using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Diagnostics;
using ZB.MOM.WW.OtOpcUa.Configuration;
using ZB.MOM.WW.OtOpcUa.Configuration.Entities;

namespace ZB.MOM.WW.OtOpcUa.ControlPlane.Tests.Harness;

/// <summary>
///     An in-memory ConfigDb that behaves like SQL Server where the InMemory provider does not (lmxopcua#868 third
///     review): a <c>FailureReason</c> longer than the column refuses the whole <c>SaveChanges</c> with a
///     <see cref="DbUpdateException"/> over SQL error 2628. It can also reject (<see cref="PoisonNodeStateUpdates"/>,
///     error 547) or fail transiently (<see cref="FailNodeStateUpdatesTransiently"/>, deadlock 1205) every update of
///     an existing <c>NodeDeploymentState</c> row — each a real <c>SqlException</c> inside EF's
///     <see cref="DbUpdateException"/>, the shape SQL Server produces (fourth review M1).
/// </summary>
public sealed class ConstraintEnforcingDbFactory(string dbName) : IDbContextFactory<OtOpcUaConfigDbContext>
{
    private readonly Interceptor _interceptor = new();

    /// <summary>Every update of an existing node row is rejected as a constraint violation.</summary>
    public bool PoisonNodeStateUpdates { get => _interceptor.Poison; set => _interceptor.Poison = value; }

    /// <summary>Every update of an existing node row fails as if the connection dropped.</summary>
    public bool FailNodeStateUpdatesTransiently { get => _interceptor.Transient; set => _interceptor.Transient = value; }

    private int _failNextContexts;

    /// <summary>The next <paramref name="count"/> context creations throw (an unreachable server).</summary>
    public void FailNextContexts(int count) => Volatile.Write(ref _failNextContexts, count);

    /// <inheritdoc />
    public OtOpcUaConfigDbContext CreateDbContext() =>
        Volatile.Read(ref _failNextContexts) > 0 && Interlocked.Decrement(ref _failNextContexts) >= 0
            ? throw new InvalidOperationException("ConfigDb unreachable (simulated)")
            : Create();

    private OtOpcUaConfigDbContext Create() => new(new DbContextOptionsBuilder<OtOpcUaConfigDbContext>()
        .UseInMemoryDatabase(dbName)
        .AddInterceptors(_interceptor)
        .Options);

    private sealed class Interceptor : SaveChangesInterceptor
    {
        public volatile bool Poison;
        public volatile bool Transient;

        public override InterceptionResult<int> SavingChanges(DbContextEventData eventData, InterceptionResult<int> result)
        {
            Check(eventData.Context!);
            return result;
        }

        public override ValueTask<InterceptionResult<int>> SavingChangesAsync(
            DbContextEventData eventData, InterceptionResult<int> result, CancellationToken cancellationToken = default)
        {
            Check(eventData.Context!);
            return ValueTask.FromResult(result);
        }

        private void Check(DbContext ctx)
        {
            foreach (var e in ctx.ChangeTracker.Entries())
            {
                var reason = e.Entity switch
                {
                    NodeDeploymentState n => n.FailureReason,
                    Deployment d => d.FailureReason,
                    _ => null,
                };
                if (reason is { Length: > FailureReasons.MaxLength })
                    throw new DbUpdateException("An error occurred while saving the entity changes.",
                        SqlExceptionFactory.Create(2628, "String or binary data would be truncated in column 'FailureReason'."));
                if (e.Entity is NodeDeploymentState && e.State == EntityState.Modified)
                {
                    if (Poison)
                        throw new DbUpdateException("An error occurred while saving the entity changes.",
                            SqlExceptionFactory.Create(547, "The UPDATE statement conflicted with a CHECK constraint."));
                    if (Transient)
                        throw new DbUpdateException("An error occurred while saving the entity changes.",
                            SqlExceptionFactory.Create(1205, "Transaction was deadlocked on lock resources and has been chosen as the deadlock victim."));
                }
            }
        }
    }
}