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

const IGNORED_DIRS = new Set([
  "node_modules",
  ".git",
  "dist",
  "build",
  "vendor",
  "__pycache__",
  ".next",
  ".turbo",
  "coverage",
  ".venv",
  "venv",
  ".tox",
  "target",
  ".cache",
  ".idea",
  ".vscode",
]);

const LANGUAGE_MAP: Record<string, string> = {
  ".ts": "typescript",
  ".tsx": "typescript",
  ".js": "javascript",
  ".jsx": "javascript",
  ".mjs": "javascript",
  ".cjs": "javascript",
  ".py": "python",
  ".go": "go",
  ".rs": "rust",
  ".java": "java",
  ".rb": "ruby",
  ".php": "php",
  ".cs": "csharp",
  ".cpp": "cpp",
  ".c": "c",
  ".h": "c",
  ".hpp": "cpp",
  ".swift": "swift",
  ".kt": "kotlin",
};

const ENTRY_POINT_NAMES = new Set([
  "index",
  "main",
  "app",
  "server",
  "mod",
  "lib",
  "__init__",
  "manage",
]);

export interface WalkedFile {
  absolutePath: string;
  relativePath: string;
  language: string;
  size: number;
  isEntryPoint: boolean;
}

async function walkDir(
  dir: string,
  rootDir: string,
  results: WalkedFile[]
): Promise<void> {
  const entries = await readdir(dir, { withFileTypes: true });

  for (const entry of entries) {
    if (IGNORED_DIRS.has(entry.name)) continue;
    if (entry.name.startsWith(".")) continue;

    const fullPath = join(dir, entry.name);

    if (entry.isDirectory()) {
      await walkDir(fullPath, rootDir, results);
      continue;
    }

    const ext = extname(entry.name);
    const language = LANGUAGE_MAP[ext];
    if (!language) continue;

    const fileStat = await stat(fullPath);
    if (fileStat.size > 500_000) continue;

    const nameWithoutExt = basename(entry.name, ext);
    const isEntryPoint = ENTRY_POINT_NAMES.has(nameWithoutExt);

    results.push({
      absolutePath: fullPath,
      relativePath: relative(rootDir, fullPath),
      language,
      size: fileStat.size,
      isEntryPoint,
    });
  }
}

export async function walkFiles(repoPath: string): Promise<WalkedFile[]> {
  const results: WalkedFile[] = [];
  await walkDir(repoPath, repoPath, results);

  results.sort((a, b) => {
    if (a.isEntryPoint && !b.isEntryPoint) return -1;
    if (!a.isEntryPoint && b.isEntryPoint) return 1;
    return a.relativePath.localeCompare(b.relativePath);
  });

  return results;
}

export async function readFileContent(filePath: string): Promise<string> {
  return readFile(filePath, "utf-8");
}

export function detectLanguage(filePath: string): string | null {
  return LANGUAGE_MAP[extname(filePath)] ?? null;
}