import { SlashCommandBuilder, ChatInputCommandInteraction } from 'discord.js';
import {
  format,
  differenceInYears,
  differenceInMonths,
  differenceInDays,
  addYears,
  isToday,
} from 'date-fns';

const BIRTHDAY_TIMESTAMP = 1582576229;

// Initialise the command data.
export const data = new SlashCommandBuilder()
  .setName('birthday')
  .setDescription("Returns ButlerBot's Birthday information.");

console.log(`Loaded ${data.name} command.`);

/**
 * Responds with ButlerBot's age and the time remaining until the next birthday.
 * @param interaction The interaction that triggered the command.
 * @returns A promise that resolves when the command is finished executing.
 */
export async function execute(
  interaction: ChatInputCommandInteraction
): Promise<void> {
  const today = new Date();
  const birthday = new Date(BIRTHDAY_TIMESTAMP * 1000);

  const ageYears = differenceInYears(today, birthday);
  const ageMonths = differenceInMonths(today, birthday) % 12;
  const ageDays = differenceInDays(today, addYears(birthday, ageYears)) % 30;

  let ageMessage = `I am ${ageYears} year`;
  ageMessage += ageYears !== 1 ? 's, ' : ', ';
  ageMessage += `${ageMonths} month`;
  ageMessage += ageMonths !== 1 ? 's ' : ' ';
  ageMessage += `and ${ageDays} day`;
  ageMessage += ageDays !== 1 ? 's ' : ' ';
  ageMessage += 'old!';

  let birthdayMessage = `I was created on ${format(birthday, 'dd MMMM yyyy')}.`;

  const nextBirthdayYear =
    today.getMonth() > birthday.getMonth() ||
    (today.getMonth() === birthday.getMonth() &&
      today.getDate() >= birthday.getDate())
      ? today.getFullYear() + 1
      : today.getFullYear();
  const nextBirthday = new Date(
    nextBirthdayYear,
    birthday.getMonth(),
    birthday.getDate()
  );
  const countdown = differenceInDays(nextBirthday, today);

  if (isToday(nextBirthday)) {
    birthdayMessage += " It's my Birthday today!";
  } else if (countdown === 1) {
    birthdayMessage += " It's my Birthday tomorrow!";
  } else {
    birthdayMessage += ` It's my Birthday in ${countdown} days!`;
  }

  const fullMessage = `${ageMessage} ${birthdayMessage}`;
  await interaction.reply(fullMessage);
}