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import { Decimal } from 'decimal.js';
const BATCH_FUND_TX_BASE_WEIGHT = 42;
const FUNDING_OUTPUT_SIZE = 43;
export class DualFundingTxFinalizer {
constructor(
readonly offerInputs: FundingInput[],
readonly offerPayoutSPK: Buffer,
readonly offerChangeSPK: Buffer,
readonly acceptInputs: FundingInput[],
readonly acceptPayoutSPK: Buffer,
readonly acceptChangeSPK: Buffer,
readonly feeRate: bigint,
readonly numContracts = 1,
) {}
private computeFees(
_inputs: FundingInput[],
payoutSPK: Buffer,
changeSPK: Buffer,
numContracts: number,
): IFees {
// If no inputs, return zero fees (matches C++ layer behavior for single-funded DLCs)
if (_inputs.length === 0) {
return { futureFee: BigInt(0), fundingFee: BigInt(0) };
}
_inputs.forEach((input) => {
Iif (input.type !== MessageType.FundingInput) {
console.error('input', input);
throw new Error('Input is not a funding input');
}
});
const inputs: FundingInput[] = _inputs.map(
(input) => input as FundingInput,
);
// https://github.com/discreetlogcontracts/dlcspecs/blob/8ee4bbe816c9881c832b1ce320b9f14c72e3506f/Transactions.md#expected-weight-of-the-contract-execution-or-refund-transaction
const futureFeeWeight = 249 + 4 * payoutSPK.length;
const futureFeeVBytes = new Decimal(futureFeeWeight)
.times(numContracts)
.div(4)
.ceil()
.toNumber();
const futureFee = this.feeRate * BigInt(futureFeeVBytes);
// https://github.com/discreetlogcontracts/dlcspecs/blob/8ee4bbe816c9881c832b1ce320b9f14c72e3506f/Transactions.md#expected-weight-of-the-funding-transaction
const inputWeight = inputs.reduce((total, input) => {
return total + 164 + input.maxWitnessLen + input.scriptSigLength();
}, 0);
const contractWeight =
(BATCH_FUND_TX_BASE_WEIGHT + FUNDING_OUTPUT_SIZE * numContracts * 4) / 2;
const outputWeight = 36 + 4 * changeSPK.length + contractWeight;
const weight = outputWeight + inputWeight;
const vbytes = new Decimal(weight).div(4).ceil().toNumber();
const fundingFee = this.feeRate * BigInt(vbytes);
return { futureFee, fundingFee };
}
private getOfferFees(): IFees {
return this.computeFees(
this.offerInputs,
this.offerPayoutSPK,
this.offerChangeSPK,
this.numContracts,
);
}
private getAcceptFees(): IFees {
return this.computeFees(
this.acceptInputs,
this.acceptPayoutSPK,
this.acceptChangeSPK,
this.numContracts,
);
}
public get offerFees(): bigint {
const { futureFee, fundingFee } = this.getOfferFees();
return futureFee + fundingFee;
}
public get offerFutureFee(): bigint {
return this.getOfferFees().futureFee;
}
public get offerFundingFee(): bigint {
return this.getOfferFees().fundingFee;
}
public get acceptFees(): bigint {
const { futureFee, fundingFee } = this.getAcceptFees();
return futureFee + fundingFee;
}
public get acceptFutureFee(): bigint {
return this.getAcceptFees().futureFee;
}
public get acceptFundingFee(): bigint {
return this.getAcceptFees().fundingFee;
}
}
export class DualClosingTxFinalizer {
constructor(
readonly initiatorInputs: FundingInput[],
readonly offerPayoutSPK: Buffer,
readonly acceptPayoutSPK: Buffer,
readonly feeRate: bigint,
) {}
private computeFees(payoutSPK: Buffer, _inputs: FundingInput[] = []): bigint {
_inputs.forEach((input) => {
if (input.type !== MessageType.FundingInput)
throw new Error('Input is not a funding input');
});
const inputs: FundingInput[] = _inputs.map(
(input) => input as FundingInput,
);
// https://gist.github.com/matthewjablack/08c36baa513af9377508111405b22e03
const inputWeight = inputs.reduce((total, input) => {
return total + 164 + input.maxWitnessLen + input.scriptSigLength();
}, 0);
const outputWeight = 36 + 4 * payoutSPK.length;
const weight = 213 + outputWeight + inputWeight;
const vbytes = new Decimal(weight).div(4).ceil().toNumber();
const fee = this.feeRate * BigInt(vbytes);
return fee;
}
private getOfferInitiatorFees(): bigint {
return this.computeFees(this.offerPayoutSPK, this.initiatorInputs);
}
private getOfferReciprocatorFees(): bigint {
return this.computeFees(this.offerPayoutSPK);
}
private getAcceptInitiatorFees(): bigint {
return this.computeFees(this.acceptPayoutSPK, this.initiatorInputs);
}
private getAcceptReciprocatorFees(): bigint {
return this.computeFees(this.acceptPayoutSPK);
}
public get offerInitiatorFees(): bigint {
return this.getOfferInitiatorFees();
}
public get offerReciprocatorFees(): bigint {
return this.getOfferReciprocatorFees();
}
public get acceptInitiatorFees(): bigint {
return this.getAcceptInitiatorFees();
}
public get acceptReciprocatorFees(): bigint {
return this.getAcceptReciprocatorFees();
}
}
interface IFees {
futureFee: bigint;
fundingFee: bigint;
}
export const getFinalizer = (
feeRate: bigint,
offerInputs?: FundingInput[],
acceptInputs?: FundingInput[],
numContracts?: number,
): DualFundingTxFinalizer => {
const input = new FundingInput();
input.maxWitnessLen = 108;
input.redeemScript = Buffer.from('', 'hex');
const fakeSPK = Buffer.from(
'0014663117d27e78eb432505180654e603acb30e8a4a',
'hex',
);
offerInputs = offerInputs || Array.from({ length: 1 }, () => input);
acceptInputs = acceptInputs || Array.from({ length: 1 }, () => input);
return new DualFundingTxFinalizer(
offerInputs,
fakeSPK,
fakeSPK,
acceptInputs,
fakeSPK,
fakeSPK,
feeRate,
numContracts,
);
};
export const getFinalizerByCount = (
feeRate: bigint,
numOfferInputs: number,
numAcceptInputs: number,
numContracts: number,
): DualFundingTxFinalizer => {
const input = new FundingInput();
input.maxWitnessLen = 108;
input.redeemScript = Buffer.from('', 'hex');
const offerInputs = Array.from({ length: numOfferInputs }, () => input);
const acceptInputs = Array.from({ length: numAcceptInputs }, () => input);
return getFinalizer(feeRate, offerInputs, acceptInputs, numContracts);
};
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