manifold/web/lib/service/create-contract.ts

import {
  Contract,
  getContractFromSlug,
  pushNewContract,
  setContract,
} from '../firebase/contracts'
import { User } from '../firebase/users'
import { randomString } from '../util/random-string'
import { slugify } from '../util/slugify'

// consider moving to cloud function for security
export async function createContract(
  question: string,
  description: string,
  initialProb: number,
  creator: User
) {
  const proposedSlug = slugify(question).substring(0, 35)

  const preexistingContract = await getContractFromSlug(proposedSlug)

  const slug = preexistingContract
    ? proposedSlug + '-' + randomString()
    : proposedSlug

  const { startYes, startNo } = calcStartPool(initialProb)

  const contract: Omit<Contract, 'id'> = {
    slug,
    outcomeType: 'BINARY',

    creatorId: creator.id,
    creatorName: creator.name,

    question: question.trim(),
    description: description.trim(),

    startPool: { YES: startYes, NO: startNo },
    pool: { YES: startYes, NO: startNo },
    dpmWeights: { YES: 0, NO: 0 },
    isResolved: false,

    // TODO: Set create time to Firestore timestamp
    createdTime: Date.now(),
    lastUpdatedTime: Date.now(),
  }

  return await pushNewContract(contract)
}

export function calcStartPool(initialProb: number, initialCapital = 200) {
  const p = initialProb / 100.0

  const startYes =
    p === 0.5
      ? p * initialCapital
      : -(initialCapital * (-p + Math.sqrt((-1 + p) * -p))) / (-1 + 2 * p)

  const startNo = initialCapital - startYes

  return { startYes, startNo }
}