feat: added compute swap logic

Author: zlace0x

src/lib/market.ts

@@ -0,0 +1,77 @@
+import { Coin, Coins, Dec } from "@terra-money/terra.js"
+
+export function computeSwap(offerCoin: Coin, askDenom: string, rates: Coins, basePool: Dec, minStabilitySpread: Dec, delta: Dec) {
+
+	// get offerCoin in sdr base denom
+	const baseOfferCoin = _computeInternalSwap(offerCoin, 'usdr', rates);
+	if (!baseOfferCoin) {
+		throw new Error(`Invalid base rate (sdr) for ${offerCoin.denom}`);
+	}
+
+	// get ask return amount from baseOfferCoin
+	const retCoin = _computeInternalSwap(baseOfferCoin, askDenom, rates);
+
+	// Skips tobin tax logic for terra <> terra swaps
+
+	// constant-product aka k in k=xy
+	const cp = new Dec(basePool.pow(2));
+
+	const terraPool = basePool.add(delta);
+	const lunaPool = cp.div(terraPool);
+
+	let offerPool: Dec, askPool: Dec;
+
+	if (offerCoin.denom === 'uluna') {
+		// Luna -> Terra swap
+		offerPool = lunaPool
+		askPool = terraPool
+	} else {
+		// Terra -> Luna swap
+		offerPool = terraPool
+		askPool = lunaPool
+	}
+
+	// Get cp(constant-product) based swap amount
+	// askBaseAmount = askPool - cp / (offerPool + offerBaseAmount)
+	// askBaseAmount is base denom(usdr) unit
+	const askBaseAmount = askPool.sub(cp.div(offerPool.plus(baseOfferCoin.amount)))
+
+	// Both baseOffer and baseAsk are usdr units, so spread can be calculated by
+	// spread = (baseOfferAmt - baseAskAmt) / baseOfferAmt
+	const baseOfferAmount = baseOfferCoin.amount;
+	let spread = baseOfferAmount.sub(askBaseAmount).div(baseOfferAmount)
+
+	if (spread.lessThan(minStabilitySpread)) {
+		spread = minStabilitySpread;
+	}
+
+	return [retCoin, spread];
+}
+
+export function coinAfterSpread(coin: Coin, spread: Dec) {
+	return new Coin(coin.denom, coin.amount.minus(coin.amount.times(spread)));
+}
+
+function _computeInternalSwap(offerCoin: Coin, askDenom: string, rates: Coins) {
+	if (offerCoin.denom == askDenom) {
+		return offerCoin;
+	}
+
+	// get rates of offer & ask denoms in uluna.
+	const offerRate = rates.get(offerCoin.denom)?.amount;
+	if (!offerRate) {
+		throw new Error("Invalid offer rate (uluna) for " + offerCoin.denom);
+	}
+	const askRate = askDenom == "uluna" ? new Dec(1) : rates.get(askDenom)?.amount;
+	if (!askRate) {
+		throw new Error("Invalid ask rate (uluna) for " + askDenom);
+	}
+
+	const retAmount = offerCoin.amount.times(askRate).dividedBy(offerRate) ?? new Dec(0)
+
+	if (retAmount.lessThanOrEqualTo(0)) {
+		throw new Error("Invalid return amount");
+	}
+
+	return new Coin(askDenom, retAmount);
+}

src/react-app-env.d.ts

@@ -0,0 +1 @@
+/// <reference types="react-scripts" />

tsconfig.json

@@ -0,0 +1,26 @@
+{
+  "compilerOptions": {
+    "target": "es5",
+    "lib": [
+      "dom",
+      "dom.iterable",
+      "esnext"
+    ],
+    "allowJs": true,
+    "skipLibCheck": true,
+    "esModuleInterop": true,
+    "allowSyntheticDefaultImports": true,
+    "strict": true,
+    "forceConsistentCasingInFileNames": true,
+    "noFallthroughCasesInSwitch": true,
+    "module": "esnext",
+    "moduleResolution": "node",
+    "resolveJsonModule": true,
+    "isolatedModules": true,
+    "noEmit": true,
+    "jsx": "react-jsx"
+  },
+  "include": [
+    "src"
+  ]
+}