// Copyright (c) 2020 Siegfried Pammer
// 
// Permission is hereby granted, free of charge, to any person obtaining a copy of this
// software and associated documentation files (the "Software"), to deal in the Software
// without restriction, including without limitation the rights to use, copy, modify, merge,
// publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons
// to whom the Software is furnished to do so, subject to the following conditions:
// 
// The above copyright notice and this permission notice shall be included in all copies or
// substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
// FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;

using ICSharpCode.Decompiler.TypeSystem;

namespace ICSharpCode.Decompiler.IL
{
	partial class DeconstructInstruction
	{
		public static readonly SlotInfo InitSlot = new SlotInfo("Init", canInlineInto: true, isCollection: true);
		public static readonly SlotInfo PatternSlot = new SlotInfo("Pattern", canInlineInto: true);
		public static readonly SlotInfo ConversionsSlot = new SlotInfo("Conversions");
		public static readonly SlotInfo AssignmentsSlot = new SlotInfo("Assignments");

		public DeconstructInstruction()
			: base(OpCode.DeconstructInstruction)
		{
			this.Init = new InstructionCollection<StLoc>(this, 0);
		}

		public readonly InstructionCollection<StLoc> Init;

		MatchInstruction pattern;
		public MatchInstruction Pattern {
			get { return this.pattern; }
			set {
				ValidateChild(value);
				SetChildInstruction(ref this.pattern, value, Init.Count);
			}
		}

		Block conversions;
		public Block Conversions {
			get { return this.conversions; }
			set {
				ValidateChild(value);
				SetChildInstruction(ref this.conversions, value, Init.Count + 1);
			}
		}

		Block assignments;
		public Block Assignments {
			get { return this.assignments; }
			set {
				ValidateChild(value);
				SetChildInstruction(ref this.assignments, value, Init.Count + 2);
			}
		}

		protected sealed override int GetChildCount()
		{
			return Init.Count + 3;
		}

		protected sealed override ILInstruction GetChild(int index)
		{
			switch (index - Init.Count)
			{
				case 0:
					return this.pattern;
				case 1:
					return this.conversions;
				case 2:
					return this.assignments;
				default:
					return this.Init[index];
			}
		}

		protected sealed override void SetChild(int index, ILInstruction value)
		{
			switch (index - Init.Count)
			{
				case 0:
					this.Pattern = (MatchInstruction)value;
					break;
				case 1:
					this.Conversions = (Block)value;
					break;
				case 2:
					this.Assignments = (Block)value;
					break;
				default:
					this.Init[index] = (StLoc)value;
					break;
			}
		}

		protected sealed override SlotInfo GetChildSlot(int index)
		{
			switch (index - Init.Count)
			{
				case 0:
					return PatternSlot;
				case 1:
					return ConversionsSlot;
				case 2:
					return AssignmentsSlot;
				default:
					return InitSlot;
			}
		}

		public sealed override ILInstruction Clone()
		{
			var clone = new DeconstructInstruction();
			clone.Init.AddRange(this.Init.Select(inst => (StLoc)inst.Clone()));
			clone.Pattern = (MatchInstruction)this.pattern.Clone();
			clone.Conversions = (Block)this.conversions.Clone();
			clone.Assignments = (Block)this.assignments.Clone();
			return clone;
		}

		protected override InstructionFlags ComputeFlags()
		{
			var flags = InstructionFlags.None;
			foreach (var inst in Init)
			{
				flags |= inst.Flags;
			}
			flags |= pattern.Flags | conversions.Flags | assignments.Flags;
			return flags;
		}

		public override InstructionFlags DirectFlags {
			get {
				return InstructionFlags.None;
			}
		}

		protected internal override void InstructionCollectionUpdateComplete()
		{
			base.InstructionCollectionUpdateComplete();
			if (pattern.Parent == this)
				pattern.ChildIndex = Init.Count;
			if (conversions.Parent == this)
				conversions.ChildIndex = Init.Count + 1;
			if (assignments.Parent == this)
				assignments.ChildIndex = Init.Count + 2;
		}

		public override void WriteTo(ITextOutput output, ILAstWritingOptions options)
		{
			WriteILRange(output, options);
			output.Write("deconstruct ");
			output.MarkFoldStart("{...}");
			output.WriteLine("{");
			output.Indent();
			output.WriteLine("init:");
			output.Indent();
			foreach (var inst in this.Init)
			{
				inst.WriteTo(output, options);
				output.WriteLine();
			}
			output.Unindent();
			output.WriteLine("pattern:");
			output.Indent();
			pattern.WriteTo(output, options);
			output.Unindent();
			output.WriteLine();
			output.Write("conversions: ");
			conversions.WriteTo(output, options);
			output.WriteLine();
			output.Write("assignments: ");
			assignments.WriteTo(output, options);
			output.Unindent();
			output.WriteLine();
			output.Write('}');
			output.MarkFoldEnd();
		}

		internal static bool IsConversionStLoc(ILInstruction inst, out ILVariable variable, out ILVariable inputVariable)
		{
			inputVariable = null;
			if (!inst.MatchStLoc(out variable, out var value))
				return false;
			ILInstruction input;
			switch (value)
			{
				case Conv conv:
					input = conv.Argument;
					break;
				//case Call { Method: { IsOperator: true, Name: "op_Implicit" }, Arguments: { Count: 1 } } call:
				//	input = call.Arguments[0];
				//	break;
				default:
					return false;
			}
			return input.MatchLdLoc(out inputVariable) || input.MatchLdLoca(out inputVariable);
		}

		internal static bool IsAssignment(ILInstruction inst, ICompilation typeSystem, out IType expectedType, out ILInstruction value)
		{
			expectedType = null;
			value = null;
			switch (inst)
			{
				case CallInstruction call:
					if (call.Method.AccessorKind != System.Reflection.MethodSemanticsAttributes.Setter)
						return false;
					for (int i = 0; i < call.Arguments.Count - 1; i++)
					{
						ILInstruction arg = call.Arguments[i];
						if (arg.Flags == InstructionFlags.None)
						{
							// OK - we accept integer literals, etc.
						}
						else if (arg.MatchLdLoc(out var v))
						{
						}
						else
						{
							return false;
						}
					}
					expectedType = call.Method.Parameters.Last().Type;
					value = call.Arguments.Last();
					return true;
				case StLoc stloc:
					expectedType = stloc.Variable.Type;
					value = stloc.Value;
					return true;
				case StObj stobj:
					var target = stobj.Target;
					while (target.MatchLdFlda(out var nestedTarget, out _))
						target = nestedTarget;
					if (target.Flags == InstructionFlags.None)
					{
						// OK - we accept integer literals, etc.
					}
					else if (target.MatchLdLoc(out var v))
					{
					}
					else
					{
						return false;
					}
					if (stobj.Target.InferType(typeSystem) is ByReferenceType brt)
						expectedType = brt.ElementType;
					else
						expectedType = SpecialType.UnknownType;
					value = stobj.Value;
					return true;
				default:
					return false;
			}
		}

		internal override void CheckInvariant(ILPhase phase)
		{
			base.CheckInvariant(phase);
			var patternVariables = new HashSet<ILVariable>();
			var conversionVariables = new HashSet<ILVariable>();

			foreach (StLoc init in this.Init)
			{
				Debug.Assert(init.Variable.IsSingleDefinition && init.Variable.LoadCount == 1);
				Debug.Assert(init.Variable.LoadInstructions[0].IsDescendantOf(assignments));
			}

			ValidatePattern(pattern);

			foreach (var inst in this.conversions.Instructions)
			{
				if (!IsConversionStLoc(inst, out var variable, out var inputVariable))
					Debug.Fail("inst is not a conversion stloc!");
				Debug.Assert(variable.IsSingleDefinition && variable.LoadCount == 1);
				Debug.Assert(variable.LoadInstructions[0].IsDescendantOf(assignments));
				Debug.Assert(patternVariables.Contains(inputVariable));
				conversionVariables.Add(variable);
			}
			Debug.Assert(this.conversions.FinalInstruction is Nop);

			foreach (var inst in assignments.Instructions)
			{
				if (!(IsAssignment(inst, typeSystem: null, out _, out var value) && value.MatchLdLoc(out var inputVariable)))
					throw new InvalidOperationException("inst is not an assignment!");
				Debug.Assert(patternVariables.Contains(inputVariable) || conversionVariables.Contains(inputVariable));
			}
			Debug.Assert(this.assignments.FinalInstruction is Nop);

			void ValidatePattern(MatchInstruction inst)
			{
				Debug.Assert(inst.IsDeconstructCall || inst.IsDeconstructTuple);
				Debug.Assert(!inst.CheckNotNull && !inst.CheckType);
				Debug.Assert(!inst.HasDesignator);
				foreach (var subPattern in inst.SubPatterns.Cast<MatchInstruction>())
				{
					if (subPattern.IsVar)
					{
						Debug.Assert(subPattern.Variable.IsSingleDefinition && subPattern.Variable.LoadCount <= 1);
						if (subPattern.Variable.LoadCount == 1)
							Debug.Assert(subPattern.Variable.LoadInstructions[0].IsDescendantOf(this));
						patternVariables.Add(subPattern.Variable);
					}
					else
					{
						ValidatePattern(subPattern);
					}
				}
			}
		}
	}
}
