npx react-native init HealthSyncApp
cd HealthSyncApp

# 安装 WatermelonDB 及依赖
npm install @nozbe/watermelondb @nozbe/nozbe-node
# iOS 平台
cd ios && pod install && cd ..

// 简单的 PN-Counter 实现
class PNCounter {
  constructor(nodeId) {
    this.nodeId = nodeId;
    this.p = { [nodeId]: 0 }; // 正计数
    this.n = { [nodeId]: 0 }; // 负计数（用于"取消服用"一剂）
  }

  // 在此节点上递增计数器
  increment() {
    this.p[this.nodeId]++;
  }

  // 获取计数器的总值
  getValue() {
    const totalP = Object.values(this.p).reduce((sum, val) => sum + val, 0);
    const totalN = Object.values(this.n).reduce((sum, val) => sum + val, 0);
    return totalP - totalN;
  }

  // 与另一个副本的计数器合并
  merge(otherCounter) {
    for (const nodeId in otherCounter.p) {
      this.p[nodeId] = Math.max(this.p[nodeId] || 0, otherCounter.p[nodeId]);
    }
    for (const nodeId in otherCounter.n) {
      this.n[nodeId] = Math.max(this.n[nodeId] || 0, otherCounter.n[nodeId]);
    }
  }
}

// --- 模拟 ---
const patientPhone = new PNCounter('phone');
const caregiverTablet = new PNCounter('tablet');

// 操作并发发生
patientPhone.increment(); // 患者离线服用一剂
caregiverTablet.increment(); // 护理人员在线记录一剂

// 现在，患者的手机恢复在线并同步
patientPhone.merge(caregiverTablet);
caregiverTablet.merge(patientPhone);

console.log(`最终剂量计数: ${patientPhone.getValue()}`); // 输出: 最终剂量计数: 2

// src/db/schema.js
import { appSchema, tableSchema } from '@nozbe/watermelondb';

export default appSchema({
  version: 1,
  tables: [
    tableSchema({
      name: 'patients',
      columns: [
        { name: 'remote_id', type: 'string', isIndexed: true },
        { name: 'name', type: 'string' },
        { name: 'primary_concern', type: 'string', isOptional: true },
        { name: 'last_updated_by_user', type: 'number' },
        // WatermelonDB 同步列
        { name: 'last_modified_at', type: 'number' },
        { name: '_status', type: 'string' },
        { name: '_changed', type: 'string' },
      ],
    }),
  ],
});

// src/db/Patient.js
import { Model } from '@nozbe/watermelondb';
import { field, text } from '@nozbe/watermelondb/decorators';

export default class Patient extends Model {
  static table = 'patients';

  @text('remote_id') remoteId;
  @text('name') name;
  @text('primary_concern') primaryConcern;
  @field('last_updated_by_user') lastUpdatedByUser;
}

// src/sync.js
import { synchronize } from '@nozbe/watermelondb/sync';
import { database } from './db'; // 你的数据库实例

const API_URL = 'https://your-health-app-backend.com';

export async function sync() {
  await synchronize({
    database,
    pullChanges: async ({ lastPulledAt, schemaVersion, migration }) => {
      try {
        const response = await fetch(`${API_URL}/sync/pull`, {
          method: 'POST',
          headers: { 'Content-Type': 'application/json' },
          body: JSON.stringify({ lastPulledAt, schemaVersion, migration }),
        });
        if (!response.ok) {
          throw new Error(await response.text());
        }

        const { changes, timestamp } = await response.json();
        return { changes, timestamp };
      } catch (error) {
        console.error('拉取更改失败:', error);
        throw error;
      }
    },
    pushChanges: async ({ changes, lastPulledAt }) => {
      try {
        const response = await fetch(`${API_URL}/sync/push`, {
          method: 'POST',
          headers: { 'Content-Type': 'application/json' },
          body: JSON.stringify({ changes, lastPulledAt }),
        });
        if (!response.ok) {
          throw new Error(await response.text());
        }
      } catch (error) {
        console.error('推送更改失败:', error);
        throw error;
      }
    },
    // 可选：记录同步进度
    log: {},
  });
}

// server/index.js
const express = require('express');
const bodyParser = require('body-parser');
const app = express();
app.use(bodyParser.json());

// 演示用的内存"数据库"
let patientsDB = {};
let lastSyncTimestamp = Date.now();

// 客户端拉取更改的端点
app.post('/sync/pull', (req, res) => {
  const { lastPulledAt } = req.body;

  const created = Object.values(patientsDB).filter(p => p.created_at > lastPulledAt);
  const updated = Object.values(patientsDB).filter(p => p.updated_at > lastPulledAt && p.created_at <= lastPulledAt);
  // 删除需要单独追踪（例如 `deleted_at` 标志）

  res.json({
    changes: {
      patients: {
        created: [], // 为简化，我们只处理更新
        updated: updated,
        deleted: [],
      },
    },
    timestamp: Date.now(),
  });
});

// 客户端推送本地更改的端点
app.post('/sync/push', (req, res) => {
  const { changes } = req.body;
  const patientChanges = changes.patients;

  if (patientChanges.created) {
    patientChanges.created.forEach(p => {
      const newId = `server_${Math.random()}`;
      patientsDB[newId] = { ...p, id: newId, created_at: Date.now(), updated_at: Date.now() };
    });
  }

  if (patientChanges.updated) {
    patientChanges.updated.forEach(p => {
        if (patientsDB[p.id]) {
            patientsDB[p.id] = { ...patientsDB[p.id], ...p, updated_at: Date.now() };
        }
    });
  }
  
  // 处理删除...

  res.sendStatus(200);
});

app.listen(3000, () => console.log('同步服务器监听端口 3000'));