How to use the @makerdao/dai.PETH function in @makerdao/dai

log.action('opening CDP...');
    const cdp = await maker.openCdp();
    const id = await cdp.id;
    log.state(`CDP ID: ${id}`);

    // calculate a collateralization ratio that will achieve the given price floor
    const collatRatio = priceEth * liquidationRatio / priceFloor;
    log.state(`Target ratio: ${collatRatio}`);

    // lock up all of our principal
    await cdp.lockEth(principal);
    log.action(`locked ${principal} ETH`);

    //get initial peth collateral
    const initialPethCollateral = await cdp.getCollateralValue(Maker.PETH);
    log.state(`${principal} ETH is worth ${initialPethCollateral}`);

    // calculate how much Dai we need to draw in order
    // to achieve the desired collateralization ratio
    let drawAmt = Math.floor(principal * priceEth / collatRatio);
    const drawTx = cdp.drawDai(drawAmt);
    await maker.service('transactionManager').confirm(drawTx);
    log.action(`drew ${drawAmt} Dai`);

    // do `iterations` round trip(s) to the exchange
    for (let i = 0; i < iterations; i++) {
      // exchange the drawn Dai for W-ETH
      let tx = await maker.service('exchange').sellDai(drawAmt, Maker.WETH);

      // observe the amount of W-ETH received from the exchange
      // by calling `fillAmount` on the returned transaction object

log.action(`exchanged ${drawAmt} Dai for ${returnedWeth}`);

      // lock all of the W-ETH we just received into our CDP
      await cdp.lockWeth(returnedWeth);
      log.action(`locked ${returnedWeth}`);

      // calculate how much Dai we need to draw in order to
      // re-attain our desired collateralization ratio
      drawAmt = Math.floor(returnedWeth.toNumber() * priceEth / collatRatio);
      await cdp.drawDai(drawAmt);
      log.action(`drew ${drawAmt} Dai`);
    }

    // get the final state of our CDP
    const [pethCollateral, debt] = await Promise.all([
      cdp.getCollateralValue(Maker.PETH),
      cdp.getDebtValue()
    ]);

    const cdpState = {
      initialPethCollateral,
      pethCollateral,
      debt,
      id,
      principal,
      iterations,
      priceFloor,
      finalDai: drawAmt
    };

    log.state(`Created CDP: ${JSON.stringify(cdpState)}`);
    return cdpState;

async getCdp(id) {
      this.cdp = await this.maker.getCdp(id);
      this.liqPrice = await this.cdp.getLiquidationPrice();
      this.isSafe = await this.cdp.isSafe();
      this.debtValue = (await this.cdp.getDebtValue()).toBigNumber();
      this.collatRatio = await this.cdp.getCollateralizationRatio();
      this.ethCollateral = (await this.cdp.getCollateralValue()).toBigNumber();
      this.pethCollateral = (await this.cdp.getCollateralValue(
        Maker.PETH
      )).toBigNumber();
      this.usdCollateral = (await this.cdp.getCollateralValue(
        Maker.USD
      )).toBigNumber();
      this.maxEthDraw = bnOver(
        this.liquidationRatio,
        this.usdCollateral,
        this.ethPrice
      ).toString();
      this.maxPethDraw = bnOver(
        this.pethPrice,
        this.pethCollateral,
        this.liquidationRatio
      ).toString();
      this.maxDaiDraw = bnOver(
        this.ethPrice,

this._proxyAddress = await this.services.getProxy();
    this.noProxy = this._proxyAddress === null;
    if (this._proxyAddress) {
      this.cdp = await this.services.getCdp(cdpId, this._proxyAddress);
    } else {
      this.cdp = await this.services.getCdp(cdpId, false);
    }

    const liqPrice = await this.cdp.getLiquidationPrice();
    this._liqPrice = liqPrice.toBigNumber().toFixed(2);
    this.isSafe = await this.cdp.isSafe();
    this.debtValue = (await this.cdp.getDebtValue()).toBigNumber();
    this._collatRatio = await this.cdp.getCollateralizationRatio();
    this.ethCollateral = (await this.cdp.getCollateralValue()).toBigNumber();
    this.pethCollateral = (
      await this.cdp.getCollateralValue(Maker.PETH)
    ).toBigNumber();
    this._usdCollateral = (
      await this.cdp.getCollateralValue(Maker.USD)
    ).toBigNumber();
  }

}
    this._proxyAddress = await this.services.getProxy();
    this.noProxy = this._proxyAddress === null;
    if (this._proxyAddress) {
      this.cdp = await this.services.getCdp(cdpId, this._proxyAddress);
    } else {
      this.cdp = await this.services.getCdp(cdpId, false);
    }
    const liqPrice = await this.cdp.getLiquidationPrice();
    this._liqPrice = liqPrice.toBigNumber().toFixed(2);
    this.isSafe = await this.cdp.isSafe();
    this.debtValue = (await this.cdp.getDebtValue()).toBigNumber();
    this._collatRatio = await this.cdp.getCollateralizationRatio();
    this.ethCollateral = (await this.cdp.getCollateralValue()).toBigNumber();
    this.pethCollateral = (
      await this.cdp.getCollateralValue(Maker.PETH)
    ).toBigNumber();
    this._usdCollateral = (
      await this.cdp.getCollateralValue(Maker.USD)
    ).toBigNumber();
  }