// Copyright (c) .NET Foundation and contributors. All rights reserved.
// Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
using System;
using ILLink.Shared.TypeSystemProxy;
using Microsoft.CodeAnalysis;
 
namespace ILLink.RoslynAnalyzer
{
	internal static class IMethodSymbolExtensions
	{
		public static bool HasImplicitThis (this IMethodSymbol method)
		{
			return !method.IsStatic;
		}
 
		/// <summary>
		/// Returns a list of the parameters pushed onto the stack before the method call (including the implicit 'this' parameter)
		/// </summary>
		public static ParameterProxyEnumerable GetParameters (this IMethodSymbol method)
		{
			return new ParameterProxyEnumerable (0, method.GetParametersCount (), new (method));
		}
 
		/// <summary>
		/// Returns a list of the parameters in the method's 'parameters' metadata section (i.e. excluding the implicit 'this' parameter)
		/// </summary>
		public static ParameterProxyEnumerable GetMetadataParameters (this IMethodSymbol method)
		{
			int implicitThisOffset = method.HasImplicitThis () ? 1 : 0;
			return new ParameterProxyEnumerable (implicitThisOffset, method.GetParametersCount (), new (method));
		}
 
		/// <summary>
		/// Gets the parameter at the <see cref="ParameterIndex"/> provided. Note ParameterIndex treat the implicit 'this' as index 0.
		/// Throws if the index is out of bounds.
		/// </summary>
		public static ParameterProxy GetParameter (this IMethodSymbol method, ParameterIndex index)
		{
			if (method.TryGetParameter (index) is not ParameterProxy param)
				throw new InvalidOperationException ($"Cannot get parameter at index {(int) index} of method {method.GetDisplayName ()} with {method.GetParametersCount ()} parameters.");
			return param;
		}
 
		/// <summary>
		/// Gets the parameter at the <see cref="ParameterIndex"/> provided. Note ParameterIndex treat the implicit 'this' as index 0.
		/// Returns null if the index is out of bounds.
		/// </summary>
		public static ParameterProxy? TryGetParameter (this IMethodSymbol method, ParameterIndex index)
		{
			if (method.GetParametersCount () <= (int) index || (int) index < 0)
				return null;
			return new ParameterProxy (new (method), index);
		}
 
		/// <summary>
		/// Gets the number of entries in the 'Parameters' section of a method's metadata (i.e. excludes the implicit 'this' from the count)
		/// </summary>
		public static int GetMetadataParametersCount (this IMethodSymbol method)
		{
			return method.Parameters.Length;
		}
 
		/// <summary>
		/// Gets the number of parameters pushed onto the stack when the method is called (including the implicit 'this' paramter)
		/// </summary>
		public static int GetParametersCount (this IMethodSymbol method)
		{
			return method.Parameters.Length + (method.HasImplicitThis () ? 1 : 0);
		}
	}
}