mapped.js

var url = require('url')

module.exports = function(mappedPaths) {

  var reverseMap = Object.create(null)

  if (typeof mappedPaths !== 'object') {
    throw new Error('A hash map of paths is required')
  }

  Object.keys(mappedPaths).forEach(function(url) {
    reverseMap[mappedPaths[url]] = url
  })

  return {

    /**
     * This is intended to be exported as a helper for the view layer
     */
    versionPath: function(urlPath) {

      if (!Array.isArray(urlPath)) {
        return mappedPaths[urlPath.toString()] || urlPath
      }

      return urlPath.map(function(singleUrl) {
        return mappedPaths[singleUrl.toString()] || singleUrl
      })
    },

    modifyMap: function(someMappedPaths) {

      Object.keys(someMappedPaths).forEach(function(url) {
        mappedPaths[url] = someMappedPaths[url]
      })

      // regenerate reverseMap. DRY?
      Object.keys(mappedPaths).forEach(function(url) {
        reverseMap[mappedPaths[url]] = url
      })

    },

    middleware: function(req, res, next) {
      // We only do this on GET and HEAD requests
      if ('GET' !== req.method && 'HEAD' !== req.method) {
        return next()
      }

      var parsedUrl = url.parse(req.url)
        , mappedUrl = reverseMap[parsedUrl.pathname]
      if (mappedUrl) {
        req.url = mappedUrl + (parsedUrl.search || '')
      }

      next()
    }
  }
}