liquidjs/src/util/async.ts

import { isPromise, isIterator } from './underscore'

export type LiquidAsync<F extends (...args: any[]) => any> =
  (sync: boolean, ...args: Parameters<F>) => ReturnType<F> | Promise<ReturnType<F>>

export function toLiquidAsync<F extends (...args: any[]) => any> (
  asyncFn: (...args: Parameters<F>) => Promise<ReturnType<F>>,
  syncFn?: F
): LiquidAsync<F> {
  const syncImpl = syncFn || asyncFn as any
  return (sync: boolean, ...args: any[]) => {
    return sync ? syncImpl(...args as Parameters<F>) : asyncFn(...args as Parameters<F>)
  }
}

// convert an async iterator to a Promise
export async function toPromise<T> (val: Generator<unknown, T, unknown> | Promise<T> | T): Promise<T> {
  if (!isIterator(val)) return val
  let value: unknown
  let done = false
  let next: 'next' | 'throw' = 'next'
  do {
    const state = val[next](value)
    done = !!state.done
    value = state.value
    next = 'next'
    try {
      if (isIterator(value)) value = toPromise(value)
      if (isPromise(value)) value = await value
    } catch (err) {
      next = 'throw'
      value = err
    }
  } while (!done)
  return value as T
}

// convert an async iterator to a value in a synchronous manner
export function toValueSync<T> (val: Generator<unknown, T, unknown> | T): T {
  if (!isIterator(val)) return val
  let value: any
  let done = false
  let next: 'next' | 'throw' = 'next'
  do {
    const state = val[next](value)
    done = !!state.done
    value = state.value
    next = 'next'
    if (isIterator(value)) {
      try {
        value = toValueSync(value)
      } catch (err) {
        next = 'throw'
        value = err
      }
    }
  } while (!done)
  return value
}