module PlainApm
  ##
  # Tracks current revision of the app.
  #
  # This enables per-deploy metrics segmentation and checking
  # for performance regressions.
  module Hooks
    class Deploy
      ##
      # Collect once, immediately on install.
      def install
        collect
      end

      def collect
        result = git_revision || hg_revision || return

        tool, revision = *result

        Agent.instance.collect(
          {"source" => tool, "revision" => revision, "name" => "deploy"}
        )
      end

      private

      # TODO: other deploy mechanisms
      #
      # Also, we might not be in the app root.
      def git_revision
        return nil unless File.exist?(".git")

        ["git", `git rev-parse --short HEAD`.strip]
      rescue Error::ENOENT # No git installed
        nil
      end

      def hg_revision
        return nil unless File.exist?(".hg")

        ["hg", `hg log -l 1 -r . -T '{node}'`]
      rescue Error::ENOENT # No mercurial installed
        nil
      end
    end
  end
end