'use strict'
  
  function formatHostname(hostname) {
    // canonicalize the hostname, so that 'oogle.com' won't match 'google.com'
    return hostname.replace(/^\.*/, '.').toLowerCase()
  }
  
  function parseNoProxyZone(zone) {
    zone = zone.trim().toLowerCase()
  
    var zoneParts = zone.split(':', 2)
      , zoneHost = formatHostname(zoneParts[0])
      , zonePort = zoneParts[1]
      , hasPort = zone.indexOf(':') > -1
  
    return {hostname: zoneHost, port: zonePort, hasPort: hasPort}
  }
  
  function uriInNoProxy(uri, noProxy) {
    var port = uri.port || (uri.protocol === 'https:' ? '443' : '80')
      , hostname = formatHostname(uri.hostname)
      , noProxyList = noProxy.split(',')
  
    // iterate through the noProxyList until it finds a match.
    return noProxyList.map(parseNoProxyZone).some(function(noProxyZone) {
      var isMatchedAt = hostname.indexOf(noProxyZone.hostname)
        , hostnameMatched = (
            isMatchedAt > -1 &&
            (isMatchedAt === hostname.length - noProxyZone.hostname.length)
          )
  
      if (noProxyZone.hasPort) {
        return (port === noProxyZone.port) && hostnameMatched
      }
  
      return hostnameMatched
    })
  }
  
  function getProxyFromURI(uri) {
    // Decide the proper request proxy to use based on the request URI object and the
    // environmental variables (NO_PROXY, HTTP_PROXY, etc.)
    // respect NO_PROXY environment variables (see: http://lynx.isc.org/current/breakout/lynx_help/keystrokes/environments.html)
  
    var noProxy = process.env.NO_PROXY || process.env.no_proxy || ''
  
    // if the noProxy is a wildcard then return null
  
    if (noProxy === '*') {
      return null
    }
  
    // if the noProxy is not empty and the uri is found return null
  
    if (noProxy !== '' && uriInNoProxy(uri, noProxy)) {
      return null
    }
  
    // Check for HTTP or HTTPS Proxy in environment Else default to null
  
    if (uri.protocol === 'http:') {
      return process.env.HTTP_PROXY ||
             process.env.http_proxy || null
    }
  
    if (uri.protocol === 'https:') {
      return process.env.HTTPS_PROXY ||
             process.env.https_proxy ||
             process.env.HTTP_PROXY  ||
             process.env.http_proxy  || null
    }
  
    // if none of that works, return null
    // (What uri protocol are you using then?)
  
    return null
  }
  
  module.exports = getProxyFromURI