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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  • Liquidity is deposited/withdrawn into multiple Bins, for which the Bin Ids are returned in array uint256[] ids.
  • Token amounts deposited/withdrawn are tracked by amounts, which is a of tuple [amountX, amountY] encoded into byte32.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 ​

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

WithdrawnFromBins ​

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

Example Handler ​

solidity
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)
}