package subsonic

import (
	"database/sql"
	"errors"
	"log/slog"
	"net/http"
	"os"
	"strconv"
	"strings"

	"github.com/mithral/vellum/internal/auth"
	"github.com/mithral/vellum/internal/progress"
	"github.com/mithral/vellum/internal/stream"
	"github.com/mithral/vellum/internal/subsonic/dto"
)

// ignoredArticles is advertised in getIndexes/getArtists. It is the list the
// Subsonic schema documents; the indexer strips a leading article so "The
// Beatles" files under B.
const ignoredArticles = "The El La Los Las Le Les"

// Handlers serves the Subsonic-compatible subset.
type Handlers struct {
	db  *sql.DB
	log *slog.Logger
	// auth is kept for parity with the other HTTP layers and for the cookie
	// credentials endpoint. Subsonic requests authenticate themselves from
	// query/form parameters, because the middleware only knows session cookies.
	auth *auth.Authenticator
}

// NewHandlers builds the Subsonic HTTP layer. It takes no cache directory:
// cover bytes are served from the assets table the scanner already populated,
// rather than triggering a fresh extraction.
func NewHandlers(db *sql.DB, log *slog.Logger, a *auth.Authenticator) *Handlers {
	return &Handlers{db: db, log: log, auth: a}
}

// Register mounts the routes. See the package comment for why /rest/ lives at
// the root and why it installs its own 404 rather than relying on the SPA
// fallback in internal/httpapi/static.go.
func (h *Handlers) Register(mux *http.ServeMux) {
	mux.HandleFunc("GET /rest/{method}", h.dispatch)
	mux.HandleFunc("POST /rest/{method}", h.dispatch)

	// Subtree fallback for /rest/ itself and multi-segment paths. Without it an
	// unknown /rest/... falls through to "/" and static.go's isAPIPath — which
	// does not recognise /rest/ — would serve the SPA shell as text/html.
	mux.HandleFunc("/rest/", h.handleUnknownRest)

	// Client configuration. This one IS cookie-authenticated: the user is in
	// the web UI, not a Subsonic client.
	mux.Handle("GET /api/v1/subsonic/credentials", h.auth.Require(h.handleCredentials))
}

func (h *Handlers) handleUnknownRest(w http.ResponseWriter, r *http.Request) {
	h.fail(w, r, dto.ErrGeneric, "unknown Subsonic method")
}

// dispatch authenticates and routes one /rest/<method>.view call. Every method
// shares the same credential scheme, so authentication happens once, here.
func (h *Handlers) dispatch(w http.ResponseWriter, r *http.Request) {
	method := strings.ToLower(strings.TrimSuffix(r.PathValue("method"), ".view"))

	u, ok := h.authenticate(r)
	if !ok {
		// The single most common integration failure: a bad credential must be
		// an envelope with code 40, not an HTTP 401. Clients read the envelope.
		h.fail(w, r, dto.ErrWrongCredentials, "Wrong username or password")
		return
	}

	switch method {
	case "ping":
		h.handlePing(w, r)
	case "getlicense":
		h.handleGetLicense(w, r)
	case "getmusicfolders":
		h.handleGetMusicFolders(w, r, u)
	case "getindexes":
		h.handleGetIndexes(w, r, u)
	case "getartists":
		h.handleGetArtists(w, r, u)
	case "getartist":
		h.handleGetArtist(w, r, u)
	case "getalbum":
		h.handleGetAlbum(w, r, u)
	case "getmusicdirectory":
		h.handleGetMusicDirectory(w, r, u)
	case "getsong":
		h.handleGetSong(w, r, u)
	case "search3":
		h.handleSearch3(w, r, u)
	case "stream":
		h.handleStream(w, r, u)
	case "getcoverart":
		h.handleGetCoverArt(w, r, u)
	case "getalbumlist2":
		h.handleGetAlbumList2(w, r, u)
	case "getrandomsongs":
		h.handleGetRandomSongs(w, r, u)
	case "scrobble":
		h.handleScrobble(w, r, u)
	case "getuser":
		h.handleGetUser(w, r, u)
	case "getplaylists":
		h.handleGetPlaylists(w, r)
	default:
		h.fail(w, r, dto.ErrGeneric, "unknown method: "+method)
	}
}

// ── system ─────────────────────────────────────────────────────────────

func (h *Handlers) handlePing(w http.ResponseWriter, r *http.Request) {
	h.write(w, r, envelope("ok"))
}

func (h *Handlers) handleGetLicense(w http.ResponseWriter, r *http.Request) {
	root := envelope("ok")
	// Vellum is not Subsonic and has no licence or trial. Clients only check
	// `valid`; a permanent valid licence is the honest answer.
	root.Add(dto.El("license", dto.At("valid", true)))
	h.write(w, r, root)
}

// ── browsing ───────────────────────────────────────────────────────────

func (h *Handlers) handleGetMusicFolders(w http.ResponseWriter, r *http.Request, u auth.User) {
	libs, err := h.audioLibraries(r.Context(), u)
	if err != nil {
		h.internal(w, r, "music folders", err)
		return
	}
	folders := dto.El("musicFolders").Arrays("musicFolder")
	for _, lib := range libs {
		folders.Add(dto.El("musicFolder", dto.At("id", lib.id), dto.At("name", lib.name)))
	}
	root := envelope("ok")
	root.Add(folders)
	h.write(w, r, root)
}

func (h *Handlers) handleGetIndexes(w http.ResponseWriter, r *http.Request, u auth.User) {
	artists, err := h.artists(r.Context(), u)
	if err != nil {
		h.internal(w, r, "indexes", err)
		return
	}
	indexes := dto.El("indexes", dto.At("ignoredArticles", ignoredArticles)).Arrays("index")
	addIndexes(indexes, artists, false)
	root := envelope("ok")
	root.Add(indexes)
	h.write(w, r, root)
}

func (h *Handlers) handleGetArtists(w http.ResponseWriter, r *http.Request, u auth.User) {
	artists, err := h.artists(r.Context(), u)
	if err != nil {
		h.internal(w, r, "artists", err)
		return
	}
	node := dto.El("artists", dto.At("ignoredArticles", ignoredArticles)).Arrays("index")
	addIndexes(node, artists, true)
	root := envelope("ok")
	root.Add(node)
	h.write(w, r, root)
}

func (h *Handlers) handleGetArtist(w http.ResponseWriter, r *http.Request, u auth.User) {
	personID, ok := dto.ParseID(r.FormValue("id"), dto.PrefixArtist)
	if !ok {
		// The synthetic "unknown artist" bucket uses ar-0.
		if r.FormValue("id") != dto.PrefixArtist+"0" {
			h.fail(w, r, dto.ErrDataNotFound, "artist not found")
			return
		}
		personID = 0
	}

	libs, err := h.audioLibraryIDs(r.Context(), u)
	if err != nil {
		h.internal(w, r, "artist", err)
		return
	}
	albums, err := h.albumsByArtist(r.Context(), libs, personID)
	if err != nil {
		h.internal(w, r, "artist albums", err)
		return
	}
	if len(albums) == 0 {
		h.fail(w, r, dto.ErrDataNotFound, "artist not found")
		return
	}

	name, _ := h.artistName(r.Context(), personID)
	artist := dto.El("artist",
		dto.At("id", dto.ArtistID(personID)),
		dto.At("name", name),
		dto.At("albumCount", int64(len(albums))),
	).Arrays("album")
	if cover := firstCover(albums); cover != 0 {
		artist.Attrs = append(artist.Attrs, dto.At("coverArt", dto.AlbumID(cover)))
	}
	for _, a := range albums {
		artist.Add(dto.AlbumNode(a))
	}
	root := envelope("ok")
	root.Add(artist)
	h.write(w, r, root)
}

func (h *Handlers) handleGetAlbum(w http.ResponseWriter, r *http.Request, u auth.User) {
	itemID, ok := dto.ParseID(r.FormValue("id"), dto.PrefixAlbum)
	if !ok {
		h.fail(w, r, dto.ErrDataNotFound, "album not found")
		return
	}
	a, ok, err := h.loadAlbum(r.Context(), u, itemID)
	if err != nil {
		h.internal(w, r, "album", err)
		return
	}
	if !ok {
		h.fail(w, r, dto.ErrDataNotFound, "album not found")
		return
	}
	tracks, err := h.tracksForItem(r.Context(), itemID)
	if err != nil {
		h.internal(w, r, "album songs", err)
		return
	}
	node := dto.AlbumNode(a).Arrays("song")
	for _, t := range tracks {
		node.Add(dto.SongNode(t))
	}
	root := envelope("ok")
	root.Add(node)
	h.write(w, r, root)
}

func (h *Handlers) handleGetSong(w http.ResponseWriter, r *http.Request, u auth.User) {
	fileIDVal, ok := dto.ParseID(r.FormValue("id"), dto.PrefixFile)
	if !ok {
		h.fail(w, r, dto.ErrDataNotFound, "song not found")
		return
	}
	t, ok, err := h.loadTrack(r.Context(), u, fileIDVal)
	if err != nil {
		h.internal(w, r, "song", err)
		return
	}
	if !ok {
		h.fail(w, r, dto.ErrDataNotFound, "song not found")
		return
	}
	root := envelope("ok")
	root.Add(dto.SongNode(t))
	h.write(w, r, root)
}

// handleGetMusicDirectory browses one level of the tree. Vellum does not store
// a parent_id for audio (the scanner groups by directory), so the hierarchy is
// derived from media_items.path: a directory id names a path prefix, and its
// children are the items whose parent directory is that prefix plus the next
// path segment of every deeper item.
func (h *Handlers) handleGetMusicDirectory(w http.ResponseWriter, r *http.Request, u auth.User) {
	id := r.FormValue("id")

	switch {
	case strings.HasPrefix(id, dto.PrefixFolder):
		libID, ok := dto.ParseID(id, dto.PrefixFolder)
		if !ok {
			h.fail(w, r, dto.ErrDataNotFound, "directory not found")
			return
		}
		h.directoryForLibrary(w, r, u, libID)
	case strings.HasPrefix(id, dto.PrefixDir):
		libID, rel, ok := dto.ParseDirID(id)
		if !ok {
			h.fail(w, r, dto.ErrDataNotFound, "directory not found")
			return
		}
		h.directoryForPath(w, r, u, libID, rel)
	case strings.HasPrefix(id, dto.PrefixAlbum):
		itemID, ok := dto.ParseID(id, dto.PrefixAlbum)
		if !ok {
			h.fail(w, r, dto.ErrDataNotFound, "directory not found")
			return
		}
		h.directoryForAlbum(w, r, u, itemID)
	case strings.HasPrefix(id, dto.PrefixArtist):
		personID, ok := dto.ParseID(id, dto.PrefixArtist)
		if !ok {
			h.fail(w, r, dto.ErrDataNotFound, "directory not found")
			return
		}
		h.directoryForArtist(w, r, u, personID)
	default:
		h.fail(w, r, dto.ErrDataNotFound, "directory not found")
	}
}

// ── search ─────────────────────────────────────────────────────────────

// handleSearch3 is the endpoint clients lean on hardest. It is answered with
// plain LIKE queries scoped to the caller's visible audio libraries rather than
// the FTS index, because the FTS index is over media_items (albums), while a
// Subsonic song is a media_files row and a Subsonic artist is a person. An
// empty query returns everything, which OpenSubsonic requires for offline sync.
func (h *Handlers) handleSearch3(w http.ResponseWriter, r *http.Request, u auth.User) {
	q := r.FormValue("query")
	artistCount, artistOffset := countOffset(r, "artistCount", "artistOffset")
	albumCount, albumOffset := countOffset(r, "albumCount", "albumOffset")
	songCount, songOffset := countOffset(r, "songCount", "songOffset")

	libs, err := h.audioLibraryIDs(r.Context(), u)
	if err != nil {
		h.internal(w, r, "search", err)
		return
	}

	artists, err := h.searchArtists(r.Context(), libs, q, artistCount, artistOffset)
	if err != nil {
		h.internal(w, r, "search artists", err)
		return
	}
	albums, err := h.searchAlbums(r.Context(), libs, q, albumCount, albumOffset)
	if err != nil {
		h.internal(w, r, "search albums", err)
		return
	}
	songs, err := h.searchSongs(r.Context(), libs, q, songCount, songOffset)
	if err != nil {
		h.internal(w, r, "search songs", err)
		return
	}

	result := dto.El("searchResult3").Arrays("artist", "album", "song")
	for _, a := range artists {
		artist := dto.El("artist", dto.At("id", dto.ArtistID(a.id)), dto.At("name", a.name), dto.At("albumCount", int64(a.albumCount)))
		if a.coverAlbum != 0 {
			artist.Attrs = append(artist.Attrs, dto.At("coverArt", dto.AlbumID(a.coverAlbum)))
		}
		result.Add(artist)
	}
	for _, a := range albums {
		result.Add(dto.AlbumNode(a))
	}
	for _, s := range songs {
		result.Add(dto.SongNode(s))
	}
	root := envelope("ok")
	root.Add(result)
	h.write(w, r, root)
}

// ── lists ──────────────────────────────────────────────────────────────

func (h *Handlers) handleGetAlbumList2(w http.ResponseWriter, r *http.Request, u auth.User) {
	kind := strings.ToLower(r.FormValue("type"))
	size := intParam(r, "size", 10, 500)
	offset := intParam(r, "offset", 0, 1_000_000)

	libs, err := h.audioLibraryIDs(r.Context(), u)
	if err != nil {
		h.internal(w, r, "album list", err)
		return
	}

	// Only newest and random are required; the alphabetical sorts are cheap and
	// are what a client pages through, so they are included. Types this server
	// cannot answer meaningfully (highest, frequent, starred, byGenre) fall back
	// to newest rather than returning an error, so a client is never stuck.
	order := "i.added_at DESC"
	where := ""
	var args []any
	switch kind {
	case "random":
		order = "RANDOM()"
	case "alphabeticalbyname":
		order = "i.sort_title"
	case "alphabeticalbyartist":
		order = "artist_name, i.sort_title"
	case "byyear":
		from := intParam(r, "fromYear", 0, 9999)
		to := intParam(r, "toYear", 0, 9999)
		where = " AND COALESCE(i.year,0) >= ? AND COALESCE(i.year,0) <= ?"
		args = append(args, from, to)
	default: // newest, recent, and every unsupported type
		order = "i.added_at DESC"
	}

	albums, err := h.albumsWhere(r.Context(), libs, where, args, order, size, offset)
	if err != nil {
		h.internal(w, r, "album list", err)
		return
	}

	list := dto.El("albumList2").Arrays("album")
	for _, a := range albums {
		list.Add(dto.AlbumNode(a))
	}
	root := envelope("ok")
	root.Add(list)
	h.write(w, r, root)
}

func (h *Handlers) handleGetRandomSongs(w http.ResponseWriter, r *http.Request, u auth.User) {
	size := intParam(r, "size", 10, 500)
	libs, err := h.audioLibraryIDs(r.Context(), u)
	if err != nil {
		h.internal(w, r, "random songs", err)
		return
	}
	songs, err := h.songsWhere(r.Context(), libs, "", nil, "RANDOM()", size, 0)
	if err != nil {
		h.internal(w, r, "random songs", err)
		return
	}
	node := dto.El("randomSongs").Arrays("song")
	for _, s := range songs {
		node.Add(dto.SongNode(s))
	}
	root := envelope("ok")
	root.Add(node)
	h.write(w, r, root)
}

// ── media ──────────────────────────────────────────────────────────────

// handleStream serves the original file. Vellum never transcodes: a request for
// any format other than raw (or none) is refused with a clear message rather
// than silently handing back the original under a different label. Range
// requests are handled by stream.ServeFile via http.ServeContent, so seeking
// works.
func (h *Handlers) handleStream(w http.ResponseWriter, r *http.Request, u auth.User) {
	format := strings.ToLower(strings.TrimSpace(r.FormValue("format")))
	if format != "" && format != "raw" {
		h.fail(w, r, dto.ErrGeneric, "transcoding is not supported by this server; request format=raw")
		return
	}
	// maxBitRate and estimateContentLength are accepted and honestly ignored:
	// there is no transcoder to apply either to. They are not rejected because
	// clients send them unconditionally.
	abs, ok, err := h.resolveAudioFile(r.Context(), u, r.FormValue("id"))
	if err != nil {
		h.internal(w, r, "stream", err)
		return
	}
	if !ok {
		h.fail(w, r, dto.ErrDataNotFound, "song not found")
		return
	}

	if err := stream.ServeFile(w, r, abs); err != nil {
		if errors.Is(err, os.ErrNotExist) {
			h.fail(w, r, dto.ErrDataNotFound, "file is not available")
			return
		}
		h.log.Error("subsonic: stream file", "err", err)
	}
}

func (h *Handlers) handleGetCoverArt(w http.ResponseWriter, r *http.Request, u auth.User) {
	itemID, ok, err := h.coverItemID(r.Context(), u, r.FormValue("id"))
	if err != nil {
		h.internal(w, r, "cover", err)
		return
	}
	if !ok {
		h.fail(w, r, dto.ErrDataNotFound, "cover art not found")
		return
	}

	var coverPath string
	err = h.db.QueryRowContext(r.Context(),
		`SELECT path FROM assets WHERE item_id = ? AND role = 'cover' LIMIT 1`, itemID).Scan(&coverPath)
	if errors.Is(err, sql.ErrNoRows) {
		h.fail(w, r, dto.ErrDataNotFound, "cover art not found")
		return
	}
	if err != nil {
		h.internal(w, r, "cover", err)
		return
	}
	if _, statErr := os.Stat(coverPath); statErr != nil {
		h.fail(w, r, dto.ErrDataNotFound, "cover art not available")
		return
	}
	w.Header().Set("Cache-Control", "public, max-age=86400")
	if err := stream.ServeFile(w, r, coverPath); err != nil {
		h.log.Error("subsonic: serve cover", "err", err)
	}
}

// ── playback reporting ─────────────────────────────────────────────────

// handleScrobble writes the client's playback position through the existing
// progress store. Subsonic's scrobble carries a wall-clock time rather than a
// position, but several clients additionally send `position` in milliseconds;
// when it is present it is honoured so the web app can resume where the client
// left off. A "now playing" notification (submission=false) records the start.
func (h *Handlers) handleScrobble(w http.ResponseWriter, r *http.Request, u auth.User) {
	ids := r.Form["id"]
	if len(ids) == 0 {
		h.fail(w, r, dto.ErrMissingParameter, "Required parameter is missing")
		return
	}
	submission := strings.ToLower(r.FormValue("submission")) != "false"

	for _, id := range ids {
		fileIDVal, ok := dto.ParseID(id, dto.PrefixFile)
		if !ok {
			continue
		}
		t, ok, err := h.loadTrack(r.Context(), u, fileIDVal)
		if err != nil {
			h.internal(w, r, "scrobble", err)
			return
		}
		if !ok {
			continue
		}

		position := int64(0)
		if v := r.FormValue("position"); v != "" {
			if n, err := strconv.ParseInt(v, 10, 64); err == nil && n >= 0 {
				position = n
			}
		}
		p := progress.Progress{
			ItemID:   t.ItemID,
			FileID:   t.FileID,
			Kind:     t.Kind,
			Position: position,
			Duration: t.DurationMS,
		}
		if t.DurationMS > 0 {
			p.Percent = float64(position) / float64(t.DurationMS)
		}
		if submission && t.DurationMS > 0 && position >= t.DurationMS {
			p.Finished = true
		}
		if _, err := progress.Put(r.Context(), h.db, u.ID, p); err != nil && !errors.Is(err, progress.ErrNoFile) {
			h.internal(w, r, "scrobble progress", err)
			return
		}
	}

	h.write(w, r, envelope("ok"))
}

// ── user ───────────────────────────────────────────────────────────────

func (h *Handlers) handleGetUser(w http.ResponseWriter, r *http.Request, u auth.User) {
	target := strings.TrimSpace(r.FormValue("username"))

	// The parameter is required by the spec; defaulting to the caller is the
	// behaviour clients expect when they omit it.
	if target != "" && !strings.EqualFold(target, u.Username) {
		if !u.IsAdmin {
			h.fail(w, r, dto.ErrNotAuthorized, "User is not authorized for the given operation")
			return
		}
		other, err := auth.GetUserByUsername(r.Context(), h.db, target)
		if errors.Is(err, sql.ErrNoRows) {
			h.fail(w, r, dto.ErrDataNotFound, "user not found")
			return
		}
		if err != nil {
			h.internal(w, r, "user", err)
			return
		}
		u = other
	}

	libIDs, err := auth.VisibleLibraryIDs(r.Context(), h.db, u)
	if err != nil {
		h.internal(w, r, "user folders", err)
		return
	}

	user := dto.El("user",
		dto.At("username", u.Username),
		dto.At("email", ""),
		dto.At("scrobblingEnabled", true),
		dto.At("adminRole", u.IsAdmin),
		dto.At("settingsRole", u.IsAdmin),
		dto.At("downloadRole", true),
		dto.At("uploadRole", false),
		dto.At("playlistRole", true),
		dto.At("coverArtRole", true),
		dto.At("commentRole", false),
		dto.At("podcastRole", false),
		dto.At("streamRole", true),
		dto.At("jukeboxRole", false),
		dto.At("shareRole", false),
		dto.At("videoConversionRole", false),
	).Arrays("folder")
	for _, id := range libIDs {
		user.Add(dto.El("folder", dto.At("id", id)))
	}
	root := envelope("ok")
	root.Add(user)
	h.write(w, r, root)
}

// handleGetPlaylists returns an empty list. Vellum has a collections table but
// no Subsonic playlist support yet; an empty <playlists/> is what keeps a
// client from erroring on login.
func (h *Handlers) handleGetPlaylists(w http.ResponseWriter, r *http.Request) {
	root := envelope("ok")
	root.Add(dto.El("playlists").Arrays("playlist"))
	h.write(w, r, root)
}

// ── helpers ────────────────────────────────────────────────────────────

func (h *Handlers) internal(w http.ResponseWriter, r *http.Request, what string, err error) {
	h.log.Error("subsonic: "+what, "err", err)
	h.fail(w, r, dto.ErrGeneric, "internal server error")
}