namespace MyApp.Linq
{
    using System;
    using System.Linq;
    using System.Linq.Expressions;

    public static class PredicateBuilder
    {
        public static Expression<Func<T, bool>> True<T>()
        {
            return f => true;
        }

        public static Expression<Func<T, bool>> False<T>()
        {
            return f => false;
        }

        public static Expression<Func<T, bool>> Or<T>(
            this Expression<Func<T, bool>> expr1,
            Expression<Func<T, bool>> expr2
        )
        {
            var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>());
            return Expression.Lambda<Func<T, bool>>
                  (Expression.OrElse(expr1.Body, invokedExpr), expr1.Parameters);
        }

        public static Expression<Func<T, bool>> And<T>(
            this Expression<Func<T, bool>> expr1,
            Expression<Func<T, bool>> expr2
        )
        {
            var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>());
            return Expression.Lambda<Func<T, bool>>
                  (Expression.AndAlso(expr1.Body, invokedExpr), expr1.Parameters);
        }
    }

}