export type AiRuntimeConfig = {
  baseUrl: string;
  apiKey: string;
  chatModel: string;
  requestTimeoutMs: number;
  maxTokens: number;
  maxRetries: number;
};

export type AiRuntimeConfigResult =
  | { success: true; config: AiRuntimeConfig }
  | { success: false; reason: string };

const DEFAULT_CHAT_MODEL = "gpt-4.1-mini";
const DEFAULT_REQUEST_TIMEOUT_MS = 20_000;
const DEFAULT_MAX_TOKENS = 1_000;
const DEFAULT_MAX_RETRIES = 0;

function readOptionalEnv(name: string): string {
  return process.env[name]?.trim() ?? "";
}

function readBoundedIntegerEnv(name: string, fallback: number, min: number, max: number): number {
  const rawValue = readOptionalEnv(name);
  if (!rawValue) {
    return fallback;
  }

  const value = Number(rawValue);
  if (!Number.isInteger(value) || value < min || value > max) {
    return fallback;
  }

  return value;
}

export function getAiRuntimeConfig(): AiRuntimeConfigResult {
  const apiKey = readOptionalEnv("AI_API_KEY");
  if (!apiKey) {
    return { success: false, reason: "AI_API_KEY 未配置" };
  }

  return {
    success: true,
    config: {
      baseUrl: readOptionalEnv("AI_BASE_URL"),
      apiKey,
      chatModel: readOptionalEnv("AI_CHAT_MODEL") || DEFAULT_CHAT_MODEL,
      requestTimeoutMs: readBoundedIntegerEnv("AI_REQUEST_TIMEOUT_MS", DEFAULT_REQUEST_TIMEOUT_MS, 1_000, 120_000),
      maxTokens: readBoundedIntegerEnv("AI_MAX_TOKENS", DEFAULT_MAX_TOKENS, 256, 2_000),
      maxRetries: readBoundedIntegerEnv("AI_MAX_RETRIES", DEFAULT_MAX_RETRIES, 0, 5),
    },
  };
}