<?php
/**
 * Settings → SMTP.
 *
 * @package Adminkeep
 */

namespace Adminkeep\Admin;

use Adminkeep\Feature\Smtp;
use Adminkeep\Service\SecretBox;
use Adminkeep\Service\SmtpConfig;
use Adminkeep\Service\SmtpImporter;
use Adminkeep\Service\SmtpPresets;

defined( 'ABSPATH' ) || exit;

/**
 * The SMTP settings screen.
 *
 * Exists only while the feature is on: Smtp::boot() is what builds it.
 */
class SmtpScreen {

	/**
	 * Page slug.
	 */
	const PAGE = 'adminkeep-smtp';

	/**
	 * Capability for the page and for saving.
	 */
	const CAPABILITY = 'manage_options';

	/**
	 * Nonce action of the settings form.
	 */
	const NONCE = 'adminkeep_smtp';

	/**
	 * Hidden field marking the settings form's submission.
	 */
	const SAVE_FIELD = 'adminkeep_smtp_save';

	/**
	 * Name of the POST array holding the settings.
	 */
	const FIELD = 'adminkeep_smtp';

	/**
	 * Query flag the save redirect carries. Not core's `updated`: every page under Settings
	 * loads wp-admin/options-head.php, which prints its own "Settings saved." for that flag, and
	 * the message would appear twice.
	 */
	const SAVED_ARG = 'adminkeep_saved';

	/**
	 * Nonce action of the test-email form.
	 */
	const TEST_NONCE = 'adminkeep_smtp_test';

	/**
	 * Hidden field marking the test-email form's submission.
	 */
	const TEST_FIELD = 'adminkeep_smtp_test_send';

	/**
	 * The recipient field of the test-email form.
	 */
	const TEST_TO_FIELD = 'adminkeep_smtp_test_to';

	/**
	 * The admin-ajax action the test form uses when its script is running.
	 */
	const TEST_ACTION = 'adminkeep_smtp_test';

	/**
	 * Nonce action of the copy-settings form.
	 */
	const IMPORT_NONCE = 'adminkeep_smtp_import';

	/**
	 * Hidden field marking the copy-settings form's submission.
	 */
	const IMPORT_FIELD = 'adminkeep_smtp_import';

	/**
	 * Query flag the copy redirect carries: what became of the password, one of the
	 * SmtpImporter::PASSWORD_* outcomes.
	 */
	const IMPORTED_ARG = 'adminkeep_smtp_imported';

	/**
	 * The source the copy box offers, by its SmtpImporter::sources() name. Also the plugin folder
	 * other_mailer() reports while that plugin is active.
	 */
	const IMPORT_SOURCE = 'wp-mail-smtp';

	/**
	 * Plugin folders of other plugins that configure the mailer.
	 *
	 * @var string[]
	 */
	const OTHER_MAILERS = array( 'wp-mail-smtp', 'fluent-smtp', 'easy-wp-smtp', 'post-smtp', 'suremails', 'smtp-mailer' );

	/**
	 * Hook suffix of the registered page.
	 *
	 * @var string
	 */
	private $hook = '';

	/**
	 * Outcome of a test email sent in this request.
	 *
	 * @var array{sent: bool, to: string, error: string, log: string}|null
	 */
	private $test_result = null;

	/**
	 * URL of the screen.
	 *
	 * @return string
	 */
	public static function url() {
		return admin_url( 'options-general.php?page=' . self::PAGE );
	}

	/**
	 * Register hooks.
	 *
	 * @return void
	 */
	public function boot() {
		add_action( 'admin_menu', array( $this, 'register_page' ) );
		add_action( 'admin_init', array( $this, 'handle_save' ), 10, 0 );
		add_action( 'admin_init', array( $this, 'handle_test' ), 10, 0 );
		add_action( 'admin_init', array( $this, 'handle_import' ), 10, 0 );
		add_filter( 'removable_query_args', array( $this, 'removable_query_args' ) );
		add_action( 'wp_ajax_' . self::TEST_ACTION, array( $this, 'ajax_test' ), 10, 0 );
		add_action( 'admin_enqueue_scripts', array( $this, 'enqueue_preset_script' ) );
		add_action( 'admin_enqueue_scripts', array( $this, 'enqueue_layout_style' ) );
	}

	/**
	 * Let WordPress strip the "settings copied" flag out of the address bar, so reloading the
	 * screen later does not report a copy that happened long ago.
	 *
	 * @param array $args Query arguments WordPress removes after the page has loaded.
	 * @return array
	 */
	public function removable_query_args( $args ) {
		$args[] = self::IMPORTED_ARG;

		return $args;
	}

	/**
	 * Add the page under Settings.
	 *
	 * @return void
	 */
	public function register_page() {
		$this->hook = (string) add_options_page(
			__( 'SMTP', 'adminkeep' ),
			__( 'SMTP', 'adminkeep' ),
			self::CAPABILITY,
			self::PAGE,
			array( $this, 'render' )
		);
	}

	/**
	 * The few lines that copy a preset into the three fields it describes.
	 *
	 * @param string $hook_suffix Current admin page.
	 * @return void
	 */
	public function enqueue_preset_script( $hook_suffix ) {
		if ( '' === $this->hook || $hook_suffix !== $this->hook ) {
			return;
		}

		wp_register_script( 'adminkeep-smtp', ADMINKEEP_URL . 'assets/js/smtp.js', array(), \Adminkeep\Assets::version( 'assets/js/smtp.js' ), true );
		wp_enqueue_script( 'adminkeep-smtp' );
		wp_localize_script(
			'adminkeep-smtp',
			'adminkeepSmtp',
			array(
				'url'     => admin_url( 'admin-ajax.php' ),
				'action'  => self::TEST_ACTION,
				'sending' => __( 'Sending…', 'adminkeep' ),
				'failed'  => __( 'The test could not be run. Reload the page and try again.', 'adminkeep' ),
			)
		);
		wp_add_inline_script(
			'adminkeep-smtp',
			'document.addEventListener("DOMContentLoaded",function(){var s=document.getElementById("adminkeep-smtp-preset");if(!s){return;}s.addEventListener("change",function(){var o=s.options[s.selectedIndex],n=document.getElementById("adminkeep-smtp-preset-note");if(n){n.textContent=o.getAttribute("data-note")||"";}if(!o.getAttribute("data-host")){return;}[["host","data-host"],["port","data-port"],["encryption","data-encryption"]].forEach(function(p){var f=document.getElementById("adminkeep-smtp-"+p[0]);if(f&&!f.disabled){f.value=o.getAttribute(p[1]);}});});});'
		);
	}

	/**
	 * Two columns: the settings, and the test email beside them. Below 960px the test drops under
	 * the settings, which is also where it sits when the stylesheet is missing.
	 *
	 * @param string $hook_suffix Current admin page.
	 * @return void
	 */
	public function enqueue_layout_style( $hook_suffix ) {
		if ( '' === $this->hook || $hook_suffix !== $this->hook ) {
			return;
		}

		wp_register_style( 'adminkeep-smtp', false, array(), ADMINKEEP_VERSION );
		wp_enqueue_style( 'adminkeep-smtp' );
		wp_add_inline_style(
			'adminkeep-smtp',
			'.adminkeep-smtp-columns{display:flex;align-items:flex-start;gap:24px}'
			. '.adminkeep-smtp-main{flex:1 1 auto;min-width:0}'
			. '.adminkeep-smtp-test{flex:0 0 340px;box-sizing:border-box;margin-top:16px;padding:4px 20px 20px;background:#fff;border:1px solid #c3c4c7}'
			. '.adminkeep-smtp-test p{overflow-wrap:anywhere}'
			. '.adminkeep-smtp-test input[type=email]{width:100%;margin-bottom:8px}'
			. '#adminkeep-smtp-test-result .notice{margin:16px 0 8px}'
			. '.adminkeep-smtp-test pre{white-space:pre-wrap;max-height:24em;overflow:auto;background:#f6f7f7;border:1px solid #c3c4c7;padding:12px}'
			. '.adminkeep-smtp-secret{display:flex;gap:8px;align-items:center;max-width:36em}'
			. '.adminkeep-smtp-secret input{flex:0 1 25em;min-width:0;margin:0}'
			. '.adminkeep-smtp-secret input:disabled::placeholder{letter-spacing:2px;color:#50575e}'
			. '.adminkeep-smtp-secret .button{flex:none;white-space:nowrap}'
			. '.adminkeep-smtp-saved{display:inline-block;margin:8px 0 0;padding:4px 10px;border-left:4px solid #00a32a;background:#edfaef;font-weight:600;color:#1d2327}'
			. '@media (max-width:960px){.adminkeep-smtp-columns{display:block}.adminkeep-smtp-test{margin-top:24px}}'
		);
	}

	/**
	 * Save the settings form.
	 *
	 * @return void
	 */
	public function handle_save() {
		if ( empty( $_POST[ self::SAVE_FIELD ] ) ) { // phpcs:ignore WordPress.Security.NonceVerification.Missing -- Checked below, once this is known to be our form.
			return;
		}

		if ( ! current_user_can( self::CAPABILITY ) ) {
			wp_die( esc_html__( 'You are not allowed to change email settings on this site.', 'adminkeep' ), '', 403 );
		}

		check_admin_referer( self::NONCE );

		// Each field is sanitized for its own type inside SmtpConfig::sanitize(); the password is
		// deliberately not text-sanitized, because it is sealed and never printed.
		// phpcs:ignore WordPress.Security.ValidatedSanitizedInput.InputNotSanitized
		$input = isset( $_POST[ self::FIELD ] ) && is_array( $_POST[ self::FIELD ] ) ? wp_unslash( $_POST[ self::FIELD ] ) : array();

		update_option(
			SmtpConfig::OPTION,
			SmtpConfig::sanitize( $input, SmtpConfig::stored(), SmtpConfig::defined_constants(), SecretBox::from_salts() ),
			false
		);

		wp_safe_redirect( add_query_arg( self::SAVED_ARG, '1', self::url() ) );
		exit;
	}

	/**
	 * The configuration this screen shows. Its own method so a test can hand the screen a
	 * configuration with constants in it; PHP would never let a test undefine a real one.
	 *
	 * @return SmtpConfig
	 */
	protected function config() {
		return SmtpConfig::from_environment();
	}

	/**
	 * Copy another plugin's SMTP connection, when the box offering it would be showing, then
	 * redirect with what became of the password. A stale or forged post while the box would be
	 * hidden copies nothing and just comes back to the screen.
	 *
	 * @return void
	 */
	public function handle_import() {
		if ( empty( $_POST[ self::IMPORT_FIELD ] ) ) { // phpcs:ignore WordPress.Security.NonceVerification.Missing -- Checked below, once this is known to be our form.
			return;
		}

		if ( ! current_user_can( self::CAPABILITY ) ) {
			wp_die( esc_html__( 'You are not allowed to change email settings on this site.', 'adminkeep' ), '', 403 );
		}

		check_admin_referer( self::IMPORT_NONCE );

		$offer  = $this->import_offer();
		$result = null === $offer ? null : $this->importer()->run( $offer['source'] );

		if ( ! is_array( $result ) ) {
			wp_safe_redirect( self::url() );
			exit;
		}

		wp_safe_redirect( add_query_arg( self::IMPORTED_ARG, $result['password'], self::url() ) );
		exit;
	}

	/**
	 * The importer. Its own method so a test can hand the screen one with constants in it.
	 *
	 * @return SmtpImporter
	 */
	protected function importer() {
		return new SmtpImporter();
	}

	/**
	 * The source the copy box offers and what copying it would do, or null when there should be
	 * no box.
	 *
	 * The box shows only when the source holds an SMTP connection with a host, and either that
	 * plugin is active or Adminkeep's own SMTP is not set up yet. So once the owner has copied,
	 * tested and deactivated it, the box goes away by itself, and settings left behind by a
	 * plugin removed years ago do not nag a site that was set up by hand.
	 *
	 * @return array{source: \Adminkeep\Service\SmtpImport\Source, preview: array}|null
	 */
	private function import_offer() {
		// The cheap test first: reading the source opens its password.
		if ( self::IMPORT_SOURCE !== $this->other_mailer() && $this->config()->is_active() ) {
			return null;
		}

		$sources = SmtpImporter::sources();
		$source  = $sources[ self::IMPORT_SOURCE ];
		$preview = $this->importer()->preview( $source );

		return is_wp_error( $preview ) ? null : array(
			'source'  => $source,
			'preview' => $preview,
		);
	}

	/**
	 * Another active plugin that also configures the mailer, if any. Its own method so a test
	 * can name one without activating a real plugin.
	 *
	 * @return string Its folder name, or empty.
	 */
	protected function other_mailer() {
		foreach ( (array) get_option( 'active_plugins', array() ) as $plugin ) {
			$folder = strtok( (string) $plugin, '/' );

			if ( in_array( $folder, self::OTHER_MAILERS, true ) ) {
				return $folder;
			}
		}

		return '';
	}

	/**
	 * Render the screen.
	 *
	 * @return void
	 */
	public function render() {
		if ( ! current_user_can( self::CAPABILITY ) ) {
			return;
		}

		$config = $this->config();
		$error  = Smtp::last_error();

		echo '<div class="wrap adminkeep-smtp-screen">';
		echo '<h1>' . Brand::heading_mark( 'smtp' ) . esc_html__( 'SMTP', 'adminkeep' ) . '</h1>'; // phpcs:ignore WordPress.Security.EscapeOutput.OutputNotEscaped -- The mark is escaped where it is built.

		if ( isset( $_GET[ self::SAVED_ARG ] ) ) { // phpcs:ignore WordPress.Security.NonceVerification.Recommended -- Read-only flag choosing a static notice.
			printf( '<div class="notice notice-success inline"><p>%s</p></div>', esc_html__( 'Settings saved.', 'adminkeep' ) );
		}

		$other = $this->other_mailer();

		$this->render_import_result( $other );

		if ( array() !== $error ) {
			printf(
				'<div class="notice notice-error inline"><p><strong>%1$s</strong> %2$s</p><p><code>%3$s</code></p></div>',
				esc_html__( 'The last email failed to send.', 'adminkeep' ),
				esc_html( wp_date( 'j M Y, H:i', $error['time'] ) ),
				esc_html( $error['message'] )
			);
		}

		if ( '' !== $other ) {
			printf(
				'<p><em>%s</em></p>',
				/* translators: %s: folder name of another plugin. */
				esc_html( sprintf( __( 'The plugin "%s" is active and also configures email. Whichever runs last decides how mail is sent; use one or the other.', 'adminkeep' ), $other ) )
			);
		}

		if ( ! $config->is_active() ) {
			printf( '<p>%s</p>', esc_html__( 'No server is set yet, so WordPress is still sending email the way it always has.', 'adminkeep' ) );
		}

		$offer = $this->import_offer();

		if ( null !== $offer ) {
			$this->render_import_box( $offer['source']->label(), $offer['preview'] );
		}

		echo '<div class="adminkeep-smtp-columns"><div class="adminkeep-smtp-main">';
		echo '<form method="post" action="' . esc_url( self::url() ) . '">';
		wp_nonce_field( self::NONCE );
		printf( '<input type="hidden" name="%s" value="1" />', esc_attr( self::SAVE_FIELD ) );

		echo '<table class="form-table" role="presentation"><tbody>';

		$this->preset_row();
		$this->text_row( $config, 'host', __( 'Server (host)', 'adminkeep' ), 'text' );
		$this->text_row( $config, 'port', __( 'Port', 'adminkeep' ), 'number' );
		$this->encryption_row( $config );
		$this->checkbox_row( $config, 'auth', __( 'Authentication', 'adminkeep' ), __( 'The server needs a username and password', 'adminkeep' ) );
		$this->text_row( $config, 'username', __( 'Username', 'adminkeep' ), 'text' );
		$this->password_row( $config );
		$this->text_row( $config, 'from_email', __( 'From address', 'adminkeep' ), 'email' );
		$this->checkbox_row( $config, 'force_from', '', __( 'Use this address for every email, even when a plugin sets its own', 'adminkeep' ) );
		$this->text_row( $config, 'from_name', __( 'From name', 'adminkeep' ), 'text' );
		$this->checkbox_row( $config, 'force_name', '', __( 'Use this name for every email, even when a plugin sets its own', 'adminkeep' ) );

		echo '</tbody></table>';

		submit_button( __( 'Save settings', 'adminkeep' ) );

		echo '</form>';
		echo '</div>';

		$this->render_test_panel( $config );

		echo '</div></div>';
	}

	/**
	 * The box offering to copy another plugin's SMTP connection. It says what is copied in words,
	 * never the values: the host, the username and the password stay out of the markup. A form of
	 * its own, so pressing it never posts the settings form's fields.
	 *
	 * @param string $label   The source plugin's name.
	 * @param array  $preview What copying would do, from SmtpImporter::preview().
	 * @return void
	 */
	private function render_import_box( $label, array $preview ) {
		$text = array(
			__( 'Copy its SMTP connection settings here: server, port, encryption, username, password, and the From address and name. Your current Adminkeep SMTP settings are replaced. Values held in wp-config.php are kept.', 'adminkeep' ),
		);

		if ( SmtpImporter::PASSWORD_UNREADABLE === $preview['password'] ) {
			$text[] = __( 'Its password could not be read, so enter the password after copying.', 'adminkeep' );
		}

		echo '<div class="notice notice-info inline adminkeep-smtp-import">';
		printf(
			'<p><strong>%1$s</strong> %2$s</p>',
			/* translators: %s: name of another SMTP plugin, such as WP Mail SMTP. */
			esc_html( sprintf( __( '%s has an SMTP server set up.', 'adminkeep' ), $label ) ),
			esc_html( implode( ' ', $text ) )
		);
		echo '<form method="post" id="adminkeep-smtp-import" action="' . esc_url( self::url() ) . '">';
		wp_nonce_field( self::IMPORT_NONCE );
		printf( '<input type="hidden" name="%s" value="1" />', esc_attr( self::IMPORT_FIELD ) );
		/* translators: %s: name of another SMTP plugin, such as WP Mail SMTP. */
		submit_button( sprintf( __( 'Copy from %s', 'adminkeep' ), $label ), 'secondary', 'adminkeep_smtp_import_submit', false );
		echo '</form></div>';
	}

	/**
	 * What the last copy did, read from the redirect's flag.
	 *
	 * @param string $other Folder of another active mailer plugin, or ''.
	 * @return void
	 */
	private function render_import_result( $other ) {
		$flag     = isset( $_GET[ self::IMPORTED_ARG ] ) ? sanitize_key( wp_unslash( (string) $_GET[ self::IMPORTED_ARG ] ) ) : ''; // phpcs:ignore WordPress.Security.NonceVerification.Recommended -- Read-only flag choosing a static notice.
		$outcomes = array( SmtpImporter::PASSWORD_COPIED, SmtpImporter::PASSWORD_KEPT, SmtpImporter::PASSWORD_UNREADABLE, SmtpImporter::PASSWORD_LOCKED );

		if ( ! in_array( $flag, $outcomes, true ) ) {
			return;
		}

		$sources = SmtpImporter::sources();
		$label   = $sources[ self::IMPORT_SOURCE ]->label();

		/* translators: %s: name of another SMTP plugin, such as WP Mail SMTP. */
		$parts = array( sprintf( __( 'SMTP settings copied from %s.', 'adminkeep' ), $label ) );

		if ( SmtpImporter::PASSWORD_UNREADABLE === $flag ) {
			$parts[] = __( 'Its password could not be read, so enter the password below and save.', 'adminkeep' );
		}

		if ( self::IMPORT_SOURCE === $other ) {
			/* translators: %s: name of another SMTP plugin, such as WP Mail SMTP. */
			$parts[] = sprintf( __( 'Send a test email from this screen, then deactivate %s so the two plugins do not both configure the mailer.', 'adminkeep' ), $label );
		} else {
			$parts[] = __( 'Send a test email from this screen to check them.', 'adminkeep' );
		}

		$class = SmtpImporter::PASSWORD_UNREADABLE === $flag ? 'notice-warning' : 'notice-success';

		echo '<div class="notice ' . esc_attr( $class ) . ' inline"><p>' . esc_html( implode( ' ', $parts ) ) . '</p></div>';
	}

	/**
	 * Outcome of a test email sent in this request.
	 *
	 * @return array|null
	 */
	public function test_result() {
		return $this->test_result;
	}

	/**
	 * Send a test email and keep what happened, including the SMTP conversation.
	 *
	 * This is the form posted the ordinary way, for when the screen's script is not running. No
	 * redirect: the result is shown by the same request, so nothing about the conversation is
	 * ever stored.
	 *
	 * @return void
	 */
	public function handle_test() {
		// admin-ajax.php fires admin_init too, and the screen's script posts this same form
		// there. That request belongs to ajax_test(); answering it here as well sends two emails.
		if ( wp_doing_ajax() ) {
			return;
		}

		if ( empty( $_POST[ self::TEST_FIELD ] ) ) { // phpcs:ignore WordPress.Security.NonceVerification.Missing -- Checked below, once this is known to be our form.
			return;
		}

		if ( ! current_user_can( self::CAPABILITY ) ) {
			wp_die( esc_html__( 'You are not allowed to send a test email on this site.', 'adminkeep' ), '', 403 );
		}

		check_admin_referer( self::TEST_NONCE );

		$this->run_test();
	}

	/**
	 * The same test, asked for by the screen's script: same gates, and the answer is the markup
	 * render_test_result() would have printed, so escaping stays on this side.
	 *
	 * @return void
	 */
	public function ajax_test() {
		if ( ! current_user_can( self::CAPABILITY ) ) {
			wp_send_json_error( null, 403 );
		}

		check_ajax_referer( self::TEST_NONCE );

		$this->run_test();

		ob_start();
		$this->render_test_result();

		wp_send_json_success( array( 'html' => (string) ob_get_clean() ) );
	}

	/**
	 * Send the test email to the posted address. Callers have already checked who is asking.
	 *
	 * @return void
	 */
	private function run_test() {
		// phpcs:disable WordPress.Security.NonceVerification.Missing -- Both callers verify the nonce before calling.
		// is_string() first: a recipient posted as an array would reach sanitize_email() and raise
		// a TypeError. Anything that is not a string is simply not an address.
		$to = isset( $_POST[ self::TEST_TO_FIELD ] ) && is_string( $_POST[ self::TEST_TO_FIELD ] ) ? sanitize_email( wp_unslash( $_POST[ self::TEST_TO_FIELD ] ) ) : '';
		// phpcs:enable WordPress.Security.NonceVerification.Missing

		$this->test_result = \Adminkeep\Service\SmtpTester::send( $to, $this->config() );
	}

	/**
	 * The test-email form and, after a test, what happened.
	 *
	 * @param SmtpConfig $config Resolved configuration.
	 * @return void
	 */
	protected function render_test_panel( SmtpConfig $config ) {
		echo '<div class="adminkeep-smtp-test">';
		echo '<h2>' . esc_html__( 'Send a test email', 'adminkeep' ) . '</h2>';

		if ( ! $config->is_active() ) {
			printf( '<p>%s</p>', esc_html__( 'No server is set, so this test goes out the way WordPress sends email by default.', 'adminkeep' ) );
		} elseif ( $config->is_locked( 'host' ) ) {
			// The host is a wp-config.php constant: never echoed, same as everywhere else on this screen.
			printf( '<p>%s</p>', esc_html__( 'Sends through the server set in wp-config.php, using the saved settings. Save first if you changed anything.', 'adminkeep' ) );
		} else {
			printf(
				'<p>%s</p>',
				/* translators: %s: SMTP host name. */
				esc_html( sprintf( __( 'Sends through %s, using the saved settings. Save first if you changed anything.', 'adminkeep' ), $config->get( 'host' ) ) )
			);
		}

		echo '<form method="post" id="adminkeep-smtp-test-form" action="' . esc_url( self::url() ) . '">';
		wp_nonce_field( self::TEST_NONCE );
		printf( '<input type="hidden" name="%s" value="1" />', esc_attr( self::TEST_FIELD ) );
		printf(
			'<label class="screen-reader-text" for="adminkeep-smtp-test-to">%1$s</label><input type="email" id="adminkeep-smtp-test-to" name="%2$s" value="%3$s" class="regular-text" required /> ',
			esc_html__( 'Send to', 'adminkeep' ),
			esc_attr( self::TEST_TO_FIELD ),
			esc_attr( wp_get_current_user()->user_email )
		);

		submit_button( __( 'Send test email', 'adminkeep' ), 'secondary', 'submit', false );

		echo '</form>';

		// Under the form, so an answer arriving from the script does not push the button away.
		echo '<div id="adminkeep-smtp-test-result" aria-live="polite">';
		$this->render_test_result();
		echo '</div>';
		echo '</div>';
	}

	/**
	 * What the last test in this request did, or nothing when there was none. Its own method
	 * because the script asks for exactly this much and drops it into the panel.
	 *
	 * @return void
	 */
	private function render_test_result() {
		if ( null !== $this->test_result ) {
			if ( $this->test_result['sent'] ) {
				printf(
					'<div class="notice notice-success inline"><p>%s</p></div>',
					/* translators: %s: email address. */
					esc_html( sprintf( __( 'The server accepted a test email for %s. Check that inbox, and its spam folder.', 'adminkeep' ), $this->test_result['to'] ) )
				);
			} else {
				printf(
					'<div class="notice notice-error inline"><p><strong>%1$s</strong> %2$s</p></div>',
					esc_html__( 'The test email was not sent.', 'adminkeep' ),
					esc_html( $this->test_result['error'] )
				);
			}

			if ( '' !== $this->test_result['log'] ) {
				printf(
					'<details%1$s><summary>%2$s</summary><pre>%3$s</pre></details>',
					$this->test_result['sent'] ? '' : ' open',
					esc_html__( 'What the server said', 'adminkeep' ),
					esc_html( $this->test_result['log'] )
				);
			}
		}
	}

	/**
	 * The line shown instead of help text when wp-config.php holds a field.
	 *
	 * @param SmtpConfig $config Resolved configuration.
	 * @param string     $key    Field key.
	 * @return void
	 */
	private function locked_note( SmtpConfig $config, $key ) {
		if ( ! $config->is_locked( $key ) ) {
			return;
		}

		printf(
			'<p class="description">%s</p>',
			/* translators: %s: name of a PHP constant. */
			esc_html( sprintf( __( 'Set in wp-config.php (%s).', 'adminkeep' ), SmtpConfig::CONSTANTS[ $key ] ) )
		);
	}

	/**
	 * The preset dropdown. Not a setting: it only fills the three fields below it.
	 *
	 * @return void
	 */
	private function preset_row() {
		echo '<tr><th scope="row"><label for="adminkeep-smtp-preset">' . esc_html__( 'Provider', 'adminkeep' ) . '</label></th><td>';
		echo '<select id="adminkeep-smtp-preset">';
		printf( '<option value="">%s</option>', esc_html__( 'Other — I will type the details', 'adminkeep' ) );

		foreach ( SmtpPresets::all() as $preset ) {
			printf(
				'<option value="%1$s" data-host="%2$s" data-port="%3$d" data-encryption="%4$s" data-note="%5$s">%6$s</option>',
				esc_attr( $preset['id'] ),
				esc_attr( $preset['host'] ),
				(int) $preset['port'],
				esc_attr( $preset['encryption'] ),
				esc_attr( SmtpPresets::note( $preset['id'] ) ),
				esc_html( $preset['label'] )
			);
		}

		echo '</select>';
		printf( '<p class="description">%s</p>', esc_html__( 'Picking a provider fills in the server, port and encryption. Nothing else is sent anywhere.', 'adminkeep' ) );
		echo '<p class="description" id="adminkeep-smtp-preset-note"></p>';
		echo '</td></tr>';
	}

	/**
	 * A one-line input.
	 *
	 * @param SmtpConfig $config Resolved configuration.
	 * @param string     $key    Field key.
	 * @param string     $label  Label.
	 * @param string     $type   Input type.
	 * @return void
	 */
	private function text_row( SmtpConfig $config, $key, $label, $type ) {
		$locked = $config->is_locked( $key );

		printf(
			'<tr><th scope="row"><label for="adminkeep-smtp-%1$s">%2$s</label></th><td><input type="%3$s" id="adminkeep-smtp-%1$s" name="%4$s[%1$s]" value="%5$s" class="%6$s"%7$s />',
			esc_attr( $key ),
			esc_html( $label ),
			esc_attr( $type ),
			esc_attr( self::FIELD ),
			// A constant's value is not echoed: wp-config.php is where it is kept private.
			esc_attr( $locked ? '' : (string) $config->get( $key ) ),
			'number' === $type ? 'small-text' : 'regular-text',
			$locked ? ' disabled="disabled"' : ''
		);

		$this->locked_note( $config, $key );

		echo '</td></tr>';
	}

	/**
	 * The encryption dropdown.
	 *
	 * @param SmtpConfig $config Resolved configuration.
	 * @return void
	 */
	private function encryption_row( SmtpConfig $config ) {
		$locked  = $config->is_locked( 'encryption' );
		// A constant's value is not echoed: wp-config.php is where it is kept private.
		$current = $locked ? '' : $config->get( 'encryption' );
		$choices = array(
			'tls'  => __( 'TLS (STARTTLS) — usual for port 587', 'adminkeep' ),
			'ssl'  => __( 'SSL — usual for port 465', 'adminkeep' ),
			'none' => __( 'None', 'adminkeep' ),
		);

		echo '<tr><th scope="row"><label for="adminkeep-smtp-encryption">' . esc_html__( 'Encryption', 'adminkeep' ) . '</label></th><td>';
		printf( '<select id="adminkeep-smtp-encryption" name="%s[encryption]"%s>', esc_attr( self::FIELD ), $locked ? ' disabled="disabled"' : '' );

		foreach ( $choices as $value => $label ) {
			printf( '<option value="%s"%s>%s</option>', esc_attr( $value ), selected( $current, $value, false ), esc_html( $label ) );
		}

		echo '</select>';
		$this->locked_note( $config, 'encryption' );
		echo '</td></tr>';
	}

	/**
	 * A checkbox.
	 *
	 * @param SmtpConfig $config Resolved configuration.
	 * @param string     $key    Field key.
	 * @param string     $label  Row heading; empty to continue the row above.
	 * @param string     $text   Text beside the box.
	 * @return void
	 */
	private function checkbox_row( SmtpConfig $config, $key, $label, $text ) {
		printf(
			'<tr><th scope="row">%1$s</th><td><label><input type="checkbox" name="%2$s[%3$s]" value="1"%4$s /> %5$s</label></td></tr>',
			esc_html( $label ),
			esc_attr( self::FIELD ),
			esc_attr( $key ),
			checked( (bool) $config->get( $key ), true, false ),
			esc_html( $text )
		);
	}

	/**
	 * The password. Always rendered empty: a saved password is kept by leaving the field blank.
	 *
	 * @param SmtpConfig $config Resolved configuration.
	 * @return void
	 */
	private function password_row( SmtpConfig $config ) {
		$locked = $config->is_locked( 'password' );
		$saved  = ! $locked && $config->has_password();

		// A saved password that still opens keeps the field disabled, so saving the form leaves it
		// alone; Remove enables the field, and what is saved from then on is what it holds, empty
		// included. One that no longer opens has to be typed again, so its field starts enabled.
		$kept = $saved && false !== $config->password();

		echo '<tr><th scope="row"><label for="adminkeep-smtp-password">' . esc_html__( 'Password', 'adminkeep' ) . '</label></th><td>';
		echo '<div class="adminkeep-smtp-secret">';
		printf(
			'<input type="password" id="adminkeep-smtp-password" name="%1$s[password]" value="" class="regular-text" autocomplete="new-password" placeholder="%2$s"%3$s />',
			esc_attr( self::FIELD ),
			// Dots as a placeholder, not a value: they show the field is filled without saying how
			// long the password is, and a placeholder can never be posted as the password.
			esc_attr( $kept ? str_repeat( '•', 16 ) : '' ),
			$locked || $kept ? ' disabled="disabled"' : ''
		);

		if ( $kept ) {
			printf(
				'<button type="button" class="button" id="adminkeep-smtp-password-remove" data-placeholder="%1$s">%2$s</button>',
				esc_attr__( 'Type a new password, or leave empty to remove it', 'adminkeep' ),
				esc_html__( 'Remove password', 'adminkeep' )
			);
		}

		echo '</div>';

		if ( $kept ) {
			printf(
				'<p class="adminkeep-smtp-saved" id="adminkeep-smtp-password-saved">%s</p>',
				esc_html__( 'Saved. Use Remove password to enter a different one.', 'adminkeep' )
			);
		}

		$this->locked_note( $config, 'password' );

		if ( $saved && ! $kept ) {
			printf( '<p class="description"><strong>%s</strong></p>', esc_html__( 'The saved password can no longer be read because this site\'s security keys changed. Enter it again.', 'adminkeep' ) );
		}

		if ( ! $locked ) {
			printf( '<p class="description">%s</p>', esc_html__( 'Stored encrypted, and never shown again once saved.', 'adminkeep' ) );
		}

		echo '</td></tr>';
	}
}