unarr/internal/library/prewarm.go

package library

import (
	"context"
	"log"
	"math"
	"sync"
	"time"

	"github.com/torrentclaw/unarr/internal/library/mediainfo"
)

// Thumbnail sampling — kept in lockstep with the web's src/lib/stream/thumbnails.ts
// (THUMB_FRACTIONS / THUMB_FALLBACK_SECS / THUMB_WIDTH) so the frames the scan
// pre-extracts are the exact ones the "file characteristics" panel requests.
var (
	thumbFractions   = []float64{0.1, 0.3, 0.5, 0.7, 0.9}
	thumbFallbackSec = []float64{30, 120, 300, 600, 1200}
)

const thumbWidth = 320

// PrewarmOptions controls scan-time sidecar extraction.
type PrewarmOptions struct {
	FFmpegPath      string // resolved ffmpeg binary; empty disables prewarm
	CacheSubtitles  bool   // library.cache_subtitles
	CacheThumbnails bool   // library.cache_thumbnails
	Workers         int    // concurrent ffmpeg jobs (each is heavy); default 2
}

// prewarmJob is one extraction unit: all text subtitles of a file in one ffmpeg
// pass (thumb=false) or a single thumbnail frame (thumb=true).
type prewarmJob struct {
	path   string
	thumb  bool
	subIdx []int   // subtitle stream indices to extract in ONE pass (subtitle job)
	posSec float64 // frame position in seconds (thumbnail job)
	width  int     // frame width (thumbnail job)
}

// PrewarmSidecars extracts text subtitles (→ WebVTT) and the panel's sample
// thumbnail frames (→ JPEG) for every scanned item into the hidden ".unarr"
// sidecar dir next to the media file, so the /sub and /thumbnail handlers serve
// them instantly. Subtitle extraction without the per-request HTTP timeout is
// what makes huge remuxes work.
//
// Best-effort and idempotent: fresh sidecars are skipped, errors are logged and
// the item moves on, and ctx cancellation (Ctrl-C / daemon shutdown) stops
// cleanly. Safe to call after every scan — only missing/stale caches do work.
func PrewarmSidecars(ctx context.Context, cache *LibraryCache, opts PrewarmOptions) {
	if cache == nil || opts.FFmpegPath == "" || (!opts.CacheSubtitles && !opts.CacheThumbnails) {
		return
	}
	workers := opts.Workers
	if workers < 1 {
		workers = 2
	}

	jobs := make(chan prewarmJob)
	var wg sync.WaitGroup
	var mu sync.Mutex
	subCached, thumbCached, failed := 0, 0, 0
	var sampleErr string // first extraction error, surfaced in the summary so a
	// systemic ffmpeg failure (vs one corrupt file) is diagnosable from "N failed".

	for i := 0; i < workers; i++ {
		wg.Add(1)
		go func() {
			defer wg.Done()
			for j := range jobs {
				if ctx.Err() != nil {
					return
				}
				if j.thumb {
					if _, ok := mediainfo.ReadCachedThumbnail(j.path, j.posSec, j.width); ok {
						continue
					}
					// A single keyframe decode is fast; 60s bounds a corrupt file.
					jctx, cancel := context.WithTimeout(ctx, 60*time.Second)
					img, err := mediainfo.ExtractThumbnailJPEG(jctx, opts.FFmpegPath, j.path, j.posSec, j.width)
					cancel()
					if err != nil { // seek past EOF / corrupt → skip
						mu.Lock()
						failed++
						if sampleErr == "" {
							sampleErr = err.Error()
						}
						mu.Unlock()
						continue
					}
					if werr := mediainfo.WriteCachedThumbnail(j.path, j.posSec, j.width, img); werr != nil {
						log.Printf("[prewarm] thumbnail write skipped (pos=%.0f path=%q): %v", j.posSec, j.path, werr)
						mu.Lock()
						failed++
						mu.Unlock()
						continue
					}
					mu.Lock()
					thumbCached++
					mu.Unlock()
					continue
				}

				// Extract only the indices not already fresh, and do them in ONE
				// ffmpeg pass — a multi-GB remux is demuxed once for all its text
				// tracks instead of once per track.
				todo := make([]int, 0, len(j.subIdx))
				for _, idx := range j.subIdx {
					if _, ok := mediainfo.ReadCachedSubtitle(j.path, idx); !ok {
						todo = append(todo, idx)
					}
				}
				if len(todo) == 0 {
					continue
				}
				// Generous per-file deadline. Subtitle packets are interleaved across
				// the whole container, so extraction is I/O-bound: it must read the
				// entire file once (all text tracks share that single pass). A 60GB
				// remux over ~75 MB/s NFS is ~14 min, so 45 min covers files up to
				// ~200GB; bounded so one corrupt/stalled file can't wedge a worker.
				// This is background + idempotent — it only runs until the cache fills.
				jctx, cancel := context.WithTimeout(ctx, 45*time.Minute)
				res, err := mediainfo.ExtractSubtitlesVTTMulti(jctx, opts.FFmpegPath, j.path, todo)
				cancel()
				if err != nil {
					mu.Lock()
					failed += len(todo)
					if sampleErr == "" {
						sampleErr = err.Error()
					}
					mu.Unlock()
					continue
				}
				for idx, vtt := range res {
					if werr := mediainfo.WriteCachedSubtitle(j.path, idx, vtt); werr != nil {
						log.Printf("[prewarm] sidecar write skipped (i=%d path=%q): %v", idx, j.path, werr)
						mu.Lock()
						failed++
						mu.Unlock()
						continue
					}
					mu.Lock()
					subCached++
					mu.Unlock()
				}
			}
		}()
	}

	go func() {
		defer close(jobs)
		for _, item := range cache.Items {
			if item.MediaInfo == nil || item.FilePath == "" {
				continue
			}
			if opts.CacheSubtitles {
				var subIdx []int
				for idx, sub := range item.MediaInfo.Subtitles {
					if mediainfo.IsTextSubtitleCodec(sub.Codec) {
						subIdx = append(subIdx, idx) // bitmap → burned in, skipped
					}
				}
				if len(subIdx) > 0 {
					select {
					case jobs <- prewarmJob{path: item.FilePath, subIdx: subIdx}:
					case <-ctx.Done():
						return
					}
				}
			}
			if opts.CacheThumbnails {
				for _, pos := range thumbPositions(item) {
					select {
					case jobs <- prewarmJob{path: item.FilePath, thumb: true, posSec: pos, width: thumbWidth}:
					case <-ctx.Done():
						return
					}
				}
			}
		}
	}()

	wg.Wait()
	if subCached > 0 || thumbCached > 0 || failed > 0 {
		if failed > 0 && sampleErr != "" {
			log.Printf("[prewarm] %d subtitles, %d thumbnails cached, %d failed (e.g. %s)", subCached, thumbCached, failed, sampleErr)
		} else {
			log.Printf("[prewarm] %d subtitles, %d thumbnails cached, %d failed", subCached, thumbCached, failed)
		}
	}
}

// thumbPositions returns the sample frame offsets (whole seconds) for an item,
// matching the web panel: fractions of a known runtime, else fixed fallbacks.
func thumbPositions(item LibraryItem) []float64 {
	var dur float64
	if item.MediaInfo != nil && item.MediaInfo.Video != nil {
		dur = item.MediaInfo.Video.Duration
	}
	src := thumbFallbackSec
	if dur > 0 {
		src = make([]float64, len(thumbFractions))
		for i, f := range thumbFractions {
			src[i] = math.Round(dur * f)
		}
	}
	// Dedup (short clips can round multiple fractions to the same second).
	seen := make(map[float64]struct{}, len(src))
	out := make([]float64, 0, len(src))
	for _, p := range src {
		if _, ok := seen[p]; ok {
			continue
		}
		seen[p] = struct{}{}
		out = append(out, p)
	}
	return out
}