o1js/src/lib/mina/v1/actions/offchain-contract-tests/ExampleContract.ts

TypeScript framework for zk-SNARKs and zkApps

import {
  SmartContract,
  method,
  state,
  PublicKey,
  UInt64,
  Experimental,
} from '../../../../../index.js';

export { offchainState, StateProof, ExampleContract };

const { OffchainState } = Experimental;

const offchainState = OffchainState(
  {
    accounts: OffchainState.Map(PublicKey, UInt64),
    totalSupply: OffchainState.Field(UInt64),
  },
  { logTotalCapacity: 10, maxActionsPerProof: 5 }
);

class StateProof extends offchainState.Proof {}

// example contract that interacts with offchain state
class ExampleContract extends SmartContract {
  @state(OffchainState.Commitments) offchainStateCommitments = offchainState.emptyCommitments();

  // o1js memoizes the offchain state by contract address so that this pattern works
  offchainState = offchainState.init(this);

  @method
  async createAccount(address: PublicKey, amountToMint: UInt64) {
    // setting `from` to `undefined` means that the account must not exist yet
    this.offchainState.fields.accounts.update(address, {
      from: undefined,
      to: amountToMint,
    });

    // TODO using `update()` on the total supply means that this method
    // can only be called once every settling cycle
    let totalSupplyOption = await this.offchainState.fields.totalSupply.get();
    let totalSupply = totalSupplyOption.orElse(0n);

    this.offchainState.fields.totalSupply.update({
      from: totalSupplyOption,
      to: totalSupply.add(amountToMint),
    });
  }

  @method
  async transfer(from: PublicKey, to: PublicKey, amount: UInt64) {
    let fromOption = await this.offchainState.fields.accounts.get(from);
    let fromBalance = fromOption.assertSome('sender account exists');

    let toOption = await this.offchainState.fields.accounts.get(to);
    let toBalance = toOption.orElse(0n);

    /**
     * Update both accounts atomically.
     *
     * This is safe, because both updates will only be accepted if both previous balances are still correct.
     */
    this.offchainState.fields.accounts.update(from, {
      from: fromOption,
      to: fromBalance.sub(amount),
    });

    this.offchainState.fields.accounts.update(to, {
      from: toOption,
      to: toBalance.add(amount),
    });
  }

  @method.returns(UInt64)
  async getSupply() {
    return (await this.offchainState.fields.totalSupply.get()).orElse(0n);
  }

  @method.returns(UInt64)
  async getBalance(address: PublicKey) {
    return (await this.offchainState.fields.accounts.get(address)).orElse(0n);
  }

  @method
  async settle(proof: StateProof) {
    await this.offchainState.settle(proof);
  }
}