// Best-effort icon resolver for radio stations.
// Order:
//   1. Radio-Browser favicon by exact-ish name (only if station.source !== 'radiobrowser', else
//      we already have it).
//   2. Scrape <link rel="icon">, <link rel="apple-touch-icon">, <meta property="og:image">
//      from the homepage HTML.
//   3. HEAD-probe /favicon.ico at the homepage origin.
// Returns the best absolute URL found, or null.

const UA = 'OnlineRadioExplorer/0.1 (+icon-scraper)';
const FETCH_TIMEOUT_MS = 8000;
const MAX_HTML_BYTES = 256 * 1024;
const RB_BASE = 'https://de1.api.radio-browser.info';

function withTimeout(ms) {
    const ctl = new AbortController();
    const t = setTimeout(() => ctl.abort(), ms);
    return { signal: ctl.signal, done: () => clearTimeout(t) };
}

async function fetchText(url) {
    const t = withTimeout(FETCH_TIMEOUT_MS);
    try {
        const res = await fetch(url, {
            headers: { 'User-Agent': UA, 'Accept': 'text/html,application/xhtml+xml' },
            redirect: 'follow',
            signal: t.signal
        });
        if (!res.ok) return null;
        const reader = res.body?.getReader();
        if (!reader) return null;
        let received = 0;
        const chunks = [];
        while (true) {
            const { done, value } = await reader.read();
            if (done) break;
            received += value.length;
            chunks.push(value);
            if (received >= MAX_HTML_BYTES) { try { await reader.cancel(); } catch { } break; }
        }
        return Buffer.concat(chunks.map((c) => Buffer.from(c))).toString('utf8');
    } catch {
        return null;
    } finally { t.done(); }
}

async function head(url) {
    const t = withTimeout(FETCH_TIMEOUT_MS);
    try {
        const res = await fetch(url, { method: 'HEAD', headers: { 'User-Agent': UA }, signal: t.signal, redirect: 'follow' });
        return res.ok;
    } catch { return false; } finally { t.done(); }
}

function abs(base, href) {
    if (!href) return null;
    try { return new URL(href, base).toString(); } catch { return null; }
}

// Extract candidate icon URLs from raw HTML. Returns array of { href, size } sorted best-first.
function parseIconCandidates(html, baseUrl) {
    const out = [];
    // <link rel="...icon..." href="..." sizes="...">
    const linkRe = /<link\b([^>]*?)\/?>/gi;
    let m;
    while ((m = linkRe.exec(html))) {
        const attrs = m[1];
        const rel = (/\brel\s*=\s*["']([^"']+)["']/i.exec(attrs) || [])[1] || '';
        if (!/icon/i.test(rel)) continue;
        const href = (/\bhref\s*=\s*["']([^"']+)["']/i.exec(attrs) || [])[1];
        if (!href) continue;
        const sizes = (/\bsizes\s*=\s*["']([^"']+)["']/i.exec(attrs) || [])[1] || '';
        const sz = parseInt((/(\d+)x\d+/.exec(sizes) || [])[1] || '0', 10);
        const apple = /apple-touch-icon/i.test(rel) ? 64 : 0; // bias: apple-touch-icons usually larger PNGs
        const u = abs(baseUrl, href);
        if (u) out.push({ href: u, score: sz + apple });
    }
    // <meta property="og:image" content="...">
    const metaRe = /<meta\b([^>]*?)\/?>/gi;
    while ((m = metaRe.exec(html))) {
        const attrs = m[1];
        const prop = (/\b(?:property|name)\s*=\s*["']([^"']+)["']/i.exec(attrs) || [])[1] || '';
        if (!/^og:image|^twitter:image/i.test(prop)) continue;
        const content = (/\bcontent\s*=\s*["']([^"']+)["']/i.exec(attrs) || [])[1];
        const u = abs(baseUrl, content);
        if (u) out.push({ href: u, score: 200 }); // og:image preferred
    }
    out.sort((a, b) => b.score - a.score);
    // de-dupe preserving order
    const seen = new Set();
    return out.filter((c) => (seen.has(c.href) ? false : (seen.add(c.href), true)));
}

async function fromRadioBrowserByName(name) {
    if (!name) return null;
    try {
        const url = `${RB_BASE}/json/stations/search?name=${encodeURIComponent(name)}&limit=3&hidebroken=true&order=clickcount&reverse=true`;
        const t = withTimeout(FETCH_TIMEOUT_MS);
        const res = await fetch(url, { headers: { 'User-Agent': UA }, signal: t.signal });
        t.done();
        if (!res.ok) return null;
        const list = await res.json();
        const target = name.toLowerCase().trim();
        const exact = list.find((s) => (s.name || '').toLowerCase().trim() === target);
        const pick = exact || list[0];
        if (pick?.favicon) return pick.favicon;
    } catch { }
    return null;
}

async function fromHomepage(homepage) {
    if (!homepage) return null;
    let base;
    try { base = new URL(homepage); } catch { return null; }
    const html = await fetchText(base.toString());
    if (html) {
        const cands = parseIconCandidates(html, base.toString());
        for (const c of cands) {
            if (await head(c.href)) return c.href;
        }
    }
    // last resort: /favicon.ico
    const ico = `${base.origin}/favicon.ico`;
    if (await head(ico)) return ico;
    return null;
}

/**
 * Try to find an icon URL for a station.
 * @param {{ name?: string, homepage?: string|null, source?: string }} station
 * @returns {Promise<string|null>}
 */
export async function scrapeIcon(station) {
    if (!station) return null;
    // For non-RB stations, RB often still has an entry → cheap win.
    if (station.source !== 'radiobrowser') {
        const rb = await fromRadioBrowserByName(station.name);
        if (rb) return rb;
    }
    return fromHomepage(station.homepage);
}