package proxy

import (
	"context"
	"encoding/json"
	"fmt"
	"io"
	"log/slog"
	"net"
	"net/http"
	"strconv"
	"strings"
	"time"

	"github.com/go-chi/chi/v5"
	"github.com/go-chi/cors"

	"github.com/Silo-Server/silo-server/internal/httpstream"
	"github.com/Silo-Server/silo-server/internal/nodeconfig"
	"github.com/Silo-Server/silo-server/internal/nodesessions"
	"github.com/Silo-Server/silo-server/internal/playback"
	"github.com/Silo-Server/silo-server/internal/streamtoken"
)

// revocationStore is the subset of *streamrevoke.Store the edge consults to
// enforce kills. IsRevoked is a pure in-memory lookup (no I/O) so it is safe on
// the per-request hot path. Nil disables enforcement.
type revocationStore interface {
	IsRevoked(sessionID string, userID int, startedAt time.Time) bool
	Refuse(w http.ResponseWriter, sessionID string, userID int, startedAt time.Time) bool
	WatchAndCutContext(ctx context.Context, w http.ResponseWriter, sessionID string, userID int, startedAt time.Time) func()
}

// Server is the HTTP handler for proxy mode.
type Server struct {
	watcher    *nodeconfig.Watcher
	tracker    *nodesessions.Tracker
	httpClient *http.Client
	egress     *egressMeter
	// subCache stores full-track PGS (.sup) extracts under the transcode dir
	// so repeat selections skip the whole-file ffmpeg demux.
	subCache *playback.SubtitleCache

	revocation revocationStore
}

// SetRevocationStore wires the kill-switch the edge consults per request. The
// store's cache is kept current out-of-band (pub/sub + poll), so the hot-path
// check is a local map read.
func (s *Server) SetRevocationStore(store revocationStore) {
	s.revocation = store
}

// NewServer creates a new proxy server backed by a config watcher and session
// tracker.
func NewServer(watcher *nodeconfig.Watcher, tracker *nodesessions.Tracker) *Server {
	return &Server{
		watcher: watcher,
		tracker: tracker,
		// No overall timeout — stream bodies are long-lived. Hung nodes are
		// bounded by the transport's response-header timeout instead.
		httpClient: &http.Client{Transport: newStreamTransport()},
		egress:     newEgressMeter(),
		subCache: playback.NewSubtitleCache(func() string {
			return watcher.Config().Playback.TranscodeDir
		}),
	}
}

// newStreamTransport tunes the proxy→transcode-node connection pool. Many
// concurrent viewers fan their segment fetches through one proxy→node pair,
// and Go's default of 2 idle connections per host causes constant connection
// churn (and TLS re-handshakes) under load. The response-header timeout
// bounds requests to a hung node; the longest legitimate server-side wait is
// the 30s manifest-readiness poll on the transcode node.
func newStreamTransport() *http.Transport {
	t := http.DefaultTransport.(*http.Transport).Clone()
	t.MaxIdleConns = 128
	t.MaxIdleConnsPerHost = 32
	t.ResponseHeaderTimeout = 60 * time.Second
	return t
}

// Handler returns the chi.Router with all proxy routes mounted.
func (s *Server) Handler() http.Handler {
	r := chi.NewRouter()
	// hls.js uses XHR for manifest/segment fetches which are subject to
	// CORS when the proxy runs on a different origin than the web app.
	r.Use(cors.Handler(cors.Options{
		AllowedOrigins: []string{"*"},
		AllowedMethods: []string{"GET", "HEAD", "OPTIONS"},
		AllowedHeaders: []string{"Accept", "Authorization", "Content-Type", "Range"},
		MaxAge:         86400,
	}))
	r.Get("/api/v1/health", s.handleHealth)
	r.Group(func(r chi.Router) {
		// Everything under /stream counts toward the node's measured
		// egress bandwidth.
		r.Use(s.meterEgress)
		r.Head("/stream/direct/{token}", s.handleDirectPlay)
		r.Get("/stream/direct/{token}", s.handleDirectPlay)
		r.Head("/stream/remux/{token}", s.handleRemux)
		r.Get("/stream/remux/{token}", s.handleRemux)
		r.Head("/stream/transcode/{token}/master.m3u8", s.handleTranscodeManifest)
		r.Get("/stream/transcode/{token}/master.m3u8", s.handleTranscodeManifest)
		r.Get("/stream/transcode/{token}/segment/{name}", s.handleTranscodeSegment)
		r.Get("/stream/subtitles/{token}/{track}/fonts", s.handleSubtitleFonts)
		r.Get("/stream/subtitles/{token}/{track}", s.handleSubtitle)
	})

	// Admin routes — bearer-auth protected.
	r.Group(func(r chi.Router) {
		r.Use(s.requireBearer)
		r.Post("/admin/force-reload", s.handleForceReload)
		r.Get("/status", s.handleStatus)
	})
	return r
}

type healthResponse struct {
	Status     string `json:"status"`
	ActiveJobs int    `json:"active_jobs"`
	EgressKbps int    `json:"egress_kbps"`
}

func (s *Server) handleHealth(w http.ResponseWriter, _ *http.Request) {
	activeJobs := 0
	if s.tracker != nil {
		activeJobs = s.tracker.ActiveCount()
	}
	w.Header().Set("Content-Type", "application/json")
	json.NewEncoder(w).Encode(healthResponse{
		Status:     "ok",
		ActiveJobs: activeJobs,
		EgressKbps: s.egress.RateKbps(),
	})
}

// requireBearer checks Authorization: Bearer {secret} for admin endpoints.
func (s *Server) requireBearer(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		cfg := s.watcher.Config()
		auth := r.Header.Get("Authorization")
		if !strings.HasPrefix(auth, "Bearer ") || strings.TrimPrefix(auth, "Bearer ") != cfg.Auth.JWTSecret {
			http.Error(w, "unauthorized", http.StatusUnauthorized)
			return
		}
		next.ServeHTTP(w, r)
	})
}

// verifyToken extracts and validates the stream token from the URL.
func (s *Server) verifyToken(w http.ResponseWriter, r *http.Request) *streamtoken.Claims {
	cfg := s.watcher.Config()
	tokenStr := chi.URLParam(r, "token")
	claims, err := streamtoken.Verify(tokenStr, cfg.Auth.JWTSecret)
	if err != nil {
		http.Error(w, "unauthorized", http.StatusUnauthorized)
		return nil
	}
	// Kill switch: a revoked session/user is refused here, on every request. For
	// chunked (HLS) playback this stops the stream on its next segment fetch and
	// refuses reconnects; long direct-play/remux pours are additionally cut mid-
	// stream by cutOnRevocation.
	// The token's iat is the credential-issue time the user-kill cutoff compares
	// against: edge requests carry no fresh auth, only this token, so a user
	// revocation kills exactly the tokens minted before it.
	if s.revocation != nil && s.revocation.Refuse(w, claims.SessionID, claims.UserID, claims.IssuedTime()) {
		return nil
	}
	return claims
}

// cutOnRevocation watches a long-lived pour (direct play / remux) and hangs up
// the socket the moment the session/user is revoked, via the shared store helper.
// Returns a stop func to cancel the watcher when the request finishes normally.
func (s *Server) cutOnRevocation(ctx context.Context, w http.ResponseWriter, claims *streamtoken.Claims) func() {
	if s.revocation == nil {
		return func() {}
	}
	return s.revocation.WatchAndCutContext(ctx, w, claims.SessionID, claims.UserID, claims.IssuedTime())
}

// releaseTracked releases one request lease with a bounded background context. The
// request context is already canceled by the time this defer runs on a client
// disconnect, which would skip the Redis DEL and leave a phantom session until
// TTL — a false over-cap window.
func (s *Server) releaseTracked(lease nodesessions.Lease) {
	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
	defer cancel()
	s.tracker.Release(ctx, lease)
}

func (s *Server) handleDirectPlay(w http.ResponseWriter, r *http.Request) {
	r = r.WithContext(httpstream.WithCutLatch(r.Context(), &httpstream.CutLatch{}))
	claims := s.verifyToken(w, r)
	if claims == nil {
		return
	}

	info := sessionInfo(s.tracker, claims, "direct_play", edgeClientIP(r))
	lease := s.tracker.Track(r.Context(), info)
	defer s.releaseTracked(lease)

	sw := &sessionByteWriter{ResponseWriter: w, tracker: s.tracker, sessionID: claims.SessionID}
	defer sw.flush()

	stop := s.cutOnRevocation(r.Context(), sw, claims)
	defer stop()

	http.ServeFile(sw, r, claims.MediaPath)
}

// sessionByteWriter attributes served bytes to a session so LastServedAt advances
// during long direct-play/remux pours (authoritative liveness). Bytes are
// flushed to the tracker in coarse chunks to avoid per-write lock churn. Unwrap
// lets the revocation connection-cut reach the socket through this layer.
type sessionByteWriter struct {
	http.ResponseWriter
	tracker   *nodesessions.Tracker
	sessionID string
	acc       int64
}

func (w *sessionByteWriter) Write(b []byte) (int, error) {
	n, err := w.ResponseWriter.Write(b)
	w.account(int64(n))
	return n, err
}

// account tallies served bytes, flushing to the tracker in coarse ~1 MiB chunks
// to avoid per-write lock churn. Shared by Write and the ReadFrom fast path.
func (w *sessionByteWriter) account(n int64) {
	if n <= 0 {
		return
	}
	w.acc += n
	if w.acc >= 1<<20 { // flush every ~1 MiB
		w.tracker.AddBytes(w.sessionID, w.acc)
		w.acc = 0
	}
}

// ReadFrom preserves the underlying writer's sendfile fast path while still
// attributing served bytes. http.ServeFile pours an *os.File through the
// ResponseWriter's io.ReaderFrom (sendfile: disk->socket inside the kernel, no
// userspace copy) — but only if it can see that method. Wrapping the writer for
// byte counting would hide it and force every direct-play/remux byte through
// userspace; forwarding here keeps zero-copy AND the count. Liveness does not
// depend on this coarse count: the session stays live from Track to Remove
// (tracker re-SETs it, never idle-prunes an open pour), so a single sendfile
// call that only tallies on return still stays visible for the whole pour.
func (w *sessionByteWriter) ReadFrom(src io.Reader) (int64, error) {
	if rf, ok := w.ResponseWriter.(io.ReaderFrom); ok {
		n, err := rf.ReadFrom(src)
		w.account(n)
		return n, err
	}
	// No sendfile fast path underneath. Copy manually — but NOT via io.Copy(w,
	// src), which would re-detect this very ReadFrom and recurse forever.
	// writeOnly exposes only Write, so io.Copy falls back to the Write loop
	// (which accounts bytes).
	return io.Copy(writeOnly{w}, src)
}

// writeOnly wraps an io.Writer to expose ONLY Write, hiding any ReadFrom so
// io.Copy cannot re-enter sessionByteWriter.ReadFrom.
type writeOnly struct{ io.Writer }

func (w *sessionByteWriter) flush() {
	if w.acc > 0 {
		w.tracker.AddBytes(w.sessionID, w.acc)
		w.acc = 0
	}
}

func (w *sessionByteWriter) Flush() {
	if f, ok := w.ResponseWriter.(http.Flusher); ok {
		f.Flush()
	}
}

func (w *sessionByteWriter) Unwrap() http.ResponseWriter {
	return w.ResponseWriter
}

func (s *Server) handleRemux(w http.ResponseWriter, r *http.Request) {
	r = r.WithContext(httpstream.WithCutLatch(r.Context(), &httpstream.CutLatch{}))
	claims := s.verifyToken(w, r)
	if claims == nil {
		return
	}

	info := sessionInfo(s.tracker, claims, "remux", edgeClientIP(r))
	lease := s.tracker.Track(r.Context(), info)
	defer s.releaseTracked(lease)

	sw := &sessionByteWriter{ResponseWriter: w, tracker: s.tracker, sessionID: claims.SessionID}
	defer sw.flush()

	stop := s.cutOnRevocation(r.Context(), sw, claims)
	defer stop()

	seekSeconds := 0.0
	if seekStr := r.URL.Query().Get("seek"); seekStr != "" {
		if v, err := strconv.ParseFloat(seekStr, 64); err == nil {
			seekSeconds = v
		}
	}
	// Honor the Dolby Vision mode frozen in the token (empty decodes as the
	// legacy auto behavior for old tokens), mirroring how the integrated
	// server's stream handler serves the same claims. Serve through sw so the
	// bytes are metered and the revocation cut can reach this response.
	_ = playback.ServeRemuxWithDVMode(sw, r, claims.MediaPath, "mp4", seekSeconds, claims.TranscodeAudio, claims.AudioTrackIndex, claims.DVProfile, playback.RemuxDVMode(claims.RemuxDVMode), s.watcher.Config().Playback.FFmpegPath)
}

func (s *Server) handleTranscodeManifest(w http.ResponseWriter, r *http.Request) {
	claims := s.verifyToken(w, r)
	if claims == nil {
		return
	}
	s.ensureTranscodeSession(r, claims)
	s.proxyToTranscodeNode(w, r, claims, "/transcode/"+transcodeTransportIDFromClaims(claims)+"/master.m3u8")
}

func (s *Server) handleTranscodeSegment(w http.ResponseWriter, r *http.Request) {
	claims := s.verifyToken(w, r)
	if claims == nil {
		return
	}
	s.ensureTranscodeSession(r, claims)
	name := chi.URLParam(r, "name")
	s.proxyToTranscodeNode(w, r, claims, "/transcode/"+transcodeTransportIDFromClaims(claims)+"/segment/"+name)
}

func transcodeTransportIDFromClaims(claims *streamtoken.Claims) string {
	if claims != nil && claims.TranscodeTransportID != "" {
		return claims.TranscodeTransportID
	}
	if claims == nil {
		return ""
	}
	return claims.SessionID
}

// ensureTranscodeSession keeps HLS sessions visible in the active stream count.
// Unlike direct play and remux, transcode playback reaches the proxy as many
// short manifest/segment requests, so the session is tracked by recent
// requests instead of request lifetime. Visibility is separate from served
// liveness: only a successful upstream media response advances LastServedAt.
func (s *Server) ensureTranscodeSession(r *http.Request, claims *streamtoken.Claims) {
	s.tracker.EnsureEphemeral(r.Context(), sessionInfo(s.tracker, claims, "transcode", edgeClientIP(r)))
}

// sessionInfo builds the node-session tracker record for a verified token,
// copying the numeric ownership keys plus the monitoring attribution (route +
// client identity) the first-class monitor view needs. clientIP is the connecting
// address observed at the edge (best-effort; the client reaches the proxy
// directly). Route/ClientName come from the token so the edge — which never sees
// the originating API path — can still tag native vs jellycompat.
func sessionInfo(tr *nodesessions.Tracker, claims *streamtoken.Claims, kind, clientIP string) nodesessions.SessionInfo {
	return nodesessions.SessionInfo{
		SessionID:   claims.SessionID,
		NodeURL:     tr.NodeURL(),
		NodeName:    tr.NodeName(),
		Type:        kind,
		Route:       claims.Origin,
		ClientIP:    clientIP,
		ClientName:  claims.ClientName,
		StartedAt:   time.Now().UTC().Format(time.RFC3339),
		AuthUserID:  claims.UserID,
		ProfileID:   claims.ProfileID,
		MediaFileID: claims.MediaFileID,
	}
}

// edgeClientIP extracts the connecting client's IP from the request, best-effort.
func edgeClientIP(r *http.Request) string {
	host, _, err := net.SplitHostPort(r.RemoteAddr)
	if err != nil {
		return r.RemoteAddr
	}
	return host
}

func (s *Server) handleSubtitle(w http.ResponseWriter, r *http.Request) {
	r = r.WithContext(httpstream.WithCutLatch(r.Context(), &httpstream.CutLatch{}))
	claims := s.verifyToken(w, r)
	if claims == nil {
		return
	}
	// Attribute subtitle bytes only when the session already has a tracker
	// record. Do not take lifecycle ownership here: Track/Remove per subtitle
	// request can delete a concurrently active media request until Batch 2 adds
	// reference-counted edge tracking.
	metered := &sessionByteWriter{ResponseWriter: w, tracker: s.tracker, sessionID: claims.SessionID}
	defer metered.flush()
	stop := s.cutOnRevocation(r.Context(), metered, claims)
	defer stop()
	w = metered

	cfg := s.watcher.Config()
	trackParam := chi.URLParam(r, "track")
	trackIndex, requestedFormat, err := playback.ParseSubtitleTrackParam(trackParam)
	if err != nil {
		http.Error(w, "invalid subtitle index", http.StatusBadRequest)
		return
	}

	// When the URL requests SUP format (e.g. /subtitles/{token}/2.sup),
	// serve the PGS track as a raw .sup elementary stream for client-side
	// bitmap rendering (libpgs). Unlike the buffered text paths below, this
	// serves the cached full-track extract when present, and otherwise
	// streams ffmpeg output directly (the client renders progressively as
	// data arrives) while teeing it into the cache for the next request.
	// Clients that manage their own sliding window opt in with ?windowed=1
	// (+ ?position=/?duration=), mirroring the API stream handler; windowed
	// requests extract only the requested slice — from the cached full
	// track when one exists (warming it in the background when not).
	if requestedFormat == "sup" {
		allowWindow, seek, duration := playback.PGSWindowRequest(r.URL.Query())
		err := s.subCache.ServeSUPExtract(w, r, playback.StreamExtractOpts{
			InputPath:       claims.MediaPath,
			TrackIndex:      trackIndex,
			SourceCodec:     "hdmv_pgs_subtitle", // .sup URLs are only generated for PGS tracks
			SeekSeconds:     seek,
			DurationSeconds: duration,
			AllowWindow:     allowWindow,
			FFmpegPath:      cfg.Playback.FFmpegPath,
		}, playback.StreamExtractSubtitle)
		if err != nil && r.Context().Err() == nil {
			// Headers already committed — log and let the client see a
			// truncated response.
			slog.ErrorContext(r.Context(), "stream subtitle (sup)", "component", "proxy", "error", err, "track", trackIndex,
				"path", claims.MediaPath, "playback_session_id", claims.SessionID)
		}
		return
	}

	// When the URL requests ASS format (e.g. /subtitles/{token}/2.ass),
	// extract as raw ASS to preserve styling for client-side rendering.
	if requestedFormat == "ass" {
		data, err := playback.ExtractSubtitleWithFormat(r.Context(), claims.MediaPath, trackIndex, "ass", cfg.Playback.FFmpegPath)
		if err != nil {
			slog.ErrorContext(r.Context(), "extract subtitle (ass)", "component", "proxy", "error", err, "track", trackIndex, "path", claims.MediaPath, "playback_session_id", claims.SessionID)
			http.Error(w, "subtitle extraction failed", http.StatusInternalServerError)
			return
		}
		playback.ServeSubtitle(w, data, "ass")
		return
	}

	data, format, err := playback.ExtractSubtitle(r.Context(), claims.MediaPath, trackIndex, cfg.Playback.FFmpegPath)
	if err != nil {
		slog.ErrorContext(r.Context(), "extract subtitle", "component", "proxy", "error", err, "track", trackIndex, "path", claims.MediaPath, "playback_session_id", claims.SessionID)
		http.Error(w, "subtitle extraction failed", http.StatusInternalServerError)
		return
	}

	vtt, err := playback.ConvertToVTT(data, format)
	if err != nil {
		slog.ErrorContext(r.Context(), "convert to vtt", "component", "proxy", "error", err, "playback_session_id", claims.SessionID)
		http.Error(w, "subtitle conversion failed", http.StatusInternalServerError)
		return
	}

	playback.ServeSubtitle(w, vtt, "vtt")
}

func (s *Server) handleSubtitleFonts(w http.ResponseWriter, r *http.Request) {
	claims := s.verifyToken(w, r)
	if claims == nil {
		return
	}
	cfg := s.watcher.Config()
	trackParam := chi.URLParam(r, "track")
	trackIndex, _, err := playback.ParseSubtitleTrackParam(trackParam)
	if err != nil {
		http.Error(w, "invalid subtitle index", http.StatusBadRequest)
		return
	}

	fonts, err := playback.ExtractAttachedSubtitleFonts(r.Context(), claims.MediaPath, cfg.Playback.FFmpegPath)
	if err != nil {
		slog.ErrorContext(r.Context(), "extract subtitle fonts", "component", "proxy", "error", err, "track", trackIndex, "path", claims.MediaPath, "playback_session_id", claims.SessionID)
		http.Error(w, "subtitle font extraction failed", http.StatusInternalServerError)
		return
	}

	w.Header().Set("Content-Type", "application/json")
	w.Header().Set("Cache-Control", "no-store")
	if err := json.NewEncoder(w).Encode(playback.EncodeSubtitleFontBundle(fonts)); err != nil {
		slog.WarnContext(r.Context(), "subtitle font response encode failed", "component", "proxy", "error", err, "playback_session_id", claims.SessionID)
	}
}

// proxyToTranscodeNode forwards the request to the transcode node specified in the claims.
func (s *Server) proxyToTranscodeNode(w http.ResponseWriter, r *http.Request, claims *streamtoken.Claims, path string) {
	cfg := s.watcher.Config()
	if claims.TranscodeNode == "" {
		http.Error(w, "no transcode node in token", http.StatusBadRequest)
		return
	}

	targetURL := claims.TranscodeNode + path
	if rawQuery := r.URL.RawQuery; rawQuery != "" {
		targetURL = fmt.Sprintf("%s?%s", targetURL, rawQuery)
	}

	req, err := http.NewRequestWithContext(r.Context(), r.Method, targetURL, nil)
	if err != nil {
		http.Error(w, "internal error", http.StatusInternalServerError)
		return
	}
	req.Header.Set("Authorization", "Bearer "+cfg.Auth.JWTSecret)
	// Forward the verified stream token so the transcode node can self-reconstruct
	// a lost session after its OWN restart: the token carries the full byte-affecting
	// recipe, so the node can re-spawn ffmpeg seeked to the requested segment instead
	// of 404ing (the integrated server already does this from the same token). The
	// node re-verifies the token independently before trusting it.
	if token := chi.URLParam(r, "token"); token != "" {
		req.Header.Set("X-Silo-Stream-Token", token)
	}

	resp, err := s.httpClient.Do(req)
	if err != nil {
		slog.ErrorContext(r.Context(), "proxy to transcode node", "component", "proxy", "error", err, "url", targetURL, "playback_session_id", claims.SessionID)
		http.Error(w, "transcode node unavailable", http.StatusBadGateway)
		return
	}
	defer resp.Body.Close()

	// Copy response headers
	for k, vv := range resp.Header {
		for _, v := range vv {
			w.Header().Add(k, v)
		}
	}
	w.WriteHeader(resp.StatusCode)
	if resp.StatusCode != http.StatusOK && resp.StatusCode != http.StatusPartialContent {
		_, _ = io.Copy(w, resp.Body)
		return
	}
	// Attribute served bytes to the session for authoritative monitoring —
	// incrementally (~1 MiB granularity), not in one post-copy tally: a slow
	// segment drain that outlives the 60s record TTL would otherwise go
	// invisible mid-pour and then post bytes to a record that no longer exists.
	// Manifest bytes are tiny; segment bytes are the real signal. Best-effort,
	// never gates. writeOnly forces the per-chunk Write path: sw.ReadFrom would
	// tally only once on return, which is the single-post-copy behavior this
	// replaces (there is no file to sendfile here — the source is the node's
	// HTTP response body).
	sw := &sessionByteWriter{ResponseWriter: w, tracker: s.tracker, sessionID: claims.SessionID}
	defer sw.flush()
	_, _ = io.Copy(writeOnly{sw}, resp.Body)
}

func (s *Server) handleForceReload(w http.ResponseWriter, r *http.Request) {
	if err := s.watcher.ForceReload(r.Context()); err != nil {
		http.Error(w, "reload failed: "+err.Error(), http.StatusInternalServerError)
		return
	}
	slog.InfoContext(r.Context(), "proxy force reload completed", slog.String("component", "proxy"))
	w.WriteHeader(http.StatusNoContent)
}

type statusResponse struct {
	ActiveSessions int `json:"active_sessions"`
}

func (s *Server) handleStatus(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("Content-Type", "application/json")
	json.NewEncoder(w).Encode(statusResponse{
		ActiveSessions: s.tracker.ActiveCount(),
	})
}