import type { Response } from 'express';
import { z } from 'zod';
import { AppDataSource } from '../config/data-source.js';
import { Budget } from '../entities/Budget.js';
import { Category } from '../entities/Category.js';
import { Expense } from '../entities/Expense.js';
import type { AuthenticatedRequest } from '../types/express.js';
import { processDueRecurringExpenses } from '../services/recurring.service.js';

const budgetSchema = z.object({
  month: z.string().regex(/^\d{4}-\d{2}$/),
  name: z.string().max(120).nullable().optional(),
  amount: z.coerce.number().positive(),
  categoryId: z.string().uuid().nullable().optional(),
  alertThresholds: z.array(z.coerce.number().min(1).max(100)).default([80, 100]),
  isActive: z.boolean().default(true)
});

const budgetRepo = () => AppDataSource.getRepository(Budget);
const categoryRepo = () => AppDataSource.getRepository(Category);
const expenseRepo = () => AppDataSource.getRepository(Expense);

const serializeBudget = (item: Budget, spent: number) => {
  const amount = Number(item.amount.toFixed(2));
  const usagePercent = amount ? Number(((spent / amount) * 100).toFixed(1)) : 0;
  const alertLevel = (item.alertThresholds ?? [80, 100]).filter((threshold) => usagePercent >= threshold).sort((a, b) => b - a)[0] ?? null;
  return {
    id: item.id,
    month: item.month,
    name: item.name,
    amount,
    spent: Number(spent.toFixed(2)),
    usagePercent,
    alertLevel,
    alertThresholds: item.alertThresholds ?? [80, 100],
    isActive: item.isActive,
    category: item.category
      ? {
          id: item.category.id,
          name: item.category.name,
          color: item.category.color,
          isSystem: item.category.isSystem,
          ownerId: item.category.user?.id ?? null
        }
      : null,
    createdAt: item.createdAt,
    updatedAt: item.updatedAt
  };
};

const getMonthRange = (month: string) => ({ startDate: `${month}-01`, endDate: `${month}-31` });

export const listBudgets = async (req: AuthenticatedRequest, res: Response) => {
  await processDueRecurringExpenses(req.user!.id);
  const month = typeof req.query.month === 'string' && /^\d{4}-\d{2}$/.test(req.query.month)
    ? req.query.month
    : `${new Date().getFullYear()}-${`${new Date().getMonth() + 1}`.padStart(2, '0')}`;

  const budgets = await budgetRepo().find({
    where: { user: { id: req.user!.id } },
    relations: { category: { user: true }, user: true },
    order: { month: 'DESC', createdAt: 'DESC' }
  });

  const monthBudgets = budgets.filter((item) => item.month === month);
  const { startDate, endDate } = getMonthRange(month);
  const expenses = await expenseRepo().find({
    where: { user: { id: req.user!.id } },
    relations: { category: true }
  });

  const scopedExpenses = expenses.filter((item) => item.expenseDate >= startDate && item.expenseDate <= endDate && item.status !== 'REJECTED' && item.status !== 'DRAFT');
  const items = monthBudgets.map((item) => {
    const spent = scopedExpenses
      .filter((expense) => !item.category || expense.category.id === item.category.id)
      .reduce((sum, expense) => sum + expense.amount, 0);
    return serializeBudget(item, spent);
  });

  const alerts = items.filter((item) => item.alertLevel !== null).map((item) => ({
    budgetId: item.id,
    message: `${item.name || item.category?.name || 'Monthly budget'} reached ${item.usagePercent}% of the limit.`,
    usagePercent: item.usagePercent,
    level: item.alertLevel
  }));

  return res.json({
    month,
    items,
    summary: {
      totalBudget: Number(items.reduce((sum, item) => sum + item.amount, 0).toFixed(2)),
      totalSpent: Number(items.reduce((sum, item) => sum + item.spent, 0).toFixed(2)),
      alerts
    }
  });
};

export const createBudget = async (req: AuthenticatedRequest, res: Response) => {
  const parsed = budgetSchema.safeParse(req.body);
  if (!parsed.success) return res.status(400).json({ message: 'Invalid budget payload', issues: parsed.error.issues });

  const category = parsed.data.categoryId
    ? await categoryRepo().findOne({
        where: [{ id: parsed.data.categoryId, isSystem: true }, { id: parsed.data.categoryId, user: { id: req.user!.id } }],
        relations: { user: true }
      })
    : null;

  if (parsed.data.categoryId && !category) return res.status(404).json({ message: 'Category not found' });

  const saved = await budgetRepo().save(
    budgetRepo().create({
      month: parsed.data.month,
      name: parsed.data.name ?? null,
      amount: parsed.data.amount,
      alertThresholds: parsed.data.alertThresholds,
      isActive: parsed.data.isActive,
      category,
      user: { id: req.user!.id } as never
    })
  );

  const full = await budgetRepo().findOneOrFail({ where: { id: saved.id }, relations: { category: { user: true }, user: true } });
  return res.status(201).json({ item: serializeBudget(full, 0) });
};

export const updateBudget = async (req: AuthenticatedRequest, res: Response) => {
  const parsed = budgetSchema.safeParse(req.body);
  if (!parsed.success) return res.status(400).json({ message: 'Invalid budget payload', issues: parsed.error.issues });

  const item = await budgetRepo().findOne({ where: { id: String(req.params.id), user: { id: req.user!.id } }, relations: { category: { user: true }, user: true } });
  if (!item) return res.status(404).json({ message: 'Budget not found' });

  const category = parsed.data.categoryId
    ? await categoryRepo().findOne({
        where: [{ id: parsed.data.categoryId, isSystem: true }, { id: parsed.data.categoryId, user: { id: req.user!.id } }],
        relations: { user: true }
      })
    : null;

  if (parsed.data.categoryId && !category) return res.status(404).json({ message: 'Category not found' });

  item.month = parsed.data.month;
  item.name = parsed.data.name ?? null;
  item.amount = parsed.data.amount;
  item.alertThresholds = parsed.data.alertThresholds;
  item.isActive = parsed.data.isActive;
  item.category = category;

  await budgetRepo().save(item);
  return res.json({ item: serializeBudget(item, 0) });
};

export const deleteBudget = async (req: AuthenticatedRequest, res: Response) => {
  const item = await budgetRepo().findOne({ where: { id: String(req.params.id), user: { id: req.user!.id } } });
  if (!item) return res.status(404).json({ message: 'Budget not found' });
  await budgetRepo().remove(item);
  return res.status(204).send();
};