<?php

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

class Argus_Correlation {

	const WATERMARK_OPTION = 'argus_wpd_correlation_watermark';
	const WINDOW_SECONDS    = 15 * MINUTE_IN_SECONDS;

	public static function run() {
		global $wpdb;
		$events_table = Argus_DB::table( 'events' );
		$since        = get_option( self::WATERMARK_OPTION, gmdate( 'Y-m-d H:i:s', time() - DAY_IN_SECONDS ) );
		$now          = current_time( 'mysql', true );

		$suspicious = $wpdb->get_results(
			$wpdb->prepare(
				"SELECT * FROM {$events_table} WHERE event_type IN ('ban','policy_observed','login_failed') AND severity IN ('high','critical') AND ip IS NOT NULL AND created_at >= %s ORDER BY created_at ASC", // phpcs:ignore
				$since
			)
		);

		if ( empty( $suspicious ) ) {
			update_option( self::WATERMARK_OPTION, $now, false );
			return 0;
		}

		$file_events = $wpdb->get_results(
			$wpdb->prepare(
				"SELECT * FROM {$events_table} WHERE event_type IN ('integrity_new_file','integrity_changed_file') AND created_at >= %s ORDER BY created_at ASC", // phpcs:ignore
				$since
			)
		);

		$by_ip = array();
		foreach ( $suspicious as $event ) {
			$by_ip[ $event->ip ][] = $event;
		}

		$correlated = 0;

		foreach ( $by_ip as $ip => $ip_events ) {
			$request_event = $ip_events[0]; 
			$request_time  = strtotime( $request_event->created_at . ' UTC' );

			$best_delta = null;
			$best_file  = null;
			$best_payload = null;

			foreach ( $file_events as $file_event ) {
				$payload    = json_decode( $file_event->payload, true );
				$file_mtime = isset( $payload['file_mtime'] ) ? strtotime( $payload['file_mtime'] . ' UTC' ) : null;
				if ( null === $file_mtime ) {
					continue;
				}

				$delta = $file_mtime - $request_time;
				if ( $delta < 0 || $delta > self::WINDOW_SECONDS ) {
					continue;
				}

				if ( null === $best_delta || $delta < $best_delta ) {
					$best_delta   = $delta;
					$best_file    = $file_event;
					$best_payload = $payload;
				}
			}

			if ( null !== $best_file ) {
				self::record_correlated_finding( $request_event, $best_file, $best_payload, $best_delta );
				$correlated++;
			}
		}

		update_option( self::WATERMARK_OPTION, $now, false );
		return $correlated;
	}

	protected static function record_correlated_finding( $request_event, $file_event, array $file_payload, $delta_seconds ) {
		Argus_Findings::record(
			'correlation',
			'critical',
			array(
				'what_happened'          => sprintf(
					'A high-severity request from %s was followed %d seconds later by a %s: %s',
					$request_event->ip,
					$delta_seconds,
					'integrity_new_file' === $file_event->event_type ? 'new file' : 'changed file',
					$file_payload['file_path'] ?? 'unknown'
				),
				'why_it_matters'         => 'A suspicious request closely followed by a filesystem change is a much stronger signal than either event alone -- this is the pattern a successful exploit-then-webshell-drop typically produces.',
				'what_argus_found'       => sprintf(
					'Request event: %s (%s, severity %s) at %s. File event: %s at %s.',
					$request_event->event_type,
					$request_event->summary,
					$request_event->severity,
					$request_event->created_at,
					$file_event->summary,
					$file_event->created_at
				),
				'when_it_happened'       => $file_event->created_at,
				'why_suspicious'         => sprintf( 'The file change happened within %d seconds of the suspicious request -- close enough in time to be a plausible cause-and-effect, though ARGUS cannot prove the same actor performed both (a filesystem write carries no IP attribution).', self::WINDOW_SECONDS ),
				'what_could_be_affected' => 'If this represents a successful exploit, the new/changed file may itself be malicious code with the same access as your web application.',
				'what_should_you_do'     => 'Review the file named above immediately, and treat the source IP as a confirmed active threat rather than a routine block.',
			),
			array(
				'request_event_id' => $request_event->id,
				'file_event_id'    => $file_event->id,
				'ip'               => $request_event->ip,
				'delta_seconds'    => $delta_seconds,
			)
		);

		Argus_Ban_Engine::ban(
			$request_event->ip,
			Argus_Ban_Engine::SOURCE_POLICY_ENGINE,
			'Correlated with a filesystem change ' . $delta_seconds . 's later',
			array( 'request_event_id' => $request_event->id, 'file_event_id' => $file_event->id ),
			Argus_Ban_Engine::LEVEL_EXTENDED
		);
	}
}