using Microsoft.EntityFrameworkCore;
using Purrse.Core.DTOs;
using Purrse.Core.Enums;
using Purrse.Core.Interfaces.Services;
using Purrse.Data;

namespace Purrse.Api.Services;

public class DashboardService : IDashboardService
{
    private readonly PurrseDbContext _db;

    public DashboardService(PurrseDbContext db) => _db = db;

    public async Task<DashboardResponse> GetDashboardAsync(Guid userId)
    {
        var accounts = await _db.Accounts
            .Where(a => a.UserId == userId && a.IsActive)
            .OrderBy(a => a.SortOrder)
            .ToListAsync();

        var assetTypes = new[] { AccountType.Checking, AccountType.Savings, AccountType.Cash, AccountType.Brokerage, AccountType.Retirement401k, AccountType.IRA };
        var totalAssets = accounts.Where(a => assetTypes.Contains(a.Type)).Sum(a => a.Balance);
        var totalLiabilities = accounts.Where(a => !assetTypes.Contains(a.Type)).Sum(a => Math.Abs(a.Balance));
        var netWorth = totalAssets - totalLiabilities;

        var accountSummaries = accounts.Select(a => new AccountSummaryResponse(a.Id, a.Name, a.Type, a.Institution, a.Balance, a.CreditLimit)).ToList();

        var now = DateTime.UtcNow;
        var startOfMonth = new DateTime(now.Year, now.Month, 1, 0, 0, 0, DateTimeKind.Utc);
        var startOfLastMonth = startOfMonth.AddMonths(-1);

        var recentTxns = await _db.Transactions
            .Include(t => t.Account).Include(t => t.Category)
            .Where(t => t.Account.UserId == userId && !t.IsVoid)
            .OrderByDescending(t => t.Date).ThenByDescending(t => t.CreatedAt)
            .Take(10)
            .Select(t => new TransactionResponse(t.Id, t.AccountId, t.Account.Name, t.Date, t.Amount,
                t.PayeeId, t.PayeeName, t.CategoryId, t.Category != null ? t.Category.Name : null,
                t.Memo, t.ReferenceNumber, t.CheckNumber, t.Type, t.Status, t.IsVoid,
                t.TransferTransactionId, t.ImportBatchId, null, t.CreatedAt))
            .ToListAsync();

        var thisMonthSpending = await _db.Transactions
            .Where(t => t.Account.UserId == userId && t.Date >= startOfMonth && t.Amount < 0 && !t.IsVoid)
            .SumAsync(t => Math.Abs(t.Amount));

        var lastMonthSpending = await _db.Transactions
            .Where(t => t.Account.UserId == userId && t.Date >= startOfLastMonth && t.Date < startOfMonth && t.Amount < 0 && !t.IsVoid)
            .SumAsync(t => Math.Abs(t.Amount));

        var changePercent = lastMonthSpending == 0 ? 0 : ((thisMonthSpending - lastMonthSpending) / lastMonthSpending) * 100;

        var spendingByCategory = await _db.Transactions
            .Where(t => t.Account.UserId == userId && t.Date >= startOfMonth && t.Amount < 0 && !t.IsVoid)
            .GroupBy(t => t.CategoryId)
            .Select(g => new { CategoryId = g.Key, Total = -g.Sum(t => t.Amount) })
            .OrderByDescending(x => x.Total)
            .Take(10)
            .ToListAsync();

        var categoryIds = spendingByCategory.Where(x => x.CategoryId.HasValue).Select(x => x.CategoryId!.Value);
        var categoryNames = await _db.Categories
            .Where(c => categoryIds.Contains(c.Id))
            .ToDictionaryAsync(c => c.Id, c => c.Name);

        var totalSpending = spendingByCategory.Sum(x => x.Total);
        var topCategories = spendingByCategory.Select(x => new CategorySpending(
            x.CategoryId.HasValue ? categoryNames.GetValueOrDefault(x.CategoryId.Value, "Unknown") : "Uncategorized",
            x.Total,
            totalSpending > 0 ? (x.Total / totalSpending) * 100 : 0,
            null)).ToList();

        var spendingSummary = new SpendingSummary(thisMonthSpending, lastMonthSpending, changePercent, topCategories);

        var upcomingBills = await _db.ScheduledTransactions
            .Include(s => s.Account)
            .Where(s => s.UserId == userId && s.IsActive && s.NextDueDate <= now.AddDays(14))
            .OrderBy(s => s.NextDueDate)
            .Take(10)
            .Select(s => new UpcomingBill(s.Id, s.PayeeName ?? "", s.Amount, s.NextDueDate, s.Account.Name, s.AutoPost))
            .ToListAsync();

        return new DashboardResponse(netWorth, totalAssets, totalLiabilities, accountSummaries,
            recentTxns, spendingSummary, upcomingBills);
    }
}