// Copyright (c) Microsoft Open Technologies, Inc. All rights reserved. See License.txt in the project root for license information.

namespace System.Data.Entity.Core.Common.Utils.Boolean
{
    using System.Collections.Generic;

    // <summary>
    // Basic visitor which reproduces the given expression tree.
    // </summary>
    // <typeparam name="T_Identifier"> Type of leaf term identifiers in expression. </typeparam>
    internal abstract class BasicVisitor<T_Identifier> : Visitor<T_Identifier, BoolExpr<T_Identifier>>
    {
        internal override BoolExpr<T_Identifier> VisitFalse(FalseExpr<T_Identifier> expression)
        {
            return expression;
        }

        internal override BoolExpr<T_Identifier> VisitTrue(TrueExpr<T_Identifier> expression)
        {
            return expression;
        }

        internal override BoolExpr<T_Identifier> VisitTerm(TermExpr<T_Identifier> expression)
        {
            return expression;
        }

        internal override BoolExpr<T_Identifier> VisitNot(NotExpr<T_Identifier> expression)
        {
            return new NotExpr<T_Identifier>(expression.Child.Accept(this));
        }

        internal override BoolExpr<T_Identifier> VisitAnd(AndExpr<T_Identifier> expression)
        {
            return new AndExpr<T_Identifier>(AcceptChildren(expression.Children));
        }

        internal override BoolExpr<T_Identifier> VisitOr(OrExpr<T_Identifier> expression)
        {
            return new OrExpr<T_Identifier>(AcceptChildren(expression.Children));
        }

        private IEnumerable<BoolExpr<T_Identifier>> AcceptChildren(IEnumerable<BoolExpr<T_Identifier>> children)
        {
            foreach (var child in children)
            {
                yield return child.Accept(this);
            }
        }
    }
}
