<?php
/**
 * AMP Helper Functions
 *
 * @package AMP
 */

/**
 * Retrieves the full AMP-specific permalink for the given post ID.
 *
 * @since 0.1
 *
 * @param int $post_id Post ID.
 *
 * @return string AMP permalink.
 */
function amp_get_permalink( $post_id ) {

	/**
	 * Filters the AMP permalink to short-circuit normal generation.
	 *
	 * Returning a non-false value in this filter will cause the `get_permalink()` to get called and the `amp_get_permalink` filter to not apply.
	 *
	 * @since 0.4
	 *
	 * @param false $url     Short-circuited URL.
	 * @param int   $post_id Post ID.
	 */
	$pre_url = apply_filters( 'amp_pre_get_permalink', false, $post_id );

	if ( false !== $pre_url ) {
		return $pre_url;
	}

	$parsed_url = wp_parse_url( get_permalink( $post_id ) );
	$structure  = get_option( 'permalink_structure' );
	if ( empty( $structure ) || ! empty( $parsed_url['query'] ) || is_post_type_hierarchical( get_post_type( $post_id ) ) ) {
		$amp_url = add_query_arg( AMP_QUERY_VAR, '', get_permalink( $post_id ) );
	} else {
		$amp_url = trailingslashit( get_permalink( $post_id ) ) . user_trailingslashit( AMP_QUERY_VAR, 'single_amp' );
	}

	/**
	 * Filters AMP permalink.
	 *
	 * @since 0.2
	 *
	 * @param false $amp_url AMP URL.
	 * @param int   $post_id Post ID.
	 */
	return apply_filters( 'amp_get_permalink', $amp_url, $post_id );
}

/**
 * Determine whether a given post supports AMP.
 *
 * @since 0.1
 * @since 0.6 Returns false when post has meta to disable AMP.
 * @see   AMP_Post_Type_Support::get_support_errors()
 *
 * @param WP_Post $post Post.
 *
 * @return bool Whether the post supports AMP.
 */
function post_supports_amp( $post ) {
	$errors = AMP_Post_Type_Support::get_support_errors( $post );

	// Return false if an error is found.
	if ( ! empty( $errors ) ) {
		return false;
	}

	switch ( get_post_meta( $post->ID, AMP_Post_Meta_Box::STATUS_POST_META_KEY, true ) ) {
		case AMP_Post_Meta_Box::ENABLED_STATUS:
			return true;

		case AMP_Post_Meta_Box::DISABLED_STATUS:
			return false;

		// Disabled by default for custom page templates, page on front and page for posts.
		default:
			$enabled = (
				! (bool) get_page_template_slug( $post )
				&&
				! (
					'page' === $post->post_type
					&&
					'page' === get_option( 'show_on_front' )
					&&
					in_array( (int) $post->ID, array(
						(int) get_option( 'page_on_front' ),
						(int) get_option( 'page_for_posts' ),
					), true )
				)
			);

			/**
			 * Filters whether default AMP status should be enabled or not.
			 *
			 * @since 0.6
			 *
			 * @param string  $status Status.
			 * @param WP_Post $post   Post.
			 */
			return apply_filters( 'amp_post_status_default_enabled', $enabled, $post );
	}
}

/**
 * Are we currently on an AMP URL?
 *
 * Note: will always return `false` if called before the `parse_query` hook.
 *
 * @return bool Whether it is the AMP endpoint.
 */
function is_amp_endpoint() {
	if ( 0 === did_action( 'parse_query' ) ) {
		_doing_it_wrong( __FUNCTION__, sprintf( esc_html__( "is_amp_endpoint() was called before the 'parse_query' hook was called. This function will always return 'false' before the 'parse_query' hook is called.", 'amp' ) ), '0.4.2' );
	}

	return false !== get_query_var( AMP_QUERY_VAR, false );
}

/**
 * Get AMP asset URL.
 *
 * @param string $file Relative path to file in assets directory.
 * @return string URL.
 */
function amp_get_asset_url( $file ) {
	return plugins_url( sprintf( 'assets/%s', $file ), AMP__FILE__ );
}