// how this CLI re-invokes itself as a child process.
//
// two shapes exist and only the build decides which one is running:
//
//   standalone   the bun-compiled executable IS the entry point. it takes the
//                CLI argv directly and there is no script to hand it.
//   entry script every other shape (dev checkout, the repository dist-cli
//                bundle) runs through the javascript runtime executing now,
//                with the script as its first argument.
//
// a presence check cannot tell them apart. inside the compiled binary
// `process.argv[1]` is a path in bun's virtual filesystem (`/$bunfs/root/...`)
// that passes `existsSync` in-process, so every site that probed argv[1]
// re-invoked itself as `rnx <bunfs path> <command>` and the child died on
// `unknown command`. the build-time constant is the only honest signal.

import { existsSync } from 'node:fs'
import { basename, dirname, join } from 'node:path'
import { fileURLToPath } from 'node:url'
import { rnxPublicBrand } from '../src/public-brand.ts'
import { IS_STANDALONE } from './standalone.ts'

export interface RnxSelfInvocation {
  /** absolute path to spawn. */
  executable: string
  /** arguments that precede the CLI's own argv. */
  prefixArgs: string[]
}

function sourceEntryPath(): string | null {
  try {
    const candidate = join(dirname(fileURLToPath(import.meta.url)), 'bin.ts')
    return existsSync(candidate) ? candidate : null
  } catch {
    return null
  }
}

function isCliEntry(path: string): boolean {
  const name = basename(path)
  return name === 'bin.ts' || name === 'bin.js'
}

export function rnxSelfInvocation(): RnxSelfInvocation {
  if (IS_STANDALONE) return { executable: process.execPath, prefixArgs: [] }
  const entry = process.argv[1]
  if (entry && isCliEntry(entry)) {
    return { executable: process.execPath, prefixArgs: [entry] }
  }
  const sourceEntry = sourceEntryPath()
  if (sourceEntry) {
    return { executable: process.execPath, prefixArgs: [sourceEntry] }
  }
  if (!entry) {
    throw new Error(`could not locate the ${rnxPublicBrand.commandName} entry script`)
  }
  return { executable: process.execPath, prefixArgs: [entry] }
}