<?php
declare(strict_types=1);

require_once __DIR__ . '/config.php';

const VISIT_COUNTER_LIVE_WINDOW_MINUTES = 5;
const VISIT_COUNTER_RETENTION_MONTHS = 13;
const VISIT_COUNTER_TOTAL_KEY = 'lifetime_total';

function visit_counter_timezone(): DateTimeZone
{
    static $timezone = null;
    if ($timezone instanceof DateTimeZone) {
        return $timezone;
    }

    $timezone = new DateTimeZone('Europe/Paris');
    return $timezone;
}

function visit_counter_now(): DateTimeImmutable
{
    return new DateTimeImmutable('now', visit_counter_timezone());
}

function visit_counter_normalize_token(mixed $token): ?string
{
    if (!is_string($token)) {
        return null;
    }

    $normalized = strtolower(trim($token));
    if ($normalized === '') {
        return null;
    }

    return preg_match('/\A[a-f0-9]{48}\z/', $normalized) === 1 ? $normalized : null;
}

function visit_counter_generate_token(): string
{
    return bin2hex(random_bytes(24));
}

function visit_counter_ensure_schema(): void
{
    static $initialized = false;
    if ($initialized) {
        return;
    }

    $pdo = db();
    $pdo->exec(
        'CREATE TABLE IF NOT EXISTS visit_counter_sessions ('
        . ' visit_token CHAR(48) NOT NULL,'
        . ' first_seen_at DATETIME NOT NULL,'
        . ' last_seen_at DATETIME NOT NULL,'
        . ' created_at DATETIME NOT NULL,'
        . ' updated_at DATETIME NOT NULL,'
        . ' PRIMARY KEY (visit_token),'
        . ' KEY idx_last_seen_at (last_seen_at)'
        . ') ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci'
    );

    $pdo->exec(
        'CREATE TABLE IF NOT EXISTS visit_counter_daily ('
        . ' visit_token CHAR(48) NOT NULL,'
        . ' visit_date DATE NOT NULL,'
        . ' created_at DATETIME NOT NULL,'
        . ' PRIMARY KEY (visit_token, visit_date),'
        . ' KEY idx_visit_date (visit_date)'
        . ') ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci'
    );

    $pdo->exec(
        'CREATE TABLE IF NOT EXISTS visit_counter_meta ('
        . ' meta_key VARCHAR(64) NOT NULL,'
        . ' meta_value BIGINT UNSIGNED NOT NULL DEFAULT 0,'
        . ' updated_at DATETIME NOT NULL,'
        . ' PRIMARY KEY (meta_key)'
        . ') ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci'
    );

    $initialized = true;
}

function visit_counter_prune_stale_data(?DateTimeImmutable $now = null): void
{
    static $pruned = false;
    if ($pruned) {
        return;
    }

    visit_counter_ensure_schema();
    $pdo = db();
    $now = $now ?? visit_counter_now();

    $sessionCutoff = $now->modify('-' . VISIT_COUNTER_RETENTION_MONTHS . ' months')->format('Y-m-d H:i:s');
    $dailyCutoff = $now->modify('-' . VISIT_COUNTER_RETENTION_MONTHS . ' months')->format('Y-m-d');

    $deleteDaily = $pdo->prepare('DELETE FROM visit_counter_daily WHERE visit_date < :cutoff');
    $deleteDaily->bindValue(':cutoff', $dailyCutoff);
    $deleteDaily->execute();

    $deleteSessions = $pdo->prepare('DELETE FROM visit_counter_sessions WHERE last_seen_at < :cutoff');
    $deleteSessions->bindValue(':cutoff', $sessionCutoff);
    $deleteSessions->execute();

    $pruned = true;
}

function visit_counter_snapshot(?DateTimeImmutable $now = null): array
{
    visit_counter_ensure_schema();
    visit_counter_prune_stale_data($now);

    $pdo = db();
    $now = $now ?? visit_counter_now();
    $threshold = $now->modify('-' . VISIT_COUNTER_LIVE_WINDOW_MINUTES . ' minutes')->format('Y-m-d H:i:s');
    $today = $now->format('Y-m-d');

    $liveStmt = $pdo->prepare('SELECT COUNT(*) FROM visit_counter_sessions WHERE last_seen_at >= :threshold');
    $liveStmt->bindValue(':threshold', $threshold);
    $liveStmt->execute();
    $live = (int) $liveStmt->fetchColumn();

    $dailyStmt = $pdo->prepare('SELECT COUNT(*) FROM visit_counter_daily WHERE visit_date = :visit_date');
    $dailyStmt->bindValue(':visit_date', $today);
    $dailyStmt->execute();
    $daily = (int) $dailyStmt->fetchColumn();

    $totalStmt = $pdo->prepare('SELECT meta_value FROM visit_counter_meta WHERE meta_key = :meta_key');
    $totalStmt->bindValue(':meta_key', VISIT_COUNTER_TOTAL_KEY);
    $totalStmt->execute();
    $totalValue = $totalStmt->fetchColumn();
    $total = $totalValue === false ? 0 : (int) $totalValue;

    if ($total === 0) {
        $fallbackStmt = $pdo->query('SELECT COUNT(*) FROM visit_counter_sessions');
        $total = (int) $fallbackStmt->fetchColumn();
    }

    return [
        'live' => $live,
        'daily' => $daily,
        'total' => $total,
        'live_window_minutes' => VISIT_COUNTER_LIVE_WINDOW_MINUTES,
        'updated_at' => $now->format(DATE_ATOM),
        'updated_label' => $now->format('H:i:s'),
    ];
}

function visit_counter_increment_total(string $timestamp): void
{
    $stmt = db()->prepare(
        'INSERT INTO visit_counter_meta (meta_key, meta_value, updated_at) VALUES (:meta_key, :meta_value, :updated_at) '
        . 'ON DUPLICATE KEY UPDATE meta_value = meta_value + 1, updated_at = :updated_at_refresh'
    );
    $stmt->bindValue(':meta_key', VISIT_COUNTER_TOTAL_KEY);
    $stmt->bindValue(':meta_value', 1, PDO::PARAM_INT);
    $stmt->bindValue(':updated_at', $timestamp);
    $stmt->bindValue(':updated_at_refresh', $timestamp);
    $stmt->execute();
}

function visit_counter_decrement_total(string $timestamp): void
{
    $stmt = db()->prepare(
        'INSERT INTO visit_counter_meta (meta_key, meta_value, updated_at) VALUES (:meta_key, :meta_value, :updated_at) '
        . 'ON DUPLICATE KEY UPDATE meta_value = CASE WHEN meta_value > 0 THEN meta_value - 1 ELSE 0 END, updated_at = :updated_at_refresh'
    );
    $stmt->bindValue(':meta_key', VISIT_COUNTER_TOTAL_KEY);
    $stmt->bindValue(':meta_value', 0, PDO::PARAM_INT);
    $stmt->bindValue(':updated_at', $timestamp);
    $stmt->bindValue(':updated_at_refresh', $timestamp);
    $stmt->execute();
}

function visit_counter_track(?string $token = null): array
{
    visit_counter_ensure_schema();
    $pdo = db();
    $now = visit_counter_now();
    visit_counter_prune_stale_data($now);

    $visitToken = visit_counter_normalize_token($token) ?? visit_counter_generate_token();
    $timestamp = $now->format('Y-m-d H:i:s');
    $visitDate = $now->format('Y-m-d');

    $pdo->beginTransaction();
    try {
        $insertSession = $pdo->prepare(
            'INSERT IGNORE INTO visit_counter_sessions (visit_token, first_seen_at, last_seen_at, created_at, updated_at) '
            . 'VALUES (:visit_token, :first_seen_at, :last_seen_at, :created_at, :updated_at)'
        );
        $insertSession->bindValue(':visit_token', $visitToken);
        $insertSession->bindValue(':first_seen_at', $timestamp);
        $insertSession->bindValue(':last_seen_at', $timestamp);
        $insertSession->bindValue(':created_at', $timestamp);
        $insertSession->bindValue(':updated_at', $timestamp);
        $insertSession->execute();

        $isNewVisitor = $insertSession->rowCount() === 1;

        if (!$isNewVisitor) {
            $updateSession = $pdo->prepare(
                'UPDATE visit_counter_sessions SET last_seen_at = :last_seen_at, updated_at = :updated_at WHERE visit_token = :visit_token'
            );
            $updateSession->bindValue(':last_seen_at', $timestamp);
            $updateSession->bindValue(':updated_at', $timestamp);
            $updateSession->bindValue(':visit_token', $visitToken);
            $updateSession->execute();
        }

        $insertDaily = $pdo->prepare(
            'INSERT IGNORE INTO visit_counter_daily (visit_token, visit_date, created_at) VALUES (:visit_token, :visit_date, :created_at)'
        );
        $insertDaily->bindValue(':visit_token', $visitToken);
        $insertDaily->bindValue(':visit_date', $visitDate);
        $insertDaily->bindValue(':created_at', $timestamp);
        $insertDaily->execute();

        if ($isNewVisitor) {
            visit_counter_increment_total($timestamp);
        }

        $pdo->commit();
    } catch (Throwable $exception) {
        if ($pdo->inTransaction()) {
            $pdo->rollBack();
        }
        throw $exception;
    }

    return [
        'token' => $visitToken,
        'counts' => visit_counter_snapshot($now),
    ];
}

function visit_counter_forget(?string $token = null): array
{
    visit_counter_ensure_schema();
    $pdo = db();
    $now = visit_counter_now();
    visit_counter_prune_stale_data($now);

    $visitToken = visit_counter_normalize_token($token);
    if ($visitToken === null) {
        return visit_counter_snapshot($now);
    }

    $timestamp = $now->format('Y-m-d H:i:s');

    $pdo->beginTransaction();
    try {
        $deleteDaily = $pdo->prepare('DELETE FROM visit_counter_daily WHERE visit_token = :visit_token');
        $deleteDaily->bindValue(':visit_token', $visitToken);
        $deleteDaily->execute();

        $deleteSession = $pdo->prepare('DELETE FROM visit_counter_sessions WHERE visit_token = :visit_token');
        $deleteSession->bindValue(':visit_token', $visitToken);
        $deleteSession->execute();

        if ($deleteSession->rowCount() > 0) {
            visit_counter_decrement_total($timestamp);
        }

        $pdo->commit();
    } catch (Throwable $exception) {
        if ($pdo->inTransaction()) {
            $pdo->rollBack();
        }
        throw $exception;
    }

    return visit_counter_snapshot($now);
}