package main

import (
	"context"
	"fmt"
	"net/url"
	"os"
	"os/signal"
	"path/filepath"
	"strings"
	"syscall"
	"time"

	"rssd/config"
	"rssd/downloader"
	"rssd/poller"
	"rssd/state"
	"rssd/ytdlp"
)

const (
	stateFile = "state.json"
)

func main() {
	fmt.Fprintf(os.Stderr, "rssd: starting\n")

	// Load configuration.
	cfgPath := os.Getenv("RSSD_CONFIG")
	if cfgPath == "" {
		cfgPath = "~/.config/rssd/config.yaml"
	}
	cfgPath = config.ExpandPath(cfgPath) // resolve ~ early for consistent path usage
	cfg, err := config.Load(cfgPath)
	if err != nil {
		fmt.Fprintf(os.Stderr, "rssd: fatal: %v\n", err)
		os.Exit(1)
	}

	// Load state — store alongside the config file.
	stateDir := filepath.Dir(cfgPath)
	sm, err := state.NewManager(filepath.Join(stateDir, stateFile))
	if err != nil {
		fmt.Fprintf(os.Stderr, "rssd: fatal: %v\n", err)
		os.Exit(1)
	}
	if err := sm.Load(); err != nil {
		fmt.Fprintf(os.Stderr, "rssd: warning: could not load state (%v), starting fresh\n", err)
	}

	// Start download worker pool.
	jobs := make(chan downloader.DownloadJob)
	pool := downloader.NewPool(cfg.Settings.DownloadPoolSize, cfg.Settings.BackoffBase, sm)
	go pool.Run(jobs)

	// Re-enqueue any "pending" jobs from a previous run that were never picked up
	// by workers, and any "downloading" jobs that were interrupted mid-download by
	// a crash or forced termination (a stuck "downloading" job would otherwise be
	// left alone forever, since the retry dispatch only handles "retrying").
	sm.ForEachJob(func(j *state.JobSnapshot) {
		if j.Status == state.StatusPending || j.Status == state.StatusDownloading {
			fmt.Fprintf(os.Stderr, "rssd: re-enqueued interrupted job %s (was %s)\n", j.EnclosureURL, j.Status)
			jobs <- jobFromSnapshot(j, cfg)
		}
	})

	fmt.Fprintf(os.Stderr, "rssd: workers started, polling feeds\n")
	sigCh := make(chan os.Signal, 1)
	signal.Notify(sigCh, syscall.SIGTERM, syscall.SIGINT)

	fmt.Fprintf(os.Stderr, "rssd: %d feeds configured, polling started\n", len(cfg.Feeds))

	// Launch a poller goroutine per feed.
	for _, feed := range cfg.Feeds {
		go pollFeed(feed, sm, jobs, cfg)
	}

	// Periodically dispatch retrying jobs whose backoff has elapsed.
	retryTicker := time.NewTicker(1 * time.Minute)
	defer retryTicker.Stop()
	go func() {
		for range retryTicker.C {
			dispatchRetries(sm, jobs, cfg.Settings.MaxRetries, cfg)
		}
	}()

	// Wait for shutdown signal.
	sig := <-sigCh
	fmt.Fprintf(os.Stderr, "rssd: received %v, shutting down...\n", sig)

	// Save final state before exiting so no progress is lost.
	if err := sm.Save(); err != nil {
		fmt.Fprintf(os.Stderr, "rssd: error saving final state: %v\n", err)
	}
	fmt.Fprintf(os.Stderr, "rssd: stopped\n")
}

func pollFeed(feed config.Feed, sm *state.Manager, jobs chan<- downloader.DownloadJob, cfg *config.Config) {
	interval := cfg.PollIntervalFor(feed)

	if isYouTubeURL(feed.URL) {
		fmt.Fprintf(os.Stderr, "rssd: polling YouTube %s every %s\n", feed.URL, interval)

		// Poll immediately on startup.
		pollYouTube(feed, sm, jobs, cfg)

		ticker := time.NewTicker(interval)
		defer ticker.Stop()
		for range ticker.C {
			pollYouTube(feed, sm, jobs, cfg)
		}
		return
	}

	fetcher := poller.NewFetcher()
	fmt.Fprintf(os.Stderr, "rssd: polling %s every %s\n", feed.URL, interval)

	// Poll immediately on startup.
	pollAndEnqueue(feed, sm, jobs, fetcher, cfg)

	ticker := time.NewTicker(interval)
	defer ticker.Stop()

	for range ticker.C {
		pollAndEnqueue(feed, sm, jobs, fetcher, cfg)
	}
}

// isYouTubeURL reports whether the feed URL points at a YouTube channel or
// playlist. Playlist URLs carry their identifier in the query string
// (e.g. /playlist?list=...), so both path and query are checked.
func isYouTubeURL(rawURL string) bool {
	u, err := url.Parse(rawURL)
	if err != nil {
		return false
	}
	host := strings.ToLower(u.Hostname())
	switch host {
	case "youtube.com", "www.youtube.com", "m.youtube.com", "music.youtube.com", "youtu.be":
	default:
		return false
	}
	p := strings.ToLower(u.Path)
	return strings.HasPrefix(p, "/channel/") || strings.HasPrefix(p, "/user/") ||
		strings.HasPrefix(p, "/@") || u.Query().Has("list")
}

// ytSettings builds ytdlp settings from the global config.
func ytSettings(cfg *config.Config) ytdlp.Settings {
	return ytdlp.Settings{BinPath: cfg.Settings.YTDlpPath}
}

// pollYouTube enumerates a YouTube channel/playlist, resolves the date and
// title of any videos not yet tracked in state, and enqueues those that pass
// the start_date filter. Existing jobs (any status) make their videos count
// as "already seen", so discovery is incremental after the first run.
func pollYouTube(feed config.Feed, sm *state.Manager, jobs chan<- downloader.DownloadJob, cfg *config.Config) {
	// A first-run backfill can resolve and enqueue many videos, so give the
	// whole pass a generous deadline; discovery itself is quick.
	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Hour)
	defer cancel()

	vids, err := ytdlp.Discovery(ctx, ytSettings(cfg), feed.URL)
	if err != nil {
		fmt.Fprintf(os.Stderr, "rssd: error discovering %s: %v\n", feed.URL, err)
		return
	}

	// Collect video IDs already tracked for this feed (any status).
	seen := make(map[string]bool, len(vids))
	sm.ForEachJob(func(j *state.JobSnapshot) {
		if j.FeedURL == feed.URL {
			seen[videoIDFromURL(j.EnclosureURL)] = true
		}
	})

	start := feed.PublishedAt()
	// Channels enumerate newest-first, so the first video older than the start
	// date is a stable boundary: everything after it is older too. Playlists
	// have no guaranteed order, so they must be walked fully and their
	// out-of-range videos recorded as skipped to avoid re-resolving them.
	newestFirst := !strings.Contains(strings.ToLower(feed.URL), "list=")

	newCount, enqueued, skipped := 0, 0, 0
	// Per-video resolve timeout. A single pathological video (JS-challenge
	// solving, region/members-only) can make yt-dlp hang; bounding each call
	// means one bad video can't stall the whole feed walk.
	resolveTimeout := 2 * time.Minute
	for _, v := range vids {
		if seen[v.ID] {
			continue
		}
		newCount++

		vctx, vcancel := context.WithTimeout(ctx, resolveTimeout)
		info, err := ytdlp.Info(vctx, ytSettings(cfg), v.ID)
		vcancel()
		if err != nil {
			fmt.Fprintf(os.Stderr, "rssd: warning: could not resolve %s: %v\n", v.ID, err)
			continue
		}

		// Out of the start_date window.
		if !start.IsZero() && !info.UploadDate.IsZero() && info.UploadDate.Before(start) {
			if newestFirst {
				// Stop at the first out-of-range video without recording it. It
				// stays "new" each poll, so it remains a stable boundary and we
				// never walk backward through older videos.
				fmt.Fprintf(os.Stderr, "rssd: %s reached pre-start-date boundary, stopping\n", feed.URL)
				break
			}
			// Playlist: record as skipped so it isn't re-resolved next poll.
			dp := computeYTDestPath(feed.OutputDir, info.UploadDate, info.Title, v.ID)
			if sm.AddJobWithStatus(feed.URL, watchURL(v.ID), dp, state.StatusSkipped, info.Duration) {
				skipped++
			}
			continue
		}

		dp := computeYTDestPath(feed.OutputDir, info.UploadDate, info.Title, v.ID)
		if !sm.AddJob(feed.URL, watchURL(v.ID), dp, cfg.Settings.MaxRetries, info.Duration) {
			continue
		}
		// Persist immediately so a crash mid-backfill doesn't lose this.
		if err := sm.Save(); err != nil {
			fmt.Fprintf(os.Stderr, "rssd: error saving state: %v\n", err)
		}
		// Enqueue; downloads run in the worker pool and overlap further
		// resolution of later videos.
		job := downloader.DownloadJob{
			FeedURL:      feed.URL,
			EnclosureURL: watchURL(v.ID),
			DestPath:     dp,
			IsYouTube:    true,
			VideoID:      v.ID,
			Duration:     info.Duration,
			YTSettings:   ytSettings(cfg),
		}
		fmt.Fprintf(os.Stderr, "rssd: enqueued %s -> %s\n", job.EnclosureURL, job.DestPath)
		jobs <- job
		enqueued++
	}

	fmt.Fprintf(os.Stderr, "rssd: %s done — %d new, %d enqueued, %d skipped\n", feed.URL, newCount, enqueued, skipped)
}

func videoIDFromURL(u string) string {
	q := strings.TrimPrefix(u, "https://www.youtube.com/watch?v=")
	if i := strings.IndexAny(q, "?&"); i >= 0 {
		q = q[:i]
	}
	return q
}

func watchURL(id string) string { return "https://www.youtube.com/watch?v=" + id }

// computeYTDestPath constructs the local file base path for a YouTube
// video: "YYYY-MM-DD - <sanitized title> [<id>]" (no extension). yt-dlp
// appends the native audio extension (usually .webm) and the downloader
// records the final path in state. The bracketed ID disambiguates
// duplicate titles.
func computeYTDestPath(outputDir string, published time.Time, title, id string) string {
	base := sanitizeFilename(title)
	if base == "" {
		base = "untitled"
	}
	name := fmt.Sprintf("%s [%s]", base, id)
	if !published.IsZero() {
		name = fmt.Sprintf("%s - %s", published.Format("2006-01-02"), name)
	}
	return filepath.Join(outputDir, name)
}

func pollAndEnqueue(feed config.Feed, sm *state.Manager, jobs chan<- downloader.DownloadJob, fetcher *poller.Fetcher, cfg *config.Config) {
	feedState := sm.FindFeedByURL(feed.URL)
	var lastModified, etag string
	if feedState != nil {
		lastModified = feedState.LastModified
		etag = feedState.ETag
	}

	result, err := fetcher.Poll(feed.URL, lastModified, etag)
	if err != nil {
		fmt.Fprintf(os.Stderr, "rssd: error polling %s: %v\n", feed.URL, err)
		return
	}
	if result.NotModified {
		fmt.Fprintf(os.Stderr, "rssd: %s unchanged (skipping)\n", feed.URL)
		return
	}

	fmt.Fprintf(os.Stderr, "rssd: %s polled — %d enclosures found\n", feed.URL, len(result.NewEnclosures))

	if len(result.NewEnclosures) == 0 {
		fmt.Fprintf(os.Stderr, "rssd: warning: %s has no enclosures in latest items\n", feed.URL)
	}

	// Save updated feed metadata for next conditional request.
	sm.UpsertFeed(feed.URL, result.LastModified, result.ETag)

	// Phase 1: Record all new enclosures in state first.
	var newlyAdded []downloader.DownloadJob
	startDate := feed.PublishedAt()
	for _, encInfo := range result.NewEnclosures {
		// Skip items older than the configured start date.
		if !startDate.IsZero() && (!encInfo.PublishedAt.IsZero() && encInfo.PublishedAt.Before(startDate)) {
			continue
		}

		destPath := computeDestPath(feed.OutputDir, encInfo)
		if sm.AddJob(feed.URL, encInfo.URL, destPath, cfg.Settings.MaxRetries, 0) {
			newlyAdded = append(newlyAdded, downloader.DownloadJob{
				FeedURL:      feed.URL,
				EnclosureURL: encInfo.URL,
				DestPath:     destPath,
			})
		}
	}

	// Commit all newly discovered jobs to disk before attempting to enqueue.
	// This ensures they survive a crash even if we block on the channel send.
	if err := sm.Save(); err != nil {
		fmt.Fprintf(os.Stderr, "rssd: error saving state: %v\n", err)
	}

	// Phase 2: Enqueue the jobs to workers.
	for _, job := range newlyAdded {
		fmt.Fprintf(os.Stderr, "rssd: enqueued %s -> %s\n", job.EnclosureURL, job.DestPath)
		jobs <- job
	}
}

// dispatchRetries scans all jobs in state and re-enqueues those whose backoff has elapsed.
func dispatchRetries(sm *state.Manager, jobs chan<- downloader.DownloadJob, maxRetries int, cfg *config.Config) {
	// Collect snapshots (lock released before any callback invocation).
	var ready []downloader.DownloadJob
	var failed []string

	sm.ForEachJob(func(snap *state.JobSnapshot) {
		if snap.Status != state.StatusRetrying {
			return
		}

		if snap.AttemptCount >= maxRetries {
			// Permanently failed — use UpdateJob to mutate the live state.
			sm.UpdateJob(snap.EnclosureURL, func(j *state.Job) {
				j.Status = state.StatusFailed
			})
			failed = append(failed, fmt.Sprintf("%s (after %d attempts: %s)",
				snap.EnclosureURL, snap.AttemptCount, snap.Error))
			return
		}

		if snap.NextAttemptAt == nil || time.Now().After(*snap.NextAttemptAt) {
			// Re-enqueue — use UpdateJob to mutate the live state.
			sm.UpdateJob(snap.EnclosureURL, func(j *state.Job) {
				j.Status = state.StatusPending
				j.NextAttemptAt = nil
			})
			ready = append(ready, jobFromSnapshot(snap, cfg))
		}
	})

	if len(failed) > 0 {
		for _, msg := range failed {
			fmt.Fprintf(os.Stderr, "rssd: %s permanently failed\n", msg)
		}
	}

	// Send to channel and persist state (lock released).
	for _, job := range ready {
		jobs <- job
	}

	if err := sm.Save(); err != nil {
		fmt.Fprintf(os.Stderr, "rssd: error saving state (retry dispatch): %v\n", err)
	}
}

// jobFromSnapshot rebuilds a DownloadJob from a persisted state snapshot,
// restoring YouTube-specific fields that aren't part of the on-disk schema.
func jobFromSnapshot(s *state.JobSnapshot, cfg *config.Config) downloader.DownloadJob {
	j := downloader.DownloadJob{
		FeedURL:      s.FeedURL,
		EnclosureURL: s.EnclosureURL,
		DestPath:     s.DestPath,
		Duration:     s.Duration,
	}
	if isYouTubeURL(s.FeedURL) {
		j.IsYouTube = true
		j.VideoID = videoIDFromURL(s.EnclosureURL)
		j.YTSettings = ytSettings(cfg)
	}
	return j
}

// sanitizeFilename replaces characters that are invalid or problematic in filenames.
func sanitizeFilename(s string) string {
	replacer := strings.NewReplacer(
		"/", "_", "\\", "_", ":", "_", "<", "_", ">", "_", "|", "_", "\"", "_", "?", "_", "*", "_",
	)
	s = replacer.Replace(s)
	for strings.Contains(s, "__") {
		s = strings.ReplaceAll(s, "__", "_")
	}
	return strings.TrimSpace(s)
}

// extFromMimeType maps common MIME types to their file extensions.
// Returns "" for unknown types.
func extFromMimeType(mime string) string {
	switch mime {
	case "audio/mpeg":
		return ".mp3"
	case "audio/mp4", "audio/x-m4a":
		return ".m4a"
	case "audio/wav":
		return ".wav"
	case "audio/ogg":
		return ".ogg"
	case "audio/flac":
		return ".flac"
	case "video/mp4":
		return ".mp4"
	case "video/webm":
		return ".webm"
	case "audio/webm":
		return ".webm"
	default:
		return ""
	}
}

// computeDestPath constructs the local file path from an enclosure URL and output directory.
// The filename is prefixed with YYYYMMDD - for chronological sorting when dates are available.
// A file extension is appended based on the enclosure's MIME type.
func computeDestPath(outputDir string, encInfo poller.EnclosureInfo) string {
	baseName := sanitizeFilename(encInfo.Title)
	if baseName == "" {
		// Fallback to enclosure URL basename if title is empty or invalid.
		parsed, err := url.Parse(encInfo.URL)
		if err != nil || parsed.Path == "" || parsed.Path == "/" {
			return filepath.Join(outputDir, strings.ReplaceAll(encInfo.URL, "/", "_"))
		}
		baseName = sanitizeFilename(filepath.Base(parsed.Path))
		if baseName == "." || baseName == "" {
			baseName = "unknown"
		}
	}

	// Append file extension from MIME type.
	if ext := extFromMimeType(encInfo.MimeType); ext != "" {
		baseName += ext
	}

	// Prepend date prefix for chronological sorting if available.
	if !encInfo.PublishedAt.IsZero() {
		datePrefix := encInfo.PublishedAt.Format("2006-01-02")
		return filepath.Join(outputDir, fmt.Sprintf("%s - %s", datePrefix, baseName))
	}

	return filepath.Join(outputDir, baseName)
}