Initial RocketPants 2.0 Version Recognition Thoughts

version_recognizers.rb

class VersionRecognizer

  attr_reader :app, :matcher

  def initialize(app, matcher)
    @app     = app
    @matcher = compile_matcher(matcher)
  end

  def extract_version(env)
    raise NotImplementedError, "You must use a subclass of VersionRecognizer that implements #extract_version(env)"
  end

  def call(env)
    if versioned_env = extract_version(env)
      env = env.merge(versioned_env)
    end
    app.call env
  end

  def version_additions(version)
    version && {'rocket_pants.request_version' => version}
  end

  def compile_matcher(input)
    if input.is_a?(String)
      Regexp.new Regexp.escape(input.to_s).gsub /:version/, "(?<version>\d+)"
    else
      input
    end
  end

end

class ContentTypeRecognizer < VersionRecognizer

  def extract_version(env)
    content_type = env['HTTP_CONTENT_TYPE']
    version = content_type[matcher, :version].try :to_i
    version_additions version
  end

end

class CustomHeaderRecognizer < VersionRecognizer

  attr_reader :header, :header_key

  def initialize(app, matcher = /(?<version>\d+)/, header = "X-API-Version")
    super app, matcher
    @header = header
    @header_key = "HTTP_#{@header.to_s.gsub("-", "_").upcase}"
  end

  def extract_version(env)
    header = env[header_key]
    version = header.presence && header[matcher, :version].try(:to_i)
    version_additions version
  end

end

# Only path-based recognition can be used to generate routes.
# We need some way to declare this and map it.
class PathRecognizer < VersionRecognizer

  attr_reader :path_regexp

  def initialize(app, matcher = /(?:v?)(?<version>\d+)/)
    super app, matcher
    @path_regexp = /\A\/#{self.matcher}(?:\/|\Z)/
  end

  def extract_version(env)
    version = env['PATH_INFO'].to_s[path_regexp, :version].try :to_i
    version_additions version
  end

end