Map promises

promiseMap.ts

import R from 'ramda'

export async function mapAsync<Type, ReturnedType>(
  promiseFunc: (value: Type) => Promise<ReturnedType>,
  values: Type[],
  chunk = 3
) {
  const processChunk = processWithFunction<Type, ReturnedType>(promiseFunc)
  const chunks = R.splitEvery(chunk, values)
  return R.flatten(await R.reduce(processChunk, Promise.resolve([]), chunks))
}

function processWithFunction<Type, ReturnedType>(promiseFunc: (x: Type) => Promise<ReturnedType>) {
  return async (acc: Promise<ReturnedType[]>, chunkOfValues: Type[]) => {
    const resolved = await acc
    const outcome = await Promise.all(chunkOfValues.map((chunk) => promiseFunc(chunk)))
    resolved.push(...outcome)
    return resolved
  }
}