class Meta_Date_Archive {

	public $start;
	public $end;
	public $dates;
	public $post_type;
	public $filters;
	public $orderby_key;


	function __construct() {
		add_action( 'wp_loaded', array( $this, 'setup' ) );
	}


	/**
	 * Sets up properties for a meta date query.
	 *
	 * @since 1.0
	 * @return void
	 */
	public function setup() {

		if ( is_admin() ) {
			return;
		}

		$this->start       = apply_filters( 'meta_date_archive_start',     'event_start_date' );
		$this->end         = apply_filters( 'meta_date_archive_end',       'event_end_date' );
		$this->post_type   = apply_filters( 'meta_date_archive_post_type', 'post' );
		$this->filters     = "meta_date_archive";

		add_action( 'pre_get_posts', array( $this, 'pre_get_posts' ), 99 );
		add_filter( 'query_vars',    array( $this, 'query_vars' ) );
		add_action( 'save_post',     array( $this, 'save_post' ) );
	}


	/**
	 * Meta date query.
	 *
	 * @since 1.0
	 * @param object  $query The WP_Query instance.
	 * @return void
	 */
	public function pre_get_posts( $query ) {

		$this->dates = array();

		$start_date      = $query->get( 'meta_archive_start_date' );
		$end_date        = $query->get( 'meta_archive_end_date' );
		$dates           = array();
		$meta_date_query = false;

		if ( $query->is_main_query() ) {
			// main queries

			if ( is_date() ) {
				// main query for date archive
				$dates           = meta_date_archive_dates();
				$meta_date_query = true;
			}
		} else {
			// external queries

			if ( !empty( $start_date ) || !empty( $end_date )  ) {
				// one of the dates is provided
				$meta_date_query = true;
			}

			if ( $meta_date_query ) {
				$dates = meta_date_archive_start_end_date( $start_date, $end_date );
			} else {
				// not the query we're looking for
				return;
			}
		}

		// not a meta date query
		if ( !$meta_date_query ) {
			return;
		}

		if ( isset( $query->query_vars['suppress_filters'] ) ) {
			$this->filters = $query->query_vars['suppress_filters'];
		}

		// we need the filters for a meta date query
		unset( $query->query_vars['suppress_filters'] );

		if ( empty( $dates ) ) {
			echo 'empty';

			// return no posts found
			//
			// not a date archives main query
			// or an external query with dates where the dates didn't validate
			// or an external query where one of the dates is missing

			$this->empty_query();
			$this->cleanup_query();
			return;
		}

		$this->dates = $dates;

		$reset_query_vars = array(
			'second' , 'minute', 'hour',
			'day', 'monthnum', 'year',
			'w', 'm', 'meta_query'
		);

		// reset date query vars
		foreach ( $reset_query_vars as $var ) {
			$query->set( $var, '' );
		}

		$locale = get_query_var('lang');
		$query->set( 'lang', $locale );

		$query->set( 'post_type', $this->post_type );
		$query->set( 'posts_per_page', get_option( 'posts_per_page' ) );

		$query->set( 'meta_key', 'event_start_date' );
		$query->set( 'orderby', 'meta_value_num' );
		$query->set( 'order', 'ASC' );

		$meta_query =  array(
			'relation' => 'AND',

			// needs to be two meta key arrays
			array(
				'key'       => $this->start,
				'compare'   => '>=',
				'value'     => $this->dates['start_date'],
				'type'      => 'DATE'
			),
			array(
				'key'       => $this->end,
				'compare'   => '<=',
				'value'     => $this->dates['end_date'],
				'type'      => 'DATE'
			),
		);

		$query->set( 'meta_query', $meta_query );

		$this->orderby_key = $query->get( 'meta_key' );

		// add the filter
		add_filter( 'get_meta_sql', array( $this, 'get_meta_sql' ), 10, 2 );

		// remove the filters down the road
		$this->cleanup_query();
	}


	/**
	 * Adds the end and start date variables to the public query variables.
	 *
	 * @since 1.0
	 * @param array   $query_vars The array of whitelisted query variables.
	 * @return array The array of whitelisted query variables.
	 */
	public function query_vars( $query_vars ) {
		$query_vars[] = 'meta_archive_start_date';
		$query_vars[] = 'meta_archive_end_date';
		return $query_vars;
	}


	/**
	 * Returns meta date archive meta sql.
	 *
	 * @since 1.0
	 * @param array   $pieces  Array containing the query's JOIN and WHERE clauses.
	 * @param array   $queries Array of meta queries.
	 * @return array Array containing the query's JOIN and WHERE clauses.
	 */
	public function get_meta_sql( $pieces, $queries ) {
		global $wpdb;

		$start_date  = $this->dates['start_date'];
		$end_date    = $this->dates['end_date'];
		$where       = "";
		$start_alias = "$wpdb->postmeta";
		$end_alias   = "mt1";
		$join        = " INNER JOIN $wpdb->postmeta ON ($wpdb->posts.ID = $wpdb->postmeta.post_id)
		                INNER JOIN $wpdb->postmeta AS mt1 ON ( $wpdb->posts.ID = mt1.post_id )";


		if ( in_array( $this->orderby_key, array( $this->start, $this->end ) ) ) {

			$where .= $wpdb->prepare( " AND ($wpdb->postmeta.meta_key = %s)", $this->orderby_key );
			$join .= " INNER JOIN $wpdb->postmeta AS mt2 ON ($wpdb->posts.ID = mt2.post_id)";
			$start_alias = "mt1";
			$end_alias   = "mt2";
		}

		$start_key = $wpdb->prepare( "{$start_alias}.meta_key = %s", $this->start );
		$end_key   = $wpdb->prepare( "{$end_alias}.meta_key = %s", $this->end );

		// after start date AND before end date
		$query = " AND ( (
        ( $start_key AND ( CAST($start_alias.meta_value AS DATE) >= %s) )
            AND ( $end_key AND ( CAST($end_alias.meta_value AS DATE) <= %s) )
        )";
		$where .= $wpdb->prepare( $query, $start_date, $end_date );

		// OR before start date AND after end end date
		$query = " OR (
        ( $start_key AND ( CAST($start_alias.meta_value AS DATE) <= %s) )
            AND ( $end_key AND ( CAST($end_alias.meta_value AS DATE) >= %s) ))";
		$where .= $wpdb->prepare( $query, $start_date, $end_date );

		// OR before start date AND (before end date AND end date after start date)
		$query = " OR (
        ( $start_key AND ( CAST($start_alias.meta_value AS DATE) <= %s) )
        AND ( $end_key
            AND ( CAST($end_alias.meta_value AS DATE) <= %s )
            AND ( CAST($end_alias.meta_value AS DATE) >= %s )
        ))";
		$where .= $wpdb->prepare( $query, $start_date, $end_date, $start_date );

		// OR after end date AND (after start date AND start date before end date) )
		$query = "OR (
        ( $end_key AND ( CAST($end_alias.meta_value AS DATE) >= %s ) )
            AND ( $start_key AND ( CAST($start_alias.meta_value AS DATE) >= %s )
            AND ( CAST($start_alias.meta_value AS DATE) <= %s )
        )))";
		$where .= $wpdb->prepare( $query, $end_date, $start_date, $end_date );

		$pieces['join']  = $join;
		$pieces['where'] = $where;

		return $pieces;
	}


	/**
	 * Adds a filter to 'the_posts' to remove filters used in pre_get_posts.
	 *
	 * @since 1.0
	 * @param object  $query The WP_Query instance.
	 * @return [type]        [description]
	 */
	private function cleanup_query() {
		add_filter( 'the_posts', array( $this, 'the_posts' ), 99, 2 );
	}


	/**
	 * Removes filters used in pre_get_posts.
	 * Restores the suppress_filters parameter if it was used.
	 *
	 * @since 1.0
	 * @param array   $posts Array with post objects.
	 * @return array Array with post objects.
	 */
	public function the_posts( $posts, $_this ) {

		if ( 'meta_date_archive' !== $this->filters ) {
			$_this->query_vars['suppress_filters'] = $this->filters;
		}

		remove_filter( 'get_meta_sql', array( $this, 'get_meta_sql' ), 10, 2 );
		remove_filter( 'posts_where',  array( $this, 'posts_where' ) );
		remove_filter( 'the_posts',    array( $this, 'the_posts' ) );
		return $posts;
	}


	/**
	 * Adds a filter to 'posts_where' to have the query return no posts.
	 *
	 * @since 1.0
	 * @return void
	 */
	private function empty_query() {
		add_filter( 'posts_where', array( $this, 'posts_where' ) );
	}


	/**
	 * Adds 1=0 to the where clause to have the query return no posts.
	 *
	 * @since 1.0
	 * @return void
	 */
	public function posts_where( $where ) {
		return $where . 'AND 1 = 0';
	}


	/**
	 * Adds the start date meta if only end date meta is provided when editing or publishing a post.
	 *
	 * @since 1.0
	 * @return void
	 */
	public function save_post( $post_id ) {

		if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) {
			return $post_id;
		}

		if ( !current_user_can( 'edit_post', $post_id ) ) {
			return $post_id;
		}

		$post_type = ( isset( $_POST['post_type'] ) ) ?  $_POST['post_type'] : '';

		if ( $this->post_type !== $post_type ) {
			return $post_id;
		}

		$end_date = get_post_meta( $post_id, $this->end, true );
		if ( !empty( $end_date ) ) {
			if ( !get_post_meta( $post_id, $this->start, true ) ) {
				update_post_meta( $post_id, $this->start, $end_date );
			}
		}
	}

}

$meta_date_archive = new Meta_Date_Archive();


/**
 * Returns start and end dates for date archives.
 *
 * @since 1.0
 * @return array Array with start and end date.
 */
function meta_date_archive_dates() {
	$year = $month = $day = $m = false;
	$start_date = $end_date = '';

	// is date archives
	if ( is_date() ) {
		$m     = ( get_query_var( 'm' ) ) ? get_query_var( 'm' ) : false;
		$year  = ( get_query_var( 'year' ) ) ? get_query_var( 'year' ) : false;
		$month = ( get_query_var( 'monthnum' ) ) ? zeroise( get_query_var( 'monthnum' ), 2 ) : false;
		$day   = ( get_query_var( 'day' ) ) ? get_query_var( 'day' ) : false;
		if ( $m ) {
			$dates = meta_date_archive_getdate( $m );
			$year  = $dates['year'];
			$month = $dates['month'];
			$day   = $dates['day'];
		}
		return meta_date_archive_validated_dates( $year, $month, $day );
	}

	return array();
}


/**
 * Returns start and end dates.
 *
 * @since 1.0
 * @param int     $start Date.
 * @param int     $end   Date.
 * @return array Array with start and end date.
 */
function meta_date_archive_start_end_date( $start = '', $end = '' ) {

	$year = $month = $day = $m = false;
	$start_date = $end_date = '';

	$start = absint( $start ); // int
	$end   = absint( $end ); // int

	// if not both dates are provided
	if ( !( $start && $end ) ) {
		return array();
	}

	$dates  = meta_date_archive_getdate( $start );
	$dates  = meta_date_archive_validated_dates( $dates['year'], $dates['month'], $dates['day'] );
	$start_date = isset( $dates['start_date'] ) ? $dates['start_date'] : '';

	$dates = meta_date_archive_getdate( $end );
	$dates = meta_date_archive_validated_dates( $dates['year'], $dates['month'], $dates['day'] );
	$end_date = isset( $dates['end_date'] ) ? $dates['end_date'] : '';

	if ( !empty( $start_date ) && !empty( $end_date ) ) {
		return compact( 'start_date', 'end_date' );
	}

	return array();
}


/**
 * Returns year, month or day from date .
 *
 * @since 1.0
 * @param string  $date Date.
 * @return array Array with year, month and day.
 */
function meta_date_archive_getdate( $date = '' ) {
	$year = $month = $day = false;
	switch ( strlen( $date ) ) {
	case 4: // Yearly
		$year = substr( $date, 0, 4 );
		break;
	case 6: // Monthly
		$year = substr( $date, 0, 4 );
		$month = substr( $date, 4, 2 );
		break;
	case 8: // Daily
		$year = substr( $date, 0, 4 );
		$month = substr( $date, 4, 2 );
		$day = substr( $date, 6, 2 );
		break;
	}

	return compact( 'year', 'month', 'day' );
}


/**
 * Returns full date validated.
 *
 * @since 1.0
 * @param integer $year  Year
 * @param integer $month Month
 * @param integer $day   Day
 * @return string Validated date.
 */
function meta_date_archive_validated_dates( $year = 0, $month = 0, $day = 0 ) {
	$start_date = $end_date = '';

	$year = absint( $year );
	$month = absint( $month );
	$day = absint( $day );

	if ( $year ) {
		// check if date exists
		if ( checkdate( '01', '01', $year ) ) {
			$start_date = $year . '0101';
			$end_date   = $year . '1231';
		}
	}

	if ( $year && $month ) {
		$month = zeroise( $month, 2 );
		// check if date exists
		if ( checkdate( $month, '01', $year ) ) {
			$start_date =  $year . $month . '01';
			$end_date   =  date( 'Ymt', mktime( 23, 59, 59, $month, 1, $year ) ); // 't' gets the last day
		}
	}

	if ( $year && $month && $day ) {
		$month = zeroise( $month, 2 );
		$day   = zeroise( $day, 2 );
		// check if date exists
		if ( checkdate( $month, $day, $year ) ) {
			$start_date =  $year . $month . $day;
			$end_date   =  $start_date;
		}
	}

	if ( empty( $start_date ) || empty( $end_date ) ) {
		return array();
	}

	return compact( 'start_date', 'end_date' );
}