LengthFunction.cs

using Queries.Core.Attributes;
using Queries.Core.Parts.Columns;
using System;

namespace Queries.Core.Parts.Functions;

/// <summary>
/// Function that computes the length of a column
/// </summary>
[Function]
public class LengthFunction : IAliasable<LengthFunction>, IColumn
{
    /// <summary>
    /// The column onto which <see cref="LengthFunction"/> will be applied
    /// </summary>
    public IColumn Column { get; }
    private string _alias;

    /// <summary>
    /// Alias sets for the function.
    /// </summary>
    public string Alias => _alias;

    /// <summary>
    /// Builds a new <see cref="LengthFunction"/> instance.
    /// </summary>
    /// <param name="column">The column onto which the function must be applied.</param>
    /// <exception cref="ArgumentNullException">if <paramref name="column"/> is <c>nulll</c></exception>
    public LengthFunction(IColumn column)
    {
        Column = column ?? throw new ArgumentNullException(nameof(column));
    }

    /// <summary>
    /// Set the alias of the function
    /// </summary>
    /// <param name="alias"></param>
    /// <returns>The current instance</returns>
    public LengthFunction As(string alias)
    {
        _alias = alias;

        return this;
    }

    /// <summary>
    /// Performs a deep copy of the current instance.
    /// </summary>
    /// <returns><see cref="LengthFunction"/></returns>
    public IColumn Clone() => new LengthFunction(Column.Clone());
}