using System.Data;
using System.IO;
using Microsoft.EntityFrameworkCore;
using UtopiaCanteenSystem.Models;

namespace UtopiaCanteenSystem.Data;

/// <summary>
/// SQLite DbContext for Labour and ScanRecord tables.
/// Database file is created in application directory on first run.
/// </summary>
public class AppDbContext : DbContext
{
    private static readonly string DbPath = Path.Combine(
        AppDomain.CurrentDomain.BaseDirectory,
        "utopia_canteen.db");

    public DbSet<Labour> Labour { get; set; }
    public DbSet<ScanRecord> ScanRecords { get; set; }
    public DbSet<AdminLoginRecord> AdminLoginRecords { get; set; }

    public AppDbContext() { }

    public AppDbContext(DbContextOptions<AppDbContext> options) : base(options) { }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        if (!optionsBuilder.IsConfigured)
            optionsBuilder.UseSqlite($"Data Source={DbPath}");
    }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        // Labour: CardId should be indexed for lookups.
        modelBuilder.Entity<Labour>(e =>
        {
            e.HasKey(x => x.Id);
            e.HasIndex(x => x.CardId);
        });

        // ScanRecord: Index for unsynced queries and by ScanTime.
        modelBuilder.Entity<ScanRecord>(e =>
        {
            e.HasKey(x => x.Id);
            e.HasIndex(x => x.IsSynced);
            e.HasIndex(x => x.ScanTime);
        });

        modelBuilder.Entity<AdminLoginRecord>(e =>
        {
            e.HasKey(x => x.Id);
            e.HasIndex(x => x.LoginTimeUtc);
        });
    }

    /// <summary>
    /// Ensures database exists and is migrated. Call on app startup.
    /// </summary>
    public void EnsureDatabaseCreated()
    {
        Database.EnsureCreated();
        UpgradeScanRecordsSchemaIfNeeded();
        EnsureAdminLoginTableExists();
    }

    /// <summary>
    /// Lightweight schema upgrade: add SiteId and DeviceId to ScanRecords if missing (no EF migrations).
    /// Does not delete any data.
    /// </summary>
    private void UpgradeScanRecordsSchemaIfNeeded()
    {
        try
        {
            var conn = Database.GetDbConnection();
            if (conn.State != ConnectionState.Open)
                conn.Open();

            var columns = new List<string>();
            using (var cmd = conn.CreateCommand())
            {
                cmd.CommandText = "SELECT name FROM pragma_table_info('ScanRecords')";
                using var r = cmd.ExecuteReader();
                while (r.Read())
                    columns.Add(r.GetString(0));
            }

            if (!columns.Contains("SiteId", StringComparer.OrdinalIgnoreCase))
            {
                using var cmd = conn.CreateCommand();
                cmd.CommandText = "ALTER TABLE ScanRecords ADD COLUMN SiteId TEXT DEFAULT ''";
                cmd.ExecuteNonQuery();
            }

            if (!columns.Contains("DeviceId", StringComparer.OrdinalIgnoreCase))
            {
                using var cmd = conn.CreateCommand();
                cmd.CommandText = "ALTER TABLE ScanRecords ADD COLUMN DeviceId TEXT DEFAULT ''";
                cmd.ExecuteNonQuery();
            }
        }
        catch
        {
            // Ignore; existing DB may already have columns or be incompatible
        }
    }

    /// <summary>
    /// Lightweight creation of AdminLoginRecords table for existing databases.
    /// </summary>
    private void EnsureAdminLoginTableExists()
    {
        try
        {
            var conn = Database.GetDbConnection();
            if (conn.State != ConnectionState.Open)
                conn.Open();

            using var cmd = conn.CreateCommand();
            cmd.CommandText =
                "CREATE TABLE IF NOT EXISTS AdminLoginRecords (" +
                "Id INTEGER PRIMARY KEY AUTOINCREMENT, " +
                "Username TEXT NOT NULL, " +
                "EmployeeId TEXT NOT NULL, " +
                "LoginTimeUtc TEXT NOT NULL)";
            cmd.ExecuteNonQuery();
        }
        catch
        {
            // Ignore; table may already exist or DB may be read-only.
        }
    }
}