/**
 * @copyright nhcarrigan
 * @license Naomi's Public License
 * @author Naomi Carrigan
 */

interface FacebookErrorResponse {
  error: {
    code:    number;
    message: string;
    type:    string;
  };
}

interface FacebookSuccessResponse {
  id: string;
}

type FacebookResponse = FacebookErrorResponse | FacebookSuccessResponse;

/**
 * Forwards an announcement to our Facebook Page.
 * @param content - The main body of the announcement.
 * @returns A message indicating the success or failure of the operation.
 */
export const announceOnFacebook = async(content: string): Promise<string> => {
  if (
    process.env.FACEBOOK_PAGE_TOKEN === undefined
    || process.env.FACEBOOK_PAGE_ID === undefined
  ) {
    return "Facebook credentials are not set.";
  }

  if (content.trim().length === 0) {
    return "No content to send to Facebook.";
  }

  const pageId = process.env.FACEBOOK_PAGE_ID;
  const accessToken = process.env.FACEBOOK_PAGE_TOKEN;

  try {
    const response = await fetch(
      `https://graph.facebook.com/v21.0/${pageId}/feed`,
      {
        body: new URLSearchParams({
          // eslint-disable-next-line @typescript-eslint/naming-convention -- Facebook API requires snake_case.
          access_token: accessToken,
          message:      content,
        }),
        headers: {
          // eslint-disable-next-line @typescript-eslint/naming-convention -- HTTP header name.
          "Content-Type": "application/x-www-form-urlencoded",
        },
        method: "POST",
      },
    );

    // eslint-disable-next-line @typescript-eslint/consistent-type-assertions -- Fetch does not accept generic.
    const result = (await response.json()) as FacebookResponse;

    if ("error" in result) {
      const errorMessage = result.error.message === ""
        ? JSON.stringify(result.error)
        : result.error.message;
      return `Failed to send message to Facebook. ${errorMessage}`;
    }

    if ("id" in result) {
      return `Successfully sent post to Facebook. Post ID: ${result.id}`;
    }

    return `Failed to send message to Facebook. Unexpected response: ${JSON.stringify(result)}`;
  } catch (error: unknown) {
    return `Failed to send message to Facebook. ${
      error instanceof Error
        ? error.message
        : String(error)
    }`;
  }
};