#45 差分 API 作成

backend/app/models/wiki_page.rb

@@ -8,14 +8,41 @@ class WikiPage < ApplicationRecord
 
   validates :title, presence: true, length: { maximum: 255 }, uniqueness: true
 
+  def sha= val
+    if val.present?
+      @sha = val
+      @page = wiki.page("#{ id }.md", @sha)
+    else
+      @page = wiki.page("#{ id }.md")
+      @sha = @page.versions.first.id
+    end
+    vers = @page.versions
+    idx = vers.find_index { |ver| ver.id == @sha }
+    @pred = vers[idx + 1]&.id
+    @succ = idx.positive? ? vers[idx - 1].id : nil
+    @sha
+  end
+
+  def sha
+    @sha
+  end
+
+  def pred
+    @pred
+  end
+
+  def succ
+    @succ
+  end
+
   def body
-    page = wiki.page("#{ id }.md")
-    page&.raw_data
+    sha = nil unless @page
+    @page&.raw_data&.force_encoding('UTF-8')
   end
 
   def set_body content, user:
-    commit_info = { name:     user.id.to_s,
-                    email:    'dummy@example.com' }
+    commit_info = { name:   user.id.to_s,
+                    email:  'dummy@example.com' }
     page = wiki.page("#{ id }.md")
     if page
       commit_info[:message] = "Updated #{ id }"