import { TransformStream } from 'stream/web'

const defaultMatcher = /\r?\n/

export type Decoder = {
  decode: (chunk: Uint8Array) => string
}

interface Options {
  decoder?: Decoder
}

export default function split(matcher?: RegExp | null, { decoder }: Options = {}) {
  matcher ??= defaultMatcher

  let rest: string | null | undefined = null

  return new TransformStream({
    start() {},
    transform(chunk, controller) {
      if (chunk) {
        if (decoder) {
          chunk = decoder.decode(chunk)
        }

        const lines = ((rest == null ? '' : rest) + chunk).split(matcher)

        rest = lines.pop()

        for (const line of lines) {
          controller.enqueue(line)
        }
      } else {
        controller.terminate()
      }
    },
  })
}