thumbsup/src/input/hierarchy.js

const path = require('path')
const Album = require('../model/album')

exports.createAlbums = function (collection, mapper, opts) {
  // returns a top-level album for the home page
  // under which all files are grouped into sub-albums
  // and finalised recursively (calculate stats, etc...)
  const home = group(collection, mapper, opts.homeAlbumName)
  home.finalize(opts)
  return home
}

function group (collection, mapper, homeAlbumName) {
  // this hashtable will contain all albums, with the full path as key
  // e.g. groups['holidays/tokyo']
  var groups = {
    // the home album is indexed as '.'
    // the value of '.' is local to this function, and doesn't appear anywhere else
    '.': new Album(homeAlbumName)
  }
  // put all files in the right albums
  // a file can be in multiple albums
  collection.forEach(function (file) {
    const albums = mapper.getAlbums(file)
    albums.forEach(albumPath => {
      if (!albumPath || albumPath === '/') {
        albumPath = '.'
      }
      createAlbumHierarchy(groups, albumPath)
      groups[albumPath].files.push(file)
    })
  })
  // return the top-level album
  return groups['.']
}

function createAlbumHierarchy (allGroupNames, segment) {
  if (!allGroupNames.hasOwnProperty(segment)) {
    // create parent albums first
    var parent = path.dirname(segment)
    if (parent !== '.') {
      createAlbumHierarchy(allGroupNames, parent)
    }
    // then create album if it doesn't exist
    // and attach it to its parent
    var lastSegment = path.basename(segment)
    allGroupNames[segment] = new Album({ title: lastSegment })
    allGroupNames[parent].albums.push(allGroupNames[segment])
  }
}