import { useSession } from 'h3';

interface DailyVisitResponse {
  message: string;
  reward: {
    coins: number;
    streakBonus: boolean;
  };
  updatedCoins: number;
}

/**
 * A helper function to safely get the authenticated user's ID from the session.
 */
async function getUserIdFromSession(event: any): Promise<number> {
  const session = await useSession(event, {
    password: process.env.SESSION_PASSWORD,
  });
  const userId = session.data?.user?.id;
  if (!userId) {
    throw createError({ statusCode: 401, statusMessage: 'Unauthorized' });
  }
  return userId;
}

/**
 * Creates a Date object for the start of a given day in UTC.
 */
function getStartOfDay(date: Date): Date {
  const startOfDay = new Date(date);
  startOfDay.setUTCHours(0, 0, 0, 0);
  return startOfDay;
}

export default defineEventHandler(async (event): Promise<DailyVisitResponse> => {
  const userId = await getUserIdFromSession(event);
  const today = getStartOfDay(new Date());

  // 1. Check if the user has already claimed the reward today
  const existingVisit = await prisma.dailyVisit.findUnique({
    where: {
      userId_date: {
        userId,
        date: today,
      },
    },
  });

  if (existingVisit) {
    throw createError({
      statusCode: 409,
      statusMessage: 'Daily visit reward has already been claimed today.',
    });
  }

  // 2. Check for a 5-day consecutive streak (i.e., visits on the 4 previous days)
  const previousDates = Array.from({ length: 4 }, (_, i) => {
    const d = new Date(today);
    d.setUTCDate(d.getUTCDate() - (i + 1));
    return d;
  });

  const priorVisitsCount = await prisma.dailyVisit.count({
    where: {
      userId,
      date: {
        in: previousDates,
      },
    },
  });

  const hasStreak = priorVisitsCount === 4;
  
  // 3. Calculate rewards and update the database in a transaction
  let totalReward = 1; // Base reward
  if (hasStreak) {
    totalReward += 10; // Streak bonus
  }

  const [, updatedUser] = await prisma.$transaction([
    prisma.dailyVisit.create({
      data: {
        userId,
        date: today,
      },
    }),
    prisma.user.update({
      where: { id: userId },
      data: {
        coins: {
          increment: totalReward,
        },
      },
    }),
  ]);

  // 4. Return the response
  return {
    message: hasStreak ? 'Daily visit and streak bonus claimed!' : 'Daily visit claimed!',
    reward: {
      coins: totalReward,
      streakBonus: hasStreak,
    },
    updatedCoins: updatedUser.coins,
  };
});