kaiwren/wrest

# frozen_string_literal: true

module Wrest
  class CacheProxy
    class << self
      def new(get, cache_store)
        if cache_store
          DefaultCacheProxy.new(get, cache_store)
        else
          NullCacheProxy.new(get)
        end
      end
    end

    class NullCacheProxy
      def initialize(get)
        @get = get
      end

      def get
        @get.invoke_without_cache_check
      end
    end

    class DefaultCacheProxy
      HOP_BY_HOP_HEADERS = %w[connection
                              keep-alive
                              proxy-authenticate
                              proxy-authorization
                              te
                              trailers
                              transfer-encoding
                              upgrade].freeze

      def initialize(get, cache_store)
        @get         = get
        @cache_store = cache_store
      end

      def log_cached_response
        Wrest.logger.debug "<*> (GET #{@get.hash}) #{@get.uri.protocol}://#{@get.uri.host}:#{@get.uri.port}#{@get.http_request.path}"
      end

      def get
        cached_response = @cache_store[@get.full_uri_string]
        return fresh_get_response if cached_response.nil?

        if cached_response.expired?
          expired_cached_response(cached_response)
        else
          log_cached_response
          cached_response
        end
      end

      def update_cache_headers_for(cached_response, new_response)
        # RFC 2616 13.5.3 (Combining Headers)
        cached_response.headers.merge!(new_response.headers.reject do |key, _value|
                                         (HOP_BY_HOP_HEADERS.include? key.downcase)
                                       end)
      end

      def cache(response)
        @cache_store[@get.full_uri_string] = response.clone if response&.cacheable?
      end

      # :nodoc:
      def fresh_get_response
        @cache_store.delete @get.full_uri_string

        response = @get.invoke_without_cache_check

        cache(response)

        response
      end

      # :nodoc:
      def get_validated_response_for(cached_response)
        new_response = send_validation_request_for(cached_response)
        if new_response.code == '304'
          update_cache_headers_for(cached_response, new_response)
          log_cached_response
          cached_response
        else
          cache(new_response)
          new_response
        end
      end

      # :nodoc:
      # Send a cache-validation request to the server. This would be the actual Get request with extra cache-validation headers.
      # If a 304 (Not Modified) is received, Wrest would use the cached_response itself. Otherwise the new response is cached and used.
      def send_validation_request_for(cached_response)
        last_modified            = cached_response.last_modified
        etag                     = cached_response.headers['etag']

        cache_validation_headers = {}
        cache_validation_headers['if-modified-since'] = last_modified unless last_modified.nil?
        cache_validation_headers['if-none-match'] = etag unless etag.nil?

        new_request = @get.build_request_without_cache_store(cache_validation_headers)

        new_request.invoke
      end

      private

      # :nodoc:
      def expired_cached_response(cached_response)
        if cached_response.can_be_validated?
          get_validated_response_for(cached_response)
        else
          fresh_get_response
        end
      end
    end
  end
end