persistence/DD.Persistence.Database.Postgres/Extensions/SpecificationExtensions.cs

using Ardalis.Specification;
using DD.Persistence.Database.Specifications;
using System.Linq.Expressions;

namespace DD.Persistence.Database.Postgres.Extensions;

// ToDo: рассмотреть возможность вынести логику в спецификации
public static class SpecificationExtensions
{
    public static ISpecification<T> Or<T>(this ISpecification<T> spec, ISpecification<T> otherSpec)
    {
        var newSpec = new EmptySpecification<T>();

        var parameter = Expression.Parameter(typeof(T), "x");

        var exprSpec1 = CombineWhereExpressions(spec.WhereExpressions, parameter);
        var exprSpec2 = CombineWhereExpressions(otherSpec.WhereExpressions, parameter);

        Expression? orExpression = exprSpec1 is not null && exprSpec2 is not null
            ? Expression.OrElse(exprSpec1, exprSpec2)
            : exprSpec1 ?? exprSpec2;

        if (orExpression is null) return newSpec;

        var lambdaExpr = Expression.Lambda<Func<T, bool>>(orExpression, parameter);

        newSpec.Query.Where(lambdaExpr);

        return newSpec;
    }

    // ToDo: Рефакторинг
    public static ISpecification<T> And<T>(this ISpecification<T> spec, ISpecification<T> otherSpec)
    {
        var newSpec = new EmptySpecification<T>();

        var parameter = Expression.Parameter(typeof(T), "x");

        var exprSpec1 = CombineWhereExpressions(spec.WhereExpressions, parameter);
        var exprSpec2 = CombineWhereExpressions(otherSpec.WhereExpressions, parameter);

        Expression? andExpression = exprSpec1 is not null && exprSpec2 is not null
            ? Expression.AndAlso(exprSpec1, exprSpec2)
            : exprSpec1 ?? exprSpec2;

        if (andExpression is null) return newSpec;

        var lambdaExpr = Expression.Lambda<Func<T, bool>>(andExpression, parameter);

        newSpec.Query.Where(lambdaExpr);

        return newSpec;
    }

    public static Expression? CombineWhereExpressions<T>(IEnumerable<WhereExpressionInfo<T>> whereExpressions, ParameterExpression parameter)
    {
        Expression? newExpr = null;
        foreach (var where in whereExpressions)
        {
            var expr = ParameterReplacerVisitor.Replace(where.Filter.Body, where.Filter.Parameters[0], parameter);
            newExpr = newExpr is null ? expr : Expression.AndAlso(newExpr, expr);
        }
        return newExpr;
    }
}

public class ParameterReplacerVisitor : ExpressionVisitor
{
    private readonly Expression _newExpression;
    private readonly ParameterExpression _oldParameter;

    private ParameterReplacerVisitor(ParameterExpression oldParameter, Expression newExpression)
    {
        _oldParameter = oldParameter;
        _newExpression = newExpression;
    }

    internal static Expression Replace(Expression expression, ParameterExpression oldParameter, Expression newExpression)
      => new ParameterReplacerVisitor(oldParameter, newExpression).Visit(expression);

    protected override Expression VisitParameter(ParameterExpression p)
      => p == _oldParameter ? _newExpression : p;
}