/wp-content/plugins/polylang/include/widget-calendar.php

<?php

if ( ! class_exists( 'WP_Widget_Calendar' ) ) {
	require_once( ABSPATH . '/wp-includes/default-widgets.php' );
}

/**
 * obliged to rewrite the whole functionnality as there is no filter on sql queries and only a filter on final output
 * code base last checked with WP 4.4.2
 * a request for making a filter on sql queries exists: http://core.trac.wordpress.org/ticket/15202
 * method used in 0.4.x: use of the get_calendar filter and overwrite the output of get_calendar function -> not very efficient (add 4 to 5 sql queries)
 * method used since 0.5: remove the WP widget and replace it by our own -> our language filter will not work if get_calendar is called directly by a theme
 *
 * @since 0.5
 */
class PLL_Widget_Calendar extends WP_Widget_Calendar {

	/**
	 * displays the widget
	 * modified version of the parent function to call our own get_calendar function
	 *
	 * @since 0.5
	 *
	 * @param array $args Display arguments including before_title, after_title, before_widget, and after_widget.
	 * @param array $instance The settings for the particular instance of the widget
	 */
	function widget( $args, $instance ) {
		/** This filter is documented in wp-includes/widgets/class-wp-widget-pages.php */
		$title = apply_filters( 'widget_title', empty( $instance['title'] ) ? '&nbsp;' : $instance['title'], $instance, $this->id_base );
		echo $args['before_widget'];
		if ( $title ) {
			echo $args['before_title'] . $title . $args['after_title'];
		}
		echo '<div id="calendar_wrap">';
		empty( PLL()->curlang ) ? get_calendar() : self::get_calendar(); #modified#
		echo '</div>';
		echo $args['after_widget'];
	}

	/**
	 * modified version of WP get_calendar function to filter the query
	 *
	 * @since 0.5
	 *
	 * @param bool $initial Optional, default is true. Use initial calendar names.
	 * @param bool $echo Optional, default is true. Set to false for return.
	 * @return string|null String when retrieving, null when displaying.
 	 */
	static function get_calendar( $initial = true, $echo = true ) {
		global $wpdb, $m, $monthnum, $year, $wp_locale, $posts;

		$join_clause = PLL()->model->post->join_clause(); #added#
		$where_clause = PLL()->model->post->where_clause( PLL()->curlang ); #added#

		$key = md5( PLL()->curlang->slug . $m . $monthnum . $year ); #modified#
		$cache = wp_cache_get( 'get_calendar', 'calendar' );

		if ( $cache && is_array( $cache ) && isset( $cache[ $key ] ) ) {
			/** This filter is documented in wp-includes/general-template.php */
			$output = apply_filters( 'get_calendar', $cache[ $key ] );

			if ( $echo ) {
				echo $output;
				return;
			}

			return $output;
		}

		if ( ! is_array( $cache ) ) {
			$cache = array();
		}

		// Quick check. If we have no posts at all, abort!
		if ( ! $posts ) {
			$gotsome = $wpdb->get_var("SELECT 1 as test FROM $wpdb->posts WHERE post_type = 'post' AND post_status = 'publish' LIMIT 1");
			if ( ! $gotsome ) {
				$cache[ $key ] = '';
				wp_cache_set( 'get_calendar', $cache, 'calendar' );
				return;
			}
		}

		if ( isset( $_GET['w'] ) ) {
			$w = (int) $_GET['w'];
		}
		// week_begins = 0 stands for Sunday
		$week_begins = (int) get_option( 'start_of_week' );
		$ts = current_time( 'timestamp' );

		// Let's figure out when we are
		if ( ! empty( $monthnum ) && ! empty( $year ) ) {
			$thismonth = zeroise( intval( $monthnum ), 2 );
			$thisyear = (int) $year;
		} elseif ( ! empty( $w ) ) {
			// We need to get the month from MySQL
			$thisyear = (int) substr( $m, 0, 4 );
			//it seems MySQL's weeks disagree with PHP's
			$d = ( ( $w - 1 ) * 7 ) + 6;
			$thismonth = $wpdb->get_var("SELECT DATE_FORMAT((DATE_ADD('{$thisyear}0101', INTERVAL $d DAY) ), '%m')");
		} elseif ( ! empty( $m ) ) {
			$thisyear = (int) substr( $m, 0, 4 );
			if ( strlen( $m ) < 6 ) {
				$thismonth = '01';
			} else {
				$thismonth = zeroise( (int) substr( $m, 4, 2 ), 2 );
			}
		} else {
			$thisyear = gmdate( 'Y', $ts );
			$thismonth = gmdate( 'm', $ts );
		}

		$unixmonth = mktime( 0, 0 , 0, $thismonth, 1, $thisyear );
		$last_day = date( 't', $unixmonth );

		// Get the next and previous month and year with at least one post
		$previous = $wpdb->get_row( "SELECT MONTH( post_date ) AS month, YEAR( post_date ) AS year
			FROM $wpdb->posts $join_clause
			WHERE post_date < '$thisyear-$thismonth-01'
			AND post_type = 'post' AND post_status = 'publish' $where_clause
				ORDER BY post_date DESC
				LIMIT 1" ); #modified#
		$next = $wpdb->get_row( "SELECT MONTH( post_date ) AS month, YEAR( post_date ) AS year
			FROM $wpdb->posts $join_clause
			WHERE post_date > '$thisyear-$thismonth-{$last_day} 23:59:59'
			AND post_type = 'post' AND post_status = 'publish' $where_clause
				ORDER BY post_date ASC
				LIMIT 1" ); #modified#

		/* translators: Calendar caption: 1: month name, 2: 4-digit year */
		$calendar_caption = _x( '%1$s %2$s', 'calendar caption' );
		$calendar_output = '<table id="wp-calendar">
		<caption>' . sprintf(
			$calendar_caption,
			$wp_locale->get_month( $thismonth ),
			date( 'Y', $unixmonth )
		) . '</caption>
		<thead>
		<tr>';

		$myweek = array();

		for ( $wdcount = 0; $wdcount <= 6; $wdcount++ ) {
			$myweek[] = $wp_locale->get_weekday( ( $wdcount + $week_begins ) % 7 );
		}

		foreach ( $myweek as $wd ) {
			$day_name = $initial ? $wp_locale->get_weekday_initial( $wd ) : $wp_locale->get_weekday_abbrev( $wd );
			$wd = esc_attr( $wd );
			$calendar_output .= "\n\t\t<th scope=\"col\" title=\"$wd\">$day_name</th>";
		}

		$calendar_output .= '
		</tr>
		</thead>

		<tfoot>
		<tr>';

		if ( $previous ) {
			$calendar_output .= "\n\t\t".'<td colspan="3" id="prev"><a href="' . get_month_link( $previous->year, $previous->month ) . '">&laquo; ' .
				$wp_locale->get_month_abbrev( $wp_locale->get_month( $previous->month ) ) .
			'</a></td>';
		} else {
			$calendar_output .= "\n\t\t".'<td colspan="3" id="prev" class="pad">&nbsp;</td>';
		}

		$calendar_output .= "\n\t\t".'<td class="pad">&nbsp;</td>';

		if ( $next ) {
			$calendar_output .= "\n\t\t".'<td colspan="3" id="next"><a href="' . get_month_link( $next->year, $next->month ) . '">' .
				$wp_locale->get_month_abbrev( $wp_locale->get_month( $next->month ) ) .
			' &raquo;</a></td>';
		} else {
			$calendar_output .= "\n\t\t".'<td colspan="3" id="next" class="pad">&nbsp;</td>';
		}

		$calendar_output .= '
		</tr>
		</tfoot>

		<tbody>
		<tr>';

		$daywithpost = array();

		// Get days with posts
		$dayswithposts = $wpdb->get_results( "SELECT DISTINCT DAYOFMONTH( post_date )
			FROM $wpdb->posts $join_clause
			WHERE post_date >= '{$thisyear}-{$thismonth}-01 00:00:00'
			AND post_type = 'post' AND post_status = 'publish' $where_clause
			AND post_date <= '{$thisyear}-{$thismonth}-{$last_day} 23:59:59'", ARRAY_N ); #modified#
		if ( $dayswithposts ) {
			foreach ( (array) $dayswithposts as $daywith ) {
				$daywithpost[] = $daywith[0];
			}
		}

		// See how much we should pad in the beginning
		$pad = calendar_week_mod( date( 'w', $unixmonth ) - $week_begins );
		if ( 0 != $pad ) {
			$calendar_output .= "\n\t\t".'<td colspan="'. esc_attr( $pad ) .'" class="pad">&nbsp;</td>';
		}

		$newrow = false;
		$daysinmonth = (int) date( 't', $unixmonth );

		for ( $day = 1; $day <= $daysinmonth; ++$day ) {
			if ( isset($newrow) && $newrow ) {
				$calendar_output .= "\n\t</tr>\n\t<tr>\n\t\t";
			}
			$newrow = false;

			if ( $day == gmdate( 'j', $ts ) &&
				$thismonth == gmdate( 'm', $ts ) &&
				$thisyear == gmdate( 'Y', $ts ) ) {
				$calendar_output .= '<td id="today">';
			} else {
				$calendar_output .= '<td>';
			}

			if ( in_array( $day, $daywithpost ) ) {
				// any posts today?
				$date_format = date( _x( 'F j, Y', 'daily archives date format' ), strtotime( "{$thisyear}-{$thismonth}-{$day}" ) );
				$label = sprintf( __( 'Posts published on %s' ), $date_format );
				$calendar_output .= sprintf(
					'<a href="%s" aria-label="%s">%s</a>',
					get_day_link( $thisyear, $thismonth, $day ),
					esc_attr( $label ),
					$day
				);
			} else {
				$calendar_output .= $day;
			}
			$calendar_output .= '</td>';

			if ( 6 == calendar_week_mod( date( 'w', mktime(0, 0 , 0, $thismonth, $day, $thisyear ) ) - $week_begins ) ) {
				$newrow = true;
			}
		}

		$pad = 7 - calendar_week_mod( date( 'w', mktime( 0, 0 , 0, $thismonth, $day, $thisyear ) ) - $week_begins );
		if ( $pad != 0 && $pad != 7 ) {
			$calendar_output .= "\n\t\t".'<td class="pad" colspan="'. esc_attr( $pad ) .'">&nbsp;</td>';
		}
		$calendar_output .= "\n\t</tr>\n\t</tbody>\n\t</table>";

		$cache[ $key ] = $calendar_output;
		wp_cache_set( 'get_calendar', $cache, 'calendar' );

		if ( $echo ) {
			/**
			 * Filter the HTML calendar output.
			 *
			 * @since 3.0.0
			 *
			 * @param string $calendar_output HTML output of the calendar.
			 */
			echo apply_filters( 'get_calendar', $calendar_output );
			return;
		}
		/** This filter is documented in wp-includes/general-template.php */
		return apply_filters( 'get_calendar', $calendar_output );
	}
}