using System;
using System.Linq;
using System.Linq.Expressions;
namespace Application.Core.Specification.Common
{
/// <summary>
/// Extension methods for adding AND and OR with parameters rebinder
/// </summary>
public static class ExpressionBuilder
{
/// <summary>
/// Compose two expressions and merge all in a new expression
/// </summary>
/// <typeparam name="T">Type of params in expression</typeparam>
/// <param name="first">Expression instance</param>
/// <param name="second">Expression to merge</param>
/// <param name="merge">Function to merge</param>
/// <returns>New merged expression</returns>
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);
}
/// <summary>
/// And operator
/// </summary>
/// <typeparam name="T">Type of params in expression</typeparam>
/// <param name="first">Right Expression in AND operation</param>
/// <param name="second">Left Expression in And operation</param>
/// <returns>New AND expression</returns>
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);
}
/// <summary>
/// Or operator
/// </summary>
/// <typeparam name="T">Type of param in expression</typeparam>
/// <param name="first">Right expression in OR operation</param>
/// <param name="second">Left expression in OR operation</param>
/// <returns>New Or expressions</returns>
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);
}
}
}