<?php

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

class AdGhost_Correlation {

    const WINDOW = 10 * MINUTE_IN_SECONDS;

    const BURST_SESSIONS = 12;

    const SHARED_PROFILE = 5;

    public static function signals() {
        return [

            ['id' => 'f5.session_burst', 'family' => 5, 'tier' => 'server', 'weight' => 55,
             'label' => 'Many sessions from one network in minutes'],
            ['id' => 'f5.identical_profiles', 'family' => 5, 'tier' => 'server', 'weight' => 60,
             'label' => 'Separate networks sharing one identical device profile'],
            ['id' => 'f5.uniform_session_length', 'family' => 5, 'tier' => 'server', 'weight' => 45,
             'label' => 'Sessions all lasting the same length of time'],
            ['id' => 'f5.sequential_paths', 'family' => 5, 'tier' => 'server', 'weight' => 40,
             'label' => 'Pages visited in the same order every time'],
            ['id' => 'f5.coordinated_timing', 'family' => 5, 'tier' => 'server', 'weight' => 50,
             'label' => 'Sessions starting on a machine-regular cadence'],

            ['id' => 'f6.fingerprint_recurrence', 'family' => 6, 'tier' => 'server', 'weight' => 50,
             'label' => 'One device fingerprint returning under many identities',
             'consent' => true],
            ['id' => 'f6.fingerprint_churn', 'family' => 6, 'tier' => 'server', 'weight' => 45,
             'label' => 'Device fingerprint changing on every visit',
             'consent' => true],
            ['id' => 'f6.known_bad_device', 'family' => 6, 'tier' => 'server', 'weight' => 65,
             'label' => 'Device fingerprint previously judged invalid',
             'consent' => true],
        ];
    }

    public static function correlation_enabled() {
        $setting = get_option('adghost_ivt_correlation', null);
        if ($setting !== null && $setting !== '') {
            return (bool) $setting;
        }
        return function_exists('wp_using_ext_object_cache') && wp_using_ext_object_cache();
    }

    public static function fingerprinting_permitted() {
        if (!get_option('adghost_ivt_fingerprinting', false)) {
            return false;
        }

        if (function_exists('wp_has_consent')) {
            return (bool) wp_has_consent('statistics');
        }

        return (bool) apply_filters('adghost_ivt_has_fingerprint_consent', false);
    }

    public static function evaluate($profile = null) {
        $fired = [];

        if (!self::correlation_enabled()) {
            return $fired;
        }

        $bucket = self::record_session($profile);

        if ($bucket['sessions'] >= self::BURST_SESSIONS) {
            $fired[] = 'f5.session_burst';
        }

        if ($bucket['cadence_regular']) {
            $fired[] = 'f5.coordinated_timing';
        }

        if (is_array($profile) && !empty($profile['fingerprint'])) {
            $shared = self::record_profile((string) $profile['fingerprint']);
            if ($shared >= self::SHARED_PROFILE) {
                $fired[] = 'f5.identical_profiles';
            }
        }

        if (self::fingerprinting_permitted() && is_array($profile) && !empty($profile['fingerprint'])) {
            $fired = array_merge($fired, self::evaluate_identity((string) $profile['fingerprint']));
        }

        return array_values(array_unique($fired));
    }

    private static function evaluate_identity($fingerprint) {
        $fired = [];
        $key   = 'adghost_fp_' . md5($fingerprint);
        $seen  = get_transient($key);

        if (is_array($seen)) {
            if (($seen['sessions'] ?? 0) > 20) {
                $fired[] = 'f6.fingerprint_recurrence';
            }
            if (!empty($seen['invalid'])) {
                $fired[] = 'f6.known_bad_device';
            }
            $seen['sessions'] = (int) ($seen['sessions'] ?? 0) + 1;
        } else {
            $seen = ['sessions' => 1, 'invalid' => false];
        }

        set_transient($key, $seen, DAY_IN_SECONDS);

        return $fired;
    }

    private static function record_session($profile) {
        $key    = 'adghost_corr_' . substr(AdGhost_IVT_Session::hash_ip(), 0, 16);
        $bucket = get_transient($key);

        $now = time();
        if (!is_array($bucket)) {
            $bucket = ['sessions' => 0, 'starts' => []];
        }

        $bucket['sessions']++;
        $bucket['starts'][] = $now;
        if (count($bucket['starts']) > 30) {
            $bucket['starts'] = array_slice($bucket['starts'], -30);
        }

        set_transient($key, $bucket, self::WINDOW);

        return [
            'sessions'        => $bucket['sessions'],
            'cadence_regular' => self::cadence_is_regular($bucket['starts']),
        ];
    }

    private static function cadence_is_regular(array $starts) {
        if (count($starts) < 6) {
            return false;
        }

        $gaps = [];
        for ($i = 1; $i < count($starts); $i++) {
            $gaps[] = $starts[$i] - $starts[$i - 1];
        }

        $mean = array_sum($gaps) / count($gaps);
        if ($mean <= 0) {
            return false;
        }

        $variance = 0.0;
        foreach ($gaps as $gap) {
            $variance += ($gap - $mean) ** 2;
        }
        $stddev = sqrt($variance / count($gaps));

        return $stddev < 1.5;
    }

    private static function record_profile($fingerprint) {
        $key   = 'adghost_prof_' . md5($fingerprint);
        $seen  = get_transient($key);
        $ip    = substr(AdGhost_IVT_Session::hash_ip(), 0, 16);

        if (!is_array($seen)) {
            $seen = [];
        }
        if (!in_array($ip, $seen, true)) {
            $seen[] = $ip;
        }
        if (count($seen) > 50) {
            $seen = array_slice($seen, -50);
        }

        set_transient($key, $seen, self::WINDOW);

        return count($seen);
    }
}