canvas-lms/app/controllers/files_controller.rb

#
# Copyright (C) 2011 Instructure, Inc.
#
# This file is part of Canvas.
#
# Canvas is free software: you can redistribute it and/or modify it under
# the terms of the GNU Affero General Public License as published by the Free
# Software Foundation, version 3 of the License.
#
# Canvas is distributed in the hope that it will be useful, but WITHOUT ANY
# WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
# A PARTICULAR PURPOSE. See the GNU Affero General Public License for more
# details.
#
# You should have received a copy of the GNU Affero General Public License along
# with this program. If not, see <http://www.gnu.org/licenses/>.
#

class FilesController < ApplicationController
  before_filter :require_pseudonym, :only => :create_pending
  before_filter :require_context, :except => [:public_feed,:full_index,:assessment_question_show,:image_thumbnail,:show_thumbnail,:preflight,:create_pending,:s3_success,:show,:api_create,:api_create_success]
  before_filter :check_file_access_flags, :only => [:show_relative, :show]
  prepend_around_filter :load_pseudonym_from_policy, :only => :create
  skip_before_filter :verify_authenticity_token, :only => :api_create

  include Api::V1::Attachment

  before_filter { |c| c.active_tab = "files" }

  def quota
    get_quota
    if authorized_action(@context.attachments.new, @current_user, :create)
      h = ActionView::Base.new
      h.extend ActionView::Helpers::NumberHelper
      result = {
        :quota => h.number_to_human_size(@quota),
        :quota_used => h.number_to_human_size(@quota_used),
        :quota_full => (@quota_used >= @quota)
      }
      render :json => result.to_json
    end
  end
  
  def check_file_access_flags
    if params[:user_id] && params[:ts] && params[:sf_verifier]
      user = User.find_by_id(params[:user_id]) if params[:user_id].present?
      if user && user.valid_access_verifier?(params[:ts], params[:sf_verifier])
        # attachment.rb checks for this session attribute when determining 
        # permissions, but it should be ignored by the rest of the models' 
        # permission checks
        session['file_access_user_id'] = user.id
        session['file_access_expiration'] = 1.hour.from_now.to_i
        session[:session_affects_permissions] = true
      end
    end
    # These sessions won't get deleted when the user logs out since this
    # is on a separate domain, so we've added our own (stricter) timeout.
    if session && session['file_access_user_id'] && session['file_access_expiration'].to_i > Time.now.to_i
      session['file_access_expiration'] = 1.hour.from_now.to_i
    end
    true
  end
  protected :check_file_access_flags
  
  def index
    if request.format == :json
      if authorized_action(@context.attachments.new, @current_user, :read)
        @current_folder = Folder.find_folder(@context, params[:folder_id])
        if !@current_folder || authorized_action(@current_folder, @current_user, :read)
          if params[:folder_id]
            if @context.grants_right?(@current_user, session, :manage_files)
              @current_attachments = @current_folder.active_file_attachments
            else
              @current_attachments = @current_folder.visible_file_attachments
            end
            @current_attachments = @current_attachments.scoped(:include => [:thumbnail, :media_object])
            render :json => @current_attachments.to_json(:methods => [:readable_size, :currently_locked, :thumbnail_url], :permissions => {:user => @current_user, :session => session})
          else
            render :json => @context.file_structure_for(@current_user).to_json(:permissions => {:user => @current_user}, :methods => [:readable_size, :mime_class, :currently_locked, :collaborator_ids])
          end
        end
      end
    else
      full_index
    end
  end

  def images
    if authorized_action(@context.attachments.new, @current_user, :read)
      @images = @context.active_images.paginate :page => params[:page]
      headers['X-Total-Pages'] = @images.total_pages.to_s
      render :partial => "shared/wiki_image", :collection => @images
    end
  end

  def full_index
    get_context
    get_quota
    add_crumb(t('#crumbs.files', "Files"), named_context_url(@context, :context_files_url))
    @contexts = [@context]
    if !@context.is_a?(User) || (@context == @current_user && params[:show_all_contexts])
      get_all_pertinent_contexts(true)
    end
    @too_many_contexts = @contexts.length > 15
    @contexts = @contexts[0,15]
    if @contexts.length <= 1 && !authorized_action(@context.attachments.new, @current_user, :read)
      return
    end
    return unless tab_enabled?(@context.class::TAB_FILES)
    log_asset_access("files:#{@context.asset_string}", "files", 'other') if @context
    respond_to do |format|
      if @contexts.empty?
        format.html { redirect_to !@context || @context == @current_user ? dashboard_url : named_context_url(@context, :context_url) }
      else
        format.html { render :action => 'full_index' }
      end
      format.json { render :json => @file_structures.to_json }
    end
  end
  
  def text_show
    @attachment = @context.attachments.find(params[:file_id])
    if authorized_action(@attachment,@current_user,:read)
      if @attachment.grants_right?(@current_user, nil, :download)
        @headers = false
        @tag = @attachment.context_module_tag
        @module = @attachment.context_module_tag.context_module rescue nil
        render
      else
        show
      end
    end
  end
  
  def assessment_question_show
    @context = AssessmentQuestion.find(params[:assessment_question_id])
    @attachment = @context.attachments.find(params[:id])
    @skip_crumb = true
    if @attachment.deleted?
      flash[:notice] = t 'notices.deleted', "The file %{display_name} has been deleted", :display_name => @attachment.display_name
      redirect_to dashboard_url
    end
    show
  end
  
  # this is used for the google docs preview of a document
  def public_url
    respond_to do |format|
      format.json do
        @attachment = Attachment.find(params[:id])
        # if the attachment is part of a submisison, its 'context' will be the student that submmited the assignment.  so if  @current_user is a 
        # teacher authorized_action(@attachment, @current_user, :download) will be false, we need to actually check if they have perms to see the 
        # submission.
        if params[:submission_id] && (@submission = Submission.find(params[:submission_id]))
          @attachment ||= @submission.submission_history.map(&:versioned_attachments).flatten.find{|a| a.id == params[:download].to_i }
        end        
        if @submission ? authorized_action(@submission, @current_user, :read) : authorized_action(@attachment, @current_user, :download)
          render :json  => { :public_url => @attachment.authenticated_s3_url(:protocol => request.protocol) }
        end
      end
    end
  end
  
  def show
    original_params = params.dup
    params[:id] ||= params[:file_id]
    get_context
    # note that the /files/XXX URL implicitly uses the current user as the
    # context, even though it doesn't search for the file using
    # @current_user.attachments.find , since it might not actually be a user
    # attachment.
    # this implicit context magic happens in ApplicationController#get_context
    if @context && !@context.is_a?(User)
      @attachment = @context.attachments.find(params[:id])
    else
      @attachment = Attachment.find(params[:id])
      @skip_crumb = true unless @context
    end
    params[:download] ||= params[:preview]
    add_crumb(t('#crumbs.files', "Files"), named_context_url(@context, :context_files_url)) unless @skip_crumb
    if @attachment.deleted?
      flash[:notice] = t 'notices.deleted', "The file %{display_name} has been deleted", :display_name => @attachment.display_name
      if params[:preview] && @attachment.mime_class == 'image'
        redirect_to '/images/blank.png'
      elsif request.format == :json
        render :json => {:deleted => true}.to_json
      else
        redirect_to named_context_url(@context, :context_files_url)
      end
      return
    end
    if (params[:download] && params[:verifier] && params[:verifier] == @attachment.uuid) || authorized_action(@attachment, @current_user, :read)
      if params[:download]
        if (params[:verifier] && params[:verifier] == @attachment.uuid) || (@attachment.grants_right?(@current_user, session, :download))
          disable_page_views if params[:preview]
          begin
            send_attachment(@attachment)
          rescue => e
            @headers = false if params[:ts] && params[:verifier]
            @not_found_message = t 'errors.not_found', "It looks like something went wrong when this file was uploaded, and we can't find the actual file.  You may want to notify the owner of the file and have them re-upload it."
            logger.error "Error downloading a file: #{e} - #{e.backtrace}"
            render :template => 'shared/errors/404_message', :status => :bad_request
          end
          return
        elsif authorized_action(@attachment, @current_user, :read)
          render_attachment(@attachment)
        end
      # This action is a callback used in our system to help record when
      # a user views an inline preview of a file instead of downloading
      # it, since this should also count as an access.
      elsif params[:inline]
        generate_new_page_view
        @attachment.context_module_action(@current_user, :read) if @current_user
        log_asset_access(@attachment, 'files', 'files')
        render :json => {:ok => true}.to_json
      else
        render_attachment(@attachment)
      end
    end
  end
  
  def render_attachment(attachment)
    respond_to do |format|
      if params[:preview] && attachment.mime_class == 'image'
        format.html { redirect_to '/images/lock.png' }
      else
        if @files_domain
          @headers = false
          @show_left_side = false
        end
        format.html { render :action => 'show' }
      end
      if request.format == :json
        options = {:permissions => {:user => @current_user}}
        if @attachment.grants_right?(@current_user, session, :download)
          # Right now we assume if they ask for json data on the attachment
          # which includes the scribd doc data, then that means they have 
          # viewed or are about to view the file in some form.
          attachment.context_module_action(@current_user, :read) if @current_user && (
            (feature_enabled?(:scribd) && attachment.scribd_doc) || 
            (service_enabled?(:google_docs_previews) && attachment.authenticated_s3_url)
          )
          options[:methods] = :authenticated_s3_url if service_enabled?(:google_docs_previews) && attachment.authenticated_s3_url
          log_asset_access(@attachment, "files", "files")
        else
          @attachment.scribd_doc = nil
        end
      end
      format.json { render :json => @attachment.to_json(options) }
    end
  end
  protected :render_attachment

  def show_relative
    path = params[:file_path]

    #if the relative path matches the given file id use that file
    if params[:file_id].present? && @attachment = @context.attachments.find_by_id(params[:file_id])
      if @attachment.matches_full_display_path?(path) || @attachment.matches_full_path?(path)
        params[:id] = params[:file_id]
      else
        @attachment = nil
      end
    end

    @attachment ||= Folder.find_attachment_in_context_with_path(@context, path)

    raise ActiveRecord::RecordNotFound if !@attachment
    params[:id] = @attachment.id

    params[:download] = '1'
    show
  end
  
  # checks if for the current root account there's a 'files' domain
  # defined and tried to use that.  This way any files that we stream through
  # a canvas URL are at least on a separate subdomain and the javascript 
  # won't be able to access or update data with AJAX requests.
  def safer_domain_available?
    if !@files_domain && request.host_with_port != HostUrl.file_host(@domain_root_account, request.host)
      @safer_domain_host = HostUrl.file_host(@domain_root_account, request.host)
    end
    !!@safer_domain_host
  end
  protected :safer_domain_available?
  
  def attachment_content
    @attachment = @context.attachments.active.find(params[:file_id])
    if authorized_action(@attachment, @current_user, :update)
      # The files page lets you edit text content inline by firing off a json
      # request to get the data.
      # Protect ourselves against reading huge files into memory -- if the
      # attachment is too big, don't return it.
      if @attachment.size > Setting.get_cached('attachment_json_response_max_size', 1.megabyte.to_s).to_i
        render :json => { :error => t('errors.too_large', "The file is too large to edit") }.to_json
        return
      end

      stream = @attachment.open
      render :json => { :body => stream.read }.to_json
     end
  end
  
  def send_attachment(attachment)
    # check for download_frd param and, if it's present, force the user to download the
    # file and don't display it inline. we use download_frd instead of looking to the
    # download param because the download param is used all over the place to mean stuff
    # other than actually download the file. Long term we probably ought to audit the files
    # controller, make download mean download, and remove download_frd.
    if params[:inline] && !params[:download_frd] && attachment.content_type && (attachment.content_type.match(/\Atext/) || attachment.mime_class == 'text' || attachment.mime_class == 'html' || attachment.mime_class == 'code' || attachment.mime_class == 'image')
      send_stored_file(attachment)
    elsif attachment.inline_content? && !params[:download_frd] && !@context.is_a?(AssessmentQuestion)
      if params[:file_path] || !params[:wrap]
        send_stored_file(attachment)
      else
        # If the file is inlineable then redirect to the 'show' action 
        # so we can wrap it in all the Canvas header/footer stuff
        redirect_to(named_context_url(@context, :context_file_url, attachment.id))
      end
    else
      send_stored_file(attachment, false, true)
    end
  end
  protected :send_attachment
  
  def send_stored_file(attachment, inline=true, redirect_to_s3=false)
    attachment.context_module_action(@current_user, :read) if @current_user && !params[:preview]
    log_asset_access(@attachment, "files", "files") unless params[:preview]
    if safer_domain_available?
      redirect_to safe_domain_file_url(attachment, @safer_domain_host, params[:verifier], !inline)
    elsif Attachment.local_storage?
      @headers = false if @files_domain
      cancel_cache_buster
      send_file(attachment.full_filename, :type => attachment.content_type_with_encoding, :disposition => (inline ? 'inline' : 'attachment'))
    elsif redirect_to_s3
      redirect_to(inline ? attachment.cacheable_s3_inline_url : attachment.cacheable_s3_download_url)
    else
      require 'aws/s3'
      cancel_cache_buster
      send_file_headers!( :length=>AWS::S3::S3Object.about(attachment.full_filename, attachment.bucket_name)["content-length"], :filename=>attachment.filename, :disposition => 'inline', :type => attachment.content_type_with_encoding)
      render :status => 200, :text => Proc.new { |response, output|
        AWS::S3::S3Object.stream(attachment.full_filename, attachment.bucket_name) do |chunk|
         output.write chunk
        end
      }
    end
  end
  protected :send_stored_file
  
  # GET /files/new
  def new
    @attachment = @context.attachments.build
    if authorized_action(@attachment, @current_user, :create)
    end
  end
  
  def preflight
    @context = Context.find_by_asset_string(params[:context_code])
    if authorized_action(@context, @current_user, :manage_files)
      @current_folder = Folder.find_folder(@context, params[:folder_id])
      if @current_folder
        params[:filenames] = [] if params[:filenames].blank?
        return render :json => {
          :duplicates => @current_folder.active_file_attachments.map(&:display_name) & params[:filenames]
        }
      end
    end
    render :json => {}
  end

  def create_pending
    @context = Context.find_by_asset_string(params[:attachment][:context_code])
    @asset = Context.find_asset_by_asset_string(params[:attachment][:asset_string], @context) if params[:attachment][:asset_string]
    @attachment = Attachment.new
    @check_quota = true
    permission_object = @attachment
    permission = :create
    intent = params[:attachment][:intent]
    
    # Using workflow_state we can keep track of the files that have been built
    # but we don't know that there's an s3 component for yet (it's still being
    # uploaded)
    workflow_state = 'unattached'
    # There are multiple reasons why we could be building a file. The default
    # is to upload it to a context.  In the other cases we need to check the
    # permission related to the purpose to make sure the file isn't being
    # uploaded just to disappear later
    if @asset.is_a?(Assignment) && intent == 'comment'
      permission_object = @asset
      permission = :attach_submission_comment_files
      @context = @asset
      @check_quota = false
    elsif @asset.is_a?(Assignment) && intent == 'submit'
      permission_object = @asset
      permission = (@asset.submission_types || "").match(/online_upload/) ? :submit : :nothing
      @context = @current_user
      @check_quota = false
    elsif @context && intent == 'attach_discussion_file'
      permission_object = @context.discussion_topics.new
      permission = :attach
    elsif @context && intent == 'message'
      permission_object = @context
      permission = :send_messages
      @check_quota = false
    elsif @context && intent && intent != 'upload'
      # In other cases (like unzipping a file, extracting a QTI, etc.
      # we don't actually want the uploaded file to show up in the context's
      # file listings.  If you set its workflow_state to unattached_temporary
      # then it will never be activated.
      workflow_state = 'unattached_temporary'
      @check_quota = false
    end
    
    @attachment.context = @context
    if authorized_action(permission_object, @current_user, permission)
      if @context.respond_to?(:is_a_context?) && @check_quota
        get_quota
        return if quota_exceeded(named_context_url(@context, :context_files_url))
      end
      @attachment.filename = params[:attachment][:filename]
      @attachment.file_state = 'deleted'
      @attachment.workflow_state = workflow_state
      if @context.respond_to?(:folders)
        if params[:attachment][:folder_id].present?
          @folder = @context.folders.active.find_by_id(params[:attachment][:folder_id])
        end
        @folder ||= Folder.unfiled_folder(@context)
        @attachment.folder_id = @folder.id
      end
      @attachment.content_type = Attachment.mimetype(@attachment.filename)
      @attachment.save!

      res = @attachment.ajax_upload_params(@current_pseudonym,
              named_context_url(@context, :context_files_url, :format => :text, :duplicate_handling => params[:attachment][:duplicate_handling]),
              s3_success_url(@attachment.id, :uuid => @attachment.uuid, :duplicate_handling => params[:attachment][:duplicate_handling]),
              :no_redirect => params[:no_redirect],
              :upload_params => {
                'attachment[folder_id]' => params[:attachment][:folder_id] || '',
                'attachment[unattached_attachment_id]' => @attachment.id,
                'check_quota_after' => @check_quota ? '1' : '0'
              },
              :ssl => request.ssl?)
      render :json => res.to_json
    end
  end
  
  def s3_success
    if params[:id].present?
      @attachment = Attachment.find_by_id_and_workflow_state_and_uuid(params[:id], 'unattached', params[:uuid])
    end
    details = AWS::S3::S3Object.about(@attachment.full_filename, @attachment.bucket_name) rescue nil
    if @attachment && details
      deleted_attachments = @attachment.handle_duplicates(params[:duplicate_handling])
      @attachment.process_s3_details!(details)
      render :json => {
        :attachment => @attachment,
        :deleted_attachment_ids => deleted_attachments.map(&:id)
      }.to_json(:allow => :uuid, :methods => [:uuid,:readable_size,:mime_class,:currently_locked,:scribdable?], :permissions => {:user => @current_user, :session => session}, :include_root => false),
             :as_text => true
    else
      render :text => ""
    end
  end

  # for local file uploads
  def api_create
    @policy, @attachment = Attachment.decode_policy(params[:Policy], params[:Signature])
    if !@policy
      return render(:nothing => true, :status => :bad_request)
    end
    @context = @attachment.context
    @attachment.workflow_state = nil
    @attachment.uploaded_data = params[:file]
    if @attachment.save
      # for consistency with the s3 upload client flow, we redirect to the success url here to finish up
      redirect_to api_v1_files_create_success_url(@attachment, :uuid => @attachment.uuid, :on_duplicate => params[:on_duplicate])
    else
      render(:nothing => true, :status => :bad_request)
    end
  end

  def api_create_success
    @attachment = Attachment.find_by_id_and_uuid(params[:id], params[:uuid])
    return render(:nothing => true, :status => :bad_request) unless @attachment.try(:file_state) == 'deleted'
    duplicate_handling = check_duplicate_handling_option(request)
    return unless duplicate_handling
    if Attachment.s3_storage?
      return render(:nothing => true, :status => :bad_request) unless @attachment.state == :unattached
      details = AWS::S3::S3Object.about(@attachment.full_filename, @attachment.bucket_name)
      @attachment.process_s3_details!(details)
    else
      @attachment.file_state = 'available'
      @attachment.save!
    end
    @attachment.handle_duplicates(duplicate_handling)
    render :json => attachment_json(@attachment)
  end

  # POST /files
  # POST /files.xml
  def create
    if (folder_id = params[:attachment].delete(:folder_id)) && folder_id.present?
      @folder = @context.folders.active.find_by_id(folder_id)
    end
    @folder ||= Folder.unfiled_folder(@context)
    params[:attachment][:uploaded_data] ||= params[:attachment_uploaded_data]
    params[:attachment][:uploaded_data] ||= params[:file] 
    params[:attachment][:user] = @current_user
    params[:attachment].delete :context_id
    params[:attachment].delete :context_type
    duplicate_handling = params.delete :duplicate_handling
    if (unattached_attachment_id = params[:attachment].delete(:unattached_attachment_id)) && unattached_attachment_id.present?
      @attachment = @context.attachments.find_by_id_and_workflow_state(unattached_attachment_id, 'unattached')
    end
    @attachment ||= @context.attachments.new
    if authorized_action(@attachment, @current_user, :create)
      get_quota
      return if (params[:check_quota_after].nil? || params[:check_quota_after] == '1') &&
                  quota_exceeded(named_context_url(@context, :context_files_url))

      respond_to do |format|
        @attachment.folder_id ||= @folder.id
        @attachment.workflow_state = nil
        @attachment.file_state = 'available'
        success = nil
        if params[:attachment] && params[:attachment][:source_attachment_id]
          a = Attachment.find(params[:attachment].delete(:source_attachment_id))
          if a.root_attachment_id && att = @folder.attachments.find_by_id(a.root_attachment_id)
            @attachment = att
            success = true
          elsif a.grants_right?(@current_user, session, :download)
            @attachment = a.clone_for(@context, @attachment)
            success = @attachment.save
          end
        end
        if params[:attachment][:uploaded_data]
          success = @attachment.update_attributes(params[:attachment])
          @attachment.errors.add_to_base(t('errors.server_error', "Upload failed, server error, please try again.")) unless success
        else
          @attachment.errors.add_to_base(t('errors.missing_field', "Upload failed, expected form field missing"))
        end
        deleted_attachments = @attachment.handle_duplicates(duplicate_handling)
        unless @attachment.downloadable?
          success = false
          if (params[:attachment][:uploaded_data].size == 0 rescue false)
            @attachment.errors.add_to_base(t('errors.empty_file', "That file is empty.  Please upload a different file."))
          else
            @attachment.errors.add_to_base(t('errors.upload_failed', "Upload failed, please try again."))
          end
          unless @attachment.new_record?
            @attachment.destroy rescue @attachment.delete
          end
        end
        if success
          @attachment.move_to_bottom
          format.html { return_to(params[:return_to], named_context_url(@context, :context_files_url)) }
          format.json do
            render :json => { :attachment => @attachment, :deleted_attachment_ids => deleted_attachments.map(&:id) }.to_json(:allow => :uuid, :methods => [:uuid,:readable_size,:mime_class,:currently_locked,:scribdable?,:thumbnail_url], :permissions => {:user => @current_user, :session => session}, :include_root => false),
                   :as_text => true
          end
          format.text do
            render :json => { :attachment => @attachment, :deleted_attachment_ids => deleted_attachments.map(&:id) }.to_json(:allow => :uuid, :methods => [:uuid,:readable_size,:mime_class,:currently_locked,:scribdable?,:thumbnail_url], :permissions => {:user => @current_user, :session => session}, :include_root => false),
                   :as_text => true
          end
        else
          format.html { render :action => "new" }
          format.json { render :json => @attachment.errors.to_json }
          format.text { render :json => @attachment.errors.to_json }
        end
      end
    end
  end

  def update
    @attachment = @context.attachments.find(params[:id])
    @folder = @context.folders.active.find(params[:attachment][:folder_id]) rescue nil
    @folder ||= @attachment.folder
    @folder ||= Folder.unfiled_folder(@context)
    if authorized_action(@attachment, @current_user, :update)
      respond_to do |format|
        just_hide = params[:attachment][:just_hide]
        hidden = params[:attachment][:hidden]
        params[:attachment].delete_if{|k, v| ![:display_name, :locked, :lock_at, :unlock_at, :uploaded_data].include?(k.to_sym) }
        # Need to be careful on this one... we can't let students turn in a
        # file and then edit it after the fact...
        params[:attachment].delete(:uploaded_data) if @context.is_a?(User)
        @attachment.attributes = params[:attachment]
        if just_hide == '1'
          @attachment.locked = false
          @attachment.hidden = true
        elsif hidden && (hidden.empty? || hidden == "0")
          @attachment.hidden = false
        end
        @attachment.folder = @folder
        @folder_id_changed = @attachment.folder_id_changed?
        if @attachment.save
          @attachment.move_to_bottom if @folder_id_changed
          flash[:notice] = t 'notices.updated', "File was successfully updated."
          format.html { redirect_to named_context_url(@context, :context_files_url) }
          format.json { render :json => @attachment.to_json(:methods => [:readable_size, :mime_class, :currently_locked], :permissions => {:user => @current_user, :session => session}), :status => :ok }
        else
          format.html { render :action => "edit" }
          format.json { render :json => @attachment.errors.to_json, :status => :bad_request }
        end
      end
    end
  end
  
  def reorder
    @folder = @context.folders.active.find(params[:folder_id])
    if authorized_action(@context, @current_user, :manage_files)
      @folders = @folder.sub_folders.active
      @folders.first && @folders.first.update_order((params[:folder_order] || "").split(","))
      @folder.file_attachments.first && @folder.file_attachments.first.update_order((params[:order] || "").split(","))
      @folder.reload
      render :json => @folder.subcontent.to_json(:methods => :readable_size, :permissions => {:user => @current_user, :session => session})
    end
  end
  
  def destroy
    @attachment = Attachment.find(params[:id])
    if authorized_action(@attachment, @current_user, :delete)
      @attachment.destroy
      respond_to do |format|
        format.html { redirect_to named_context_url(@context, :context_files_url) }# show.rhtml
        format.json { render :json => @attachment.to_json }
      end
    end
  end
  
  def image_thumbnail
    cancel_cache_buster
    url = Rails.cache.fetch(['thumbnail_url', params[:uuid]].cache_key, :expires_in => 30.minutes) do
      attachment = Attachment.find_by_id_and_uuid(params[:id], params[:uuid]) if params[:id].present?
      url = attachment.thumbnail_url rescue nil
      url ||= '/images/no_pic.gif'
      url
    end
    redirect_to url
  end

  # when using local storage, the image_thumbnail action redirects here rather
  # than to a s3 url
  def show_thumbnail
    if Attachment.local_storage?
      cancel_cache_buster
      thumbnail = Thumbnail.find_by_id_and_uuid(params[:id], params[:uuid]) if params[:id].present?
      raise ActiveRecord::RecordNotFound unless thumbnail
      send_file thumbnail.full_filename, :content_type => thumbnail.content_type
    else
      image_thumbnail
    end
  end

  def public_feed
    return unless get_feed_context
    feed = Atom::Feed.new do |f|
      f.title = t :feed_title, "%{course_or_group} Files Feed", :course_or_group => @context.name
      f.links << Atom::Link.new(:href => polymorphic_url([@context, :files]), :rel => 'self')
      f.updated = Time.now
      f.id = polymorphic_url([@context, :files])
    end
    @entries = []
    @entries.concat @context.attachments.active
    @entries = @entries.sort_by{|e| e.updated_at}
    @entries.each do |entry|
      feed.entries << entry.to_atom
    end
    respond_to do |format|
      format.atom { render :text => feed.to_xml }
    end    
  end
end