using System;

using System.Diagnostics.CodeAnalysis;

using System.Reflection;

using System.Threading;

using System.Threading.Tasks;

using Npgsql.BackendMessages;

// ReSharper disable StaticMemberInGenericType

namespace Npgsql.TypeHandling

{

delegate T ReadDelegate<T>(NpgsqlTypeHandler handler, NpgsqlReadBuffer buffer, int columnLength, FieldDescription? fieldDescription = null);

delegate ValueTask<T> ReadAsyncDelegate<T>(NpgsqlTypeHandler handler, NpgsqlReadBuffer buffer, int columnLen, bool async, FieldDescription? fieldDescription = null);

delegate int ValidateAndGetLengthDelegate<T>(NpgsqlTypeHandler handler, T value, ref NpgsqlLengthCache? lengthCache, NpgsqlParameter? parameter);

delegate Task WriteAsyncDelegate<T>(NpgsqlTypeHandler handler, T value, NpgsqlWriteBuffer buffer, NpgsqlLengthCache? lengthCache, NpgsqlParameter? parameter, bool async, CancellationToken cancellationToken = default);

static class NullableHandler<T>

{

public static readonly Type? UnderlyingType;

[NotNull] public static readonly ReadDelegate<T>? Read;

[NotNull] public static readonly ReadAsyncDelegate<T>? ReadAsync;

[NotNull] public static readonly ValidateAndGetLengthDelegate<T>? ValidateAndGetLength;

[NotNull] public static readonly WriteAsyncDelegate<T>? WriteAsync;

public static bool Exists => UnderlyingType != null;

static NullableHandler()

{

UnderlyingType = Nullable.GetUnderlyingType(typeof(T));

if (UnderlyingType == null)

return;

Read = NullableHandler.CreateDelegate<ReadDelegate<T>>(UnderlyingType, NullableHandler.ReadMethod);

ReadAsync = NullableHandler.CreateDelegate<ReadAsyncDelegate<T>>(UnderlyingType, NullableHandler.ReadAsyncMethod);

ValidateAndGetLength = NullableHandler.CreateDelegate<ValidateAndGetLengthDelegate<T>>(UnderlyingType, NullableHandler.ValidateMethod);

WriteAsync = NullableHandler.CreateDelegate<WriteAsyncDelegate<T>>(UnderlyingType, NullableHandler.WriteAsyncMethod);

}

}

static class NullableHandler

{

internal static readonly MethodInfo ReadMethod = new ReadDelegate<int?>(Read<int>).Method.GetGenericMethodDefinition();

internal static readonly MethodInfo ReadAsyncMethod = new ReadAsyncDelegate<int?>(ReadAsync<int>).Method.GetGenericMethodDefinition();

internal static readonly MethodInfo ValidateMethod = new ValidateAndGetLengthDelegate<int?>(ValidateAndGetLength).Method.GetGenericMethodDefinition();

internal static readonly MethodInfo WriteAsyncMethod = new WriteAsyncDelegate<int?>(WriteAsync).Method.GetGenericMethodDefinition();

static T? Read<T>(NpgsqlTypeHandler handler, NpgsqlReadBuffer buffer, int columnLength, FieldDescription? fieldDescription)

where T : struct

=> handler.Read<T>(buffer, columnLength, fieldDescription);

static async ValueTask<T?> ReadAsync<T>(NpgsqlTypeHandler handler, NpgsqlReadBuffer buffer, int columnLength, bool async, FieldDescription? fieldDescription)

where T : struct

=> await handler.Read<T>(buffer, columnLength, async, fieldDescription);

static int ValidateAndGetLength<T>(NpgsqlTypeHandler handler, T? value, ref NpgsqlLengthCache? lengthCache, NpgsqlParameter? parameter)

where T : struct

=> value.HasValue ? handler.ValidateAndGetLength(value.Value, ref lengthCache, parameter) : 0;

static Task WriteAsync<T>(NpgsqlTypeHandler handler, T? value, NpgsqlWriteBuffer buffer, NpgsqlLengthCache? lengthCache, NpgsqlParameter? parameter, bool async, CancellationToken cancellationToken = default)

where T : struct

=> value.HasValue

? handler.WriteWithLengthInternal(value.Value, buffer, lengthCache, parameter, async, cancellationToken)

: handler.WriteWithLengthInternal(DBNull.Value, buffer, lengthCache, parameter, async, cancellationToken);

internal static TDelegate CreateDelegate<TDelegate>(Type underlyingType, MethodInfo method)

where TDelegate : Delegate

=> (TDelegate)method.MakeGenericMethod(underlyingType).CreateDelegate(typeof(TDelegate));

}

}