<?php
/**
 * Strict low-volume connected-platform event contract. No hooks or transport.
 *
 * @package abtestkit
 */

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

final class ABTestKit_Connected_Event {
    const MAX_BYTES = 4096;
    const MAX_AGE = 30 * DAY_IN_SECONDS;

    /** Generate an opaque UUID without deriving identity from site content. */
    public static function new_id() {
        try {
            $bytes = random_bytes( 16 );
            $bytes[6] = chr( ( ord( $bytes[6] ) & 0x0f ) | 0x40 );
            $bytes[8] = chr( ( ord( $bytes[8] ) & 0x3f ) | 0x80 );
            $hex = bin2hex( $bytes );
            return substr( $hex, 0, 8 ) . '-' . substr( $hex, 8, 4 ) . '-' . substr( $hex, 12, 4 ) . '-' . substr( $hex, 16, 4 ) . '-' . substr( $hex, 20 );
        } catch ( Exception $error ) {
            return new WP_Error( 'abtestkit_connected_random_failed' );
        }
    }

    public static function valid_id( $value ) : bool {
        return is_string( $value ) && 1 === preg_match( '/^[a-f0-9]{8}-[a-f0-9]{4}-4[a-f0-9]{3}-[89ab][a-f0-9]{3}-[a-f0-9]{12}$/D', $value );
    }

    /** Reject unknown fields, including nested data, instead of silently stripping them. */
    private static function exact_keys( array $value, array $expected ) : bool {
        $keys = array_keys( $value );
        sort( $keys );
        sort( $expected );
        return $keys === $expected;
    }

    /**
     * Return a canonical envelope or a secret-safe error. Timestamps are UTC.
     * Site/account ownership is supplied by authenticated ingestion, never here.
     */
    public static function validate( array $event, int $now ) {
        $invalid = new WP_Error( 'abtestkit_connected_invalid_event' );
        if ( ! self::exact_keys( $event, array( 'schema_version', 'event_id', 'installation_id', 'event_name', 'occurred_at', 'plugin_version', 'test_ref', 'payload' ) ) ) {
            return $invalid;
        }
        if (
            1 !== $event['schema_version'] ||
            ! self::valid_id( $event['event_id'] ) || ! self::valid_id( $event['installation_id'] ) ||
            ! is_int( $event['occurred_at'] ) || $event['occurred_at'] <= 0 ||
            $event['occurred_at'] > $now + 300 || $event['occurred_at'] <= $now - self::MAX_AGE ||
            ! is_string( $event['plugin_version'] ) || strlen( $event['plugin_version'] ) > 32 ||
            1 !== preg_match( '/^[0-9]+\.[0-9]+\.[0-9]+(?:[-+][0-9A-Za-z.-]+)?$/D', $event['plugin_version'] ) ||
            ! is_string( $event['event_name'] ) || ! is_array( $event['payload'] )
        ) {
            return $invalid;
        }

        $site_events = array( 'onboarding_started', 'onboarding_completed', 'plugin_deactivated' );
        $experiment_states = array(
            'experiment_baseline' => array( 'draft', 'running', 'paused', 'winner', 'complete' ),
            'experiment_created' => array( 'draft', 'running' ),
            'experiment_launched' => array( 'running' ),
            'experiment_paused' => array( 'paused' ),
            'experiment_resumed' => array( 'running' ),
            'experiment_completed' => array( 'complete' ),
            'experiment_deleted' => array( 'draft', 'running', 'paused', 'winner', 'complete' ),
            'winner_declared' => array( 'winner' ),
            'first_impression_recorded' => array( 'running', 'paused', 'winner', 'complete' ),
            'both_variants_recorded' => array( 'running', 'paused', 'winner', 'complete' ),
            'first_conversion_recorded' => array( 'running', 'paused', 'winner', 'complete' ),
            'first_order_attributed' => array( 'running', 'paused', 'winner', 'complete' ),
            'first_revenue_attributed' => array( 'running', 'paused', 'winner', 'complete' ),
        );
        $payload = $event['payload'];
        if ( 'wizard_step_reached' === $event['event_name'] ) {
            if (
                null !== $event['test_ref'] ||
                ! self::exact_keys( $payload, array( 'evidence', 'goal', 'kind', 'session_ref', 'step' ) ) ||
                'observed' !== $payload['evidence'] ||
                ! in_array( $payload['step'], array( 'select_type', 'select_custom_code_type', 'select_control', 'version_b_source', 'review_versions', 'choose_conversion_type', 'set_destination_url', 'set_scroll_depth', 'select_click_targets', 'summary' ), true ) ||
                ! in_array( $payload['kind'], array( 'unknown', 'page', 'post', 'product', 'reusable_section', 'custom_css', 'custom_html', 'custom_javascript' ), true ) ||
                ! in_array( $payload['goal'], array( 'unknown', 'clicks', 'form', 'destination_url', 'scroll_depth', 'add_to_cart', 'purchase' ), true ) ||
                ! is_string( $payload['session_ref'] ) ||
                1 !== preg_match( '/^wizard_[a-f0-9]{32}$/D', $payload['session_ref'] )
            ) {
                return $invalid;
            }
        } elseif ( in_array( $event['event_name'], $site_events, true ) ) {
            if ( null !== $event['test_ref'] || ! self::exact_keys( $payload, array( 'evidence' ) ) || 'observed' !== $payload['evidence'] ) {
                return $invalid;
            }
        } else {
            $keys = array( 'kind', 'goal', 'status', 'evidence' );
            if ( 'winner_declared' === $event['event_name'] ) {
                $keys = array_merge( $keys, array( 'winner', 'winner_basis' ) );
            }
            if (
                ! isset( $experiment_states[ $event['event_name'] ] ) ||
                ! is_string( $event['test_ref'] ) ||
                1 !== preg_match( '/^test_[A-Za-z0-9_-]{43}$/D', $event['test_ref'] ) ||
                ! self::exact_keys( $payload, $keys )
            ) {
                return $invalid;
            }
            if (
                ! in_array( $payload['kind'], array( 'page', 'post', 'product', 'reusable_section', 'custom_css', 'custom_html', 'custom_javascript' ), true ) ||
                ! in_array( $payload['goal'], array( 'clicks', 'form', 'destination_url', 'scroll_depth', 'add_to_cart', 'purchase' ), true ) ||
                ! in_array( $payload['status'], $experiment_states[ $event['event_name'] ], true ) ||
                ( 'experiment_baseline' === $event['event_name'] ? 'baseline' : 'observed' ) !== $payload['evidence']
            ) {
                return $invalid;
            }
            if ( 'winner_declared' === $event['event_name'] && ( ! in_array( $payload['winner'], array( 'A', 'B' ), true ) || 'statistical_decision' !== $payload['winner_basis'] ) ) {
                return $invalid;
            }
            if ( in_array( $event['event_name'], array( 'first_order_attributed', 'first_revenue_attributed' ), true ) && 'purchase' !== $payload['goal'] ) {
                return $invalid;
            }
        }

        // Canonical ordering makes replay identity independent of JSON key order.
        ksort( $payload );
        $event['payload'] = $payload;
        ksort( $event );
        $json = wp_json_encode( $event, JSON_UNESCAPED_SLASHES );
        return is_string( $json ) && strlen( $json ) <= self::MAX_BYTES ? $event : $invalid;
    }
}