// file-discovery.mjs — Walk directory tree, filter, binary detection
// Zero dependencies (Node.js builtins only).

import { readdir, stat, readFile } from 'node:fs/promises';
import { join, relative, extname } from 'node:path';

// Extensions we scan (text-based)
const TEXT_EXTENSIONS = new Set([
  '.js', '.mjs', '.cjs', '.ts', '.mts', '.cts', '.jsx', '.tsx',
  '.py', '.pyw',
  '.json', '.jsonc', '.json5',
  '.yaml', '.yml',
  '.toml',
  '.md', '.mdx',
  '.sh', '.bash', '.zsh',
  '.env', '.env.local', '.env.example',
  '.cfg', '.ini', '.conf',
  '.xml', '.html', '.htm', '.svg',
  '.css', '.scss', '.sass', '.less',
  '.glsl', '.frag', '.vert', '.shader', '.wgsl',  // GPU shader source
  '.sql',
  '.rs', '.go', '.java', '.kt', '.cs', '.c', '.cpp', '.h', '.hpp',
  '.rb', '.php', '.lua', '.swift', '.m',
  '.txt', '.csv', '.log',
  '.lock',  // package-lock.json, yarn.lock, etc.
  '.dockerfile', '',  // Dockerfile, Makefile, etc. (no extension)
]);

// Directories to always skip
const SKIP_DIRS = new Set([
  'node_modules', '.git', '.hg', '.svn',
  '__pycache__', '.pytest_cache', '.mypy_cache',
  'dist', 'build', '.next', '.nuxt',
  '.venv', 'venv', 'env',
  'coverage', '.nyc_output',
  '.angular', '.cache',
]);

// Max file size to read (512KB)
const MAX_FILE_SIZE = 512 * 1024;

/**
 * Discover all scannable files under a target path.
 * @param {string} targetPath - Absolute path to scan
 * @param {object} [opts]
 * @param {number} [opts.maxFiles=5000] - Stop after this many files
 * @param {number} [opts.maxFileSize=524288] - Skip files larger than this
 * @returns {Promise<{ files: FileInfo[], skipped: number, truncated: boolean }>}
 *
 * @typedef {{ absPath: string, relPath: string, ext: string, size: number }} FileInfo
 */
export async function discoverFiles(targetPath, opts = {}) {
  const maxFiles = opts.maxFiles || 5000;
  const maxFileSize = opts.maxFileSize || MAX_FILE_SIZE;
  const files = [];
  let skipped = 0;
  let truncated = false;

  async function walk(dir) {
    if (truncated) return;
    let entries;
    try {
      entries = await readdir(dir, { withFileTypes: true });
    } catch {
      skipped++;
      return;
    }

    for (const entry of entries) {
      if (truncated) return;
      const fullPath = join(dir, entry.name);

      if (entry.isDirectory()) {
        if (SKIP_DIRS.has(entry.name) || entry.name.startsWith('.')) {
          // Allow .claude-plugin and .github but skip most dot dirs
          if (entry.name !== '.claude-plugin' && entry.name !== '.github' && entry.name !== '.claude') {
            continue;
          }
        }
        await walk(fullPath);
      } else if (entry.isFile()) {
        const ext = extname(entry.name).toLowerCase();
        // Accept known text extensions or extensionless files (Dockerfile, Makefile, etc.)
        const isKnownText = TEXT_EXTENSIONS.has(ext);
        const isExtensionless = ext === '' && !entry.name.startsWith('.');

        if (!isKnownText && !isExtensionless) {
          skipped++;
          continue;
        }

        let fileSize;
        try {
          const st = await stat(fullPath);
          if (st.size > maxFileSize) {
            skipped++;
            continue;
          }
          if (st.size === 0) {
            skipped++;
            continue;
          }
          fileSize = st.size;
        } catch {
          skipped++;
          continue;
        }

        files.push({
          absPath: fullPath,
          relPath: relative(targetPath, fullPath),
          ext,
          size: fileSize,
        });

        if (files.length >= maxFiles) {
          truncated = true;
          return;
        }
      }
    }
  }

  await walk(targetPath);
  return { files, skipped, truncated };
}

/**
 * Read file content as UTF-8 string, with binary detection.
 * Returns null if file appears to be binary.
 * @param {string} absPath
 * @returns {Promise<string|null>}
 */
export async function readTextFile(absPath) {
  try {
    const buf = await readFile(absPath);
    // Quick binary check: look for null bytes in first 8KB
    const checkLen = Math.min(buf.length, 8192);
    for (let i = 0; i < checkLen; i++) {
      if (buf[i] === 0) return null;
    }
    return buf.toString('utf-8');
  } catch {
    return null;
  }
}