<?php
/**
 * Updates from the plugin's own release feed.
 *
 * WordPress only offers updates for plugins it knows a source for. This is
 * that source: the Gitea repository named in the plugin header's "Update URI".
 *
 * It hooks `update_plugins_{$hostname}` rather than rewriting the update
 * transient by hand. That filter is the supported path since WordPress 5.8 and
 * it brings one guarantee worth more than the tidiness: a plugin with an
 * "Update URI" pointing away from wordpress.org is never asked about there, so
 * a .org plugin that happens to share this slug can never be pushed onto a
 * shop running this one.
 *
 * Nothing about the site is sent. The request is a plain unauthenticated GET
 * for a file every visitor to that repository can read, and the user agent is
 * overridden because WordPress's default one carries the site's own URL in it.
 *
 * @package WC_Email_Discount_Manager
 */

if ( ! defined( 'ABSPATH' ) ) {
	exit;
}

/**
 * Offers releases from the repository named in the plugin header.
 */
class WC_EDM_Updater {

	/**
	 * Where the answer is cached between checks.
	 */
	const TRANSIENT = 'wc_edm_release_feed';

	/**
	 * How long that cache lives. WordPress checks for updates twice a day; a
	 * shorter window would only add requests, a longer one would delay a fix.
	 */
	const TTL = 6 * HOUR_IN_SECONDS;

	/**
	 * Hook into the update check for our own host only.
	 */
	public function __construct() {
		$host = $this->host();

		if ( ! $host ) {
			return;
		}

		add_filter( "update_plugins_{$host}", array( $this, 'offer_update' ), 10, 2 );

		// Without this the old answer is served for up to six hours after an
		// update, and the plugins screen keeps offering a version already
		// installed.
		add_action( 'upgrader_process_complete', array( $this, 'forget' ), 10, 0 );
	}

	/**
	 * Memoised update URI, so the plugin file is read at most once a request.
	 *
	 * @var string|null
	 */
	private static $uri = null;

	/**
	 * The repository this plugin updates from, as stated in its own header.
	 *
	 * Read from the header rather than a constant so that there is exactly one
	 * place saying where updates come from — but memoised, because the filter
	 * is registered on every request a shop serves, not just in wp-admin, and
	 * get_file_data() opens and scans the file each time it is asked.
	 *
	 * @return string
	 */
	public static function update_uri() {
		if ( null === self::$uri ) {
			$data      = get_file_data( WC_EDM_PLUGIN_FILE, array( 'uri' => 'Update URI' ) );
			self::$uri = isset( $data['uri'] ) ? trim( $data['uri'] ) : '';
		}

		return self::$uri;
	}

	/**
	 * Hostname of the update URI, or an empty string when there is none.
	 *
	 * @return string
	 */
	private function host() {
		$host = wp_parse_url( self::update_uri(), PHP_URL_HOST );

		return is_string( $host ) ? $host : '';
	}

	/**
	 * Answer WordPress's update check for this plugin.
	 *
	 * Always returns what the feed says, even when it is the version already
	 * installed: WordPress compares the versions itself, and a plugin that
	 * answers "no update" by returning false never appears in the no_update
	 * list — which is what the "Enable auto-updates" link on the plugins
	 * screen is built from. Staying silent here is how a plugin ends up
	 * unable to auto-update while looking perfectly configured.
	 *
	 * @param array|false $update      Update offered so far.
	 * @param array       $plugin_data Headers of the installed plugin.
	 * @return array|false
	 */
	public function offer_update( $update, $plugin_data ) {
		$release = $this->latest_release();

		if ( ! $release ) {
			return $update;
		}

		return array(
			'slug'         => dirname( plugin_basename( WC_EDM_PLUGIN_FILE ) ),
			'version'      => $release['version'],
			'package'      => $release['package'],
			'url'          => $release['url'],
			'tested'       => $release['tested'],
			'requires'     => isset( $plugin_data['RequiresWP'] ) ? $plugin_data['RequiresWP'] : '',
			'requires_php' => isset( $plugin_data['RequiresPHP'] ) ? $plugin_data['RequiresPHP'] : '',
		);
	}

	/**
	 * Drop the cached feed.
	 */
	public function forget() {
		delete_transient( self::TRANSIENT );
	}

	/**
	 * Read the newest release from the repository.
	 *
	 * @return array|null { version, package, url, tested }, or null.
	 */
	private function latest_release() {
		$cached = get_transient( self::TRANSIENT );

		if ( is_array( $cached ) ) {
			return $cached;
		}
		if ( 'none' === $cached ) {
			// A failure is cached too, briefly. Otherwise an unreachable host
			// turns every admin page load into a blocking HTTP request.
			return null;
		}

		$uri = self::update_uri();
		$api = $this->api_url( $uri );

		if ( ! $api ) {
			return null;
		}

		$response = wp_remote_get(
			$api,
			array(
				'timeout' => 10,
				'headers' => array( 'Accept' => 'application/json' ),
				// WordPress's default user agent is
				// "WordPress/6.8; https://the-shop.example" — it would tell
				// the update host which shops are running this plugin. This
				// plugin does not report that anywhere, so it must not leak
				// it here either.
				'user-agent' => 'wc-email-discount-manager updater',
			)
		);

		if ( is_wp_error( $response ) || 200 !== (int) wp_remote_retrieve_response_code( $response ) ) {
			set_transient( self::TRANSIENT, 'none', 15 * MINUTE_IN_SECONDS );
			return null;
		}

		$body = json_decode( wp_remote_retrieve_body( $response ), true );

		if ( ! is_array( $body ) || empty( $body['tag_name'] ) ) {
			set_transient( self::TRANSIENT, 'none', 15 * MINUTE_IN_SECONDS );
			return null;
		}

		$package = '';
		$tested  = '';

		foreach ( isset( $body['assets'] ) ? $body['assets'] : array() as $asset ) {
			if ( empty( $asset['name'] ) || empty( $asset['browser_download_url'] ) ) {
				continue;
			}
			if ( substr( $asset['name'], -4 ) === '.zip' ) {
				$package = $asset['browser_download_url'];
			}
		}

		// The release notes carry the compatibility line the release workflow
		// writes, so wp-admin can show what this version was actually tested
		// against instead of what the previous one claimed.
		if ( ! empty( $body['body'] ) && preg_match( '/^Tested up to:\s*(\S+)/mi', $body['body'], $m ) ) {
			$tested = $m[1];
		}

		if ( '' === $package ) {
			// A release with no zip attached is a half-finished release.
			// Offering it would hand WordPress a download it cannot install.
			set_transient( self::TRANSIENT, 'none', 15 * MINUTE_IN_SECONDS );
			return null;
		}

		$release = array(
			'version' => ltrim( $body['tag_name'], 'vV' ),
			'package' => $package,
			'url'     => ! empty( $body['html_url'] ) ? $body['html_url'] : $uri,
			'tested'  => $tested,
		);

		set_transient( self::TRANSIENT, $release, self::TTL );

		return $release;
	}

	/**
	 * Turn the repository's web address into its "latest release" API address.
	 *
	 * https://gitea.example/owner/repo
	 *   -> https://gitea.example/api/v1/repos/owner/repo/releases/latest
	 *
	 * Derived rather than configured, so the plugin header stays the single
	 * place that says where updates come from.
	 *
	 * @param string $uri Repository web address.
	 * @return string Empty when the address is not a repository address.
	 */
	private function api_url( $uri ) {
		$parts = wp_parse_url( $uri );

		if ( empty( $parts['scheme'] ) || empty( $parts['host'] ) || empty( $parts['path'] ) ) {
			return '';
		}

		$segments = array_values( array_filter( explode( '/', $parts['path'] ) ) );

		if ( count( $segments ) < 2 ) {
			return '';
		}

		return sprintf(
			'%s://%s/api/v1/repos/%s/%s/releases/latest',
			$parts['scheme'],
			$parts['host'],
			rawurlencode( $segments[0] ),
			rawurlencode( $segments[1] )
		);
	}
}