import type { RichContent } from "../../model/interfaces.ts";
import type { RichContentProvider } from "../rich-content-service.ts";
import { extractOgTag, fetchWithTimeout } from "../rich-content-service.ts";

function extractVideoId(url: string): string | null {
  try {
    const u = new URL(url);
    if (u.hostname === "youtu.be") {
      return u.pathname.slice(1).split("/")[0] || null;
    }
    if (u.hostname === "youtube.com" || u.hostname === "www.youtube.com") {
      if (u.pathname === "/watch" || u.pathname.startsWith("/watch?")) {
        return u.searchParams.get("v");
      }
      if (
        u.pathname.startsWith("/embed/") || u.pathname.startsWith("/shorts/")
      ) {
        return u.pathname.split("/")[2] || null;
      }
    }
  } catch {
    // invalid URL
  }
  return null;
}

function extractPlaylistId(url: string): string | null {
  try {
    return new URL(url).searchParams.get("list");
  } catch {
    return null;
  }
}

/**
 * Extract the playback offset in seconds from a YouTube URL.
 * Accepts `t` (plain seconds, `90s`, or `1h2m3s` / `20m5s` forms) and `start`
 * (plain seconds). Returns null when absent or unparseable.
 */
function extractStartSeconds(url: string): number | null {
  let raw: string | null;
  try {
    const u = new URL(url);
    raw = u.searchParams.get("t") ?? u.searchParams.get("start");
  } catch {
    return null;
  }
  if (!raw) return null;

  const plain = /^\d+$/.exec(raw);
  if (plain) return Number(raw);

  const hms = /^(?:(\d+)h)?(?:(\d+)m)?(?:(\d+)s)?$/i.exec(raw);
  if (!hms || (!hms[1] && !hms[2] && !hms[3])) return null;
  return Number(hms[1] ?? 0) * 3600 + Number(hms[2] ?? 0) * 60 +
    Number(hms[3] ?? 0);
}

/** Matches /channel/UC…, /@handle, /c/name, /user/name */
function extractChannelPath(url: string): string | null {
  try {
    const u = new URL(url);
    if (u.hostname === "youtube.com" || u.hostname === "www.youtube.com") {
      if (
        u.pathname.startsWith("/channel/") ||
        u.pathname.startsWith("/@") ||
        u.pathname.startsWith("/c/") ||
        u.pathname.startsWith("/user/")
      ) {
        return u.pathname;
      }
    }
  } catch {
    // invalid URL
  }
  return null;
}

async function fetchOEmbed(
  url: string,
): Promise<{ title?: string; thumbnailUrl?: string }> {
  try {
    const oembedUrl = `https://www.youtube.com/oembed?url=${
      encodeURIComponent(url)
    }&format=json`;
    const res = await fetchWithTimeout(oembedUrl);
    if (res.ok) {
      const data = await res.json() as {
        title?: string;
        thumbnail_url?: string;
      };
      return { title: data.title, thumbnailUrl: data.thumbnail_url };
    }
  } catch {
    // oembed failed — carry on
  }
  return {};
}

export const youtubeProvider: RichContentProvider = {
  name: "youtube",

  matches(url: string): boolean {
    return (
      extractVideoId(url) !== null ||
      extractPlaylistId(url) !== null ||
      extractChannelPath(url) !== null
    );
  },

  async fetch(url: string): Promise<RichContent> {
    const videoId = extractVideoId(url);
    const listId = extractPlaylistId(url);
    const channelPath = extractChannelPath(url);

    // ── Channel ───────────────────────────────────────────────────────────────
    if (channelPath && !videoId) {
      // oEmbed doesn't support channel URLs — scrape og:image from the page instead
      let title: string | undefined;
      let thumbnailUrl: string | undefined;
      try {
        const res = await fetchWithTimeout(url);
        if (res.ok) {
          const html = await res.text();
          title = extractOgTag(html, "title");
          thumbnailUrl = extractOgTag(html, "image");
        }
      } catch {
        // scrape failed — carry on with undefined values
      }
      return {
        type: "youtube",
        siteName: "YouTube",
        url,
        title,
        thumbnailUrl,
        // channels are not embeddable as a player
      };
    }

    // ── Playlist (no specific video) ──────────────────────────────────────────
    if (listId && !videoId) {
      const { title, thumbnailUrl } = await fetchOEmbed(url);
      return {
        type: "youtube",
        siteName: "YouTube",
        url,
        title,
        thumbnailUrl,
        embedUrl:
          `https://www.youtube.com/embed/videoseries?list=${listId}&rel=0`,
      };
    }

    // ── Video (with optional playlist context) ────────────────────────────────
    const thumbnailUrl = `https://img.youtube.com/vi/${videoId}/hqdefault.jpg`;
    const { title } = await fetchOEmbed(url);

    const embedParams = new URLSearchParams({ rel: "0" });
    if (listId) embedParams.set("list", listId);
    const start = extractStartSeconds(url);
    if (start) embedParams.set("start", String(start));

    return {
      type: "youtube",
      siteName: "YouTube",
      url,
      videoId: videoId!,
      title,
      thumbnailUrl,
      embedUrl: `https://www.youtube.com/embed/${videoId}?${embedParams}`,
    };
  },
};