import fs from 'node:fs';
import path from 'node:path';
import dotenv from 'dotenv';

const loadedFiles = new Set<string>();
const loadedKeys = new Set<string>();

/**
 * Load `.env` from the current working directory.
 * If `mode` is provided, also load `.env.<mode>` and let it override `.env`.
 * Existing process env values keep highest priority.
 */
export function ensureRuntimeEnvLoaded(mode?: string): void {
  loadEnvFile(path.resolve(process.cwd(), '.env'));

  const normalizedMode = mode?.trim();
  if (!normalizedMode) {
    return;
  }

  loadEnvFile(path.resolve(process.cwd(), `.env.${normalizedMode}`));
}

function loadEnvFile(filePath: string): void {
  if (loadedFiles.has(filePath) || !fs.existsSync(filePath)) {
    return;
  }

  const parsed = dotenv.parse(fs.readFileSync(filePath));
  for (const [key, value] of Object.entries(parsed)) {
    if (process.env[key] !== undefined && !loadedKeys.has(key)) {
      continue;
    }

    process.env[key] = value;
    loadedKeys.add(key);
  }

  loadedFiles.add(filePath);
}