sell bet

functions/src/index.ts

@@ -5,3 +5,4 @@ admin.initializeApp()
 export * from './keep-awake'
 export * from './place-bet'
 export * from './resolve-market'
+export * from './sell-bet'

functions/src/sell-bet.ts

@@ -0,0 +1,150 @@
+import * as admin from 'firebase-admin'
+import * as functions from 'firebase-functions'
+
+import { CREATOR_FEE, PLATFORM_FEE } from './resolve-market'
+import { Bet } from './types/bet'
+import { Contract } from './types/contract'
+import { User } from './types/user'
+
+export const sellBet = functions.runWith({ minInstances: 1 }).https.onCall(
+  async (
+    data: {
+      contractId: string
+      betId: string
+    },
+    context
+  ) => {
+    const userId = context?.auth?.uid
+    if (!userId) return { status: 'error', message: 'Not authorized' }
+
+    const { contractId, betId } = data
+
+    // run as transaction to prevent race conditions
+    return await firestore.runTransaction(async (transaction) => {
+      const userDoc = firestore.doc(`users/${userId}`)
+      const userSnap = await transaction.get(userDoc)
+      if (!userSnap.exists)
+        return { status: 'error', message: 'User not found' }
+      const user = userSnap.data() as User
+
+      const contractDoc = firestore.doc(`contracts/${contractId}`)
+      const contractSnap = await transaction.get(contractDoc)
+      if (!contractSnap.exists)
+        return { status: 'error', message: 'Invalid contract' }
+      const contract = contractSnap.data() as Contract
+
+      const betDoc = firestore.doc(`contracts/${contractId}/bets/${betId}`)
+      const betSnap = await transaction.get(betDoc)
+      if (!betSnap.exists)
+        return { status: 'error', message: 'Invalid bet' }
+      const bet = betSnap.data() as Bet
+
+      if (bet.isSold)
+        return { status: 'error', message: 'Bet already sold' }
+
+      const newBetDoc = firestore
+        .collection(`contracts/${contractId}/bets`)
+        .doc()
+
+      const { newBet, newPool, newDpmWeights, newBalance, creatorFee } = getSellBetInfo(
+        user,
+        bet,
+        contract,
+        newBetDoc.id
+      )
+
+      const creatorDoc = firestore.doc(`users/${contract.creatorId}`)
+      const creatorSnap = await transaction.get(creatorDoc)
+      if (creatorSnap.exists) {
+        const creator = creatorSnap.data() as User
+        const creatorNewBalance = creator.balance + creatorFee
+        transaction.update(creatorDoc, { balance: creatorNewBalance })
+      }
+
+      transaction.update(betDoc, { isSold: true })
+      transaction.create(newBetDoc, newBet)
+      transaction.update(contractDoc, {
+        pool: newPool,
+        dpmWeights: newDpmWeights,
+      })
+      transaction.update(userDoc, { balance: newBalance })
+
+      return { status: 'success' }
+    })
+  }
+)
+
+const firestore = admin.firestore()
+
+const getSellBetInfo = (
+  user: User,
+  bet: Bet,
+  contract: Contract,
+  newBetId: string
+) => {
+  const { id: betId, amount, dpmWeight, outcome } = bet
+
+  const { YES: yesPool, NO: noPool } = contract.pool
+  const { YES: yesWeights, NO: noWeights } = contract.dpmWeights
+
+  // average implied probability after selling bet position
+  const p = outcome === 'YES'
+    ? (amount +
+      noPool * Math.atan((yesPool - amount) / noPool) -
+      noPool * Math.atan(yesPool / noPool)) /
+    amount
+
+    : yesPool * (Math.atan((amount - noPool) / yesPool) + Math.atan(noPool / yesPool)) /
+    amount
+
+
+  const [sellYesAmount, sellNoAmount] = outcome === 'YES'
+    ? [
+      p * amount,
+      p * dpmWeight / yesWeights * noPool,
+    ]
+    : [
+      p * dpmWeight / noWeights * yesPool,
+      p * amount,
+    ]
+
+  const newPool = { YES: yesPool - sellYesAmount, NO: noPool - sellNoAmount }
+
+  const newDpmWeights =
+    outcome === 'YES'
+      ? { YES: yesWeights - dpmWeight, NO: noWeights }
+      : { YES: yesWeights, NO: noWeights - dpmWeight }
+
+  const probBefore = yesPool ** 2 / (yesPool ** 2 + noPool ** 2)
+  const probAverage = p
+  const probAfter = newPool.YES ** 2 / (newPool.YES ** 2 + newPool.NO ** 2)
+
+  const keep = 1 - CREATOR_FEE - PLATFORM_FEE
+
+  const [saleAmount, creatorFee] = outcome === 'YES'
+    ? [{ YES: sellYesAmount, NO: keep * sellNoAmount }, CREATOR_FEE * sellNoAmount]
+    : [{ YES: keep * sellYesAmount, NO: sellNoAmount }, CREATOR_FEE * sellYesAmount]
+
+  console.log('SELL M$', amount, outcome, 'at', p, 'prob', 'for M$', saleAmount.YES + saleAmount.NO, 'creator fee: M$', creatorFee)
+
+  const newBet: Bet = {
+    id: newBetId,
+    userId: user.id,
+    contractId: contract.id,
+    amount: -amount,
+    dpmWeight: -dpmWeight,
+    outcome,
+    probBefore,
+    probAverage,
+    probAfter,
+    createdTime: Date.now(),
+    sale: {
+      amount: saleAmount,
+      betId
+    }
+  }
+
+  const newBalance = user.balance + sellYesAmount + sellNoAmount
+
+  return { newBet, newPool, newDpmWeights, newBalance, creatorFee }
+}

functions/src/types/bet.ts

@@ -2,11 +2,21 @@ export type Bet = {
   id: string
   userId: string
   contractId: string
-  amount: number // Amount of bet
-  outcome: 'YES' | 'NO' // Chosen outcome
-  createdTime: number
+
+  amount: number // bet size; negative if SELL bet
+  outcome: 'YES' | 'NO'
+  dpmWeight: number // dynamic parimutuel pool weight; negative if SELL bet
+
   probBefore: number
   probAverage: number
   probAfter: number
-  dpmWeight: number // Dynamic Parimutuel weight
+
+  sale?: {
+    amount: { YES: number, NO: number } // amount user makes from YES and NO pools from sale
+    betId: string // id of bet being sold
+  }
+  
+  isSold?: boolean // true if this BUY bet has been sold 
+
+  createdTime: number
 }

web/components/bets-list.tsx

@@ -17,6 +17,7 @@ import {
   resolvedPayout,
 } from '../lib/calculation/contract'
 import clsx from 'clsx'
+import { cloudFunction } from '../lib/firebase/api-call'
 
 export function BetsList(props: { user: User }) {
   const { user } = props
@@ -240,6 +241,7 @@ export function ContractBetsTable(props: {
             <th>Probability</th>
             {!isResolved && <th>Est. max payout</th>}
             <th>{isResolved ? <>Payout</> : <>Current value</>}</th>
+            {!isResolved && <th></th>}
           </tr>
         </thead>
         <tbody>
@@ -254,7 +256,7 @@ export function ContractBetsTable(props: {
 
 function BetRow(props: { bet: Bet; contract: Contract }) {
   const { bet, contract } = props
-  const { amount, outcome, createdTime, probBefore, probAfter, dpmWeight } = bet
+  const { amount, outcome, createdTime, probBefore, probAfter, dpmWeight, sale, isSold } = bet
   const { isResolved } = contract
 
   return (
@@ -275,10 +277,21 @@ function BetRow(props: { bet: Bet; contract: Contract }) {
             : currentValue(contract, bet)
         )}
       </td>
+
+      {!isResolved && !sale && !isSold &&
+        <td>
+          <button className='btn' onClick={async e => {
+            e.preventDefault()
+            await sellBet({ contractId: contract.id, betId: bet.id })
+          }}>Sell</button>
+        </td>
+      }
     </tr>
   )
 }
 
+const sellBet = cloudFunction('sellBet')
+
 function OutcomeLabel(props: { outcome: 'YES' | 'NO' | 'CANCEL' }) {
   const { outcome } = props
 

web/lib/firebase/api-call.ts

@@ -0,0 +1,6 @@
+import { getFunctions, httpsCallable } from 'firebase/functions'
+
+const functions = getFunctions()
+
+export const cloudFunction = (name: string) => httpsCallable(functions, name)
+

web/lib/firebase/bets.ts

@@ -11,12 +11,22 @@ export type Bet = {
   id: string
   userId: string
   contractId: string
-  amount: number // Amount of bet
-  outcome: 'YES' | 'NO' // Chosen outcome
-  dpmWeight: number // Dynamic Parimutuel weight
+
+  amount: number // bet size; negative if SELL bet
+  outcome: 'YES' | 'NO'
+  dpmWeight: number // dynamic parimutuel pool weight; negative if SELL bet
+
   probBefore: number
   probAverage: number
   probAfter: number
+
+  sale?: {
+    amount: { YES: number, NO: number } // amount user makes from YES and NO pools from sale
+    betId: string // id of bet being sold
+  }
+  
+  isSold?: boolean // true if this BUY bet has been sold 
+
   createdTime: number
 }
 

web/lib/util/format.ts

@@ -6,11 +6,11 @@ const formatter = new Intl.NumberFormat('en-US', {
 })
 
 export function formatMoney(amount: number) {
-  return 'M$ ' + formatter.format(amount).substring(1)
+  return 'M$ ' + formatter.format(amount).replace('$', '')
 }
 
 export function formatWithCommas(amount: number) {
-  return formatter.format(amount).substring(1)
+  return formatter.format(amount).replace('$', '')
 }
 
 export function formatPercent(zeroToOne: number) {