/**
 * Custom ESM Loader that adds .js extensions to imports without extensions
 */

import { resolve as pathResolve, dirname, extname, isAbsolute } from 'node:path';
import { fileURLToPath, pathToFileURL } from 'node:url';
import { existsSync } from 'node:fs';

/**
 * Resolve hook - adds .js extension to imports without extensions
 */
export async function resolve(specifier, context, nextResolve) {
  // Log everything unconditionally
  console.log(`[loader] resolve called: ${specifier}`);

  // Skip node built-ins and package imports
  if (specifier.startsWith('node:') || specifier.startsWith('@') || !specifier.includes('/')) {
    return nextResolve(specifier, context);
  }

  // Check if specifier needs .js extension added
  if (!extname(specifier)) {
    // Calculate the absolute path
    let absolutePath;

    if (isAbsolute(specifier)) {
      absolutePath = specifier;
    } else if (specifier.startsWith('./') || specifier.startsWith('../')) {
      // For relative imports, resolve from parent directory
      const { parentURL } = context;
      let parentDir;
      if (parentURL) {
        try {
          parentDir = dirname(fileURLToPath(parentURL));
        } catch {
          parentDir = process.cwd();
        }
      } else {
        parentDir = process.cwd();
      }
      absolutePath = pathResolve(parentDir, specifier);
    } else {
      // Not a path we handle
      return nextResolve(specifier, context);
    }

    console.log(`[loader] absolute path: ${absolutePath}`);

    // Try adding .js extension
    const pathWithJs = absolutePath + '.js';
    console.log(`[loader] trying: ${pathWithJs}, exists: ${existsSync(pathWithJs)}`);

    if (existsSync(pathWithJs)) {
      const url = pathToFileURL(pathWithJs).href;
      console.log(`[loader] resolved to: ${url}`);
      return {
        shortCircuit: true,
        url,
      };
    }

    // Try as directory with index.js
    const pathAsIndex = pathResolve(absolutePath, 'index.js');
    console.log(`[loader] trying index: ${pathAsIndex}, exists: ${existsSync(pathAsIndex)}`);

    if (existsSync(pathAsIndex)) {
      const url = pathToFileURL(pathAsIndex).href;
      console.log(`[loader] resolved to: ${url}`);
      return {
        shortCircuit: true,
        url,
      };
    }
  }

  // Default resolution
  return nextResolve(specifier, context);
}