using System;
using System.Collections.Generic;
using System.Collections.Immutable;
using System.Linq;
using System.Reflection.Metadata;
using System.Reflection.Metadata.Ecma335;
using System.Reflection.PortableExecutable;
using System.Text;
using System.Threading.Tasks;
using ICSharpCode.Decompiler.Disassembler;
using ICSharpCode.Decompiler.Semantics;
using ICSharpCode.Decompiler.TypeSystem;
using ICSharpCode.Decompiler.TypeSystem.Implementation;
using ICSharpCode.Decompiler.Util;

using static ICSharpCode.Decompiler.Metadata.ILOpCodeExtensions;

namespace ICSharpCode.Decompiler.CSharp
{
	class RequiredNamespaceCollector
	{
		public static void CollectNamespaces(DecompilerTypeSystem typeSystem, HashSet<string> namespaces)
		{
			foreach (var type in typeSystem.MainAssembly.GetAllTypeDefinitions()) {
				CollectNamespaces(type, typeSystem, namespaces);
			}
		}

		public static void CollectNamespaces(IEntity entity, DecompilerTypeSystem typeSystem, HashSet<string> namespaces)
		{
			if (entity == null)
				return;
			switch (entity) {
				case ITypeDefinition td:
					namespaces.Add(td.Namespace);
					HandleAttributes(td.Attributes, namespaces);

					foreach (var typeParam in td.TypeParameters) {
						HandleAttributes(typeParam.Attributes, namespaces);
					}

					foreach (var baseType in td.DirectBaseTypes) {
						CollectNamespacesForTypeReference(baseType, namespaces);
					}

					foreach (var nestedType in td.NestedTypes) {
						CollectNamespaces(nestedType, typeSystem, namespaces);
					}

					foreach (var field in td.Fields) {
						CollectNamespaces(field, typeSystem, namespaces);
					}

					foreach (var property in td.Properties) {
						CollectNamespaces(property, typeSystem, namespaces);
					}

					foreach (var @event in td.Events) {
						CollectNamespaces(@event, typeSystem, namespaces);
					}

					foreach (var method in td.Methods) {
						CollectNamespaces(method, typeSystem, namespaces);
					}
					break;
				case IField field:
					HandleAttributes(field.Attributes, namespaces);
					CollectNamespacesForTypeReference(field.ReturnType, namespaces);
					break;
				case IMethod method:
					HandleAttributes(method.Attributes, namespaces);
					CollectNamespacesForTypeReference(method.ReturnType, namespaces);
					foreach (var param in method.Parameters) {
						HandleAttributes(param.Attributes, namespaces);
						CollectNamespacesForTypeReference(param.Type, namespaces);
					}
					foreach (var typeParam in method.TypeParameters) {
						HandleAttributes(typeParam.Attributes, namespaces);
					}
					if (!method.MetadataToken.IsNil && method.HasBody) {
						var reader = typeSystem.ModuleDefinition.Reader;
						var methodDef = typeSystem.ModuleDefinition.GetMetadataReader().GetMethodDefinition((MethodDefinitionHandle)method.MetadataToken);
						var body = reader.GetMethodBody(methodDef.RelativeVirtualAddress);
						CollectNamespacesFromMethodBody(body, reader, typeSystem, namespaces);
					}
					break;
				case IProperty property:
					HandleAttributes(property.Attributes, namespaces);
					CollectNamespaces(property.Getter, typeSystem, namespaces);
					CollectNamespaces(property.Setter, typeSystem, namespaces);
					break;
				case IEvent @event:
					HandleAttributes(@event.Attributes, namespaces);
					CollectNamespaces(@event.AddAccessor, typeSystem, namespaces);
					CollectNamespaces(@event.RemoveAccessor, typeSystem, namespaces);
					break;
				default:
					throw new NotImplementedException();
			}
		}

		static void CollectNamespacesForTypeReference(IType type, HashSet<string> namespaces)
		{
			switch (type) {
				case ArrayType arrayType:
					namespaces.Add(arrayType.Namespace);
					CollectNamespacesForTypeReference(arrayType.ElementType, namespaces);
					break;
				case ParameterizedType parameterizedType:
					namespaces.Add(parameterizedType.Namespace);
					CollectNamespacesForTypeReference(parameterizedType.GenericType, namespaces);
					foreach (var arg in parameterizedType.TypeArguments)
						CollectNamespacesForTypeReference(arg, namespaces);
					break;
				case ByReferenceType byReferenceType:
					CollectNamespacesForTypeReference(byReferenceType.ElementType, namespaces);
					break;
				case PointerType pointerType:
					CollectNamespacesForTypeReference(pointerType.ElementType, namespaces);
					break;
				default:
					namespaces.Add(type.Namespace);
					break;
			}
		}

		public static void CollectNamespaces(EntityHandle entity, DecompilerTypeSystem typeSystem, HashSet<string> namespaces)
		{
			CollectNamespaces(entity.Kind.IsTypeKind() ? (IEntity)typeSystem.ResolveAsType(entity).GetDefinition() : typeSystem.ResolveAsMember(entity), typeSystem, namespaces);
		}

		static void HandleAttributes(IEnumerable<IAttribute> attributes, HashSet<string> namespaces)
		{
			foreach (var attr in attributes) {
				namespaces.Add(attr.AttributeType.Namespace);
				foreach (var arg in attr.PositionalArguments) {
					namespaces.Add(arg.Type.Namespace);
					if (arg is TypeOfResolveResult torr)
						namespaces.Add(torr.ReferencedType.Namespace);
				}
				foreach (var arg in attr.NamedArguments) {
					namespaces.Add(arg.Value.Type.Namespace);
					if (arg.Value is TypeOfResolveResult torr)
						namespaces.Add(torr.ReferencedType.Namespace);
				}
			}
		}

		static void CollectNamespacesFromMethodBody(MethodBodyBlock method, PEReader reader, DecompilerTypeSystem typeSystem, HashSet<string> namespaces)
		{
			var instructions = method.GetILReader();
			var metadata = reader.GetMetadataReader();

			if (!method.LocalSignature.IsNil) {
				var localSignature = metadata.GetStandaloneSignature(method.LocalSignature).DecodeLocalSignature(TypeReferenceSignatureDecoder.Instance, default);
				foreach (var type in localSignature)
					CollectNamespacesForTypeReference(typeSystem.ResolveFromSignature(type), namespaces);
			}

			foreach (var region in method.ExceptionRegions) {
				if (region.CatchType.IsNil) continue;
				CollectNamespacesForTypeReference(typeSystem.ResolveAsType(region.CatchType), namespaces);
			}

			while (instructions.RemainingBytes > 0) {
				var opCode = instructions.DecodeOpCode();
				switch (opCode.GetOperandType()) {
					case Metadata.OperandType.Field:
					case Metadata.OperandType.Method:
					case Metadata.OperandType.Sig:
					case Metadata.OperandType.Tok:
					case Metadata.OperandType.Type:
						var handle = MetadataTokens.EntityHandle(instructions.ReadInt32());
						if (handle.Kind.IsTypeKind())
							CollectNamespacesForTypeReference(typeSystem.ResolveAsType(handle), namespaces);
						else
							CollectNamespacesForMemberReference(typeSystem.ResolveAsMember(handle), namespaces);
						break;
					default:
						instructions.SkipOperand(opCode);
						break;
				}
			}
		}

		static void CollectNamespacesForMemberReference(IMember member, HashSet<string> namespaces)
		{
			switch (member) {
				case IField field:
					CollectNamespacesForTypeReference(field.DeclaringType, namespaces);
					CollectNamespacesForTypeReference(field.ReturnType, namespaces);
					break;
				case IMethod method:
					CollectNamespacesForTypeReference(method.DeclaringType, namespaces);
					CollectNamespacesForTypeReference(method.ReturnType, namespaces);
					foreach (var param in method.Parameters)
						CollectNamespacesForTypeReference(param.Type, namespaces);
					foreach (var arg in method.TypeArguments)
						CollectNamespacesForTypeReference(arg, namespaces);
					break;
				default:
					throw new NotImplementedException();
			}
		}
	}
}