Loan backend: Add loanAmount field to Bet, manage loans up to max loan amount per market -- buy, sell, and resolve.

common/bet.ts

@@ -4,6 +4,7 @@ export type Bet = {
   contractId: string
 
   amount: number // bet size; negative if SELL bet
+  loanAmount?: number
   outcome: string
   shares: number // dynamic parimutuel pool weight; negative if SELL bet
 
@@ -21,3 +22,5 @@ export type Bet = {
 
   createdTime: number
 }
+
+export const MAX_LOAN_PER_CONTRACT = 20

common/new-bet.ts

@@ -1,4 +1,5 @@
-import { Bet } from './bet'
+import * as _ from 'lodash'
+import { Bet, MAX_LOAN_PER_CONTRACT } from './bet'
 import {
   calculateShares,
   getProbability,
@@ -11,6 +12,7 @@ export const getNewBinaryBetInfo = (
   user: User,
   outcome: 'YES' | 'NO',
   amount: number,
+  loanAmount: number,
   contract: Contract,
   newBetId: string
 ) => {
@@ -45,6 +47,7 @@ export const getNewBinaryBetInfo = (
     userId: user.id,
     contractId: contract.id,
     amount,
+    loanAmount,
     shares,
     outcome,
     probBefore,
@@ -52,7 +55,7 @@ export const getNewBinaryBetInfo = (
     createdTime: Date.now(),
   }
 
-  const newBalance = user.balance - amount
+  const newBalance = user.balance - (amount - loanAmount)
 
   return { newBet, newPool, newTotalShares, newTotalBets, newBalance }
 }
@@ -61,6 +64,7 @@ export const getNewMultiBetInfo = (
   user: User,
   outcome: string,
   amount: number,
+  loanAmount: number,
   contract: Contract,
   newBetId: string
 ) => {
@@ -85,6 +89,7 @@ export const getNewMultiBetInfo = (
     userId: user.id,
     contractId: contract.id,
     amount,
+    loanAmount,
     shares,
     outcome,
     probBefore,
@@ -92,7 +97,16 @@ export const getNewMultiBetInfo = (
     createdTime: Date.now(),
   }
 
-  const newBalance = user.balance - amount
+  const newBalance = user.balance - (amount - loanAmount)
 
   return { newBet, newPool, newTotalShares, newTotalBets, newBalance }
 }
+
+export const getLoanAmount = (yourBets: Bet[], newBetAmount: number) => {
+  const prevLoanAmount = _.sumBy(yourBets, (bet) => bet.loanAmount ?? 0)
+  const loanAmount = Math.min(
+    newBetAmount,
+    MAX_LOAN_PER_CONTRACT - prevLoanAmount
+  )
+  return loanAmount
+}

common/payouts.ts

@@ -161,3 +161,12 @@ export const getPayoutsMultiOutcome = (
     .map(({ userId, payout }) => ({ userId, payout }))
     .concat([{ userId: contract.creatorId, payout: creatorPayout }]) // add creator fee
 }
+
+export const getLoanPayouts = (bets: Bet[]) => {
+  const betsWithLoans = bets.filter((bet) => bet.loanAmount)
+  const betsByUser = _.groupBy(betsWithLoans, (bet) => bet.userId)
+  const loansByUser = _.mapValues(betsByUser, (bets) =>
+    _.sumBy(bets, (bet) => -(bet.loanAmount ?? 0))
+  )
+  return _.toPairs(loansByUser).map(([userId, payout]) => ({ userId, payout }))
+}

common/sell-bet.ts

@@ -11,7 +11,7 @@ export const getSellBetInfo = (
   newBetId: string
 ) => {
   const { pool, totalShares, totalBets } = contract
-  const { id: betId, amount, shares, outcome } = bet
+  const { id: betId, amount, shares, outcome, loanAmount } = bet
 
   const adjShareValue = calculateShareValue(contract, bet)
 
@@ -57,7 +57,7 @@ export const getSellBetInfo = (
     },
   }
 
-  const newBalance = user.balance + saleAmount
+  const newBalance = user.balance + saleAmount - (loanAmount ?? 0)
 
   return {
     newBet,

functions/src/create-answer.ts

@@ -3,10 +3,11 @@ import * as admin from 'firebase-admin'
 
 import { Contract } from '../../common/contract'
 import { User } from '../../common/user'
-import { getNewMultiBetInfo } from '../../common/new-bet'
+import { getLoanAmount, getNewMultiBetInfo } from '../../common/new-bet'
 import { Answer } from '../../common/answer'
 import { getContract, getValues } from './utils'
 import { sendNewAnswerEmail } from './emails'
+import { Bet } from '../../common/bet'
 
 export const createAnswer = functions.runWith({ minInstances: 1 }).https.onCall(
   async (
@@ -55,6 +56,11 @@ export const createAnswer = functions.runWith({ minInstances: 1 }).https.onCall(
       if (closeTime && Date.now() > closeTime)
         return { status: 'error', message: 'Trading is closed' }
 
+      const yourBetsSnap = await transaction.get(
+        contractDoc.collection('bets').where('userId', '==', userId)
+      )
+      const yourBets = yourBetsSnap.docs.map((doc) => doc.data() as Bet)
+
       const [lastAnswer] = await getValues<Answer>(
         firestore
           .collection(`contracts/${contractId}/answers`)
@@ -92,8 +98,17 @@ export const createAnswer = functions.runWith({ minInstances: 1 }).https.onCall(
         .collection(`contracts/${contractId}/bets`)
         .doc()
 
+      const loanAmount = getLoanAmount(yourBets, amount)
+
       const { newBet, newPool, newTotalShares, newTotalBets, newBalance } =
-        getNewMultiBetInfo(user, answerId, amount, contract, newBetDoc.id)
+        getNewMultiBetInfo(
+          user,
+          answerId,
+          amount,
+          loanAmount,
+          contract,
+          newBetDoc.id
+        )
 
       transaction.create(newBetDoc, newBet)
       transaction.update(contractDoc, {

functions/src/place-bet.ts

@@ -3,7 +3,13 @@ import * as admin from 'firebase-admin'
 
 import { Contract } from '../../common/contract'
 import { User } from '../../common/user'
-import { getNewBinaryBetInfo, getNewMultiBetInfo } from '../../common/new-bet'
+import {
+  getLoanAmount,
+  getNewBinaryBetInfo,
+  getNewMultiBetInfo,
+} from '../../common/new-bet'
+import { Bet } from '../../common/bet'
+import { getValues } from './utils'
 
 export const placeBet = functions.runWith({ minInstances: 1 }).https.onCall(
   async (
@@ -46,6 +52,11 @@ export const placeBet = functions.runWith({ minInstances: 1 }).https.onCall(
       if (closeTime && Date.now() > closeTime)
         return { status: 'error', message: 'Trading is closed' }
 
+      const yourBetsSnap = await transaction.get(
+        contractDoc.collection('bets').where('userId', '==', userId)
+      )
+      const yourBets = yourBetsSnap.docs.map((doc) => doc.data() as Bet)
+
       if (outcomeType === 'FREE_RESPONSE') {
         const answerSnap = await transaction.get(
           contractDoc.collection('answers').doc(outcome)
@@ -58,16 +69,26 @@ export const placeBet = functions.runWith({ minInstances: 1 }).https.onCall(
         .collection(`contracts/${contractId}/bets`)
         .doc()
 
+      const loanAmount = getLoanAmount(yourBets, amount)
+
       const { newBet, newPool, newTotalShares, newTotalBets, newBalance } =
         outcomeType === 'BINARY'
           ? getNewBinaryBetInfo(
               user,
               outcome as 'YES' | 'NO',
               amount,
+              loanAmount,
+              contract,
+              newBetDoc.id
+            )
+          : getNewMultiBetInfo(
+              user,
+              outcome,
+              amount,
+              loanAmount,
               contract,
               newBetDoc.id
             )
-          : getNewMultiBetInfo(user, outcome, amount, contract, newBetDoc.id)
 
       transaction.create(newBetDoc, newBet)
       transaction.update(contractDoc, {

functions/src/resolve-market.ts

@@ -7,7 +7,11 @@ import { User } from '../../common/user'
 import { Bet } from '../../common/bet'
 import { getUser, payUser } from './utils'
 import { sendMarketResolutionEmail } from './emails'
-import { getPayouts, getPayoutsMultiOutcome } from '../../common/payouts'
+import {
+  getLoanPayouts,
+  getPayouts,
+  getPayoutsMultiOutcome,
+} from '../../common/payouts'
 import { removeUndefinedProps } from '../../common/util/object'
 
 export const resolveMarket = functions
@@ -99,9 +103,14 @@ export const resolveMarket = functions
           ? getPayoutsMultiOutcome(resolutions, contract, openBets)
           : getPayouts(outcome, contract, openBets, resolutionProbability)
 
+      const loanPayouts = getLoanPayouts(openBets)
+
       console.log('payouts:', payouts)
 
-      const groups = _.groupBy(payouts, (payout) => payout.userId)
+      const groups = _.groupBy(
+        [...payouts, ...loanPayouts],
+        (payout) => payout.userId
+      )
       const userPayouts = _.mapValues(groups, (group) =>
         _.sumBy(group, (g) => g.payout)
       )