<?php
/**
 * Prints the scheduled elements script on the front end.
 *
 * @package Yangra\Conditional
 */

namespace Yangra\Conditional\Scheduling;

defined( 'ABSPATH' ) || exit;

/**
 * On pages where at least one schedule applies, adds to <head>:
 *
 * - an enqueued inline style that hides every scheduled target until the
 *   script has run (`html:not(.yangra-conditional-js)`). Visitors without
 *   JavaScript, or whose browser blocks or delays the script, never see
 *   content before or after its window, but they also miss content that is
 *   live;
 * - the schedules and the script from build/frontend/schedules.js, inline at
 *   the top of <head>, so targets are hidden before the page body is drawn
 *   (no flash of content). Its first line adds the class that turns the
 *   style above off.
 *
 * Decided in the browser, with the visitor's clock, so it works the same on
 * cached pages. It isn't protection: the targets are still in the HTML.
 */
class ScheduleRuntime {

	const SCRIPT_ID = 'yangra-conditional-schedules';

	/**
	 * Class the script adds to <html> as soon as it runs.
	 */
	const JS_CLASS = 'yangra-conditional-js';

	/**
	 * Scheduled elements.
	 *
	 * @var ScheduledElements
	 */
	private $schedules;

	/**
	 * Constructor.
	 *
	 * @param ScheduledElements $schedules Scheduled elements.
	 */
	public function __construct( ScheduledElements $schedules ) {
		$this->schedules = $schedules;
	}

	/**
	 * Registers hooks.
	 *
	 * @return void
	 */
	public function register(): void {
		add_action( 'wp_enqueue_scripts', array( $this, 'enqueue' ) );
		add_action( 'wp_head', array( $this, 'print' ), 1 );
	}

	/**
	 * Enqueues the style that hides every scheduled target until the script
	 * has run.
	 *
	 * @return void
	 */
	public function enqueue(): void {
		$data = $this->data();
		if ( null === $data || '' === $this->script() ) {
			return;
		}

		wp_register_style( self::SCRIPT_ID, false, array(), YANGRA_CONDITIONAL_VERSION );
		wp_enqueue_style( self::SCRIPT_ID );
		wp_add_inline_style( self::SCRIPT_ID, self::hiding_css( $data['schedules'] ) );
	}

	/**
	 * CSS that hides every target of the schedules while <html> doesn't have
	 * the class the script adds.
	 *
	 * @param array<int, array{targets: array<int, string>}> $schedules Schedules.
	 * @return string
	 */
	public static function hiding_css( array $schedules ): string {
		$targets = array();
		foreach ( $schedules as $schedule ) {
			$targets = array_merge( $targets, $schedule['targets'] );
		}
		// Targets are validated class and ID names, so they're safe in CSS.
		$selectors = array_map(
			static function ( string $target ): string {
				return 'html:not(.' . self::JS_CLASS . ') ' . $target;
			},
			array_values( array_unique( $targets ) )
		);

		return implode( ',', $selectors ) . '{display:none!important}';
	}

	/**
	 * The data the script needs on the current page, or null when no schedule
	 * applies. Times are in milliseconds, for JavaScript.
	 *
	 * @return array{schedules: array<int, array{targets: array<int, string>, show: int|null, hide: int|null}>, now?: int}|null
	 */
	public function data(): ?array {
		$queried   = is_singular() ? (int) get_queried_object_id() : 0;
		$schedules = array();
		foreach ( $this->schedules->for_page( $queried ) as $schedule ) {
			$schedules[] = array(
				'targets' => $schedule['targets'],
				'show'    => null === $schedule['show_at'] ? null : $schedule['show_at'] * 1000,
				'hide'    => null === $schedule['hide_at'] ? null : $schedule['hide_at'] * 1000,
			);
		}
		if ( array() === $schedules ) {
			return null;
		}

		/**
		 * Filters the data printed for the scheduled elements script. Pro adds
		 * `now` (ms) while an admin previews a date and time: the script's
		 * clock starts there instead of at the visitor's time.
		 *
		 * @param mixed $data    `schedules`, each with `targets`, `show` and `hide` (ms, or null).
		 *                       Anything but an array is ignored, and `schedules` can't be changed.
		 * @param int   $queried Post ID of the page being viewed, or 0.
		 */
		$data = apply_filters( 'yangra_conditional_schedule_runtime_data', array( 'schedules' => $schedules ), $queried );
		$data = is_array( $data ) ? $data : array();
		if ( isset( $data['now'] ) && ! is_int( $data['now'] ) ) {
			unset( $data['now'] );
		}
		$data['schedules'] = $schedules;

		return $data;
	}

	/**
	 * Prints the script. Its first line marks <html>, which turns off the
	 * style that hides every target; the script then hides only those that
	 * should be hidden now.
	 *
	 * @return void
	 */
	public function print(): void {
		$data = $this->data();
		if ( null === $data ) {
			return;
		}
		$script = $this->script();
		if ( '' === $script ) {
			return;
		}

		wp_print_inline_script_tag(
			'document.documentElement.classList.add(' . wp_json_encode( self::JS_CLASS ) . ");\n"
			. 'window.yangraConditionalSchedules = ' . wp_json_encode( $data, JSON_HEX_TAG | JSON_HEX_AMP ) . ";\n" . $script,
			array( 'id' => self::SCRIPT_ID )
		);
	}

	/**
	 * The built script, or '' when it hasn't been built.
	 *
	 * @return string
	 */
	private function script(): string {
		$file = YANGRA_CONDITIONAL_PATH . 'build/frontend/schedules.js';
		if ( ! is_readable( $file ) ) {
			return '';
		}

		// A local file in the plugin, read to print inline.
		return trim( (string) file_get_contents( $file ) ); // phpcs:ignore WordPress.WP.AlternativeFunctions.file_get_contents_file_get_contents
	}
}