export type PostalMessageInput = {
  to: string[];
  subject: string;
  plainBody: string;
  htmlBody: string;
};

export type PostalClient = {
  enabled: boolean;
  sendMessage: (input: PostalMessageInput) => Promise<void>;
};

export type CreatePostalClientOptions = {
  baseUrl: string;
  apiKey: string;
  from: string;
  fetchImpl?: typeof fetch;
};

export type CreatePostalClientFromEnvOptions = {
  baseUrlEnv?: string;
  apiKeyEnv?: string;
  fromEnv?: string;
  env?: Record<string, string | undefined>;
  fetchImpl?: typeof fetch;
};

export function createPostalClient(options: CreatePostalClientOptions): PostalClient {
  const baseUrl = options.baseUrl.trim();
  const apiKey = options.apiKey.trim();
  const from = options.from.trim();
  const fetchImpl = options.fetchImpl ?? fetch;
  const enabled = baseUrl.length > 0 && apiKey.length > 0 && from.length > 0;

  return {
    enabled,
    async sendMessage(input: PostalMessageInput): Promise<void> {
      if (!enabled || input.to.length === 0) {
        return;
      }

      const endpoint = new URL("/api/v1/send/message", ensureTrailingSlash(baseUrl));
      const response = await fetchImpl(endpoint, {
        method: "POST",
        headers: {
          "Content-Type": "application/json",
          "X-Server-API-Key": apiKey
        },
        body: JSON.stringify({
          from,
          to: input.to,
          subject: input.subject,
          plain_body: input.plainBody,
          html_body: input.htmlBody
        })
      });

      const payload = (await response.json().catch(() => null)) as { status?: string } | null;
      if (!response.ok || payload?.status !== "success") {
        throw new Error(`postal_send_failed:${response.status}`);
      }
    }
  };
}

export function createPostalClientFromEnv(options: CreatePostalClientFromEnvOptions = {}): PostalClient {
  const env = options.env ?? process.env;

  return createPostalClient({
    baseUrl: env[options.baseUrlEnv ?? "POSTAL_URL"] ?? "",
    apiKey: env[options.apiKeyEnv ?? "POSTAL_API_KEY"] ?? "",
    from: env[options.fromEnv ?? "POSTAL_MESSAGE_FROM"] ?? "",
    fetchImpl: options.fetchImpl
  });
}

function ensureTrailingSlash(value: string): string {
  return value.endsWith("/") ? value : `${value}/`;
}