server.js

const express = require('express');
const cors = require('cors');
const dotenv = require('dotenv');
const { compareEstimates } = require('./lib/compare');
const { simulateOnFork } = require('./lib/simulate');
const { ethers } = require('ethers'); // 新增

dotenv.config();

const app = express();
app.use(cors());
app.use(express.json({ limit: '1mb' }));

const PORT = process.env.PORT || 4000;
const DEFAULT_FROM = process.env.DEFAULT_FROM;

const CHAIN_CONFIG = [
  {
    name: 'Ethereum',
    chainId: 1,
    nativeSymbol: 'ETH',
    rpcEnvKey: 'MAINNET_RPC',
  },
  {
    name: 'Optimism',
    chainId: 10,
    nativeSymbol: 'ETH',
    rpcEnvKey: 'OPTIMISM_RPC',
  },
  {
    name: 'Arbitrum',
    chainId: 42161,
    nativeSymbol: 'ETH',
    rpcEnvKey: 'ARBITRUM_RPC',
  },
  {
    name: 'Base',
    chainId: 8453,
    nativeSymbol: 'ETH',
    rpcEnvKey: 'BASE_RPC',
  },
  {
    name: 'Polygon',
    chainId: 137,
    nativeSymbol: 'MATIC',
    rpcEnvKey: 'POLYGON_RPC',
  },
];

// 构建启用的链（有 RPC 才会启用）
function buildActiveChains() {
  return CHAIN_CONFIG.map((chain) => {
    const rpcUrl = process.env[chain.rpcEnvKey];
    return rpcUrl
      ? {
          ...chain,
          rpcUrl,
        }
      : null;
  }).filter(Boolean);
}

// 健康检查
app.get('/health', (req, res) => {
  res.json({ ok: true, chains: buildActiveChains().map((c) => c.name) });
});

/**
 * 新增路由：查询单条链的 gas price
 * 示例：
 * http://localhost:4000/gas?chain=ethereum
 */
app.get('/gas', async (req, res) => {
  try {
    const { chain } = req.query;

    if (!chain) {
      return res.status(400).json({ error: '缺少 chain 参数，例如 ?chain=ethereum' });
    }

    const chains = buildActiveChains();
    const target = chains.find(c => c.name.toLowerCase() === chain.toLowerCase());

    if (!target) {
      return res.status(404).json({ error: `链 ${chain} 未配置或不受支持` });
    }

    const provider = new ethers.JsonRpcProvider(target.rpcUrl);
    const gasPrice = await provider.getGasPrice();

    res.json({
      chain: target.name,
      gasPrice: gasPrice.toString(),          // Wei
      gasPriceGwei: ethers.formatUnits(gasPrice, 'gwei'), // Gwei
    });

  } catch (err) {
    res.status(500).json({ error: err.message });
  }
});

/**
 * 比较不同链的 estimateGas
 */
app.post('/estimate', async (req, res) => {
  try {
    const { to, data, value = '0x0', from = DEFAULT_FROM, gasLimit } = req.body || {};
    if (!to || !data) {
      return res.status(400).json({ error: '`to` 和 `data` 为必填字段' });
    }

    const chains = buildActiveChains();
    if (!chains.length) {
      return res.status(400).json({ error: '未配置任何 RPC，请检查 .env' });
    }

    const tx = { to, data, value };
    if (from) tx.from = from;
    if (gasLimit) tx.gasLimit = gasLimit;

    const estimates = await compareEstimates({ tx, chains });
    res.json({ estimates });

  } catch (err) {
    res.status(500).json({ error: err.message });
  }
});

/**
 * 本地 Hardhat fork 模拟
 */
app.post('/simulate', async (req, res) => {
  try {
    const { to, data, value = '0x0', from = DEFAULT_FROM, gasLimit } = req.body || {};
    if (!to || !data) {
      return res.status(400).json({ error: '`to` 和 `data` 为必填字段' });
    }

    const rpcUrl = process.env.HARDHAT_FORK_RPC || 'http://127.0.0.1:8545';
    const tx = { to, data, value };
    if (from) tx.from = from;
    if (gasLimit) tx.gasLimit = gasLimit;

    const result = await simulateOnFork({ tx, rpcUrl });
    res.json(result);

  } catch (err) {
    res.status(500).json({ error: err.message });
  }
});

app.listen(PORT, () => {
  console.log(`🚀 CrossChain Gas Optimizer API running on http://localhost:${PORT}`);
});