import { Readability } from "@mozilla/readability";
import { parseHTML } from "linkedom";
import TurndownService from "turndown";

export interface MarkdownExtraction {
  title: string;
  markdown: string;
}

const REMOVE_SELECTORS = [
  "script",
  "style",
  "iframe",
  "frame",
  "object",
  "embed",
  "form",
  "input",
  "button",
  "select",
  "textarea",
  "template",
  "noscript",
].join(",");

function safeAbsoluteUrl(value: string, baseUrl: string, allowFragment: boolean): string | undefined {
  const trimmed = value.trim();
  if (!trimmed) return undefined;
  if (allowFragment && trimmed.startsWith("#")) return trimmed;
  try {
    const resolved = new URL(trimmed, baseUrl);
    if (resolved.protocol === "http:" || resolved.protocol === "https:") return resolved.toString();
    if (allowFragment && resolved.protocol === "mailto:") return resolved.toString();
  } catch {
    // Invalid links are removed below.
  }
  return undefined;
}

function sanitizeDocument(document: Document, baseUrl: string): void {
  for (const node of Array.from(document.querySelectorAll(REMOVE_SELECTORS))) node.remove();
  for (const element of Array.from(document.querySelectorAll("*"))) {
    for (const attribute of Array.from(element.attributes)) {
      const name = attribute.name.toLowerCase();
      if (name.startsWith("on") || name === "srcdoc") element.removeAttribute(attribute.name);
    }
  }

  for (const element of Array.from(document.querySelectorAll("a[href], area[href]"))) {
    const value = element.getAttribute("href");
    const safe = value ? safeAbsoluteUrl(value, baseUrl, true) : undefined;
    if (safe) element.setAttribute("href", safe);
    else element.removeAttribute("href");
  }
  for (const element of Array.from(document.querySelectorAll("img[src], source[src], video[src], audio[src]"))) {
    const value = element.getAttribute("src");
    const safe = value ? safeAbsoluteUrl(value, baseUrl, false) : undefined;
    if (safe) element.setAttribute("src", safe);
    else element.removeAttribute("src");
  }
  for (const element of Array.from(document.querySelectorAll("img[srcset], source[srcset]"))) {
    const srcset = element.getAttribute("srcset") ?? "";
    const rewritten = srcset
      .split(",")
      .map((candidate: string) => candidate.trim())
      .filter(Boolean)
      .flatMap((candidate: string) => {
        const [rawUrl, ...descriptor] = candidate.split(/\s+/);
        const safe = rawUrl ? safeAbsoluteUrl(rawUrl, baseUrl, false) : undefined;
        return safe ? [`${safe}${descriptor.length > 0 ? ` ${descriptor.join(" ")}` : ""}`] : [];
      });
    if (rewritten.length > 0) element.setAttribute("srcset", rewritten.join(", "));
    else element.removeAttribute("srcset");
  }
}

function cleanTitle(value: string | null | undefined, fallback: string): string {
  const title = value?.replace(/\s+/g, " ").trim();
  return title || fallback;
}

function titleFromUrl(url: string): string {
  const parsed = new URL(url);
  return parsed.pathname.split("/").filter(Boolean).at(-1) || parsed.hostname;
}

function normalizeMarkdown(markdown: string): string {
  return markdown
    .replace(/\u00a0/g, " ")
    .replace(/[ \t]+$/gm, "")
    .replace(/\n{4,}/g, "\n\n\n")
    .trim();
}

export function extractMarkdownFromHtml(html: string, finalUrl: string): MarkdownExtraction {
  const parsed = parseHTML(html);
  const document = parsed.document as unknown as Document;
  sanitizeDocument(document, finalUrl);

  const documentTitle = cleanTitle(document.querySelector("title")?.textContent, titleFromUrl(finalUrl));
  const article = new Readability(document).parse();
  const title = cleanTitle(article?.title, documentTitle);
  const contentHtml = article?.content || document.body?.innerHTML || document.documentElement?.innerHTML || "";

  const articleDocument = parseHTML(`<article>${contentHtml}</article>`).document as unknown as Document;
  sanitizeDocument(articleDocument, finalUrl);
  const turndown = new TurndownService({
    headingStyle: "atx",
    codeBlockStyle: "fenced",
    bulletListMarker: "-",
    emDelimiter: "*",
    strongDelimiter: "**",
  });
  turndown.remove(["script", "style", "iframe", "object", "embed", "form"]);
  const body = articleDocument.querySelector("article")?.innerHTML ?? contentHtml;
  let markdown = normalizeMarkdown(turndown.turndown(body));
  if (!markdown) markdown = title;
  if (!/^#\s+/m.test(markdown)) markdown = `# ${title}\n\n${markdown}`;
  return { title, markdown };
}

export function markdownFromPlainText(text: string, finalUrl: string): MarkdownExtraction {
  const title = titleFromUrl(finalUrl);
  const markdown = normalizeMarkdown(text);
  return { title, markdown: /^#\s+/m.test(markdown) ? markdown : `# ${title}\n\n${markdown}` };
}