Server

Server/src/server.ts

@@ -0,0 +1,122 @@
+import express from 'express'
+
+const app = express()
+const port = 3000
+
+const fee = 0.05 // 0.01 = 1%
+
+function countLiquidity (sharesHeld: number[]): number {
+  return sharesHeld.reduce((acc, val) => acc + val, 0)
+}
+
+function calculateMarginalPrice (team: number, sharesHeld: number[]): number {
+  const liquidity = countLiquidity(sharesHeld)
+  const exps = sharesHeld.map(shares => Math.exp(shares / liquidity))
+  const sumExp = exps.reduce((acc, val) => acc + val, 0)
+  return exps[team] / sumExp
+}
+
+function countBets (userShares: UserShare[]): number[] {
+  return Object.values(userShares.reduce((acc, curr) => {
+    const index = Object.keys(acc).length
+    acc[index] = Object.values(curr).reduce((a: number, b: number) => a + b, 0)
+    return acc
+  }, {}))
+}
+
+function calculateCost (sharesHeld: number[]): number {
+  const liquidity = countLiquidity(sharesHeld)
+  const exps = sharesHeld.map(shares => Math.exp(shares / liquidity))
+  const sumExp = exps.reduce((acc, val) => acc + val, 0)
+  const lnSumExp = Math.log(sumExp)
+  const result = liquidity * lnSumExp
+  if (Number.isNaN(result)) return 0
+  return result
+}
+
+function placeBet (userShares: UserShare[], userId: number, team: number, sharesBought: number): UserShare[] {
+  const initialCost = calculateCost(countBets(userShares))
+
+  if (sharesBought === undefined || sharesBought === null || sharesBought <= 0) {
+    console.log('No shares bought')
+    return userShares
+  }
+
+  sharesBought *= 1 - fee
+
+  if (team === undefined || userShares[team] === undefined) {
+    console.log('Invalid team')
+    return userShares
+  }
+
+  const newUserShares = userShares
+
+  if (newUserShares[team][userId] === undefined) newUserShares[team][userId] = 0
+  newUserShares[team][userId] += sharesBought
+
+  const transactionCost = calculateCost(countBets(userShares)) - initialCost
+
+  if (transactionCost > userBalances[userId]) {
+    console.log('Not enough balance')
+    return userShares
+  }
+
+  userBalances[userId] -= transactionCost
+
+  return newUserShares
+}
+
+interface UserShare { [key: number]: number }
+
+const userBalances: UserShare = { 1: 1000, 2: 1000, 3: 1000, 4: 1000 }
+let userShares: UserShare[] = [{ 0: 1 }, { 0: 1 }]
+
+// app.get('/bets', (_, res) => {
+//   const bets = countBets(userShares)
+//   const odds = bets.map((_, i) => {
+//     return calculateMarginalPrice(i, bets).toFixed(4)
+//   })
+
+//   res.send(JSON.stringify({
+//     bets,
+//     odds
+//   }))
+// })
+
+app.get('/bets', (req, res) => {
+  const userId: number = parseInt(req.query.userId as unknown as string)
+  const team: number = parseInt(req.query.team as unknown as string)
+  const sharesBought: number = parseInt(req.query.sharesBought as unknown as string)
+
+  if (sharesBought === undefined || sharesBought === null || sharesBought <= 0) {
+    res.send('No shares bought')
+  }
+
+  if (team === undefined || userShares[team] === undefined) {
+    res.send('Invalid team')
+    return
+  }
+
+  userShares = placeBet(userShares, userId, team, sharesBought)
+
+  const bets = countBets(userShares)
+  const odds: number[] = bets.map((_, i) => {
+    return calculateMarginalPrice(i, bets).toFixed(4) as unknown as number
+  })
+
+  res.send(JSON.stringify({
+    bets,
+    odds,
+    yourBets: userShares.map((shares, team) => {
+      const userBets = shares[userId] ?? 0
+      return {
+        shares: userBets,
+        winPayout: userBets * 1 / odds[team]
+      }
+    })
+  }))
+})
+
+app.listen(port, () => {
+  console.log(`Server is running on http://localhost:${port}`)
+})