Pagination using collections: Backbone.js

pagger.coffee

class Pager
  constructor: (collection, attributes) ->
    @collection   = collection
    @currentPage  = attributes.current_page
    @totalPages   = attributes.total_pages
    @perPage      = attributes.per_page
    @totalEntries = attributes.total_entries
    @pages        = @visiblePageNumbers().map (page) =>
                      page:       page
                      path:       @buildPath page
                      createLink: page isnt @currentPage and page isnt '...'

  visiblePageNumbers: ->
    innerWindow = 3
    outerWindow = 0
    windowFrom  = @currentPage - innerWindow
    windowTo    = @currentPage + innerWindow

    if windowTo > @totalPages
      windowFrom -= windowTo - @totalPages
      windowTo   = @totalPages

    if windowFrom < 1
      windowTo   += 1 - windowFrom
      windowFrom = 1
      windowTo   = @totalPages if windowTo > @totalPages

    visible  = [1..@totalPages]
    leftGap  = [Math.min(2 + outerWindow, windowFrom)...windowFrom]
    rightGap = [Math.min(windowTo + 1, @totalPages - outerWindow)...(@totalPages - outerWindow)]

    if leftGap.length > 1
      visible = _(visible).reject (page) -> _(leftGap).include(page)
      visible.splice(outerWindow + 1, 0, '...')

    if rightGap.length > 1
      visible = _(visible).reject (page) -> _(rightGap).include(page)
      visible.splice(visible.length - outerWindow - 1, 0, '...')

    visible
  render: -> if @totalPages > 1 then JST.pager(this) else ''

  buildPath: (page) ->
    "#/#{ _([ @collection._filter, page ]).compact().join('/') }"


  isFirstPage: -> @currentPage == 1
  isLastPage:  -> @currentPage == @totalPages
  prevPath:    -> @buildPath @currentPage - 1
  nextPath:    -> @buildPath @currentPage + 1