using System; using System.Collections.Generic; using System.Linq; using System.Linq.Expressions; namespace AsbCloudInfrastructure; /// <summary> /// stolen from https://github.com/lotosbin/BinbinPredicateBuilder /// </summary> public static class PredicateBuilder { /// <summary> /// Combines the first predicate with the second using the logical "and". /// </summary> public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second) { return first.Compose(second, Expression.AndAlso); } /// <summary> /// Combines the first predicate with the second using the logical "or". /// </summary> public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second) { return first.Compose(second, Expression.OrElse); } /// <summary> /// Negates the predicate. /// </summary> public static Expression<Func<T, bool>> Not<T>(this Expression<Func<T, bool>> expression) { var negated = Expression.Not(expression.Body); return Expression.Lambda<Func<T, bool>>(negated, expression.Parameters); } private static Expression<T> Compose<T>(this Expression<T> first, Expression<T> second, Func<Expression, Expression, Expression> merge) { var map = first.Parameters .Select((f, i) => new { f, s = second.Parameters[i] }) .ToDictionary(p => p.s, p => p.f); var tryReplaceParametr = (Expression node) => { if (node is ParameterExpression parameter) if (map.TryGetValue(parameter, out ParameterExpression? replacement)) return replacement; return node; }; var secondBody = ParameterRebinder.ReplaceParameters(map, second.Body); return Expression.Lambda<T>(merge(first.Body, secondBody), first.Parameters); } class ParameterRebinder : ExpressionVisitor { private readonly Dictionary<ParameterExpression, ParameterExpression> map; private ParameterRebinder(Dictionary<ParameterExpression, ParameterExpression> map) { this.map = map; } public static Expression ReplaceParameters(Dictionary<ParameterExpression, ParameterExpression> map, Expression exp) { return new ParameterRebinder(map).Visit(exp); } protected override Expression VisitParameter(ParameterExpression parametr) { if (map.TryGetValue(parametr, out ParameterExpression? replacement)) parametr = replacement; return parametr; } } }