<?php

namespace app\common\service;

use think\Env;

/**
 * 本地模型服务：按上下文长度自动选择模型
 *
 * - 短上下文  -> 小模型（显存为大模型一半），对应 base.model_url1
 * - 长上下文  -> 大模型，对应 base.model_url
 *
 * 选择规则：上下文字符数 <= 阈值 用小模型；超过阈值 用大模型。
 * 两个端点模型名相同（base.model）。
 *
 * 用法：
 *   $svc = new LocalModelService();
 *   $res = $svc->chat([
 *       ['role' => 'system', 'content' => '...'],
 *       ['role' => 'user',   'content' => '...'],
 *   ]);
 *   // $res['ok'], $res['content'], $res['tier'](small|large), $res['context_len']
 *
 *   // 只要文本结果：
 *   $text = $svc->complete($systemPrompt, $userPrompt);
 */
class LocalModelService
{
    /** 上下文长度阈值（字符数）：<= 用小模型，> 用大模型 */
    const CONTEXT_THRESHOLD = 3000;

    /** 请求超时（秒） */
    const TIMEOUT = 120;

    /** 小模型端点（短上下文，显存一半） */
    private $smallUrl;

    /** 大模型端点（长上下文） */
    private $largeUrl;

    /** 模型名（两端点相同） */
    private $model;

    /** 上下文长度阈值（字符数） */
    private $threshold;

    public function __construct()
    {
        // 小模型 -> base.model_url1，大模型 -> base.model_url，模型名同为 base.model
        $this->smallUrl = $this->normalizeChatUrl((string)Env::get('base.model_url1', ''));
        $this->largeUrl = $this->normalizeChatUrl((string)Env::get('base.model_url', ''));
        $this->model    = trim((string)Env::get('base.model', ''));
        $this->threshold = self::CONTEXT_THRESHOLD;
    }

    /**
     * 发起一次对话，按上下文长度自动选模型。
     *
     * @param array $messages OpenAI 格式 messages
     * @param array $options  可选：
     *                        - temperature (float, 默认 0.2)
     *                        - max_tokens  (int, 可选)
     *                        - force_tier  ('small'|'large') 强制指定模型，跳过长度判断
     *                        - extra       (array) 透传到请求体的额外字段
     * @return array{ok:bool, content:string, tier:string, model:string, url:string, context_len:int, error:string}
     */
    public function chat(array $messages, array $options = [])
    {
        $contextLen = $this->measureMessages($messages);

        $tier = isset($options['force_tier']) && in_array($options['force_tier'], ['small', 'large'], true)
            ? $options['force_tier']
            : $this->pickTier($contextLen);

        $endpoint = $this->resolveEndpoint($tier);

        $result = [
            'ok'          => false,
            'content'     => '',
            'tier'        => $tier,
            'model'       => $endpoint['model'],
            'url'         => $endpoint['url'],
            'context_len' => $contextLen,
            'error'       => '',
        ];

        if ($endpoint['url'] === '' || $endpoint['model'] === '') {
            $result['error'] = $tier . ' 模型未配置（检查 .env [base] model_url / model_url1 / model）';
            return $result;
        }

        $payload = [
            'model'       => $endpoint['model'],
            'temperature' => isset($options['temperature']) ? (float)$options['temperature'] : 0.2,
            'messages'    => $messages,
        ];
        if (isset($options['max_tokens']) && intval($options['max_tokens']) > 0) {
            $payload['max_tokens'] = intval($options['max_tokens']);
        }
        if (isset($options['extra']) && is_array($options['extra'])) {
            $payload = array_merge($payload, $options['extra']);
        }

        $content = $this->postChat($endpoint['url'], $payload, $err);
        if ($content === null) {
            $result['error'] = $err !== '' ? $err : 'LLM 请求失败';
            return $result;
        }

        $result['ok'] = true;
        $result['content'] = $content;
        return $result;
    }

    /**
     * 便捷方法：传 system + user，返回纯文本内容（失败返回空字符串）。
     */
    public function complete($systemPrompt, $userPrompt, array $options = [])
    {
        $messages = [];
        if (trim((string)$systemPrompt) !== '') {
            $messages[] = ['role' => 'system', 'content' => (string)$systemPrompt];
        }
        $messages[] = ['role' => 'user', 'content' => (string)$userPrompt];

        $res = $this->chat($messages, $options);
        return $res['ok'] ? $res['content'] : '';
    }

    /**
     * 根据上下文长度选择 tier。
     */
    public function pickTier($contextLen)
    {
        return $contextLen > $this->threshold ? 'large' : 'small';
    }

    /**
     * 统计 messages 的上下文长度（所有 content 字符数之和）。
     */
    public function measureMessages(array $messages)
    {
        $len = 0;
        foreach ($messages as $m) {
            if (isset($m['content']) && is_string($m['content'])) {
                $len += mb_strlen($m['content']);
            }
        }
        return $len;
    }

    /**
     * 返回某 tier 的端点配置（模型名两端点相同）。
     */
    private function resolveEndpoint($tier)
    {
        $url = $tier === 'large' ? $this->largeUrl : $this->smallUrl;
        return ['url' => $url, 'model' => $this->model];
    }

    private function postChat($url, array $payload, &$err = '')
    {
        $err = '';
        $ch = curl_init();
        curl_setopt($ch, CURLOPT_URL, $url);
        curl_setopt($ch, CURLOPT_POST, true);
        curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($payload, JSON_UNESCAPED_UNICODE));
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
        curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
        curl_setopt($ch, CURLOPT_CONNECTTIMEOUT, 15);
        curl_setopt($ch, CURLOPT_TIMEOUT, self::TIMEOUT);

        $headers = ['Content-Type: application/json'];
        curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);

        $raw = curl_exec($ch);
        if ($raw === false) {
            $err = 'curl error: ' . curl_error($ch);
            curl_close($ch);
            return null;
        }
        $httpCode = intval(curl_getinfo($ch, CURLINFO_HTTP_CODE));
        curl_close($ch);

        if ($httpCode < 200 || $httpCode >= 300) {
            $err = 'http ' . $httpCode . ': ' . mb_substr((string)$raw, 0, 300);
            return null;
        }

        $data = json_decode($raw, true);
        if (!is_array($data)) {
            $err = 'invalid json response';
            return null;
        }
        if (isset($data['choices'][0]['message']['content'])) {
            return (string)$data['choices'][0]['message']['content'];
        }
        if (isset($data['content'])) {
            return (string)$data['content'];
        }
        $err = 'no content in response: ' . mb_substr((string)$raw, 0, 300);
        return null;
    }

    /**
     * 根地址自动补 /v1/chat/completions。
     */
    private function normalizeChatUrl($url)
    {
        $url = trim((string)$url);
        if ($url === '') {
            return '';
        }
        if (stripos($url, 'chat/completions') !== false) {
            return $url;
        }
        return rtrim($url, '/') . '/v1/chat/completions';
    }
}