introduce query filter for REST API

Enabled WP REST API to query for ticker slug, GMT timestamp and limit
parameter as used by AJAX calls. This is done in preparation for
migration to WP REST instead of WP AJAX.

includes/class-api.php

@@ -0,0 +1,73 @@
+<?php
+/**
+ * Liveticker: Plugin API class.
+ *
+ * This file contains the plugin's REST API extensions.
+ *
+ * @package SCLiveticker
+ */
+
+namespace SCLiveticker;
+
+// Exit if accessed directly.
+if ( ! defined( 'ABSPATH' ) ) {
+	exit;
+}
+
+/**
+ * Liveticker.
+ *
+ * @since 1.2
+ */
+class Api {
+	/**
+	 * Filter tick queries by ticker slug and date.
+	 *
+	 * @param array            $args    Query vars.
+	 * @param \WP_REST_Request $request The REST request.
+	 *
+	 * @return array Filtered query values.
+	 */
+	public static function tick_query_filter( $args, $request ) {
+		// Extract arguments.
+		$ticker_slug = $request->get_param( 'ticker' );
+		$limit       = intval( $request->get_param( 'limit' ) );
+		$last_poll   = intval( $request->get_param( 'last' ) );
+
+		if ( ! empty( $ticker_slug ) ) {
+			$args['tax_query'][] = array(
+				'taxonomy' => 'scliveticker_ticker',
+				'field'    => 'slug',
+				'terms'    => $ticker_slug,
+			);
+		}
+
+		if ( ! empty( $limit ) ) {
+			$args['posts_per_page'] = $limit;
+		}
+
+		if ( $last_poll > 0 ) {
+			$last_poll = explode(
+				',',
+				gmdate(
+					'Y,m,d,H,i,s',
+					$last_poll
+				)
+			);
+
+			$args['date_query'] = array(
+				'column' => 'post_date_gmt',
+				'after'  => array(
+					'year'   => intval( $last_poll[0] ),
+					'month'  => intval( $last_poll[1] ),
+					'day'    => intval( $last_poll[2] ),
+					'hour'   => intval( $last_poll[3] ),
+					'minute' => intval( $last_poll[4] ),
+					'second' => intval( $last_poll[5] ),
+				),
+			);
+		}
+
+		return $args;
+	}
+}