app/fake_records/diff.rb

class Diff < FakeRecord
  attr_reader :repository, :oid, :changed_files

  def self.find(opts)
    new(opts)
  end

  def initialize(opts)
    @repository = Repository.find_by_path(opts[:repository_id])
    @commit_id = compute_ref(repository, opts[:ref])

    @oid = @commit_id[:oid]
    @changed_files = repository.changed_files(oid)

    @computed = false
  end

  def compute
    if !@computed
      @diff = repository.git.diff(oid)
      if @diff == :diff_too_large
        changed_files.each do |file_change|
          file_change.diff = @diff
        end
      else
        raw_diffs = @diff.split('diff --git ')[1..-1]

        changed_files.each do |file_change|
          diff = raw_diffs.
            select { |d| d[2..-1].start_with?(file_change.old_path) }.first
          file_change.diff = diff_without_metadata(diff, file_change.status)
        end
      end
      @computed = true
    end

    @computed
  end

  protected

  def compute_ref(repository, ref)
    repository.commit_id(ref || Settings.git.default_branch)
  end

  def diff_without_metadata(diff, status)
    diff.split("\n", metadata_line_count(status)).last[0..-1]
  end

  def metadata_line_count(status)
    case status
    when :added
      6
    when :deleted
      6
    when :modified
      5
    when :renamed
      5
    end
  end
end