Create Wiki migration task.

This commit adds a new Rake task for migrating all of your existing
Wiki content from your database into new Gollum repositories.

The bulk of the logic happens within the `WikiToGollumMigrator`
class which is decently test covered and located in the lib directory.

The new Rake task can be executed by running:

   `bundle exec rake gitlab:wiki:migrate`

It will output a nice log of every project that it migrates along
with success or failure messages.

I have used it on my own installation to migrate my Wikis successfully.

1 files changed, 114 insertions, 0 deletions

diff --git a/spec/lib/wiki_to_gollum_migrator_spec.rb b/spec/lib/wiki_to_gollum_migrator_spec.rb
new file mode 100644
index 00000000000..a784d836d62
--- /dev/null
+++ b/spec/lib/wiki_to_gollum_migrator_spec.rb
@@ -0,0 +1,114 @@
+require "spec_helper"
+
+describe WikiToGollumMigrator do
+
+  def create_wiki_for(project)
+    3.times { @pages[project.id] << create_page(project) }
+  end
+
+  def create_revisions_for(project)
+    @pages[project.id].each do |page|
+      create_revision(page)
+    end
+  end
+
+  def create_page(project)
+    page = project.wikis.new(title: "Page #{rand(1000)}", content: "Content")
+    page.user = project.owner
+    page.slug = page.title.parameterize
+    page.save!
+    page
+  end
+
+  def create_revision(page)
+    revision = page.dup
+    revision.content = "Updated Content"
+    revision.save!
+  end
+
+  def create_temp_repo(path)
+    FileUtils.mkdir_p path
+    command = "git init --quiet --bare #{path};"
+    system(command)
+  end
+
+  before do
+    @repo_path = "#{Rails.root}/tmp/test-git-base-path"
+    @projects = []
+    @pages = Hash.new {|h,k| h[k] = Array.new }
+
+    @projects << create(:project)
+    @projects << create(:project)
+
+    @projects.each do |project|
+      create_wiki_for project
+      create_revisions_for project
+    end
+
+    @project_without_wiki = create(:project)
+  end
+
+  context "Before the migration" do
+    it "has two projects with valid wikis" do
+      @projects.each do |project|
+        pages = project.wikis.group(:slug).all
+        pages.count.should == 3
+      end
+    end
+
+    it "has two revision for each page" do
+      @projects.each do |project|
+        @pages[project.id].each do |page|
+          revisions = project.wikis.where(slug: page.slug)
+          revisions.count.should == 2
+        end
+      end
+    end
+  end
+
+  describe "#initialize" do
+    it "finds all projects that have existing wiki pages" do
+      Project.count.should == 3
+      subject.projects.count.should == 2
+    end
+  end
+
+  context "#migrate!" do
+    before do
+      Gitlab::Shell.any_instance.stub(:add_repository) do |path|
+        create_temp_repo("#{@repo_path}/#{path}.git")
+      end
+
+      subject.stub(:log).as_null_object
+
+      subject.migrate!
+    end
+
+    it "creates a new Gollum Wiki for each project" do
+      @projects.each do |project|
+        wiki_path = project.path_with_namespace + ".wiki.git"
+        full_path = @repo_path + "/" + wiki_path
+        File.exist?(full_path).should be_true
+        File.directory?(full_path).should be_true
+      end
+    end
+
+    it "creates a gollum page for each unique Wiki page" do
+      @projects.each do |project|
+        wiki = GollumWiki.new(project, nil)
+        wiki.pages.count.should == 3
+      end
+    end
+
+    it "creates a new revision for each old revision of the page" do
+      @projects.each do |project|
+        wiki = GollumWiki.new(project, nil)
+        wiki.pages.each do |page|
+          page.versions.count.should == 2
+        end
+      end
+    end
+  end
+
+
+end