veza/veza-backend-api/internal/handlers/embed_handler.go

package handlers

import (
	"context"
	"errors"
	"fmt"
	"html"
	"net/http"
	"strings"

	"github.com/gin-gonic/gin"
	"github.com/google/uuid"
	"go.uber.org/zap"
	"gorm.io/gorm"

	"veza-backend-api/internal/models"
)

// EmbedHandler renders the standalone /embed/track/:id HTML page +
// the /oembed JSON envelope. v1.0.9 W3 Day 15.
//
// The HTML page is intentionally not the SPA — it's a static-ish
// document with a <audio> element + minimal styling so it loads fast
// and renders inside iframe sandboxes (Twitter cards, Facebook,
// embeds in blogs, etc).
type EmbedHandler struct {
	db          *gorm.DB
	frontendURL string
	apiBaseURL  string
	logger      *zap.Logger
}

// NewEmbedHandler wires the handler. apiBaseURL is the URL prefix
// the backend serves on (e.g. https://api.veza.fr) — used to
// construct the audio source URL inside the embed page. frontendURL
// is used for the "Open in Veza" link + as the canonical URL for OG
// tags.
func NewEmbedHandler(db *gorm.DB, frontendURL, apiBaseURL string, logger *zap.Logger) *EmbedHandler {
	if logger == nil {
		logger = zap.NewNop()
	}
	return &EmbedHandler{db: db, frontendURL: frontendURL, apiBaseURL: apiBaseURL, logger: logger}
}

// EmbedTrack renders GET /embed/track/:id as a standalone HTML page.
// Public (no auth) — only public tracks are returned. DMCA-blocked
// tracks return 451 ; private tracks return 404 (don't leak existence).
//
// The page sets `X-Frame-Options: ALLOWALL` so it can be iframed.
// We DON'T include the global CSP frame-ancestors directive on this
// route (it's set on SPA routes only by the security middleware).
//
// @Summary      Embed widget for a track
// @Description  Standalone HTML widget (audio player + minimal styling) for embedding via iframe. Public, no auth. Twitter/Facebook scrapers ingest the OG tags inside.
// @Tags         Embed
// @Produce      html
// @Param        id   path  string  true  "Track UUID"
// @Success      200  {string}  string  "HTML embed page"
// @Failure      404  {string}  string  "Track not found or not public"
// @Failure      451  {string}  string  "DMCA takedown in force"
// @Router       /embed/track/{id} [get]
func (h *EmbedHandler) EmbedTrack(c *gin.Context) {
	trackID, err := uuid.Parse(c.Param("id"))
	if err != nil {
		c.String(http.StatusBadRequest, "invalid track id")
		return
	}
	track, err := h.fetchPublicTrack(c.Request.Context(), trackID)
	if err != nil {
		if errors.Is(err, gorm.ErrRecordNotFound) {
			c.String(http.StatusNotFound, "track not found")
			return
		}
		if errors.Is(err, errDmcaBlocked) {
			c.String(http.StatusUnavailableForLegalReasons, "track unavailable: subject to a DMCA takedown notice")
			return
		}
		h.logger.Error("embed: failed to fetch track", zap.Error(err))
		c.String(http.StatusInternalServerError, "failed to load track")
		return
	}

	// Allow iframing. The global helmet CSP doesn't apply here.
	c.Header("X-Frame-Options", "ALLOWALL")
	c.Header("Content-Security-Policy", "frame-ancestors *")
	c.Header("Cache-Control", "public, max-age=300")
	c.Data(http.StatusOK, "text/html; charset=utf-8", []byte(h.renderEmbed(track)))
}

// OEmbed renders GET /oembed?url=<frontend_track_url>&format=json.
// oEmbed spec: https://oembed.com/. We support type=rich with an
// HTML iframe pointing back at /embed/track/:id.
//
// @Summary      oEmbed endpoint
// @Description  Returns oEmbed JSON for a Veza track URL. Used by Twitter, Slack, Discord etc. for in-line previews. format=xml is not supported.
// @Tags         Embed
// @Produce      json
// @Param        url     query  string  true  "Veza track URL (must point at /tracks/:id)"
// @Param        format  query  string  false "Must be 'json' (default)"
// @Param        maxwidth  query  int   false "Optional max iframe width"
// @Success      200  {object}  map[string]interface{}  "oEmbed envelope"
// @Failure      400  {string}  string  "Bad URL or unsupported format"
// @Failure      404  {string}  string  "Track not found"
// @Router       /oembed [get]
func (h *EmbedHandler) OEmbed(c *gin.Context) {
	rawURL := c.Query("url")
	format := c.DefaultQuery("format", "json")
	if format != "" && format != "json" {
		c.String(http.StatusNotImplemented, "only format=json is supported")
		return
	}

	// Extract the track UUID from the URL. We accept anything that
	// looks like /tracks/<uuid> ; the host check is best-effort
	// (we don't strictly require it to match frontendURL — that would
	// reject staging URLs, custom domains, etc).
	trackID, ok := extractTrackIDFromURL(rawURL)
	if !ok {
		c.String(http.StatusBadRequest, "url must point to a track page (/tracks/<uuid>)")
		return
	}

	track, err := h.fetchPublicTrack(c.Request.Context(), trackID)
	if err != nil {
		if errors.Is(err, gorm.ErrRecordNotFound) {
			c.String(http.StatusNotFound, "track not found")
			return
		}
		if errors.Is(err, errDmcaBlocked) {
			c.String(http.StatusUnavailableForLegalReasons, "track unavailable")
			return
		}
		h.logger.Error("oembed: failed to fetch track", zap.Error(err))
		c.String(http.StatusInternalServerError, "failed to load track")
		return
	}

	// Width / height : a Twitter card is 480×270 ; SoundCloud uses
	// 100% width × 166 px tall for compact players. We pick a width
	// that respects ?maxwidth, default 480.
	width := 480
	if w := c.Query("maxwidth"); w != "" {
		if iw, err := parseSafeInt(w); err == nil && iw >= 240 && iw <= 1280 {
			width = iw
		}
	}
	height := 166

	embedURL := strings.TrimSuffix(h.apiBaseURL, "/") + "/embed/track/" + track.ID.String()
	htmlIframe := fmt.Sprintf(
		`<iframe src="%s" width="%d" height="%d" frameborder="0" allow="autoplay" allowtransparency="true" loading="lazy"></iframe>`,
		html.EscapeString(embedURL), width, height,
	)

	c.Header("Cache-Control", "public, max-age=3600")
	c.JSON(http.StatusOK, gin.H{
		"version":       "1.0",
		"type":          "rich",
		"provider_name": "Veza",
		"provider_url":  h.frontendURL,
		"title":         track.Title,
		"author_name":   track.Artist,
		"width":         width,
		"height":        height,
		"html":          htmlIframe,
	})
}

// errDmcaBlocked is the sentinel returned from fetchPublicTrack
// when the track row exists but DmcaBlocked=true.
var errDmcaBlocked = errors.New("track is dmca-blocked")

// fetchPublicTrack returns the track if and only if it is public AND
// not DMCA-blocked AND not soft-deleted. Any other state (private,
// blocked, missing) is reported as gorm.ErrRecordNotFound except for
// the dmca case, which gets its own sentinel so the caller can return
// 451.
func (h *EmbedHandler) fetchPublicTrack(ctx context.Context, id uuid.UUID) (*models.Track, error) {
	// We use a raw GORM query rather than going through TrackService
	// to keep the embed handler dependency-light + cacheable.
	var track models.Track
	if err := h.db.WithContext(ctx).Where("id = ?", id).First(&track).Error; err != nil {
		return nil, err
	}
	if track.DmcaBlocked {
		return nil, errDmcaBlocked
	}
	if !track.IsPublic {
		return nil, gorm.ErrRecordNotFound
	}
	return &track, nil
}

// renderEmbed builds the standalone HTML page. Kept inline (no
// template file) so the asset is self-contained — no risk of a
// missing template path in production.
func (h *EmbedHandler) renderEmbed(track *models.Track) string {
	canonical := strings.TrimSuffix(h.frontendURL, "/") + "/tracks/" + track.ID.String()
	streamURL := strings.TrimSuffix(h.apiBaseURL, "/") + "/api/v1/tracks/" + track.ID.String() + "/stream"

	title := html.EscapeString(track.Title)
	artist := html.EscapeString(track.Artist)
	if artist == "" {
		artist = "Veza"
	}
	canonicalEsc := html.EscapeString(canonical)
	streamURLEsc := html.EscapeString(streamURL)

	return fmt.Sprintf(`<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width,initial-scale=1">
<title>%s — %s</title>
<link rel="canonical" href="%s">

<!-- Open Graph (Facebook, LinkedIn, Discord) -->
<meta property="og:type" content="music.song">
<meta property="og:title" content="%s">
<meta property="og:site_name" content="Veza">
<meta property="og:url" content="%s">
<meta property="og:audio" content="%s">
<meta property="og:audio:type" content="audio/mpeg">
<meta property="music:musician" content="%s">

<!-- Twitter Cards -->
<meta name="twitter:card" content="player">
<meta name="twitter:title" content="%s">
<meta name="twitter:player" content="%s">
<meta name="twitter:player:width" content="480">
<meta name="twitter:player:height" content="166">

<style>
  *{box-sizing:border-box}
  body{margin:0;font:14px/1.4 system-ui,-apple-system,sans-serif;background:#111;color:#eee}
  .player{display:flex;flex-direction:column;height:100vh;padding:14px;gap:8px}
  .meta{display:flex;flex-direction:column;gap:2px}
  .title{font-weight:600;font-size:15px;color:#fff}
  .artist{font-size:13px;color:#aaa}
  .controls audio{width:100%%;outline:none}
  .footer{margin-top:auto;font-size:11px;color:#888;display:flex;justify-content:space-between}
  .footer a{color:#aaa;text-decoration:none}
  .footer a:hover{text-decoration:underline}
</style>
</head>
<body>
<div class="player">
  <div class="meta">
    <div class="title">%s</div>
    <div class="artist">%s</div>
  </div>
  <div class="controls">
    <audio controls preload="metadata" src="%s">
      Your browser does not support the audio element.
    </audio>
  </div>
  <div class="footer">
    <span>Veza</span>
    <a href="%s" target="_blank" rel="noopener">Open in Veza →</a>
  </div>
</div>
</body>
</html>`,
		title, artist, canonicalEsc,
		title, canonicalEsc, streamURLEsc, artist,
		title, html.EscapeString(strings.TrimSuffix(h.apiBaseURL, "/")+"/embed/track/"+track.ID.String()),
		title, artist, streamURLEsc, canonicalEsc,
	)
}

// extractTrackIDFromURL parses /tracks/<uuid> out of a URL string.
// We don't validate scheme / host — keeps the handler permissive
// across staging, custom domains, localhost dev.
func extractTrackIDFromURL(raw string) (uuid.UUID, bool) {
	if raw == "" {
		return uuid.Nil, false
	}
	idx := strings.Index(raw, "/tracks/")
	if idx < 0 {
		return uuid.Nil, false
	}
	tail := raw[idx+len("/tracks/"):]
	// strip any trailing ?query / #frag / / segment
	for _, sep := range []string{"?", "#", "/"} {
		if i := strings.Index(tail, sep); i >= 0 {
			tail = tail[:i]
		}
	}
	id, err := uuid.Parse(tail)
	if err != nil {
		return uuid.Nil, false
	}
	return id, true
}

func parseSafeInt(s string) (int, error) {
	n := 0
	for _, c := range s {
		if c < '0' || c > '9' {
			return 0, errors.New("not an integer")
		}
		n = n*10 + int(c-'0')
		if n > 100_000 {
			return 0, errors.New("too large")
		}
	}
	return n, nil
}