import type { Node } from '../jostraca'

import { cmp, each } from '../jostraca'


const DEFAULT_MARKERS: [string, string] = ['#--START--#\n', '\n#--END--#']


/** The props `Inject` reads. */
type InjectProps = {

  /**
   * Path of the file to edit, below the enclosing folder. It must
   * already exist: Inject rewrites the region between the markers, it
   * does not create a file.
   */
  name: string

  /**
   * The start and end marker pair. Both must be non-empty; the default
   * pair is `#--START--#\n` and `\n#--END--#`.
   */
  markers?: [string, string]

  /**
   * Leave the target alone. Coerced with `!!`, so any truthy value
   * excludes.
   */
  exclude?: boolean
}


// Resolve the marker pair, rejecting a half-specified one.
//
// The markers become a `start(.*?)end` regex, and an empty marker turns
// that into a zero-width match — which is not a marker, it is regex
// fallout. An empty START matched at position 0 and replaced everything up
// to the end marker; an empty PAIR interleaved the injected body between
// every single character of the file. Neither was designed, neither is
// usable, and the Go port could not reproduce either (its scan loop hung
// outright on an empty start marker, since nothing advanced).
//
// So: a pair with exactly one empty marker is rejected, and a pair with
// both empty is treated as "not supplied" — which is what the Go port
// already did, and is the only reading that lets both stacks agree.
function markersOf(markers: InjectProps['markers']): string[] {
  if (null == markers) {
    return DEFAULT_MARKERS
  }

  const start = null == markers[0] ? '' : '' + markers[0]
  const end = null == markers[1] ? '' : '' + markers[1]

  if ('' === start && '' === end) {
    return DEFAULT_MARKERS
  }

  if ('' === start || '' === end) {
    throw new Error('Inject: both markers must be non-empty, got ' +
      JSON.stringify([start, end]))
  }

  return [start, end]
}


const Inject = cmp<InjectProps>(function Inject(props, children) {
  const node: Node = props.ctx$.node

  node.kind = 'inject'
  node.name = props.name
  node.meta.markers = markersOf(props.markers)
  node.exclude = null == props.exclude ? node.exclude : !!props.exclude

  each(children, { call: true })
})



export {
  Inject
}

export type {
  InjectProps
}