add_action( 'pre_get_posts', 'date_archive_query' );

function date_archive_query( $query ) {

	if ( !is_admin() && $query->is_main_query() ) {
		// not an admin page and is the main query

		if ( is_date() ) {
			// date archive

			$dates = get_start_and_end_date();

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

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

			$query->set( 'post_type', 'post' );
			$query->set( 'posts_per_page', 10 );
			$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'       => 'event_end_date',
					'compare'   => '<=',
					'value'     => $dates['end_date'],
					'type'      => 'DATE'
				),
				array(
					'key'       => 'event_start_date',
					'compare'   => '>=',
					'value'     => $dates['start_date'],
					'type'      => 'DATE'
				),

			);

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

			// add the filter
			add_filter( 'get_meta_sql', 'get_meta_sql_date', 10, 2 );

			// remove the filter down the road
			add_filter( 'the_posts', 'remove_get_meta_sql_filter' );
		}
	}
}


function get_start_and_end_date() {

	//check what type of date archive we are on and if query vars are available
	$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 ) {
		// Custom permalinks structure is not enabled
		switch ( strlen( $m ) ) {
		case 4: // Yearly
			$year = substr( $m, 0, 4 );
			break;
		case 6: // Monthly
			$year = substr( $m, 0, 4 );
			$month = substr( $m, 4, 2 );
			break;
		case 8: // Daily
			$year = substr( $m, 0, 4 );
			$month = substr( $m, 4, 2 );
			$day = substr( $m, 6, 2 );
			break;
		}
	}

	if ( is_year() && $year ) {
		$start_date = $year . '0101';
		$end_date   = $year . '1231';
	}

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

	if ( is_day() && $year && $month && $day ) {
		$start_date =  $year . $month . $day;
		$end_date   =  $start_date;
	}

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


// sortable posts by custom date field for long period events
function get_meta_sql_date( $pieces, $queries ) {
	global $wpdb;

	$event_start_date = $event_end_date = '';

	// get start and end date from query
	foreach ( $queries as $q ) {

		if ( !isset( $q['key'] ) ) {
			return $pieces;
		}

		if ( 'event_start_date' === $q['key'] ) {
			$event_start_date = isset( $q['value'] ) ?  $q['value'] : '';
		}
		if ( 'event_end_date' === $q['key'] ) {
			$event_end_date = isset( $q['value'] ) ?  $q['value'] : '';
		}
	}

	if ( ( '' === trim( $event_start_date ) ) || ( '' === trim( $event_end_date ) ) ) {
		return $pieces;
	}

	// Match all meta table aliases with their meta keys (wp_postmeta or mt1, mt2 etc..).
	$pattern = "/($wpdb->postmeta|mt\d+)\.meta_key\s*=\s*'(event_start_date|event_end_date)'/";
	preg_match_all( $pattern  , $pieces['where'], $matches );

	if ( !( isset( $matches[1] ) && isset( $matches[2] ) ) ) {
		return $pieces;
	}

	if ( empty( $matches[1] ) || empty( $matches[2] ) ) {
		return $pieces;
	}

	$query = $start_prefix = $end_prefix = '';
	$prefix = $keys = array();

	// count is 3 with 'orderby' and a 'meta_key'
	if ( ( 3 === count( $matches[2] ) ) && ( 3 === count( $matches[1] ) ) ) {
		$query .= " AND ({$matches[1][0]}.meta_key = '{$matches[2][0]}')";
		$prefix = array_slice( $matches[1], 1 );
		$keys   = array_slice( $matches[2], 1 );
	} else {
		if ( ( 2 === count( $matches[2] ) ) && ( 2 === count( $matches[1] ) ) ) {
			$prefix  = $matches[1];
			$keys   = $matches[2];
		} else {
			// Wrong query
			return $pieces;
		}
	}

	foreach ( $keys as $key => $value ) {
		if ( 'event_start_date' === $value ) {
			$start_prefix = $prefix[ $key ];
		}
		if ( 'event_end_date' === $value ) {
			$end_prefix = $prefix[ $key ];
		}
	}

	if ( empty( $start_prefix ) || empty( $end_prefix ) || $start_prefix === $end_prefix ) {
		return $pieces;
	}

	// after start date AND before end date
	$_query = " AND (
        ( $start_prefix.meta_key = 'event_start_date' AND ( CAST($start_prefix.meta_value AS DATE) >= %s) )
        AND ( $end_prefix.meta_key = 'event_end_date' AND ( CAST($end_prefix.meta_value AS DATE) <= %s) )
    )";
	$query .= $wpdb->prepare( $_query, $event_start_date, $event_end_date );

	// OR before start date AND after end end date
	$_query = " OR (
        ( $start_prefix.meta_key = 'event_start_date' AND ( CAST($start_prefix.meta_value AS DATE) <= %s) )
        AND ( $end_prefix.meta_key = 'event_end_date' AND ( CAST($end_prefix.meta_value AS DATE) >= %s) )
    )";
	$query .= $wpdb->prepare( $_query, $event_start_date, $event_end_date );

	// OR before start date AND (before end date AND end date after start date)
	$_query = " OR (
        ( $start_prefix.meta_key = 'event_start_date' AND ( CAST($start_prefix.meta_value AS DATE) <= %s) )
        AND ( $end_prefix.meta_key = 'event_end_date'
            AND ( CAST($end_prefix.meta_value AS DATE) <= %s )
            AND ( CAST($end_prefix.meta_value AS DATE) >= %s )
        )
    )";
	$query .= $wpdb->prepare( $_query, $event_start_date, $event_end_date, $event_start_date );

	// OR after end date AND (after start date AND start date before end date) )
	$_query = "OR (
        ( $end_prefix.meta_key = 'event_end_date' AND ( CAST($end_prefix.meta_value AS DATE) >= %s ) )
        AND ( $start_prefix.meta_key = 'event_start_date'
            AND ( CAST($start_prefix.meta_value AS DATE) >= %s )
            AND ( CAST($start_prefix.meta_value AS DATE) <= %s )
        )
    )";
	$query .= $wpdb->prepare( $_query, $event_end_date, $event_start_date, $event_end_date );

	$pieces['where'] = $query;

	return $pieces;
}


function remove_get_meta_sql_filter( $posts ) {
	remove_filter( 'get_meta_sql', 'get_meta_sql_date', 10, 2 );
	return $posts;
}


add_action( 'save_post', 'validate_event_meta' );

// adds event_start_date meta if only event_end_date was submitted.
function validate_event_meta( $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 ( 'post' !== $post_type ) {
		return $post_id;
	}

	$event_end_date = get_post_meta( $post_id, 'event_end_date', true );
	if ( !empty( $event_end_date ) ) {
		if ( !get_post_meta( $post_id, 'event_start_date', true ) ) {
			update_post_meta( $post_id, 'event_start_date', $event_end_date );
		}
	}
}