module MiniCheck
  class RackApp
    attr_accessor :checks
    attr_accessor :path

    CONTENT_TYPE_HEADER = 'Content-Type'.freeze
    JSON_MIME_TYPE = 'application/json'.freeze
    REQUEST_METHOD = 'REQUEST_METHOD'.freeze
    PATH_INFO = 'PATH_INFO'.freeze

    def initialize args = {}
      set_attributes args
    end

    def checks
      @checks ||= ChecksCollection.new
    end

    def call env
      case "#{env[REQUEST_METHOD]} #{env[PATH_INFO]}"
      when "GET #{path}"
        checks.run
        [status, default_headers, [body]]
      else
        host_app.call(env)
      end
    end

    def register name, &block
      checks.register name, &block
    end

    def new(app)
      dup.tap do |copy|
        copy.host_app = app
      end
    end

    private

    def default_headers
      { CONTENT_TYPE_HEADER => JSON_MIME_TYPE }
    end

    def set_attributes args = {}
      args.each do |k,v|
        send("#{k}=", v)
      end
    end

    def body
      checks.to_hash.to_json
    end

    def status
      checks.healthy? ? 200 : 500
    end

    protected

    attr_accessor :host_app

    def host_app
      @host_app ||= lambda { |env|  [404, {}, []] }
    end
  end
end