package api

import (
	"context"
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"errors"
	"net/http"
	"sort"
	"strings"
	"time"

	"github.com/ponzischeme89/memby/server/internal/cache"
	"github.com/ponzischeme89/memby/server/internal/emby"
	"github.com/ponzischeme89/memby/server/internal/store"
)

type remoteTrailer struct {
	URL  string `json:"Url"`
	Name string `json:"Name"`
}

type trailerSubject struct {
	Name           string          `json:"Name"`
	RemoteTrailers []remoteTrailer `json:"RemoteTrailers"`
}

type trailerCandidate struct {
	ID        string          `json:"id"`
	Provider  string          `json:"provider"`
	Name      string          `json:"name,omitempty"`
	SourceURL string          `json:"sourceUrl,omitempty"`
	LocalItem json.RawMessage `json:"localItem,omitempty"`
	Priority  int             `json:"priority"`
}

type trailerManifest struct {
	SubjectID  string             `json:"subjectId"`
	Title      string             `json:"title"`
	Candidates []trailerCandidate `json:"candidates"`
}

type trailerAvailability struct {
	Available bool     `json:"available"`
	Providers []string `json:"providers"`
}

type resolveTrailerRequest struct {
	ExcludedCandidateIDs []string `json:"excludedCandidateIds"`
}

type trailerPlaybackResponse struct {
	CandidateID   string `json:"candidateId"`
	Provider      string `json:"provider"`
	URL           string `json:"url"`
	SourceURL     string `json:"sourceUrl,omitempty"`
	Title         string `json:"title"`
	ItemID        string `json:"itemId,omitempty"`
	MediaSourceID string `json:"mediaSourceId,omitempty"`
	PlaySessionID string `json:"playSessionId,omitempty"`
	PlayMethod    string `json:"playMethod,omitempty"`
}

type trailerReportRequest struct {
	CandidateID string `json:"candidateId"`
	Provider    string `json:"provider"`
	Phase       string `json:"phase"`
	Reason      string `json:"reason,omitempty"`
}

func (s *Server) handleTrailers(w http.ResponseWriter, r *http.Request, sess store.Session) {
	itemID := strings.TrimSpace(r.PathValue("id"))
	if itemID == "" {
		writeError(w, http.StatusBadRequest, "item id is required")
		return
	}
	manifest, err := s.trailerManifest(r.Context(), sess, itemID)
	if err != nil {
		s.writeUpstreamError(r.Context(), w, err, "could not inspect trailers")
		return
	}
	providers := make([]string, 0, len(manifest.Candidates))
	seen := map[string]bool{}
	for _, candidate := range manifest.Candidates {
		if !seen[candidate.Provider] {
			seen[candidate.Provider] = true
			providers = append(providers, candidate.Provider)
		}
	}
	writeJSON(w, http.StatusOK, trailerAvailability{
		Available: len(manifest.Candidates) > 0,
		Providers: providers,
	})
}

func (s *Server) handleResolveTrailer(w http.ResponseWriter, r *http.Request, sess store.Session) {
	itemID := strings.TrimSpace(r.PathValue("id"))
	if itemID == "" {
		writeError(w, http.StatusBadRequest, "item id is required")
		return
	}
	var request resolveTrailerRequest
	if r.Body != nil && json.NewDecoder(http.MaxBytesReader(w, r.Body, 8<<10)).Decode(&request) != nil {
		writeError(w, http.StatusBadRequest, "invalid trailer request")
		return
	}
	excluded := make(map[string]bool, len(request.ExcludedCandidateIDs))
	for _, id := range request.ExcludedCandidateIDs {
		excluded[strings.TrimSpace(id)] = true
	}
	manifest, err := s.trailerManifest(r.Context(), sess, itemID)
	if err != nil {
		s.writeUpstreamError(r.Context(), w, err, "could not inspect trailers")
		return
	}
	for _, candidate := range s.preferredTrailerCandidates(r.Context(), sess, manifest) {
		if excluded[candidate.ID] {
			continue
		}
		if len(candidate.LocalItem) > 0 {
			if resolved, resolveErr := s.resolveLocalTrailer(r.Context(), sess, manifest, candidate); resolveErr == nil {
				writeJSON(w, http.StatusOK, resolved)
				return
			}
			continue
		}
		// Remote pages are resolved on the television. YouTube signs direct media URLs for
		// the resolving IP, so resolving here can make the URL unusable from the viewer's
		// network and makes provider traffic appear to come from the gateway.
		writeJSON(w, http.StatusOK, trailerPlaybackResponse{
			CandidateID: candidate.ID,
			Provider:    candidate.Provider,
			SourceURL:   candidate.SourceURL,
			Title:       trailerTitle(manifest.Title, candidate.Name),
			PlayMethod:  "DirectPlay",
		})
		return
	}
	writeError(w, http.StatusNotFound, "no playable trailer is available")
}

func (s *Server) handleTrailerReport(w http.ResponseWriter, r *http.Request, sess store.Session) {
	itemID := strings.TrimSpace(r.PathValue("id"))
	var report trailerReportRequest
	if itemID == "" || json.NewDecoder(http.MaxBytesReader(w, r.Body, 8<<10)).Decode(&report) != nil {
		writeError(w, http.StatusBadRequest, "invalid trailer report")
		return
	}
	report.CandidateID = strings.TrimSpace(report.CandidateID)
	report.Provider = strings.ToLower(strings.TrimSpace(report.Provider))
	report.Phase = strings.ToLower(strings.TrimSpace(report.Phase))
	if report.CandidateID == "" || report.Provider == "" ||
		(report.Phase != "started" && report.Phase != "failed" && report.Phase != "completed") {
		writeError(w, http.StatusBadRequest, "invalid trailer report")
		return
	}
	fields := []any{
		"item_id", itemID,
		"provider", report.Provider,
		"candidate", report.CandidateID,
		"source_ip", requestClientIP(r),
	}
	if reason := strings.TrimSpace(report.Reason); reason != "" {
		fields = append(fields, "reason", reason)
	}
	s.loggerFor(r.Context()).Info("trailer playback "+report.Phase, fields...)
	if report.Phase == "started" {
		s.rememberTrailerCandidate(r.Context(), sess, itemID, report.CandidateID)
	}
	w.WriteHeader(http.StatusNoContent)
}

func (s *Server) preferredTrailerCandidates(
	ctx context.Context,
	sess store.Session,
	manifest trailerManifest,
) []trailerCandidate {
	out := append([]trailerCandidate(nil), manifest.Candidates...)
	if s.cache == nil {
		return out
	}
	preferred, err := s.cache.Get(ctx, cache.UserKey(sess.EmbyUserID, "trailer-success:v1:"+manifest.SubjectID))
	if err != nil || len(preferred) == 0 {
		return out
	}
	id := string(preferred)
	sort.SliceStable(out, func(i, j int) bool {
		return out[i].ID == id && out[j].ID != id
	})
	return out
}

func (s *Server) rememberTrailerCandidate(
	ctx context.Context,
	sess store.Session,
	itemID string,
	candidateID string,
) {
	if s.cache != nil && candidateID != "" {
		_ = s.cache.Set(
			ctx,
			cache.UserKey(sess.EmbyUserID, "trailer-success:v1:"+itemID),
			[]byte(candidateID),
			30*time.Minute,
		)
	}
}

func (s *Server) resolveLocalTrailer(
	ctx context.Context,
	sess store.Session,
	manifest trailerManifest,
	candidate trailerCandidate,
) (trailerPlaybackResponse, error) {
	item, err := emby.Summarise(candidate.LocalItem)
	if err != nil || item.ID == "" {
		return trailerPlaybackResponse{}, errors.New("unreadable local trailer")
	}
	_, mediaSourceID, playSessionID, negotiatedURL, playMethod := s.playbackSubtitles(
		ctx,
		credentials(sess),
		item.ID,
		0,
		nil,
		"",
		false,
		s.effectivePlaybackCapabilities(ctx, sess),
	)
	streamURL := s.emby.StreamURL(credentials(sess), item.ID)
	if negotiatedURL != "" {
		streamURL = negotiatedURL
	}
	if streamURL == "" {
		return trailerPlaybackResponse{}, errors.New("empty local trailer stream")
	}
	return trailerPlaybackResponse{
		CandidateID:   candidate.ID,
		Provider:      candidate.Provider,
		URL:           streamURL,
		Title:         trailerTitle(manifest.Title, candidate.Name),
		ItemID:        item.ID,
		MediaSourceID: mediaSourceID,
		PlaySessionID: playSessionID,
		PlayMethod:    playMethod,
	}, nil
}

func (s *Server) trailerManifest(ctx context.Context, sess store.Session, itemID string) (trailerManifest, error) {
	// A film Radarr is tracking has no Emby record to ask about local or remote trailers,
	// so its chain is built from what Radarr knows. It joins here rather than beside the
	// detail route because everything downstream — availability, resolve, report, the
	// player's walk through the candidates — is then unchanged for both kinds of subject.
	if movieID, ok := radarrMovieID(itemID); ok && strings.HasPrefix(itemID, radarrItemPrefix) {
		return s.radarrTrailerManifest(ctx, itemID, movieID)
	}
	key := cache.UserKey(sess.EmbyUserID, "trailers:v2:"+itemID)
	if s.cache != nil {
		if raw, err := s.cache.Get(ctx, key); err == nil {
			var cached trailerManifest
			if json.Unmarshal(raw, &cached) == nil {
				return cached, nil
			}
		}
	}

	type localResult struct {
		items *emby.ItemsResult
		err   error
	}
	type itemResult struct {
		raw json.RawMessage
		err error
	}
	localResultCh := make(chan localResult, 1)
	itemResultCh := make(chan itemResult, 1)
	go func() {
		items, err := s.emby.LocalTrailers(ctx, credentials(sess), itemID)
		localResultCh <- localResult{items: items, err: err}
	}()
	go func() {
		raw, err := s.emby.Item(ctx, credentials(sess), itemID, "RemoteTrailers")
		itemResultCh <- itemResult{raw: raw, err: err}
	}()
	localAnswer, itemAnswer := <-localResultCh, <-itemResultCh
	locals, localErr := localAnswer.items, localAnswer.err
	item, itemErr := itemAnswer.raw, itemAnswer.err
	if localErr != nil && itemErr != nil {
		return trailerManifest{}, errors.Join(localErr, itemErr)
	}
	partial := localErr != nil || itemErr != nil
	manifest := trailerManifest{SubjectID: itemID, Candidates: []trailerCandidate{}}
	if itemErr == nil {
		var subject trailerSubject
		if json.Unmarshal(item, &subject) == nil {
			manifest.Title = strings.TrimSpace(subject.Name)
			for _, remote := range subject.RemoteTrailers {
				provider := trailerProvider(remote.URL)
				if provider == "" {
					continue
				}
				manifest.Candidates = append(manifest.Candidates, trailerCandidate{
					ID:        trailerCandidateID(provider, remote.URL),
					Provider:  provider,
					Name:      strings.TrimSpace(remote.Name),
					SourceURL: strings.TrimSpace(remote.URL),
					Priority:  remoteTrailerPriority(provider, remote.Name),
				})
			}
		}
	}
	if localErr == nil && locals != nil {
		for _, raw := range locals.Items {
			summary, summaryErr := emby.Summarise(raw)
			if summaryErr != nil || summary.ID == "" {
				continue
			}
			manifest.Candidates = append(manifest.Candidates, trailerCandidate{
				ID:        trailerCandidateID("local", summary.ID),
				Provider:  "local",
				Name:      summary.Name,
				LocalItem: raw,
				Priority:  20,
			})
		}
	}
	manifest.Candidates = uniqueTrailerCandidates(manifest.Candidates)
	sort.SliceStable(manifest.Candidates, func(i, j int) bool {
		return manifest.Candidates[i].Priority < manifest.Candidates[j].Priority
	})
	if partial && len(manifest.Candidates) == 0 {
		return trailerManifest{}, errors.Join(localErr, itemErr)
	}
	if encoded, err := json.Marshal(manifest); err == nil && s.cache != nil && !partial {
		_ = s.cache.Set(ctx, key, encoded, s.cfg.ItemTTL)
	}
	return manifest, nil
}

func trailerProvider(raw string) string {
	value := strings.ToLower(raw)
	switch {
	case strings.Contains(value, "youtube.com/"), strings.Contains(value, "youtube-nocookie.com/"), strings.Contains(value, "youtu.be/"):
		return "youtube"
	case strings.Contains(value, "apple.com/"), strings.Contains(value, "apple.co/"):
		return "apple"
	default:
		return ""
	}
}

func remoteTrailerPriority(provider, name string) int {
	official := strings.Contains(strings.ToLower(name), "official")
	switch {
	case provider == "apple":
		// Apple-hosted trailer media is an official first-party source even when Emby
		// supplies no useful label for it.
		return 0
	case provider == "youtube" && official:
		return 10
	default:
		return 30
	}
}

func trailerCandidateID(provider, source string) string {
	digest := sha256.Sum256([]byte(provider + "\x00" + strings.TrimSpace(source)))
	return provider + "-" + hex.EncodeToString(digest[:8])
}

func uniqueTrailerCandidates(candidates []trailerCandidate) []trailerCandidate {
	seen := map[string]bool{}
	out := make([]trailerCandidate, 0, len(candidates))
	for _, candidate := range candidates {
		if candidate.ID == "" || seen[candidate.ID] {
			continue
		}
		seen[candidate.ID] = true
		out = append(out, candidate)
	}
	return out
}

func trailerTitle(subject, candidate string) string {
	if strings.TrimSpace(subject) != "" {
		return strings.TrimSpace(subject) + " trailer"
	}
	if strings.TrimSpace(candidate) != "" {
		return strings.TrimSpace(candidate)
	}
	return "Trailer"
}