chore: Add DataSystem contract definition (#338)

Author: jsonbailey

lib/ldclient-rb/impl/datasystem.rb

@@ -0,0 +1,296 @@
+module LaunchDarkly
+  module Impl
+    #
+    # Mixin that defines the required methods of a data system implementation. The data system
+    # is responsible for managing the SDK's data model, including storage, retrieval, and change
+    # detection for feature flag configurations.
+    #
+    # This module also contains supporting classes and additional mixins for data system
+    # implementations, such as DataAvailability, Update, and protocol-specific mixins.
+    #
+    # For operations that can fail, use {LaunchDarkly::Result} from util.rb.
+    #
+    # Application code should not need to implement this directly; it is used internally by the
+    # SDK's data system implementations.
+    #
+    # @private
+    #
+    module DataSystem
+      #
+      # Starts the data system.
+      #
+      # This method will return immediately. The provided event will be set when the system
+      # has reached an initial state (either permanently failed, e.g. due to bad auth, or succeeded).
+      #
+      # @param ready_event [Concurrent::Event] Event to set when initialization is complete
+      # @return [void]
+      #
+      def start(ready_event)
+        raise NotImplementedError, "#{self.class} must implement #start"
+      end
+
+      #
+      # Halts the data system. Should be called when the client is closed to stop any long running
+      # operations.
+      #
+      # @return [void]
+      #
+      def stop
+        raise NotImplementedError, "#{self.class} must implement #stop"
+      end
+
+      #
+      # Returns an interface for tracking the status of the data source.
+      #
+      # The data source is the mechanism that the SDK uses to get feature flag configurations, such
+      # as a streaming connection (the default) or poll requests.
+      #
+      # @return [LaunchDarkly::Interfaces::DataSource::StatusProvider]
+      #
+      def data_source_status_provider
+        raise NotImplementedError, "#{self.class} must implement #data_source_status_provider"
+      end
+
+      #
+      # Returns an interface for tracking the status of a persistent data store.
+      #
+      # The provider has methods for checking whether the data store is (as far
+      # as the SDK knows) currently operational, tracking changes in this
+      # status, and getting cache statistics. These are only relevant for a
+      # persistent data store; if you are using an in-memory data store, then
+      # this method will return a stub object that provides no information.
+      #
+      # @return [LaunchDarkly::Interfaces::DataStore::StatusProvider]
+      #
+      def data_store_status_provider
+        raise NotImplementedError, "#{self.class} must implement #data_store_status_provider"
+      end
+
+      #
+      # Returns an interface for tracking changes in feature flag configurations.
+      #
+      # @return [LaunchDarkly::Interfaces::FlagTracker]
+      #
+      def flag_tracker
+        raise NotImplementedError, "#{self.class} must implement #flag_tracker"
+      end
+
+      #
+      # Indicates what form of data is currently available.
+      #
+      # @return [Symbol] One of DataAvailability constants
+      #
+      def data_availability
+        raise NotImplementedError, "#{self.class} must implement #data_availability"
+      end
+
+      #
+      # Indicates the ideal form of data attainable given the current configuration.
+      #
+      # @return [Symbol] One of DataAvailability constants
+      #
+      def target_availability
+        raise NotImplementedError, "#{self.class} must implement #target_availability"
+      end
+
+      #
+      # Returns the data store used by the data system.
+      #
+      # @return [Object] The read-only store
+      #
+      def store
+        raise NotImplementedError, "#{self.class} must implement #store"
+      end
+
+      #
+      # Injects the flag value evaluation function used by the flag tracker to
+      # compute FlagValueChange events. The function signature should be
+      # (key, context) -> value.
+      #
+      # This method must be called after initialization to enable the flag tracker
+      # to compute value changes for flag change listeners.
+      #
+      # @param eval_fn [Proc] The evaluation function
+      # @return [void]
+      #
+      def set_flag_value_eval_fn(eval_fn)
+        raise NotImplementedError, "#{self.class} must implement #set_flag_value_eval_fn"
+      end
+
+      #
+      # Represents the availability of data in the SDK.
+      #
+      class DataAvailability
+        # The SDK has no data and will evaluate flags using the application-provided default values.
+        DEFAULTS = :defaults
+
+        # The SDK has data, not necessarily the latest, which will be used to evaluate flags.
+        CACHED = :cached
+
+        # The SDK has obtained, at least once, the latest known data from LaunchDarkly.
+        REFRESHED = :refreshed
+
+        ALL = [DEFAULTS, CACHED, REFRESHED].freeze
+
+        #
+        # Returns whether this availability level is **at least** as good as the other.
+        #
+        # @param [Symbol] self_level The current availability level
+        # @param [Symbol] other The other availability level to compare against
+        # @return [Boolean] true if this availability level is at least as good as the other
+        #
+        def self.at_least?(self_level, other)
+          return true if self_level == other
+          return true if self_level == REFRESHED
+          return true if self_level == CACHED && other == DEFAULTS
+
+          false
+        end
+      end
+
+      #
+      # Mixin that defines the required methods of a diagnostic accumulator implementation.
+      # The diagnostic accumulator is used for collecting and reporting diagnostic events
+      # to LaunchDarkly for monitoring SDK performance and behavior.
+      #
+      # Application code should not need to implement this directly; it is used internally by the SDK.
+      #
+      module DiagnosticAccumulator
+        #
+        # Record a stream initialization.
+        #
+        # @param timestamp [Float] The timestamp
+        # @param duration [Float] The duration
+        # @param failed [Boolean] Whether it failed
+        # @return [void]
+        #
+        def record_stream_init(timestamp, duration, failed)
+          raise NotImplementedError, "#{self.class} must implement #record_stream_init"
+        end
+
+        #
+        # Record events in a batch.
+        #
+        # @param events_in_batch [Integer] The number of events
+        # @return [void]
+        #
+        def record_events_in_batch(events_in_batch)
+          raise NotImplementedError, "#{self.class} must implement #record_events_in_batch"
+        end
+
+        #
+        # Create an event and reset the accumulator.
+        #
+        # @param dropped_events [Integer] The number of dropped events
+        # @param deduplicated_users [Integer] The number of deduplicated users
+        # @return [Object] The diagnostic event
+        #
+        def create_event_and_reset(dropped_events, deduplicated_users)
+          raise NotImplementedError, "#{self.class} must implement #create_event_and_reset"
+        end
+      end
+
+      #
+      # Mixin that defines the required methods for components that can receive a diagnostic accumulator.
+      # Components that include this mixin can report diagnostic information to LaunchDarkly for
+      # monitoring SDK performance and behavior.
+      #
+      # Application code should not need to implement this directly; it is used internally by the SDK.
+      #
+      module DiagnosticSource
+        #
+        # Set the diagnostic_accumulator to be used for reporting diagnostic events.
+        #
+        # @param diagnostic_accumulator [DiagnosticAccumulator] The accumulator
+        # @return [void]
+        #
+        def set_diagnostic_accumulator(diagnostic_accumulator)
+          raise NotImplementedError, "#{self.class} must implement #set_diagnostic_accumulator"
+        end
+      end
+
+      #
+      # Mixin that defines the required methods of an initializer implementation. An initializer
+      # is a component capable of retrieving a single data result, such as from the LaunchDarkly
+      # polling API.
+      #
+      # The intent of initializers is to quickly fetch an initial set of data, which may be stale
+      # but is fast to retrieve. This initial data serves as a foundation for a Synchronizer to
+      # build upon, enabling it to provide updates as new changes occur.
+      #
+      # Application code should not need to implement this directly; it is used internally by the SDK.
+      #
+      module Initializer
+        #
+        # Fetch should retrieve the initial data set for the data source, returning
+        # a Basis object on success, or an error message on failure.
+        #
+        # @return [LaunchDarkly::Result] A Result containing either a Basis or an error message
+        #
+        def fetch
+          raise NotImplementedError, "#{self.class} must implement #fetch"
+        end
+      end
+
+      #
+      # Update represents the results of a synchronizer's ongoing sync method.
+      #
+      class Update
+        # @return [Symbol] The state of the data source
+        attr_reader :state
+
+        # @return [ChangeSet, nil] The change set if available
+        attr_reader :change_set
+
+        # @return [LaunchDarkly::Interfaces::DataSource::ErrorInfo, nil] Error information if applicable
+        attr_reader :error
+
+        # @return [Boolean] Whether to revert to FDv1
+        attr_reader :revert_to_fdv1
+
+        # @return [String, nil] The environment ID if available
+        attr_reader :environment_id
+
+        #
+        # @param state [Symbol] The state of the data source
+        # @param change_set [ChangeSet, nil] The change set if available
+        # @param error [LaunchDarkly::Interfaces::DataSource::ErrorInfo, nil] Error information if applicable
+        # @param revert_to_fdv1 [Boolean] Whether to revert to FDv1
+        # @param environment_id [String, nil] The environment ID if available
+        #
+        def initialize(state:, change_set: nil, error: nil, revert_to_fdv1: false, environment_id: nil)
+          @state = state
+          @change_set = change_set
+          @error = error
+          @revert_to_fdv1 = revert_to_fdv1
+          @environment_id = environment_id
+        end
+      end
+
+      #
+      # Mixin that defines the required methods of a synchronizer implementation. A synchronizer
+      # is a component capable of synchronizing data from an external data source, such as a
+      # streaming or polling API.
+      #
+      # It is responsible for yielding Update objects that represent the current state of the
+      # data source, including any changes that have occurred since the last synchronization.
+      #
+      # Application code should not need to implement this directly; it is used internally by the SDK.
+      #
+      module Synchronizer
+        #
+        # Sync should begin the synchronization process for the data source, yielding
+        # Update objects until the connection is closed or an unrecoverable error
+        # occurs.
+        #
+        # @yield [Update] Yields Update objects as synchronization progresses
+        # @return [void]
+        #
+        def sync
+          raise NotImplementedError, "#{self.class} must implement #sync"
+        end
+      end
+    end
+  end
+end
+