9 files changed, 105 insertions, 17 deletions

diff --git a/app/controllers/admin_controller.rb b/app/controllers/admin_controller.rb
index 3fa0519..6ab2135 100644
--- a/app/controllers/admin_controller.rb
+++ b/app/controllers/admin_controller.rb
@@ -5,10 +5,10 @@ class AdminController < ApplicationController
   before_action :login_required
 
   def index
-    @drafts = Node.where("draft_id IS NOT NULL")
+    @drafts = Node.where("draft_id IS NOT NULL OR autosave_id IS NOT NULL")
       .limit(50).order("updated_at desc")
 
-    @drafts_count = Node.where("draft_id IS NOT NULL").count
+    @drafts_count = Node.where("draft_id IS NOT NULL OR autosave_id IS NOT NULL").count
 
     @recent_changes = Node.where(
       "updated_at < ? AND updated_at > ? AND parent_id IS NOT NULL",
diff --git a/app/controllers/nodes_controller.rb b/app/controllers/nodes_controller.rb
index 38d42d9..d1538e1 100644
--- a/app/controllers/nodes_controller.rb
+++ b/app/controllers/nodes_controller.rb
@@ -72,7 +72,7 @@ class NodesController < ApplicationController
     if @node.autosave
       flash.now[:notice] =
         "This page has unsaved changes from a previous session, shown below. " \
-        "Save to keep them, or use \"Discard changes\" below to go back to the last saved version."
+        "Save to keep them, or use \"Discard Autosave\" below to go back to the last saved version."
     elsif freshly_locked
       flash.now[:notice] = "Node locked and ready to edit"
     end
diff --git a/app/controllers/revisions_controller.rb b/app/controllers/revisions_controller.rb
index 9acb26f..4b0c549 100644
--- a/app/controllers/revisions_controller.rb
+++ b/app/controllers/revisions_controller.rb
@@ -21,10 +21,18 @@ class RevisionsController < ApplicationController
       params[:start_revision], params[:end_revision] = 1, 1
     end
 
-    @start      = @node.pages.find_by_revision( params[:start_revision] )
-    @end        = @node.pages.find_by_revision( params[:end_revision] )
-    @diff_view  = params[:view] == "side_by_side" ? :side_by_side : :inline
-    @diff       = @end.diff_against( @start, view: @diff_view )
+    @start = @node.resolve_page_reference(params[:start_revision])
+    @end   = @node.resolve_page_reference(params[:end_revision])
+
+    if @start.nil? || @end.nil?
+      flash[:error] = "That comparison is no longer available."
+      redirect_to(node_path(@node)) and return
+    end
+
+    @diff_view              = params[:view] == "side_by_side" ? :side_by_side : :inline
+    @diff                   = @end.diff_against(@start, view: @diff_view)
+    @available_layer_pairs  = @node.available_layer_pairs
+    @locked_by_other        = @node.locked? && @node.lock_owner != current_user
   end
 
   def show
diff --git a/app/helpers/revisions_helper.rb b/app/helpers/revisions_helper.rb
index fdb51f8..a629013 100644
--- a/app/helpers/revisions_helper.rb
+++ b/app/helpers/revisions_helper.rb
@@ -1,2 +1,7 @@
 module RevisionsHelper
+  # Human-readable label for a diff endpoint -- "head"/"draft"/"autosave"
+  # get their name; anything else is a revision number.
+  def describe_page_reference(ref)
+    %w[head draft autosave].include?(ref.to_s) ? ref.to_s.capitalize : "revision #{ref}"
+  end
 end
diff --git a/app/models/node.rb b/app/models/node.rb
index 7675ab6..82d9954 100644
--- a/app/models/node.rb
+++ b/app/models/node.rb
@@ -123,6 +123,27 @@ class Node < ApplicationRecord
     self.draft.reload
   end
 
+  def resolve_page_reference ref
+    case ref.to_s
+    when "head" then head
+    when "draft" then draft
+    when "autosave" then autosave
+    else pages.find_by_revision(ref)
+    end
+  end
+
+  # Which layer-pairs are meaningful to compare right now, given this
+  # node's actual state. Head vs autosave only shows up when no draft
+  # sits between them -- with a draft present, autosave is compared
+  # against the draft, never past it straight to head.
+  def available_layer_pairs
+    pairs = []
+    pairs << [:head, :draft]     if head && draft
+    pairs << [:draft, :autosave] if draft && autosave
+    pairs << [:head, :autosave]  if head && autosave && !draft
+    pairs
+  end
+
   def find_or_create_draft current_user
     self.wipe_draft!
     if draft && self.lock_owner == current_user
diff --git a/app/views/admin/index.html.erb b/app/views/admin/index.html.erb
index 77b45f4..c67ccb3 100644
--- a/app/views/admin/index.html.erb
+++ b/app/views/admin/index.html.erb
@@ -82,9 +82,9 @@
 </div>
 
 <div id="current_drafts_table">
-  
-  <h2>Current Drafts (<%= @drafts_count %>)</h2>
-  
+
+  <h2>Current Drafts & Autosaves (<%= @drafts_count %>)</h2>
+
   <table class="node_table">
     <tr class="header">
       <th class="node_id">ID</th>
@@ -92,6 +92,7 @@
       <th class="actions">Actions</th>
       <th class="editor">Locked by</th>
       <th class="revision">Rev.</th>
+      <th class="autosave">Autosave</th>
     </tr>
     <% @drafts.each do |node| %>
     <tr class="<%= cycle("even", "odd") %>">
@@ -103,6 +104,9 @@
       <td class="actions">
         <%= link_to 'show',      node_path(node) %>
         <%= link_to 'Revisions', node_revisions_path(node) %>
+        <% if pair = node.available_layer_pairs.last %>
+          <%= link_to 'diff', diff_node_revisions_path(node, start_revision: pair.first, end_revision: pair.last) %>
+        <% end %>
       </td>
       <td>
         <%= node.lock_owner.login if node.lock_owner %>
@@ -110,6 +114,9 @@
       <td>
         <%= link_to ( node.draft ? node.draft.revision : (node.head ? node.head.revision : "EMPTY" ) ), node_revisions_path(node) %>
       </td>
+      <td class="autosave">
+        <%= node.autosave ? "unsaved changes" : "" %>
+      </td>
     </tr>
     <% end %>
   </table>
diff --git a/app/views/nodes/edit.html.erb b/app/views/nodes/edit.html.erb
index cdc9b36..1c19410 100644
--- a/app/views/nodes/edit.html.erb
+++ b/app/views/nodes/edit.html.erb
@@ -6,9 +6,16 @@
         disabled: @node.autosave.present? %>
 
   <% if @node.autosave || (@node.draft && @node.head) %>
-    <%= button_to (@node.draft && !@node.autosave ? 'Destroy Draft' : 'Discard changes'),
+    <%= button_to (@node.draft && !@node.autosave ? 'Destroy Draft' : 'Discard Autosave'),
           revert_node_path(@node), method: :put,
           form: { data: { confirm: "This cannot be undone. Continue?" }, class: 'button_to destructive' } %>
+    <% if pair = @node.available_layer_pairs.find { |p| p.include?(:autosave) } %>
+      <%= button_to 'What changed?',
+            diff_node_revisions_path(@node),
+            method: :get,
+            params: { start_revision: pair.first, end_revision: pair.last },
+            form: { class: 'button_to computation' } %>
+    <% end %>
   <% end %>
 
   <%= submit_tag "Save Draft", form: dom_id(@node, :edit) %>
diff --git a/app/views/nodes/show.html.erb b/app/views/nodes/show.html.erb
index 036caf2..2469310 100644
--- a/app/views/nodes/show.html.erb
+++ b/app/views/nodes/show.html.erb
@@ -32,6 +32,16 @@
           <% end %>
         </div>
 
+        <% @node.available_layer_pairs.each do |pair| %>
+          <div class="node_info_item">
+            <%= button_to "Diff #{pair.first.to_s.capitalize} vs. #{pair.last.to_s.capitalize}",
+                  diff_node_revisions_path(@node),
+                  method: :get,
+                  params: { start_revision: pair.first, end_revision: pair.last },
+                  form: { class: 'button_to computation' } %>
+          </div>
+        <% end %>
+
         <% unless locked_by_other %>
           <% if @node.draft && !@node.autosave %>
             <div class="node_info_item">
@@ -41,7 +51,7 @@
           <% end %>
           <% if @node.draft || @node.autosave %>
             <div class="node_info_item">
-              <%= button_to (@node.draft && !@node.autosave ? 'Destroy Draft' : 'Discard changes'),
+              <%= button_to (@node.draft && !@node.autosave ? 'Destroy Draft' : 'Discard Autosave'),
                     revert_node_path(@node), method: :put,
                     form: { data: { confirm: "This cannot be undone. Continue?" }, class: 'button_to destructive' } %>
             </div>
diff --git a/app/views/revisions/diff.html.erb b/app/views/revisions/diff.html.erb
index d7bb528..3157dca 100644
--- a/app/views/revisions/diff.html.erb
+++ b/app/views/revisions/diff.html.erb
@@ -4,11 +4,41 @@
   <%= link_to 'Revisions', node_revisions_path(@node) %>
 </p>
 
-<%= form_tag diff_node_revisions_path do %>
-  <%= select_tag :start_revision, options_for_select(@node.pages.map{|x| x.revision}, params[:start_revision].to_i) %>
-  <%= select_tag :end_revision, options_for_select(@node.pages.map{|x| x.revision}, params[:end_revision].to_i) %>
-  <%= select_tag :view, options_for_select([['Inline', 'inline'], ['Side by side', 'side_by_side']], @diff_view) %>
-  <%= submit_tag 'Diff' %>
+<p class="diff_comparison_label">
+  Comparing <strong><%= describe_page_reference(params[:start_revision]) %></strong>
+  against <strong><%= describe_page_reference(params[:end_revision]) %></strong>
+</p>
+
+<% numeric_comparison = params[:start_revision].to_s =~ /\A\d+\z/ && params[:end_revision].to_s =~ /\A\d+\z/ %>
+
+<% if numeric_comparison %>
+  <%= form_tag diff_node_revisions_path do %>
+    <%= select_tag :start_revision, options_for_select(@node.pages.map{|x| x.revision}, params[:start_revision].to_i) %>
+    <%= select_tag :end_revision, options_for_select(@node.pages.map{|x| x.revision}, params[:end_revision].to_i) %>
+    <%= select_tag :view, options_for_select([['Inline', 'inline'], ['Side by side', 'side_by_side']], @diff_view) %>
+    <%= submit_tag 'Diff' %>
+  <% end %>
+<% else %>
+  <p class="node_action_bar standalone_action_bar"><%= link_to 'Compare two numbered revisions instead', node_revisions_path(@node) %></p>
+<% end %>
+
+<% if @available_layer_pairs.present? %>
+  <p class="node_action_bar standalone_action_bar">
+    <% @available_layer_pairs.each do |pair| %>
+      <% next if [params[:start_revision].to_s, params[:end_revision].to_s].sort == pair.map(&:to_s).sort %>
+      <%= button_to "Diff #{pair.first.to_s.capitalize} vs. #{pair.last.to_s.capitalize}",
+            diff_node_revisions_path(@node),
+            method: :get,
+            params: { start_revision: pair.first, end_revision: pair.last, view: @diff_view },
+            form: { class: 'button_to computation' } %>
+    <% end %>
+
+    <% if !@locked_by_other && (@node.autosave || @node.draft) %>
+      <%= button_to (@node.draft && !@node.autosave ? 'Destroy Draft' : 'Discard Autosave'),
+            revert_node_path(@node), method: :put,
+            form: { data: { confirm: "This cannot be undone. Continue?" }, class: 'button_to destructive' } %>
+    <% end %>
+  </p>
 <% end %>
 
 <div id="diffview">