {
		tmpFile.Close()
		os.Remove(tmpFile.Name())
		return "", err
	}
	if err := tmpFile.Close(); err != nil {
		os.Remove(tmpFile.Name())
		return "", err
	}
	return tmpFile.Name(), nil
}

func (s *DownloadService) finalizeError(id int64, err error) {
	s.flushLogs(id)
	if markErr := s.repo.MarkError(id, err.Error()); markErr != nil {
		log.Printf("download %d: failed to record error: %v", id, markErr)
	}
}

// ErrCancelled reports that a download was deliberately stopped (deleted, queue
// cleared, or shutdown) rather than having failed. Callers distinguish it so a
// cancellation isn't logged as an error.
var ErrCancelled = errors.New("download cancelled")

// finalizeCancelled records a stopped download.
//
// A shutdown (parent already cancelled) deliberately leaves the row
// "downloading": ResetStalledDownloads re-queues it on the next start, so
// stopping the server resumes the download instead of losing it. Only a
// user-initiated cancel is terminal. The row may already be deleted in that
// case — cancellation usually arrives via Delete — so a missing row is fine.
func (s *DownloadService) finalizeCancelled(parent context.Context, id int64) error {
	s.flushLogs(id)

	if parent.Err() != nil {
		return ErrCancelled
	}

	if err := s.repo.MarkCompleted(id, "cancelled"); err != nil {
		log.Printf("download %d: failed to record cancellation: %v", id, err)
	}
	return ErrCancelled
}

// flushLogs persists whatever output has accumulated for a download.
func (s *DownloadService) flushLogs(id int64) {
	logs := s.cache.FlushLogs(id)
	if logs == "" {
		return
	}
	if err := s.repo.AppendLogs(id, logs); err != nil {
		log.Printf("download %d: failed to persist logs: %v", id, err)
	}
}

// resolveBaseLibraryDir returns the absolute library directory a download writes
// into, applying the optional per-download OutputDir while rejecting any path
// that escapes the library root.
func (s *DownloadService) resolveBaseLibraryDir(d *models.Download) (string, error) {
	if !d.OutputDir.Valid || d.OutputDir.String == "" {
		return s.cfg.LibraryDir, nil
	}
	// Reuse the library service's guard so both entry points enforce the boundary
	// the same way — it resolves symlinks, which a plain prefix check does not.
	dir, err := s.librarySvc.ResolveWithinLibrary(d.OutputDir.String)
	if err != nil {
		return "", fmt.Errorf("invalid output directory: %w", err)
	}
	return dir, nil
}

// importDownloadedItems moves each downloaded item from the temp dir into the
// library and returns the number of items successfully imported. Per-item
// failures are logged and skipped (a playlist with a few bad entries still
// imports the rest); a non-nil error means the import couldn't even start.
//
// A cancel stops the import between items and returns ctx.Err() with the count
// imported so far. Importing a long playlist takes real time (a move plus an
// ffprobe per file), so a deleted download must not keep filling the library.
func (s *DownloadService) importDownloadedItems(ctx context.Context, d *models.Download, tempDownloadDir, mode, ytdlpFlags string) (int, error) {
	entries, err := os.ReadDir(tempDownloadDir)
	if err != nil {
		return 0, err
	}

	baseLibraryDir, err := s.resolveBaseLibraryDir(d)
	if err != nil {
		return 0, err
	}
	if err := os.MkdirAll(baseLibraryDir, 0755); err != nil {
		return 0, err
	}

	var itemDirs []string
	for _, entry := range entries {
		if !entry.IsDir() {
			continue
		}
		name := entry.Name()
		if strings.HasPrefix(name, "item-") {
			itemDirs = append(itemDirs, filepath.Join(tempDownloadDir, name))
		}
	}
	sort.Strings(itemDirs)

	imported := 0
	for _, itemDir := range itemDirs {
		if err := ctx.Err(); err != nil {
			return imported, err
		}
		if err := s.importItemDir(ctx, d.URL, itemDir, baseLibraryDir, mode, ytdlpFlags); err != nil {
			// A cancelled item isn't a bad item: stop instead of logging a warning
			// for it and every one that follows.
			if ctx.Err() != nil {
				return imported, ctx.Err()
			}
			log.Printf("warning: failed to import item %s: %v", itemDir, err)
			continue
		}
		imported++
	}

	// The temp dir (and any leftovers from failed imports) is removed by the
	// caller's deferred cleanup, so partial state never leaks even on a crash.
	return imported, nil
}

func (s *DownloadService) importItemDir(ctx context.Context, url, itemDir, baseLibraryDir, mode, ytdlpFlags string) error {
	entries, err := os.ReadDir(itemDir)
	if err != nil {
		return err
	}

	var mediaFiles []os.DirEntry
	var infoJSONPath string
	var subtitleFiles []string

	for _, entry := range entries {
		if entry.IsDir() {
			continue
		}
		name := entry.Name()
		path := filepath.Join(itemDir, name)
		ext := strings.ToLower(filepath.Ext(name))

		if isInfoJSON(name) {
			infoJSONPath = path
			continue
		}
		if ext == ".vtt" || ext == ".srt" || ext == ".ass" || ext == ".ssa" {
			subtitleFiles = append(subtitleFiles, path)
			continue
		}

		mtype, err := mimetype.DetectFile(path)
		if err == nil && mtype != nil && (strings.HasPrefix(mtype.String(), "audio/") || strings.HasPrefix(mtype.String(), "video/")) {
			mediaFiles = append(mediaFiles, entry)
		}
	}

	if len(mediaFiles) == 0 {
		return fmt.Errorf("no media files found in %s", itemDir)
	}

	info := readInfoJSON(infoJSONPath)
	name := s.deriveItemName(itemDir, info, mediaFiles)
	videoID := info.ID

	// Last point at which nothing has been written to the library yet: give up
	// here on a cancel rather than part-way through, which would leave a folder
	// with some of its files and no marker — or, in overwrite mode, delete the
	// existing item and not replace it.
	if err := ctx.Err(); err != nil {
		return err
	}

	// Overwrite mode: replace the existing copy of this video in place rather than
	// creating a duplicate folder. Removing the old dir lets uniqueDir reuse its
	// name (or land on the new title if it changed upstream).
	if mode == "overwrite" && videoID != "" {
		if existing, ok := s.librarySvc.FindByVideoID(baseLibraryDir, videoID); ok {
			if rel, err := filepath.Rel(s.cfg.LibraryDir, existing); err == nil {
				s.librarySvc.evictCachedScan(filepath.ToSlash(rel))
			}
			os.RemoveAll(existing)
		}
	}

	targetDir := s.uniqueDir(baseLibraryDir, name)
	if err := os.MkdirAll(targetDir, 0755); err != nil {
		return err
	}

	if infoJSONPath != "" {
		if err := moveFile(infoJSONPath, filepath.Join(targetDir, "info.json")); err != nil {
			return err
		}
	}

	for _, entry := range mediaFiles {
		if err := moveFile(filepath.Join(itemDir, entry.Name()), filepath.Join(targetDir, entry.Name())); err != nil {
			return err
		}
	}

	// Probe each media file's duration once, here in the worker (off the request
	// path), and cache it in the marker so the library never has to probe while
	// serving pages. Files we can't probe simply get no duration.
	fileDurations := make(map[string]int)
	for _, entry := range mediaFiles {
		if d, ok := probeDuration(ctx, s.cfg.FFprobePath, filepath.Join(targetDir, entry.Name())); ok {
			fileDurations[entry.Name()] = d
		}
	}

	if len(subtitleFiles) > 0 {
		subtitlesDir := filepath.Join(targetDir, subtitlesDirName)
		if err := os.MkdirAll(subtitlesDir, 0755); err != nil {
			return err
		}
		for _, sf := range subtitleFiles {
			if err := moveFile(sf, filepath.Join(subtitlesDir, filepath.Base(sf))); err != nil {
				return err
			}
		}
	}

	metadata := models.ItemMetadata{
		Name:          name,
		SourceURL:     url,
		VideoID:       videoID,
		YtdlpFlags:    ytdlpFlags,
		FileDurations: fileDurations,
	}

	return s.librarySvc.writeMetadata(targetDir, metadata)
}

// infoJSON is the subset of yt-dlp's info.json VidArchive reads. ID is the
// stable item identity; within a single subscription's own directory it is
// enough to match items, so the extractor is not needed.
type infoJSON struct {
	ID          string `json:"id"`
	Title       string `json:"title"`
	Description string `json:"description"`
	WebpageURL  string `json:"webpage_url"`
}

// readInfoJSON parses an info.json. A missing, unreadable or malformed file
// yields a zero-value struct: every caller treats absent fields as "unknown"
// and falls back, so there is nothing to distinguish.
func readInfoJSON(infoJSONPath string) infoJSON {
	var info infoJSON
	if infoJSONPath == "" {
		return info
	}
	data, err := os.ReadFile(infoJSONPath)
	if err != nil {
		return info
	}
	if err := json.Unmarshal(data, &info); err != nil {
		log.Printf("ignoring malformed %s: %v", infoJSONPath, err)
		return infoJSON{}
	}
	return info
}

// refreshAndAddNew handles a metadata-mode run. The main pass used
// --skip-download, so tempDownloadDir holds only info.json files. Existing
// library items have their markers refreshed in place; entries with no existing
// match are genuinely new and are downloaded as full items in a second pass.
func (s *DownloadService) refreshAndAddNew(ctx context.Context, d *models.Download, preset *models.Preset, tempDownloadDir, ytdlpFlags string) error {
	// The library dir is not created here: a refresh that matches everything
	// writes nothing, and importDownloadedItems creates it when a second pass
	// actually has an item to add.
	baseLibraryDir, err := s.resolveBaseLibraryDir(d)
	if err != nil {
		return err
	}

	entries, err := os.ReadDir(tempDownloadDir)
	if err != nil {
		return err
	}

	var newURLs []string
	for _, entry := range entries {
		if err := ctx.Err(); err != nil {
			return err
		}
		if !entry.IsDir() || !strings.HasPrefix(entry.Name(), "item-") {
			continue
		}
		itemDir := filepath.Join(tempDownloadDir, entry.Name())
		infoJSONPath := findInfoJSON(itemDir)
		if infoJSONPath == "" {
			continue
		}
		info := readInfoJSON(infoJSONPath)
		if info.ID == "" {
			continue
		}
		if existing, ok := s.librarySvc.FindByVideoID(baseLibraryDir, info.ID); ok {
			if err := s.applyMetadata(existing, info); err != nil {
				log.Printf("warning: failed to refresh metadata for %s: %v", itemDir, err)
			}
			continue
		}
		if info.WebpageURL != "" {
			newURLs = append(newURLs, info.WebpageURL)
		}
	}

	if len(newURLs) == 0 {
		return nil
	}
	return s.downloadFresh(ctx, d, preset, newURLs, ytdlpFlags)
}

// downloadFresh fetches the given item URLs as full downloads (media + info.json)
// and imports them into the download's library directory. Metadata mode uses this
// to add entries that don't exist in the library yet.
func (s *DownloadService) downloadFresh(ctx context.Context, d *models.Download, preset *models.Preset, urls []string, ytdlpFlags string) error {
	tempDir := s.tempNewDirFor(d.ID)
	if err := os.MkdirAll(tempDir, 0755); err != nil {
		return err
	}
	defer os.RemoveAll(tempDir)

	args := s.presetSvc.BuildArgs(preset, d.FormatOverride, d.CustomFlags)
	args, cleanup := s.appendCookies(args)
	defer cleanup()
	args = append(args, "--write-info-json")
	args = append(args, "-P", tempDir)
	args = append(args, "-o", "item-%(autonumber)05d/%(title)s.%(ext)s")
	args = append(args, urls...)

	runErr := s.runYTDLP(ctx, d, args)
	// A cancelled second pass has nothing worth importing.
	if ctx.Err() != nil {
		return runErr
	}
	// Import whatever succeeded even if some entries errored.
	if _, err := s.importDownloadedItems(ctx, d, tempDir, "", ytdlpFlags); err != nil {
		log.Printf("warning: failed to import new metadata-mode items: %v", err)
	}
	return runErr
}

// applyMetadata rewrites an existing item's marker (name/description/identity)
// from a fresh info.json without touching its media.
func (s *DownloadService) applyMetadata(existing string, info infoJSON) error {
	meta, err := s.librarySvc.readMetadata(existing)
	if err != nil {
		return fmt.Errorf("read metadata for %s: %w", existing, err)
	}
	if info.Title != "" {
		meta.Name = info.Title
	}
	if info.Description != "" {
		meta.Description = info.Description
	}
	if meta.SourceURL == "" && info.WebpageURL != "" {
		meta.SourceURL = info.WebpageURL
	}
	meta.VideoID = info.ID

	if err := s.librarySvc.writeMetadata(existing, meta); err != nil {
		return err
	}
	if rel, err := filepath.Rel(s.cfg.LibraryDir, existing); err == nil {
		s.librarySvc.evictCachedScan(filepath.ToSlash(rel))
	}
	return nil
}

// isInfoJSON reports whether a file name is yt-dlp's metadata sidecar. yt-dlp
// writes "<title>.info.json" next to the media, but a bare "info.json" is what
// an already-imported item holds.
func isInfoJSON(name string) bool {
	return name == "info.json" || strings.HasSuffix(name, ".info.json")
}

// findInfoJSON returns the path to an info.json directly inside itemDir, or "".
func findInfoJSON(itemDir string) string {
	entries, err := os.ReadDir(itemDir)
	if err != nil {
		return ""
	}
	for _, entry := range entries {
		if entry.IsDir() {
			continue
		}
		name := entry.Name()
		if isInfoJSON(name) {
			return filepath.Join(itemDir, name)
		}
	}
	return ""
}

// pruneSubscription mirrors the source by deleting items in the subscription's
// directory that are no longer present upstream. It enumerates the current id
// set with a cheap flat-playlist listing; it never prunes when that enumeration
// fails or returns nothing, so a dead URL or network error can't wipe the dir.
func (s *DownloadService) pruneSubscription(ctx context.Context, d *models.Download, sub *models.Subscription) {
	baseLibraryDir, err := s.resolveBaseLibraryDir(d)
	if err != nil {
		log.Printf("subscription %d prune skipped: %v", sub.ID, err)
		return
	}

	keep, err := s.enumeratePlaylistIDs(ctx, sub.URL)
	if err != nil {
		log.Printf("subscription %d prune skipped: enumeration failed: %v", sub.ID, err)
		return
	}
	if len(keep) == 0 {
		log.Printf("subscription %d prune skipped: source returned no entries", sub.ID)
		return
	}

	removed, err := s.librarySvc.PruneToIDSet(baseLibraryDir, keep)
	if err != nil {
		log.Printf("subscription %d prune error: %v", sub.ID, err)
		return
	}
	if removed > 0 {
		log.Printf("subscription %d pruned %d item(s) removed upstream", sub.ID, removed)
	}
}

// enumeratePlaylistIDs lists the current video-id set for a URL without
// downloading, using yt-dlp --flat-playlist. Cookies are applied so private
// playlists enumerate correctly. Ids alone are sufficient to match items within
// a subscription's own directory (see FindByVideoID / PruneToIDSet).
func (s *DownloadService) enumeratePlaylistIDs(ctx context.Context, url string) (map[string]bool, error) {
	args := []string{"--flat-playlist", "--no-warnings", "--print", "%(id)s"}

	args, cleanup := s.appendCookies(args)
	defer cleanup()
	args = append(args, url)

	out, err := exec.CommandContext(ctx, s.cfg.YTDLPPath, args...).Output()
	if err != nil {
		return nil, err
	}

	keep := make(map[string]bool)
	for _, line := range strings.Split(string(out), "\n") {
		id := strings.TrimSpace(line)
		// yt-dlp prints "NA" for a missing field; never treat that as a real id.
		if id == "" || id == "NA" {
			continue
		}
		keep[id] = true
	}
	return keep, nil
}

// deriveItemName names the imported item after its title, falling back to the
// largest media file's base name when there is no usable info.json.
func (s *DownloadService) deriveItemName(itemDir string, info infoJSON, mediaFiles []os.DirEntry) string {
	if info.Title != "" {
		return sanitizeDirName(info.Title)
	}

	var largest os.DirEntry
	var maxSize int64
	for _, f := range mediaFiles {
		st, err := os.Stat(filepath.Join(itemDir, f.Name()))
		if err == nil && (largest == nil || st.Size() > maxSize) {
			largest, maxSize = f, st.Size()
		}
	}
	if largest == nil {
		largest = mediaFiles[0]
	}
	base := strings.TrimSuffix(largest.Name(), filepath.Ext(largest.Name()))
	return sanitizeDirName(base)
}

func (s *DownloadService) uniqueDir(base, name string) string {
	dir := filepath.Join(base, name)
	if _, err := os.Stat(dir); os.IsNotExist(err) {
		return dir
	}
	for i := 1; ; i++ {
		candidate := fmt.Sprintf("%s-%d", dir, i)
		if _, err := os.Stat(candidate); os.IsNotExist(err) {
			return candidate
		}
	}
}

// moveFile moves src to dst, falling back to copy-and-delete when the two are on
// different filesystems. The temp and library directories are independently
// configurable, so they can legitimately live on separate mounts — where a plain
// rename fails with EXDEV.
func moveFile(src, dst string) error {
	if err := os.Rename(src, dst); err == nil {
		return nil
	} else if !errors.Is(err, syscall.EXDEV) {
		return err
	}

	in, err := os.Open(src)
	if err != nil {
		return err
	}
	defer in.Close()

	info, err := in.Stat()
	if err != nil {
		return err
	}

	out, err := os.OpenFile(dst, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, info.Mode())
	if err != nil {
		return err
	}

	if _, err := io.Copy(out, in); err != nil {
		out.Close()
		os.Remove(dst)
		return err
	}
	// Close explicitly: a deferred close would hide a flush error on the copy.
	if err := out.Close(); err != nil {
		os.Remove(dst)
		return err
	}

	return os.Remove(src)
}

func sanitizeDirName(name string) string {
	name = strings.TrimSpace(name)
	replacer := strings.NewReplacer(
		"/", "-",
		"\\", "-",
		":", "-",
		"*", "-",
		"?", "-",
		"\"", "-",
		"<", "-",
		">", "-",
		"|", "-",
	)
	name = replacer.Replace(name)
	name = strings.TrimSpace(name)
	if name == "" {
		name = "untitled"
	}
	return name
}

// probeDuration returns the duration of a media file in whole seconds. The bool
// is false when ffprobe is unavailable or the file has no usable duration.
func probeDuration(ctx context.Context, ffprobePath, path string) (int, bool) {
	out, err := exec.CommandContext(ctx, ffprobePath, "-v", "error",
		"-show_entries", "format=duration",
		"-of", "default=nw=1:nk=1", path).Output()
	if err != nil {
		return 0, false
	}
	f, err := strconv.ParseFloat(strings.TrimSpace(string(out)), 64)
	if err != nil || f <= 0 {
		return 0, false
	}
	return int(f + 0.5), true
}

// ytFormat mirrors the subset of yt-dlp's per-format JSON (-J) we surface.
// Numeric fields are pointers so an absent value (null/omitted) is distinct
// from a real zero.
type ytFormat struct {
	FormatID       string   `json:"format_id"`
	Ext            string   `json:"ext"`
	Resolution     string   `json:"resolution"`
	Width          *int     `json:"width"`
	Height         *int     `json:"height"`
	FPS            *float64 `json:"fps"`
	VCodec         string   `json:"vcodec"`
	ACodec         string   `json:"acodec"`
	AudioChannels  *int     `json:"audio_channels"`
	Filesize       *int64   `json:"filesize"`
	FilesizeApprox *int64   `json:"filesize_approx"`
	FormatNote     string   `json:"format_note"`
}

// parseFormatJSON reads yt-dlp's single-JSON dump (-J) and returns the available
// formats. For a single video the formats live at the top level; for a playlist
// URL we fall back to the first entry's formats so the picker still shows
// something useful.
func parseFormatJSON(data []byte) ([]*models.FormatInfo, error) {
	var top struct {
		Formats []ytFormat `json:"formats"`
		Entries []struct {
			Formats []ytFormat `json:"formats"`
		} `json:"entries"`
	}
	if err := json.Unmarshal(data, &top); err != nil {
		return nil, fmt.Errorf("parse yt-dlp JSON: %w", err)
	}

	raw := top.Formats
	if len(raw) == 0 && len(top.Entries) > 0 {
		raw = top.Entries[0].Formats
	}

	formats := make([]*models.FormatInfo, 0, len(raw))
	for _, f := range raw {
		formats = append(formats, f.toFormatInfo())
	}
	return formats, nil
}

func (f ytFormat) toFormatInfo() *models.FormatInfo {
	fi := &models.FormatInfo{
		ID:   f.FormatID,
		Ext:  f.Ext,
		Note: f.FormatNote,
	}

	switch {
	case f.Resolution != "":
		fi.Resolution = f.Resolution
	case f.Width != nil && f.Height != nil && *f.Width > 0 && *f.Height > 0:
		fi.Resolution = fmt.Sprintf("%dx%d", *f.Width, *f.Height)
	}

	if f.FPS != nil && *f.FPS > 0 {
		fi.FPS = strconv.FormatFloat(*f.FPS, 'f', -1, 64)
	}
	if f.AudioChannels != nil && *f.AudioChannels > 0 {
		fi.Channels = strconv.Itoa(*f.AudioChannels)
	}

	// Prefer the video codec; fall back to the audio codec for audio-only formats.
	if f.VCodec != "" && f.VCodec != "none" {
		fi.Codec = f.VCodec
	} else if f.ACodec != "" && f.ACodec != "none" {
		fi.Codec = f.ACodec
	}

	if f.Filesize != nil && *f.Filesize > 0 {
		fi.FileSize = util.FormatBytes(*f.Filesize)
	} else if f.FilesizeApprox != nil && *f.FilesizeApprox > 0 {
		fi.FileSize = "~" + util.FormatBytes(*f.FilesizeApprox)
	}

	return fi
}

func sqlNullInt64(v int64) sql.NullInt64 {
	return sql.NullInt64{Int64: v, Valid: true}
}

// reservedFlags are yt-dlp options VidArchive always sets itself; user custom
// flags must not pass them (or a conflicting inverse). The value describes what
// the option controls, for the failure message.
var reservedFlags = map[string]string{
	"-o":           "the output template",
	"--output":     "the output template",
	"-P":           "the download path",
	"--paths":      "the download path",
	"--cookies":    "cookies (set these in Settings instead)",
	"--no-cookies": "cookies (set these in Settings instead)",
	"--newline":    "progress output formatting (VidArchive sets this to stream logs)",

	// These hand yt-dlp an arbitrary command or binary to run. VidArchive passes
	// custom flags through verbatim, so allowing them would turn the preset form
	// into remote command execution.
	"--exec":                     "running external commands (not permitted)",
	"--exec-before-download":     "running external commands (not permitted)",
	"--postprocessor-args":       "post-processor arguments (not permitted)",
	"--ppa":                      "post-processor arguments (not permitted)",
	"--downloader":               "selecting an external downloader (not permitted)",
	"--external-downloader":      "selecting an external downloader (not permitted)",
	"--downloader-args":          "external downloader arguments (not permitted)",
	"--external-downloader-args": "external downloader arguments (not permitted)",
}

// reservedSubscriptionFlags are additionally reserved for subscription runs,
// where VidArchive drives info-json writing and the refresh mode.
var reservedSubscriptionFlags = map[string]string{
	"--write-info-json":     "info-json writing (needed to track item identity)",
	"--no-write-info-json":  "info-json writing (needed to track item identity)",
	"--download-archive":    "the download archive (managed by Skip mode)",
	"--no-download-archive": "the download archive (managed by Skip mode)",
	"--skip-download":       "media downloading (managed by Metadata mode)",
	"--no-skip-download":    "media downloading (managed by Metadata mode)",
}

// checkReservedFlags rejects custom flags that clash with options VidArchive
// controls, naming the offender. It matches both "--flag" and "--flag=value".
func checkReservedFlags(customFlags string, isSubscription bool) error {
	for _, tok := range strings.Fields(customFlags) {
		// Both "--flag value" and "--flag=value" name the same option.
		name, _, _ := strings.Cut(tok, "=")

		desc, ok := reservedFlags[name]
		if !ok && isSubscription {
			desc, ok = reservedSubscriptionFlags[name]
		}
		if ok {
			return fmt.Errorf("custom flag %q conflicts with VidArchive's handling of %s; remove it and try again", tok, desc)
		}
	}
	return nil
}