# Copyright 2010 Google Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#      http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

require 'httpadapter'
require 'json'

require 'google/api_client/discovery'

module Google
  # TODO(bobaman): Document all this stuff.

  ##
  # This class manages communication with a single API.
  class APIClient
    ##
    # An error which is raised when there is an unexpected response or other
    # transport error that prevents an operation from succeeding.
    class TransmissionError < StandardError
    end

    def initialize(options={})
      @options = {
        # TODO: What configuration options need to go here?
      }.merge(options)
      # Force immediate type-checking and short-cut resolution
      self.parser
      self.authorization
      self.http_adapter
      return self
    end

    ##
    # Returns the parser used by the client.
    def parser
      unless @options[:parser]
        require 'google/api_client/parsers/json_parser'
        # NOTE: Do not rely on this default value, as it may change
        @options[:parser] = JSONParser
      end
      return @options[:parser]
    end

    ##
    # Returns the authorization mechanism used by the client.
    #
    # @return [#generate_authenticated_request] The authorization mechanism.
    def authorization
      case @options[:authorization]
      when :oauth_1, :oauth
        require 'signet/oauth_1/client'
        # NOTE: Do not rely on this default value, as it may change
        @options[:authorization] = Signet::OAuth1::Client.new(
          :temporary_credential_uri =>
            'https://www.google.com/accounts/OAuthGetRequestToken',
          :authorization_uri =>
            'https://www.google.com/accounts/OAuthAuthorizeToken',
          :token_credential_uri =>
            'https://www.google.com/accounts/OAuthGetAccessToken',
          :client_credential_key => 'anonymous',
          :client_credential_secret => 'anonymous'
        )
      when nil
        # No authorization mechanism
      else
        if !@options[:authorization].respond_to?(
            :generate_authenticated_request)
          raise TypeError,
            'Expected authorization mechanism to respond to ' +
            '#generate_authenticated_request.'
        end
      end
      return @options[:authorization]
    end

    ##
    # Sets the authorization mechanism used by the client.
    #
    # @param [#generate_authenticated_request] new_authorization
    #   The new authorization mechanism.
    def authorization=(new_authorization)
      @options[:authorization] = new_authorization
      return self.authorization
    end

    ##
    # Returns the HTTP adapter used by the client.
    def http_adapter
      return @options[:http_adapter] ||= (begin
        require 'httpadapter/adapters/net_http'
        @options[:http_adapter] = HTTPAdapter::NetHTTPRequestAdapter
      end)
    end

    ##
    # Returns the URI for the discovery document.
    #
    # @return [Addressable::URI] The URI of the discovery document.
    def discovery_uri
      return @options[:discovery_uri] ||= (begin
        if @options[:service]
          service_id = @options[:service]
          service_version = @options[:service_version] || 'v1'
          Addressable::URI.parse(
            "http://www.googleapis.com/discovery/0.1/describe" +
            "?api=#{service_id}"
          )
        else
          raise ArgumentError,
            'Missing required configuration value, :discovery_uri.'
        end
      end)
    end

    ##
    # Returns the parsed discovery document.
    #
    # @return [Hash] The parsed JSON from the discovery document.
    def discovery_document
      return @discovery_document ||= (begin
        request = ['GET', self.discovery_uri.to_s, [], []]
        response = self.transmit_request(request)
        status, headers, body = response
        if status == 200 # TODO(bobaman) Better status code handling?
          merged_body = StringIO.new
          body.each do |chunk|
            merged_body.write(chunk)
          end
          merged_body.rewind
          JSON.parse(merged_body.string)
        else
          raise TransmissionError,
            "Could not retrieve discovery document at: #{self.discovery_uri}"
        end
      end)
    end

    ##
    # Returns a list of services this client instance has performed discovery
    # for.  This may return multiple versions of the same service.
    #
    # @return [Array]
    #   A list of discovered <code>Google::APIClient::Service</code> objects.
    def discovered_services
      return @discovered_services ||= (begin
        service_names = self.discovery_document['data'].keys()
        services = []
        for service_name in service_names
          versions = self.discovery_document['data'][service_name]
          for service_version in versions.keys()
            service_description =
              self.discovery_document['data'][service_name][service_version]
            services << ::Google::APIClient::Service.new(
              service_name,
              service_version,
              service_description
            )
          end
        end
        services
      end)
    end

    ##
    # Returns the service object for a given service name and service version.
    #
    # @param [String, Symbol] service_name The service name.
    # @param [String] service_version The desired version of the service.
    #
    # @return [Google::APIClient::Service] The service object.
    def discovered_service(service_name, service_version='v1')
      if !service_name.kind_of?(String) && !service_name.kind_of?(Symbol)
        raise TypeError,
          "Expected String or Symbol, got #{service_name.class}."
      end
      service_name = service_name.to_s
      for service in self.discovered_services
        if service.name == service_name &&
            service.version.to_s == service_version.to_s
          return service
        end
      end
      return nil
    end

    ##
    # Returns the method object for a given RPC name and service version.
    #
    # @param [String, Symbol] rpc_name The RPC name of the desired method.
    # @param [String] service_version The desired version of the service.
    #
    # @return [Google::APIClient::Method] The method object.
    def discovered_method(rpc_name, service_version='v1')
      if !rpc_name.kind_of?(String) && !rpc_name.kind_of?(Symbol)
        raise TypeError,
          "Expected String or Symbol, got #{rpc_name.class}."
      end
      rpc_name = rpc_name.to_s
      for service in self.discovered_services
        # This looks kinda weird, but is not a real problem because there's
        # almost always only one service, and this is memoized anyhow.
        if service.version.to_s == service_version.to_s
          return service.to_h[rpc_name] if service.to_h[rpc_name]
        end
      end
      return nil
    end

    ##
    # Returns the service object with the highest version number.
    #
    # <em>Warning</em>: This method should be used with great care. As APIs
    # are updated, minor differences between versions may cause
    # incompatibilities. Requesting a specific version will avoid this issue.
    #
    # @param [String, Symbol] service_name The name of the service.
    #
    # @return [Google::APIClient::Service] The service object.
    def latest_service_version(service_name)
      if !service_name.kind_of?(String) && !service_name.kind_of?(Symbol)
        raise TypeError,
          "Expected String or Symbol, got #{service_name.class}."
      end
      service_name = service_name.to_s
      return (self.discovered_services.select do |service|
        service.name == service_name
      end).sort.last
    end

    ##
    # Generates a request.
    #
    # @param [Google::APIClient::Method, String] api_method
    #   The method object or the RPC name of the method being executed.
    # @param [Hash, Array] parameters
    #   The parameters to send to the method.
    # @param [String] body The body of the request.
    # @param [Hash, Array] headers The HTTP headers for the request.
    # @param [Hash] options
    #   The configuration parameters for the request.
    #   - <code>:service_version</code> — 
    #     The service version.  Only used if <code>api_method</code> is a
    #     <code>String</code>.  Defaults to <code>'v1'</code>.
    #   - <code>:parser</code> — 
    #     The parser for the response.
    #   - <code>:authorization</code> — 
    #     The authorization mechanism for the response.  Used only if
    #     <code>:signed</code> is <code>true</code>.
    #   - <code>:signed</code> — 
    #     <code>true</code> if the request must be signed, <code>false</code>
    #     otherwise.  Defaults to <code>true</code> if an authorization
    #     mechanism has been set, <code>false</code> otherwise.
    #
    # @return [Array] The generated request.
    #
    # @example
    #   request = client.generate_request(
    #     'chili.activities.list',
    #     {'scope' => '@self', 'userId' => '@me', 'alt' => 'json'}
    #   )
    #   method, uri, headers, body = request
    def generate_request(
        api_method, parameters={}, body='', headers=[], options={})
      options={
        :parser => self.parser,
        :service_version => 'v1',
        :authorization => self.authorization
      }.merge(options)
      # The default value for the :signed option depends on whether an
      # authorization mechanism has been set.
      if options[:authorization]
        options = {:signed => true}.merge(options)
      else
        options = {:signed => false}.merge(options)
      end
      if api_method.kind_of?(String) || api_method.kind_of?(Symbol)
        api_method = self.discovered_method(
          api_method.to_s, options[:service_version]
        )
      elsif !api_method.kind_of?(::Google::APIClient::Method)
        raise TypeError,
          "Expected String, Symbol, or Google::APIClient::Method, " +
          "got #{api_method.class}."
      end
      unless api_method
        raise ArgumentError, "API method could not be found."
      end
      request = api_method.generate_request(parameters, body, headers)
      if options[:signed]
        request = self.sign_request(request, options[:authorization])
      end
      return request
    end

    ##
    # Generates a request and transmits it.
    #
    # @param [Google::APIClient::Method, String] api_method
    #   The method object or the RPC name of the method being executed.
    # @param [Hash, Array] parameters
    #   The parameters to send to the method.
    # @param [String] body The body of the request.
    # @param [Hash, Array] headers The HTTP headers for the request.
    # @param [Hash] options
    #   The configuration parameters for the request.
    #   - <code>:service_version</code> — 
    #     The service version.  Only used if <code>api_method</code> is a
    #     <code>String</code>.  Defaults to <code>'v1'</code>.
    #   - <code>:adapter</code> — 
    #     The HTTP adapter.
    #   - <code>:parser</code> — 
    #     The parser for the response.
    #   - <code>:authorization</code> — 
    #     The authorization mechanism for the response.  Used only if
    #     <code>:signed</code> is <code>true</code>.
    #   - <code>:signed</code> — 
    #     <code>true</code> if the request must be signed, <code>false</code>
    #     otherwise.  Defaults to <code>true</code>.
    #
    # @return [Array] The response from the API.
    #
    # @example
    #   response = client.execute(
    #     'chili.activities.list',
    #     {'scope' => '@self', 'userId' => '@me', 'alt' => 'json'}
    #   )
    #   status, headers, body = response
    def execute(api_method, parameters={}, body='', headers=[], options={})
      request = self.generate_request(
        api_method, parameters, body, headers, options
      )
      return self.transmit_request(
        request,
        options[:adapter] || self.http_adapter
      )
    end

    ##
    # Transmits the request using the current HTTP adapter.
    #
    # @param [Array] request The request to transmit.
    # @param [#transmit] adapter The HTTP adapter.
    #
    # @return [Array] The response from the server.
    def transmit_request(request, adapter=self.http_adapter)
      ::HTTPAdapter.transmit(request, adapter)
    end

    ##
    # Signs a request using the current authorization mechanism.
    #
    # @param [Array] request The request to sign.
    # @param [#generate_authenticated_request] authorization
    #   The authorization mechanism.
    #
    # @return [Array] The signed request.
    def sign_request(request, authorization=self.authorization)
      return authorization.generate_authenticated_request(
        :request => request
      )
    end
  end
end

require 'google/api_client/version'