// Copyright 2004-2021 Castle Project - http://www.castleproject.org/
// 
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// 
//     http://www.apache.org/licenses/LICENSE-2.0
// 
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

namespace Castle.DynamicProxy.Generators.Emitters.SimpleAST
{
	using System;
	using System.Reflection.Emit;

	internal class IfNullExpression : IExpression, IStatement
	{
		private readonly IExpressionOrStatement ifNotNull;
		private readonly IExpressionOrStatement ifNull;
		private readonly Reference reference;
		private readonly IExpression expression;

		public IfNullExpression(Reference reference, IExpressionOrStatement ifNull, IExpressionOrStatement ifNotNull = null)
		{
			this.reference = reference ?? throw new ArgumentNullException(nameof(reference));
			this.ifNull = ifNull;
			this.ifNotNull = ifNotNull;
		}

		public IfNullExpression(IExpression expression, IExpressionOrStatement ifNull, IExpressionOrStatement ifNotNull = null)
		{
			this.expression = expression ?? throw new ArgumentNullException(nameof(expression));
			this.ifNull = ifNull;
			this.ifNotNull = ifNotNull;
		}

		public void Emit(ILGenerator gen)
		{
			if (reference != null)
			{
				ArgumentsUtil.EmitLoadOwnerAndReference(reference, gen);
			}
			else if (expression != null)
			{
				expression.Emit(gen);
			}

			var notNull = gen.DefineLabel();
			gen.Emit(OpCodes.Brtrue_S, notNull);
			ifNull.Emit(gen);
			gen.MarkLabel(notNull);
			if (ifNotNull != null) // yeah, I know that reads funny :)
			{
				ifNotNull.Emit(gen);
			}
		}
	}
}