All files / src sin.js

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1x
   
function fold (updates, state, event) {
  return Promise
    .all(updates.map(update => update(state, event)))
}
 
function sin () {
  let key = Math.random().toString(16).slice(4)
  let updates = Array.from(arguments).slice(1, arguments.length)
  let signal = arguments[0]
 
  if (!signal || !signal.emit) {
    throw new Error('[Sin] requires an emitter source')
  }
 
  return (state, event) => {
    if (event.type === key) {
      return event.payload
    }
 
    Promise
      .resolve(fold(updates, state, event))
      .then(res => {
        let collected = res
          .reduce(newState => ({ state, ...newState }), state)
 
        signal.emit({
          type: key,
          payload: collected
        })
      })
 
    return state
  }
}
 
export default sin