<?php
/**
 * LLM Chat API - AI聊天接口（带对话管理）
 * 支持：创建/删除/切换对话，消息历史持久化
 */

require_once('./include/db_info.inc.php');
require_once('./include/setlang.php');
require_once('./include/const.inc.php');

// ---- SSE 辅助函数 ----
function sse_send($event, $data) {
    echo "event: $event\ndata: " . json_encode($data, JSON_UNESCAPED_UNICODE) . "\n\n";
    @ob_flush();
    @flush();
}

function sse_error($msg) {
    sse_send("error", ["message" => $msg]);
}

// ---- 基础校验 ----
if (!isset($OJ_LLM_ENABLED) || !$OJ_LLM_ENABLED) {
    header("Content-Type: application/json; charset=utf-8");
    echo json_encode(["error" => "AI聊天功能未开启"], JSON_UNESCAPED_UNICODE);
    exit;
}

session_start();
if (!isset($_SESSION[$OJ_NAME . '_user_id'])) {
    header("Content-Type: application/json; charset=utf-8");
    echo json_encode(["error" => "请先登录"], JSON_UNESCAPED_UNICODE);
    exit;
}

$user_id = $_SESSION[$OJ_NAME . '_user_id'];

// ---- 自动建表 ----
pdo_query("CREATE TABLE IF NOT EXISTS `llm_chat_session` (
    `session_id` INT AUTO_INCREMENT PRIMARY KEY,
    `user_id` VARCHAR(48) NOT NULL,
    `title` VARCHAR(200) NOT NULL DEFAULT '新对话',
    `create_time` DATETIME NOT NULL,
    `update_time` DATETIME NOT NULL,
    INDEX `idx_user` (`user_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;");

pdo_query("CREATE TABLE IF NOT EXISTS `llm_chat_message` (
    `id` INT AUTO_INCREMENT PRIMARY KEY,
    `session_id` INT NOT NULL,
    `role` VARCHAR(20) NOT NULL,
    `content` TEXT NOT NULL,
    `create_time` DATETIME NOT NULL,
    INDEX `idx_session` (`session_id`),
    INDEX `idx_session_role` (`session_id`, `id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;");

// ---- GET 请求 ----
if ($_SERVER['REQUEST_METHOD'] === 'GET') {
    header("Content-Type: application/json; charset=utf-8");
    $action = isset($_GET['action']) ? $_GET['action'] : '';
    
    if ($action === 'sessions') {
        $sessions = pdo_query(
            "SELECT `session_id`, `title`, `create_time`, `update_time` FROM `llm_chat_session` WHERE `user_id`=? ORDER BY `update_time` DESC",
            $user_id
        );
        echo json_encode(["sessions" => $sessions !== -1 ? $sessions : []], JSON_UNESCAPED_UNICODE);
        
    } elseif ($action === 'messages') {
        $session_id = isset($_GET['session_id']) ? intval($_GET['session_id']) : 0;
        if ($session_id <= 0) { echo json_encode(["error" => "无效的会话ID"]); exit; }
        
        $check = pdo_query("SELECT 1 FROM `llm_chat_session` WHERE `session_id`=? AND `user_id`=?", $session_id, $user_id);
        if (empty($check) || $check === -1) { echo json_encode(["error" => "无权访问"]); exit; }
        
        $messages = pdo_query("SELECT `role`, `content` FROM `llm_chat_message` WHERE `session_id`=? ORDER BY `id` ASC", $session_id);
        echo json_encode(["messages" => $messages !== -1 ? $messages : []], JSON_UNESCAPED_UNICODE);
        
    } elseif ($action === 'last_session') {
        $last = pdo_query("SELECT `session_id` FROM `llm_chat_session` WHERE `user_id`=? ORDER BY `update_time` DESC LIMIT 1", $user_id);
        echo json_encode(["session_id" => (!empty($last) && $last !== -1) ? intval($last[0]['session_id']) : 0], JSON_UNESCAPED_UNICODE);
    }
    exit;
}

// ---- DELETE 请求 ----
if ($_SERVER['REQUEST_METHOD'] === 'DELETE') {
    header("Content-Type: application/json; charset=utf-8");
    $input = json_decode(file_get_contents('php://input'), true);
    $session_id = isset($input['session_id']) ? intval($input['session_id']) : 0;
    if ($session_id <= 0) { echo json_encode(["error" => "无效的会话ID"]); exit; }
    
    $check = pdo_query("SELECT 1 FROM `llm_chat_session` WHERE `session_id`=? AND `user_id`=?", $session_id, $user_id);
    if (empty($check) || $check === -1) { echo json_encode(["error" => "无权删除"]); exit; }
    
    pdo_query("DELETE FROM `llm_chat_message` WHERE `session_id`=?", $session_id);
    pdo_query("DELETE FROM `llm_chat_session` WHERE `session_id`=?", $session_id);
    echo json_encode(["success" => true], JSON_UNESCAPED_UNICODE);
    exit;
}

// ---- POST 请求 ----
$input = json_decode(file_get_contents('php://input'), true);
if (!$input) { header("Content-Type: application/json; charset=utf-8"); echo json_encode(["error" => "无效请求"]); exit; }

$action = isset($input['action']) ? $input['action'] : 'chat';

// 创建新会话
if ($action === 'create_session') {
    header("Content-Type: application/json; charset=utf-8");
    $title = isset($input['title']) ? trim($input['title']) : '新对话';
    $now = date('Y-m-d H:i:s');
    $session_id = pdo_query("INSERT INTO `llm_chat_session` (`user_id`, `title`, `create_time`, `update_time`) VALUES (?, ?, ?, ?)", $user_id, $title, $now, $now);
    echo json_encode(["session_id" => $session_id, "title" => $title], JSON_UNESCAPED_UNICODE);
    exit;
}

// 重命名会话
if ($action === 'rename_session') {
    header("Content-Type: application/json; charset=utf-8");
    $session_id = isset($input['session_id']) ? intval($input['session_id']) : 0;
    $title = isset($input['title']) ? trim($input['title']) : '';
    if ($session_id <= 0 || empty($title)) { echo json_encode(["error" => "参数错误"]); exit; }
    pdo_query("UPDATE `llm_chat_session` SET `title`=? WHERE `session_id`=? AND `user_id`=?", $title, $session_id, $user_id);
    echo json_encode(["success" => true], JSON_UNESCAPED_UNICODE);
    exit;
}

// ---- 聊天（流式SSE） ----
$message = isset($input['message']) ? trim($input['message']) : '';
$session_id = isset($input['session_id']) ? intval($input['session_id']) : 0;

if (empty($message)) { header("Content-Type: application/json; charset=utf-8"); echo json_encode(["error" => "消息不能为空"]); exit; }

// 自动创建会话
if ($session_id <= 0) {
    $now = date('Y-m-d H:i:s');
    $auto_title = mb_substr($message, 0, 20, 'UTF-8');
    if (mb_strlen($message, 'UTF-8') > 20) $auto_title .= '...';
    $session_id = pdo_query("INSERT INTO `llm_chat_session` (`user_id`, `title`, `create_time`, `update_time`) VALUES (?, ?, ?, ?)", $user_id, $auto_title, $now, $now);
}

// 验证归属
$check = pdo_query("SELECT 1 FROM `llm_chat_session` WHERE `session_id`=? AND `user_id`=?", $session_id, $user_id);
if (empty($check) || $check === -1) { header("Content-Type: application/json; charset=utf-8"); echo json_encode(["error" => "无权访问"]); exit; }

// 保存用户消息
$now = date('Y-m-d H:i:s');
pdo_query("INSERT INTO `llm_chat_message` (`session_id`, `role`, `content`, `create_time`) VALUES (?, 'user', ?, ?)", $session_id, $message, $now);
pdo_query("UPDATE `llm_chat_session` SET `update_time`=? WHERE `session_id`=?", $now, $session_id);

// 获取历史（最近10条上下文）
$history = pdo_query("SELECT `role`, `content` FROM `llm_chat_message` WHERE `session_id`=? ORDER BY `id` DESC LIMIT 11", $session_id);
$messages = [];
if ($history !== -1 && !empty($history)) {
    $history = array_reverse($history);
    $recent = array_slice($history, 0, -1);
    $recent = array_slice($recent, -10);
    foreach ($recent as $msg) {
        $messages[] = ['role' => $msg['role'], 'content' => $msg['content']];
    }
}
$messages[] = ['role' => 'user', 'content' => $message];

// ---- SSE 响应头 ----
header("Content-Type: text/event-stream; charset=utf-8");
header("Cache-Control: no-cache");
header("X-Accel-Buffering: no");
if (function_exists('apache_setenv')) @apache_setenv('no-gzip', '1');
@ini_set('zlib.output_compression', 0);
@ini_set('implicit_flush', 1);
while (ob_get_level()) ob_end_flush();

sse_send("session", ["session_id" => $session_id]);

// ---- 系统提示词 ----
$system_prompt = <<<'EOP'
你是一位名叫"MiniMax老师"的AI助教，正在与学生进行日常对话。

你的职责：
1. 用亲切、友好的语气和学生交流
2. 回答学生的各种问题，包括但不限于学习、生活、编程概念等
3. 提供有帮助的信息和建议
4. 使用中文回答

严格禁止的行为：
1. 绝对不要帮助学生解答任何编程题目、算法题、数据结构题等OJ题目
2. 绝对不要提供任何题目的解题思路、代码实现或算法分析
3. 如果学生询问关于具体OJ题目的问题，请礼貌地拒绝并解释你需要自己思考来完成题目
4. 不要帮助学生完成任何看起来像是作业或考试的编程任务

你可以做的事情：
- 解释编程概念和原理（不针对具体题目）
- 讨论学习方法和技巧
- 回答日常生活问题
- 聊天闲谈
- 其他与做题无关的问题
EOP;

$api_url = isset($OJ_LLM_API_URL) ? $OJ_LLM_API_URL : "https://api.minimaxi.com/anthropic/v1/messages";
$api_key = isset($OJ_LLM_API_KEY) ? $OJ_LLM_API_KEY : "";
$model = isset($OJ_LLM_MODEL) ? $OJ_LLM_MODEL : "MiniMax-M2.7";
$max_tokens = isset($OJ_LLM_MAX_TOKENS) ? intval($OJ_LLM_MAX_TOKENS) : 2048;
$timeout = isset($OJ_LLM_TIMEOUT) ? intval($OJ_LLM_TIMEOUT) : 120;

if (empty($api_key)) { sse_error("API Key未配置"); exit; }

$request_body = json_encode([
    "model" => $model, "max_tokens" => $max_tokens, "system" => $system_prompt,
    "temperature" => 0.8, "stream" => true, "messages" => $messages
]);

// ---- 流式转发 ----
$GLOBALS['_llm_alive'] = true;
$GLOBALS['_llm_full_text'] = "";
$GLOBALS['_llm_buffer'] = "";
register_shutdown_function(function() { $GLOBALS['_llm_alive'] = false; });

$ch = curl_init($api_url);
curl_setopt_array($ch, [
    CURLOPT_POST => true, CURLOPT_POSTFIELDS => $request_body,
    CURLOPT_HTTPHEADER => ["Content-Type: application/json", "x-api-key: " . $api_key, "anthropic-version: 2023-06-01"],
    CURLOPT_RETURNTRANSFER => false, CURLOPT_TIMEOUT => $timeout, CURLOPT_CONNECTTIMEOUT => 10,
    CURLOPT_SSL_VERIFYPEER => true,
    CURLOPT_WRITEFUNCTION => function($ch, $chunk) use (&$_llm_alive, &$_llm_full_text, &$_llm_buffer) {
        if (!$_llm_alive) return 0;
        $_llm_buffer .= $chunk;
        while (($pos = strpos($_llm_buffer, "\n")) !== false) {
            $line = substr($_llm_buffer, 0, $pos);
            $_llm_buffer = substr($_llm_buffer, $pos + 1);
            $line = trim($line);
            if (empty($line)) continue;
            if (strncmp($line, "data: ", 6) === 0) {
                $json_str = substr($line, 6);
                if ($json_str === "[DONE]") continue;
                $data = json_decode($json_str, true);
                if (!$data) continue;
                $type = isset($data['type']) ? $data['type'] : '';
                if ($type === 'content_block_delta' && isset($data['delta']['text'])) {
                    $_llm_full_text .= $data['delta']['text'];
                    sse_send("chunk", ["text" => $data['delta']['text']]);
                } elseif ($type === 'message_delta' && isset($data['delta']['stop_reason'])) {
                    if (in_array($data['delta']['stop_reason'], ['end_turn', 'max_tokens'])) {
                        sse_send("done", []);
                        return 0;
                    }
                } elseif (in_array($type, ['message_start', 'ping', 'content_block_start', 'content_block_stop'])) {
                    continue;
                } elseif ($type === 'error') {
                    sse_send("error", ["message" => "API错误: " . (isset($data['error']['message']) ? $data['error']['message'] : '未知')]);
                    return 0;
                }
            }
        }
        return strlen($chunk);
    }
]);

$result = curl_exec($ch);
$http_code = curl_getinfo($ch, CURLINFO_HTTP_CODE);
$curl_error = curl_error($ch);
curl_close($ch);

// 保存AI回复
if (!empty($_llm_full_text)) {
    $save_now = date('Y-m-d H:i:s');
    pdo_query("INSERT INTO `llm_chat_message` (`session_id`, `role`, `content`, `create_time`) VALUES (?, 'assistant', ?, ?)", $session_id, $_llm_full_text, $save_now);
}

if (!$_llm_alive) exit;
if ($result === false && empty($_llm_full_text)) { sse_error("网络请求失败: " . ($curl_error ?: "未知")); exit; }
if (empty($_llm_full_text) && $http_code !== 200) { sse_error("API请求失败 (HTTP $http_code)"); exit; }
if (empty($_llm_full_text)) { sse_error("API返回为空"); exit; }
?>