Plugin code to add <amp-auto-ads> on WordPress sites powered by the official AMP plugin

## amp-auto-ads.php
<?php
/**
 * AMP Auto Ads for AdSense (WordPress Plugin)
 *
 * Plugin installation instructions:
 *
 *  1. Click the “Download ZIP” button.
 *  2. Rename the downloaded ZIP file to “amp-auto-ads.zip”
 *  3. In the WordPress admin, go to Plugins > Add New
 *  4. Click the Upload Plugin button.
 *  5. Select the “amp-auto-ads.zip” file and click “Install now”.
 *  6. Click “Activate”
 *  7. Lastly, navigate to the plugin’s settings in Settings > Reading to provide the AdSense publisher ID.
 *
 * @package   AMP_Auto_Ads
 * @author    Weston Ruter, Google
 * @license   GPL-2.0-or-later
 * @copyright 2019 Google Inc.
 *
 * @wordpress-plugin
 * Plugin Name: AMP Auto Ads for AdSense
 * Description: Demonstration for how to add <code>&lt;amp-auto-ads&gt;</code> to your page. Supply AdSense publisher ID in Reading settings.
 * Plugin URI:  https://gist.github.com/westonruter/a41573b932e24810b09949136b9a8445
 * Version:     0.4.0
 * Author:      Weston Ruter, Google
 * Author URI:  https://weston.ruter.net/
 * License:     GNU General Public License v2 (or later)
 * License URI: http://www.gnu.org/licenses/gpl-2.0.html
 */

namespace AMP_Auto_Ads;

const OPTION_NAME = 'amp_auto_ads_pub_id';

/**
 * Get publisher ID.
 *
 * @return string ID.
 */
function get_pub_id() {
	return get_option( OPTION_NAME, '' );
}

/**
 * Filter plugin action links to add settings.
 *
 * @param string[] $action_links Action links.
 * @return string[] Action links.
 */
function filter_plugin_action_links( $action_links ) {
	$action_links['settings'] = sprintf(
		'<a href="%s">%s</a>',
		esc_url( admin_url( 'options-reading.php' ) . '#' . OPTION_NAME ),
		esc_html__( 'Settings', 'amp-auto-ads' )
	);
	return $action_links;
}
add_filter( 'plugin_action_links_' . str_replace( WP_PLUGIN_DIR . '/', '', __FILE__ ), __NAMESPACE__ . '\filter_plugin_action_links' );

/**
 * Register setting.
 */
function register_setting() {
	\register_setting(
		'reading',
		OPTION_NAME,
		[
			'type'              => 'string',
			'sanitize_callback' => 'sanitize_text_field',
			'default'           => '',
			'description'       => esc_html__( 'AdSense Publisher ID', 'amp-auto-ads' ),
		]
	);

	add_settings_field(
		OPTION_NAME,
		esc_html__( 'AdSense Publisher ID', 'amp-auto-ads' ),
		function () {
			printf(
				'<p><input id="%s" name="%s" value="%s"></p><p class="description">%s</p>',
				esc_attr( OPTION_NAME ),
				esc_attr( OPTION_NAME ),
				esc_attr( get_pub_id() ),
				esc_html__( 'This is used for AMP Auto Ads.' )
			);
		},
		'reading',
		'default',
		[
			'label_for' => OPTION_NAME,
		]
	);
}
add_action( 'admin_init', __NAMESPACE__ . '\register_setting' );


/**
 * Print the amp-auto-ads element.
 */
function print_component() {
	$pub_id = get_pub_id();
	if ( empty( $pub_id ) ) {
		return;
	}
	printf( '<amp-auto-ads type="adsense" data-ad-client="%s"></amp-auto-ads>', esc_attr( $pub_id ) );
}

// Print the <amp-auto-ads> component at the start of the <body> for themes that support wp_body_open().
add_action(
	'wp_body_open',
	function() {
		if ( function_exists( 'is_amp_endpoint' ) && is_amp_endpoint() ) {
			print_component();
		}
	}
);

/*
 * If theme does does not support wp_body_open, then this fallback is used to print the component int he footer.
 * The docs specify that <amp-auto-ads> *should* be placed at the start of the <body> but this is not a hard requirement.
 */
add_action(
	'wp_footer',
	function() {
		if ( ! did_action( 'wp_body_open' ) && function_exists( 'is_amp_endpoint' ) && is_amp_endpoint() ) {
			print_component();
		}
	}
);

// Classic mode.
add_filter(
	'amp_post_template_data',
	function( $data ) {
		$data['amp_component_scripts'] = array_merge(
			$data['amp_component_scripts'],
			[
				'amp-auto-ads' => true,
			]
		);
		return $data;
	}
);

add_action( 'amp_post_template_body_open', __NAMESPACE__ . '\print_component' ); // Available as of AMP v1.2.1.

add_action(
	'amp_post_template_footer',
	function() {
		if ( ! did_action( 'amp_post_template_body_open' ) ) {
			print_component();
		}
	}
);
	<?php
	/**
	* AMP Auto Ads for AdSense (WordPress Plugin)
	*
	* Plugin installation instructions:
	*
	* 1. Click the “Download ZIP” button.
	* 2. Rename the downloaded ZIP file to “amp-auto-ads.zip”
	* 3. In the WordPress admin, go to Plugins > Add New
	* 4. Click the Upload Plugin button.
	* 5. Select the “amp-auto-ads.zip” file and click “Install now”.
	* 6. Click “Activate”
	* 7. Lastly, navigate to the plugin’s settings in Settings > Reading to provide the AdSense publisher ID.
	*
	* @package AMP_Auto_Ads
	* @author Weston Ruter, Google
	* @license GPL-2.0-or-later
	* @copyright 2019 Google Inc.
	*
	* @wordpress-plugin
	* Plugin Name: AMP Auto Ads for AdSense
	* Description: Demonstration for how to add <code><amp-auto-ads></code> to your page. Supply AdSense publisher ID in Reading settings.
	* Plugin URI: https://gist.github.com/westonruter/a41573b932e24810b09949136b9a8445
	* Version: 0.4.0
	* Author: Weston Ruter, Google
	* Author URI: https://weston.ruter.net/
	* License: GNU General Public License v2 (or later)
	* License URI: http://www.gnu.org/licenses/gpl-2.0.html
	*/

	namespace AMP_Auto_Ads;

	const OPTION_NAME = 'amp_auto_ads_pub_id';

	/**
	* Get publisher ID.
	*
	* @return string ID.
	*/
	function get_pub_id() {
	return get_option( OPTION_NAME, '' );
	}

	/**
	* Filter plugin action links to add settings.
	*
	* @param string[] $action_links Action links.
	* @return string[] Action links.
	*/
	function filter_plugin_action_links( $action_links ) {
	$action_links['settings'] = sprintf(
	'<a href="%s">%s</a>',
	esc_url( admin_url( 'options-reading.php' ) . '#' . OPTION_NAME ),
	esc_html__( 'Settings', 'amp-auto-ads' )
	);
	return $action_links;
	}
	add_filter( 'plugin_action_links_' . str_replace( WP_PLUGIN_DIR . '/', '', __FILE__ ), __NAMESPACE__ . '\filter_plugin_action_links' );

	/**
	* Register setting.
	*/
	function register_setting() {
	\register_setting(
	'reading',
	OPTION_NAME,
	[
	'type' => 'string',
	'sanitize_callback' => 'sanitize_text_field',
	'default' => '',
	'description' => esc_html__( 'AdSense Publisher ID', 'amp-auto-ads' ),
	]
	);

	add_settings_field(
	OPTION_NAME,
	esc_html__( 'AdSense Publisher ID', 'amp-auto-ads' ),
	function () {
	printf(
	'<p><input id="%s" name="%s" value="%s"></p><p class="description">%s</p>',
	esc_attr( OPTION_NAME ),
	esc_attr( OPTION_NAME ),
	esc_attr( get_pub_id() ),
	esc_html__( 'This is used for AMP Auto Ads.' )
	);
	},
	'reading',
	'default',
	[
	'label_for' => OPTION_NAME,
	]
	);
	}
	add_action( 'admin_init', __NAMESPACE__ . '\register_setting' );


	/**
	* Print the amp-auto-ads element.
	*/
	function print_component() {
	$pub_id = get_pub_id();
	if ( empty( $pub_id ) ) {
	return;
	}
	printf( '<amp-auto-ads type="adsense" data-ad-client="%s"></amp-auto-ads>', esc_attr( $pub_id ) );
	}

	// Print the <amp-auto-ads> component at the start of the <body> for themes that support wp_body_open().
	add_action(
	'wp_body_open',
	function() {
	if ( function_exists( 'is_amp_endpoint' ) && is_amp_endpoint() ) {
	print_component();
	}
	}
	);

	/*
	* If theme does does not support wp_body_open, then this fallback is used to print the component int he footer.
	* The docs specify that <amp-auto-ads> should be placed at the start of the <body> but this is not a hard requirement.
	*/
	add_action(
	'wp_footer',
	function() {
	if ( ! did_action( 'wp_body_open' ) && function_exists( 'is_amp_endpoint' ) && is_amp_endpoint() ) {
	print_component();
	}
	}
	);

	// Classic mode.
	add_filter(
	'amp_post_template_data',
	function( $data ) {
	$data['amp_component_scripts'] = array_merge(
	$data['amp_component_scripts'],
	[
	'amp-auto-ads' => true,
	]
	);
	return $data;
	}
	);

	add_action( 'amp_post_template_body_open', __NAMESPACE__ . '\print_component' ); // Available as of AMP v1.2.1.

	add_action(
	'amp_post_template_footer',
	function() {
	if ( ! did_action( 'amp_post_template_body_open' ) ) {
	print_component();
	}
	}
	);