import { existsSync, readdirSync, readFileSync, unlinkSync, watch, writeFileSync } from 'node:fs';
import path from 'node:path';
import postcss from 'postcss';
import * as sass from 'sass';

const packageDirectory = path.join(__dirname, '..');
const sourceDirectory = path.join(packageDirectory, 'src');
const loadPaths = [sourceDirectory, path.join(packageDirectory, '../../node_modules/include-media/dist')];
const compiler = sass.initCompiler();

generateAll();

if (process.argv.includes('--watch')) {
  watchModuleStylesheets();
} else {
  compiler.dispose();
}

function generateAll() {
  const files = findModuleStylesheets();

  for (const file of files) {
    generate(file);
  }

  console.log(`Generated type definitions for ${files.length} .module.scss files`);
}

function findModuleStylesheets(): string[] {
  return readdirSync(sourceDirectory, { encoding: 'utf8', recursive: true })
    .filter((file) => file.endsWith('.module.scss'))
    .sort()
    .map((file) => path.join(sourceDirectory, file));
}

function watchModuleStylesheets() {
  console.log(`Watching ${sourceDirectory} for .module.scss changes`);

  watch(sourceDirectory, { recursive: true }, (_event, filename) => {
    if (!filename || !filename.endsWith('.module.scss')) {
      return;
    }

    const file = path.join(sourceDirectory, filename);

    try {
      if (existsSync(file)) {
        generate(file);
      } else if (existsSync(getTypesFilepath(file))) {
        unlinkSync(getTypesFilepath(file));
      }
    } catch (error) {
      console.error(String(error));
    }
  });
}

function generate(file: string) {
  const { css } = compiler.compile(file, { loadPaths, quietDeps: true });
  const content = formatTypesFile(extractClassNames(css));
  const typesFilepath = getTypesFilepath(file);

  if (!existsSync(typesFilepath) || readFileSync(typesFilepath, 'utf8') !== content) {
    writeFileSync(typesFilepath, content);
    console.log(`Generated ${path.relative(packageDirectory, typesFilepath)}`);
  }
}

function extractClassNames(css: string): string[] {
  const classNames = new Set<string>();
  const stylesheet = postcss.parse(css);

  stylesheet.walkAtRules('keyframes', (atRule) => {
    classNames.add(atRule.params);
  });

  stylesheet.walkRules((rule) => {
    if (rule.selector === ':export') {
      rule.walkDecls((declaration) => {
        classNames.add(declaration.prop);
      });
    } else {
      const localSelector = rule.selector.replace(/:global\([^)]*\)/g, '');

      for (const [, className] of localSelector.matchAll(/\.(-?[A-Za-z_][\w-]*)/g)) {
        classNames.add(className);
      }
    }
  });

  return [...classNames].sort();
}

function formatTypesFile(classNames: string[]): string {
  return [
    '// Generated by scripts/generate-scss-types.ts - do not edit.',
    'declare const styles: {',
    ...classNames.map((className) => `  readonly ${formatKey(className)}: string;`),
    '};',
    '',
    'export default styles;',
    '',
  ].join('\n');
}

function formatKey(className: string): string {
  return /^[A-Za-z_$][\w$]*$/.test(className) ? className : `'${className}'`;
}

function getTypesFilepath(file: string): string {
  return `${file}.d.ts`;
}