mango-v4-ui/components/swap/useTokenMax.tsx

import { Bank, Group, MangoAccount } from '@blockworks-foundation/mango-v4'
import Decimal from 'decimal.js'
import { useMemo } from 'react'
import mangoStore from '@store/mangoStore'
import { floorToDecimal } from '../../utils/numbers'
import useMangoAccount from '../../hooks/useMangoAccount'
import useMangoGroup from 'hooks/useMangoGroup'
import { PublicKey } from '@solana/web3.js'

export const getMaxWithdrawForBank = (
  group: Group,
  bank: Bank,
  mangoAccount: MangoAccount,
  allowBorrow = false
): Decimal => {
  const accountBalance = mangoAccount.getTokenBalanceUi(bank)
  const vaultBalance = group.getTokenVaultBalanceByMintUi(bank.mint)
  const maxBorrow = mangoAccount.getMaxWithdrawWithBorrowForTokenUi(
    group,
    bank.mint
  )
  const maxWithdraw = allowBorrow
    ? Decimal.min(vaultBalance, maxBorrow)
    : bank.initAssetWeight.toNumber() === 0
    ? Decimal.min(accountBalance, vaultBalance)
    : Decimal.min(accountBalance, vaultBalance, maxBorrow)
  return Decimal.max(0, maxWithdraw)
}

export const getTokenInMax = (
  mangoAccount: MangoAccount,
  inputMint: PublicKey,
  outputMint: PublicKey,
  group: Group,
  useMargin: boolean
) => {
  const inputBank = group.getFirstBankByMint(inputMint)
  const outputBank = group.getFirstBankByMint(outputMint)

  if (!group || !inputBank || !mangoAccount || !outputBank) {
    return {
      amount: new Decimal(0.0),
      decimals: 6,
      amountWithBorrow: new Decimal(0.0),
    }
  }

  const inputReduceOnly = inputBank.areBorrowsReduceOnly()
  const outputReduceOnly = outputBank.areDepositsReduceOnly()

  const inputTokenBalance = new Decimal(
    mangoAccount.getTokenBalanceUi(inputBank)
  )

  const outputTokenBalance = new Decimal(
    mangoAccount.getTokenBalanceUi(outputBank)
  )

  const maxAmountWithoutMargin =
    (inputTokenBalance.gt(0) && !outputReduceOnly) ||
    (outputReduceOnly && outputTokenBalance.lt(0))
      ? inputTokenBalance
      : new Decimal(0)

  const rawMaxUiAmountWithBorrow = mangoAccount.getMaxSourceUiForTokenSwap(
    group,
    inputBank.mint,
    outputBank.mint
  )

  const maxUiAmountWithBorrow =
    outputReduceOnly && (outputTokenBalance.gt(0) || outputTokenBalance.eq(0))
      ? new Decimal(0)
      : rawMaxUiAmountWithBorrow > 0
      ? floorToDecimal(rawMaxUiAmountWithBorrow, inputBank.mintDecimals)
      : new Decimal(0)

  const inputBankVaultBalance = floorToDecimal(
    group
      .getTokenVaultBalanceByMintUi(inputBank.mint)
      .toFixed(inputBank.mintDecimals),
    inputBank.mintDecimals
  )

  const maxAmount = useMargin
    ? Decimal.min(
        maxAmountWithoutMargin,
        inputBankVaultBalance,
        maxUiAmountWithBorrow
      )
    : Decimal.min(
        maxAmountWithoutMargin,
        inputBankVaultBalance,
        maxUiAmountWithBorrow
      )

  const maxAmountWithBorrow = inputReduceOnly
    ? Decimal.min(maxAmountWithoutMargin, inputBankVaultBalance)
    : Decimal.min(maxUiAmountWithBorrow, inputBankVaultBalance)

  return {
    amount: maxAmount,
    amountWithBorrow: maxAmountWithBorrow,
    decimals: inputBank.mintDecimals,
  }
}

interface TokenMaxResults {
  amount: Decimal
  amountWithBorrow: Decimal
  decimals: number
}

export const useTokenMax = (useMargin = true): TokenMaxResults => {
  const { mangoAccount } = useMangoAccount()
  const { group } = useMangoGroup()
  const inputBank = mangoStore((s) => s.swap.inputBank)
  const outputBank = mangoStore((s) => s.swap.outputBank)

  const tokenInMax = useMemo(() => {
    try {
      if (mangoAccount && group && inputBank && outputBank) {
        return getTokenInMax(
          mangoAccount,
          inputBank.mint,
          outputBank.mint,
          group,
          useMargin
        )
      }
    } catch (e) {
      console.warn('Error in useTokenMax:  ', e)
    }
    return {
      amount: new Decimal(0),
      amountWithBorrow: new Decimal(0),
      decimals: 6,
    }
  }, [mangoAccount, group, useMargin, inputBank, outputBank])

  return tokenInMax
}