<?php
/**
 * Admin email notifications: immediate, digest and rate-limited delivery.
 *
 * @package Enrollment_Verifier_Logger
 */

defined( 'ABSPATH' ) || exit;

/**
 * Listens to evlfl_event_logged and emails site administrators. Never throws.
 */
class EVLFL_Notifier {

	const DIGEST_HOOK   = 'evlfl_send_digest';   // Recurring (hourly or daily delivery).
	const OVERFLOW_HOOK = 'evlfl_send_overflow'; // One-off summary when the hourly rate limit is hit.
	const PENDING       = 'evlfl_pending_digest';
	const MAX_PENDING   = 500;
	const MAX_LINES     = 50;

	/**
	 * Repository.
	 *
	 * @var EVLFL_Logger
	 */
	private $logger;

	/**
	 * Constructor.
	 *
	 * @param EVLFL_Logger $logger Repository.
	 */
	public function __construct( EVLFL_Logger $logger ) {
		$this->logger = $logger;
	}

	/**
	 * Hooks.
	 *
	 * @return void
	 */
	public function init() {
		add_action( 'evlfl_event_logged', array( $this, 'on_event_logged' ), 10, 2 );
		add_action( self::DIGEST_HOOK, array( $this, 'send_digest' ) );
		add_action( self::OVERFLOW_HOOK, array( $this, 'send_digest' ) );
		add_action( 'init', array( $this, 'sync_schedule' ), 20 );
	}

	/**
	 * Placeholders usable in the subject and body.
	 *
	 * @return array<string,string> token (without braces) => description.
	 */
	public static function placeholders() {
		return array(
			'site_name'           => __( 'Site title', 'accesstrace-for-learndash' ),
			'user_name'           => __( 'Student display name', 'accesstrace-for-learndash' ),
			'user_email'          => __( 'Student email (only if enabled)', 'accesstrace-for-learndash' ),
			'course_title'        => __( 'Course title', 'accesstrace-for-learndash' ),
			'action'              => __( 'Enrolled / Unenrolled', 'accesstrace-for-learndash' ),
			'source'              => __( 'Source', 'accesstrace-for-learndash' ),
			'trigger'             => __( 'Trigger', 'accesstrace-for-learndash' ),
			'status'              => __( 'Valid / Invalid / Unknown', 'accesstrace-for-learndash' ),
			'confidence'          => __( 'Confidence', 'accesstrace-for-learndash' ),
			'verification_reason' => __( 'Why the status was given', 'accesstrace-for-learndash' ),
			'event_time'          => __( 'Event time (site time)', 'accesstrace-for-learndash' ),
			'log_url'             => __( 'Link to the event in wp-admin', 'accesstrace-for-learndash' ),
		);
	}

	/**
	 * Built-in subject.
	 *
	 * @return string
	 */
	public static function default_subject() {
		return __( '[{site_name}] {action}: {user_name} / {course_title} ({status})', 'accesstrace-for-learndash' );
	}

	/**
	 * Built-in body.
	 *
	 * @return string
	 */
	public static function default_body() {
		return __( "Hello,\n\nAccessTrace logged a LearnDash enrollment change on {site_name}.\n\nUser: {user_name} ({user_email})\nCourse: {course_title}\nAction: {action}\nSource: {source} (trigger: {trigger})\nStatus: {status} - {verification_reason}\nWhen: {event_time}\n\nView details: {log_url}", 'accesstrace-for-learndash' );
	}

	/**
	 * Hook: an event was written to the log.
	 *
	 * @param int   $id    Row ID.
	 * @param array $event Normalized event.
	 * @return void
	 */
	public function on_event_logged( $id = 0, $event = array() ) {
		try {
			$id = absint( $id );
			if ( $id < 1 || ! is_array( $event ) ) {
				return;
			}
			$cfg = EVLFL_Settings::all()['email'];
			if ( empty( $cfg['enabled'] ) || ! $this->matches( $cfg, $event, $id ) ) {
				return;
			}
			if ( 'immediate' !== $cfg['delivery'] ) {
				$this->queue( $id );
				return;
			}
			if ( ! $this->take_rate_slot( (int) $cfg['rate_limit'] ) ) {
				$this->queue( $id );
				if ( ! wp_next_scheduled( self::OVERFLOW_HOOK ) ) {
					wp_schedule_single_event( time() + HOUR_IN_SECONDS, self::OVERFLOW_HOOK );
				}
				return;
			}
			$this->send( $cfg, $this->subject_for( $cfg, $event, $id ), $this->body_for( $cfg, $event, $id ) );
		} catch ( \Throwable $e ) {
			$this->debug( $e );
		}
	}

	/**
	 * Send the queued events as one email (digest cron or rate-limit overflow).
	 *
	 * @return void
	 */
	public function send_digest() {
		try {
			$cfg     = EVLFL_Settings::all()['email'];
			$pending = get_option( self::PENDING, array() );
			$ids     = isset( $pending['ids'] ) && is_array( $pending['ids'] ) ? array_map( 'absint', $pending['ids'] ) : array();
			$dropped = isset( $pending['dropped'] ) ? absint( $pending['dropped'] ) : 0;
			if ( ! $ids ) {
				return;
			}
			delete_option( self::PENDING ); // Clear first so a slow send cannot be sent twice.
			if ( empty( $cfg['enabled'] ) ) {
				return;
			}
			$rows  = $this->logger->get_by_ids( array_slice( $ids, 0, self::MAX_LINES ) );
			$total = count( $ids ) + $dropped;
			$html  = 'html' === $cfg['format'];
			$lines = array();
			foreach ( $rows as $row ) {
				$v       = $this->values( $cfg, $row, (int) $row['id'], false );
				$lines[] = sprintf( '%1$s | %2$s | %3$s | %4$s | %5$s (%6$s)', $v['event_time'], $v['action'], $v['user_name'], $v['course_title'], $v['status'], $v['source'] );
			}
			$intro = sprintf(
				/* translators: 1: number of events, 2: site title. */
				_n( 'AccessTrace logged %1$s enrollment event on %2$s.', 'AccessTrace logged %1$s enrollment events on %2$s.', $total, 'accesstrace-for-learndash' ),
				number_format_i18n( $total ),
				$this->site_name()
			);
			if ( $total > count( $lines ) ) {
				/* translators: %s: number of events not listed. */
				$lines[] = sprintf( __( '...and %s more. Open the log for the full list.', 'accesstrace-for-learndash' ), number_format_i18n( $total - count( $lines ) ) );
			}
			$footer = __( 'View the log:', 'accesstrace-for-learndash' ) . ' ' . $this->logs_url();
			$body   = $html
				? '<p>' . esc_html( $intro ) . '</p><p>' . implode( '<br>', array_map( 'esc_html', $lines ) ) . '</p><p>' . esc_html__( 'View the log:', 'accesstrace-for-learndash' ) . ' <a href="' . esc_url( $this->logs_url() ) . '">' . esc_html( $this->logs_url() ) . '</a></p>'
				: $intro . "\n\n" . implode( "\n", $lines ) . "\n\n" . $footer;
			/* translators: 1: site title, 2: number of events. */
			$subject = sprintf( __( '[%1$s] AccessTrace summary: %2$s events', 'accesstrace-for-learndash' ), $this->site_name(), number_format_i18n( $total ) );
			$this->send( $cfg, $subject, $body );
		} catch ( \Throwable $e ) {
			$this->debug( $e );
		}
	}

	/**
	 * Send a test email to the first recipient using sample data and the saved settings.
	 *
	 * @return bool
	 */
	public function send_test() {
		try {
			$cfg    = EVLFL_Settings::all()['email'];
			$sample = array(
				'user_id'             => get_current_user_id(),
				'course_id'           => 0,
				'action'              => EVLFL_Event::ACTION_UNENROLLED,
				'source'              => 'admin',
				'event_trigger'       => 'manual',
				'status'              => 'valid',
				'confidence'          => 'detected',
				'verification_reason' => __( 'This is a test message with sample data.', 'accesstrace-for-learndash' ),
				'event_time'          => gmdate( 'Y-m-d H:i:s' ),
			);
			$to     = self::recipients( $cfg );
			return $this->send( $cfg, '[TEST] ' . $this->subject_for( $cfg, $sample, 0 ), $this->body_for( $cfg, $sample, 0 ), array_slice( $to, 0, 1 ) );
		} catch ( \Throwable $e ) {
			$this->debug( $e );
			return false;
		}
	}

	/**
	 * Keep the recurring digest schedule in line with the settings.
	 *
	 * @return void
	 */
	public function sync_schedule() {
		$cfg     = EVLFL_Settings::all()['email'];
		$wanted  = ( ! empty( $cfg['enabled'] ) && in_array( $cfg['delivery'], array( 'hourly', 'daily' ), true ) ) ? $cfg['delivery'] : '';
		$current = wp_get_schedule( self::DIGEST_HOOK );
		if ( (string) $current === $wanted ) {
			return;
		}
		wp_clear_scheduled_hook( self::DIGEST_HOOK );
		if ( '' !== $wanted ) {
			wp_schedule_event( time() + HOUR_IN_SECONDS, $wanted, self::DIGEST_HOOK );
		}
	}

	/**
	 * Remove scheduled events (deactivation/uninstall).
	 *
	 * @return void
	 */
	public static function clear_schedules() {
		wp_clear_scheduled_hook( self::DIGEST_HOOK );
		wp_clear_scheduled_hook( self::OVERFLOW_HOOK );
	}

	/**
	 * Recipients: configured addresses, else the site admin email.
	 *
	 * @param array $cfg Email settings.
	 * @return string[]
	 */
	public static function recipients( array $cfg ) {
		$out = array();
		foreach ( explode( ',', (string) $cfg['recipients'] ) as $address ) {
			$address = sanitize_email( trim( $address ) );
			if ( is_email( $address ) ) {
				$out[] = $address;
			}
		}
		if ( ! $out ) {
			$admin = sanitize_email( (string) get_option( 'admin_email' ) );
			if ( is_email( $admin ) ) {
				$out[] = $admin;
			}
		}
		return $out;
	}

	/**
	 * Does the event match the configured triggers and sources?
	 *
	 * @param array $cfg   Email settings.
	 * @param array $event Event.
	 * @param int   $id    Row ID.
	 * @return bool
	 */
	private function matches( array $cfg, array $event, $id ) {
		$match = false;
		$on    = (array) $cfg['notify_on'];
		if ( in_array( 'all', $on, true ) ) {
			$match = true;
		} elseif ( in_array( (string) $event['action'], $on, true ) ) {
			$match = true; // "enrolled" / "unenrolled" use the action value.
		} elseif ( in_array( (string) $event['status'], $on, true ) && in_array( $event['status'], array( 'invalid', 'unknown' ), true ) ) {
			$match = true;
		}
		$sources = (array) $cfg['sources'];
		if ( $match && $sources && ! in_array( (string) $event['source'], $sources, true ) ) {
			$match = false;
		}
		/**
		 * Filters whether an admin email is sent for a logged event.
		 *
		 * @param bool  $match Whether the settings say to send.
		 * @param array $event Normalized event.
		 * @param int   $id    Log row ID.
		 */
		return (bool) apply_filters( 'evlfl_should_notify', $match, $event, $id );
	}

	/**
	 * Add an event to the digest queue.
	 *
	 * @param int $id Row ID.
	 * @return void
	 */
	private function queue( $id ) {
		$pending = get_option( self::PENDING, array() );
		$pending = is_array( $pending ) ? $pending : array();
		$ids     = isset( $pending['ids'] ) && is_array( $pending['ids'] ) ? $pending['ids'] : array();
		$dropped = isset( $pending['dropped'] ) ? absint( $pending['dropped'] ) : 0;
		if ( count( $ids ) >= self::MAX_PENDING ) {
			++$dropped;
		} else {
			$ids[] = $id;
		}
		update_option(
			self::PENDING,
			array(
				'ids'     => $ids,
				'dropped' => $dropped,
			),
			false
		);
	}

	/**
	 * Count one immediate email against this hour's limit.
	 *
	 * @param int $limit Max emails per hour.
	 * @return bool True when a slot was available.
	 */
	private function take_rate_slot( $limit ) {
		$key   = 'evlfl_mail_rate_' . gmdate( 'YmdH' );
		$count = (int) get_transient( $key );
		if ( $count >= $limit ) {
			return false;
		}
		set_transient( $key, $count + 1, 2 * HOUR_IN_SECONDS );
		return true;
	}

	/**
	 * Subject for one event.
	 *
	 * @param array $cfg   Settings.
	 * @param array $event Event.
	 * @param int   $id    Row ID.
	 * @return string
	 */
	private function subject_for( array $cfg, array $event, $id ) {
		$template = '' !== trim( (string) $cfg['subject'] ) ? (string) $cfg['subject'] : self::default_subject();
		$subject  = $this->fill( $template, $this->values( $cfg, $event, $id, false ) );
		return trim( preg_replace( '/[\r\n]+/', ' ', wp_strip_all_tags( $subject ) ) );
	}

	/**
	 * Body for one event.
	 *
	 * @param array $cfg   Settings.
	 * @param array $event Event.
	 * @param int   $id    Row ID.
	 * @return string
	 */
	private function body_for( array $cfg, array $event, $id ) {
		$template = '' !== trim( (string) $cfg['body'] ) ? (string) $cfg['body'] : self::default_body();
		if ( 'html' === $cfg['format'] ) {
			$values            = $this->values( $cfg, $event, $id, true );
			$values['log_url'] = '<a href="' . esc_url( $this->url_for( $id ) ) . '">' . esc_html( $this->url_for( $id ) ) . '</a>';
			return nl2br( $this->fill( esc_html( $template ), $values ) );
		}
		return $this->fill( $template, $this->values( $cfg, $event, $id, false ) );
	}

	/**
	 * Replace {tokens}. Unknown tokens stay as written.
	 *
	 * @param string $template Template.
	 * @param array  $values   token => value (already safe for the output format).
	 * @return string
	 */
	private function fill( $template, array $values ) {
		$map = array();
		foreach ( $values as $token => $value ) {
			$map[ '{' . $token . '}' ] = $value;
		}
		return strtr( $template, $map );
	}

	/**
	 * Placeholder values.
	 *
	 * @param array $cfg    Settings.
	 * @param array $event  Event row.
	 * @param int   $id     Row ID (0 for a test).
	 * @param bool  $escape Escape each value for HTML.
	 * @return array<string,string>
	 */
	private function values( array $cfg, array $event, $id, $escape ) {
		$user    = get_userdata( absint( $event['user_id'] ) );
		$course  = absint( $event['course_id'] ) > 0 ? get_post( absint( $event['course_id'] ) ) : null;
		$ts      = strtotime( (string) $event['event_time'] . ' UTC' );
		$deleted = static function ( $label, $n ) {
			/* translators: 1: "User" or "Course", 2: ID. */
			return sprintf( __( '[Deleted %1$s #%2$d]', 'accesstrace-for-learndash' ), $label, $n );
		};

		$values = array(
			'site_name'           => $this->site_name(),
			'user_name'           => $user ? $user->display_name : $deleted( __( 'User', 'accesstrace-for-learndash' ), absint( $event['user_id'] ) ),
			'user_email'          => ( $user && ! empty( $cfg['include_user_email'] ) ) ? $user->user_email : __( '[hidden]', 'accesstrace-for-learndash' ),
			'course_title'        => $course ? $course->post_title : ( 0 === absint( $event['course_id'] ) ? __( 'Sample course', 'accesstrace-for-learndash' ) : $deleted( __( 'Course', 'accesstrace-for-learndash' ), absint( $event['course_id'] ) ) ),
			'action'              => EVLFL_Event::label( 'action', $event['action'] ),
			'source'              => EVLFL_Event::label( 'source', $event['source'] ),
			'trigger'             => EVLFL_Event::label( 'trigger', $event['event_trigger'] ),
			'status'              => EVLFL_Event::label( 'status', $event['status'] ),
			'confidence'          => EVLFL_Event::label( 'confidence', $event['confidence'] ),
			'verification_reason' => isset( $event['verification_reason'] ) ? (string) $event['verification_reason'] : '',
			'event_time'          => false !== $ts ? wp_date( get_option( 'date_format' ) . ' ' . get_option( 'time_format' ), $ts ) : '',
			'log_url'             => $this->url_for( $id ),
		);
		foreach ( $values as $token => $value ) {
			$value            = wp_strip_all_tags( (string) $value );
			$values[ $token ] = $escape ? esc_html( $value ) : $value;
		}
		return $values;
	}

	/**
	 * Admin URL of one event (or the list for a test).
	 *
	 * @param int $id Row ID.
	 * @return string
	 */
	private function url_for( $id ) {
		$args = array( 'page' => EVLFL_Plugin::LOGS_PAGE );
		if ( $id > 0 ) {
			$args['evlfl_event'] = absint( $id );
		}
		return add_query_arg( $args, admin_url( 'admin.php' ) );
	}

	/**
	 * Admin URL of the log list.
	 *
	 * @return string
	 */
	private function logs_url() {
		return $this->url_for( 0 );
	}

	/**
	 * Site title as plain text.
	 *
	 * @return string
	 */
	private function site_name() {
		return wp_specialchars_decode( (string) get_bloginfo( 'name' ), ENT_QUOTES );
	}

	/**
	 * Send through wp_mail().
	 *
	 * @param array      $cfg     Settings.
	 * @param string     $subject Subject.
	 * @param string     $body    Body (HTML when the format is html).
	 * @param array|null $to      Override recipients.
	 * @return bool
	 */
	private function send( array $cfg, $subject, $body, $to = null ) {
		$to = null === $to ? self::recipients( $cfg ) : $to;
		if ( ! $to ) {
			return false;
		}
		$headers = array();
		if ( 'html' === $cfg['format'] ) {
			$headers[] = 'Content-Type: text/html; charset=UTF-8';
		}
		if ( '' !== $cfg['from_email'] && is_email( $cfg['from_email'] ) ) {
			$name      = '' !== $cfg['from_name'] ? $cfg['from_name'] : $this->site_name();
			$headers[] = 'From: ' . str_replace( array( "\r", "\n" ), '', $name ) . ' <' . $cfg['from_email'] . '>';
		}
		return (bool) wp_mail( $to, $subject, $body, $headers );
	}

	/**
	 * Debug-only logging.
	 *
	 * @param \Throwable $e Error.
	 * @return void
	 */
	private function debug( $e ) {
		if ( defined( 'WP_DEBUG' ) && WP_DEBUG ) {
			error_log( 'EVL notifier error: ' . get_class( $e ) . ': ' . $e->getMessage() ); // phpcs:ignore WordPress.PHP.DevelopmentFunctions.error_log_error_log
		}
	}
}