using System;
using Microsoft.CodeAnalysis;
using Semmle.Extraction.Entities;

namespace Semmle.Extraction.CSharp.Entities
{
    class LocalVariable : CachedSymbol<ISymbol>
    {
        LocalVariable(Context cx, ISymbol init, Expression parent, bool isVar, Extraction.Entities.Location declLocation)
            : base(cx, init)
        {
            Parent = parent;
            IsVar = isVar;
            DeclLocation = declLocation;
        }

        readonly Expression Parent;
        readonly bool IsVar;
        readonly Extraction.Entities.Location DeclLocation;

        public override IId Id => new Key(Parent, "_", symbol.Name, ";localvar");

        public override void Populate()
        {
            Context.Emit(Tuples.localvars(
                this,
                IsRef ? 3 : IsConst ? 2 : 1,
                symbol.Name,
                IsVar ? 1 : 0,
                Type.TypeRef,
                Parent));

            Context.Emit(Tuples.localvar_location(this, DeclLocation));

            DefineConstantValue();
        }

        public static LocalVariable Create(Context cx, ISymbol local, Expression parent, bool isVar, Extraction.Entities.Location declLocation)
        {
            return LocalVariableFactory.Instance.CreateEntity(cx, local, parent, isVar, declLocation);
        }

        /// <summary>
        /// Gets the local variable entity for <paramref name="local"/> which must
        /// already have been created.
        /// </summary>
        public static LocalVariable GetAlreadyCreated(Context cx, ISymbol local) => LocalVariableFactory.Instance.CreateEntity(cx, local, null, false, null);

        bool IsConst
        {
            get
            {
                var local = symbol as ILocalSymbol;
                return local != null && local.IsConst;
            }
        }

        bool IsRef
        {
            get
            {
                var local = symbol as ILocalSymbol;
                return local != null && local.IsRef;
            }
        }

        Type Type
        {
            get
            {
                var local = symbol as ILocalSymbol;
                return local == null ? Parent.Type : Type.Create(Context, local.Type);
            }
        }

        void DefineConstantValue()
        {
            var local = symbol as ILocalSymbol;
            if (local != null && local.HasConstantValue)
            {
                Context.Emit(Tuples.constant_value(this, Expression.ValueAsString(local.ConstantValue)));
            }
        }

        class LocalVariableFactory : ICachedEntityFactory<(ISymbol, Expression, bool, Extraction.Entities.Location), LocalVariable>
        {
            public static readonly LocalVariableFactory Instance = new LocalVariableFactory();

            public LocalVariable Create(Context cx, (ISymbol, Expression, bool, Extraction.Entities.Location) init) =>
                new LocalVariable(cx, init.Item1, init.Item2, init.Item3, init.Item4);
        }

        public override TrapStackBehaviour TrapStackBehaviour => TrapStackBehaviour.NeedsLabel;
    }
}
