manifold/functions/src/sell-bet.ts

import * as admin from 'firebase-admin'
import { z } from 'zod'

import { APIError, newEndpoint, validate } from './api'
import { Contract } from '../../common/contract'
import { User } from '../../common/user'
import { Bet } from '../../common/bet'
import { getSellBetInfo } from '../../common/sell-bet'
import { addObjects, removeUndefinedProps } from '../../common/util/object'

const bodySchema = z.object({
  contractId: z.string(),
  betId: z.string(),
})

export const sellbet = newEndpoint(['POST'], async (req, [bettor, _]) => {
  const { contractId, betId } = validate(bodySchema, req.body)

  // run as transaction to prevent race conditions
  return await firestore.runTransaction(async (transaction) => {
    const userDoc = firestore.doc(`users/${bettor.id}`)
    const userSnap = await transaction.get(userDoc)
    if (!userSnap.exists) throw new APIError(400, 'User not found.')
    const user = userSnap.data() as User

    const contractDoc = firestore.doc(`contracts/${contractId}`)
    const contractSnap = await transaction.get(contractDoc)
    if (!contractSnap.exists) throw new APIError(400, 'Contract not found.')
    const contract = contractSnap.data() as Contract

    const { closeTime, mechanism, collectedFees, volume } = contract
    if (mechanism !== 'dpm-2')
      throw new APIError(400, 'You can only sell bets on DPM-2 contracts.')
    if (closeTime && Date.now() > closeTime)
      throw new APIError(400, 'Trading is closed.')

    const betDoc = firestore.doc(`contracts/${contractId}/bets/${betId}`)
    const betSnap = await transaction.get(betDoc)
    if (!betSnap.exists) throw new APIError(400, 'Bet not found.')
    const bet = betSnap.data() as Bet

    if (bettor.id !== bet.userId)
      throw new APIError(400, 'The specified bet does not belong to you.')
    if (bet.isSold)
      throw new APIError(400, 'The specified bet is already sold.')

    const { newBet, newPool, newTotalShares, newTotalBets, fees } =
      getSellBetInfo(bet, contract)

    /* eslint-disable-next-line @typescript-eslint/no-non-null-assertion */
    const saleAmount = newBet.sale!.amount
    const newBalance = user.balance + saleAmount - (bet.loanAmount ?? 0)
    const newBetDoc = firestore.collection(`contracts/${contractId}/bets`).doc()

    transaction.update(userDoc, { balance: newBalance })
    transaction.update(betDoc, { isSold: true })
    transaction.create(newBetDoc, { id: betDoc.id, userId: user.id, ...newBet })
    transaction.update(
      contractDoc,
      removeUndefinedProps({
        pool: newPool,
        totalShares: newTotalShares,
        totalBets: newTotalBets,
        collectedFees: addObjects(fees, collectedFees),
        volume: volume + Math.abs(newBet.amount),
      })
    )

    return {}
  })
})

const firestore = admin.firestore()