/* ****************************************************************************

 *

 * Copyright (c) Microsoft Corporation. 

 *

 * This source code is subject to terms and conditions of the Microsoft Public License. A 

 * copy of the license can be found in the License.html file at the root of this distribution. If 

 * you cannot locate the  Microsoft Public License, please send an email to 

 * dlr@microsoft.com. By using this source code in any fashion, you are agreeing to be bound 

 * by the terms of the Microsoft Public License.

 *

 * You must not remove this notice, or any other, from this software.

 *

 *

 * ***************************************************************************/



#if !CLR2

using System.Linq.Expressions;

#else

using Microsoft.Scripting.Ast;

#endif



using System;

using System.Collections.Generic;

using System.Dynamic;

using System.Reflection;

using System.Diagnostics;

using Microsoft.Scripting.Utils;

using AstUtils = Microsoft.Scripting.Ast.Utils;



namespace Microsoft.Scripting.Actions.Calls {

    using Ast = Expression;



    internal sealed class ParamsArgBuilder : ArgBuilder {

        private readonly int _start;

        private readonly int _expandedCount;

        private readonly Type _elementType;



        internal ParamsArgBuilder(ParameterInfo info, Type elementType, int start, int expandedCount) 

            : base(info) {



            Assert.NotNull(elementType);

            Debug.Assert(start >= 0);

            Debug.Assert(expandedCount >= 0);



            _start = start;

            _expandedCount = expandedCount;

            _elementType = elementType;

        }



        // Consumes all expanded arguments. 

        // Collapsed arguments are fetched from resolver provided storage, not from actual argument expressions.

        public override int ConsumedArgumentCount {

            get { return _expandedCount; }

        }



        public override int Priority {

            get { return 4; }

        }



        internal protected override Expression ToExpression(OverloadResolver resolver, RestrictedArguments args, bool[] hasBeenUsed) {

            var actualArgs = resolver.GetActualArguments();

            int splatIndex = actualArgs.SplatIndex;

            int collapsedCount = actualArgs.CollapsedCount;

            int firstSplatted = actualArgs.FirstSplattedArg;



            var result = new Expression[2 + _expandedCount + (collapsedCount > 0 ? 2 : 0)];

            var arrayVariable = resolver.GetTemporary(_elementType.MakeArrayType(), "a");

            int e = 0;

            result[e++] = Ast.Assign(arrayVariable, Ast.NewArrayBounds(_elementType, Ast.Constant(_expandedCount + collapsedCount)));



            int itemIndex = 0;

            int i = _start;

            while (true) {

                // inject loop copying collapsed items:

                if (i == splatIndex) {

                    var indexVariable = resolver.GetTemporary(typeof(int), "t");



                    // for (int t = 0; t <= {collapsedCount}; t++) {

                    //   a[{itemIndex} + t] = CONVERT<ElementType>(list.get_Item({splatIndex - firstSplatted} + t))

                    // }

                    result[e++] = Ast.Assign(indexVariable, AstUtils.Constant(0));

                    result[e++] = AstUtils.Loop(

                        Ast.LessThan(indexVariable, Ast.Constant(collapsedCount)),

                        // TODO: not implemented in the old interpreter

                        // Ast.PostIncrementAssign(indexVariable),

                        Ast.Assign(indexVariable, Ast.Add(indexVariable, AstUtils.Constant(1))),

                        Ast.Assign(

                            Ast.ArrayAccess(arrayVariable, Ast.Add(AstUtils.Constant(itemIndex), indexVariable)),

                            resolver.Convert(

                                new DynamicMetaObject(

                                    resolver.GetSplattedItemExpression(Ast.Add(AstUtils.Constant(splatIndex - firstSplatted), indexVariable)), 

                                    BindingRestrictions.Empty

                                ),

                                null,

                                ParameterInfo, 

                                _elementType

                            )

                        ),

                        null

                    );



                    itemIndex += collapsedCount;

                }



                if (i >= _start + _expandedCount) {

                    break;

                }



                Debug.Assert(!hasBeenUsed[i]);

                hasBeenUsed[i] = true;                



                result[e++] = Ast.Assign(

                    Ast.ArrayAccess(arrayVariable, AstUtils.Constant(itemIndex++)),

                    resolver.Convert(args.GetObject(i), args.GetType(i), ParameterInfo, _elementType)

                );



                i++;

            }



            result[e++] = arrayVariable;



            Debug.Assert(e == result.Length);

            return Ast.Block(result);

        }



        protected internal override Func<object[], object> ToDelegate(OverloadResolver resolver, RestrictedArguments args, bool[] hasBeenUsed) {

            if (resolver.GetActualArguments().CollapsedCount > 0) {

                return null;

            }

            

            var indexes = new List<Func<object[], object>>(_expandedCount);



            for (int i = _start; i < _start + _expandedCount; i++) {

                if (!hasBeenUsed[i]) {

                    indexes.Add(resolver.GetConvertor(i + 1, args.GetObject(i), ParameterInfo, _elementType));

                    hasBeenUsed[i] = true;

                }

            }



            if (_elementType == typeof(object)) {

                return new ParamArrayDelegate<object>(indexes.ToArray(), _start).MakeParamsArray;

            }



            Type genType = typeof(ParamArrayDelegate<>).MakeGenericType(_elementType);

            return (Func<object[], object>)Delegate.CreateDelegate(

                typeof(Func<object[], object>), 

                Activator.CreateInstance(genType, indexes.ToArray(), _start),

                genType.GetMethod("MakeParamsArray"));

        }



        class ParamArrayDelegate<T> {

            private readonly Func<object[], object>[] _indexes;

            private readonly int _start;



            public ParamArrayDelegate(Func<object[], object>[] indexes, int start) {

                _indexes = indexes;

                _start = start;

            }



            public T[] MakeParamsArray(object[] args) {

                T[] res = new T[_indexes.Length];

                for (int i = 0; i < _indexes.Length; i++) {

                    if (_indexes[i] == null) {

                        res[i] = (T)args[_start + i + 1];

                    } else {

                        res[i] = (T)_indexes[i](args);

                    }

                }



                return res;

            }

        }



        public override Type Type {

            get {

                return _elementType.MakeArrayType();

            }

        }



        public override ArgBuilder Clone(ParameterInfo newType) {

            return new ParamsArgBuilder(newType, newType.ParameterType.GetElementType(), _start, _expandedCount);

        }

    }

}