OffsetHelper
The OffsetHelper contract simplifies the carbon offsetting (retirement) process.
The OffsetHelper is a peripheral contract that simplifies the experience of buying and redeeming carbon reference tokens and retiring TCO2 tokens. The contract lives in this repository.
In more exact terms, the OffsetHelper abstracts the process of retiring TCO2, which normally looks like so:
user exchanges USDC for BCT/NCT tokens at one of the DEXs (Uniswap, Sushiswap, etc. depending on network)
user interacts with the BCT/NCT token contract to redeem the tokens for TCO2
user interacts with the TCO2 token contract to retire the TCO2
With the OffsetHelper contract, the user only needs to interact with the OffsetHelper contract, which will take care of the rest of the contract calls in a single transaction.
In these methods, "auto" refers to the fact that these methods use autoRedeem()
in order to automatically choose a TCO2 token corresponding to the oldest tokenized carbon project in the specified token pool. There are no fees incurred by the user when using autoRedeem()
, i.e., the user receives 1 TCO2 token for each carbon reference token e.g., NCT redeemed.
Testing the OffsetHelper on testnet may lead to an Error: execution reverted
as the OffsetHelper depends on available liquidity in some DEX pools, which can not always be guaranteed.
Approvals
The OffsetHelper is a smart contract that calls other smart contracts. As a security measure, users need to approve
the OffsetHelper contract address, so the other smart contracts accept interactions routed through this address.
Note: you must approve the pool contract in the TCO2 token that is to be deposited in order for the pool to be able to transfer the TCO2 on your behalf.
Accepted tokens
Functions
autoOffsetExactOutToken
Retire carbon credits using the oldest TCO2 tokens available from the specified Toucan token pool by sending ERC20 tokens (cUSD, USDC, WETH, WMATIC).
The view
helper function calculateNeededTokenAmount()
should be called before using autoOffsetExactOutToken()
, to determine how many native tokens (e.g., MATIC) must be sent to the OffsetHelper
contract in order to retire the specified amount of TCO2 tokens.
This function:
Swaps the ERC20 token sent to the contract for the specified carbon reference token
Redeems the reference tokens received for the lowest quality TCO2 tokens available
Retires the TCO2 tokens
Note: The user must approve the ERC20 token that will be used for the swap.
Parameters
Return Values
autoOffsetExactInToken
Retire carbon credits using the oldest TCO2 tokens available from the specified Toucan carbon pool by swapping ERC20 tokens (cUSD
, USDC
, WETH
, WMATIC
). All of provided "in
" token is consumed for retirement.
The view
helper function calculateExpectedPoolTokenForToken()
can be used to calculate the expected amount of TCO2s that will be offset using autoOffsetExactInToken()
.
This function:
Swaps the ERC20 token sent to the contract for the specified carbon reference token
Redeems the reference token for the lowest quality TCO2 tokens available
Retires the TCO2 tokens
Note: The client must approve the ERC20 token that is sent to the contract.
Parameters
Return Values
autoOffsetExactOutETH
Retire carbon credits using the oldest TCO2 tokens available from the specified Toucan token pool by sending native tokens e.g., MATIC.
Note: While this method refers to "ETH", it actually refers to the blockchain's native token, and will use WMATIC on Polygon.
The view
helper function calculateNeededETHAmount()
should be called before using autoOffsetExactOutETH()
, to determine how much native tokens e.g., MATIC must be sent to the OffsetHelper
contract in order to retire the specified amount of carbon.
This function:
Swaps the native token e.g. MATIC sent to the contract for the specified pool token
Redeems the pool token for the poorest quality TCO2 tokens available
Retires the TCO2 tokens
If the user sends too much native tokens, the leftover amount will be sent back to the user. This function is only available on Polygon, not on Celo.
Parameters
Return Values
autoOffsetExactInETH
Retire carbon credits using the oldest TCO2 tokens available from the specified Toucan token pool by sending native tokens e.g., MATIC. All provided native tokens is consumed for offsetting.
The view
helper function calculateExpectedPoolTokenForETH()
can be used to calculate the expected amount of TCO2s that will be offset using autoOffsetExactInETH()
.
This function:
Swaps the native token e.g. MATIC sent to the contract for the specified pool token
Redeems the pool token for the poorest quality TCO2 tokens available
Retires the TCO2 tokens
This function is only available on Polygon, not on Celo.
Parameters
Return Values
autoOffsetPoolToken
Retire carbon credits using the oldest TCO2 tokens available by sending Toucan carbon reference tokens, e.g., NCT.
This function:
Redeems the reference tokens for the poorest quality TCO2 tokens available
Retires the TCO2 tokens
Note: The user must approve the carbon reference token to be swapped.
Parameters
Return Values
swapExactOutToken
Swap eligible ERC20 tokens for Toucan carbon reference tokens (BCT/NCT) on a DEX.
Note: The user must approve the carbon reference token to be swapped.
Parameters
swapExactInToken
Swap eligible ERC20 tokens for Toucan carbon reference tokens (BCT/NCT) on a DEX. All provided ERC20 tokens will be swapped.
Note: The user must approve the carbon reference token to be swapped.
Parameters
Return Values
swapExactOutETH
Swap native tokens (e.g., MATIC) for Toucan carbon reference tokens (BCT/NCT) on a DEX. Remaining native tokens that were not consumed by the swap are returned.
Parameters
swapExactInETH
Swap native tokens (e.g., MATIC) for Toucan carbon reference tokens (BCT/NCT) on a DEX. All provided native tokens will be swapped.
Parameters
Return Values
autoRedeem
Auto-redeems the specified amount of NCT / BCT for default TCO2 tokens.
Note: The user must approve the carbon reference token to be redeemed.
Parameters
Return Values
autoRetire
Retire the specified TCO2 tokens.
The account sending the transaction needs to hold enough of each of the TCO2 tokens specified for this function to execute.
Parameters
calculateNeededTokenAmount
Returns how much of the specified ERC20 token is required in order to swap for the desired amount of a Toucan carbon reference token such as NCT.
Parameters
Return Values
calculateExpectedPoolTokenForToken
Calculates the expected amount of Toucan carbon reference token that can be acquired by swapping the provided amount of ERC20 token.
Parameters
Return Values
calculateNeededETHAmount
Return how much native tokens e.g, MATIC is required in order to swap for the desired amount of a Toucan carbon reference token, e.g., NCT.
Parameters
Return Values
calculateExpectedPoolTokenForETH
Calculates the expected amount of Toucan carbon reference tokens that can be acquired by swapping the provided amount of native tokens e.g., MATIC.
Parameters
Return Values
isPoolAddressEligible
Checks if an address identifies a Toucan carbon pool.
Parameters
Return Values
isERC20AddressEligible
Checks if ERC20 Token is supported for swapping. Check the accepted tokens.
Parameters
Return Values
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