Introduce a config module to manage configuration (#22)

* Introduce a config module to manage configuration

* Remove public modifier

packages/cli/src/config/config.ts

@@ -0,0 +1,110 @@
+import yargs from 'yargs/yargs';
+import { hideBin } from 'yargs/helpers';
+import * as dotenv from 'dotenv';
+import * as fs from 'node:fs';
+import * as path from 'node:path';
+import process from 'node:process';
+
+const DEFAULT_GEMINI_MODEL = 'gemini-2.5-flash-preview-04-17';
+
+export class Config {
+  private apiKey: string;
+  private model: string;
+  private targetDir: string;
+  private extraArgs: (string | number)[]; // Captures positional arguments
+
+  constructor(apiKey: string, model: string, targetDir: string, extraArgs: (string | number)[]) {
+    this.apiKey = apiKey;
+    this.model = model;
+    this.targetDir = targetDir;
+    this.extraArgs = extraArgs;
+  }
+
+  getApiKey(): string {
+    return this.apiKey;
+  }
+
+  getModel(): string {
+    return this.model;
+  }
+
+  getTargetDir(): string {
+    return this.targetDir;
+  }
+
+  getExtraArgs(): (string | number)[] {
+    return this.extraArgs;
+  }
+}
+
+export function loadConfig(): Config {
+  loadEnvironment();
+  const argv = parseArguments();
+  return new Config(
+    process.env.GEMINI_API_KEY || "",
+    argv.model || process.env.GEMINI_API_KEY || DEFAULT_GEMINI_MODEL,
+    argv.target_dir || process.cwd(),
+    argv._,
+  );
+}
+
+export const globalConfig = loadConfig(); // TODO(jbd): Remove global state.
+
+interface CliArgs {
+  target_dir: string | undefined;
+  model: string | undefined;
+  _: (string | number)[]; // Captures positional arguments
+  // Add other expected args here if needed
+  // e.g., verbose?: boolean;
+}
+
+function parseArguments(): CliArgs {
+  const argv = yargs(hideBin(process.argv))
+    .option('target_dir', {
+      alias: 'd',
+      type: 'string',
+      description:
+        'The target directory for Gemini operations. Defaults to the current working directory.',
+    })
+    .option('model', {
+      alias: 'm',
+      type: 'string',
+      description: `The Gemini model to use. Defaults to ${DEFAULT_GEMINI_MODEL}.`,
+      default: DEFAULT_GEMINI_MODEL,
+    })
+    .help()
+    .alias('h', 'help')
+    .strict() // Keep strict mode to error on unknown options
+    .argv;
+
+  // Cast to the interface to ensure the structure aligns with expectations
+  // Use `unknown` first for safer casting if types might not perfectly match
+  return argv as unknown as CliArgs;
+}
+
+
+function findEnvFile(startDir: string): string | null {
+  // Start search from the provided directory (e.g., current working directory)
+  let currentDir = path.resolve(startDir); // Ensure absolute path
+  while (true) {
+    const envPath = path.join(currentDir, '.env');
+    if (fs.existsSync(envPath)) {
+      return envPath;
+    }
+
+    const parentDir = path.dirname(currentDir);
+    if (parentDir === currentDir || !parentDir) {
+      return null;
+    }
+    currentDir = parentDir;
+  }
+}
+
+function loadEnvironment(): void {
+  // Start searching from the current working directory by default
+  const envFilePath = findEnvFile(process.cwd());
+  if (!envFilePath) {
+    return;
+  }
+  dotenv.config({ path: envFilePath });
+}