feat(contracts): handle contract events

[1cedrus]

This PR addresses a task in #110 as the title said which adds:

• Contract events executor which provides some useful methods (is, as, meta).
• Contract events decoder (for supported contract metadata versions and not multiple anonymous events contract only).

A piece of code that tries to call a contract message, decode emitted events, and print out if it is Flipped event:

  const api = await LegacyClient.new(new WsProvider('ws://127.0.0.1:9944'));
  const contract = new Contract<FlipperContractApi>(api, METADATA, CONTRACT_ADDRESS);

  const dryRun = await contract.query.flip({ caller: alicePair.address });
  const tx = contract.tx.flip({ gasLimit: dryRun.raw.gasRequired });

  await tx.signAndSend(alicePair, ({ status, events }: any) => {
    if (status.type === 'Finalized') {
      events
        .filter((eventRecord: FrameSystemEventRecord) => api.events.contracts.ContractEmitted.is(eventRecord.event))
        .forEach((one: FrameSystemEventRecord) => {
          const decodedEvent = contract.decodeEvent(one);

          if (decodedEvent && contract.events.Flipped.is(decodedEvent)) {
            console.log(decodedEvent);
          }
        });
    }
  });

• Also, an events interface generator that helps to interact with API more easily (type suggestion):

  • Generated events interface file
  • Flipper contract has only one event is Flipped:
    
  • Flipped contains these data:
    

• Unit tests and e2e tests for added features.

[sinzii]

Awesome work! Thanks for the additional specs 🚀