79 lines
2.3 KiB
JavaScript
79 lines
2.3 KiB
JavaScript
// src/brain/context-trimmer.js
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// 上下文裁剪器 — 从前端迁出的核心脑逻辑
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// 职责：基于滑动窗口策略，在 token 预算内裁剪消息历史
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'use strict';
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const CONTEXT_CONFIG = {
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maxTokens: 200000, // 编号登录用户 200k
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maxTokensGuest: 32000, // 访客 32k
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systemPromptReserve: 8000, // 系统提示词预留
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overflowStrategy: 'sliding-window',
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};
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/**
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* 估算文本 token 数
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* CJK 字符约 1.5 字/token，拉丁字符约 4 字/token
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* @param {string} text
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* @returns {number}
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*/
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function estimateTokens(text) {
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if (!text) return 0;
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const s = String(text);
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let cjk = 0, lat = 0;
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for (let i = 0; i < s.length; i++) {
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const c = s.charCodeAt(i);
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if ((c >= 0x4E00 && c <= 0x9FFF) || (c >= 0x3000 && c <= 0x30FF) || (c >= 0xAC00 && c <= 0xD7AF)) {
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cjk++;
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} else {
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lat++;
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}
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}
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return Math.ceil(cjk / 1.5 + lat / 4);
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}
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/**
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* 滑动窗口裁剪消息
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* @param {Array} systemMessages - 系统消息数组 [{role:'system', content:'...'}]
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* @param {Array} messages - 用户/助手消息历史
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* @param {Object} opts
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* @param {boolean} opts.isGuest - 是否为访客
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* @param {number} opts.contextBudget - 模型路由建议的上下文窗口（可覆盖默认值）
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* @returns {{ messages: Array, trimmed: number, totalTokens: number }}
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*/
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function trimMessages(systemMessages, messages, opts = {}) {
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const { isGuest = false, contextBudget = 0 } = opts;
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// 确定 token 上限
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let limit;
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if (contextBudget > 0) {
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limit = contextBudget;
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} else {
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limit = isGuest ? CONTEXT_CONFIG.maxTokensGuest : CONTEXT_CONFIG.maxTokens;
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}
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const sysTokens = systemMessages.reduce((n, m) => n + estimateTokens(m.content), 0);
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const reserve = Math.max(sysTokens, CONTEXT_CONFIG.systemPromptReserve);
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const budget = limit - reserve;
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// 从最新消息向前累加，保留预算内的消息
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const kept = [];
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let used = 0;
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for (let i = messages.length - 1; i >= 0; i--) {
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const t = estimateTokens(messages[i].content);
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if (used + t > budget && kept.length > 0) break;
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kept.unshift(messages[i]);
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used += t;
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}
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const trimmed = messages.length - kept.length;
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return {
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messages: [...systemMessages, ...kept],
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trimmed,
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totalTokens: reserve + used,
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};
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}
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module.exports = { trimMessages, estimateTokens, CONTEXT_CONFIG };
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