// Copyright (c) 2015 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.Diagnostics;
using System.Linq;
using ICSharpCode.Decompiler.TypeSystem;
using ICSharpCode.Decompiler.TypeSystem.Implementation;
using ICSharpCode.Decompiler.Util;

namespace ICSharpCode.Decompiler.IL.Transforms
{
	/// <summary>
	/// Constructs compound assignments and inline assignments.
	/// </summary>
	public class TransformAssignment : IStatementTransform
	{
		StatementTransformContext context;
		
		void IStatementTransform.Run(Block block, int pos, StatementTransformContext context)
		{
			this.context = context;
			if (TransformInlineAssignmentStObjOrCall(block, pos) || TransformInlineAssignmentLocal(block, pos)) {
				// both inline assignments create a top-level stloc which might affect inlining
				context.RequestRerun();
				return;
			}
			if (TransformPostIncDecOperatorWithInlineStore(block, pos)
				|| TransformPostIncDecOperator(block, pos)
				|| TransformPostIncDecOperatorLocal(block, pos))
			{
				// again, new top-level stloc might need inlining:
				context.RequestRerun();
				return;
			}
		}

		/// <code>
		/// stloc s(value)
		/// stloc l(ldloc s)
		/// stobj(..., ldloc s)
		///   where ... is pure and does not use s or l,
		///   and where neither the 'stloc s' nor the 'stobj' truncates
		/// -->
		/// stloc l(stobj (..., value))
		/// </code>
		/// e.g. used for inline assignment to instance field
		/// 
		/// -or-
		/// 
		/// <code>
		/// stloc s(value)
		/// stobj (..., ldloc s)
		///   where ... is pure and does not use s, and where the 'stobj' does not truncate
		/// -->
		/// stloc s(stobj (..., value))
		/// </code>
		/// e.g. used for inline assignment to static field
		/// 
		/// -or-
		/// 
		/// <code>
		/// stloc s(value)
		/// call set_Property(..., ldloc s)
		///   where the '...' arguments are pure and not using 's'
		/// -->
		/// stloc s(Block InlineAssign { call set_Property(..., stloc i(value)); final: ldloc i })
		///   new temporary 'i' has type of the property; transform only valid if 'stloc i' doesn't truncate
		/// </code>
		bool TransformInlineAssignmentStObjOrCall(Block block, int pos)
		{
			var inst = block.Instructions[pos] as StLoc;
			// in some cases it can be a compiler-generated local
			if (inst == null || (inst.Variable.Kind != VariableKind.StackSlot && inst.Variable.Kind != VariableKind.Local))
				return false;
			if (IsImplicitTruncation(inst.Value, inst.Variable.Type)) {
				// 'stloc s' is implicitly truncating the value
				return false;
			}
			ILVariable local;
			int nextPos;
			if (block.Instructions[pos + 1] is StLoc localStore) { // with extra local
				if (localStore.Variable.Kind != VariableKind.Local || !localStore.Value.MatchLdLoc(inst.Variable))
					return false;
				// if we're using an extra local, we'll delete "s", so check that that doesn't have any additional uses
				if (!(inst.Variable.IsSingleDefinition && inst.Variable.LoadCount == 2))
					return false;
				local = localStore.Variable;
				nextPos = pos + 2;
			} else {
				local = inst.Variable;
				localStore = null;
				nextPos = pos + 1;
			}
			if (block.Instructions[nextPos] is StObj stobj) {
				if (!stobj.Value.MatchLdLoc(inst.Variable))
					return false;
				if (!SemanticHelper.IsPure(stobj.Target.Flags) || inst.Variable.IsUsedWithin(stobj.Target))
					return false;
				if (IsImplicitTruncation(inst.Value, stobj.Type)) {
					// 'stobj' is implicitly truncating the value
					return false;
				}
				context.Step("Inline assignment stobj", stobj);
				block.Instructions.Remove(localStore);
				block.Instructions.Remove(stobj);
				stobj.Value = inst.Value;
				inst.ReplaceWith(new StLoc(local, stobj));
				// note: our caller will trigger a re-run, which will call HandleStObjCompoundAssign if applicable
				return true;
			} else if (block.Instructions[nextPos] is CallInstruction call) {
				// call must be a setter call:
				if (!(call.OpCode == OpCode.Call || call.OpCode == OpCode.CallVirt))
					return false;
				if (call.ResultType != StackType.Void || call.Arguments.Count == 0)
					return false;
				if (!call.Method.Equals((call.Method.AccessorOwner as IProperty)?.Setter))
					return false;
				if (!call.Arguments.Last().MatchLdLoc(inst.Variable))
					return false;
				foreach (var arg in call.Arguments.SkipLast(1)) {
					if (!SemanticHelper.IsPure(arg.Flags) || inst.Variable.IsUsedWithin(arg))
						return false;
				}
				if (IsImplicitTruncation(inst.Value, call.Method.Parameters.Last().Type)) {
					// setter call is implicitly truncating the value
					return false;
				}
				// stloc s(Block InlineAssign { call set_Property(..., stloc i(value)); final: ldloc i })
				context.Step("Inline assignment call", call);
				block.Instructions.Remove(localStore);
				block.Instructions.Remove(call);
				var newVar = context.Function.RegisterVariable(VariableKind.StackSlot, call.Method.Parameters.Last().Type);
				call.Arguments[call.Arguments.Count - 1] = new StLoc(newVar, inst.Value);
				var inlineBlock = new Block(BlockKind.CallInlineAssign) {
					Instructions = { call },
					FinalInstruction = new LdLoc(newVar)
				};
				inst.ReplaceWith(new StLoc(local, inlineBlock));
				// because the ExpressionTransforms don't look into inline blocks, manually trigger HandleCallCompoundAssign
				if (HandleCallCompoundAssign(call, context)) {
					// if we did construct a compound assignment, it should have made our inline block redundant:
					if (inlineBlock.Instructions.Single().MatchStLoc(newVar, out var compoundAssign)) {
						Debug.Assert(newVar.IsSingleDefinition && newVar.LoadCount == 1);
						inlineBlock.ReplaceWith(compoundAssign);
					}
				}
				return true;
			} else {
				return false;
			}
		}
		
		static ILInstruction UnwrapSmallIntegerConv(ILInstruction inst, out Conv conv)
		{
			conv = inst as Conv;
			if (conv != null && conv.Kind == ConversionKind.Truncate && conv.TargetType.IsSmallIntegerType()) {
				// for compound assignments to small integers, the compiler emits a "conv" instruction
				return conv.Argument;
			} else {
				return inst;
			}
		}

		static bool ValidateCompoundAssign(BinaryNumericInstruction binary, Conv conv, IType targetType)
		{
			if (!CompoundAssignmentInstruction.IsBinaryCompatibleWithType(binary, targetType))
				return false;
			if (conv != null && !(conv.TargetType == targetType.ToPrimitiveType() && conv.CheckForOverflow == binary.CheckForOverflow))
				return false; // conv does not match binary operation
			return true;
		}
		
		static bool MatchingGetterAndSetterCalls(CallInstruction getterCall, CallInstruction setterCall)
		{
			if (getterCall == null || setterCall == null || !IsSameMember(getterCall.Method.AccessorOwner, setterCall.Method.AccessorOwner))
				return false;
			var owner = getterCall.Method.AccessorOwner as IProperty;
			if (owner == null || !IsSameMember(getterCall.Method, owner.Getter) || !IsSameMember(setterCall.Method, owner.Setter))
				return false;
			if (setterCall.Arguments.Count != getterCall.Arguments.Count + 1)
				return false;
			// Ensure that same arguments are passed to getterCall and setterCall:
			for (int j = 0; j < getterCall.Arguments.Count; j++) {
				if (!SemanticHelper.IsPure(getterCall.Arguments[j].Flags))
					return false;
				if (!getterCall.Arguments[j].Match(setterCall.Arguments[j]).Success)
					return false;
			}
			return true;
		}

		/// <summary>
		/// Transform compound assignments where the return value is not being used,
		/// or where there's an inlined assignment within the setter call.
		/// </summary>
		/// <remarks>
		/// Called by ExpressionTransforms.
		/// </remarks>
		internal static bool HandleCallCompoundAssign(CallInstruction setterCall, StatementTransformContext context)
		{
			// callvirt set_Property(ldloc S_1, binary.op(callvirt get_Property(ldloc S_1), value))
			// ==> compound.op.new(callvirt get_Property(ldloc S_1), value)
			var setterValue = setterCall.Arguments.LastOrDefault();
			var storeInSetter = setterValue as StLoc;
			if (storeInSetter != null) {
				// callvirt set_Property(ldloc S_1, stloc v(binary.op(callvirt get_Property(ldloc S_1), value)))
				// ==> stloc v(compound.op.new(callvirt get_Property(ldloc S_1), value))
				setterValue = storeInSetter.Value;
			}
			setterValue = UnwrapSmallIntegerConv(setterValue, out var conv);
			if (!(setterValue is BinaryNumericInstruction binary))
				return false;
			var getterCall = binary.Left as CallInstruction;
			if (!MatchingGetterAndSetterCalls(getterCall, setterCall))
				return false;
			IType targetType = getterCall.Method.ReturnType;
			if (!ValidateCompoundAssign(binary, conv, targetType))
				return false;
			if (storeInSetter != null && storeInSetter.Variable.Type.IsSmallIntegerType()) {
				// 'stloc v' implicitly truncates.
				// Ensure that type of 'v' must match type of the property:
				if (storeInSetter.Variable.Type.GetSize() != targetType.GetSize())
					return false;
				if (storeInSetter.Variable.Type.GetSign() != targetType.GetSign())
					return false;
			}
			context.Step($"Compound assignment to '{getterCall.Method.AccessorOwner.Name}'", setterCall);
			ILInstruction newInst = new CompoundAssignmentInstruction(
				binary, getterCall, binary.Right,
				getterCall.Method.ReturnType, CompoundAssignmentType.EvaluatesToNewValue);
			if (storeInSetter != null) {
				storeInSetter.Value = newInst;
				newInst = storeInSetter;
				context.RequestRerun(); // moving stloc to top-level might trigger inlining
			}
			setterCall.ReplaceWith(newInst);
			return true;
		}

		/// <summary>
		/// stobj(target, binary.op(ldobj(target), ...))
		///   where target is pure
		/// => compound.op(target, ...)
		/// </summary>
		/// <remarks>
		/// Called by ExpressionTransforms.
		/// </remarks>
		internal static bool HandleStObjCompoundAssign(StObj inst, ILTransformContext context)
		{
			if (!(UnwrapSmallIntegerConv(inst.Value, out var conv) is BinaryNumericInstruction binary))
				return false;
			if (!(binary.Left is LdObj ldobj))
				return false;
			if (!inst.Target.Match(ldobj.Target).Success)
				return false;
			if (!SemanticHelper.IsPure(ldobj.Target.Flags))
				return false;
			// ldobj.Type may just be 'int' (due to ldind.i4) when we're actually operating on a 'ref MyEnum'.
			// Try to determine the real type of the object we're modifying:
			IType targetType = ldobj.Target.InferType();
			if (targetType.Kind == TypeKind.Pointer || targetType.Kind == TypeKind.ByReference) {
				targetType = ((TypeWithElementType)targetType).ElementType;
				if (targetType.Kind == TypeKind.Unknown || targetType.GetSize() != ldobj.Type.GetSize()) {
					targetType = ldobj.Type;
				}
			} else {
				targetType = ldobj.Type;
			}
			if (!ValidateCompoundAssign(binary, conv, targetType))
				return false;
			context.Step("compound assignment", inst);
			inst.ReplaceWith(new CompoundAssignmentInstruction(
				binary, binary.Left, binary.Right,
				targetType, CompoundAssignmentType.EvaluatesToNewValue));
			return true;
		}

		/// <code>
		/// stloc s(value)
		/// stloc l(ldloc s)
		///   where neither 'stloc s' nor 'stloc l' truncates the value
		/// -->
		/// stloc s(stloc l(value))
		/// </code>
		bool TransformInlineAssignmentLocal(Block block, int pos)
		{
			var inst = block.Instructions[pos] as StLoc;
			var nextInst = block.Instructions.ElementAtOrDefault(pos + 1) as StLoc;
			if (inst == null || nextInst == null)
				return false;
			if (inst.Variable.Kind != VariableKind.StackSlot)
				return false;
			Debug.Assert(!inst.Variable.Type.IsSmallIntegerType());
			if (!(nextInst.Variable.Kind == VariableKind.Local || nextInst.Variable.Kind == VariableKind.Parameter))
				return false;
			if (!nextInst.Value.MatchLdLoc(inst.Variable))
				return false;
			if (IsImplicitTruncation(inst.Value, inst.Variable.Type)) {
				// 'stloc s' is implicitly truncating the stack value
				return false;
			}
			if (IsImplicitTruncation(inst.Value, nextInst.Variable.Type)) {
				// 'stloc l' is implicitly truncating the stack value
				return false;
			}
			context.Step("Inline assignment to local variable", inst);
			var value = inst.Value;
			var var = nextInst.Variable;
			var stackVar = inst.Variable;
			block.Instructions.RemoveAt(pos);
			nextInst.ReplaceWith(new StLoc(stackVar, new StLoc(var, value)));
			return true;
		}

		/// <summary>
		/// Gets whether 'stobj type(..., value)' would evaluate to a different value than 'value'
		/// due to implicit truncation.
		/// </summary>
		static internal bool IsImplicitTruncation(ILInstruction value, IType type, bool allowNullableValue = false)
		{
			if (!type.IsSmallIntegerType()) {
				// Implicit truncation in ILAst only happens for small integer types;
				// other types of implicit truncation in IL cause the ILReader to insert
				// conv instructions.
				return false;
			}
			// With small integer types, test whether the value might be changed by
			// truncation (based on type.GetSize()) followed by sign/zero extension (based on type.GetSign()).
			// (it's OK to have false-positives here if we're unsure)
			if (value.MatchLdcI4(out int val)) {
				switch (type.GetEnumUnderlyingType().GetDefinition()?.KnownTypeCode) {
					case KnownTypeCode.Boolean:
						return !(val == 0 || val == 1);
					case KnownTypeCode.Byte:
						return !(val >= byte.MinValue && val <= byte.MaxValue);
					case KnownTypeCode.SByte:
						return !(val >= sbyte.MinValue && val <= sbyte.MaxValue);
					case KnownTypeCode.Int16:
						return !(val >= short.MinValue && val <= short.MaxValue);
					case KnownTypeCode.UInt16:
					case KnownTypeCode.Char:
						return !(val >= ushort.MinValue && val <= ushort.MaxValue);
				}
			} else if (value is Conv conv) {
				return conv.TargetType != type.ToPrimitiveType();
			} else if (value is Comp) {
				return false; // comp returns 0 or 1, which always fits
			} else {
				IType inferredType = value.InferType();
				if (allowNullableValue) {
					inferredType = NullableType.GetUnderlyingType(inferredType);
				}
				if (inferredType.Kind != TypeKind.Unknown) {
					return !(inferredType.GetSize() <= type.GetSize() && inferredType.GetSign() == type.GetSign());
				}
			}
			return true;
		}
		
		/// <code>
		/// stloc s(ldloc l)
		/// stloc l(binary.op(ldloc s, ldc.i4 1))
		/// -->
		/// stloc s(block {
		/// 	stloc s2(ldloc l)
		/// 	stloc l(binary.op(ldloc s2, ldc.i4 1))
		/// 	final: ldloc s2
		/// })
		/// </code>
		bool TransformPostIncDecOperatorLocal(Block block, int pos)
		{
			var inst = block.Instructions[pos] as StLoc;
			var nextInst = block.Instructions.ElementAtOrDefault(pos + 1) as StLoc;
			if (inst == null || nextInst == null || !inst.Value.MatchLdLoc(out var loadVar) || !ILVariableEqualityComparer.Instance.Equals(loadVar, nextInst.Variable))
				return false;
			var binary = nextInst.Value as BinaryNumericInstruction;
			if (inst.Variable.Kind != VariableKind.StackSlot || nextInst.Variable.Kind == VariableKind.StackSlot || binary == null)
				return false;
			if (binary.IsLifted)
				return false;
			if ((binary.Operator != BinaryNumericOperator.Add && binary.Operator != BinaryNumericOperator.Sub) || !binary.Left.MatchLdLoc(inst.Variable) || !binary.Right.MatchLdcI4(1))
				return false;
			context.Step($"TransformPostIncDecOperatorLocal", inst);
			if (loadVar != nextInst.Variable) {
				// load and store are two different variables, that were split from the same variable
				context.Function.RecombineVariables(loadVar, nextInst.Variable);
			}
			var tempStore = context.Function.RegisterVariable(VariableKind.StackSlot, inst.Variable.Type);
			var assignment = new Block(BlockKind.PostfixOperator);
			assignment.Instructions.Add(new StLoc(tempStore, new LdLoc(loadVar)));
			assignment.Instructions.Add(new StLoc(loadVar, new BinaryNumericInstruction(binary.Operator, new LdLoc(tempStore), new LdcI4(1), binary.CheckForOverflow, binary.Sign)));
			assignment.FinalInstruction = new LdLoc(tempStore);
			inst.Value = assignment;
			block.Instructions.RemoveAt(pos + 1); // remove nextInst
			return true;
		}
		
		/// <summary>
		/// Gets whether 'inst' is a possible store for use as a compound store.
		/// </summary>
		bool IsCompoundStore(ILInstruction inst, out IType storeType, out ILInstruction value)
		{
			value = null;
			storeType = null;
			if (inst is StObj stobj) {
				storeType = stobj.Type;
				value = stobj.Value;
				return SemanticHelper.IsPure(stobj.Target.Flags);
			} else if (inst is CallInstruction call && (call.OpCode == OpCode.Call || call.OpCode == OpCode.CallVirt)) {
				if (call.Method.Parameters.Count == 0) {
					return false;
				}
				foreach (var arg in call.Arguments.SkipLast(1)) {
					if (!SemanticHelper.IsPure(arg.Flags)) {
						return false;
					}
				}
				storeType = call.Method.Parameters.Last().Type;
				value = call.Arguments.Last();
				return IsSameMember(call.Method, (call.Method.AccessorOwner as IProperty)?.Setter);
			} else {
				return false;
			}
		}

		bool IsMatchingCompoundLoad(ILInstruction load, ILInstruction store, ILVariable forbiddenVariable)
		{
			if (load is LdObj ldobj && store is StObj stobj) {
				Debug.Assert(SemanticHelper.IsPure(stobj.Target.Flags));
				if (!SemanticHelper.IsPure(ldobj.Target.Flags))
					return false;
				if (forbiddenVariable.IsUsedWithin(ldobj.Target))
					return false;
				return ldobj.Target.Match(stobj.Target).Success;
			} else if (MatchingGetterAndSetterCalls(load as CallInstruction, store as CallInstruction)) {
				if (forbiddenVariable.IsUsedWithin(load))
					return false;
				return true;
			} else {
				return false;
			}
		}

		/// <code>
		/// stobj(target, binary.add(stloc l(ldobj(target)), ldc.i4 1))
		///   where target is pure and does not use 'l', and the 'stloc l' does not truncate
		/// -->
		/// stloc l(compound.op.old(ldobj(target), ldc.i4 1))
		/// 
		///  -or-
		/// 
		/// call set_Prop(args..., binary.add(stloc l(call get_Prop(args...)), ldc.i4 1))
		///   where args.. are pure and do not use 'l', and the 'stloc l' does not truncate
		/// -->
		/// stloc l(compound.op.old(call get_Prop(target), ldc.i4 1))
		/// </code>
		/// <remarks>
		/// Even though this transform operates only on a single expression, it's not an expression transform
		/// as the result value of the expression changes (this is OK only for statements in a block).
		/// </remarks>
		bool TransformPostIncDecOperatorWithInlineStore(Block block, int pos)
		{
			var store = block.Instructions[pos];
			if (!IsCompoundStore(store, out var targetType, out var value))
				return false;
			var binary = UnwrapSmallIntegerConv(value, out var conv) as BinaryNumericInstruction;
			if (binary == null || !binary.Right.MatchLdcI4(1))
				return false;
			if (!(binary.Operator == BinaryNumericOperator.Add || binary.Operator == BinaryNumericOperator.Sub))
				return false;
			if (!(binary.Left is StLoc stloc))
				return false;
			if (!(stloc.Variable.Kind == VariableKind.Local || stloc.Variable.Kind == VariableKind.StackSlot))
				return false;
			if (!IsMatchingCompoundLoad(stloc.Value, store, stloc.Variable))
				return false;
			if (!ValidateCompoundAssign(binary, conv, targetType))
				return false;
			if (IsImplicitTruncation(stloc.Value, stloc.Variable.Type))
				return false;
			context.Step("TransformPostIncDecOperatorWithInlineStore", store);
			block.Instructions[pos] = new StLoc(stloc.Variable, new CompoundAssignmentInstruction(
				binary, stloc.Value, binary.Right, targetType, CompoundAssignmentType.EvaluatesToOldValue));
			return true;
		}

		/// <code>
		/// stloc l(ldobj(target))
		/// stobj(target, binary.op(ldloc l, ldc.i4 1))
		///   target is pure and does not use 'l', 'stloc does not truncate'
		/// -->
		/// stloc l(compound.op.old(ldobj(target), ldc.i4 1))
		/// </code>
		/// <remarks>
		/// This pattern occurs with legacy csc for static fields, and with Roslyn for most post-increments.
		/// </remarks>
		bool TransformPostIncDecOperator(Block block, int i)
		{
			var inst = block.Instructions[i] as StLoc;
			var store = block.Instructions.ElementAtOrDefault(i + 1);
			if (inst == null || store == null)
				return false;
			if (!IsCompoundStore(store, out var targetType, out var value))
				return false;
			if (!IsMatchingCompoundLoad(inst.Value, store, inst.Variable))
				return false;
			var binary = UnwrapSmallIntegerConv(value, out var conv) as BinaryNumericInstruction;
			if (binary == null || !binary.Left.MatchLdLoc(inst.Variable) || !binary.Right.MatchLdcI4(1))
				return false;
			if (!(binary.Operator == BinaryNumericOperator.Add || binary.Operator == BinaryNumericOperator.Sub))
				return false;
			if (!ValidateCompoundAssign(binary, conv, targetType))
				return false;
			if (IsImplicitTruncation(value, targetType))
				return false;
			context.Step("TransformPostIncDecOperator", inst);
			inst.Value = new CompoundAssignmentInstruction(binary, inst.Value, binary.Right, targetType, CompoundAssignmentType.EvaluatesToOldValue);
			block.Instructions.RemoveAt(i + 1);
			if (inst.Variable.IsSingleDefinition && inst.Variable.LoadCount == 0) {
				// dead store -> it was a statement-level post-increment
				inst.ReplaceWith(inst.Value);
			}
			return true;
		}
		
		static bool IsSameMember(IMember a, IMember b)
		{
			if (a == null || b == null)
				return false;
			a = a.MemberDefinition;
			b = b.MemberDefinition;
			return a.Equals(b);
		}
	}
}