Smart Contract — PactumBilling

Reference documentation for the PactumBilling Solidity contract.

Overview

PactumBilling is the on-chain component of the Pactum billing system. It manages USDC deposits from end-users, holds funds in escrow, and enables the platform operator to settle usage charges by moving funds from user balances to merchant balances in batches.

Contract: PactumBilling.sol Solidity Version: ^0.8.20 Chain: Arc Testnet (Chain ID: 5042002) Token: USDC at 0x3600000000000000000000000000000000000000

[!IMPORTANT] USDC on Arc has dual views: native 18-decimal and ERC-20 6-decimal. This contract uses the 6-decimal ERC-20 view for all operations.

Contract Architecture

State Variables

Variable	Type	Visibility	Description
`usdc`	`IERC20`	`public`	USDC token contract reference
`platformOperator`	`address`	`public`	Address authorized to call settlement functions
`userBalances`	`mapping(address => uint256)`	`public`	Deposited USDC per user
`merchantBalances`	`mapping(address => uint256)`	`public`	Earned USDC per merchant

Functions

`deposit(uint256 amount)`

Allows a user to deposit USDC into the contract. The user must first call approve() on the USDC token contract, granting the PactumBilling contract an allowance.

Parameter	Type	Description
`amount`	`uint256`	Amount of USDC to deposit (6-decimal precision)

Requirements:

amount > 0
USDC transferFrom must succeed (requires prior approve)

Emits: Deposited(user, amount)

`batchSettleUsage(address[] users, address[] merchants, uint256[] amounts)`

Settles off-chain usage charges in a single transaction. Moves funds from user balances to merchant balances. Only callable by the platform operator.

Parameter	Type	Description
`users`	`address[]`	Array of user addresses being charged
`merchants`	`address[]`	Array of merchant addresses receiving payment
`amounts`	`uint256[]`	Array of USDC amounts to transfer

Requirements:

Caller must be platformOperator
All arrays must have equal length
Each userBalances[user] >= amount

Emits: UsageSettled(user, merchant, amount) for each settlement

`withdrawUser(uint256 amount)`

Allows a user to withdraw their remaining unused USDC balance from the contract.

Parameter	Type	Description
`amount`	`uint256`	Amount to withdraw

Requirements:

userBalances[msg.sender] >= amount

Emits: UserWithdrawn(user, amount)

`withdrawMerchant(uint256 amount)`

Allows a merchant to withdraw their earned USDC from the contract.

Parameter	Type	Description
`amount`	`uint256`	Amount to withdraw

Requirements:

merchantBalances[msg.sender] >= amount

Emits: MerchantWithdrawn(merchant, amount)

`setOperator(address newOperator)`

Transfers the platform operator role to a new address. Only callable by the current operator.

Parameter	Type	Description
`newOperator`	`address`	New operator address

Requirements:

Caller must be current platformOperator
newOperator != address(0)

Events

Event	Parameters	Description
`Deposited`	`user (indexed)`, `amount`	User deposited USDC
`UsageSettled`	`user (indexed)`, `merchant (indexed)`, `amount`	Usage charge settled from user to merchant
`UserWithdrawn`	`user (indexed)`, `amount`	User withdrew unused balance
`MerchantWithdrawn`	`merchant (indexed)`, `amount`	Merchant withdrew earned fees

Interaction Flow

A typical lifecycle:

Arc Testnet Configuration

Property	Value
Chain ID	`5042002`
RPC	`https://rpc.testnet.arc.network`
Explorer	`https://testnet.arcscan.app`
USDC Address	`0x3600000000000000000000000000000000000000`
USDC Decimals	`6` (ERC-20 view)
Faucet	Circle Faucet