using System;
using System.Collections.Generic;
using System.Linq;
using Jint.Native.Object;
using Jint.Parser;
using Jint.Parser.Ast;
using Jint.Runtime;
using Jint.Runtime.Environments;

namespace Jint.Native.Function
{
    public sealed class FunctionConstructor : FunctionInstance, IConstructor
    {
        private FunctionConstructor(Engine engine):base(engine, null, null, false)
        {
        }

        public static FunctionConstructor CreateFunctionConstructor(Engine engine)
        {
            var obj = new FunctionConstructor(engine);
            obj.Extensible = true;

            // The initial value of Function.prototype is the standard built-in Function prototype object
            obj.PrototypeObject = FunctionPrototype.CreatePrototypeObject(engine);
            
            // The value of the [[Prototype]] internal property of the Function constructor is the standard built-in Function prototype object 
            obj.Prototype = obj.PrototypeObject;
            
            obj.FastAddProperty("prototype", obj.PrototypeObject, false, false, false);

            obj.FastAddProperty("length", 1, false, false, false);

            return obj;
        }

        public void Configure()
        {

        }

        public FunctionPrototype PrototypeObject { get; private set; }

        public override object Call(object thisObject, object[] arguments)
        {
            return Construct(arguments);
        }

        public ObjectInstance Construct(object[] arguments)
        {
            var argCount = arguments.Length;
            string p = "";
            string body = "";

            if (argCount == 1)
            {
                body = TypeConverter.ToString(arguments[0]);
            }
            else if (argCount > 1)
            {
                var firstArg = arguments[0];
                p = TypeConverter.ToString(firstArg);
                for (var k = 1; k < argCount - 1; k++)
                {
                    var nextArg = arguments[k];
                    p += "," + TypeConverter.ToString(nextArg);
                }

                body = TypeConverter.ToString(arguments[argCount-1]);
            }
            body = TypeConverter.ToString(body);
            
            // todo: ensure parsable as parameter list
            var parameters = p.Split(new [] {','}, StringSplitOptions.RemoveEmptyEntries);
            var parser = new JavaScriptParser();
            FunctionExpression function;
            try
            {
                var functionExpression = "function(" + p + ") { " + body + "}";
                function = parser.ParseFunctionExpression(functionExpression); 
            }
            catch (ParserError)
            {
                throw new JavaScriptException(Engine.SyntaxError);
            }

            // todo: check if there is not a way to use the FunctionExpression directly instead of creating a FunctionDeclaration
            var functionObject = new ScriptFunctionInstance(
                Engine,
                new FunctionDeclaration
                    {
                        Type = SyntaxNodes.FunctionDeclaration,
                        Body = new BlockStatement
                            {
                                Type = SyntaxNodes.BlockStatement,
                                Body = new [] { function.Body }
                            },
                        Parameters = parameters.Select(x => new Identifier
                            {
                                Type = SyntaxNodes.Identifier,
                                Name = x
                            }).ToArray(),
                        FunctionDeclarations = new List<FunctionDeclaration>(),
                        VariableDeclarations = new List<VariableDeclaration>()
                    },  
                LexicalEnvironment.NewDeclarativeEnvironment(Engine, Engine.ExecutionContext.LexicalEnvironment),
                function.Strict
                ) { Extensible = true };

            return functionObject;
            
        }

        /// <summary>
        /// http://www.ecma-international.org/ecma-262/5.1/#sec-13.2
        /// </summary>
        /// <param name="functionDeclaration"></param>
        /// <returns></returns>
        public FunctionInstance CreateFunctionObject(FunctionDeclaration functionDeclaration)
        {
            var functionObject = new ScriptFunctionInstance(
                Engine,
                functionDeclaration,
                LexicalEnvironment.NewDeclarativeEnvironment(Engine, Engine.ExecutionContext.LexicalEnvironment),
                functionDeclaration.Strict
                ) { Extensible = true };

            return functionObject;
        }

        private FunctionInstance _throwTypeError;

        public FunctionInstance ThrowTypeError
        {
            get
            {
                if (_throwTypeError != null)
                {
                    return _throwTypeError;
                }

                _throwTypeError = new ThrowTypeError(Engine);
                return _throwTypeError;
            }
        }

        public object Apply(object thisObject, object[] arguments)
        {
            if (arguments.Length != 2)
            {
                throw new ArgumentException("Apply has to be called with two arguments.");
            }

            var func = thisObject as ICallable;
            var thisArg = arguments[0];
            var argArray = arguments[1];

            if (func == null)
            {
                throw new JavaScriptException(Engine.TypeError);
            }

            if (argArray == Null.Instance || argArray == Undefined.Instance)
            {
                return func.Call(thisArg, Arguments.Empty);
            }

            var argArrayObj = argArray as ObjectInstance;
            if (argArrayObj == null)
            {
                throw new JavaScriptException(Engine.TypeError);
            }

            var len = argArrayObj.Get("length");
            var n = TypeConverter.ToUint32(len);
            var argList = new List<object>();
            for (var index = 0; index < n; index++)
            {
                var indexName = index.ToString();
                var nextArg = argArrayObj.Get(indexName);
                argList.Add(nextArg);
            }
            return func.Call(thisArg, argList.ToArray());
        }
    }
}