import fs from 'node:fs/promises';
import path from 'node:path';

const GLOB_CHARS = /[*?]/;
const DOCS_FILE = /\.mdx?$/i;
const REGEX_SPECIAL = /[.+^${}()|\\[\]]/;
const SKIPPED_DIRS = new Set(['.git', 'node_modules']);

function toPosix(filePath: string): string {
  return filePath.split(path.sep).join('/');
}

function normalizeArg(arg: string): string {
  return toPosix(arg).replace(/^\.\//, '');
}

function globToRegExp(pattern: string): RegExp {
  let source = '';
  let i = 0;
  while (i < pattern.length) {
    const char = pattern[i]!;
    if (char === '*') {
      if (pattern[i + 1] === '*') {
        if (pattern[i + 2] === '/') {
          source += '(?:[^/]+/)*';
          i += 3;
        } else {
          source += '.*';
          i += 2;
        }
      } else {
        source += '[^/]*';
        i += 1;
      }
    } else if (char === '?') {
      source += '[^/]';
      i += 1;
    } else {
      source += REGEX_SPECIAL.test(char) ? `\\${char}` : char;
      i += 1;
    }
  }
  return new RegExp(`^${source}$`);
}

async function isFile(filePath: string): Promise<boolean> {
  try {
    return (await fs.stat(filePath)).isFile();
  } catch {
    return false;
  }
}

async function walk(baseDir: string, dir = ''): Promise<string[]> {
  const entries = await fs.readdir(path.join(baseDir, dir), { withFileTypes: true });
  const files: string[] = [];
  for (const entry of entries) {
    if (SKIPPED_DIRS.has(entry.name)) continue;
    const rel = dir ? `${dir}/${entry.name}` : entry.name;
    if (entry.isDirectory()) {
      files.push(...(await walk(baseDir, rel)));
    } else {
      files.push(rel);
    }
  }
  return files;
}

export async function resolveExplicitFiles(baseDir: string, args: string[]): Promise<string[]> {
  let allFiles: string[] | null = null;
  const matched: string[] = [];
  const unmatched: string[] = [];

  for (const arg of args) {
    const pattern = normalizeArg(arg);
    if (GLOB_CHARS.test(pattern)) {
      allFiles = allFiles ?? (await walk(baseDir));
      const regex = globToRegExp(pattern);
      const hits = allFiles.filter((file) => DOCS_FILE.test(file) && regex.test(file)).sort();
      if (hits.length === 0) {
        unmatched.push(arg);
      } else {
        matched.push(...hits);
      }
    } else if (await isFile(path.join(baseDir, pattern))) {
      matched.push(pattern);
    } else {
      unmatched.push(arg);
    }
  }

  if (unmatched.length > 0) {
    throw new Error(
      `No matching files for: ${unmatched.join(', ')} (globs match .md and .mdx files)`
    );
  }

  return [...new Set(matched)];
}