Tiobon.Web.Core/Tiobon.Core.Common/Extensions/ExpressionCombiner.cs

using System.Linq.Expressions;

namespace Tiobon.Core.Common.Helper;

public static class ExpressionCombiner
{
    public static Expression<Func<T, bool>> Combine<T>(Expression<Func<T, bool>> expression1, Expression<Func<T, bool>> expression2)
    {
        if (expression1 == null && expression2 == null)
        {
            return null;
        }

        if (expression1 == null)
        {
            return expression2;
        }

        if (expression2 == null)
        {
            return expression1;
        }

        var parameter = Expression.Parameter(typeof(T));

        var leftVisitor = new ReplaceExpressionVisitor(expression1.Parameters[0], parameter);
        var left = leftVisitor.Visit(expression1.Body);

        var rightVisitor = new ReplaceExpressionVisitor(expression2.Parameters[0], parameter);
        var right = rightVisitor.Visit(expression2.Body);

        return Expression.Lambda<Func<T, bool>>(Expression.AndAlso(left, right), parameter);
    }

    class ReplaceExpressionVisitor : ExpressionVisitor
    {
        private readonly Expression _oldValue;
        private readonly Expression _newValue;

        public ReplaceExpressionVisitor(Expression oldValue, Expression newValue)
        {
            _oldValue = oldValue;
            _newValue = newValue;
        }

        public override Expression Visit(Expression node)
        {
            if (node == _oldValue)
            {
                return _newValue;
            }

            return base.Visit(node);
        }
    }
}