Connected.Framework/Connected.Expressions/Expressions/ExpressionExtensions.cs

using Connected.Interop;
using System.Linq.Expressions;

namespace Connected.Expressions;

internal static class ExpressionExtensions
{
    public static Expression Equal(this Expression left, Expression right)
    {
        ConvertExpressions(ref left, ref right);

        return Expression.Equal(left, right);
    }

    public static Expression NotEqual(this Expression left, Expression right)
    {
        ConvertExpressions(ref left, ref right);

        return Expression.NotEqual(left, right);
    }

    public static Expression GreaterThan(this Expression left, Expression right)
    {
        ConvertExpressions(ref left, ref right);

        return Expression.GreaterThan(left, right);
    }

    public static Expression GreaterThanOrEqual(this Expression left, Expression right)
    {
        ConvertExpressions(ref left, ref right);

        return Expression.GreaterThanOrEqual(left, right);
    }

    public static Expression LessThan(this Expression left, Expression right)
    {
        ConvertExpressions(ref left, ref right);

        return Expression.LessThan(left, right);
    }

    public static Expression LessThanOrEqual(this Expression left, Expression right)
    {
        ConvertExpressions(ref left, ref right);

        return Expression.LessThanOrEqual(left, right);
    }

    public static Expression And(this Expression left, Expression right)
    {
        ConvertExpressions(ref left, ref right);

        return Expression.And(left, right);
    }

    public static Expression Or(this Expression left, Expression right)
    {
        ConvertExpressions(ref left, ref right);

        return Expression.Or(left, right);
    }

    public static Expression Binary(this Expression left, ExpressionType op, Expression right)
    {
        ConvertExpressions(ref left, ref right);

        return Expression.MakeBinary(op, left, right);
    }

    private static void ConvertExpressions(ref Expression left, ref Expression right)
    {
        if (left.Type != right.Type)
        {
            var isNullable1 = Nullables.IsNullableType(left.Type);
            var isNullable2 = Nullables.IsNullableType(right.Type);

            if (isNullable1 || isNullable2)
            {
                if (Nullables.GetNonNullableType(left.Type) == Nullables.GetNonNullableType(right.Type))
                {
                    if (!isNullable1)
                        left = Expression.Convert(left, right.Type);
                    else if (!isNullable2)
                        right = Expression.Convert(right, left.Type);
                }
            }
        }
    }

    public static Expression[] Split(this Expression expression, params ExpressionType[] binarySeparators)
    {
        var list = new List<Expression>();

        Split(expression, list, binarySeparators);

        return list.ToArray();
    }

    private static void Split(Expression expression, List<Expression> list, ExpressionType[] binarySeparators)
    {
        if (expression is not null)
        {
            if (binarySeparators.Contains(expression.NodeType))
            {
                if (expression is BinaryExpression bex)
                {
                    Split(bex.Left, list, binarySeparators);
                    Split(bex.Right, list, binarySeparators);
                }
            }
            else
                list.Add(expression);
        }
    }

    public static Expression? Join(this IEnumerable<Expression> list, ExpressionType binarySeparator)
    {
        if (list is not null)
        {
            var array = list.ToArray();

            if (array.Any())
                return array.Aggregate((x1, x2) => Expression.MakeBinary(binarySeparator, x1, x2));
        }

        return null;
    }
}