// Package trailer resolves remote trailer pages to native media streams.
package trailer

import (
	"bytes"
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"html"
	"io"
	"net/http"
	"net/url"
	"regexp"
	"sort"
	"strings"
	"sync"
	"time"
)

const (
	maxPageBytes = 2 << 20
	cacheTTL     = 30 * time.Minute
)

var ErrUnavailable = errors.New("trailer unavailable")

type Source struct {
	Provider string
	URL      string
}

type Result struct {
	URL      string
	MimeType string
}

type Provider interface {
	Name() string
	Supports(string) bool
	Resolve(context.Context, string) (Result, error)
}

type cacheEntry struct {
	result    Result
	expiresAt time.Time
}

// Resolver is an ordered provider chain with a short-lived successful mapping cache.
// The cached value avoids repeating YouTube page resolution on Back → Trailer while its
// signed media URL is still useful; failures are never cached.
type Resolver struct {
	providers []Provider
	mu        sync.Mutex
	cache     map[string]cacheEntry
}

func New(client *http.Client) *Resolver {
	if client == nil {
		client = &http.Client{Timeout: 8 * time.Second}
	}
	return &Resolver{
		providers: []Provider{newAppleProvider(client), newYouTubeProvider(client)},
		cache:     map[string]cacheEntry{},
	}
}

func (r *Resolver) Resolve(ctx context.Context, source Source) (Result, error) {
	key := strings.ToLower(strings.TrimSpace(source.Provider)) + "\x00" + strings.TrimSpace(source.URL)
	now := time.Now()
	r.mu.Lock()
	if cached, ok := r.cache[key]; ok && cached.expiresAt.After(now) {
		r.mu.Unlock()
		return cached.result, nil
	}
	delete(r.cache, key)
	r.mu.Unlock()

	for _, provider := range r.providers {
		if source.Provider != "" && !strings.EqualFold(source.Provider, provider.Name()) {
			continue
		}
		if !provider.Supports(source.URL) {
			continue
		}
		result, err := provider.Resolve(ctx, source.URL)
		if err != nil {
			return Result{}, err
		}
		r.mu.Lock()
		r.cache[key] = cacheEntry{result: result, expiresAt: now.Add(cacheTTL)}
		if len(r.cache) > 128 {
			for candidate, entry := range r.cache {
				if entry.expiresAt.Before(now) {
					delete(r.cache, candidate)
				}
			}
		}
		r.mu.Unlock()
		return result, nil
	}
	return Result{}, ErrUnavailable
}

func (r *Resolver) Invalidate(source Source) {
	key := strings.ToLower(strings.TrimSpace(source.Provider)) + "\x00" + strings.TrimSpace(source.URL)
	r.mu.Lock()
	delete(r.cache, key)
	r.mu.Unlock()
}

type appleProvider struct{ client *http.Client }

func newAppleProvider(client *http.Client) Provider { return &appleProvider{client: client} }
func (*appleProvider) Name() string                 { return "apple" }
func (*appleProvider) Supports(raw string) bool {
	parsed, err := url.Parse(raw)
	return err == nil && (isHostOrSubdomain(parsed.Hostname(), "apple.com") ||
		isHostOrSubdomain(parsed.Hostname(), "apple.co"))
}

func (p *appleProvider) Resolve(ctx context.Context, raw string) (Result, error) {
	if looksLikeMediaURL(raw) {
		return p.validate(ctx, raw)
	}
	body, err := fetchLimited(ctx, p.client, raw, maxPageBytes, "text/html")
	if err != nil {
		return Result{}, err
	}
	links := mediaLinks(string(body))
	if len(links) == 0 {
		return Result{}, ErrUnavailable
	}
	sort.SliceStable(links, func(i, j int) bool { return mediaQuality(links[i]) > mediaQuality(links[j]) })
	for _, candidate := range links {
		if result, err := p.validate(ctx, candidate); err == nil {
			return result, nil
		}
	}
	return Result{}, ErrUnavailable
}

func (p *appleProvider) validate(ctx context.Context, raw string) (Result, error) {
	contentType, err := validateMediaURL(ctx, p.client, raw)
	if err != nil {
		return Result{}, err
	}
	return Result{URL: raw, MimeType: contentType}, nil
}

var appleMediaURL = regexp.MustCompile(`https?:\\?/\\?/[^"'<> ]+\.(?:mov|mp4|m3u8)(?:\?[^"'<> ]*)?`)

func mediaLinks(body string) []string {
	matches := appleMediaURL.FindAllString(body, -1)
	seen := map[string]bool{}
	out := make([]string, 0, len(matches))
	for _, match := range matches {
		candidate := html.UnescapeString(strings.ReplaceAll(match, `\/`, `/`))
		if !seen[candidate] {
			seen[candidate] = true
			out = append(out, candidate)
		}
	}
	return out
}

func mediaQuality(raw string) int {
	lower := strings.ToLower(raw)
	for _, quality := range []int{2160, 1440, 1080, 720, 480, 360} {
		if strings.Contains(lower, fmt.Sprintf("%d", quality)) {
			return quality
		}
	}
	return 0
}

type youTubeProvider struct{ client *http.Client }

func newYouTubeProvider(client *http.Client) Provider { return &youTubeProvider{client: client} }
func (*youTubeProvider) Name() string                 { return "youtube" }
func (*youTubeProvider) Supports(raw string) bool     { return youtubeVideoID(raw) != "" }

func (p *youTubeProvider) Resolve(ctx context.Context, raw string) (Result, error) {
	videoID := youtubeVideoID(raw)
	if videoID == "" {
		return Result{}, ErrUnavailable
	}
	responses := []func(context.Context, string) (youtubePlayer, error){
		p.innerTubePlayer,
		p.watchPagePlayer,
	}
	for _, load := range responses {
		player, err := load(ctx, videoID)
		if err != nil || !strings.EqualFold(player.PlayabilityStatus.Status, "OK") {
			continue
		}
		// YouTube's formats list contains progressive audio+video streams. AdaptiveFormats
		// are separate tracks and would begin silently if handed straight to Media3.
		formats := player.StreamingData.Formats
		sort.SliceStable(formats, func(i, j int) bool {
			return formats[i].Height > formats[j].Height ||
				(formats[i].Height == formats[j].Height && formats[i].Bitrate > formats[j].Bitrate)
		})
		for _, format := range formats {
			// Native playback needs one progressive stream carrying both tracks. Adaptive
			// video-only formats are deliberately skipped rather than starting silent.
			if format.URL == "" || !strings.Contains(format.MimeType, "video/") {
				continue
			}
			contentType, validationErr := validateMediaURL(ctx, p.client, format.URL)
			if validationErr == nil {
				return Result{URL: format.URL, MimeType: contentType}, nil
			}
		}
	}
	return Result{}, ErrUnavailable
}

type youtubePlayer struct {
	PlayabilityStatus struct {
		Status string `json:"status"`
	} `json:"playabilityStatus"`
	StreamingData struct {
		Formats         []youtubeFormat `json:"formats"`
		AdaptiveFormats []youtubeFormat `json:"adaptiveFormats"`
	} `json:"streamingData"`
}

type youtubeFormat struct {
	URL      string `json:"url"`
	MimeType string `json:"mimeType"`
	Height   int    `json:"height"`
	Bitrate  int    `json:"bitrate"`
}

func (p *youTubeProvider) innerTubePlayer(ctx context.Context, videoID string) (youtubePlayer, error) {
	payload := map[string]any{
		"videoId": videoID, "contentCheckOk": true, "racyCheckOk": true,
		"context": map[string]any{"client": map[string]any{
			"clientName": "ANDROID", "clientVersion": "20.10.38", "hl": "en", "gl": "NZ",
		}},
	}
	body, _ := json.Marshal(payload)
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, "https://www.youtube.com/youtubei/v1/player", bytes.NewReader(body))
	if err != nil {
		return youtubePlayer{}, err
	}
	req.Header.Set("Content-Type", "application/json")
	req.Header.Set("User-Agent", "com.google.android.youtube/20.10.38 (Linux; U; Android 12) gzip")
	return p.doPlayer(req)
}

func (p *youTubeProvider) watchPagePlayer(ctx context.Context, videoID string) (youtubePlayer, error) {
	req, err := http.NewRequestWithContext(ctx, http.MethodGet,
		"https://www.youtube.com/watch?v="+url.QueryEscape(videoID)+"&bpctr=9999999999&has_verified=1", nil)
	if err != nil {
		return youtubePlayer{}, err
	}
	req.Header.Set("User-Agent", "Mozilla/5.0 (Linux; Android 12; Android TV) AppleWebKit/537.36 Chrome/122 Safari/537.36")
	body, err := p.do(req)
	if err != nil {
		return youtubePlayer{}, err
	}
	for _, marker := range []string{"ytInitialPlayerResponse = ", `"playerResponse":`} {
		if raw := balancedJSONObject(body, marker); raw != "" {
			var player youtubePlayer
			if json.Unmarshal([]byte(raw), &player) == nil {
				return player, nil
			}
		}
	}
	return youtubePlayer{}, ErrUnavailable
}

func (p *youTubeProvider) doPlayer(req *http.Request) (youtubePlayer, error) {
	body, err := p.do(req)
	if err != nil {
		return youtubePlayer{}, err
	}
	var player youtubePlayer
	if err := json.Unmarshal([]byte(body), &player); err != nil {
		return youtubePlayer{}, err
	}
	return player, nil
}

func (p *youTubeProvider) do(req *http.Request) (string, error) {
	resp, err := p.client.Do(req)
	if err != nil {
		return "", err
	}
	defer resp.Body.Close()
	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		return "", ErrUnavailable
	}
	body, err := io.ReadAll(io.LimitReader(resp.Body, maxPageBytes+1))
	if err != nil || len(body) > maxPageBytes {
		return "", ErrUnavailable
	}
	return string(body), nil
}

func youtubeVideoID(raw string) string {
	parsed, err := url.Parse(strings.TrimSpace(raw))
	if err != nil {
		return ""
	}
	host := strings.TrimPrefix(strings.ToLower(parsed.Hostname()), "www.")
	var id string
	switch {
	case host == "youtu.be":
		id = strings.Trim(parsed.Path, "/")
	case isHostOrSubdomain(host, "youtube.com"), isHostOrSubdomain(host, "youtube-nocookie.com"):
		id = parsed.Query().Get("v")
		if id == "" {
			parts := strings.Split(strings.Trim(parsed.Path, "/"), "/")
			if len(parts) == 2 && (parts[0] == "embed" || parts[0] == "shorts") {
				id = parts[1]
			}
		}
	}
	if len(id) != 11 {
		return ""
	}
	for _, char := range id {
		if !(char == '-' || char == '_' || char >= 'a' && char <= 'z' ||
			char >= 'A' && char <= 'Z' || char >= '0' && char <= '9') {
			return ""
		}
	}
	return id
}

func isHostOrSubdomain(host, root string) bool {
	host = strings.ToLower(strings.TrimSuffix(strings.TrimSpace(host), "."))
	root = strings.ToLower(strings.TrimSuffix(strings.TrimSpace(root), "."))
	return host == root || strings.HasSuffix(host, "."+root)
}

func balancedJSONObject(body, marker string) string {
	start := strings.Index(body, marker)
	if start < 0 {
		return ""
	}
	start += len(marker)
	for start < len(body) && body[start] != '{' {
		start++
	}
	if start == len(body) {
		return ""
	}
	depth, quoted, escaped := 0, false, false
	for index := start; index < len(body); index++ {
		char := body[index]
		if quoted {
			if escaped {
				escaped = false
			} else if char == '\\' {
				escaped = true
			} else if char == '"' {
				quoted = false
			}
			continue
		}
		switch char {
		case '"':
			quoted = true
		case '{':
			depth++
		case '}':
			depth--
			if depth == 0 {
				return body[start : index+1]
			}
		}
	}
	return ""
}

func looksLikeMediaURL(raw string) bool {
	path := strings.ToLower(strings.Split(raw, "?")[0])
	return strings.HasSuffix(path, ".mov") || strings.HasSuffix(path, ".mp4") || strings.HasSuffix(path, ".m3u8")
}

func validateMediaURL(ctx context.Context, client *http.Client, raw string) (string, error) {
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, raw, nil)
	if err != nil {
		return "", err
	}
	req.Header.Set("Range", "bytes=0-0")
	req.Header.Set("User-Agent", "Memby trailer resolver")
	resp, err := client.Do(req)
	if err != nil {
		return "", err
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK && resp.StatusCode != http.StatusPartialContent {
		return "", ErrUnavailable
	}
	contentType := strings.ToLower(strings.TrimSpace(strings.Split(resp.Header.Get("Content-Type"), ";")[0]))
	if !strings.HasPrefix(contentType, "video/") && contentType != "application/vnd.apple.mpegurl" &&
		contentType != "application/x-mpegurl" && contentType != "application/octet-stream" {
		return "", ErrUnavailable
	}
	return contentType, nil
}

func fetchLimited(ctx context.Context, client *http.Client, raw string, limit int64, accept string) ([]byte, error) {
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, raw, nil)
	if err != nil {
		return nil, err
	}
	req.Header.Set("Accept", accept)
	req.Header.Set("User-Agent", "Mozilla/5.0 (Linux; Android TV) AppleWebKit/537.36 Safari/537.36")
	resp, err := client.Do(req)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()
	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		return nil, ErrUnavailable
	}
	body, err := io.ReadAll(io.LimitReader(resp.Body, limit+1))
	if err != nil || int64(len(body)) > limit {
		return nil, ErrUnavailable
	}
	return body, nil
}