# Copyright 2017 Google LLC
#
# 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
#
#     https://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 "delegate"

module Google
  module Cloud
    module Pubsub
      class Snapshot
        ##
        # Snapshot::List is a special case Array with additional values.
        class List < DelegateClass(::Array)
          ##
          # If not empty, indicates that there are more snapshots
          # that match the request and this value should be passed to
          # the next {Google::Cloud::Pubsub::Project#snapshots} to continue.
          attr_accessor :token

          ##
          # @private Create a new Snapshot::List with an array of values.
          def initialize arr = []
            @prefix = nil
            @token = nil
            @max = nil
            super arr
          end

          ##
          # Whether there a next page of snapshots.
          #
          # @return [Boolean]
          #
          # @example
          #   require "google/cloud/pubsub"
          #
          #   pubsub = Google::Cloud::Pubsub.new
          #
          #   snapshots = pubsub.snapshots
          #   if snapshots.next?
          #     next_snapshots = snapshots.next
          #   end
          #
          def next?
            !token.nil?
          end

          ##
          # Retrieve the next page of snapshots.
          #
          # @return [Snapshot::List]
          #
          # @example
          #   require "google/cloud/pubsub"
          #
          #   pubsub = Google::Cloud::Pubsub.new
          #
          #   snapshots = pubsub.snapshots
          #   if snapshots.next?
          #     next_snapshots = snapshots.next
          #   end
          #
          def next
            return nil unless next?
            ensure_service!
            next_snapshots
          end

          ##
          # Retrieves remaining results by repeatedly invoking {#next} until
          # {#next?} returns `false`. Calls the given block once for each
          # result, which is passed as the argument to the block.
          #
          # An Enumerator is returned if no block is given.
          #
          # This method will make repeated API calls until all remaining results
          # are retrieved. (Unlike `#each`, for example, which merely iterates
          # over the results returned by a single API call.) Use with caution.
          #
          # @param [Integer] request_limit The upper limit of API requests to
          #   make to load all snapshots. Default is no limit.
          # @yield [snapshot] The block for accessing each snapshot.
          # @yieldparam [Snapshot] snapshot The snapshot object.
          #
          # @return [Enumerator]
          #
          # @example Iterating each snapshot by passing a block:
          #   require "google/cloud/pubsub"
          #
          #   pubsub = Google::Cloud::Pubsub.new
          #
          #   snapshots = pubsub.snapshots
          #   snapshots.all do |snapshot|
          #     puts snapshot.name
          #   end
          #
          # @example Using the enumerator by not passing a block:
          #   require "google/cloud/pubsub"
          #
          #   pubsub = Google::Cloud::Pubsub.new
          #
          #   snapshots = pubsub.snapshots
          #   all_names = snapshots.all.map do |snapshot|
          #     snapshot.name
          #   end
          #
          # @example Limit the number of API calls made:
          #   require "google/cloud/pubsub"
          #
          #   pubsub = Google::Cloud::Pubsub.new
          #
          #   snapshots = pubsub.snapshots
          #   snapshots.all(request_limit: 10) do |snapshot|
          #     puts snapshot.name
          #   end
          #
          def all request_limit: nil
            request_limit = request_limit.to_i if request_limit
            unless block_given?
              return enum_for(:all, request_limit: request_limit)
            end
            results = self
            loop do
              results.each { |r| yield r }
              if request_limit
                request_limit -= 1
                break if request_limit < 0
              end
              break unless results.next?
              results = results.next
            end
          end

          ##
          # @private New Snapshots::List from a
          # Google::Pubsub::V1::ListSnapshotsRequest object.
          def self.from_grpc grpc_list, service, max = nil
            subs = new(Array(grpc_list.snapshots).map do |grpc|
              Snapshot.from_grpc grpc, service
            end)
            token = grpc_list.next_page_token
            token = nil if token == ""
            subs.instance_variable_set "@token",   token
            subs.instance_variable_set "@service", service
            subs.instance_variable_set "@max",     max
            subs
          end

          protected

          ##
          # @private Raise an error unless an active connection to the service
          # is available.
          def ensure_service!
            raise "Must have active connection to service" unless @service
          end

          def next_snapshots
            options = { prefix: @prefix, token: @token, max: @max }
            grpc = @service.list_snapshots options
            self.class.from_grpc grpc, @service, @max
          end
        end
      end
    end
  end
end