<?php

/**

 * Speculative loading functions.

 *

 * @package WordPress

 * @subpackage Speculative Loading

 * @since 6.8.0

 */

/**

 * Returns the speculation rules configuration.

 *

 * @since 6.8.0

 *

 * @return array<string, string>|null Associative array with 'mode' and 'eagerness' keys, or null if speculative

 *                                    loading is disabled.

 */

function wp_get_speculation_rules_configuration(): ?array {

	// By default, speculative loading is only enabled for sites with pretty permalinks when no user is logged in.

	if ( ! is_user_logged_in() && get_option( 'permalink_structure' ) ) {

		$config = array(

			'mode'      => 'auto',

			'eagerness' => 'auto',

		);

	} else {

		$config = null;

	}

	/**

	 * Filters the way that speculation rules are configured.

	 *

	 * The Speculation Rules API is a web API that allows to automatically prefetch or prerender certain URLs on the

	 * page, which can lead to near-instant page load times. This is also referred to as speculative loading.

	 *

	 * There are two aspects to the configuration:

	 * * The "mode" (whether to "prefetch" or "prerender" URLs).

	 * * The "eagerness" (whether to speculatively load URLs in an "eager", "moderate", or "conservative" way).

	 *

	 * By default, the speculation rules configuration is decided by WordPress Core ("auto"). This filter can be used

	 * to force a certain configuration, which could for instance load URLs more or less eagerly.

	 *

	 * For logged-in users or for sites that are not configured to use pretty permalinks, the default value is `null`,

	 * indicating that speculative loading is entirely disabled.

	 *

	 * @since 6.8.0

	 * @see https://developer.chrome.com/docs/web-platform/prerender-pages

	 *

	 * @param array<string, string>|null $config Associative array with 'mode' and 'eagerness' keys, or `null`. The

	 *                                           default value for both of the keys is 'auto'. Other possible values

	 *                                           for 'mode' are 'prefetch' and 'prerender'. Other possible values for

	 *                                           'eagerness' are 'eager', 'moderate', and 'conservative'. The value

	 *                                           `null` is used to disable speculative loading entirely.

	 */

	$config = apply_filters( 'wp_speculation_rules_configuration', $config );

	// Allow the value `null` to indicate that speculative loading is disabled.

	if ( null === $config ) {

		return null;

	}

	// Sanitize the configuration and replace 'auto' with current defaults.

	$default_mode      = 'prefetch';

	$default_eagerness = 'conservative';

	if ( ! is_array( $config ) ) {

		return array(

			'mode'      => $default_mode,

			'eagerness' => $default_eagerness,

		);

	}

	if (

		! isset( $config['mode'] ) ||

		'auto' === $config['mode'] ||

		! WP_Speculation_Rules::is_valid_mode( $config['mode'] )

	) {

		$config['mode'] = $default_mode;

	}

	if (

		! isset( $config['eagerness'] ) ||

		'auto' === $config['eagerness'] ||

		! WP_Speculation_Rules::is_valid_eagerness( $config['eagerness'] ) ||

		// 'immediate' is a valid eagerness, but for safety WordPress does not allow it for document-level rules.

		'immediate' === $config['eagerness']

	) {

		$config['eagerness'] = $default_eagerness;

	}

	return array(

		'mode'      => $config['mode'],

		'eagerness' => $config['eagerness'],

	);

}

/**

 * Returns the full speculation rules data based on the configuration.

 *

 * Plugins with features that rely on frontend URLs to exclude from prefetching or prerendering should use the

 * {@see 'wp_speculation_rules_href_exclude_paths'} filter to ensure those URL patterns are excluded.

 *

 * Additional speculation rules other than the default rule from WordPress Core can be provided by using the

 * {@see 'wp_load_speculation_rules'} action and amending the passed WP_Speculation_Rules object.

 *

 * @since 6.8.0

 * @access private

 *

 * @return WP_Speculation_Rules|null Object representing the speculation rules to use, or null if speculative loading

 *                                   is disabled in the current context.

 */

function wp_get_speculation_rules(): ?WP_Speculation_Rules {

	$configuration = wp_get_speculation_rules_configuration();

	if ( null === $configuration ) {

		return null;

	}

	$mode      = $configuration['mode'];

	$eagerness = $configuration['eagerness'];

	$prefixer = new WP_URL_Pattern_Prefixer();

	$base_href_exclude_paths = array(

		$prefixer->prefix_path_pattern( '/wp-*.php', 'site' ),

		$prefixer->prefix_path_pattern( '/wp-admin/*', 'site' ),

		$prefixer->prefix_path_pattern( '/*', 'uploads' ),

		$prefixer->prefix_path_pattern( '/*', 'content' ),

		$prefixer->prefix_path_pattern( '/*', 'plugins' ),

		$prefixer->prefix_path_pattern( '/*', 'template' ),

		$prefixer->prefix_path_pattern( '/*', 'stylesheet' ),

	);

	/*

	 * If pretty permalinks are enabled, exclude any URLs with query parameters.

	 * Otherwise, exclude specifically the URLs with a `_wpnonce` query parameter or any other query parameter

	 * containing the word `nonce`.

	 */

	if ( get_option( 'permalink_structure' ) ) {

		$base_href_exclude_paths[] = $prefixer->prefix_path_pattern( '/*\\?(.+)', 'home' );

	} else {

		$base_href_exclude_paths[] = $prefixer->prefix_path_pattern( '/*\\?*(^|&)*nonce*=*', 'home' );

	}

	/**

	 * Filters the paths for which speculative loading should be disabled.

	 *

	 * All paths should start in a forward slash, relative to the root document. The `*` can be used as a wildcard.

	 * If the WordPress site is in a subdirectory, the exclude paths will automatically be prefixed as necessary.

	 *

	 * Note that WordPress always excludes certain path patterns such as `/wp-login.php` and `/wp-admin/*`, and those

	 * cannot be modified using the filter.

	 *

	 * @since 6.8.0

	 *

	 * @param string[] $href_exclude_paths Additional path patterns to disable speculative loading for.

	 * @param string   $mode               Mode used to apply speculative loading. Either 'prefetch' or 'prerender'.

	 */

	$href_exclude_paths = (array) apply_filters( 'wp_speculation_rules_href_exclude_paths', array(), $mode );

	// Ensure that:

	// 1. There are no duplicates.

	// 2. The base paths cannot be removed.

	// 3. The array has sequential keys (i.e. array_is_list()).

	$href_exclude_paths = array_values(

		array_unique(

			array_merge(

				$base_href_exclude_paths,

				array_map(

					static function ( string $href_exclude_path ) use ( $prefixer ): string {

						return $prefixer->prefix_path_pattern( $href_exclude_path );

					},

					$href_exclude_paths

				)

			)

		)

	);

	$speculation_rules = new WP_Speculation_Rules();

	$main_rule_conditions = array(

		// Include any URLs within the same site.

		array(

			'href_matches' => $prefixer->prefix_path_pattern( '/*' ),

		),

		// Except for excluded paths.

		array(

			'not' => array(

				'href_matches' => $href_exclude_paths,

			),

		),

		// Also exclude rel=nofollow links, as certain plugins use that on their links that perform an action.

		array(

			'not' => array(

				'selector_matches' => 'a[rel~="nofollow"]',

			),

		),

		// Also exclude links that are explicitly marked to opt out, either directly or via a parent element.

		array(

			'not' => array(

				'selector_matches' => ".no-{$mode}, .no-{$mode} a",

			),

		),

	);

	// If using 'prerender', also exclude links that opt out of 'prefetch' because it's part of 'prerender'.

	if ( 'prerender' === $mode ) {

		$main_rule_conditions[] = array(

			'not' => array(

				'selector_matches' => '.no-prefetch, .no-prefetch a',

			),

		);

	}

	$speculation_rules->add_rule(

		$mode,

		'main',

		array(

			'source'    => 'document',

			'where'     => array(

				'and' => $main_rule_conditions,

			),

			'eagerness' => $eagerness,

		)

	);

	/**

	 * Fires when speculation rules data is loaded, allowing to amend the rules.

	 *

	 * @since 6.8.0

	 *

	 * @param WP_Speculation_Rules $speculation_rules Object representing the speculation rules to use.

	 */

	do_action( 'wp_load_speculation_rules', $speculation_rules );

	return $speculation_rules;

}

/**

 * Prints the speculation rules.

 *

 * For browsers that do not support speculation rules yet, the `script[type="speculationrules"]` tag will be ignored.

 *

 * @since 6.8.0

 * @access private

 */

function wp_print_speculation_rules(): void {

	$speculation_rules = wp_get_speculation_rules();

	if ( null === $speculation_rules ) {

		return;

	}

	wp_print_inline_script_tag(

		(string) wp_json_encode(

			$speculation_rules

		),

		array( 'type' => 'speculationrules' )

	);

}