PHP Sorter abstraction

sorter.php

<?php namespace Sorter;

class Sorter
{
	/**
	 * Apply sorting logic to a given DB query. Look-up the model's rules to allow/disallow and alias sorting types
	 *
	 * @param  $sort_by   string  Sorting subject
	 * @param  $direction integer 1 or -1
	 * @param  $query     string
	 * @param  $model     string
	 * @return string
	 */

	public static function apply($sort_by, $direction, $query, $model)
	{
		$rules     = self::load_rules($model);
		$direction = $direction == -1 ? -1 : 1;

		if(array_key_exists($sort_by, $rules))
		{
			return self::inject($query, $rules[$sort_by], $direction);
		}
		else
		{
			if(! empty($rules))
			{
				reset($rules);
				return self::inject($query, current($rules), $direction);
			}
			else
			{
				return str_replace(':sort', '', $query);
			}
		}
	}

	/**
	 * Replaces :sort in original query string with the generated sorting query
	 *
	 * @param  $query     string
	 * @param  $column    string
	 * @param  $direction integer
	 * @return string
	 */

	private static function inject($query, $column, $direction)
	{
		return str_replace(':sort', 'ORDER BY ' . $column . ' ' . ($direction == -1 ? 'DESC' : 'ASC'), $query);
	}

	/**
	 * Load (static) rules and aliases from a model, return an empty array if none exist
	 *
	 * @param  $model string
	 * @return array
	 */

	private static function load_rules($model)
	{
		$rules = $model::$rules;

		if(! $rules)
			$rules = array();

		return $rules;
	}
}

Example implementation:

<?php

class Post extends Eloquent
{
    public static $sort_rules = array(
        'age' => 'posts.created_at',
    );

    public static function all($sort = 'age', $direction = -1, $offset = 0, $limit = 20)
    {
        return DB::query(
            Sorter\Sorter::apply($sort, $direction, "SELECT posts.*, users.name FROM posts LEFT JOIN users ON users.id = posts.user_id :sort LIMIT ?, ?", "Post"),
            array($offset, $limit)
        );
    }
}

(With Eloquent, naming your own function all is not advisable because of conflicts and whatnot, but for exemplary reason and because it looks good I use it here)

And therefore, in a controller/router, here in Laravel:

<?php

Route::get('posts', function()
{
    # /posts?sort=age&dir=1
    return View::make('posts.list', array(
        'posts' => Post::all(Input::get('sort', 'age'), Input::get('dir', -1)),
    ));
});