const url = require("url")
const validatePackageName = require("./validatePackageName")

const URLFormat = /^\/((?:@[^/@]+\/)?[^/@]+)(?:@([^/]+))?(\/.*)?$/

function decodeParam(param) {
  if (param) {
    try {
      return decodeURIComponent(param)
    } catch (error) {
      // Ignore invalid params.
    }
  }

  return ""
}

function parsePackageURL(packageURL) {
  const { pathname, search, query } = url.parse(packageURL, true)

  const match = URLFormat.exec(pathname)

  // Disallow invalid URL formats.
  if (match == null) return null

  const packageName = match[1]

  // Disallow invalid npm package names.
  if (!validatePackageName(packageName)) return null

  const packageVersion = decodeParam(match[2]) || "latest"
  const filename = decodeParam(match[3])

  return {
    // If the URL is /@scope/name@version/file.js?main=browser:
    pathname, // /@scope/name@version/path.js
    search, // ?main=browser
    query, // { main: 'browser' }
    packageName, // @scope/name
    packageVersion, // version
    filename // /file.js
  }
}

module.exports = parsePackageURL