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import { type BunPlugin, plugin } from "bun";
import type * as esbuild from "esbuild";
import type * as Hast from "hast";
import type * as Mdast from "mdast";

import { common, createStarryNight } from "@wooorm/starry-night";

export interface OutlineItem {
  id: string;
  content: string;
  level: number;
  children: OutlineItem[];
}

// StarryNight crashes when tries to create an instance other than top-level.
// maybe its hack or WASM (Oniguruma) related bug.
const starryNight = await createStarryNight(common);

export const markdownPlugin = {
  name: "Markdown loader",
  async setup(build) {
    const { file } = await import("bun");

    const { fromMarkdown } = await import("mdast-util-from-markdown");
    const { toHast, defaultHandlers } = await import("mdast-util-to-hast");
    const { toString: mdastToString } = await import("mdast-util-to-string");
    const { raw } = await import("hast-util-raw");
    const { toHtml } = await import("hast-util-to-html");
    const { find } = await import("unist-util-find");
    const { toString: hastToString } = await import("hast-util-to-string");

    build.onLoad({ filter: /\.md$/ }, async ({ path }) => {
      const mdast = fromMarkdown(await file(path).text());

      const outline: OutlineItem[] = [];
      const outlineStack: OutlineItem[] = [];

      const hast = raw(
        toHast(mdast, {
          // The function cannot properly handle CommonMark without this stupid option
          allowDangerousHtml: true,
          handlers: {
            heading(state, node: Mdast.Heading) {
              const text = mdastToString(node);

              const id = encodeURIComponent(
                text.replace(/[ ,.]/g, "_").toLowerCase(),
              );

              while (
                outlineStack[outlineStack.length - 1] &&
                outlineStack[outlineStack.length - 1].level >= node.depth
              ) {
                const removed = outlineStack.pop()!;

                const parent = outlineStack[outlineStack.length - 1];
                if (!parent) {
                  outline.push(removed);
                  break;
                }

                parent.children.push(removed);
              }

              outlineStack.push({
                id,
                content: text,
                level: node.depth,
                children: [],
              });

              const before = defaultHandlers.heading(state, node);

              const after: Hast.Element = {
                type: "element",
                tagName: before.tagName,
                properties: { id },
                children: [
                  {
                    type: "element",
                    tagName: "a",
                    properties: { href: `#${id}` },
                    children: before.children,
                  },
                ],
              };

              state.patch(node, after);

              return after;
            },
            code(state, node: Mdast.Code) {
              const value = node.value ? node.value + "\n" : "";
              const scope = node.lang
                ? starryNight.flagToScope(node.lang)
                : null;

              const children: Hast.ElementContent[] = scope
                ? starryNight
                    .highlight(value, scope)
                    .children.filter(
                      (child): child is Hast.ElementContent =>
                        child.type === "element" ||
                        child.type === "text" ||
                        child.type === "raw",
                    )
                : [
                    {
                      type: "text",
                      value,
                    },
                  ];

              const code: Hast.Element = {
                type: "element",
                tagName: "code",
                properties: {},
                children,
                data: node.meta ? { meta: node.meta } : {},
              };

              state.patch(node, code);

              const pre: Hast.Element = {
                type: "element",
                tagName: "pre",
                properties: {},
                children: [state.applyData(node, code)],
              };

              state.patch(node, pre);

              return pre;
            },
          },
        }),
      );

      while (outlineStack.length > 0) {
        const removed = outlineStack.pop()!;
        const parent = outlineStack[outlineStack.length - 1];

        if (!parent) {
          outline.push(removed);
          break;
        }

        parent.children.push(removed);
      }

      const h1 = find(
        hast,
        // @ts-expect-error: unist-util-find has broken type definition
        (node) => node.type === "element" && node.tagName === "h1",
      );

      // @ts-expect-error: unist-util-find has broken type definition
      const title = h1 ? hastToString(h1) : null;

      const html = toHtml(hast);

      return {
        loader: "js",
        contents:
          "export default " +
          JSON.stringify(html) +
          "; export const title = " +
          JSON.stringify(title) +
          "; export const outline = " +
          JSON.stringify(outline),
      };
    });
  },
} satisfies BunPlugin & esbuild.Plugin;

await plugin(markdownPlugin);