<?php namespace Illuminate\Database\Eloquent\Relations;

use Illuminate\Database\Eloquent\Model;
use Illuminate\Database\Eloquent\Builder;
use Illuminate\Database\Query\Expression;
use Illuminate\Database\Eloquent\Collection;

class HasManyThrough extends Relation {

	/**
	 * The distance parent model instance.
	 *
	 * @var \Illuminate\Database\Eloquent\Model
	 */
	protected $farParent;

	/**
	 * The near key on the relationship.
	 *
	 * @var string
	 */
	protected $firstKey;

	/**
	 * The far key on the relationship.
	 *
	 * @var string
	 */
	protected $secondKey;

	/**
	 * Create a new has many relationship instance.
	 *
	 * @param  \Illuminate\Database\Eloquent\Builder  $query
	 * @param  \Illuminate\Database\Eloquent\Model  $parent
	 * @param  string  $firstKey
	 * @param  string  $secondKey
	 * @return void
	 */
	public function __construct(Builder $query, Model $farParent, Model $parent, $firstKey, $secondKey)
	{
		$this->firstKey = $firstKey;
		$this->secondKey = $secondKey;
		$this->farParent = $farParent;

		parent::__construct($query, $parent);
	}

	/**
	 * Set the base constraints on the relation query.
	 *
	 * @return void
	 */
	public function addConstraints()
	{
		$parentTable = $this->parent->getTable();

		$this->setJoin();

		if (static::$constraints)
		{
			$this->query->where($parentTable.'.'.$this->firstKey, '=', $this->farParent->getKey());
		}
	}

	/**
	 * Add the constraints for a relationship count query.
	 *
	 * @param  \Illuminate\Database\Eloquent\Builder  $query
	 * @param  \Illuminate\Database\Eloquent\Builder  $parent
	 * @return \Illuminate\Database\Eloquent\Builder
	 */
	public function getRelationCountQuery(Builder $query, Builder $parent)
	{
		$parentTable = $this->parent->getTable();

		$this->setJoin($query);

		$query->select(new Expression('count(*)'));

		$key = $this->wrap($parentTable.'.'.$this->firstKey);

		return $query->where($this->getHasCompareKey(), '=', new Expression($key));
	}

	/**
	 * Set the join clause on the query.
	 *
	 * @param  \Illuminate\Database\Eloquent\Builder|null  $query
	 * @return void
	 */
	protected function setJoin(Builder $query = null)
	{
		$query = $query ?: $this->query;

		$foreignKey = $this->related->getTable().'.'.$this->secondKey;

		$query->join($this->parent->getTable(), $this->getQualifiedParentKeyName(), '=', $foreignKey);
	}

	/**
	 * Set the constraints for an eager load of the relation.
	 *
	 * @param  array  $models
	 * @return void
	 */
	public function addEagerConstraints(array $models)
	{
		$table = $this->parent->getTable();

		$this->query->whereIn($table.'.'.$this->firstKey, $this->getKeys($models));
	}

	/**
	 * Initialize the relation on a set of models.
	 *
	 * @param  array   $models
	 * @param  string  $relation
	 * @return array
	 */
	public function initRelation(array $models, $relation)
	{
		foreach ($models as $model)
		{
			$model->setRelation($relation, $this->related->newCollection());
		}

		return $models;
	}

	/**
	 * Match the eagerly loaded results to their parents.
	 *
	 * @param  array   $models
	 * @param  \Illuminate\Database\Eloquent\Collection  $results
	 * @param  string  $relation
	 * @return array
	 */
	public function match(array $models, Collection $results, $relation)
	{
		$dictionary = $this->buildDictionary($results);

		// Once we have the dictionary we can simply spin through the parent models to
		// link them up with their children using the keyed dictionary to make the
		// matching very convenient and easy work. Then we'll just return them.
		foreach ($models as $model)
		{
			$key = $model->getKey();

			if (isset($dictionary[$key]))
			{
				$value = $this->related->newCollection($dictionary[$key]);

				$model->setRelation($relation, $value);
			}
		}

		return $models;
	}

	/**
	 * Build model dictionary keyed by the relation's foreign key.
	 *
	 * @param  \Illuminate\Database\Eloquent\Collection  $results
	 * @return array
	 */
	protected function buildDictionary(Collection $results)
	{
		$dictionary = array();

		$foreign = $this->firstKey;

		// First we will create a dictionary of models keyed by the foreign key of the
		// relationship as this will allow us to quickly access all of the related
		// models without having to do nested looping which will be quite slow.
		foreach ($results as $result)
		{
			$dictionary[$result->{$foreign}][] = $result;
		}

		return $dictionary;
	}

	/**
	 * Get the results of the relationship.
	 *
	 * @return mixed
	 */
	public function getResults()
	{
		return $this->get();
	}

	/**
	 * Execute the query as a "select" statement.
	 *
	 * @param  array  $columns
	 * @return \Illuminate\Database\Eloquent\Collection
	 */
	public function get($columns = array('*'))
	{
		// First we'll add the proper select columns onto the query so it is run with
		// the proper columns. Then, we will get the results and hydrate out pivot
		// models with the result of those columns as a separate model relation.
		$select = $this->getSelectColumns($columns);

		$models = $this->query->addSelect($select)->getModels();

		// If we actually found models we will also eager load any relationships that
		// have been specified as needing to be eager loaded. This will solve the
		// n + 1 query problem for the developer and also increase performance.
		if (count($models) > 0)
		{
			$models = $this->query->eagerLoadRelations($models);
		}

		return $this->related->newCollection($models);
	}

	/**
	 * Set the select clause for the relation query.
	 *
	 * @param  array  $columns
	 * @return \Illuminate\Database\Eloquent\Relations\BelongsToMany
	 */
	protected function getSelectColumns(array $columns = array('*'))
	{
		if ($columns == array('*'))
		{
			$columns = array($this->related->getTable().'.*');
		}

		return array_merge($columns, array($this->parent->getTable().'.'.$this->firstKey));
	}

	/**
	 * Get a paginator for the "select" statement.
	 *
	 * @param  int    $perPage
	 * @param  array  $columns
	 * @return \Illuminate\Pagination\Paginator
	 */
	public function paginate($perPage = null, $columns = array('*'))
	{
		$this->query->addSelect($this->getSelectColumns($columns));

		$pager = $this->query->paginate($perPage, $columns);

		return $pager;
	}

	/**
	 * Get the key name of the parent model.
	 *
	 * @return string
	 */
	protected function getQualifiedParentKeyName()
	{
		return $this->parent->getQualifiedKeyName();
	}

	/**
	 * Get the key for comparing against the parent key in "has" query.
	 *
	 * @return string
	 */
	public function getHasCompareKey()
	{
		return $this->farParent->getQualifiedKeyName();
	}

}