<?php
/**
 * Sends Client Monitor alerts to a Slack channel.
 *
 * @package TurtleReport
 */

namespace TurtleReport\Attention;

use TurtleReport\Support\Crypto;
use TurtleReport\Support\Text;

defined( 'ABSPATH' ) || exit;

/**
 * Posts to a Slack incoming webhook. The webhook URL is a secret (anyone with
 * it can post to the channel), so it's stored encrypted and never sent to
 * the browser. Only https://hooks.slack.com/services/… URLs are accepted, so
 * the setting can't be used to make the server call anywhere else.
 */
final class Slack {

	const OPTION = 'turtlereport_slack';

	const PREFIX = 'https://hooks.slack.com/services/';

	/**
	 * Encryption.
	 *
	 * @var Crypto
	 */
	private $crypto;

	/**
	 * Constructor.
	 *
	 * @param Crypto $crypto Encryption.
	 */
	public function __construct( Crypto $crypto ) {
		$this->crypto = $crypto;
	}

	/**
	 * Whether a URL looks like a Slack incoming webhook.
	 *
	 * @param string $url URL.
	 * @return bool
	 */
	public static function valid_url( $url ) {
		return (bool) preg_match( '#^https://hooks\.slack\.com/services/[A-Za-z0-9]+/[A-Za-z0-9]+/[A-Za-z0-9]+$#D', (string) $url );
	}

	/**
	 * Whether a webhook is saved.
	 *
	 * @return bool
	 */
	public function configured() {
		return '' !== $this->url();
	}

	/**
	 * Saves the webhook URL.
	 *
	 * @param string $url URL.
	 * @return bool False when the URL isn't a Slack webhook.
	 */
	public function save( $url ) {
		$url = trim( (string) $url );
		if ( ! self::valid_url( $url ) ) {
			return false;
		}
		update_option( self::OPTION, $this->crypto->encrypt( $url ), false );
		return true;
	}

	/**
	 * Removes the webhook URL.
	 *
	 * @return void
	 */
	public function forget() {
		delete_option( self::OPTION );
	}

	/**
	 * The last part of the saved webhook, for "Saved (…abc12)".
	 *
	 * @return string
	 */
	public function hint() {
		$url = $this->url();
		return '' === $url ? '' : '…' . substr( $url, -5 );
	}

	/**
	 * Sends an alert.
	 *
	 * @param array  $alert  Presenter::present() output.
	 * @param string $note   Optional note from the person sharing it.
	 * @param string $sender Who shared it.
	 * @return true|\WP_Error
	 */
	public function send_alert( array $alert, $note = '', $sender = '' ) {
		return $this->post( self::message( $alert, $note, $sender ) );
	}

	/**
	 * Sends a test message.
	 *
	 * @param string $sender Who asked.
	 * @return true|\WP_Error
	 */
	public function send_test( $sender = '' ) {
		$text = '' !== $sender
			/* translators: %s: person's name. */
			? sprintf( __( 'TurtleReport is connected to this channel. %s sent this test from the Client Monitor settings.', 'turtlereport' ), $sender )
			: __( 'TurtleReport is connected to this channel.', 'turtlereport' );
		return $this->post(
			array(
				'text'   => $text,
				'blocks' => array(
					array(
						'type' => 'section',
						'text' => array(
							'type' => 'mrkdwn',
							'text' => ':white_check_mark: ' . self::esc( $text ),
						),
					),
				),
			)
		);
	}

	/**
	 * The Slack message for an alert: a plain-text fallback and Block Kit blocks.
	 *
	 * @param array  $alert  Presented alert.
	 * @param string $note   Note.
	 * @param string $sender Who shared it.
	 * @return array
	 */
	public static function message( array $alert, $note = '', $sender = '' ) {
		$high   = 'high' === $alert['severity'];
		$title  = $alert['siteName'] . ': ' . ( '' !== (string) $alert['kind'] ? $alert['kind'] : $alert['title'] );
		$where  = self::where( $alert );
		$blocks = array(
			array(
				'type' => 'header',
				'text' => array(
					'type'  => 'plain_text',
					'text'  => self::cut( $title, 150 ),
					'emoji' => true,
				),
			),
			array(
				'type' => 'section',
				'text' => array(
					'type' => 'mrkdwn',
					'text' => ( $high ? ':red_circle:' : ':large_orange_circle:' ) . ' *' . self::esc( $high ? __( 'High priority', 'turtlereport' ) : __( 'Worth a look', 'turtlereport' ) ) . '* · *' . self::esc( self::cut( (string) $alert['headline'], 300 ) ) . '*' . ( '' !== $where ? "\n" . $where : '' ),
				),
			),
		);
		$note   = trim( (string) $note );
		if ( '' !== $note ) {
			$who      = '' !== $sender ? $sender : __( 'Note', 'turtlereport' );
			$blocks[] = array(
				'type' => 'section',
				'text' => array(
					'type' => 'mrkdwn',
					'text' => '> *' . self::esc( $who ) . ':* ' . self::esc( self::cut( $note, 1000 ) ),
				),
			);
		}
		if ( ! empty( $alert['metrics'] ) ) {
			$fields = array();
			foreach ( array_slice( $alert['metrics'], 0, 4 ) as $m ) {
				$fields[] = array(
					'type' => 'mrkdwn',
					'text' => '*' . self::esc( $m['label'] ) . "*\n" . self::esc( $m['value'] . ( '' !== (string) $m['change'] ? ' (' . $m['change'] . ')' : '' ) ),
				);
			}
			$blocks[] = array(
				'type'   => 'section',
				'fields' => $fields,
			);
		}
		if ( ! empty( $alert['insights'] ) ) {
			$blocks[] = array(
				'type' => 'section',
				'text' => array(
					'type' => 'mrkdwn',
					'text' => '*' . self::esc( __( 'What the data suggests', 'turtlereport' ) ) . "*\n" . self::esc( self::cut( implode( ' ', $alert['insights'] ), 2800 ) ),
				),
			);
		}
		if ( ! empty( $alert['checks'] ) ) {
			$lines = array();
			foreach ( array_values( $alert['checks'] ) as $i => $check ) {
				$lines[] = ( $i + 1 ) . '. ' . self::esc( $check );
			}
			$blocks[] = array(
				'type' => 'section',
				'text' => array(
					'type' => 'mrkdwn',
					'text' => '*' . self::esc( __( 'Recommended next checks', 'turtlereport' ) ) . "*\n" . self::cut( implode( "\n", $lines ), 2800 ),
				),
			);
		}
		$blocks[] = array(
			'type'     => 'actions',
			'elements' => array(
				array(
					'type' => 'button',
					'text' => array(
						'type' => 'plain_text',
						'text' => __( 'Open the report', 'turtlereport' ),
					),
					'url'  => (string) $alert['reportUrl'],
				),
			),
		);
		$context  = array_filter(
			array(
				isset( $alert['confidence']['text'] ) ? (string) $alert['confidence']['text'] : '',
				(string) $alert['basis'],
				/* translators: %s: person's name. */
				'' !== $sender ? sprintf( __( 'Shared by %s from TurtleReport', 'turtlereport' ), $sender ) : '',
			),
			static function ( $part ) {
				return '' !== $part; }
		);
		$blocks[] = array(
			'type'     => 'context',
			'elements' => array(
				array(
					'type' => 'mrkdwn',
					'text' => self::esc( self::cut( implode( ' · ', $context ), 2900 ) ),
				),
			),
		);
		return array(
			'text'   => $alert['siteName'] . ': ' . $alert['title'] . ' — ' . $alert['summary'],
			'blocks' => $blocks,
		);
	}

	/**
	 * The same alert as plain text, for "Copy for Slack" (or email, or a ticket).
	 *
	 * @param array $alert Presented alert.
	 * @return string
	 */
	public static function plain( array $alert ) {
		$lines   = array();
		$lines[] = $alert['siteName'] . ' · ' . $alert['kind'] . ' (' . ( 'high' === $alert['severity'] ? __( 'High priority', 'turtlereport' ) : __( 'Worth a look', 'turtlereport' ) ) . ')';
		$lines[] = $alert['headline'];
		if ( '' !== (string) $alert['url'] ) {
			$lines[] = $alert['url'];
		}
		if ( ! empty( $alert['metrics'] ) ) {
			$lines[] = '';
			foreach ( $alert['metrics'] as $m ) {
				$lines[] = '• ' . $m['label'] . ': ' . $m['value'] . ( '' !== (string) $m['change'] ? ' (' . $m['change'] . ')' : '' );
			}
		}
		if ( ! empty( $alert['insights'] ) ) {
			$lines[] = '';
			$lines[] = __( 'What the data suggests', 'turtlereport' ) . ':';
			$lines[] = implode( ' ', $alert['insights'] );
		}
		if ( ! empty( $alert['checks'] ) ) {
			$lines[] = '';
			$lines[] = __( 'Recommended next checks', 'turtlereport' ) . ':';
			foreach ( array_values( $alert['checks'] ) as $i => $check ) {
				$lines[] = ( $i + 1 ) . '. ' . $check;
			}
		}
		$lines[] = '';
		if ( ! empty( $alert['confidence']['text'] ) ) {
			$lines[] = $alert['confidence']['text'];
		}
		$lines[] = $alert['basis'];
		return implode( "\n", $lines );
	}

	/**
	 * The affected address as a Slack link, or ''.
	 *
	 * @param array $alert Presented alert.
	 * @return string
	 */
	private static function where( array $alert ) {
		$url = (string) $alert['url'];
		if ( '' === $url || ! preg_match( '#^https?://#i', $url ) ) {
			return '' !== (string) $alert['path'] ? self::esc( $alert['path'] ) : '';
		}
		$url = str_replace( array( '<', '>', '|', ' ' ), array( '%3C', '%3E', '%7C', '%20' ), $url );
		return '<' . $url . '|' . self::esc( '' !== (string) $alert['path'] && '/' === substr( (string) $alert['path'], 0, 1 ) ? $alert['path'] : $url ) . '>';
	}

	/**
	 * Posts a payload to the webhook.
	 *
	 * @param array $payload Payload.
	 * @return true|\WP_Error
	 */
	private function post( array $payload ) {
		$url = $this->url();
		if ( '' === $url ) {
			return new \WP_Error( 'turtlereport_slack_missing', __( 'Add a Slack webhook in Settings → Client Monitor first.', 'turtlereport' ) );
		}
		$response = wp_remote_post(
			$url,
			array(
				'timeout'     => 10,
				'redirection' => 0,
				'headers'     => array( 'Content-Type' => 'application/json; charset=utf-8' ),
				'body'        => wp_json_encode( $payload ),
			)
		);
		if ( is_wp_error( $response ) ) {
			/* translators: %s: network error. */
			return new \WP_Error( 'turtlereport_slack_network', sprintf( __( 'Couldn\'t reach Slack: %s', 'turtlereport' ), $response->get_error_message() ) );
		}
		$code = (int) wp_remote_retrieve_response_code( $response );
		$body = trim( (string) wp_remote_retrieve_body( $response ) );
		if ( 200 === $code ) {
			return true;
		}
		switch ( $body ) {
			case 'no_service':
			case 'invalid_token':
			case 'no_team':
				$message = __( 'Slack doesn\'t recognise this webhook any more. It may have been removed: create a new one and save it in Settings → Client Monitor.', 'turtlereport' );
				break;
			case 'channel_is_archived':
				$message = __( 'The Slack channel for this webhook is archived. Create a webhook for another channel.', 'turtlereport' );
				break;
			case 'action_prohibited':
				$message = __( 'A Slack admin has blocked posting to this channel.', 'turtlereport' );
				break;
			case 'invalid_blocks':
			case 'invalid_payload':
				$message = __( 'Slack refused the message format. Please report this to the plugin author.', 'turtlereport' );
				break;
			default:
				/* translators: 1: HTTP status, 2: Slack's answer. */
				$message = sprintf( __( 'Slack answered %1$d: %2$s', 'turtlereport' ), $code, self::cut( sanitize_text_field( $body ), 120 ) );
		}
		return new \WP_Error( 'turtlereport_slack_failed', $message );
	}

	/**
	 * The decrypted webhook URL, or ''.
	 *
	 * @return string
	 */
	private function url() {
		$stored = get_option( self::OPTION, '' );
		if ( ! is_string( $stored ) || '' === $stored ) {
			return '';
		}
		$url = (string) $this->crypto->decrypt( $stored );
		return self::valid_url( $url ) ? $url : '';
	}

	/**
	 * Escapes text for Slack mrkdwn (&, < and >).
	 *
	 * @param string $text Text.
	 * @return string
	 */
	private static function esc( $text ) {
		return str_replace( array( '&', '<', '>' ), array( '&amp;', '&lt;', '&gt;' ), (string) $text );
	}

	/**
	 * Shortens text to a length limit Slack enforces.
	 *
	 * @param string $text Text.
	 * @param int    $max  Characters.
	 * @return string
	 */
	private static function cut( $text, $max ) {
		$text = (string) $text;
		return Text::length( $text ) <= $max ? $text : Text::substr( $text, 0, $max - 1 ) . '…';
	}
}