using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Reflection;
using System.Reflection.Emit;
using JetBrains.Annotations;
using NetSerializer;
using Robust.Shared.GameObjects;

namespace Robust.Shared.Serialization;

/// <summary>
/// Generated delta states store ONE <see cref="IAutoGeneratedComponentDeltaState.ChangedFields"/> bitmask and ONE
/// field per networked component field. This serializer writes the mask first, then only writes fields whose bits are
/// set. This allows a single generated delta state to represent any dirty-field combination without serializing the
/// unchanged fields.
/// If you misuse this your networked states will probably explode!
/// </summary>
internal sealed class NetComponentDeltaStateSerializer : IDynamicTypeSerializer
{
    public bool Handles(Type type)
    {
        return typeof(IAutoGeneratedComponentDeltaState).IsAssignableFrom(type);
    }

    public IEnumerable<Type> GetSubtypes(Type type)
    {
        yield return typeof(ulong);

        foreach (var field in GetDeltaFields(type))
        {
            yield return field.FieldType;
        }
    }

    public void GenerateWriterMethod(Serializer serializer, Type type, ILGenerator il)
    {
        // arg0: Serializer, arg1: Stream, arg2: value
        var getChangedFields = typeof(IAutoGeneratedComponentDeltaState)
            .GetProperty(nameof(IAutoGeneratedComponentDeltaState.ChangedFields))!
            .GetMethod!;
        var writeMask = typeof(Primitives)
            .GetMethod(nameof(Primitives.WritePrimitive), [typeof(Stream), typeof(ulong)])!;

        var changedFields = il.DeclareLocal(typeof(ulong));

        il.Emit(OpCodes.Ldarg_2);
        il.Emit(OpCodes.Castclass, typeof(IAutoGeneratedComponentDeltaState));
        il.Emit(OpCodes.Callvirt, getChangedFields);
        il.Emit(OpCodes.Stloc, changedFields);

        il.Emit(OpCodes.Ldarg_1);
        il.Emit(OpCodes.Ldloc, changedFields);
        il.Emit(OpCodes.Call, writeMask);

        foreach (var field in GetDeltaFields(type))
        {
            var endField = il.DefineLabel();
            var mask = 1UL << field.GetCustomAttribute<NetworkedDeltaFieldAttribute>()!.Index;

            il.Emit(OpCodes.Ldloc, changedFields);
            il.Emit(OpCodes.Ldc_I8, unchecked((long) mask));
            il.Emit(OpCodes.And);
            il.Emit(OpCodes.Brfalse, endField);

            // Primitive types count as sealed
            // We need this to handle inheritors of abstract types, such as SoundSpecifier
            var writeField = field.FieldType.IsSealed
                ? WriteFieldMethod.MakeGenericMethod(field.FieldType)
                : WriteFieldObjectMethod;
            il.Emit(OpCodes.Ldarg_0);
            il.Emit(OpCodes.Ldarg_1);
            il.Emit(OpCodes.Ldarg_2);
            il.Emit(OpCodes.Ldfld, field);
            il.Emit(OpCodes.Call, writeField);

            il.MarkLabel(endField);
        }

        il.Emit(OpCodes.Ret);
    }

    public void GenerateReaderMethod(Serializer serializer, Type type, ILGenerator il)
    {
        // arg0: Serializer, arg1: Stream, arg2: out value
        var setChangedFields = typeof(IAutoGeneratedComponentDeltaState)
            .GetProperty(nameof(IAutoGeneratedComponentDeltaState.ChangedFields))!
            .SetMethod!;
        var readMask = typeof(Primitives)
            .GetMethod(nameof(Primitives.ReadPrimitive), [typeof(Stream), typeof(ulong).MakeByRefType()])!;

        var changedFields = il.DeclareLocal(typeof(ulong));

        il.Emit(OpCodes.Ldarg_2);
        il.Emit(OpCodes.Ldtoken, type);
        il.Emit(OpCodes.Call, typeof(Type).GetMethod(nameof(Type.GetTypeFromHandle), BindingFlags.Public | BindingFlags.Static)!);
        il.Emit(
            OpCodes.Call,
            // Beats me but matches the other serializers.
#pragma warning disable SYSLIB0050
            typeof(System.Runtime.Serialization.FormatterServices)
                .GetMethod(nameof(System.Runtime.Serialization.FormatterServices.GetUninitializedObject), BindingFlags.Public | BindingFlags.Static)!);
#pragma warning restore SYSLIB0050
        il.Emit(OpCodes.Castclass, type);
        il.Emit(OpCodes.Stind_Ref);

        il.Emit(OpCodes.Ldarg_1);
        il.Emit(OpCodes.Ldloca_S, changedFields);
        il.Emit(OpCodes.Call, readMask);

        il.Emit(OpCodes.Ldarg_2);
        il.Emit(OpCodes.Ldind_Ref);
        il.Emit(OpCodes.Castclass, typeof(IAutoGeneratedComponentDeltaState));
        il.Emit(OpCodes.Ldloc, changedFields);
        il.Emit(OpCodes.Callvirt, setChangedFields);

        foreach (var field in GetDeltaFields(type))
        {
            var endField = il.DefineLabel();
            var mask = 1UL << field.GetCustomAttribute<NetworkedDeltaFieldAttribute>()!.Index;

            il.Emit(OpCodes.Ldloc, changedFields);
            il.Emit(OpCodes.Ldc_I8, unchecked((long) mask));
            il.Emit(OpCodes.And);
            il.Emit(OpCodes.Brfalse, endField);

            // Primitive types count as sealed
            // We need this to handle inheritors of abstract types, such as SoundSpecifier
            var readField = field.FieldType.IsSealed
                ? ReadFieldMethod.MakeGenericMethod(field.FieldType)
                : ReadFieldObjectMethod;
            il.Emit(OpCodes.Ldarg_0);
            il.Emit(OpCodes.Ldarg_1);
            il.Emit(OpCodes.Ldarg_2);
            il.Emit(OpCodes.Ldind_Ref);
            il.Emit(OpCodes.Ldflda, field);
            il.Emit(OpCodes.Call, readField);

            il.MarkLabel(endField);
        }

        il.Emit(OpCodes.Ret);
    }

    private static IEnumerable<FieldInfo> GetDeltaFields(Type type)
    {
        return type.GetFields(BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance)
            .Select(field => (Field: field, Attribute: field.GetCustomAttribute<NetworkedDeltaFieldAttribute>()))
            .Where(tuple => tuple.Attribute != null)
            .OrderBy(tuple => tuple.Attribute!.Index)
            .Select(tuple => tuple.Field);
    }

    private static readonly MethodInfo WriteFieldMethod = typeof(NetComponentDeltaStateSerializer)
        .GetMethod(nameof(WriteField), BindingFlags.Static | BindingFlags.NonPublic)!;

    private static readonly MethodInfo WriteFieldObjectMethod = typeof(NetComponentDeltaStateSerializer)
        .GetMethod(nameof(WriteFieldObject), BindingFlags.Static | BindingFlags.NonPublic)!;

    private static readonly MethodInfo ReadFieldMethod = typeof(NetComponentDeltaStateSerializer)
        .GetMethod(nameof(ReadField), BindingFlags.Static | BindingFlags.NonPublic)!;

    private static readonly MethodInfo ReadFieldObjectMethod = typeof(NetComponentDeltaStateSerializer)
        .GetMethod(nameof(ReadFieldObject), BindingFlags.Static | BindingFlags.NonPublic)!;

    [UsedImplicitly]
    private static void WriteField<T>(Serializer serializer, Stream stream, T value)
    {
        serializer.SerializeDirect(stream, value);
    }

    [UsedImplicitly]
    private static void WriteFieldObject(Serializer serializer, Stream stream, object value)
    {
        serializer.Serialize(stream, value);
    }

    [UsedImplicitly]
    private static void ReadField<T>(Serializer serializer, Stream stream, out T value)
    {
        serializer.DeserializeDirect(stream, out value);
    }

    [UsedImplicitly]
    private static void ReadFieldObject(Serializer serializer, Stream stream, out object value)
    {
        serializer.Deserialize(stream, out value);
    }
}