feat: add config schema and loader with env var expansion

src/config/loader.ts

@@ -0,0 +1,37 @@
+import { readFileSync } from 'fs';
+import { parse } from 'yaml';
+import { configSchema, type Config } from './schema.js';
+
+function expandEnvVars(value: string): string {
+  return value.replace(/\$\{([^}]+)\}/g, (_, envVar) => {
+    const envValue = process.env[envVar];
+    if (envValue === undefined) {
+      throw new Error(`Environment variable ${envVar} is not set`);
+    }
+    return envValue;
+  });
+}
+
+function expandEnvVarsInObject(obj: unknown): unknown {
+  if (typeof obj === 'string') {
+    return expandEnvVars(obj);
+  }
+  if (Array.isArray(obj)) {
+    return obj.map(expandEnvVarsInObject);
+  }
+  if (obj !== null && typeof obj === 'object') {
+    const result: Record<string, unknown> = {};
+    for (const [key, value] of Object.entries(obj)) {
+      result[key] = expandEnvVarsInObject(value);
+    }
+    return result;
+  }
+  return obj;
+}
+
+export function loadConfig(configPath: string): Config {
+  const rawContent = readFileSync(configPath, 'utf-8');
+  const rawConfig = parse(rawContent);
+  const expandedConfig = expandEnvVarsInObject(rawConfig);
+  return configSchema.parse(expandedConfig);
+}