import { Marked } from "marked";
import type { Renderer, Token } from "marked";
import { markedHighlight } from "marked-highlight";
import hljs from "highlight.js";
import GithubSlugger from "github-slugger";
import DOMPurify from "isomorphic-dompurify";
import { applyAction, deserialize } from "$app/forms";

export const ALLOWED_MIME_TYPES = ["image/jpeg", "image/png", "image/svg+xml", "image/webp"];

const createMarkdownParser = (showToc = true) => {
  const marked = new Marked();

  marked.use({
    async: false,
    pedantic: false,
    gfm: true
  });

  marked.use(
    markedHighlight({
      async: false,
      langPrefix: "language-",
      highlight(code, lang) {
        const language = hljs.getLanguage(lang) ? lang : "plaintext";
        return hljs.highlight(code, { language }).value;
      }
    })
  );

  const unescapeTest = /&(#(?:\d+)|(?:#x[0-9A-Fa-f]+)|(?:\w+));?/gi;

  const unescape = (html: string) => {
    return html.replace(unescapeTest, (_, n) => {
      n = n.toLowerCase();
      if (n === "colon") return ":";
      if (n.charAt(0) === "#") {
        return n.charAt(1) === "x"
          ? String.fromCharCode(parseInt(n.substring(2), 16))
          : String.fromCharCode(+n.substring(1));
      }
      return "";
    });
  };

  let slugger = new GithubSlugger();
  let headings: { text: string; raw: string; level: number; id: string }[] = [];
  let sectionStack: { level: number; id: string }[] = [];

  const gfmHeadingId = ({ prefix = "", showToc = true } = {}) => {
    return {
      renderer: {
        heading(this: Renderer, { tokens, depth }: { tokens: Token[]; depth: number }) {
          const text = this.parser.parseInline(tokens);
          const raw = unescape(this.parser.parseInline(tokens, this.parser.textRenderer))
            .trim()
            .replace(/<[!a-z].*?>/gi, "");
          const level = depth;
          const id = `${prefix}${slugger.slug(raw.toLowerCase())}`;
          const heading = { level, text, id, raw };
          headings.push(heading);

          let closingSections = "";
          while (sectionStack.length > 0 && sectionStack[sectionStack.length - 1].level >= level) {
            sectionStack.pop();
            closingSections += "</section>";
          }

          sectionStack.push({ level, id });
          const openingSection = `<section id="${id}">`;

          return `
            ${closingSections}
            ${openingSection}
            <h${level}>
              <a href="#${id}">${text}</a>
            </h${level}>
          `;
        }
      },
      hooks: {
        preprocess(src: string) {
          headings = [];
          sectionStack = [];
          slugger = new GithubSlugger();

          return src;
        },
        postprocess(html: string) {
          const closingRemainingSection = "</section>".repeat(sectionStack.length);

          let tableOfContents = "";
          if (showToc && headings.length > 0) {
            const tocItems = [];
            let currentLevel = 0;

            for (const { id, text, level } of headings) {
              while (currentLevel < level - 1) {
                tocItems.push("<ul>");
                currentLevel++;
              }
              while (currentLevel > level - 1) {
                tocItems.push("</ul>");
                currentLevel--;
              }
              tocItems.push(`<li><a href="#${id}">${text}</a>`);
              if (level > currentLevel) {
                tocItems.push("<ul>");
                currentLevel = level;
              } else {
                tocItems.push("</li>");
              }
            }

            while (currentLevel > 0) {
              tocItems.push("</ul></li>");
              currentLevel--;
            }

            tableOfContents = `
              <section id="table-of-contents">
                <h2>
                  <a href="#table-of-contents">Table of contents</a>
                </h2>
                ${tocItems.join("")}
              </section>
            `;
          }

          return `
            ${tableOfContents}
            ${html}
            ${closingRemainingSection}
          `;
        }
      }
    };
  };

  marked.use(gfmHeadingId({ showToc: showToc }));

  return marked;
};

export const md = (markdownContent: string, showToc = true) => {
  const marked = createMarkdownParser(showToc);
  const html = DOMPurify.sanitize(marked.parse(markdownContent) as string);

  return html;
};

export const handleImagePaste = async (event: ClipboardEvent, API_BASE_PREFIX: string) => {
  const clipboardItems = Array.from(event.clipboardData?.items || []);
  const file = clipboardItems.find((item) => item.type.startsWith("image/"));

  if (!file) return null;

  event.preventDefault();

  const fileObject = file.getAsFile();

  if (!fileObject) return;

  const formData = new FormData();
  formData.append("file", fileObject);

  const request = await fetch("?/pasteImage", {
    method: "POST",
    body: formData
  });

  const result = deserialize(await request.clone().text());
  applyAction(result);

  const response = await request.json();

  if (JSON.parse(response.data)[1]) {
    const fileId = JSON.parse(response.data)[3];
    const fileUrl = `${API_BASE_PREFIX}/rpc/retrieve_file?id=${fileId}`;

    const target = event.target as HTMLTextAreaElement;
    const newContent =
      target.value.slice(0, target.selectionStart) +
      `![](${fileUrl})` +
      target.value.slice(target.selectionStart);

    return newContent;
  } else {
    return "";
  }
};