Replace current Wiki system with Gollum Wikis.

This commit replaces the old database backed Wiki system with the
excellent Gollum git based Wiki system.

The UI has been updated to allow for utilizing the extra features
that Gollum provides. Specifically:

* Edit page now allows you to choose the content format.
* Edit page allows you to provide a commit message for the change.
* History page now shows Format, Commit Message, and Commit Hash.
* A new Git Access page has been added with the Wiki Repo URL.
* The default page has been changed to Home from Index to match
the Gollum standard.

The old Wiki model has been left in tact to provide for the
development of a migration script that will move all content stored
in the old Wiki system into new Gollum Wikis.

app/models/gollum_wiki.rb

@@ -0,0 +1,125 @@
+class GollumWiki
+
+  MARKUPS = {
+    "Markdown"         => :markdown,
+    "Textile"          => :textile,
+    "RDoc"             => :rdoc,
+    "Org-mode"         => :org,
+    "Creole"           => :creole,
+    "reStructuredText" => :rest,
+    "AsciiDoc"         => :asciidoc,
+    "MediaWiki"        => :mediawiki,
+    "Pod"              => :post
+  }
+
+  class CouldNotCreateWikiError < StandardError; end
+
+  # Returns a string describing what went wrong after
+  # an operation fails.
+  attr_reader :error_message
+
+  def initialize(project, user = nil)
+    @project = project
+    @user = user
+  end
+
+  def path_with_namespace
+    @project.path_with_namespace + ".wiki"
+  end
+
+  def url_to_repo
+    gitlab_shell.url_to_repo(path_with_namespace)
+  end
+
+  def ssh_url_to_repo
+    url_to_repo
+  end
+
+  def http_url_to_repo
+    http_url = [Gitlab.config.gitlab.url, "/", path_with_namespace, ".git"].join('')
+  end
+
+  # Returns the Gollum::Wiki object.
+  def wiki
+    @wiki ||= begin
+      Gollum::Wiki.new(path_to_repo)
+    rescue Grit::NoSuchPathError
+      create_repo!
+    end
+  end
+
+  # Returns an Array of Gitlab WikiPage instances or an
+  # empty Array if this Wiki has no pages.
+  def pages
+    wiki.pages.map { |page| WikiPage.new(self, page, true) }
+  end
+
+  # Returns the last 30 Commit objects accross the entire
+  # repository.
+  def recent_history
+    Commit.fresh_commits(wiki.repo, 30)
+  end
+
+  # Finds a page within the repository based on a tile
+  # or slug.
+  #
+  # title - The human readable or parameterized title of
+  #         the page.
+  #
+  # Returns an initialized WikiPage instance or nil
+  def find_page(title, version = nil)
+    if page = wiki.page(title, version)
+      WikiPage.new(self, page, true)
+    else
+      nil
+    end
+  end
+
+  def create_page(title, content, format = :markdown, message = nil)
+    commit = commit_details(:created, message, title)
+
+    wiki.write_page(title, format, content, commit)
+  rescue Gollum::DuplicatePageError => e
+    @error_message = "Duplicate page: #{e.message}"
+    return false
+  end
+
+  def update_page(page, content, format = :markdown, message = nil)
+    commit = commit_details(:updated, message, page.title)
+
+    wiki.update_page(page, page.name, format, content, commit)
+  end
+
+  def delete_page(page, message = nil)
+    wiki.delete_page(page, commit_details(:deleted, message, page.title))
+  end
+
+  private
+
+  def create_repo!
+    if gitlab_shell.add_repository(path_with_namespace)
+      Gollum::Wiki.new(path_to_repo)
+    else
+      raise CouldNotCreateWikiError
+    end
+  end
+
+  def commit_details(action, message = nil, title = nil)
+    commit_message = message || default_message(action, title)
+
+    {email: @user.email, name: @user.name, message: commit_message}
+  end
+
+  def default_message(action, title)
+    "#{@user.username} #{action} page: #{title}"
+  end
+
+  def gitlab_shell
+    @gitlab_shell ||= Gitlab::Shell.new
+  end
+
+  def path_to_repo
+    @path_to_repo ||= File.join(Gitlab.config.gitlab_shell.repos_path, "#{path_with_namespace}.git")
+  end
+
+end

app/models/wiki_page.rb

@@ -0,0 +1,181 @@
+class WikiPage
+  include ActiveModel::Validations
+  include ActiveModel::Conversion
+  include StaticModel
+  extend ActiveModel::Naming
+
+  def self.primary_key
+    'slug'
+  end
+
+  def self.model_name
+    ActiveModel::Name.new(self, nil, 'wiki')
+  end
+
+  def to_key
+    [:slug]
+  end
+
+  validates :title, presence: true
+  validates :content, presence: true
+
+  # The Gitlab GollumWiki instance.
+  attr_reader :wiki
+
+  # The raw Gollum::Page instance.
+  attr_reader :page
+
+  # The attributes Hash used for storing and validating
+  # new Page values before writing to the Gollum repository.
+  attr_accessor :attributes
+
+  def initialize(wiki, page = nil, persisted = false)
+    @wiki       = wiki
+    @page       = page
+    @persisted  = persisted
+    @attributes = {}.with_indifferent_access
+
+    set_attributes if persisted?
+  end
+
+  # The escaped URL path of this page.
+  def slug
+    @attributes[:slug]
+  end
+
+  alias :to_param :slug
+
+  # The formatted title of this page.
+  def title
+    @attributes[:title] || ""
+  end
+
+  # Sets the title of this page.
+  def title=(new_title)
+    @attributes[:title] = new_title
+  end
+
+  # The raw content of this page.
+  def content
+    @attributes[:content]
+  end
+
+  # The processed/formatted content of this page.
+  def formatted_content
+    @attributes[:formatted_content]
+  end
+
+  # The markup format for the page.
+  def format
+    @attributes[:format] || :markdown
+  end
+
+  # The commit message for this page version.
+  def message
+    version.try(:message)
+  end
+
+  # The Gitlab Commit instance for this page.
+  def version
+    return nil unless persisted?
+
+    @version ||= Commit.new(@page.version)
+  end
+
+  # Returns an array of Gitlab Commit instances.
+  def versions
+    return [] unless persisted?
+
+    @page.versions.map { |v| Commit.new(v) }
+  end
+
+  # Returns the Date that this latest version was
+  # created on.
+  def created_at
+    @page.version.date
+  end
+
+  # Returns boolean True or False if this instance
+  # is an old version of the page.
+  def historical?
+    @page.historical?
+  end
+
+  # Returns boolean True or False if this instance
+  # has been fully saved to disk or not.
+  def persisted?
+    @persisted == true
+  end
+
+  # Creates a new Wiki Page.
+  #
+  # attr - Hash of attributes to set on the new page.
+  #       :title   - The title for the new page.
+  #       :content - The raw markup content.
+  #       :format  - Optional symbol representing the
+  #                  content format. Can be any type
+  #                  listed in the GollumWiki::MARKUPS
+  #                  Hash.
+  #       :message - Optional commit message to set on
+  #                  the new page.
+  #
+  # Returns the String SHA1 of the newly created page
+  # or False if the save was unsuccessful.
+  def create(attr = {})
+    @attributes.merge!(attr)
+
+    save :create_page, title, content, format, message
+  end
+
+  # Updates an existing Wiki Page, creating a new version.
+  #
+  # new_content - The raw markup content to replace the existing.
+  # format      - Optional symbol representing the content format.
+  #               See GollumWiki::MARKUPS Hash for available formats.
+  # message     - Optional commit message to set on the new version.
+  #
+  # Returns the String SHA1 of the newly created page
+  # or False if the save was unsuccessful.
+  def update(new_content = "", format = :markdown, message = nil)
+    @attributes[:content] = new_content
+    @attributes[:format] = format
+
+    save :update_page, @page, content, format, message
+  end
+
+  # Destroys the WIki Page.
+  #
+  # Returns boolean True or False.
+  def delete
+    if wiki.delete_page(@page)
+      true
+    else
+      false
+    end
+  end
+
+  private
+
+  def set_attributes
+    attributes[:slug] = @page.escaped_url_path
+    attributes[:title] = @page.title
+    attributes[:content] = @page.raw_data
+    attributes[:formatted_content] = @page.formatted_data
+    attributes[:format] = @page.format
+  end
+
+  def save(method, *args)
+    if valid? && wiki.send(method, *args)
+      @page = wiki.wiki.paged(title)
+
+      set_attributes
+
+      @persisted = true
+    else
+      errors.add(:base, wiki.error_message) if wiki.error_message
+      @persisted = false
+    end
+    @persisted
+  end
+
+end