Utopia-Canteen-System/Services/SyncService.cs

using Microsoft.EntityFrameworkCore;
using MySqlConnector;
using UtopiaCanteenSystem.Data;
using UtopiaCanteenSystem.Models;

namespace UtopiaCanteenSystem.Services;

/// <summary>
/// Scheduled sync: fetches unsynced lunch_order_transactions, inserts them into MySQL database,
/// marks them as synced in SQLite, and periodically cleans up old synced rows.
/// </summary>
public class SyncService : ISyncService
{
    private readonly IDbContextFactory<AppDbContext> _dbFactory;
    private readonly IConfigService _configService;

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

    public async Task SyncNowAsync(CancellationToken cancellationToken = default)
    {
        var connectionString = _configService.GetMySqlConnectionString();
        // TODO: For local testing only. Set MySqlConnectionString in appsettings.json or via config to avoid hardcoding.
        if (string.IsNullOrWhiteSpace(connectionString))
            connectionString = "Server=localhost;Database=canteen_prod;User=root;Password=Root@12345_;Port=3306;";

        List<ScanRecord> toSync;
        using (var db = _dbFactory.CreateDbContext())
        {
            toSync = await db.LunchOrderTransactions
                .Where(r => !r.IsSynced)
                .OrderBy(r => r.ScanTime)
                .ToListAsync(cancellationToken)
                .ConfigureAwait(false);
        }

        if (toSync.Count == 0)
            return;

        try
        {
            // Insert into MySQL using transaction for atomicity
            await using var mysqlConn = new MySqlConnection(connectionString);
            await mysqlConn.OpenAsync(cancellationToken).ConfigureAwait(false);

            await using var transaction = await mysqlConn.BeginTransactionAsync(cancellationToken).ConfigureAwait(false);

            try
            {
                // Use INSERT IGNORE to handle duplicates (unique key on DeviceId, DeviceLocalRowId)
                // This ensures no duplicates even if sync runs multiple times
                var insertSql = @"
                    INSERT IGNORE INTO lunch_order_transactions 
                        (DeviceLocalRowId, ScanTimeUtc, SiteId, DeviceId, CardId, IpAddress, ReceivedAtUtc)
                    VALUES 
                        (@DeviceLocalRowId, @ScanTimeUtc, @SiteId, @DeviceId, @CardId, @IpAddress, UTC_TIMESTAMP(3))";

                await using var cmd = new MySqlCommand(insertSql, mysqlConn, transaction);

                foreach (var record in toSync)
                {
                    cmd.Parameters.Clear();
                    cmd.Parameters.AddWithValue("@DeviceLocalRowId", record.Id);
                    cmd.Parameters.AddWithValue("@ScanTimeUtc", record.ScanTime);
                    cmd.Parameters.AddWithValue("@SiteId", record.SiteId ?? string.Empty);
                    cmd.Parameters.AddWithValue("@DeviceId", record.DeviceId ?? string.Empty);
                    cmd.Parameters.AddWithValue("@CardId", record.CardId ?? string.Empty);
                    cmd.Parameters.AddWithValue("@IpAddress", record.IpAddress ?? string.Empty);

                    var rowsAffected = await cmd.ExecuteNonQueryAsync(cancellationToken).ConfigureAwait(false);
                    // Note: INSERT IGNORE returns 0 if row already exists (duplicate), 1 if inserted
                }

                // Commit MySQL transaction
                await transaction.CommitAsync(cancellationToken).ConfigureAwait(false);

                // Only mark as synced in SQLite after successful MySQL insert
                var ids = toSync.Select(r => r.Id).ToList();
                using (var db = _dbFactory.CreateDbContext())
                {
                    var records = await db.LunchOrderTransactions
                        .Where(r => ids.Contains(r.Id))
                        .ToListAsync(cancellationToken)
                        .ConfigureAwait(false);
                    foreach (var record in records)
                        record.IsSynced = true;

                    await db.SaveChangesAsync(cancellationToken).ConfigureAwait(false);
                }

                // Day-end cleanup: delete only synced rows from previous days.
                await CleanupOldSyncedRowsAsync(cancellationToken).ConfigureAwait(false);
            }
            catch (Exception ex)
            {
                // Rollback MySQL transaction on error
                try
                {
                    await transaction.RollbackAsync(cancellationToken).ConfigureAwait(false);
                }
                catch
                {
                    // Ignore rollback errors
                }
                
                // Log error for debugging (you can replace with proper logging)
                System.Diagnostics.Debug.WriteLine($"Sync error: {ex.Message}");
                System.Diagnostics.Debug.WriteLine($"Stack trace: {ex.StackTrace}");
                
                throw; // Re-throw to be caught by outer catch
            }
        }
        catch (Exception ex)
        {
            // Log error for debugging (you can replace with proper logging)
            System.Diagnostics.Debug.WriteLine($"Sync failed: {ex.Message}");
            System.Diagnostics.Debug.WriteLine($"Stack trace: {ex.StackTrace}");
            
            // Leave records intact; will retry on next run
        }
    }

    /// <summary>
    /// Deletes only synced rows (IsSynced = 1) where ScanTime is before the start of today (local day).
    /// </summary>
    private async Task CleanupOldSyncedRowsAsync(CancellationToken cancellationToken)
    {
        // Define "today" by the local calendar day, but ScanTime is stored as UTC.
        var startOfTodayLocal = DateTime.Today;
        var startUtc = startOfTodayLocal.ToUniversalTime();

        using var db = _dbFactory.CreateDbContext();
        var oldSynced = await db.LunchOrderTransactions
            .Where(r => r.IsSynced && r.ScanTime < startUtc)
            .ToListAsync(cancellationToken)
            .ConfigureAwait(false);

        if (oldSynced.Count == 0)
            return;

        db.LunchOrderTransactions.RemoveRange(oldSynced);
        await db.SaveChangesAsync(cancellationToken).ConfigureAwait(false);
    }
}