Budgeteer/BudgetApp/Services/DashboardService.cs

using BudgetApp.Data.Entities;
using BudgetApp.Data.Interfaces;
using BudgetApp.Services.Models;

namespace BudgetApp.Services;

public class DashboardService(ITransactionRepository transactionRepository, IAccountRepository accountRepository, ICategoryRepository categoryRepository)
{
    public async Task<DashboardData> GetDashboardDataAsync(string userId, DateTime? from = null, DateTime? to = null)
    {
        await categoryRepository.EnsureDefaultCategoriesAsync(userId);
        var windowEnd = to ?? DateTime.Today.AddDays(30);
        await transactionRepository.MaterializeRecurringTransactionsAsync(userId, windowEnd);

        var accounts = await accountRepository.GetAccountsAsync(userId);
        var categories = await categoryRepository.GetCategoriesAsync(userId);

        var windowStart = from ?? DateTime.Today.AddDays(-30);

        var fetchStart = windowStart < DateTime.Today ? windowStart : DateTime.Today;
        var fetchEnd = windowEnd > DateTime.Today ? windowEnd : DateTime.Today;
        var allTransactions = await transactionRepository.GetTransactionsInRangeAsync(userId, fetchStart, fetchEnd);

        var recent = allTransactions
            .Where(t => (t.Date.Date >= windowStart.Date && t.Date.Date <= DateTime.Today)
                     || (t.IsPaid && t.Date.Date > DateTime.Today && t.Date.Date <= windowEnd.Date))
            .OrderByDescending(t => t.Date)
            .ToList();

        var upcoming = allTransactions
            .Where(t => t.Date.Date > DateTime.Today && t.Date.Date <= windowEnd.Date && !t.IsPaid)
            .OrderBy(t => t.Date)
            .ToList();

        var chartData = BuildChartData(accounts, allTransactions, windowStart, windowEnd);

        return new DashboardData
        {
            Accounts = accounts,
            Categories = categories,
            RecentTransactions = recent,
            UpcomingTransactions = upcoming,
            ChartData = chartData,
            CurrencySymbol = accounts.FirstOrDefault()?.GetSymbol() ?? "£"
        };
    }

    internal static ChartData BuildChartData(List<Account> accounts, List<Transaction> transactions, DateTime startDate, DateTime endDate)
    {
        var today = DateTime.Today;
        var labels = new List<string>();
        var datasets = new List<ChartDataset>();
        var dayTransactionLabels = new List<List<string>>();

        for (var d = startDate; d <= endDate; d = d.AddDays(1))
        {
            labels.Add(d.ToString("MMM dd"));

            // Paid future transactions are excluded — their effect is already in CurrentBalance
            var dayTxns = transactions
                .Where(t => t.Date.Date == d.Date && !(t.IsPaid && t.Date.Date > today))
                .Select(t => $"{(t.Type == TransactionType.Income ? "+" : "-")}{t.Account.FormatAmount(t.Amount)} {t.Description} ({t.Account.Name})")
                .ToList();
            dayTransactionLabels.Add(dayTxns);
        }

        foreach (var account in accounts)
        {
            var accountTransactions = transactions
                .Where(t => t.AccountId == account.Id)
                .OrderBy(t => t.Date)
                .ToList();

            var dataPoints = new List<decimal>();
            var runningBalance = account.CurrentBalance;

            if (startDate.Date <= today)
            {
                runningBalance = accountTransactions.Where(t => t.Date.Date >= startDate.Date && t.Date.Date <= today)
                    .OrderByDescending(t => t.Date)
                    .Aggregate(runningBalance, (current, t) => current - (t.Type == TransactionType.Income ? t.Amount : -t.Amount));
            }
            else
            {
                // Future-only window: project forward from CurrentBalance using only unpaid transactions
                runningBalance += accountTransactions.Where(t => t.Date.Date > today && t.Date.Date < startDate.Date && !t.IsPaid)
                    .OrderBy(t => t.Date)
                    .Sum(t => t.Type == TransactionType.Income ? t.Amount : -t.Amount);
            }

            for (var d = startDate; d <= endDate; d = d.AddDays(1))
            {
                var dayTxns = accountTransactions.Where(t => t.Date.Date == d.Date && !(t.IsPaid && t.Date.Date > today));
                runningBalance += dayTxns.Sum(t => t.Type == TransactionType.Income ? t.Amount : -t.Amount);
                dataPoints.Add(runningBalance);
            }

            datasets.Add(new ChartDataset
            {
                Label = account.Name,
                Color = account.Color,
                Data = dataPoints,
                CurrencySymbol = account.GetSymbol()
            });
        }

        return new ChartData
        {
            Labels = labels,
            Datasets = datasets,
            DayTransactionLabels = dayTransactionLabels
        };
    }
}