Add liquidation bot example script that uses the SDK

filter-repo/1-included-paths

@@ -4,6 +4,7 @@ docs/
 packages/decimal/
 packages/frontend/
 packages/dev-frontend/
+packages/examples/
 packages/providers/
 packages/subgraph/
 packages/lib/

packages/examples/package.json

@@ -0,0 +1,14 @@
+{
+  "name": "@liquity/examples",
+  "version": "0.0.1",
+  "private": true,
+  "dependencies": {
+    "@liquity/lib-base": "^0.0.1",
+    "@liquity/lib-ethers": "^0.0.1",
+    "chalk": "^4.1.0",
+    "ethers": "^5.0.0"
+  },
+  "scripts": {
+    "liqbot": "node src/liqbot.js"
+  }
+}

packages/examples/src/liqbot.js

@@ -0,0 +1,144 @@
+const { red, blue, green, yellow, dim, bold } = require("chalk");
+
+const { JsonRpcProvider } = require("@ethersproject/providers");
+const { Wallet } = require("@ethersproject/wallet");
+
+const { Decimal, Trove, LUSD_LIQUIDATION_RESERVE } = require("@liquity/lib-base");
+const { EthersLiquity, EthersLiquityWithStore } = require("@liquity/lib-ethers");
+
+function log(message) {
+  console.log(`${dim(`[${new Date().toLocaleTimeString()}]`)} ${message}`);
+}
+
+const info = message => log(`${blue("ℹ")} ${message}`);
+const warn = message => log(`${yellow("‼")} ${message}`);
+const error = message => log(`${red("✖")} ${message}`);
+const success = message => log(`${green("✔")} ${message}`);
+
+async function main() {
+  // Replace URL if not using a local node
+  const provider = new JsonRpcProvider("http://localhost:8545");
+  const wallet = new Wallet(process.env.PRIVATE_KEY).connect(provider);
+  const liquity = await EthersLiquity.connect(wallet, { useStore: "blockPolled" });
+
+  liquity.store.onLoaded = () => {
+    info("Waiting for price drops...");
+    tryToLiquidate(liquity);
+  };
+
+  liquity.store.subscribe(({ newState, oldState }) => {
+    // Try to liquidate whenever the price drops
+    if (newState.price.lt(oldState.price)) {
+      tryToLiquidate(liquity);
+    }
+  });
+
+  liquity.store.start();
+}
+
+/**
+ * @param {Decimal} [price]
+ * @returns {(trove: [string, Trove]) => boolean}
+ */
+const underCollateralized = price => ([, trove]) => trove.collateralRatioIsBelowMinimum(price);
+
+/**
+ * @param {[string, Trove]}
+ * @param {[string, Trove]}
+ */
+const byDescendingCollateral = ([, { collateral: a }], [, { collateral: b }]) =>
+  b.gt(a) ? 1 : b.lt(a) ? -1 : 0;
+
+/**
+ * @param {[string[], Trove[]]}
+ * @param {[string, Trove]}
+ * @returns {[string[], Trove[]]}
+ */
+const unzip = ([addresses, troves], [address, trove]) => [
+  addresses.concat(address),
+  troves.concat(trove)
+];
+
+/**
+ * @param {EthersLiquityWithStore} [liquity]
+ */
+async function tryToLiquidate(liquity) {
+  const { store } = liquity;
+
+  const [gasPrice, riskiestTroves] = await Promise.all([
+    liquity.connection.provider
+      .getGasPrice()
+      .then(bn => Decimal.fromBigNumberString(bn.toHexString())),
+
+    liquity.getTroves({
+      first: 1000,
+      sortedBy: "ascendingCollateralRatio"
+    })
+  ]);
+
+  const [addresses, troves] = riskiestTroves
+    .filter(underCollateralized(store.state.price))
+    .sort(byDescendingCollateral)
+    .slice(0, 40)
+    .reduce(unzip, [[], []]);
+
+  if (troves.length === 0) {
+    // Nothing to liquidate
+    return;
+  }
+
+  try {
+    const liquidation = await liquity.populate.liquidate(addresses, { gasPrice: gasPrice.hex });
+    const gasLimit = liquidation.rawPopulatedTransaction.gasLimit.toNumber();
+    const expectedCost = gasPrice.mul(gasLimit).mul(store.state.price);
+
+    const total = troves.reduce((a, b) => a.add(b));
+    const expectedCompensation = total.collateral
+      .mul(0.005)
+      .mul(store.state.price)
+      .add(LUSD_LIQUIDATION_RESERVE.mul(troves.length));
+
+    if (expectedCost.gt(expectedCompensation)) {
+      // In reality, the TX cost will be lower than this thanks to storage refunds, but let's be
+      // on the safe side.
+      warn(
+        "Skipping liquidation due to high TX cost " +
+          `($${expectedCost.toString(2)} > $${expectedCompensation.toString(2)}).`
+      );
+      return;
+    }
+
+    info(`Attempting to liquidate ${troves.length} Trove(s)...`);
+
+    const tx = await liquidation.send();
+    const receipt = await tx.waitForReceipt();
+
+    if (receipt.status === "failed") {
+      error(`TX ${receipt.rawReceipt.transactionHash} failed.`);
+      return;
+    }
+
+    const { collateralGasCompensation, lusdGasCompensation, liquidatedAddresses } = receipt.details;
+    const gasCost = gasPrice.mul(receipt.rawReceipt.gasUsed.toNumber()).mul(store.state.price);
+    const totalCompensation = collateralGasCompensation
+      .mul(store.state.price)
+      .add(lusdGasCompensation);
+
+    success(
+      `Received ${bold(`${collateralGasCompensation.toString(4)} ETH`)} + ` +
+        `${bold(`${lusdGasCompensation.toString(2)} LUSD`)} compensation (` +
+        (totalCompensation.gte(gasCost)
+          ? `${green(`$${totalCompensation.sub(gasCost).toString(2)}`)} profit`
+          : `${red(`$${gasCost.sub(totalCompensation).toString(2)}`)} loss`) +
+        `) for liquidating ${liquidatedAddresses.length} Trove(s).`
+    );
+  } catch (err) {
+    error("Unexpected error:");
+    console.error(err);
+  }
+}
+
+main().catch(err => {
+  console.error(err);
+  process.exit(1);
+});