/**
 * McFly SSR logic
 */

import { ELEMENT_NODE, parse, renderSync, walkSync } from "ultrahtml";
import { parseScript } from "esprima";

export default eventHandler(async (event) => {
  const { path } = event;
  let html = await getHtml(path);

  // transforms
  const transforms = [doSetUp, deleteServerScripts, insertRegistry];
  if (html) {
    for (const transform of transforms) {
      html = transform(html.toString());
    }
  }

  return html ?? new Response("Not found", { status: 404 });
});

const getHtml = async (path: string) => {
  const rawPath = path[path.length - 1] === "/" ? path.slice(0, -1) : path;
  const filename = rawPath === "" ? "/index.html" : `${rawPath}.html`;
  const fallback = getPath(rawPath + "/index.html");
  const filePath = getPath(filename);
  let html = await useStorage().getItem(filePath);
  if (!html) html = await useStorage().getItem(fallback);
  if (!html) html = await useStorage().getItem(getPath("/404.html"));

  return html;
};

function getPath(filename: string) {
  return `assets/pages${filename}`;
}

function insertRegistry(html: string): string {
  // temporary; use ultrahtml later
  const registryScript =
    '<script type="module" src="./.output/registry.js"></script>';

  const ast = parse(html);

  let hasCustomElements = false;

  walkSync(ast, (node) => {
    if (node.type === ELEMENT_NODE && node.name.includes("-")) {
      hasCustomElements = true;
    }
  });

  // insert registry script to head
  if (hasCustomElements)
    walkSync(ast, (node) => {
      if (node.type === ELEMENT_NODE && node.name === "head") {
        node.children.push(parse(registryScript));
      }
    });

  return renderSync(ast);
}

function doSetUp(html: string) {
  const ast = parse(html);
  const serverScripts = [];
  walkSync(ast, (node) => {
    const { attributes } = node;
    const attributeKeys = Object.keys(attributes ?? {});
    const isServerScript = attributeKeys.some((key) => key.includes("server:"));
    if (
      node.type === ELEMENT_NODE &&
      node.name === "script" &&
      isServerScript
    ) {
      const scripts = node.children.map((child) => child.value);
      const script = cleanScript(scripts);
      serverScripts.push(script);
    }
  });

  const setupMap = {};
  serverScripts.forEach((script: string) => {
    const { body } = parseScript(script);
    const keys = body
      .filter((node) => node.type === "VariableDeclaration")
      .map((node) => node.declarations[0].id.name);
    const constructor = `(function(){}.constructor)(\`${script}; return {${keys.join(
      ","
    )}}\`);`;
    const evalStore = eval(constructor);
    Object.assign(setupMap, new evalStore());
  });

  const regex = /{{(.*?)}}/g;
  var match;

  while ((match = regex.exec(html))) {
    let [key, value] = match;
    value = value.replace(/\s/g, "");
    html = html.replace(key, setupMap[value]);
  }

  return html;
}

function deleteServerScripts(html: string): string {
  const ast = parse(html);
  walkSync(ast, (node) => {
    const { attributes } = node;
    const attributeKeys = Object.keys(attributes ?? {});
    const isServerScript = attributeKeys.some((key) => key.includes("server:"));
    if (isServerScript) {
      node.parent.children.splice(node.parent.children.indexOf(node), 1);
    }
  });

  return renderSync(ast);
}

function cleanScript(scripts: string[]): string {
  let script = scripts.map((s) => s.trim()).join(" ");

  script = removeComments(script);

  return script.replace(/\n/g, "").replace(/\s+/g, " ");
}

function isComment(node) {
  return (
    node.type === "Line" ||
    node.type === "Block" ||
    node.type === "BlockComment" ||
    node.type === "LineComment"
  );
}

function removeComments(script: string) {
  const entries = [];
  parseScript(script, { comment: true }, function (node, meta) {
    if (isComment(node)) {
      entries.push({
        start: meta.start.offset,
        end: meta.end.offset,
      });
    }
  });

  entries
    .sort((a, b) => {
      return b.end - a.end;
    })
    .forEach((n) => {
      script = script.slice(0, n.start) + script.slice(n.end);
    });
  return script;
}