function decodeHtmlEntities(str: string): string {
  return str
    .replace(/&/gi, "&")
    .replace(/&lt;/gi, "<")
    .replace(/&gt;/gi, ">")
    .replace(/&quot;/gi, '"')
    .replace(/&apos;/gi, "'")
    .replace(/&#(\d+);/g, (_, dec) => String.fromCodePoint(Number(dec)))
    .replace(
      /&#x([0-9a-f]+);/gi,
      (_, hex) => String.fromCodePoint(parseInt(hex, 16)),
    );
}

/**
 * Find the first `<meta>` tag whose `attr` equals `value` and return its
 * `content` (either attribute ordering). Each tag is matched in isolation so
 * the `content` capture can never span across tag boundaries.
 */
function extractMetaContent(
  html: string,
  attr: string,
  value: string,
): string | undefined {
  const escaped = value.replace(/[.*+?^${}()|[\]\\]/g, "\\$&");
  const keyRe = new RegExp(`\\b${attr}=["']${escaped}["']`, "i");
  const contentRe = /\bcontent=(["'])([\s\S]*?)\1/i;
  const tagRe = /<meta\b[^>]*>/gi;
  let m: RegExpExecArray | null;
  while ((m = tagRe.exec(html)) !== null) {
    const tag = m[0];
    if (!keyRe.test(tag)) continue;
    const content = contentRe.exec(tag);
    if (content) return decodeHtmlEntities(content[2]);
  }
  return undefined;
}

export function extractOgTag(
  html: string,
  tag: string,
): string | undefined {
  return extractMetaContent(html, "property", `og:${tag}`);
}

/** Extract content from `<meta name="…" content="…">` (both attribute orderings). */
export function extractMetaName(
  html: string,
  name: string,
): string | undefined {
  return extractMetaContent(html, "name", name);
}

/** Extract the text content of the `<title>` element. */
export function extractPageTitle(html: string): string | undefined {
  const match = html.match(/<title[^>]*>([^<]+)<\/title>/i);
  return match ? decodeHtmlEntities(match[1].trim()) : undefined;
}

// ── Brand color helpers ───────────────────────────────────────────────────────

/**
 * Find the page's `theme-color`.
 *
 * Sites routinely ship the tag twice, scoped by `media`, and often list the
 * dark-scheme one first — so unlike `extractMetaName` this can't just take the
 * first match. Prefer the unscoped tag, then the light-scheme one, then any.
 */
export function extractThemeColor(html: string): string | undefined {
  const tagRe = /<meta\b[^>]*>/gi;
  const contentRe = /\bcontent=(["'])([\s\S]*?)\1/i;
  const mediaRe = /\bmedia=(["'])([\s\S]*?)\1/i;
  let unscoped: string | undefined;
  let light: string | undefined;
  let any: string | undefined;

  let m: RegExpExecArray | null;
  while ((m = tagRe.exec(html)) !== null) {
    const tag = m[0];
    if (!/\bname=["']theme-color["']/i.test(tag)) continue;
    const content = contentRe.exec(tag)?.[2];
    if (!content) continue;
    const media = mediaRe.exec(tag)?.[2];
    if (!media) unscoped ??= content;
    else if (/light/i.test(media)) light ??= content;
    any ??= content;
  }
  return unscoped ?? light ?? any;
}

/** Extract the `color` of `<link rel="mask-icon">` (Safari pinned tabs). */
export function extractMaskIconColor(html: string): string | undefined {
  const linkRe = /<link[^>]+>/gi;
  let m: RegExpExecArray | null;
  while ((m = linkRe.exec(html)) !== null) {
    const tag = m[0];
    if (!/\brel=["'][^"']*mask-icon[^"']*["']/i.test(tag)) continue;
    const color = /\bcolor=(["'])([\s\S]*?)\1/i.exec(tag)?.[2];
    if (color) return color;
  }
  return undefined;
}

// The handful of named colors that actually show up in `theme-color`. The full
// 148-name table isn't worth carrying for the long tail.
const NAMED_COLORS: Record<string, string> = {
  black: "#000000",
  white: "#ffffff",
  red: "#ff0000",
  green: "#008000",
  blue: "#0000ff",
  yellow: "#ffff00",
  orange: "#ffa500",
  purple: "#800080",
  gray: "#808080",
  grey: "#808080",
  silver: "#c0c0c0",
  maroon: "#800000",
  navy: "#000080",
  teal: "#008080",
  olive: "#808000",
  lime: "#00ff00",
  aqua: "#00ffff",
  cyan: "#00ffff",
  fuchsia: "#ff00ff",
  magenta: "#ff00ff",
};

function clampByte(n: number): number {
  return Math.max(0, Math.min(255, Math.round(n)));
}

/**
 * Normalize a CSS color to canonical lowercase `#rrggbb`, or `undefined` when
 * it isn't one of the forms sites actually use. Alpha is dropped — the color is
 * only ever used as a tint over the app's own surface.
 */
export function normalizeCssColor(raw: string | undefined): string | undefined {
  if (!raw) return undefined;
  const value = raw.trim().toLowerCase();

  const named = NAMED_COLORS[value];
  if (named) return named;

  const hex = /^#([0-9a-f]{3,8})$/.exec(value)?.[1];
  if (hex) {
    if (hex.length === 3 || hex.length === 4) {
      const [r, g, b] = [...hex.slice(0, 3)];
      return `#${r}${r}${g}${g}${b}${b}`;
    }
    if (hex.length === 6 || hex.length === 8) return `#${hex.slice(0, 6)}`;
    return undefined;
  }

  const rgb = /^rgba?\(([^)]+)\)$/.exec(value)?.[1];
  if (rgb) {
    const parts = rgb.split(/[\s,/]+/).filter(Boolean).slice(0, 3);
    if (parts.length !== 3) return undefined;
    const bytes = parts.map((p) => {
      const n = parseFloat(p);
      if (!Number.isFinite(n)) return NaN;
      return clampByte(p.endsWith("%") ? (n / 100) * 255 : n);
    });
    if (bytes.some(Number.isNaN)) return undefined;
    return `#${bytes.map((b) => b.toString(16).padStart(2, "0")).join("")}`;
  }

  return undefined;
}

// ── JSON-LD helpers (file-private) ────────────────────────────────────────────

type JsonLdResult = {
  title?: string;
  description?: string;
  thumbnailUrl?: string;
};

function ldString(v: unknown): string | undefined {
  if (typeof v === "string" && v.trim()) return v.trim();
  if (Array.isArray(v) && typeof v[0] === "string" && v[0].trim()) {
    return v[0].trim();
  }
  return undefined;
}

function ldImage(v: unknown): string | undefined {
  if (
    typeof v === "string" &&
    (v.startsWith("http://") || v.startsWith("https://"))
  ) return v;
  if (Array.isArray(v)) return ldImage(v[0]);
  if (v && typeof v === "object") {
    const o = v as Record<string, unknown>;
    return ldImage(o.url ?? o.contentUrl);
  }
  return undefined;
}

function ldExtractNode(data: unknown): JsonLdResult {
  if (Array.isArray(data)) {
    for (const item of data) {
      const r = ldExtractNode(item);
      if (r.title || r.thumbnailUrl) return r;
    }
    return {};
  }
  if (!data || typeof data !== "object") return {};
  const o = data as Record<string, unknown>;
  if (o["@graph"]) return ldExtractNode(o["@graph"]);
  return {
    title: ldString(o.name ?? o.headline),
    description: ldString(o.description),
    thumbnailUrl: ldImage(o.image ?? o.thumbnailUrl ?? o.thumbnail),
  };
}

/**
 * Parse every `<script type="application/ld+json">` block and return the first
 * node that yields a title or image. Handles `@graph`, arrays, and the common
 * `image` shapes (string, string[], ImageObject).
 */
export function extractJsonLd(html: string): JsonLdResult {
  const pattern =
    /<script[^>]+type=["']application\/ld\+json["'][^>]*>([\s\S]*?)<\/script>/gi;
  let match: RegExpExecArray | null;
  while ((match = pattern.exec(html)) !== null) {
    try {
      const result = ldExtractNode(JSON.parse(match[1]));
      if (result.title || result.thumbnailUrl) return result;
    } catch { /* invalid JSON — skip */ }
  }
  return {};
}

/**
 * Return the `src` of the first `<img>` whose declared width or height is at
 * least `minSize` pixels (default 200). Skips data URIs. Resolves relative URLs.
 */
export function extractLargeImage(
  html: string,
  baseUrl: string,
  minSize = 200,
): string | undefined {
  const imgPattern = /<img[^>]+>/gi;
  let match: RegExpExecArray | null;
  while ((match = imgPattern.exec(html)) !== null) {
    const tag = match[0];
    const src = /\bsrc=["']([^"']+)["']/i.exec(tag)?.[1];
    if (!src || src.startsWith("data:")) continue;
    const w = parseInt(/\bwidth=["']?(\d+)/i.exec(tag)?.[1] ?? "0");
    const h = parseInt(/\bheight=["']?(\d+)/i.exec(tag)?.[1] ?? "0");
    if (w >= minSize && h >= minSize) {
      try {
        return new URL(src, baseUrl).toString();
      } catch {
        continue;
      }
    }
  }
  return undefined;
}

/**
 * Collect all `<link rel="icon">` / `<link rel="apple-touch-icon">` tags, rank
 * them by declared size (largest wins), and return the best resolved URL.
 * Falls back to the first match when no `sizes` attribute is present.
 *
 * SVG icons are ranked above everything: they carry no `sizes` attribute, so
 * they'd otherwise score 0 and lose to a 16×16 PNG, yet they scale cleanly to
 * whatever size the placeholder renders them at.
 */
export function extractBestIcon(
  html: string,
  baseUrl: string,
): string | undefined {
  const linkRe = /<link[^>]+>/gi;
  const relRe = /\brel=["']([^"']+)["']/i;
  const hrefRe = /\bhref=["']([^"']+)["']/i;
  const sizesRe = /\bsizes=["']([^"']+)["']/i;

  const candidates: { href: string; area: number }[] = [];

  let m: RegExpExecArray | null;
  while ((m = linkRe.exec(html)) !== null) {
    const tag = m[0];
    const rel = relRe.exec(tag)?.[1] ?? "";
    if (!/\bicon\b/i.test(rel) && !/apple-touch-icon/i.test(rel)) continue;
    const href = hrefRe.exec(tag)?.[1];
    if (!href) continue;
    const sizesStr = sizesRe.exec(tag)?.[1] ?? "";
    const sm = sizesStr.match(/(\d+)x(\d+)/i);
    const isSvg = /\.svg(\?|$)/i.test(href) ||
      /\btype=["']image\/svg\+xml["']/i.test(tag);
    const area = isSvg
      ? Number.MAX_SAFE_INTEGER
      : sm
      ? parseInt(sm[1]) * parseInt(sm[2])
      : 0;
    try {
      candidates.push({ href: new URL(href, baseUrl).toString(), area });
    } catch {
      continue;
    }
  }

  if (candidates.length === 0) return undefined;
  candidates.sort((a, b) => b.area - a.area);
  return candidates[0].href;
}

/**
 * Return the `src` of the first `<img>` that looks like content rather than UI
 * chrome. Skips SVGs, data URIs, and images whose filename matches common
 * icon/logo/nav patterns (logo, icon, sprite, favicon, avatar, banner, etc.).
 * Resolves relative and protocol-relative URLs.
 */
const UI_IMAGE_KEYWORDS = new Set([
  "logo",
  "icon",
  "sprite",
  "favicon",
  "avatar",
  "banner",
  "header",
  "nav",
  "menu",
  "cart",
  "search",
  "tracking",
  "pixel",
  "bg",
  "background",
]);

function isUiImage(src: string): boolean {
  if (/\.svg(\?|$)/i.test(src)) return true;
  const filename = src.split("?")[0].split("/").pop() ?? "";
  const baseName = filename.replace(/\.[^.]+$/, ""); // strip extension
  // Split on common filename separators (-, _, .) and check each token
  return baseName.toLowerCase().split(/[-_.]/).some((t) =>
    UI_IMAGE_KEYWORDS.has(t)
  );
}

/**
 * Return the `src` of the first `<img>` that looks like content rather than UI
 * chrome. Skips SVGs, data URIs, and images whose filename tokens match common
 * icon/logo/nav patterns (logo, icon, sprite, etc.).
 * Resolves relative and protocol-relative URLs.
 */
export function extractFirstContentImage(
  html: string,
  baseUrl: string,
): string | undefined {
  const imgPattern = /<img[^>]+>/gi;
  let match: RegExpExecArray | null;
  while ((match = imgPattern.exec(html)) !== null) {
    const tag = match[0];
    const src = /\bsrc=["']([^"']+)["']/i.exec(tag)?.[1];
    if (!src || src.startsWith("data:")) continue;
    if (isUiImage(src)) continue;
    try {
      return new URL(src, baseUrl).toString();
    } catch {
      continue;
    }
  }
  return undefined;
}

/**
 * Extract `href` from the first `<link rel="…">` whose rel contains `relFragment`,
 * resolved to an absolute URL using `baseUrl`.
 */
export function extractLinkHref(
  html: string,
  relFragment: string,
  baseUrl: string,
): string | undefined {
  const escaped = relFragment.replace(/[.*+?^${}()|[\]\\]/g, "\\$&");
  const patterns = [
    new RegExp(
      `<link[^>]+rel=["'][^"']*${escaped}[^"']*["'][^>]+href=["']([^"']+)["']`,
      "i",
    ),
    new RegExp(
      `<link[^>]+href=["']([^"']+)["'][^>]+rel=["'][^"']*${escaped}[^"']*["']`,
      "i",
    ),
  ];
  for (const pattern of patterns) {
    const match = html.match(pattern);
    if (match) {
      try {
        return new URL(match[1], baseUrl).toString();
      } catch {
        return undefined;
      }
    }
  }
  return undefined;
}