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;
				case "ToString" when method.Parameters.Count == 0:
					return IsGeneratedToString(method);
				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;
			if (property.IsSealed)
				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 == null || body.Instructions.Count != 1)
				return false;
			if (!(body.Instructions.Single() 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);
		}

		private bool IsGeneratedToString(IMethod method)
		{
			Debug.Assert(method.Name == "ToString");
			if (!method.IsOverride)
				return false;
			if (method.IsSealed)
				return false;
			if (method.GetAttributes().Any() || method.GetReturnTypeAttributes().Any())
				return false;
			var body = DecompileBody(method);
			if (body == null)
				return false;
			// stloc stringBuilder(newobj StringBuilder..ctor())
			if (!body.Instructions[0].MatchStLoc(out var stringBuilder, out var stringBuilderInit))
				return false;
			if (!(stringBuilderInit is NewObj { Arguments: { Count: 0 }, Method: { DeclaringTypeDefinition: { Name: "StringBuilder", Namespace: "System.Text" } } }))
				return false;
			// callvirt Append(ldloc stringBuilder, ldstr "R")
			if (!MatchAppendCallWithValue(body.Instructions[1], recordTypeDef.Name))
				return false;
			// callvirt Append(ldloc stringBuilder, ldstr " { ")
			if (!MatchAppendCallWithValue(body.Instructions[2], " { "))
				return false;
			// if (callvirt PrintMembers(ldloc this, ldloc stringBuilder)) { trueInst }
			if (!body.Instructions[3].MatchIfInstruction(out var condition, out var trueInst))
				return true;
			if (!(condition is CallVirt { Method: { Name: "PrintMembers" } } printMembersCall))
				return false;
			if (printMembersCall.Arguments.Count != 2)
				return false;
			if (!printMembersCall.Arguments[0].MatchLdThis())
				return false;
			if (!printMembersCall.Arguments[1].MatchLdLoc(stringBuilder))
				return false;
			// trueInst: callvirt Append(ldloc stringBuilder, ldstr " ")
			if (!MatchAppendCallWithValue(Block.Unwrap(trueInst), " "))
				return false;
			// callvirt Append(ldloc stringBuilder, ldstr "}")
			if (!MatchAppendCallWithValue(body.Instructions[4], "}"))
				return false;
			// leave IL_0000 (callvirt ToString(ldloc stringBuilder))
			if (!(body.Instructions[5] is Leave leave))
				return false;
			if (!(leave.Value is CallVirt { Method: { Name: "ToString" } } toStringCall))
				return false;
			if (toStringCall.Arguments.Count != 1)
				return false;
			return toStringCall.Arguments[0].MatchLdLoc(stringBuilder);

			bool MatchAppendCall(ILInstruction inst, out string val)
			{
				val = null;
				if (!(inst is CallVirt { Method: { Name: "Append" } } call))
					return false;
				if (call.Arguments.Count != 2)
					return false;
				if (!call.Arguments[0].MatchLdLoc(stringBuilder))
					return false;
				return call.Arguments[1].MatchLdStr(out val);
			}

			bool MatchAppendCallWithValue(ILInstruction inst, string val)
			{
				return MatchAppendCall(inst, out string tmp) && tmp == val;
			}
		}

		Block 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.CSharp1);
			var transforms = CSharpDecompiler.GetILTransforms();
			// Remove the last couple transforms -- we don't need variable names etc. here
			int lastBlockTransform = transforms.FindLastIndex(t => t is BlockILTransform);
			transforms.RemoveRange(lastBlockTransform + 1, transforms.Count - (lastBlockTransform + 1));
			il.RunTransforms(transforms,
				new ILTransformContext(il, typeSystem, debugInfo: null, settings) {
					CancellationToken = cancellationToken
				});
			if (il.Body is BlockContainer container)
			{
				return container.EntryPoint;
			}
			else if (il.Body is Block block)
			{
				return block;
			}
			else
			{
				return null;
			}
		}
	}
}