require "rack/oauth2/models"
require "rack/oauth2/server/errors"
require "rack/oauth2/server/utils"
require "rack/oauth2/server/helper"
require "rack/oauth2/server/version"


module Rack
  module OAuth2

    # Implements an OAuth 2 Authorization Server, based on http://tools.ietf.org/html/draft-ietf-oauth-v2-10
    class Server

      class << self
        # Return AuthRequest from authorization request handle.
        def get_auth_request(authorization)
          AuthRequest.find(authorization)
        end

        # Returns Client from client identifier.
        def get_client(client_id)
          Client.find(client_id)
        end

        # Returns AccessToken from token.
        def get_access_token(token)
          AccessToken.from_token(token)
        end

        # Returns all AccessTokens for an identity.
        def list_access_tokens(identity)
          AccessToken.from_identity(identity)
        end

      end

      # Options are:
      # - :access_token_path -- Path for requesting access token. By convention
      #   defaults to /oauth/access_token.
      # - :authenticator -- For username/password authorization. A block that
      #   receives the credentials and returns identity string (e.g. user ID) or
      #   nil.
      # - :authorization_types -- Array of supported authorization types.
      #   Defaults to ["code", "token"], and you can change it to just one of
      #   these names.
      # - :authorize_path --  Path for requesting end-user authorization. By
      #   convention defaults to /oauth/authorize.
      # - :database -- Mongo::DB instance.
      # - :realm -- Authorization realm that will show up in 401 responses.
      #   Defaults to use the request host name.
      # - :scopes -- Array listing all supported scopes, e.g. %w{read write}.
      # - :logger -- The logger to use. Under Rails, defaults to use the Rails
      #   logger.  Will use Rack::Logger if available.
      Options = Struct.new(:access_token_path, :authenticator, :authorization_types,
        :authorize_path, :database, :realm, :scopes, :logger)

      def initialize(app, options = Options.new, &authenticator)
        @app = app
        @options = options
        @options.authenticator ||= authenticator
        @options.access_token_path ||= "/oauth/access_token"
        @options.authorize_path ||= "/oauth/authorize"
        @options.authorization_types ||=  %w{code token}
      end

      # @see Options
      attr_reader :options

      def call(env)
        # Use options.database if specified.
        org_database, Server.database = Server.database, options.database || Server.database
        logger = options.logger || env["rack.logger"]
        request = OAuthRequest.new(env)

        # 3.  Obtaining End-User Authorization
        # Flow starts here.
        return request_authorization(request, logger) if request.path == options.authorize_path
        # 4.  Obtaining an Access Token
        return respond_with_access_token(request, logger) if request.path == options.access_token_path

        # 5.  Accessing a Protected Resource
        if request.authorization
          # 5.1.1.  The Authorization Request Header Field
          token = request.credentials if request.oauth?
        else
          # 5.1.2.  URI Query Parameter
          # 5.1.3.  Form-Encoded Body Parameter
          token = request.GET["oauth_token"] || request.POST["oauth_token"]
        end

        if token
          begin
            access_token = AccessToken.from_token(token)
            raise InvalidTokenError if access_token.nil? || access_token.revoked
            raise ExpiredTokenError if access_token.expires_at && access_token.expires_at <= Time.now.utc
            request.env["oauth.access_token"] = token
            request.env["oauth.identity"] = access_token.identity
            logger.info "Authorized #{access_token.identity}" if logger
          rescue Error=>error
            # 5.2.  The WWW-Authenticate Response Header Field
            logger.info "HTTP authorization failed #{error.code}" if logger
            return unauthorized(request, error)
          rescue =>ex
            logger.info "HTTP authorization failed #{ex.message}" if logger
            return unauthorized(request)
          end

          # We expect application to use 403 if request has insufficient scope,
          # and return appropriate WWW-Authenticate header.
          response = @app.call(env)
          if response[0] == 403
            scope = response[1]["oauth.no_scope"] || ""
            scope = scope.join(" ") if scope.respond_to?(:join)
            challenge = 'OAuth realm="%s", error="insufficient_scope", scope="%s"' % [(options.realm || request.host), scope]
            return [403, { "WWW-Authenticate"=>challenge }, []]
          else
            return response
          end
        else
          response = @app.call(env)
          if response[1] && response[1]["oauth.no_access"]
            # OAuth access required.
            return unauthorized(request)
          elsif response[1] && response[1]["oauth.authorization"]
            # 3.  Obtaining End-User Authorization
            # Flow ends here.
            return authorization_response(response, logger)
          else
            return response
          end
        end
      ensure
        Server.database = org_database
      end

    protected

      # Get here for authorization request. Check the request parameters and
      # redirect with an error if we find any issue. Otherwise, create a new
      # authorization request, set in oauth.request and pass control to the
      # application.
      def request_authorization(request, logger)
        state = request.GET["state"]
        if request.GET["authorization"]
          auth_request = self.class.get_auth_request(request.GET["authorization"]) rescue nil
          if !auth_request || auth_request.revoked
            logger.error "Invalid authorization request #{auth_request}" if logger
            return bad_request("Invalid authorization request")
          end
          client = self.class.get_client(auth_request.client_id)

        else

          # 3.  Obtaining End-User Authorization
          begin
            redirect_uri = Utils.parse_redirect_uri(request.GET["redirect_uri"])
          rescue InvalidRequestError=>error
            logger.error "Authorization request with invalid redirect_uri: #{request.GET["redirect_uri"]} #{error.message}" if logger
            return bad_request(error.message)
          end

          begin
            # 3. Obtaining End-User Authorization
            client = get_client(request)
            raise RedirectUriMismatchError unless client.redirect_uri.nil? || client.redirect_uri == redirect_uri.to_s
            requested_scope = request.GET["scope"].to_s.split.uniq.join(" ")
            response_type = request.GET["response_type"].to_s
            raise UnsupportedResponseTypeError unless options.authorization_types.include?(response_type)
            if scopes = options.scopes
              allowed_scope = scopes.respond_to?(:all?) ? scopes : scopes.split
              raise InvalidScopeError unless requested_scope.split.all? { |v| allowed_scope.include?(v) }
            end
            # Create object to track authorization request and let application
            # handle the rest.
            auth_request = AuthRequest.create(client.id, requested_scope, redirect_uri.to_s, response_type, state)
          rescue Error=>error
            logger.error "Authorization request error: #{error.code} #{error.message}" if logger
            params = Rack::Utils.parse_query(redirect_uri.query).merge(:error=>error.code, :error_description=>error.message, :state=>state)
            redirect_uri.query = Rack::Utils.build_query(params)
            return redirect_to(redirect_uri)
          end
        end

        request.env["oauth.authorization"] = auth_request.id.to_s
        logger.info "Request #{auth_request.id}: Client #{client.display_name} requested #{auth_request.response_type} with scope #{auth_request.scope}" if logger
        return @app.call(request.env)
      end

      # Get here on completion of the authorization. Authorization response in
      # oauth.response either grants or denies authroization. In either case, we
      # redirect back with the proper response.
      def authorization_response(response, logger)
        status, headers, body = response
        auth_request = self.class.get_auth_request(headers["oauth.authorization"])
        redirect_uri = URI.parse(auth_request.redirect_uri)
        if status == 401
          auth_request.deny!
        else
          auth_request.grant! headers["oauth.identity"]
        end
        # 3.1.  Authorization Response
        if auth_request.response_type == "code" && auth_request.grant_code
          logger.info "Request #{auth_request.id}: Client #{auth_request.client_id} granted access code #{auth_request.grant_code}" if logger
          params = { :code=>auth_request.grant_code, :scope=>auth_request.scope, :state=>auth_request.state }
          params = Rack::Utils.parse_query(redirect_uri.query).merge(params)
          redirect_uri.query = Rack::Utils.build_query(params)
          return redirect_to(redirect_uri)
        elsif auth_request.response_type == "token" && auth_request.access_token
          logger.info "Request #{auth_request.id}: Client #{auth_request.client_id} granted access token #{auth_request.access_token}" if logger
          params = { :access_token=>auth_request.access_token, :scope=>auth_request.scope, :state=>auth_request.state }
          redirect_uri.fragment = Rack::Utils.build_query(params)
          return redirect_to(redirect_uri)
        else
          logger.info "Request #{auth_request.id}: Client #{auth_request.client_id} denied authorization" if logger
          params = Rack::Utils.parse_query(redirect_uri.query).merge(:error=>:access_denied, :state=>auth_request.state)
          redirect_uri.query = Rack::Utils.build_query(params)
          return redirect_to(redirect_uri)
        end
      end

      # 4.  Obtaining an Access Token
      def respond_with_access_token(request, logger)
        return [405, { "Content-Type"=>"application/json" }, ["POST only"]] unless request.post?
        # 4.2.  Access Token Response
        begin
          client = get_client(request)
          case request.POST["grant_type"]
          when "authorization_code"
            # 4.1.1.  Authorization Code
            grant = AccessGrant.from_code(request.POST["code"])
            raise InvalidGrantError unless grant && client.id == grant.client_id
            raise InvalidGrantError unless grant.redirect_uri.nil? || grant.redirect_uri == Utils.parse_redirect_uri(request.POST["redirect_uri"]).to_s
            access_token = grant.authorize!
          when "password"
            raise UnsupportedGrantType unless options.authenticator
            # 4.1.2.  Resource Owner Password Credentials
            username, password = request.POST.values_at("username", "password")
            requested_scope = request.POST["scope"].to_s.split.uniq.join(" ")
            raise InvalidGrantError unless username && password
            identity = options.authenticator.call(username, password)
            raise InvalidGrantError unless identity
            if scopes = options.scopes
              allowed_scope = scopes.respond_to?(:all?) ? scopes : scopes.split
              raise InvalidScopeError unless requested_scope.split.all? { |v| allowed_scope.include?(v) }
            end
            access_token = AccessToken.get_token_for(identity, requested_scope.to_s, client.id)
          else raise UnsupportedGrantType
          end
          logger.info "Access token #{access_token.token} granted to client #{client.display_name}, identity #{access_token.identity}" if logger
          response = { :access_token=>access_token.token }
          response[:scope] = access_token.scope unless access_token.scope.empty?
          return [200, { "Content-Type"=>"application/json", "Cache-Control"=>"no-store" }, response.to_json]
          # 4.3.  Error Response
        rescue Error=>error
          logger.error "Access token request error: #{error.code} #{error.message}" if logger
          return unauthorized(request, error) if InvalidClientError === error && request.basic?
          return [400, { "Content-Type"=>"application/json", "Cache-Control"=>"no-store" }, 
                  { :error=>error.code, :error_description=>error.message }.to_json]
        end
      end

      # Returns client from request based on credentials. Raises
      # InvalidClientError if client doesn't exist or secret doesn't match.
      def get_client(request)
        # 2.1  Client Password Credentials
        if request.basic?
          client_id, client_secret = request.credentials
        elsif request.form_data?
          client_id, client_secret = request.POST.values_at("client_id", "client_secret")
        else
          client_id, client_secret = request.GET.values_at("client_id", "client_secret")
        end
        client = self.class.get_client(client_id)
        raise InvalidClientError unless client && client.secret == client_secret
        raise InvalidClientError if client.revoked
        return client
      rescue BSON::InvalidObjectId
        raise InvalidClientError
      end

      # Rack redirect response. The argument is typically a URI object.
      def redirect_to(uri)
        return [302, { "Location"=>uri.to_s }, []]
      end

      def bad_request(message)
        return [400, { "Content-Type"=>"text/plain" }, [message]]
      end

      # Returns WWW-Authenticate header.
      def unauthorized(request, error = nil)
        challenge = 'OAuth realm="%s"' % (options.realm || request.host)
        challenge << ', error="%s", error_description="%s"' % [error.code, error.message] if error
        return [401, { "WWW-Authenticate"=>challenge }, []]
      end

      # Wraps Rack::Request to expose Basic and OAuth authentication
      # credentials.
      class OAuthRequest < Rack::Request

        AUTHORIZATION_KEYS = %w{HTTP_AUTHORIZATION X-HTTP_AUTHORIZATION X_HTTP_AUTHORIZATION}

        # Returns authorization header.
        def authorization
          @authorization ||= AUTHORIZATION_KEYS.inject(nil) { |auth, key| auth || @env[key] }
        end

        # True if authentication scheme is OAuth.
        def oauth?
          authorization[/^oauth/i] if authorization
        end

        # True if authentication scheme is Basic.
        def basic?
          authorization[/^basic/i] if authorization
        end

        # If Basic auth, returns username/password, if OAuth, returns access
        # token.
        def credentials
          basic? ? authorization.gsub(/\n/, "").split[1].unpack("m*").first.split(/:/, 2) :
          oauth? ? authorization.gsub(/\n/, "").split[1] : nil
        end
      end

    end

  end
end