<?php

/**
 * Health Check Endpoint
 *
 * Returns system health status for monitoring tools.
 * Does not require authentication - suitable for load balancer health checks.
 *
 * Returns:
 * - 200 OK: System is healthy
 * - 503 Service Unavailable: System has issues
 */

// Don't apply rate limiting to health checks - they should always respond
header('Content-Type: application/json');
header('Cache-Control: no-cache, no-store, must-revalidate');

$startTime = microtime(true);
$checks = [];
$healthy = true;

// Check 1: Database connectivity
try {
    require_once dirname(__DIR__) . '/config/config.php';
    require_once dirname(__DIR__) . '/helpers/Database.php';

    $conn = Database::getConnection();

    // Quick query to verify connection is actually working
    $result = $conn->query('SELECT 1');
    if ($result && $result->fetch_row()) {
        $checks['database'] = [
            'status' => 'ok',
            'message' => 'Connected'
        ];
    } else {
        $checks['database'] = [
            'status' => 'error',
            'message' => 'Query failed'
        ];
        $healthy = false;
    }
} catch (Exception $e) {
    $checks['database'] = [
        'status' => 'error',
        'message' => 'Connection failed'
    ];
    $healthy = false;
}

// Check 2: File system (uploads directory writable)
$uploadDir = $GLOBALS['config']['UPLOAD_DIR'] ?? dirname(__DIR__) . '/uploads';
if (is_dir($uploadDir) && is_writable($uploadDir)) {
    $checks['filesystem'] = [
        'status' => 'ok',
        'message' => 'Writable'
    ];
} else {
    $checks['filesystem'] = [
        'status' => 'warning',
        'message' => 'Upload directory not writable'
    ];
    // Don't mark as unhealthy - this might be intentional
}

// Check 3: Session storage
$sessionPath = session_save_path() ?: sys_get_temp_dir();
if (is_dir($sessionPath) && is_writable($sessionPath)) {
    $checks['sessions'] = [
        'status' => 'ok',
        'message' => 'Writable'
    ];
} else {
    $checks['sessions'] = [
        'status' => 'error',
        'message' => 'Session storage not writable'
    ];
    $healthy = false;
}

// Check 4: Rate limit storage
$rateLimitDir = sys_get_temp_dir() . '/tinker_tickets_ratelimit';
if (!is_dir($rateLimitDir)) {
    @mkdir($rateLimitDir, 0755, true);
}
if (is_dir($rateLimitDir) && is_writable($rateLimitDir)) {
    $checks['rate_limit'] = [
        'status' => 'ok',
        'message' => 'Writable'
    ];
} else {
    $checks['rate_limit'] = [
        'status' => 'warning',
        'message' => 'Rate limit storage not writable'
    ];
}

// Check 5: Required PHP extensions (catches e.g. a PHP upgrade silently
// dropping php-ldap, which breaks avatars with no other visible error).
$requirements = require dirname(__DIR__) . '/config/requirements.php';
$missingExt = array_values(array_filter(
    $requirements['required_extensions'],
    fn($ext) => !extension_loaded($ext)
));
if (empty($missingExt)) {
    $checks['php_extensions'] = [
        'status' => 'ok',
        'message' => 'All required extensions loaded'
    ];
} else {
    $checks['php_extensions'] = [
        'status' => 'error',
        'message' => 'Missing extensions: ' . implode(', ', $missingExt)
    ];
    $healthy = false;
}

// Check 6: PHP version meets the declared minimum
if (version_compare(PHP_VERSION, $requirements['min_php_version'], '>=')) {
    $checks['php_version'] = [
        'status' => 'ok',
        'message' => PHP_VERSION
    ];
} else {
    $checks['php_version'] = [
        'status' => 'error',
        'message' => sprintf('PHP %s < required %s', PHP_VERSION, $requirements['min_php_version'])
    ];
    $healthy = false;
}

// Check 7: memory_limit / max_execution_time sanity (warnings, not fatal — a
// low default doesn't fail requests until something large actually runs, so
// surface it here rather than waiting for a mysterious failure under load).
$memLimitIni = ini_get('memory_limit');
$memLimitUnit = strtolower(substr(trim($memLimitIni), -1));
$memLimitBytes = $memLimitIni === '-1'
    ? -1
    : (int)$memLimitIni * match ($memLimitUnit) {
        'g' => 1024 * 1024 * 1024,
        'm' => 1024 * 1024,
        'k' => 1024,
        default => 1,
    };
$minMemBytes = $requirements['min_memory_limit_mb'] * 1024 * 1024;
if ($memLimitBytes === -1 || $memLimitBytes >= $minMemBytes) {
    $checks['memory_limit'] = ['status' => 'ok', 'message' => $memLimitIni];
} else {
    $checks['memory_limit'] = [
        'status' => 'warning',
        'message' => sprintf('%s is below the recommended minimum %dM', $memLimitIni, $requirements['min_memory_limit_mb'])
    ];
}

$maxExecTime = (int)ini_get('max_execution_time');
if ($maxExecTime === 0 || $maxExecTime >= $requirements['min_max_execution_time']) {
    $checks['max_execution_time'] = ['status' => 'ok', 'message' => (string)$maxExecTime];
} else {
    $checks['max_execution_time'] = [
        'status' => 'warning',
        'message' => sprintf('%ds is below the recommended minimum %ds', $maxExecTime, $requirements['min_max_execution_time'])
    ];
}

// Calculate response time
$responseTime = round((microtime(true) - $startTime) * 1000, 2);

// Set status code
http_response_code($healthy ? 200 : 503);

// This endpoint is unauthenticated, so expose only a coarse per-component status
// and never the diagnostic messages (they leak PHP_VERSION, exact missing
// extension names, and filesystem paths to anonymous callers).
$publicChecks = [];
foreach ($checks as $name => $check) {
    $publicChecks[$name] = ['status' => $check['status']];
}

// Return response
echo json_encode([
    'status' => $healthy ? 'healthy' : 'unhealthy',
    'timestamp' => date('c'),
    'response_time_ms' => $responseTime,
    'checks' => $publicChecks,
    'version' => '1.0.0'
], JSON_PRETTY_PRINT);