<?php

namespace App\Utilities;

use Illuminate\Support\Facades\Artisan;
use PDO;
use RuntimeException;
use Throwable;

class SystemDatabaseConfiguration
{
    private string $environmentPath;

    public function __construct(?string $environmentPath = null)
    {
        $this->environmentPath = $environmentPath ?: base_path('.env');
    }

    public function current(): array
    {
        $connectionName = (string) config('database.default', 'mysql');
        $connection = (array) config('database.connections.' . $connectionName, []);
        $options = (array) ($connection['options'] ?? []);

        return [
            'connection' => $connectionName,
            'driver' => (string) ($connection['driver'] ?? $connectionName),
            'host' => (string) (
                data_get($connection, 'write.host.0')
                ?? data_get($connection, 'read.host.0')
                ?? ($connection['host'] ?? '')
            ),
            'port' => (int) ($connection['port'] ?? 3306),
            'database' => (string) ($connection['database'] ?? ''),
            'username' => (string) ($connection['username'] ?? ''),
            'password' => (string) ($connection['password'] ?? ''),
            'prefix' => (string) ($connection['prefix'] ?? ''),
            'tls_required' => isset($options[PDO::MYSQL_ATTR_SSL_CA])
                || isset($options[PDO::MYSQL_ATTR_SSL_CIPHER]),
        ];
    }

    /**
     * @return array{cipher:string,user_count:int,prefix:string}
     */
    public function probe(array $settings): array
    {
        if (($settings['driver'] ?? 'mysql') !== 'mysql') {
            throw new RuntimeException('系统数据库目前只支持 MariaDB/MySQL。');
        }

        $options = [
            PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
            PDO::ATTR_TIMEOUT => 8,
        ];

        if (! empty($settings['tls_required'])) {
            $options[PDO::MYSQL_ATTR_SSL_CIPHER] = 'DEFAULT';

            if (defined('PDO::MYSQL_ATTR_SSL_VERIFY_SERVER_CERT')) {
                $options[constant('PDO::MYSQL_ATTR_SSL_VERIFY_SERVER_CERT')] = false;
            }
        }

        try {
            $pdo = new PDO(
                sprintf(
                    'mysql:host=%s;port=%d;dbname=%s;charset=utf8mb4',
                    $settings['host'],
                    $settings['port'],
                    $settings['database']
                ),
                $settings['username'],
                $settings['password'],
                $options
            );

            $cipher = (string) ($pdo
                ->query("SHOW SESSION STATUS LIKE 'Ssl_cipher'")
                ->fetch(PDO::FETCH_NUM)[1] ?? '');

            if (! empty($settings['tls_required']) && $cipher === '') {
                throw new RuntimeException('数据库连接没有启用 TLS 加密。');
            }

            $tableNames = $pdo->query(
                'SELECT table_name FROM information_schema.tables '
                . 'WHERE table_schema = DATABASE()'
            )->fetchAll(PDO::FETCH_COLUMN);
            $prefix = $this->detectTablePrefix(
                array_map('strval', $tableNames),
                $this->current()['prefix']
            );

            $userCount = (int) $pdo->query(
                'SELECT COUNT(*) FROM `' . str_replace('`', '``', $prefix . 'users') . '`'
            )->fetchColumn();

            if ($userCount < 1) {
                throw new RuntimeException('目标库没有任何用户，已拒绝切换。');
            }

            return ['cipher' => $cipher, 'user_count' => $userCount, 'prefix' => $prefix];
        } catch (RuntimeException $exception) {
            throw $exception;
        } catch (Throwable $exception) {
            throw new RuntimeException('系统数据库连接测试失败。', 0, $exception);
        }
    }

    public function persist(array $settings): string
    {
        if (! is_file($this->environmentPath) || ! is_writable($this->environmentPath)) {
            throw new RuntimeException('服务器私有启动配置不可写，未执行切换。');
        }

        $current = file_get_contents($this->environmentPath);

        if ($current === false) {
            throw new RuntimeException('无法读取服务器私有启动配置。');
        }

        $backupDirectory = storage_path('app/system-database-config-backups');

        if (! is_dir($backupDirectory) && ! mkdir($backupDirectory, 0700, true) && ! is_dir($backupDirectory)) {
            throw new RuntimeException('无法创建系统数据库配置备份目录。');
        }

        $backupPath = $backupDirectory . DIRECTORY_SEPARATOR . 'runtime-env-' . now()->format('Ymd-His') . '.backup';

        if (file_put_contents($backupPath, $current, LOCK_EX) === false) {
            throw new RuntimeException('系统数据库配置备份失败，未执行切换。');
        }

        chmod($backupPath, 0600);

        $prefix = array_key_exists('prefix', $settings)
            ? (string) $settings['prefix']
            : $this->current()['prefix'];
        $this->assertValidPrefix($prefix);

        $updated = $this->replaceEnvironmentValues($current, [
            'DB_CONNECTION' => 'mysql',
            'DB_HOST' => (string) $settings['host'],
            'DB_PORT' => (string) $settings['port'],
            'DB_DATABASE' => (string) $settings['database'],
            'DB_USERNAME' => (string) $settings['username'],
            'DB_PASSWORD' => (string) $settings['password'],
            'DB_PREFIX' => $prefix,
            'MYSQL_ATTR_SSL_CIPHER' => ! empty($settings['tls_required']) ? 'DEFAULT' : '',
            'MYSQL_ATTR_SSL_VERIFY_SERVER_CERT' => 'false',
            // 系统数据库保存后统一读取共享云数据库配置，不再要求开发机
            // 另外维护完整的 DB_<SOURCE>_* 连接参数。
            'UPSTREAM_STORED_CONFIG_ENABLED' => 'true',
            'UPSTREAM_LOCAL_CONFIG_ENABLED' => 'false',
        ]);

        if (file_put_contents($this->environmentPath, $updated, LOCK_EX) === false) {
            file_put_contents($this->environmentPath, $current, LOCK_EX);
            throw new RuntimeException('系统数据库配置保存失败，已恢复原配置。');
        }

        Artisan::call('config:clear');

        return $backupPath;
    }

    /**
     * 根据一组完整的系统必需表自动识别目标库表前缀。
     *
     * @param array<int,string> $tableNames
     */
    public function detectTablePrefix(array $tableNames, string $preferredPrefix = ''): string
    {
        $requiredTables = ['migrations', 'users', 'roles', 'user_roles', 'user_companies', 'settings'];
        $candidates = null;

        foreach ($requiredTables as $requiredTable) {
            $matchingPrefixes = [];

            foreach ($tableNames as $tableName) {
                if ($tableName !== $requiredTable && ! str_ends_with($tableName, '_' . $requiredTable)) {
                    continue;
                }

                $prefix = substr($tableName, 0, strlen($tableName) - strlen($requiredTable));

                try {
                    $this->assertValidPrefix($prefix);
                    $matchingPrefixes[] = $prefix;
                } catch (RuntimeException) {
                    continue;
                }
            }

            $matchingPrefixes = array_values(array_unique($matchingPrefixes));
            $candidates = $candidates === null
                ? $matchingPrefixes
                : array_values(array_intersect($candidates, $matchingPrefixes));
        }

        if ($candidates === null || $candidates === []) {
            throw new RuntimeException('目标库缺少系统必需表，已拒绝切换。');
        }

        if (in_array($preferredPrefix, $candidates, true)) {
            return $preferredPrefix;
        }

        if (count($candidates) !== 1) {
            throw new RuntimeException('目标库存在多套系统表，无法自动确定表前缀。');
        }

        return $candidates[0];
    }

    private function assertValidPrefix(string $prefix): void
    {
        if (strlen($prefix) > 50 || preg_match('/^[A-Za-z0-9_]*$/D', $prefix) !== 1) {
            throw new RuntimeException('目标库系统表前缀不安全，已拒绝切换。');
        }
    }

    private function replaceEnvironmentValues(string $environment, array $values): string
    {
        $lines = preg_split('/\r\n|\r|\n/', $environment) ?: [];

        foreach ($values as $key => $value) {
            $replacement = $key . '=' . $this->encodeEnvironmentValue((string) $value);
            $found = false;

            foreach ($lines as $index => $line) {
                if (preg_match('/^' . preg_quote($key, '/') . '=/', $line) === 1) {
                    $lines[$index] = $replacement;
                    $found = true;
                    break;
                }
            }

            if (! $found) {
                $lines[] = $replacement;
            }
        }

        return rtrim(implode("\n", $lines), "\n") . "\n";
    }

    private function encodeEnvironmentValue(string $value): string
    {
        return '"' . str_replace(
            ['\\', '"', '$', "\r", "\n"],
            ['\\\\', '\\"', '\\$', '', '\\n'],
            $value
        ) . '"';
    }
}