import 'dotenv/config';
import type { ProxyConfig } from './types.js';

/**
 * Reads a required environment variable or aborts the process.
 */
function requireEnv(name: string): string {
    const value = process.env[name]?.trim();
    if (!value) {
        console.error(`[FATAL] Missing required environment variable: ${name}`);
        process.exit(1);
    }
    return value;
}

/**
 * Reads an optional environment variable with a fallback default.
 */
function optionalEnv(name: string, fallback: string): string {
    return process.env[name]?.trim() || fallback;
}

/**
 * Parses and validates all environment variables into a typed, frozen config object.
 * Aborts the process immediately if required variables are missing.
 */
export function loadConfig(): ProxyConfig {
    const config: ProxyConfig = {
        anthropicApiKey: process.env['ANTHROPIC_API_KEY']?.trim() || undefined,
        proxyAuthToken: requireEnv('PROXY_AUTH_TOKEN'),
        port: parseInt(optionalEnv('PORT', '7860'), 10),
        host: optionalEnv('HOST', '0.0.0.0'),
        logLevel: optionalEnv('LOG_LEVEL', 'info'),
        rateLimitMax: parseInt(optionalEnv('RATE_LIMIT_MAX', '100'), 10),
        rateLimitWindowMs: parseInt(optionalEnv('RATE_LIMIT_WINDOW_MS', '60000'), 10),
        bodyLimit: parseInt(optionalEnv('BODY_LIMIT', '5242880'), 10),
        corsOrigin: optionalEnv('CORS_ORIGIN', ''),
        anthropicBaseUrl: optionalEnv('ANTHROPIC_BASE_URL', 'https://api.anthropic.com'),
        upstreamTimeoutMs: parseInt(optionalEnv('UPSTREAM_TIMEOUT_MS', '300000'), 10),
        geminiApiKey: process.env['GEMINI_API_KEY']?.trim() || undefined,
        geminiBaseUrl: optionalEnv('GEMINI_BASE_URL', 'https://generativelanguage.googleapis.com'),
    };

    // At least one provider must be configured
    if (!config.anthropicApiKey && !config.geminiApiKey) {
        console.error('[FATAL] At least one provider API key must be set (ANTHROPIC_API_KEY and/or GEMINI_API_KEY)');
        process.exit(1);
    }

    // Validate numeric values
    if (isNaN(config.port) || config.port < 1 || config.port > 65535) {
        console.error(`[FATAL] Invalid PORT value: ${process.env['PORT']}`);
        process.exit(1);
    }

    return Object.freeze(config);
}