import { getUserIdFromSession } from '../../../utils/auth';

interface CompletionResponse {
  message: string;
  reward: {
    coins: number;
  };
  updatedCoins: number;
}

/**
 * Creates a Date object for the start of a given day in UTC.
 * This is duplicated here as per the instruction not to create new shared utilities.
 */
function getStartOfDay(date: Date): Date {
  const startOfDay = new Date(date);
  startOfDay.setUTCHours(0, 0, 0, 0);
  return startOfDay;
}

export default defineEventHandler(async (event): Promise<CompletionResponse> => {
  const userId = await getUserIdFromSession(event);
  const habitId = parseInt(event.context.params?.id || '', 10);

  if (isNaN(habitId)) {
    throw createError({ statusCode: 400, statusMessage: 'Invalid habit ID.' });
  }

  const habit = await prisma.habit.findFirst({
    where: { id: habitId, userId },
  });

  if (!habit) {
    throw createError({ statusCode: 404, statusMessage: 'Habit not found.' });
  }

  const today = new Date();
  const dayOfWeek = today.getDay(); // 0 (Sunday) to 6 (Saturday)
  if (!(habit.daysOfWeek as number[]).includes(dayOfWeek)) {
    throw createError({ statusCode: 400, statusMessage: 'Habit is not active today.' });
  }

  // Normalize date to the beginning of the day for consistent checks
  const startOfToday = getStartOfDay(new Date()); // Correctly get a Date object

  const existingCompletion = await prisma.habitCompletion.findFirst({
    where: {
      habitId: habitId,
      date: startOfToday, // Use precise equality check
    },
  });

  if (existingCompletion) {
    throw createError({ statusCode: 409, statusMessage: 'Habit already completed today.' });
  }

  const rewardCoins = 3;
  const [, updatedUser] = await prisma.$transaction([
    prisma.habitCompletion.create({
      data: {
        habitId: habitId,
        date: startOfToday, // Save the normalized date
      },
    }),
    prisma.user.update({
      where: { id: userId },
      data: {
        coins: {
          increment: rewardCoins,
        },
      },
    }),
  ]);

  return {
    message: 'Habit completed successfully!',
    reward: {
      coins: rewardCoins,
    },
    updatedCoins: updatedUser.coins,
  };
});