require 'faraday'

module FaradayMiddleware
  # Middleware to automatically decompress response bodies. If the
  # "Accept-Encoding" header wasn't set in the request, this sets it to
  # "gzip,deflate" and appropriately handles the compressed response from the
  # server. This resembles what Ruby 1.9+ does internally in Net::HTTP#get.
  #
  # This middleware is NOT necessary when these adapters are used:
  # - net_http on Ruby 1.9+
  # - net_http_persistent on Ruby 2.0+
  # - em_http
  class Gzip < Faraday::Middleware
    dependency 'zlib'

    ACCEPT_ENCODING = 'Accept-Encoding'.freeze
    CONTENT_ENCODING = 'Content-Encoding'.freeze
    CONTENT_LENGTH = 'Content-Length'.freeze
    SUPPORTED_ENCODINGS = 'gzip,deflate'.freeze
    RUBY_ENCODING = '1.9'.respond_to?(:force_encoding)

    def call(env)
      env[:request_headers][ACCEPT_ENCODING] ||= SUPPORTED_ENCODINGS
      @app.call(env).on_complete do |response_env|
        case response_env[:response_headers][CONTENT_ENCODING]
        when 'gzip'
          reset_body(response_env, &method(:uncompress_gzip))
        when 'deflate'
          reset_body(response_env, &method(:inflate))
        end
      end
    end

    def reset_body(env)
      env[:body] = yield(env[:body])
      env[:response_headers].delete(CONTENT_ENCODING)
      env[:response_headers][CONTENT_LENGTH] = env[:body].length
    end

    def uncompress_gzip(body)
      io = StringIO.new(body)
      gzip_reader = if RUBY_ENCODING
        Zlib::GzipReader.new(io, :encoding => 'ASCII-8BIT')
      else
        Zlib::GzipReader.new(io)
      end
      gzip_reader.read
    end

    def inflate(body)
      Zlib::Inflate.inflate(body)
    end
  end
end
