import { getUserIdFromSession } from '../../../utils/auth';
import { REWARDS } from '../../../utils/economy';
import prisma from '../../../utils/prisma';
import { applyStreakMultiplier } from '../../../utils/streak';

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

// Helper to get the start of the day in UTC
function getStartOfDay(date: Date): Date {
  const d = new Date(date);
  d.setUTCHours(0, 0, 0, 0);
  return d;
}

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.' });
  }

  // Fetch user and habit in parallel
  const [user, habit] = await Promise.all([
    prisma.user.findUnique({ where: { id: userId } }),
    prisma.habit.findFirst({ where: { id: habitId, userId } })
  ]);

  if (!user) {
    throw createError({ statusCode: 401, statusMessage: 'User not found.' });
  }
  if (!habit) {
    throw createError({ statusCode: 404, statusMessage: 'Habit not found.' });
  }

  const today = new Date();
  const jsDayOfWeek = today.getDay(); // 0 (Sunday) to 6 (Saturday)
  
  // Convert JS day (Sun=0) to the application's convention (Mon=0, Sun=6)
  const appDayOfWeek = (jsDayOfWeek === 0) ? 6 : jsDayOfWeek - 1;

  if (!(habit.daysOfWeek as number[]).includes(appDayOfWeek)) {
    throw createError({ statusCode: 400, statusMessage: 'Habit is not active today.' });
  }

  const startOfToday = getStartOfDay(today);

  const existingCompletion = await prisma.habitCompletion.findFirst({
    where: {
      habitId: habitId,
      date: startOfToday,
    },
  });

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

  // Apply the streak multiplier to the base reward
  const baseReward = REWARDS.HABITS.COMPLETION;
  const finalReward = applyStreakMultiplier(baseReward, user.dailyStreak);

  const village = await prisma.village.findUnique({ where: { userId } });

  const [, updatedUser] = await prisma.$transaction([
    prisma.habitCompletion.create({
      data: {
        habitId: habitId,
        date: startOfToday,
      },
    }),
    prisma.user.update({
      where: { id: userId },
      data: {
        coins: {
          increment: finalReward.coins,
        },
        exp: {
          increment: finalReward.exp,
        },
      },
    }),
    ...(village ? [prisma.villageEvent.create({
      data: {
        villageId: village.id,
        type: 'HABIT_COMPLETION',
        message: `Привычка "${habit.name}" выполнена, принеся вам ${finalReward.coins} монет и ${finalReward.exp} опыта.${user.dailyStreak > 1 ? ` Ваша серия визитов (x${user.dailyStreak}) ${user.dailyStreak === 2 ? 'удвоила' : 'утроила'} награду!` : ''}`,
        coins: finalReward.coins,
        exp: finalReward.exp,
      }
    })] : []),
  ]);

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