package web

import (
	"bytes"
	"context"
	"crypto/sha256"
	"database/sql"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"image"
	_ "image/gif"
	_ "image/jpeg"
	_ "image/png"
	"io"
	"net/http"
	"os"
	"path/filepath"
	"sort"
	"sync"
	"time"

	"git.noroutes.net/NoRoutes/vibetunes/internal/artistphoto"
	"git.noroutes.net/NoRoutes/vibetunes/internal/database"
	"git.noroutes.net/NoRoutes/vibetunes/internal/netguard"
)

// maxArtistPhotoBytes bounds a single downloaded artist photo, the same
// way internal/podcasts bounds enclosure downloads.
const maxArtistPhotoBytes = 8 << 20

// artistPhotoCacheTTL mirrors internal/subsonic's enrichmentCacheTTL:
// artist photos change essentially never, so a long TTL avoids
// repeatedly hitting fanart.tv/Wikidata for the same artist.
const artistPhotoCacheTTL = 30 * 24 * time.Hour

var artistPhotoClient = &artistphoto.Client{}

func (h *Web) artistPhotoDir() string {
	return filepath.Join(h.Config.DataDir, "artist-photos")
}

// maybeFetchArtistPhoto kicks off a best-effort background fetch of an
// artist's photo the first time their page is viewed. It never blocks
// the caller and is a no-op unless artist photos are enabled and no
// photo (auto-fetched or manually set) is already on file — every
// artist is attempted regardless of whether it has a tagged
// MusicBrainz ID, since artistphoto.Client can resolve a photo by name
// alone via Wikidata.
func (h *Web) maybeFetchArtistPhoto(artist *database.Artist) {
	if !h.Config.EnableArtistPhotos || artist.CoverArtID.Valid || artist.PhotoManual {
		return
	}
	go h.fetchAndStoreArtistPhoto(artist)
}

func (h *Web) fetchAndStoreArtistPhoto(artist *database.Artist) {
	ctx, cancel := context.WithTimeout(context.Background(), 120*time.Second)
	defer cancel()
	if status, err := h.fetchAndStoreArtistPhotoResult(ctx, artist, false); err != nil {
		h.Log.Warn("artist photo fetch failed", "artist_id", artist.ID, "status", status, "error", err)
	}
}

// artistPhotoCacheKey is what a lookup result is cached/looked-up under:
// the artist's MusicBrainz ID when tagged, or else a name-derived key
// (real MBIDs are UUIDs, so this can never collide with one) — an
// artist resolved by name still benefits from the same negative/
// positive caching as a tagged one.
func artistPhotoCacheKey(artist *database.Artist) string {
	if artist.MusicBrainzID != "" {
		return artist.MusicBrainzID
	}
	return "name:" + artist.Name
}

// resolveArtistPhotoURL resolves a photo URL for artist, using the
// cached result unless bypassCache is set (the manual "refresh all"
// admin action bypasses it, so a previous failed/empty lookup doesn't
// hide a photo that might exist now).
func (h *Web) resolveArtistPhotoURL(ctx context.Context, artist *database.Artist, bypassCache bool) (string, error) {
	cacheKey := artistPhotoCacheKey(artist)
	if !bypassCache {
		if cached, ok := readArtistPhotoCache(h.DB, cacheKey); ok {
			return cached, nil
		}
	}
	u, err := artistPhotoClient.FetchPhotoURL(ctx, artist.MusicBrainzID, artist.Name, h.Config.FanartTVAPIKey)
	if err != nil {
		return "", err
	}
	if raw, err := json.Marshal(struct {
		URL string `json:"url"`
	}{u}); err == nil {
		_ = database.PutCachedExternalMetadata(h.DB, "artist_photo", cacheKey, "combined", string(raw))
	}
	return u, nil
}

// fetchAndStoreArtistPhotoResult resolves and stores a photo for one
// artist, returning a short human-readable status plus the underlying
// error (if any) so callers that report to a person (RefreshAllArtistPhotos)
// can show exactly what went wrong, not just log-and-forget.
func (h *Web) fetchAndStoreArtistPhotoResult(ctx context.Context, artist *database.Artist, bypassCache bool) (status string, err error) {
	photoURL, err := h.resolveArtistPhotoURL(ctx, artist, bypassCache)
	if err != nil {
		return "lookup failed", err
	}
	if photoURL == "" {
		return "no photo found", nil
	}

	localPath, contentHash, mimeType, err := h.downloadImage(ctx, photoURL)
	if err != nil {
		return "download failed", err
	}
	if _, err := database.UpsertArtistCoverArt(h.DB, artist.ID, "external", localPath, mimeType, contentHash, 0, 0, false); err != nil {
		return "store failed", err
	}
	return "fetched", nil
}

// ArtistPhotoOutcome is the per-artist result of a bulk photo refresh
// (see RefreshAllArtistPhotos), surfaced to an admin so failures are
// visible instead of just falling back to the default placeholder with
// no explanation.
type ArtistPhotoOutcome struct {
	ArtistID   string
	ArtistName string
	Status     string
	Error      string
}

// RefreshAllArtistPhotos attempts to (re-)fetch a photo for every
// artist with no manual photo override, bypassing the cached "nothing
// found" result so a previous failure doesn't silently persist
// forever. A small worker pool keeps a large library from serializing
// one slow network call after another.
func (h *Web) RefreshAllArtistPhotos(ctx context.Context) ([]ArtistPhotoOutcome, error) {
	artists, err := database.ListArtists(h.DB)
	if err != nil {
		return nil, err
	}

	results := make([]ArtistPhotoOutcome, len(artists))
	type job struct {
		idx    int
		artist *database.Artist
	}
	jobs := make(chan job)

	const workers = 4
	var wg sync.WaitGroup
	for i := 0; i < workers; i++ {
		wg.Add(1)
		go func() {
			defer wg.Done()
			for j := range jobs {
				results[j.idx] = h.refreshOneArtistPhoto(ctx, j.artist)
			}
		}()
	}
	for i, a := range artists {
		jobs <- job{i, a}
	}
	close(jobs)
	wg.Wait()

	sort.Slice(results, func(i, k int) bool { return results[i].ArtistName < results[k].ArtistName })
	return results, nil
}

func (h *Web) refreshOneArtistPhoto(ctx context.Context, artist *database.Artist) ArtistPhotoOutcome {
	out := ArtistPhotoOutcome{ArtistID: artist.ID, ArtistName: artist.Name}
	if artist.PhotoManual {
		out.Status = "skipped (manual photo set)"
		return out
	}

	fetchCtx, cancel := context.WithTimeout(ctx, 120*time.Second)
	defer cancel()
	status, err := h.fetchAndStoreArtistPhotoResult(fetchCtx, artist, true)
	out.Status = status
	if err != nil {
		out.Error = err.Error()
	}
	return out
}

func readArtistPhotoCache(db *sql.DB, cacheKey string) (string, bool) {
	dataJSON, fetchedAt, found, err := database.GetCachedExternalMetadata(db, "artist_photo", cacheKey, "combined")
	if err != nil || !found || time.Since(fetchedAt) > artistPhotoCacheTTL {
		return "", false
	}
	var payload struct {
		URL string `json:"url"`
	}
	if err := json.Unmarshal([]byte(dataJSON), &payload); err != nil {
		return "", false
	}
	return payload.URL, true
}

// downloadImage fetches sourceURL through an SSRF-safe client
// (internal/netguard, the same protection used for podcast feeds and
// enclosures) and hands the body to storeImageBytes. Used both for
// auto-fetched artist photos and admin-supplied photo/cover URLs.
func (h *Web) downloadImage(ctx context.Context, sourceURL string) (localPath, contentHash, mimeType string, err error) {
	if err := netguard.ValidateURL(sourceURL); err != nil {
		return "", "", "", err
	}
	client := netguard.NewSafeHTTPClient(15*time.Second, false)
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, sourceURL, nil)
	if err != nil {
		return "", "", "", err
	}
	req.Header.Set("User-Agent", "VibeSonic/1.0 (+https://git.noroutes.net/NoRoutes/vibetunes)")
	resp, err := client.Do(req)
	if err != nil {
		return "", "", "", err
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		return "", "", "", fmt.Errorf("artist photo download: HTTP %d", resp.StatusCode)
	}

	body, err := io.ReadAll(io.LimitReader(resp.Body, maxArtistPhotoBytes+1))
	if err != nil {
		return "", "", "", err
	}
	if len(body) > maxArtistPhotoBytes {
		return "", "", "", fmt.Errorf("artist photo exceeds maximum allowed size of %d bytes", maxArtistPhotoBytes)
	}
	return h.storeImageBytes(body)
}

// storeImageBytes validates that body actually decodes as an image,
// then saves it under the artist-photos cache directory keyed by its
// content hash (so re-fetching or re-uploading the same bytes reuses
// the same file). Used both for artist photos and album cover
// overrides — the directory name is a historical artifact, not a
// restriction on what's stored there.
func (h *Web) storeImageBytes(body []byte) (localPath, contentHash, mimeType string, err error) {
	if _, _, err := image.Decode(bytes.NewReader(body)); err != nil {
		return "", "", "", fmt.Errorf("not a valid image: %w", err)
	}
	mimeType = http.DetectContentType(body)
	sum := sha256.Sum256(body)
	contentHash = hex.EncodeToString(sum[:])[:16]

	dir := h.artistPhotoDir()
	if err := os.MkdirAll(dir, 0o755); err != nil {
		return "", "", "", err
	}
	localPath = filepath.Join(dir, contentHash+extensionForMIME(mimeType))
	if _, err := os.Stat(localPath); err == nil {
		return localPath, contentHash, mimeType, nil
	}
	tmp := localPath + ".tmp"
	if err := os.WriteFile(tmp, body, 0o644); err != nil {
		return "", "", "", err
	}
	if err := os.Rename(tmp, localPath); err != nil {
		return "", "", "", err
	}
	return localPath, contentHash, mimeType, nil
}

func extensionForMIME(mimeType string) string {
	switch mimeType {
	case "image/png":
		return ".png"
	case "image/gif":
		return ".gif"
	default:
		return ".jpg"
	}
}