import type { Manifest } from '../types'

/**
 * Determines whether the specified value is a package manifest.
 */
export function isManifest(obj: any): obj is Manifest {
  return obj
    && typeof obj === 'object'
    && isOptionalString(obj.name)
    && isOptionalString(obj.version)
    && isOptionalString(obj.description)
}

/**
 * Determines whether the specified value is a string, null, or undefined.
 */
function isOptionalString(value: any): value is string | undefined {
  const type = typeof value
  return value === null
    || type === 'undefined'
    || type === 'string'
}