Utopia-Canteen-System/Services/RfidService.cs

using Microsoft.EntityFrameworkCore;
using System.Threading;
using System.Threading.Tasks;
using UtopiaCanteenSystem.Data;
using UtopiaCanteenSystem.Helpers;
using UtopiaCanteenSystem.Models;

namespace UtopiaCanteenSystem.Services;

/// <summary>
/// Handles RFID scan logic: validates input, enforces configurable timeout,
/// and saves scan events to SQLite (lunch_order_transactions table).
/// </summary>
public class RfidService : IRfidService
{
    private readonly IDbContextFactory<AppDbContext> _dbFactory;
    private readonly IConfigService _configService;

    public RfidService(IDbContextFactory<AppDbContext> dbFactory, IConfigService configService)
    {
        _dbFactory = dbFactory;
        _configService = configService;
    }

    public (bool Success, string Message) ProcessScan(string cardId)
    {
        var result = ProcessScanDetailed(cardId);
        return (result.Success, result.Message);
    }

    public ScanResult ProcessScanDetailed(string cardId)
    {
        if (string.IsNullOrWhiteSpace(cardId))
            return new ScanResult(false, "Card ID cannot be empty.", 0);

        cardId = cardId.Trim();
        var nowUtc = DateTime.UtcNow;

        using var db = _dbFactory.CreateDbContext();

        var timeoutSeconds = _configService.GetScanTimeoutSeconds();
        if (timeoutSeconds <= 0)
            timeoutSeconds = 60;

        var windowStart = nowUtc.AddSeconds(-timeoutSeconds);

        // Enforce timeout: no duplicate scan within the timeout window
        var lastInWindow = db.LunchOrderTransactions
            .Where(r => r.CardId == cardId)
            .Where(r => r.ScanTime >= windowStart)
            .OrderByDescending(r => r.ScanTime)
            .FirstOrDefault();

        if (lastInWindow != null)
        {
            var remaining = GetCooldownRemainingSeconds(nowUtc, lastInWindow.ScanTime, timeoutSeconds);
            return new ScanResult(
                false,
                $"One order per customer within {FormatTimeout(timeoutSeconds)}. Ask this customer to rescan after countdown.",
                remaining);
        }

        // Optional: prevent any scan within the timeout window (any card).
        var lastAnyScanInWindow = db.LunchOrderTransactions
            .Where(r => r.ScanTime >= windowStart)
            .OrderByDescending(r => r.ScanTime)
            .FirstOrDefault();

        if (lastAnyScanInWindow != null)
        {
            var remaining = GetCooldownRemainingSeconds(nowUtc, lastAnyScanInWindow.ScanTime, timeoutSeconds);
            return new ScanResult(
                false,
                $"Only one order at a time within {FormatTimeout(timeoutSeconds)}. Ask this customer to rescan after countdown.",
                remaining);
        }

        var record = new ScanRecord
        {
            CardId = cardId,
            ScanTime = nowUtc,
            IsSynced = false,
            SiteId = _configService.GetSiteId(),
            DeviceId = _configService.GetDeviceId()
        };
        db.LunchOrderTransactions.Add(record);
        db.SaveChanges();

        return new ScanResult(true, "Order recorded successfully.", 0);
    }

    public ScanRecord? GetLastScan()
    {
        using var db = _dbFactory.CreateDbContext();
        return db.LunchOrderTransactions
            .OrderByDescending(r => r.ScanTime)
            .FirstOrDefault();
    }

    public IReadOnlyList<ScanRecord> GetLastScans(int count)
    {
        if (count <= 0) return Array.Empty<ScanRecord>();
        using var db = _dbFactory.CreateDbContext();
        return db.LunchOrderTransactions
            .OrderByDescending(r => r.ScanTime)
            .Take(count)
            .ToList();
    }

    public IReadOnlyList<ScanRecord> GetScansForToday()
    {
        var startOfTodayLocal = DateTime.Today;
        var startOfTomorrowLocal = startOfTodayLocal.AddDays(1);
        var startUtc = startOfTodayLocal.ToUniversalTime();
        var endUtc = startOfTomorrowLocal.ToUniversalTime();
        using var db = _dbFactory.CreateDbContext();
        return db.LunchOrderTransactions
            .Where(r => r.ScanTime >= startUtc && r.ScanTime < endUtc)
            .OrderByDescending(r => r.ScanTime)
            .ToList();
    }

    public int GetTodayScanCount()
    {
        // Define "today" by the local calendar day, but ScanTime is stored as UTC.
        // Convert local day boundaries to UTC for correct comparisons.
        var startOfTodayLocal = DateTime.Today;
        var startOfTomorrowLocal = startOfTodayLocal.AddDays(1);
        var startUtc = startOfTodayLocal.ToUniversalTime();
        var endUtc = startOfTomorrowLocal.ToUniversalTime();

        using var db = _dbFactory.CreateDbContext();
        return db.LunchOrderTransactions
            .Count(r => r.ScanTime >= startUtc && r.ScanTime < endUtc);
    }

    public async Task<int> GetTodayScanCountAsync(CancellationToken cancellationToken = default)
    {
        // Define "today" by the local calendar day, but ScanTime is stored as UTC.
        // Convert local day boundaries to UTC for correct comparisons.
        var startOfTodayLocal = DateTime.Today;
        var startOfTomorrowLocal = startOfTodayLocal.AddDays(1);
        var startUtc = startOfTodayLocal.ToUniversalTime();
        var endUtc = startOfTomorrowLocal.ToUniversalTime();

        await using var db = await _dbFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
        return await db.LunchOrderTransactions
            .CountAsync(r => r.ScanTime >= startUtc && r.ScanTime < endUtc, cancellationToken)
            .ConfigureAwait(false);
    }

    public async Task<int> GetTotalScanCountAsync(CancellationToken cancellationToken = default)
    {
        await using var db = await _dbFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
        return await db.LunchOrderTransactions.CountAsync(cancellationToken).ConfigureAwait(false);
    }

    public async Task<int> GetTotalScanCountForCardAsync(string cardId, CancellationToken cancellationToken = default)
    {
        if (string.IsNullOrWhiteSpace(cardId))
            return 0;

        cardId = cardId.Trim();

        await using var db = await _dbFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
        return await db.LunchOrderTransactions
            .CountAsync(r => r.CardId == cardId, cancellationToken)
            .ConfigureAwait(false);
    }

    public async Task<int> GetTodayScanCountForCardAsync(string cardId, CancellationToken cancellationToken = default)
    {
        if (string.IsNullOrWhiteSpace(cardId))
            return 0;

        cardId = cardId.Trim();

        // Define "today" by the local calendar day, but ScanTime is stored as UTC.
        // Convert local day boundaries to UTC for correct comparisons.
        var startOfTodayLocal = DateTime.Today;
        var startOfTomorrowLocal = startOfTodayLocal.AddDays(1);
        var startUtc = startOfTodayLocal.ToUniversalTime();
        var endUtc = startOfTomorrowLocal.ToUniversalTime();

        await using var db = await _dbFactory.CreateDbContextAsync(cancellationToken).ConfigureAwait(false);
        return await db.LunchOrderTransactions
            .CountAsync(r => r.CardId == cardId && r.ScanTime >= startUtc && r.ScanTime < endUtc, cancellationToken)
            .ConfigureAwait(false);
    }

    private static string FormatTimeout(int seconds)
    {
        if (seconds <= 0)
            return "the timeout window";

        var minutes = seconds / 60;
        var secs = seconds % 60;

        if (minutes == 0)
            return secs == 1 ? "1 second" : $"{secs} seconds";

        if (secs == 0)
            return minutes == 1 ? "1 minute" : $"{minutes} minutes";

        var minutePart = minutes == 1 ? "1 minute" : $"{minutes} minutes";
        var secondPart = secs == 1 ? "1 second" : $"{secs} seconds";
        return $"{minutePart} {secondPart}";
    }

    private static int GetCooldownRemainingSeconds(DateTime nowUtc, DateTime lastScanUtc, int timeoutSeconds)
    {
        // Remaining = (lastScan + timeout) - now. Use ceiling so UI shows a whole-second countdown.
        var endUtc = lastScanUtc.AddSeconds(timeoutSeconds);
        var remaining = (int)Math.Ceiling((endUtc - nowUtc).TotalSeconds);
        return Math.Max(0, remaining);
    }
}