import { highlightTextSegments, type TextHighlight } from "@/lib/guides/highlights";

const ALLOWED_TAGS = new Set([
  "a",
  "blockquote",
  "br",
  "code",
  "em",
  "li",
  "ol",
  "p",
  "pre",
  "s",
  "span",
  "strong",
  "u",
  "ul",
]);

const BLOCKED_CONTENT = /<(script|style|iframe|object|embed|svg|math|template)\b[^>]*>[\s\S]*?<\/\1\s*>/gi;
const HTML_COMMENT = /<!--[\s\S]*?-->/g;
const TAG = /<\/?([a-zA-Z][a-zA-Z0-9-]*)([^>]*)>/g;
const ATTRIBUTE = /([a-zA-Z_:][a-zA-Z0-9_:.-]*)\s*=\s*("[^"]*"|'[^']*'|[^\s"'=<>`]+)/g;
const HEX_COLOR = /^#[0-9a-fA-F]{6}$/;
const RGB_COLOR = /^rgb\(\s*(\d{1,3})\s*,\s*(\d{1,3})\s*,\s*(\d{1,3})\s*\)$/i;

function normalizeRichTextColor(value: string): string | null {
  const color = value.trim();
  if (HEX_COLOR.test(color)) return color.toUpperCase();

  const rgb = color.match(RGB_COLOR);
  if (!rgb) return null;
  const channels = rgb.slice(1).map(Number);
  if (channels.some((channel) => channel > 255)) return null;
  return `#${channels.map((channel) => channel.toString(16).padStart(2, "0")).join("")}`.toUpperCase();
}

export function sanitizeRichTextUrl(value: string): string {
  const url = value.trim();
  if (!url) return "";

  try {
    const parsed = new URL(url, "https://example.invalid");
    return ["http:", "https:", "mailto:"].includes(parsed.protocol) ? url : "";
  } catch {
    return "";
  }
}

function escapeAttribute(value: string): string {
  return value
    .replaceAll("&", "&amp;")
    .replaceAll('"', "&quot;")
    .replaceAll("<", "&lt;")
    .replaceAll(">", "&gt;");
}

function escapeHtml(value: string): string {
  return escapeAttribute(value).replaceAll("'", "&#39;");
}

function attributeValue(rawAttributes: string, name: string): string {
  for (const match of rawAttributes.matchAll(ATTRIBUTE)) {
    if (match[1].toLowerCase() === name) {
      return match[2].replace(/^['"]|['"]$/g, "");
    }
  }
  return "";
}

export function sanitizeRichTextHtml(value: string): string {
  return value
    .replace(BLOCKED_CONTENT, "")
    .replace(HTML_COMMENT, "")
    .replace(TAG, (tag, rawName: string, rawAttributes: string) => {
      const name = rawName.toLowerCase();
      if (!ALLOWED_TAGS.has(name)) return "";
      if (tag.startsWith("</")) return name === "br" ? "" : `</${name}>`;
      if (name === "br") return "<br>";

      if (name === "a") {
        const href = sanitizeRichTextUrl(attributeValue(rawAttributes, "href"));
        return href
          ? `<a href="${escapeAttribute(href)}" target="_blank" rel="noopener noreferrer">`
          : "<a>";
      }

      if (name === "span") {
        const style = attributeValue(rawAttributes, "style");
        const color = normalizeRichTextColor(
          style.match(/(?:^|;)\s*color\s*:\s*([^;]+?)\s*(?:;|$)/i)?.[1] ?? "",
        );
        return color
          ? `<span style="color: ${color}">`
          : "<span>";
      }

      return `<${name}>`;
    });
}

export function isRichTextHtml(value: string): boolean {
  return /<(?:p|br|strong|em|u|s|a|span|ul|ol|li|blockquote|pre|code)\b/i.test(value);
}

export function normalizeExtraRichText(
  body: string,
  highlights: readonly TextHighlight[] = [],
): string {
  if (isRichTextHtml(body)) return sanitizeRichTextHtml(body);

  const content = highlightTextSegments(body, highlights)
    .map((segment) => {
      const text = escapeHtml(segment.text).replaceAll("\n", "<br>");
      return segment.color && HEX_COLOR.test(segment.color)
        ? `<span style="color: ${segment.color.toUpperCase()}">${text}</span>`
        : text;
    })
    .join("");

  return content ? `<p>${content}</p>` : "";
}