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

namespace Purrse.Api.Services;

public class AccountService : IAccountService
{
    private readonly PurrseDbContext _db;

    public AccountService(PurrseDbContext db)
    {
        _db = db;
    }

    public async Task<List<AccountResponse>> GetAllAsync(Guid userId)
    {
        return await _db.Accounts
            .Where(a => a.UserId == userId)
            .OrderBy(a => a.SortOrder).ThenBy(a => a.Name)
            .Select(a => MapToResponse(a))
            .ToListAsync();
    }

    public async Task<AccountResponse?> GetByIdAsync(Guid userId, Guid accountId)
    {
        var account = await _db.Accounts
            .Include(a => a.LoanDetail)
            .FirstOrDefaultAsync(a => a.Id == accountId && a.UserId == userId);
        return account == null ? null : MapToResponse(account);
    }

    public async Task<AccountResponse> CreateAsync(Guid userId, CreateAccountRequest request)
    {
        var account = new Account
        {
            Id = Guid.NewGuid(),
            UserId = userId,
            Name = request.Name,
            Type = request.Type,
            Institution = request.Institution,
            AccountNumber = request.AccountNumber,
            Balance = request.Balance,
            CreditLimit = request.CreditLimit,
            InterestRate = request.InterestRate,
            Notes = request.Notes,
            SortOrder = await _db.Accounts.CountAsync(a => a.UserId == userId)
        };

        _db.Accounts.Add(account);
        await _db.SaveChangesAsync();
        return MapToResponse(account);
    }

    public async Task<AccountResponse> UpdateAsync(Guid userId, Guid accountId, UpdateAccountRequest request)
    {
        var account = await _db.Accounts.FirstOrDefaultAsync(a => a.Id == accountId && a.UserId == userId)
            ?? throw new KeyNotFoundException("Account not found");

        account.Name = request.Name;
        account.Institution = request.Institution;
        account.AccountNumber = request.AccountNumber;
        account.CreditLimit = request.CreditLimit;
        account.InterestRate = request.InterestRate;
        account.Notes = request.Notes;
        account.IsActive = request.IsActive;
        account.SortOrder = request.SortOrder;
        account.UpdatedAt = DateTime.UtcNow;

        await _db.SaveChangesAsync();
        return MapToResponse(account);
    }

    public async Task DeleteAsync(Guid userId, Guid accountId)
    {
        var account = await _db.Accounts.FirstOrDefaultAsync(a => a.Id == accountId && a.UserId == userId)
            ?? throw new KeyNotFoundException("Account not found");

        _db.Accounts.Remove(account);
        await _db.SaveChangesAsync();
    }

    public async Task<List<BalanceHistoryEntry>> GetBalanceHistoryAsync(Guid userId, Guid accountId, DateTime startDate, DateTime endDate)
    {
        var account = await _db.Accounts.FirstOrDefaultAsync(a => a.Id == accountId && a.UserId == userId)
            ?? throw new KeyNotFoundException("Account not found");

        var transactions = await _db.Transactions
            .Where(t => t.AccountId == accountId && t.Date >= startDate && t.Date <= endDate && !t.IsVoid)
            .OrderBy(t => t.Date)
            .ToListAsync();

        var balanceBefore = account.Balance - await _db.Transactions
            .Where(t => t.AccountId == accountId && !t.IsVoid)
            .SumAsync(t => t.Amount);

        var priorSum = await _db.Transactions
            .Where(t => t.AccountId == accountId && t.Date < startDate && !t.IsVoid)
            .SumAsync(t => t.Amount);

        var runningBalance = balanceBefore + priorSum;
        var entries = new List<BalanceHistoryEntry>();

        foreach (var group in transactions.GroupBy(t => t.Date.Date))
        {
            runningBalance += group.Sum(t => t.Amount);
            entries.Add(new BalanceHistoryEntry(group.Key, runningBalance));
        }

        return entries;
    }

    public async Task RecalculateBalanceAsync(Guid accountId)
    {
        var account = await _db.Accounts.FindAsync(accountId);
        if (account == null) return;

        var sum = await _db.Transactions
            .Where(t => t.AccountId == accountId && !t.IsVoid)
            .SumAsync(t => t.Amount);

        account.Balance = sum;
        account.UpdatedAt = DateTime.UtcNow;
        await _db.SaveChangesAsync();
    }

    private static AccountResponse MapToResponse(Account a) => new(
        a.Id, a.Name, a.Type, a.Institution, a.AccountNumber,
        a.Balance, a.CreditLimit, a.InterestRate,
        a.IsActive, a.IsClosed, a.Notes, a.SortOrder, a.CreatedAt,
        a.LoanDetail != null
    );
}