<?php
/**
 * Plugin Name: Cache-Control Test Scripts
 * Description: Registers and enqueues a set of render-blocking test scripts served via admin-ajax, each replicating one of the caching scenarios handled by the Enqueued Assets audit. See https://github.com/WordPress/performance/pull/2481.
 * Author: Weston Ruter
 * Version: 1.0.0
 * License: GPL-2.0-or-later
 *
 * @package CacheControlTestScripts
 */

namespace CacheControlTestScripts;

const ACTION_PREFIX = 'cctest_';

/**
 * Gets the test scenarios.
 *
 * Each scenario is rendered as a blocking `<script src>` pointing at admin-ajax, and the
 * corresponding ajax handler emits the body and headers below with a `text/javascript` content type.
 *
 * The `headers` are the *only* caching-related headers sent: the handler first strips the
 * `Cache-Control`, `Expires`, `Last-Modified`, and `ETag` headers that admin-ajax would otherwise
 * send (via nocache_headers()), then applies exactly what each scenario specifies.
 *
 * @return array<string, array{label: string, body: string, headers: array<string, string>, expected: string}>
 */
function get_scenarios(): array {
	$past   = gmdate( 'D, d M Y H:i:s', time() - DAY_IN_SECONDS ) . ' GMT';
	$future = gmdate( 'D, d M Y H:i:s', time() + YEAR_IN_SECONDS ) . ' GMT';
	$now    = gmdate( 'D, d M Y H:i:s' ) . ' GMT';

	return array(
		// Cacheable: passes the audit.
		'max_age_3600'    => array(
			'label'    => 'Cache-Control: max-age=3600 (cacheable)',
			'body'     => "console.log( 'Hello World: cacheable' );",
			'headers'  => array( 'Cache-Control' => 'max-age=3600' ),
			'expected' => 'pass',
		),

		// Zero-byte body but cacheable: flagged as zero_size.
		'zero_size'       => array(
			'label'    => 'Zero-byte body (max-age=3600)',
			'body'     => '',
			'headers'  => array( 'Cache-Control' => 'max-age=3600' ),
			'expected' => 'error: zero_size',
		),

		// no-store: cannot be cached at all.
		'no_store'        => array(
			'label'    => 'Cache-Control: no-store',
			'body'     => "console.log( 'Hello World: not stored' );",
			'headers'  => array( 'Cache-Control' => 'no-store' ),
			'expected' => 'error: not_cacheable (unqualified)',
		),

		// no-cache: revalidation forced on every request.
		'no_cache'        => array(
			'label'    => 'Cache-Control: no-cache',
			'body'     => "console.log( 'Hello World: not cached' );",
			'headers'  => array( 'Cache-Control' => 'no-cache' ),
			'expected' => 'error: not_cacheable (soft)',
		),

		// max-age=0: permits caching but forces revalidation.
		'max_age_0'       => array(
			'label'    => 'Cache-Control: max-age=0',
			'body'     => "console.log( 'Hello World: max-age=0' );",
			'headers'  => array( 'Cache-Control' => 'max-age=0' ),
			'expected' => 'error: not_cacheable (soft)',
		),

		// max-age="0" with whitespace: parsed numerically, still flagged.
		'max_age_quoted'  => array(
			'label'    => 'Cache-Control: max-age = "0"',
			'body'     => "console.log( 'Hello World: max-age quoted zero' );",
			'headers'  => array( 'Cache-Control' => 'max-age = "0"' ),
			'expected' => 'error: not_cacheable (soft)',
		),

		// Past Expires, no Cache-Control: already expired.
		'expires_past'    => array(
			'label'    => 'Expires in the past (no Cache-Control)',
			'body'     => "console.log( 'Hello World: expired' );",
			'headers'  => array( 'Expires' => $past ),
			'expected' => 'error: not_cacheable (soft)',
		),

		// Invalid Expires, no Cache-Control: treated as already expired.
		'expires_invalid' => array(
			'label'    => 'Expires invalid/unparseable (no Cache-Control)',
			'body'     => "console.log( 'Hello World: invalid expires' );",
			'headers'  => array( 'Expires' => 'this-is-not-a-date' ),
			'expected' => 'error: not_cacheable (soft)',
		),

		// Future Expires, no Cache-Control: passes.
		'expires_future'  => array(
			'label'    => 'Expires in the future (no Cache-Control)',
			'body'     => "console.log( 'Hello World: future expires' );",
			'headers'  => array( 'Expires' => $future ),
			'expected' => 'pass',
		),

		// No Cache-Control, no Expires, no validator: cannot be cached.
		'no_headers'      => array(
			'label'    => 'No Cache-Control, no Expires, no validator',
			'body'     => "console.log( 'Hello World: no cache headers' );",
			'headers'  => array(),
			'expected' => 'error: not_cacheable (soft)',
		),

		// No Cache-Control, no Expires, but Last-Modified validator present: passes via heuristic caching.
		'validator'       => array(
			'label'    => 'No Cache-Control/Expires but Last-Modified present',
			'body'     => "console.log( 'Hello World: heuristic via Last-Modified' );",
			'headers'  => array( 'Last-Modified' => $now ),
			'expected' => 'pass',
		),
	);
}

/**
 * Gets the admin-ajax URL for a scenario.
 *
 * @param string $slug Scenario slug.
 * @return string URL.
 */
function get_scenario_url( string $slug ): string {
	return add_query_arg( 'action', ACTION_PREFIX . $slug, admin_url( 'admin-ajax.php' ) );
}

/**
 * Registers the admin-ajax handlers for each scenario.
 */
function register_ajax_handlers(): void {
	foreach ( array_keys( get_scenarios() ) as $slug ) {
		$handler = static function () use ( $slug ): void {
			serve_scenario( $slug );
		};
		add_action( 'wp_ajax_' . ACTION_PREFIX . $slug, $handler );
		add_action( 'wp_ajax_nopriv_' . ACTION_PREFIX . $slug, $handler );
	}
}
add_action( 'init', __NAMESPACE__ . '\\register_ajax_handlers' );

/**
 * Serves a single scenario's script body with its configured headers.
 *
 * @param string $slug Scenario slug.
 */
function serve_scenario( string $slug ): void {
	$scenarios = get_scenarios();
	if ( ! isset( $scenarios[ $slug ] ) ) {
		status_header( 404 );
		exit;
	}
	$scenario = $scenarios[ $slug ];

	// admin-ajax sends nocache headers and a text/html content type; strip the caching ones so each
	// scenario starts from a clean slate and controls exactly which caching headers are present.
	header_remove( 'Cache-Control' );
	header_remove( 'Expires' );
	header_remove( 'Last-Modified' );
	header_remove( 'ETag' );

	header( 'Content-Type: text/javascript' );

	foreach ( $scenario['headers'] as $name => $value ) {
		header( $name . ': ' . $value );
	}

	echo $scenario['body']; // phpcs:ignore WordPress.Security.EscapeOutput.OutputNotEscaped -- This is JavaScript, not HTML.
	exit;
}

/**
 * Enqueues all scenario scripts as render-blocking scripts in the head on the front end.
 *
 * They are enqueued without a loading strategy (no defer/async) and in the head so that the
 * Enqueued Assets audit treats them as render-blocking external scripts to be audited.
 */
function enqueue_scripts(): void {
	foreach ( array_keys( get_scenarios() ) as $slug ) {
		$handle = 'cctest-' . str_replace( '_', '-', $slug );
		wp_enqueue_script(
			$handle,
			get_scenario_url( $slug ),
			array(),
			null, // Do not append a ver query arg.
			false // In the head (render-blocking).
		);
	}
}
add_action( 'wp_enqueue_scripts', __NAMESPACE__ . '\\enqueue_scripts' );