//
// assign.cs: Assignments.
//
// Author:
//   Miguel de Icaza (miguel@ximian.com)
//   Martin Baulig (martin@ximian.com)
//   Marek Safar (marek.safar@gmail.com)	
//
// Dual licensed under the terms of the MIT X11 or GNU GPL
//
// Copyright 2001, 2002, 2003 Ximian, Inc.
// Copyright 2004-2008 Novell, Inc
//
using System;
using System.Reflection;
using System.Reflection.Emit;
using System.Collections;

namespace Mono.CSharp {

	/// <summary>
	///   This interface is implemented by expressions that can be assigned to.
	/// </summary>
	/// <remarks>
	///   This interface is implemented by Expressions whose values can not
	///   store the result on the top of the stack.
	///
	///   Expressions implementing this (Properties, Indexers and Arrays) would
	///   perform an assignment of the Expression "source" into its final
	///   location.
	///
	///   No values on the top of the stack are expected to be left by
	///   invoking this method.
	/// </remarks>
	public interface IAssignMethod {
		//
		// This is an extra version of Emit. If leave_copy is `true'
		// A copy of the expression will be left on the stack at the
		// end of the code generated for EmitAssign
		//
		void Emit (EmitContext ec, bool leave_copy);

		//
		// This method does the assignment
		// `source' will be stored into the location specified by `this'
		// if `leave_copy' is true, a copy of `source' will be left on the stack
		// if `prepare_for_load' is true, when `source' is emitted, there will
		// be data on the stack that it can use to compuatate its value. This is
		// for expressions like a [f ()] ++, where you can't call `f ()' twice.
		//
		void EmitAssign (EmitContext ec, Expression source, bool leave_copy, bool prepare_for_load);

		/*
		For simple assignments, this interface is very simple, EmitAssign is called with source
		as the source expression and leave_copy and prepare_for_load false.

		For compound assignments it gets complicated.

		EmitAssign will be called as before, however, prepare_for_load will be
		true. The @source expression will contain an expression
		which calls Emit. So, the calls look like:

		this.EmitAssign (ec, source, false, true) ->
			source.Emit (ec); ->
				[...] ->
					this.Emit (ec, false); ->
					end this.Emit (ec, false); ->
				end [...]
			end source.Emit (ec);
		end this.EmitAssign (ec, source, false, true)


		When prepare_for_load is true, EmitAssign emits a `token' on the stack that
		Emit will use for its state.

		Let's take FieldExpr as an example. assume we are emitting f ().y += 1;

		Here is the call tree again. This time, each call is annotated with the IL
		it produces:

		this.EmitAssign (ec, source, false, true)
			call f
			dup

			Binary.Emit ()
				this.Emit (ec, false);
				ldfld y
				end this.Emit (ec, false);

				IntConstant.Emit ()
				ldc.i4.1
				end IntConstant.Emit

				add
			end Binary.Emit ()

			stfld
		end this.EmitAssign (ec, source, false, true)

		Observe two things:
			1) EmitAssign left a token on the stack. It was the result of f ().
			2) This token was used by Emit

		leave_copy (in both EmitAssign and Emit) tells the compiler to leave a copy
		of the expression at that point in evaluation. This is used for pre/post inc/dec
		and for a = x += y. Let's do the above example with leave_copy true in EmitAssign

		this.EmitAssign (ec, source, true, true)
			call f
			dup

			Binary.Emit ()
				this.Emit (ec, false);
				ldfld y
				end this.Emit (ec, false);

				IntConstant.Emit ()
				ldc.i4.1
				end IntConstant.Emit

				add
			end Binary.Emit ()

			dup
			stloc temp
			stfld
			ldloc temp
		end this.EmitAssign (ec, source, true, true)

		And with it true in Emit

		this.EmitAssign (ec, source, false, true)
			call f
			dup

			Binary.Emit ()
				this.Emit (ec, true);
				ldfld y
				dup
				stloc temp
				end this.Emit (ec, true);

				IntConstant.Emit ()
				ldc.i4.1
				end IntConstant.Emit

				add
			end Binary.Emit ()

			stfld
			ldloc temp
		end this.EmitAssign (ec, source, false, true)

		Note that these two examples are what happens for ++x and x++, respectively.
		*/
	}

	/// <summary>
	///   An Expression to hold a temporary value.
	/// </summary>
	/// <remarks>
	///   The LocalTemporary class is used to hold temporary values of a given
	///   type to "simulate" the expression semantics on property and indexer
	///   access whose return values are void.
	///
	///   The local temporary is used to alter the normal flow of code generation
	///   basically it creates a local variable, and its emit instruction generates
	///   code to access this value, return its address or save its value.
	///
	///   If `is_address' is true, then the value that we store is the address to the
	///   real value, and not the value itself.
	///
	///   This is needed for a value type, because otherwise you just end up making a
	///   copy of the value on the stack and modifying it. You really need a pointer
	///   to the origional value so that you can modify it in that location. This
	///   Does not happen with a class because a class is a pointer -- so you always
	///   get the indirection.
	///
	///   The `is_address' stuff is really just a hack. We need to come up with a better
	///   way to handle it.
	/// </remarks>
	public class LocalTemporary : Expression, IMemoryLocation {
		LocalBuilder builder;
		bool is_address;

		public LocalTemporary (Type t) : this (t, false) {}

		public LocalTemporary (Type t, bool is_address)
		{
			type = t;
			eclass = ExprClass.Value;
			this.is_address = is_address;
		}

		public LocalTemporary (LocalBuilder b, Type t)
		{
			type = t;
			eclass = ExprClass.Value;
			loc = Location.Null;
			builder = b;
		}

		public void Release (EmitContext ec)
		{
			ec.FreeTemporaryLocal (builder, type);
			builder = null;
		}

		public override Expression CreateExpressionTree (EmitContext ec)
		{
			throw new NotSupportedException ("ET");
		}

		public override Expression DoResolve (EmitContext ec)
		{
			return this;
		}

		public override void Emit (EmitContext ec)
		{
			ILGenerator ig = ec.ig;

			if (builder == null)
				throw new InternalErrorException ("Emit without Store, or after Release");

			ig.Emit (OpCodes.Ldloc, builder);
			// we need to copy from the pointer
			if (is_address)
				LoadFromPtr (ig, type);
		}

		// NB: if you have `is_address' on the stack there must
		// be a managed pointer. Otherwise, it is the type from
		// the ctor.
		public void Store (EmitContext ec)
		{
			ILGenerator ig = ec.ig;
			if (builder == null)
				builder = ec.GetTemporaryLocal (is_address ? TypeManager.GetReferenceType (type): type);

			ig.Emit (OpCodes.Stloc, builder);
		}

		public void AddressOf (EmitContext ec, AddressOp mode)
		{
			if (builder == null)
				builder = ec.GetTemporaryLocal (is_address ? TypeManager.GetReferenceType (type): type);

			// if is_address, than this is just the address anyways,
			// so we just return this.
			ILGenerator ig = ec.ig;

			if (is_address)
				ig.Emit (OpCodes.Ldloc, builder);
			else
				ig.Emit (OpCodes.Ldloca, builder);
		}

		public bool PointsToAddress {
			get {
				return is_address;
			}
		}
	}

	/// <summary>
	///   The Assign node takes care of assigning the value of source into
	///   the expression represented by target.
	/// </summary>
	public class Assign : ExpressionStatement {
		protected Expression target, source;

		protected Assign (Expression target, Expression source, Location loc)
		{
			this.target = target;
			this.source = source;
			this.loc = loc;
		}
		
		public override Expression CreateExpressionTree (EmitContext ec)
		{
			Report.Error (832, loc, "An expression tree cannot contain an assignment operator");
			return null;
		}

		public Expression Target {
			get { return target; }
		}

		public Expression Source {
			get { return source; }
		}

		public override Expression DoResolve (EmitContext ec)
		{
			bool ok = true;
			source = source.Resolve (ec);
						
			if (source == null) {
				ok = false;
				source = EmptyExpression.Null;
			}

			target = target.ResolveLValue (ec, source, Location);

			if (target == null || !ok)
				return null;

			Type target_type = target.Type;
			Type source_type = source.Type;

			eclass = ExprClass.Value;
			type = target_type;

			if (!(target is IAssignMethod)) {
				Error_ValueAssignment (loc);
				return null;
			}

			if ((source.eclass == ExprClass.Type) && (source is TypeExpr)) {
				source.Error_UnexpectedKind (ec.DeclContainer, "variable or value", loc);
				return null;
			} else if ((RootContext.Version == LanguageVersion.ISO_1) &&
				   (source is MethodGroupExpr)){
				((MethodGroupExpr) source).ReportUsageError ();
				return null;
			}

			if (TypeManager.IsEqual (target_type, source_type)) {
				if (target.eclass == ExprClass.Variable) {
					New n = source as New;
					if (n == null)
						return this;

					if (n.HasInitializer) {
						n.SetTargetVariable (target);
					} else if (target_type.IsValueType) {
						n.SetTargetVariable (target);
						return n;
					}
				}

				return this;
			}

			return ResolveConversions (ec);
		}

		protected virtual Expression ResolveConversions (EmitContext ec)
		{
			source = Convert.ImplicitConversionRequired (ec, source, target.Type, loc);
			if (source == null)
				return null;

			return this;
		}

		void Emit (EmitContext ec, bool is_statement)
		{
			((IAssignMethod) target).EmitAssign (ec, source, !is_statement, this is CompoundAssign);
		}

		public override void Emit (EmitContext ec)
		{
			Emit (ec, false);
		}

		public override void EmitStatement (EmitContext ec)
		{
			Emit (ec, true);
		}

		protected override void CloneTo (CloneContext clonectx, Expression t)
		{
			Assign _target = (Assign) t;

			_target.target = target.Clone (clonectx);
			_target.source = source.Clone (clonectx);
		}
	}

	class SimpleAssign : Assign {
		public SimpleAssign (Expression target, Expression source)
			: this (target, source, target.Location)
		{
		}

		public SimpleAssign (Expression target, Expression source, Location loc)
			: base (target, source, loc)
		{
		}

		bool CheckEqualAssign (Expression t)
		{
			if (source is Assign) {
				Assign a = (Assign) source;
				if (t.Equals (a.Target))
					return true;
				return a is SimpleAssign && ((SimpleAssign) a).CheckEqualAssign (t);
			}
			return t.Equals (source);
		}

		public override Expression DoResolve (EmitContext ec)
		{
			Expression e = base.DoResolve (ec);
			if (e == null || e != this)
				return e;

			if (CheckEqualAssign (target))
				Report.Warning (1717, 3, loc, "Assignment made to same variable; did you mean to assign something else?");

			return this;
		}
	}

	// This class implements fields and events class initializers
	public class FieldInitializer : Assign
	{
		//
		// Keep resolved value because field initializers have their own rules
		//
		ExpressionStatement resolved;

		public FieldInitializer (FieldBuilder field, Expression expression)
			: base (new FieldExpr (field, expression.Location, true), expression, expression.Location)
		{
			if (!field.IsStatic)
				((FieldExpr)target).InstanceExpression = CompilerGeneratedThis.Instance;
		}

		public override Expression DoResolve (EmitContext ec)
		{
			// Field initializer can be resolved (fail) many times
			if (source == null)
				return null;

			if (resolved == null)
				resolved = base.DoResolve (ec) as ExpressionStatement;

			return resolved;
		}

		public override void EmitStatement (EmitContext ec)
		{
			if (resolved == null)
				return;
			
			if (resolved != this)
				resolved.EmitStatement (ec);
			else
				base.EmitStatement (ec);
		}
		
		public bool IsComplexInitializer {
			get { return !(source is Constant); }
		}

		public bool IsDefaultInitializer {
			get {
				Constant c = source as Constant;
				if (c == null)
					return false;
				
				FieldExpr fe = (FieldExpr)target;
				return c.IsDefaultInitializer (fe.Type);
			}
		}
	}

	class EventAddOrRemove : ExpressionStatement {
		EventExpr target;
		Binary.Operator op;
		Expression source;

		public EventAddOrRemove (Expression target, Binary.Operator op, Expression source, Location loc)
		{
			this.target = target as EventExpr;
			this.op = op;
			this.source = source;
			this.loc = loc;
		}

		public override Expression CreateExpressionTree (EmitContext ec)
		{
			return new SimpleAssign (target, source).CreateExpressionTree (ec);
		}

		public override Expression DoResolve (EmitContext ec)
		{
			eclass = ExprClass.Value;
			type = target.Type;

			source = source.Resolve (ec);
			if (source == null)
				return null;

			Type stype = source.Type;
			if (source.eclass == ExprClass.MethodGroup || stype == TypeManager.anonymous_method_type) {
				if (RootContext.Version != LanguageVersion.ISO_1) {
					source = Convert.ImplicitConversionRequired (ec, source, type, loc);
					if (source == null)
						return null;
					stype = source.Type;
				}
			} else if (!TypeManager.Equals (type, stype) && !(source is NullLiteral))
				return null;

			return this;
		}

		public override void Emit (EmitContext ec)
		{
			throw new InternalErrorException ("don't know what to emit");
		}

		public override void EmitStatement (EmitContext ec)
		{
			target.EmitAddOrRemove (ec, op == Binary.Operator.Addition, source);
		}
	}

	//
	// This class is used for compound assignments.
	//
	class CompoundAssign : Assign {
		Binary.Operator op;
		Expression original_source;

		public CompoundAssign (Binary.Operator op, Expression target, Expression source)
			: base (target, source, target.Location)
		{
			original_source = source;
			this.op = op;
		}

		// !!! What a stupid name
		public class Helper : Expression {
			Expression child;
			public Helper (Expression child)
			{
				this.child = child;
				this.loc = child.Location;
			}

			public override Expression CreateExpressionTree (EmitContext ec)
			{
				throw new NotSupportedException ("ET");
			}

			public override Expression DoResolve (EmitContext ec)
			{
				child = child.Resolve (ec);
				if (child == null)
					return null;
				type = child.Type;
				eclass = ExprClass.Value;
				return this;
			}

			public override void Emit (EmitContext ec)
			{
				child.Emit (ec);
			}
		}

		public override Expression DoResolve (EmitContext ec)
		{
			original_source = original_source.Resolve (ec);
			if (original_source == null)
				return null;

			using (ec.Set (EmitContext.Flags.InCompoundAssignment)) {
				target = target.Resolve (ec);
			}
			
			if (target == null)
				return null;

			if (target is MethodGroupExpr){
				Error_CannotAssign (((MethodGroupExpr)target).Name, target.ExprClassName);
				return null;
			}

			if (target is EventExpr)
				return new EventAddOrRemove (target, op, original_source, loc).DoResolve (ec);

			//
			// Only now we can decouple the original source/target
			// into a tree, to guarantee that we do not have side
			// effects.
			//
			source = new Binary (op, new Helper (target), original_source, true);
			return base.DoResolve (ec);
		}

		protected override Expression ResolveConversions (EmitContext ec)
		{
			// source might have changed to BinaryDelegate
			Type target_type = target.Type;
			Type source_type = source.Type;
			Binary b = source as Binary;
			if (b == null)
				return base.ResolveConversions (ec);

			// FIXME: Restrict only to predefined operators

			//
			// 1. if the source is explicitly convertible to the
			//    target_type
			//
			source = Convert.ExplicitConversion (ec, source, target_type, loc);
			if (source == null){
				original_source.Error_ValueCannotBeConverted (ec, loc, target_type, true);
				return null;
			}

			//
			// 2. and the original right side is implicitly convertible to
			// the type of target
			//
			if (Convert.ImplicitConversionExists (ec, original_source, target_type))
				return this;

			//
			// In the spec 2.4 they added: or if type of the target is int
			// and the operator is a shift operator...
			//
			if (source_type == TypeManager.int32_type && (b.Oper & Binary.Operator.ShiftMask) != 0)
				return this;

			original_source.Error_ValueCannotBeConverted (ec, loc, target_type, false);
			return null;
		}

		protected override void CloneTo (CloneContext clonectx, Expression t)
		{
			CompoundAssign target = (CompoundAssign) t;

			target.original_source = original_source.Clone (clonectx);
		}
	}
}