Implement Wiki#preview_page.

README.md

@@ -383,6 +383,13 @@ Get a specific version of a given static file:
 
     wiki.file('asset.js', '5ec521178e0eec4dc39741a8978a2ba6616d0f0a')
 
+Get an in-memory Page preview (useful for generating previews for web
+interfaces):
+
+    preview = wiki.preview_page("My Page", "# Contents", :markdown)
+    preview.formatted_data
+    # => "<h1>Contents</h1>"
+
 Methods that write to the repository require a Hash of commit data that takes
 the following form:
 

lib/gollum/wiki.rb

@@ -84,6 +84,25 @@ module Gollum
       @file_class.new(self).find(name, version)
     end
 
+    # Public: Create an in-memory Page with the given data and format. This
+    # is useful for previewing what content will look like before committing
+    # it to the repository.
+    #
+    # name   - The String name of the page.
+    # format - The Symbol format of the page.
+    # data   - The new String contents of the page.
+    #
+    # Returns the in-memory Gollum::Page.
+    def preview_page(name, data, format)
+      page = @page_class.new(self)
+      ext = @page_class.format_to_ext(format.to_sym)
+      path = @page_class.cname(name) + '.' + ext
+      blob = OpenStruct.new(:name => path, :data => data)
+      page.populate(blob, path)
+      page.version = self.repo.commit("HEAD")
+      page
+    end
+
     # Public: Write a new version of a page to the Gollum repo root.
     #
     # name   - The String name of the page.

test/test_wiki.rb

@@ -40,6 +40,20 @@ context "Wiki" do
   end
 end
 
+context "Wiki page previewing" do
+  setup do
+    @path = testpath("examples/lotr.git")
+    @wiki = Gollum::Wiki.new(@path)
+  end
+
+  test "preview_page" do
+    page = @wiki.preview_page("Test", "# Bilbo", :markdown)
+    assert_equal "# Bilbo", page.raw_data
+    assert_equal "<h1>Bilbo</h1>", page.formatted_data
+    assert_equal "Test.md", page.name
+  end
+end
+
 context "Wiki page writing" do
   setup do
     @path = testpath("examples/test.git")