import { readFileSync, existsSync } from "fs";
// TODO import.meta.resolve is supposed to accomplish this without "path"
import path from "path";
import { stringify, parse } from "css";

const internal = (file) =>
  path.resolve(path.dirname(new URL(import.meta.url).pathname), file);

export function style(options) {
  if (options.inline || options.css === "none") return "";

  const rules = load(options);
  const schemes = rules.find(({ media }) => media)
    ? `<meta name="color-scheme" content="dark light">`
    : "";
  return `\n${schemes}\n<style>${stringify(
    {
      stylesheet: { rules: reduceVariables(rules, options) },
    },
    { compress: true }
  )}</style>`;
}

export function inline(options) {
  const rules = load(options);
  return function inlineCSS(tag) {
    if (options.css === "none" || !(options.inline || options.body)) return "";

    const styles = reduceVariables(rules, options)
      .filter(({ selectors }) => selectors && selectors.includes(tag))
      .reduce((style, { declarations }) => {
        declarations.forEach(({ property, value }) => {
          style = `${style}${property}:${value};`;
        });
        return style;
      }, "");
    return styles !== "" ? ` style="${styles}"` : "";
  };
}

export function load(options) {
  if (options.css === "none") return [];
  options.css = options.css
    ? options.css
    : options.body
    ? "gmi.css"
    : "gmi-web.css";

  if (
    !["gmi.css", "gmi-web.css"].includes(options.css) &&
    !existsSync(options.css)
  )
    throw new Error(`Cannot find file ${options.css}.`);

  return parse(
    readFileSync(
      path.resolve(
        ["gmi-web.css", "gmi.css"].includes(options.css)
          ? internal(options.css)
          : resolve(options.css)
      ),
      "utf-8"
    )
  ).stylesheet.rules;
}

export function rootVariables(rules) {
  const root = rules.find(
    ({ selectors }) => selectors && selectors.includes(":root")
  );
  if (!root) return {};
  return root.declarations.reduce(
    (obj, { property, value }) =>
      !/^\-\-/.test(property)
        ? obj
        : Object.assign(obj, { [property.replace("--", "")]: value }),
    {}
  );
}

function reduceVariables(rules, options = {}) {
  const defaultVariables = rootVariables(rules);
  const CSS_VAR = /(^var\(\-\-(?<key>.+)\)|(?<val>.+))/;
  const reduce = (rule) =>
    Object.assign(
      rule,
      rule.declarations
        ? {
            declarations: rule.declarations.map((declaration) => {
              let { key, val } = CSS_VAR.exec(declaration.value).groups;
              // only one level of variable referencing is supported
              key =
                CSS_VAR.exec(options[key] || defaultVariables[key]).groups
                  .key || key;
              return Object.assign(declaration, {
                value: key
                  ? options[key] || defaultVariables[key]
                  : declaration.value,
              });
            }),
          }
        : {}
    );
  return rules
    .map(reduce)
    .map((rule) => {
      if (!rule.media) return rule;
      return Object.assign(rule, {
        rules: rule.rules.map(reduce),
      });
    })
    .filter(
      ({ selectors, media }) =>
        media || (selectors && !selectors.includes(":root"))
    );
}