using After;
using System.Reflection;

namespace BeforeAfter.Tests;

/// <summary>
/// Tests for the AFTER situation (Yak 02): plain domain objects (no
/// <see cref="DbBase"/>), DTOs (records) carrying the data including the
/// relations, hand-written mappers, and a WebApp that consumes only DTOs.
/// </summary>
public class AfterTests
{
    private const BindingFlags AllMembers =
        BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Static;

    // ---------------------------------------------------------------------
    // (1) The leak is gone: Client/Order do NOT derive from DbBase and expose
    //     no DbContext-typed property or field (reflection).
    // ---------------------------------------------------------------------
    [Theory]
    [InlineData(typeof(Client))]
    [InlineData(typeof(Order))]
    public void Domain_objects_are_plain__no_DbBase_no_DbContext_member(Type type)
    {
        // Not DbBase, and not a derived type either (walk the base chain):
        for (var t = type; t is not null && t != typeof(object); t = t.BaseType)
            Assert.NotSame(typeof(DbBase), t);

        // No DbContext-typed member, public or private:
        foreach (var p in type.GetProperties(AllMembers))
            Assert.True(p.PropertyType != typeof(DbContext),
                $"{type.Name}.{p.Name} leaks a DbContext-typed property");
        foreach (var f in type.GetFields(AllMembers))
            Assert.True(f.FieldType != typeof(DbContext),
                $"{type.Name}.{f.Name} leaks a DbContext-typed field");
    }

    // ---------------------------------------------------------------------
    // (2) Mappers map all scalar fields, in both directions.
    // ---------------------------------------------------------------------
    [Fact]
    public void ToClientDto_maps_all_scalar_fields()
    {
        var id = Guid.NewGuid();
        var client = new Client { Id = id, Name = "Acme" };

        var dto = Mappers.ToClientDto(client);

        Assert.Equal(id, dto.Id);
        Assert.Equal("Acme", dto.Name);
    }

    [Fact]
    public void ToOrderDto_maps_all_scalar_fields()
    {
        var id = Guid.NewGuid();
        var order = new Order { Id = id, Description = "one" };

        var dto = Mappers.ToOrderDto(order);

        Assert.Equal(id, dto.Id);
        Assert.Equal("one", dto.Description);
    }

    [Fact]
    public void FromClientDto_maps_all_scalar_fields()
    {
        var id = Guid.NewGuid();
        var dto = new ClientDto { Id = id, Name = "Acme" };

        var client = Mappers.FromClientDto(dto);

        Assert.Equal(id, client.Id);
        Assert.Equal("Acme", client.Name);
    }

    [Fact]
    public void FromOrderDto_maps_all_scalar_fields()
    {
        var id = Guid.NewGuid();
        var dto = new OrderDto { Id = id, Description = "one" };

        var order = Mappers.FromOrderDto(dto);

        Assert.Equal(id, order.Id);
        Assert.Equal("one", order.Description);
    }

    // ---------------------------------------------------------------------
    // (3) Mappers map the relations: Client.Orders -> ClientDto.Orders, and the
    //     Order.Client / OrderDto.ClientDto back-references stay consistent.
    // ---------------------------------------------------------------------
    [Fact]
    public void ToClientDto_maps_orders_and_keeps_the_back_reference_consistent()
    {
        var client = new Client { Name = "Acme" };
        var order = new Order { Description = "one" };
        client.Orders.Add(order);

        var dto = Mappers.ToClientDto(client);
        var orderDto = Assert.Single(dto.Orders);

        // The order is mapped with the client's data:
        Assert.Equal(order.Id, orderDto.Id);
        Assert.Equal(order.Description, orderDto.Description);

        // The back-reference cycle is resolved to the SAME dto reference:
        Assert.Same(dto, orderDto.ClientDto);
    }

    [Fact]
    public void FromClientDto_wires_the_order_client_back_reference()
    {
        var orderDto = new OrderDto { Description = "one" };
        var dto = new ClientDto { Name = "Acme", Orders = new[] { orderDto } };

        var client = Mappers.FromClientDto(dto);
        var order = Assert.Single(client.Orders);

        Assert.Equal(orderDto.Description, order.Description);
        // Navigation fix-up: the reconstructed order points at the client:
        Assert.Same(client, order.Client);
    }

    // ---------------------------------------------------------------------
    // (4) Round-trips preserve all state (compared by values, not reference).
    // ---------------------------------------------------------------------
    [Fact]
    public void Domain_round_trip_preserves_all_state()
    {
        var client = new Client { Id = Guid.NewGuid(), Name = "Acme" };
        var order = new Order { Id = Guid.NewGuid(), Description = "one" };
        client.Orders.Add(order);

        var roundTrip = Mappers.FromClientDto(Mappers.ToClientDto(client));

        Assert.Equal(client.Id, roundTrip.Id);
        Assert.Equal(client.Name, roundTrip.Name);
        var roundTripOrder = Assert.Single(roundTrip.Orders);
        Assert.Equal(order.Id, roundTripOrder.Id);
        Assert.Equal(order.Description, roundTripOrder.Description);
        // The back-reference is still consistent on the reconstructed graph:
        Assert.Same(roundTrip, roundTripOrder.Client);
    }

    [Fact]
    public void Dto_round_trip_preserves_all_state()
    {
        var client = new Client { Id = Guid.NewGuid(), Name = "Acme" };
        var order = new Order { Id = Guid.NewGuid(), Description = "one" };
        client.Orders.Add(order);
        var dto = Mappers.ToClientDto(client);
        var dtoOrder = dto.Orders[0];

        var roundTrip = Mappers.ToClientDto(Mappers.FromClientDto(dto));

        Assert.Equal(dto.Id, roundTrip.Id);
        Assert.Equal(dto.Name, roundTrip.Name);
        var roundTripOrder = Assert.Single(roundTrip.Orders);
        Assert.Equal(dtoOrder.Id, roundTripOrder.Id);
        Assert.Equal(dtoOrder.Description, roundTripOrder.Description);
        Assert.Same(roundTrip, roundTripOrder.ClientDto);
    }

    // ---------------------------------------------------------------------
    // (5) Mappers do not mutate their inputs (snapshot fields, map, compare).
    // ---------------------------------------------------------------------
    [Fact]
    public void ToClientDto_does_not_mutate_the_domain()
    {
        var client = new Client { Id = Guid.NewGuid(), Name = "Acme" };
        var order = new Order { Id = Guid.NewGuid(), Description = "one" };
        client.Orders.Add(order);
        var ordersCount = client.Orders.Count;

        Mappers.ToClientDto(client);
        Mappers.ToOrderDto(order);

        Assert.Equal("Acme", client.Name);
        Assert.Equal(ordersCount, client.Orders.Count);
        Assert.Same(client, order.Client);          // back-reference untouched
        Assert.Equal("one", order.Description);
    }

    [Fact]
    public void FromClientDto_does_not_mutate_the_dto()
    {
        var orderDto = new OrderDto { Description = "one" };
        var dto = new ClientDto { Id = Guid.NewGuid(), Name = "Acme", Orders = new[] { orderDto } };

        Mappers.FromClientDto(dto);
        Mappers.FromOrderDto(orderDto);

        Assert.Equal("Acme", dto.Name);
        Assert.Same(orderDto, Assert.Single(dto.Orders));   // collection untouched
        Assert.Null(orderDto.ClientDto);                   // back-reference untouched
        Assert.Equal("one", orderDto.Description);
    }

    // ---------------------------------------------------------------------
    // (6) The after WebApp consumes only DTOs: its public API references no
    //     domain (Client/Order) or persistence (DbContext/DbBase) type.
    // ---------------------------------------------------------------------
    private static readonly Type[] BannedTypes =
        [typeof(Client), typeof(Order), typeof(DbContext), typeof(DbBase)];

    private static IEnumerable<Type> TypeAndArguments(Type t)
    {
        yield return t;
        if (t.IsGenericType)
            foreach (var arg in t.GetGenericArguments())
                foreach (var nested in TypeAndArguments(arg))
                    yield return nested;
        if (t.IsArray && t.GetElementType() is { } elem)
            foreach (var nested in TypeAndArguments(elem))
                yield return nested;
    }

    [Fact]
    public void After_WebApp_public_api_references_no_domain_or_db_types()
    {
        var app = typeof(WebApp);
        var banned = BannedTypes.ToList();

        foreach (var m in app.GetMethods(BindingFlags.Public | BindingFlags.Instance | BindingFlags.Static))
        {
            var signature = m.GetParameters()
                .Select(p => p.ParameterType)
                .Append(m.ReturnType)
                .ToList();
            foreach (var t in signature.SelectMany(TypeAndArguments))
                Assert.False(banned.Contains(t),
                    $"WebApp.{m.Name}({string.Join(", ", signature)}) references banned type {t}");
        }

        foreach (var p in app.GetProperties(BindingFlags.Public | BindingFlags.Instance | BindingFlags.Static))
            foreach (var t in TypeAndArguments(p.PropertyType))
                Assert.False(banned.Contains(t),
                    $"WebApp.{p.Name} references banned type {t}");
    }

    [Fact]
    public void After_WebApp_consumes_dtos()
    {
        var app = new WebApp();
        var client = new Client { Id = Guid.NewGuid(), Name = "Acme" };
        var order = new Order { Id = Guid.NewGuid(), Description = "order one" };
        client.Orders.Add(order);

        var view = app.ShowClient(Mappers.ToClientDto(client));

        Assert.Contains("Acme", view);
        Assert.Contains("order one", view);
    }

    // ---------------------------------------------------------------------
    // (7) Persistence still works through the fake DbContext in the after
    //     world: explicit Save, distinct ids, tracking — and even a saved
    //     domain object keeps no back-reference to the context.
    // ---------------------------------------------------------------------
    [Fact]
    public void DbContext_saves_plain_domain_objects_and_tracks_them()
    {
        var db = new DbContext();
        var client = new Client { Name = "Acme" };
        var order = new Order { Description = "one" };
        client.Orders.Add(order);

        Assert.Equal(Guid.Empty, client.Id);
        db.Save(client);
        db.Save(order);

        Assert.NotEqual(Guid.Empty, client.Id);
        Assert.NotEqual(Guid.Empty, order.Id);
        Assert.NotEqual(client.Id, order.Id);
        Assert.True(db.IsTracked(client));
        Assert.True(db.IsTracked(order));
        Assert.Equal(2, db.Tracked.Count);
    }

    [Fact]
    public void Saving_twice_does_not_reassign_the_id()
    {
        var db = new DbContext();
        var client = new Client { Name = "Acme" };
        db.Save(client);
        var id = client.Id;

        db.Save(client);

        Assert.Equal(id, client.Id);
        Assert.Single(db.Tracked);
    }

    [Fact]
    public void A_saved_domain_object_keeps_no_reference_to_the_context()
    {
        var db = new DbContext();
        var client = new Client { Name = "Acme" };
        db.Save(client);

        // Saved (the id was assigned by the context) ...
        Assert.NotEqual(Guid.Empty, client.Id);
        Assert.True(db.IsTracked(client));

        // ... but there is no way back to the context through the domain
        // object: no DbContext-typed member exists on it (test 1), so the
        // only "receipt" is the plain Id value.
        var dto = Mappers.ToClientDto(client);
        Assert.Equal(client.Id, dto.Id);   // the id flows on into the DTO
    }
}