using System;
using System.Diagnostics;
using System.Linq;
using System.Reflection.Metadata;
using System.Threading;

using ICSharpCode.Decompiler.IL;
using ICSharpCode.Decompiler.IL.Transforms;
using ICSharpCode.Decompiler.TypeSystem;

namespace ICSharpCode.Decompiler.CSharp
{
	class RecordDecompiler
	{
		readonly IDecompilerTypeSystem typeSystem;
		readonly ITypeDefinition recordTypeDef;
		readonly CancellationToken cancellationToken;

		public RecordDecompiler(IDecompilerTypeSystem dts, ITypeDefinition recordTypeDef, CancellationToken cancellationToken)
		{
			this.typeSystem = dts;
			this.recordTypeDef = recordTypeDef;
			this.cancellationToken = cancellationToken;
		}

		bool IsRecordType(IType type)
		{
			return type.GetDefinition() == recordTypeDef
				&& type.TypeArguments.SequenceEqual(recordTypeDef.TypeParameters);
		}

		/// <summary>
		/// Gets whether the member of the record type will be automatically generated by the compiler.
		/// </summary>
		public bool MethodIsGenerated(IMethod method)
		{
			switch (method.Name)
			{
				// Some members in records are always compiler-generated and lead to a
				// "duplicate definition" error if we emit the generated code.
				case "op_Equality":
				case "op_Inequality":
				{
					// Don't emit comparison operators into C# record definition
					// Note: user can declare additional operator== as long as they have
					// different parameter types.
					return method.Parameters.Count == 2
						&& method.Parameters.All(p => IsRecordType(p.Type));
				}
				case "Equals" when method.Parameters.Count == 1:
				{
					IType paramType = method.Parameters[0].Type;
					if (paramType.IsKnownType(KnownTypeCode.Object))
					{
						// override bool Equals(object? obj): always generated
						return true;
					}
					else if (IsRecordType(paramType))
					{
						// virtual bool Equals(R? other): generated unless user-declared
						return false;
					}
					else
					{
						return false;
					}
				}
				case "<Clone>$" when method.Parameters.Count == 0:
					// Always generated; Method name cannot be expressed in C#
					return true;
				default:
					return false;
			}
		}

		internal bool PropertyIsGenerated(IProperty property)
		{
			switch (property.Name)
			{
				case "EqualityContract":
					return IsGeneratedEqualityContract(property);
				default:
					return false;
			}
		}

		private bool IsGeneratedEqualityContract(IProperty property)
		{
			// Generated member:
			// protected virtual Type EqualityContract {
			//    [CompilerGenerated] get => typeof(R);
			// }
			Debug.Assert(property.Name == "EqualityContract");
			if (property.Accessibility != Accessibility.Protected)
				return false;
			if (!(property.IsVirtual || property.IsOverride))
				return false;
			var getter = property.Getter;
			if (!(getter != null && !property.CanSet))
				return false;
			if (property.GetAttributes().Any())
				return false;
			if (getter.GetReturnTypeAttributes().Any())
				return false;
			var attrs = getter.GetAttributes().ToList();
			if (attrs.Count != 1)
				return false;
			if (!attrs[0].AttributeType.IsKnownType(KnownAttribute.CompilerGenerated))
				return false;
			var body = DecompileBody(getter);
			if (!(body?.SingleInstruction() is Leave leave))
				return false;
			// leave IL_0000 (call GetTypeFromHandle(ldtypetoken R))
			if (!TransformExpressionTrees.MatchGetTypeFromHandle(leave.Value, out IType ty))
				return false;
			return IsRecordType(ty);
		}

		BlockContainer DecompileBody(IMethod method)
		{
			if (method == null || method.MetadataToken.IsNil)
				return null;
			var metadata = typeSystem.MainModule.metadata;

			var methodDefHandle = (MethodDefinitionHandle)method.MetadataToken;
			var methodDef = metadata.GetMethodDefinition(methodDefHandle);
			if (!methodDef.HasBody())
				return null;

			var genericContext = new GenericContext(
				classTypeParameters: recordTypeDef.TypeParameters,
				methodTypeParameters: null);
			var body = typeSystem.MainModule.PEFile.Reader.GetMethodBody(methodDef.RelativeVirtualAddress);
			var ilReader = new ILReader(typeSystem.MainModule);
			var il = ilReader.ReadIL(methodDefHandle, body, genericContext, ILFunctionKind.TopLevelFunction, cancellationToken);
			var settings = new DecompilerSettings(LanguageVersion.CSharp2);
			il.RunTransforms(CSharpDecompiler.EarlyILTransforms(),
				new ILTransformContext(il, typeSystem, debugInfo: null, settings) {
					CancellationToken = cancellationToken
				});
			return (BlockContainer)il.Body;
		}
	}
}