Operation state

Since middlewares are meant to be composed, they need an easy way to send metadata about the operation down the chain of middleware. To accomplish this, each middleware context has a state object. The state is read by using ctx.getState() and written using ctx.setState(newState) or ctx.setState((prevState) => newState). The API of setState is meant to be similar to React's one. For example:

airgram.use(({ setState }, next) => {
  setState({ foo: 'bar' })
  return next()
})

airgram.use(async ({ getState }) => {
  console.log(`foo = ${getState().foo}`);
  // output: foo = bar
})

In order to set the initial state, pass it by the request options.

async function downloadFile(file) {
  //
}

// Initial state
const state = { download: true }

// Pass state
airgram.api.getFile({ fileId: 1 }, { state }).then(({ getState }) => {
  const { willBeDownloaded } = getState()
  console.info(`willBeDownloaded: ${willBeDownloaded}`) // output: true
})

// Get and update state in a middleware
airgram.on('getFile', async ({ getState, setState }, next) => {
  const { download } = getState()
  if(download) {
    setState({ willBeDownloaded: true })
    const { response } = await next()
    await downloadFile(response)
  } else {
    return next()
  }
})