SubstringFunction.cs

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

namespace Queries.Core.Parts.Functions;

/// <summary>
/// "SUBSTRING" function.
/// </summary>
[Function]
public class SubstringFunction : IColumn, IAliasable<SubstringFunction>
{
    /// <summary>
    /// Column the function will be applied to
    /// </summary>
    public IColumn Column { get;  }

    /// <summary>
    /// Defines where the substring extraction will start
    /// </summary>
    public int Start { get; }

    /// <summary>
    /// Defines the length of the extracted substring
    /// </summary>
    public int? Length { get; }

    /// <summary>
    /// Builds a new <see cref="SubstringFunction"/> instance.
    /// </summary>
    /// <param name="column">Column onto which the </param>
    /// <param name="start">index of the position where to start the substring</param>
    /// <param name="length">positive integer</param>
    /// <exception cref="ArgumentNullException">if <paramref name="column"/> is <see langword="null" />.</exception>
    /// <exception cref="ArgumentOutOfRangeException">if either :
    ///     - <paramref name="start"/> is less than <c>0</c> <see langword="null" />,
    ///     - <paramref name="length"/> is less than <c>0</c>.
    /// </exception>
    public SubstringFunction(IColumn column, int start, int? length = null)
    {
        if (start < 0)
        {
            throw new ArgumentOutOfRangeException(nameof(start), start, $"{nameof(start)} must be greater or equal to 0");
        }

        if (length.HasValue && length.Value < 0)
        {
            throw new ArgumentOutOfRangeException(nameof(length), length, $"{nameof(length)} must be greater or equal to 0");
        }

        Column = column ?? throw new ArgumentNullException(nameof(column), $"{nameof(column)} cannot be null");
        Start = start;
        Length = length;
    }

    ///<inheritdoc/>
    public string Alias { get; private set; }

    /// <summary>
    /// Defines an alias for the <see cref="SubstringFunction"/>
    /// </summary>
    /// <param name="alias">The new alias</param>
    /// <returns></returns>
    public SubstringFunction As(string alias)
    {
        // TODO Validate the alias ?
        Alias = alias;
        return this;
    }

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