Tracking Pool Balances

The LBPair contract emits DepositedToBins and WithdrawnFromBins events when users add or remove liquidity from the market.

We track the user balances in LBPairs by parsing these events.

• Liquidity is deposited/withdrawn into multiple Bins, for which the Bin Ids are returned in array uint256[] ids.

• Token amounts deposited/withdrawn are tracked by amounts, which is a of tuple [amountX, amountY] encoded into byte32.

• The arrays amounts[] and ids[] correspond to the token amounts and Bin Ids of each corresponding Bin.

• See Byte32 Decoding for more details.

DepositedToBins

    // ILBPair.sol
    event DepositedToBins(
      address indexed sender, 
      address indexed to, 
      uint256[] ids, 
      bytes32[] amounts
    );

WithdrawnFromBins

    // ILBPair.sol
    event WithdrawnFromBins(
      address indexed sender, 
      address indexed to, 
      uint256[] ids, 
      bytes32[] amounts
    );

Example Handler

export function handleDepositedToBins(event: DepositedToBins): void {

  // We can get the tokenX and tokenY from the LBPair
  const lbPair = LBPair.load(event.address.toHexString())
  const tokenX = lbPair.tokenX
  const tokenY = lbPair.tokenY

  // get user
  const user = User.load(event.to.toHexString())

  // get amounts
  const amounts = event.params.amounts
  let amountX = 0
  let amountY = 0
  for (let i=0; i < amounts.length; i++) {
    const _amounts = amounts[i]
    // NOTE: reverse bytes to convert to big endianness
    amounts.reverse()
    const _amountX = decodeX(_amounts)
    const _amountY = decodeY(_amounts)
    amountX += _amountX
    amountY += _amountY
  }
}

// Assemblyscript API
// https://thegraph.com/docs/en/developing/assemblyscript-api/
function decodeX(packedAmounts: Bytes): BigInt {
  // Read the right 128 bits of the 256 bits
  return BigInt.fromUnsignedBytes(packedAmounts).bitAnd(BigInt.fromI32(2).pow(128).minus(BigInt.fromI32(1)))
}

function decodeY(packedAmounts: Bytes): BigInt {
  // Read the left 128 bits of the 256 bits
  return BigInt.fromUnsignedBytes(packedAmounts).rightShift(128)
}