LinqUnit

using System;

using System.Linq;

using System.Linq.Expressions;

using System.Reflection;

using System.Runtime.Serialization.Formatters.Binary;

using System.IO;

using System.Runtime.Serialization;

using System.Collections.Generic;

namespace ZoomCommerce.App.Common

{

public static class LinqUtil

{

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<T> Compose<T>(this Expression<T> first, Expression<T> second, Func<Expression, Expression, Expression> merge)

{

// build parameter map (from parameters of second to parameters of first)

var map = first.Parameters.Select((f, i) => new { f, s = second.Parameters[i] }).ToDictionary(p => p.s, p => p.f);

// replace parameters in the second lambda expression with parameters from the first

var secondBody = ParameterRebinder.ReplaceParameters(map, second.Body);

// apply composition of lambda expression bodies to parameters from the first expression

return Expression.Lambda<T>(merge(first.Body, secondBody), first.Parameters);

}

//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.Or(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.And(expr1.Body, invokedExpr), expr1.Parameters);

//}

public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second)

{

return first.Compose(second, Expression.And);

}

public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second)

{

return first.Compose(second, Expression.Or);

}

}

public class ParameterRebinder : ExpressionVisitor

{

private readonly Dictionary<ParameterExpression, ParameterExpression> map;

public ParameterRebinder(Dictionary<ParameterExpression, ParameterExpression> map)

{

this.map = map ?? new Dictionary<ParameterExpression, ParameterExpression>();

}

public static Expression ReplaceParameters(Dictionary<ParameterExpression, ParameterExpression> map, Expression exp)

{

return new ParameterRebinder(map).Visit(exp);

}

protected override Expression VisitParameter(ParameterExpression p)

{

ParameterExpression replacement;

if (map.TryGetValue(p, out replacement))

{

p = replacement;

}

return base.VisitParameter(p);

}

}

}