import { spawnSync } from 'node:child_process'
import { createHash } from 'node:crypto'
import { existsSync, readFileSync } from 'node:fs'

/**
 * The git description of the checkout of dir now, a commit or a tag changing it without a restart; outside a
 * checkout, or without git, the variable named fallbackVariable, which a container image sets, or "dev".
 */
export function gitVersion(dir: string, fallbackVariable: string) {
  const described = spawnSync('git', ['describe', '--tags', '--always', '--dirty'], { cwd: dir, encoding: 'utf8' })
  return described.status === 0 ? described.stdout.trim() : process.env[fallbackVariable] || 'dev'
}

/**
 * Ctrl-C and SIGTERM, which watch mode sends on a restart, call close and end the process when it settles, or after 5
 * seconds.
 */
export function exitOnSignals(close: () => Promise<unknown>) {
  for (const signal of ['SIGINT', 'SIGTERM'] as const) {
    process.on(signal, () => {
      setTimeout(() => process.exit(0), 5000).unref()
      void close().then(() => process.exit(0))
    })
  }
}

/**
 * The JSON object of the file at path, and its version, the SHA-256 of the bytes. With missingAsEmpty a missing file
 * reads as {}, whose version is that of "{}". A file that cannot be read, invalid JSON or another value than an
 * object throws with the reason.
 */
export function readJsonObject(path: string, options: { missingAsEmpty: boolean }): { data: Record<string, unknown>; version: string } {
  let bytes: Buffer
  let data: unknown
  try {
    bytes = options.missingAsEmpty && !existsSync(path) ? Buffer.from('{}') : readFileSync(path)
    data = JSON.parse(bytes.toString('utf8'))
  } catch (error) {
    throw new Error(`${path} cannot be read: ${(error as Error).message}`)
  }
  if (data === null || typeof data !== 'object' || Array.isArray(data)) {
    throw new Error(`${path} must hold a JSON object`)
  }
  return { data: data as Record<string, unknown>, version: createHash('sha256').update(bytes).digest('hex') }
}