using Mono.Cecil.Cil;
using System;

namespace Mono.Cecil {
	internal sealed class GenericParameterResolver {
		internal static TypeReference ResolveReturnTypeIfNeeded (MethodReference methodReference)
		{
			if (methodReference.DeclaringType.IsArray && methodReference.Name == "Get")
				return methodReference.ReturnType;

			var genericInstanceMethod = methodReference as GenericInstanceMethod;
			var declaringGenericInstanceType = methodReference.DeclaringType as GenericInstanceType;

			if (genericInstanceMethod == null && declaringGenericInstanceType == null)
				return methodReference.ReturnType;

			return ResolveIfNeeded (genericInstanceMethod, declaringGenericInstanceType, methodReference.ReturnType);
		}

		internal static TypeReference ResolveFieldTypeIfNeeded (FieldReference fieldReference)
		{
			return ResolveIfNeeded (null, fieldReference.DeclaringType as GenericInstanceType, fieldReference.FieldType);
		}

		internal static TypeReference ResolveParameterTypeIfNeeded (MethodReference method, ParameterReference parameter)
		{
			var genericInstanceMethod = method as GenericInstanceMethod;
			var declaringGenericInstanceType = method.DeclaringType as GenericInstanceType;

			if (genericInstanceMethod == null && declaringGenericInstanceType == null)
				return parameter.ParameterType;

			return ResolveIfNeeded (genericInstanceMethod, declaringGenericInstanceType, parameter.ParameterType);
		}

		internal static TypeReference ResolveVariableTypeIfNeeded (MethodReference method, VariableReference variable)
		{
			var genericInstanceMethod = method as GenericInstanceMethod;
			var declaringGenericInstanceType = method.DeclaringType as GenericInstanceType;

			if (genericInstanceMethod == null && declaringGenericInstanceType == null)
				return variable.VariableType;

			return ResolveIfNeeded (genericInstanceMethod, declaringGenericInstanceType, variable.VariableType);
		}

		private static TypeReference ResolveIfNeeded (IGenericInstance genericInstanceMethod, IGenericInstance declaringGenericInstanceType, TypeReference parameterType)
		{
			var byRefType = parameterType as ByReferenceType;
			if (byRefType != null)
				return ResolveIfNeeded (genericInstanceMethod, declaringGenericInstanceType, byRefType);

			var arrayType = parameterType as ArrayType;
			if (arrayType != null)
				return ResolveIfNeeded (genericInstanceMethod, declaringGenericInstanceType, arrayType);

			var genericInstanceType = parameterType as GenericInstanceType;
			if (genericInstanceType != null)
				return ResolveIfNeeded (genericInstanceMethod, declaringGenericInstanceType, genericInstanceType);

			var genericParameter = parameterType as GenericParameter;
			if (genericParameter != null)
				return ResolveIfNeeded (genericInstanceMethod, declaringGenericInstanceType, genericParameter);

			var requiredModifierType = parameterType as RequiredModifierType;
			if (requiredModifierType != null && ContainsGenericParameters (requiredModifierType))
				return ResolveIfNeeded (genericInstanceMethod, declaringGenericInstanceType, requiredModifierType.ElementType);

			if (ContainsGenericParameters (parameterType))
				throw new Exception ("Unexpected generic parameter.");

			return parameterType;
		}

		private static TypeReference ResolveIfNeeded (IGenericInstance genericInstanceMethod, IGenericInstance genericInstanceType, GenericParameter genericParameterElement)
		{
			return (genericParameterElement.MetadataType == MetadataType.MVar)
				? (genericInstanceMethod != null ? genericInstanceMethod.GenericArguments[genericParameterElement.Position] : genericParameterElement)
				: genericInstanceType.GenericArguments[genericParameterElement.Position];
		}

		private static ArrayType ResolveIfNeeded (IGenericInstance genericInstanceMethod, IGenericInstance genericInstanceType, ArrayType arrayType)
		{
			return new ArrayType (ResolveIfNeeded (genericInstanceMethod, genericInstanceType, arrayType.ElementType), arrayType.Rank);
		}

		private static ByReferenceType ResolveIfNeeded (IGenericInstance genericInstanceMethod, IGenericInstance genericInstanceType, ByReferenceType byReferenceType)
		{
			return new ByReferenceType (ResolveIfNeeded (genericInstanceMethod, genericInstanceType, byReferenceType.ElementType));
		}

		private static GenericInstanceType ResolveIfNeeded (IGenericInstance genericInstanceMethod, IGenericInstance genericInstanceType, GenericInstanceType genericInstanceType1)
		{
			if (!ContainsGenericParameters (genericInstanceType1))
				return genericInstanceType1;

			var newGenericInstance = new GenericInstanceType (genericInstanceType1.ElementType);

			foreach (var genericArgument in genericInstanceType1.GenericArguments) {
				if (!genericArgument.IsGenericParameter) {
					newGenericInstance.GenericArguments.Add (ResolveIfNeeded (genericInstanceMethod, genericInstanceType, genericArgument));
					continue;
				}

				var genParam = (GenericParameter)genericArgument;

				switch (genParam.Type) {
					case GenericParameterType.Type: {
							if (genericInstanceType == null)
								throw new NotSupportedException ();

							newGenericInstance.GenericArguments.Add (genericInstanceType.GenericArguments[genParam.Position]);
						}
						break;

					case GenericParameterType.Method: {
							if (genericInstanceMethod == null)
								newGenericInstance.GenericArguments.Add (genParam);
							else
								newGenericInstance.GenericArguments.Add (genericInstanceMethod.GenericArguments[genParam.Position]);
						}
						break;
				}
			}

			return newGenericInstance;
		}

		private static bool ContainsGenericParameters (TypeReference typeReference)
		{
			var genericParameter = typeReference as GenericParameter;
			if (genericParameter != null)
				return true;

			var arrayType = typeReference as ArrayType;
			if (arrayType != null)
				return ContainsGenericParameters (arrayType.ElementType);

			var pointerType = typeReference as PointerType;
			if (pointerType != null)
				return ContainsGenericParameters (pointerType.ElementType);

			var byRefType = typeReference as ByReferenceType;
			if (byRefType != null)
				return ContainsGenericParameters (byRefType.ElementType);

			var sentinelType = typeReference as SentinelType;
			if (sentinelType != null)
				return ContainsGenericParameters (sentinelType.ElementType);

			var pinnedType = typeReference as PinnedType;
			if (pinnedType != null)
				return ContainsGenericParameters (pinnedType.ElementType);

			var requiredModifierType = typeReference as RequiredModifierType;
			if (requiredModifierType != null)
				return ContainsGenericParameters (requiredModifierType.ElementType);

			var genericInstance = typeReference as GenericInstanceType;
			if (genericInstance != null) {
				foreach (var genericArgument in genericInstance.GenericArguments) {
					if (ContainsGenericParameters (genericArgument))
						return true;
				}

				return false;
			}

			if (typeReference is TypeSpecification)
				throw new NotSupportedException ();

			return false;
		}
	}
}