michael@0: /* This Source Code Form is subject to the terms of the Mozilla Public
michael@0:  * License, v. 2.0. If a copy of the MPL was not distributed with this
michael@0:  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0: 
michael@0: "use strict";
michael@0: 
michael@0: #ifndef MERGED_COMPARTMENT
michael@0: 
michael@0: this.EXPORTED_SYMBOLS = [
michael@0:   "Measurement",
michael@0:   "Provider",
michael@0: ];
michael@0: 
michael@0: const {utils: Cu} = Components;
michael@0: 
michael@0: const MILLISECONDS_PER_DAY = 24 * 60 * 60 * 1000;
michael@0: 
michael@0: #endif
michael@0: 
michael@0: Cu.import("resource://gre/modules/Promise.jsm");
michael@0: Cu.import("resource://gre/modules/Preferences.jsm");
michael@0: Cu.import("resource://gre/modules/Task.jsm");
michael@0: Cu.import("resource://gre/modules/Log.jsm");
michael@0: Cu.import("resource://services-common/utils.js");
michael@0: 
michael@0: 
michael@0: 
michael@0: /**
michael@0:  * Represents a collection of related pieces/fields of data.
michael@0:  *
michael@0:  * This is an abstract base type.
michael@0:  *
michael@0:  * This type provides the primary interface for storing, retrieving, and
michael@0:  * serializing data.
michael@0:  *
michael@0:  * Each measurement consists of a set of named fields. Each field is primarily
michael@0:  * identified by a string name, which must be unique within the measurement.
michael@0:  *
michael@0:  * Each derived type must define the following properties:
michael@0:  *
michael@0:  *   name -- String name of this measurement. This is the primary way
michael@0:  *     measurements are distinguished within a provider.
michael@0:  *
michael@0:  *   version -- Integer version of this measurement. This is a secondary
michael@0:  *     identifier for a measurement within a provider. The version denotes
michael@0:  *     the behavior of this measurement and the composition of its fields over
michael@0:  *     time. When a new field is added or the behavior of an existing field
michael@0:  *     changes, the version should be incremented. The initial version of a
michael@0:  *     measurement is typically 1.
michael@0:  *
michael@0:  *   fields -- Object defining the fields this measurement holds. Keys in the
michael@0:  *     object are string field names. Values are objects describing how the
michael@0:  *     field works. The following properties are recognized:
michael@0:  *
michael@0:  *       type -- The string type of this field. This is typically one of the
michael@0:  *         FIELD_* constants from the Metrics.Storage type.
michael@0:  *
michael@0:  *
michael@0:  * FUTURE: provide hook points for measurements to supplement with custom
michael@0:  * storage needs.
michael@0:  */
michael@0: this.Measurement = function () {
michael@0:   if (!this.name) {
michael@0:     throw new Error("Measurement must have a name.");
michael@0:   }
michael@0: 
michael@0:   if (!this.version) {
michael@0:     throw new Error("Measurement must have a version.");
michael@0:   }
michael@0: 
michael@0:   if (!Number.isInteger(this.version)) {
michael@0:     throw new Error("Measurement's version must be an integer: " + this.version);
michael@0:   }
michael@0: 
michael@0:   if (!this.fields) {
michael@0:     throw new Error("Measurement must define fields.");
michael@0:   }
michael@0: 
michael@0:   for (let [name, info] in Iterator(this.fields)) {
michael@0:     if (!info) {
michael@0:       throw new Error("Field does not contain metadata: " + name);
michael@0:     }
michael@0: 
michael@0:     if (!info.type) {
michael@0:       throw new Error("Field is missing required type property: " + name);
michael@0:     }
michael@0:   }
michael@0: 
michael@0:   this._log = Log.repository.getLogger("Services.Metrics.Measurement." + this.name);
michael@0: 
michael@0:   this.id = null;
michael@0:   this.storage = null;
michael@0:   this._fields = {};
michael@0: 
michael@0:   this._serializers = {};
michael@0:   this._serializers[this.SERIALIZE_JSON] = {
michael@0:     singular: this._serializeJSONSingular.bind(this),
michael@0:     daily: this._serializeJSONDay.bind(this),
michael@0:   };
michael@0: }
michael@0: 
michael@0: Measurement.prototype = Object.freeze({
michael@0:   SERIALIZE_JSON: "json",
michael@0: 
michael@0:   /**
michael@0:    * Obtain a serializer for this measurement.
michael@0:    *
michael@0:    * Implementations should return an object with the following keys:
michael@0:    *
michael@0:    *   singular -- Serializer for singular data.
michael@0:    *   daily -- Serializer for daily data.
michael@0:    *
michael@0:    * Each item is a function that takes a single argument: the data to
michael@0:    * serialize. The passed data is a subset of that returned from
michael@0:    * this.getValues(). For "singular," data.singular is passed. For "daily",
michael@0:    * data.days.get(<day>) is passed.
michael@0:    *
michael@0:    * This function receives a single argument: the serialization format we
michael@0:    * are requesting. This is one of the SERIALIZE_* constants on this base type.
michael@0:    *
michael@0:    * For SERIALIZE_JSON, the function should return an object that
michael@0:    * JSON.stringify() knows how to handle. This could be an anonymous object or
michael@0:    * array or any object with a property named `toJSON` whose value is a
michael@0:    * function. The returned object will be added to a larger document
michael@0:    * containing the results of all `serialize` calls.
michael@0:    *
michael@0:    * The default implementation knows how to serialize built-in types using
michael@0:    * very simple logic. If small encoding size is a goal, the default
michael@0:    * implementation may not be suitable. If an unknown field type is
michael@0:    * encountered, the default implementation will error.
michael@0:    *
michael@0:    * @param format
michael@0:    *        (string) A SERIALIZE_* constant defining what serialization format
michael@0:    *        to use.
michael@0:    */
michael@0:   serializer: function (format) {
michael@0:     if (!(format in this._serializers)) {
michael@0:       throw new Error("Don't know how to serialize format: " + format);
michael@0:     }
michael@0: 
michael@0:     return this._serializers[format];
michael@0:   },
michael@0: 
michael@0:   /**
michael@0:    * Whether this measurement contains the named field.
michael@0:    *
michael@0:    * @param name
michael@0:    *        (string) Name of field.
michael@0:    *
michael@0:    * @return bool
michael@0:    */
michael@0:   hasField: function (name) {
michael@0:     return name in this.fields;
michael@0:   },
michael@0: 
michael@0:   /**
michael@0:    * The unique identifier for a named field.
michael@0:    *
michael@0:    * This will throw if the field is not known.
michael@0:    *
michael@0:    * @param name
michael@0:    *        (string) Name of field.
michael@0:    */
michael@0:   fieldID: function (name) {
michael@0:     let entry = this._fields[name];
michael@0: 
michael@0:     if (!entry) {
michael@0:       throw new Error("Unknown field: " + name);
michael@0:     }
michael@0: 
michael@0:     return entry[0];
michael@0:   },
michael@0: 
michael@0:   fieldType: function (name) {
michael@0:     let entry = this._fields[name];
michael@0: 
michael@0:     if (!entry) {
michael@0:       throw new Error("Unknown field: " + name);
michael@0:     }
michael@0: 
michael@0:     return entry[1];
michael@0:   },
michael@0: 
michael@0:   _configureStorage: function () {
michael@0:     let missing = [];
michael@0:     for (let [name, info] in Iterator(this.fields)) {
michael@0:       if (this.storage.hasFieldFromMeasurement(this.id, name)) {
michael@0:         this._fields[name] =
michael@0:           [this.storage.fieldIDFromMeasurement(this.id, name), info.type];
michael@0:         continue;
michael@0:       }
michael@0: 
michael@0:       missing.push([name, info.type]);
michael@0:     }
michael@0: 
michael@0:     if (!missing.length) {
michael@0:       return CommonUtils.laterTickResolvingPromise();
michael@0:     }
michael@0: 
michael@0:     // We only perform a transaction if we have work to do (to avoid
michael@0:     // extra SQLite overhead).
michael@0:     return this.storage.enqueueTransaction(function registerFields() {
michael@0:       for (let [name, type] of missing) {
michael@0:         this._log.debug("Registering field: " + name + " " + type);
michael@0:         let id = yield this.storage.registerField(this.id, name, type);
michael@0:         this._fields[name] = [id, type];
michael@0:       }
michael@0:     }.bind(this));
michael@0:   },
michael@0: 
michael@0:   //---------------------------------------------------------------------------
michael@0:   // Data Recording Functions
michael@0:   //
michael@0:   // Functions in this section are used to record new values against this
michael@0:   // measurement instance.
michael@0:   //
michael@0:   // Generally speaking, these functions will throw if the specified field does
michael@0:   // not exist or if the storage function requested is not appropriate for the
michael@0:   // type of that field. These functions will also return a promise that will
michael@0:   // be resolved when the underlying storage operation has completed.
michael@0:   //---------------------------------------------------------------------------
michael@0: 
michael@0:   /**
michael@0:    * Increment a daily counter field in this measurement by 1.
michael@0:    *
michael@0:    * By default, the counter for the current day will be incremented.
michael@0:    *
michael@0:    * If the field is not known or is not a daily counter, this will throw.
michael@0:    *
michael@0:    *
michael@0:    *
michael@0:    * @param field
michael@0:    *        (string) The name of the field whose value to increment.
michael@0:    * @param date
michael@0:    *        (Date) Day on which to increment the counter.
michael@0:    * @param by
michael@0:    *        (integer) How much to increment by.
michael@0:    * @return Promise<>
michael@0:    */
michael@0:   incrementDailyCounter: function (field, date=new Date(), by=1) {
michael@0:     return this.storage.incrementDailyCounterFromFieldID(this.fieldID(field),
michael@0:                                                          date, by);
michael@0:   },
michael@0: 
michael@0:   /**
michael@0:    * Record a new numeric value for a daily discrete numeric field.
michael@0:    *
michael@0:    * @param field
michael@0:    *        (string) The name of the field to append a value to.
michael@0:    * @param value
michael@0:    *        (Number) Number to append.
michael@0:    * @param date
michael@0:    *        (Date) Day on which to append the value.
michael@0:    *
michael@0:    * @return Promise<>
michael@0:    */
michael@0:   addDailyDiscreteNumeric: function (field, value, date=new Date()) {
michael@0:     return this.storage.addDailyDiscreteNumericFromFieldID(
michael@0:                           this.fieldID(field), value, date);
michael@0:   },
michael@0: 
michael@0:   /**
michael@0:    * Record a new text value for a daily discrete text field.
michael@0:    *
michael@0:    * This is like `addDailyDiscreteNumeric` but for daily discrete text fields.
michael@0:    */
michael@0:   addDailyDiscreteText: function (field, value, date=new Date()) {
michael@0:     return this.storage.addDailyDiscreteTextFromFieldID(
michael@0:                           this.fieldID(field), value, date);
michael@0:   },
michael@0: 
michael@0:   /**
michael@0:    * Record the last seen value for a last numeric field.
michael@0:    *
michael@0:    * @param field
michael@0:    *        (string) The name of the field to set the value of.
michael@0:    * @param value
michael@0:    *        (Number) The value to set.
michael@0:    * @param date
michael@0:    *        (Date) When this value was recorded.
michael@0:    *
michael@0:    * @return Promise<>
michael@0:    */
michael@0:   setLastNumeric: function (field, value, date=new Date()) {
michael@0:     return this.storage.setLastNumericFromFieldID(this.fieldID(field), value,
michael@0:                                                   date);
michael@0:   },
michael@0: 
michael@0:   /**
michael@0:    * Record the last seen value for a last text field.
michael@0:    *
michael@0:    * This is like `setLastNumeric` except for last text fields.
michael@0:    */
michael@0:   setLastText: function (field, value, date=new Date()) {
michael@0:     return this.storage.setLastTextFromFieldID(this.fieldID(field), value,
michael@0:                                                date);
michael@0:   },
michael@0: 
michael@0:   /**
michael@0:    * Record the most recent value for a daily last numeric field.
michael@0:    *
michael@0:    * @param field
michael@0:    *        (string) The name of a daily last numeric field.
michael@0:    * @param value
michael@0:    *        (Number) The value to set.
michael@0:    * @param date
michael@0:    *        (Date) Day on which to record the last value.
michael@0:    *
michael@0:    * @return Promise<>
michael@0:    */
michael@0:   setDailyLastNumeric: function (field, value, date=new Date()) {
michael@0:     return this.storage.setDailyLastNumericFromFieldID(this.fieldID(field),
michael@0:                                                        value, date);
michael@0:   },
michael@0: 
michael@0:   /**
michael@0:    * Record the most recent value for a daily last text field.
michael@0:    *
michael@0:    * This is like `setDailyLastNumeric` except for a daily last text field.
michael@0:    */
michael@0:   setDailyLastText: function (field, value, date=new Date()) {
michael@0:     return this.storage.setDailyLastTextFromFieldID(this.fieldID(field),
michael@0:                                                     value, date);
michael@0:   },
michael@0: 
michael@0:   //---------------------------------------------------------------------------
michael@0:   // End of data recording APIs.
michael@0:   //---------------------------------------------------------------------------
michael@0: 
michael@0:   /**
michael@0:    * Obtain all values stored for this measurement.
michael@0:    *
michael@0:    * The default implementation obtains all known types from storage. If the
michael@0:    * measurement provides custom types or stores values somewhere other than
michael@0:    * storage, it should define its own implementation.
michael@0:    *
michael@0:    * This returns a promise that resolves to a data structure which is
michael@0:    * understood by the measurement's serialize() function.
michael@0:    */
michael@0:   getValues: function () {
michael@0:     return this.storage.getMeasurementValues(this.id);
michael@0:   },
michael@0: 
michael@0:   deleteLastNumeric: function (field) {
michael@0:     return this.storage.deleteLastNumericFromFieldID(this.fieldID(field));
michael@0:   },
michael@0: 
michael@0:   deleteLastText: function (field) {
michael@0:     return this.storage.deleteLastTextFromFieldID(this.fieldID(field));
michael@0:   },
michael@0: 
michael@0:   /**
michael@0:    * This method is used by the default serializers to control whether a field
michael@0:    * is included in the output.
michael@0:    *
michael@0:    * There could be legacy fields in storage we no longer care about.
michael@0:    *
michael@0:    * This method is a hook to allow measurements to change this behavior, e.g.,
michael@0:    * to implement a dynamic fieldset.
michael@0:    *
michael@0:    * You will also need to override `fieldType`.
michael@0:    *
michael@0:    * @return (boolean) true if the specified field should be included in
michael@0:    *                   payload output.
michael@0:    */
michael@0:   shouldIncludeField: function (field) {
michael@0:     return field in this._fields;
michael@0:   },
michael@0: 
michael@0:   _serializeJSONSingular: function (data) {
michael@0:     let result = {"_v": this.version};
michael@0: 
michael@0:     for (let [field, data] of data) {
michael@0:       // There could be legacy fields in storage we no longer care about.
michael@0:       if (!this.shouldIncludeField(field)) {
michael@0:         continue;
michael@0:       }
michael@0: 
michael@0:       let type = this.fieldType(field);
michael@0: 
michael@0:       switch (type) {
michael@0:         case this.storage.FIELD_LAST_NUMERIC:
michael@0:         case this.storage.FIELD_LAST_TEXT:
michael@0:           result[field] = data[1];
michael@0:           break;
michael@0: 
michael@0:         case this.storage.FIELD_DAILY_COUNTER:
michael@0:         case this.storage.FIELD_DAILY_DISCRETE_NUMERIC:
michael@0:         case this.storage.FIELD_DAILY_DISCRETE_TEXT:
michael@0:         case this.storage.FIELD_DAILY_LAST_NUMERIC:
michael@0:         case this.storage.FIELD_DAILY_LAST_TEXT:
michael@0:           continue;
michael@0: 
michael@0:         default:
michael@0:           throw new Error("Unknown field type: " + type);
michael@0:       }
michael@0:     }
michael@0: 
michael@0:     return result;
michael@0:   },
michael@0: 
michael@0:   _serializeJSONDay: function (data) {
michael@0:     let result = {"_v": this.version};
michael@0: 
michael@0:     for (let [field, data] of data) {
michael@0:       if (!this.shouldIncludeField(field)) {
michael@0:         continue;
michael@0:       }
michael@0: 
michael@0:       let type = this.fieldType(field);
michael@0: 
michael@0:       switch (type) {
michael@0:         case this.storage.FIELD_DAILY_COUNTER:
michael@0:         case this.storage.FIELD_DAILY_DISCRETE_NUMERIC:
michael@0:         case this.storage.FIELD_DAILY_DISCRETE_TEXT:
michael@0:         case this.storage.FIELD_DAILY_LAST_NUMERIC:
michael@0:         case this.storage.FIELD_DAILY_LAST_TEXT:
michael@0:           result[field] = data;
michael@0:           break;
michael@0: 
michael@0:         case this.storage.FIELD_LAST_NUMERIC:
michael@0:         case this.storage.FIELD_LAST_TEXT:
michael@0:           continue;
michael@0: 
michael@0:         default:
michael@0:           throw new Error("Unknown field type: " + type);
michael@0:       }
michael@0:     }
michael@0: 
michael@0:     return result;
michael@0:   },
michael@0: });
michael@0: 
michael@0: 
michael@0: /**
michael@0:  * An entity that emits data.
michael@0:  *
michael@0:  * A `Provider` consists of a string name (must be globally unique among all
michael@0:  * known providers) and a set of `Measurement` instances.
michael@0:  *
michael@0:  * The main role of a `Provider` is to produce metrics data and to store said
michael@0:  * data in the storage backend.
michael@0:  *
michael@0:  * Metrics data collection is initiated either by a manager calling a
michael@0:  * `collect*` function on `Provider` instances or by the `Provider` registering
michael@0:  * to some external event and then reacting whenever they occur.
michael@0:  *
michael@0:  * `Provider` implementations interface directly with a storage backend. For
michael@0:  * common stored values (daily counters, daily discrete values, etc),
michael@0:  * implementations should interface with storage via the various helper
michael@0:  * functions on the `Measurement` instances. For custom stored value types,
michael@0:  * implementations will interact directly with the low-level storage APIs.
michael@0:  *
michael@0:  * Because multiple providers exist and could be responding to separate
michael@0:  * external events simultaneously and because not all operations performed by
michael@0:  * storage can safely be performed in parallel, writing directly to storage at
michael@0:  * event time is dangerous. Therefore, interactions with storage must be
michael@0:  * deferred until it is safe to perform them.
michael@0:  *
michael@0:  * This typically looks something like:
michael@0:  *
michael@0:  *   // This gets called when an external event worthy of recording metrics
michael@0:  *   // occurs. The function receives a numeric value associated with the event.
michael@0:  *   function onExternalEvent (value) {
michael@0:  *     let now = new Date();
michael@0:  *     let m = this.getMeasurement("foo", 1);
michael@0:  *
michael@0:  *     this.enqueueStorageOperation(function storeExternalEvent() {
michael@0:  *
michael@0:  *       // We interface with storage via the `Measurement` helper functions.
michael@0:  *       // These each return a promise that will be resolved when the
michael@0:  *       // operation finishes. We rely on behavior of storage where operations
michael@0:  *       // are executed single threaded and sequentially. Therefore, we only
michael@0:  *       // need to return the final promise.
michael@0:  *       m.incrementDailyCounter("foo", now);
michael@0:  *       return m.addDailyDiscreteNumericValue("my_value", value, now);
michael@0:  *     }.bind(this));
michael@0:  *
michael@0:  *   }
michael@0:  *
michael@0:  *
michael@0:  * `Provider` is an abstract base class. Implementations must define a few
michael@0:  * properties:
michael@0:  *
michael@0:  *   name
michael@0:  *     The `name` property should be a string defining the provider's name. The
michael@0:  *     name must be globally unique for the application. The name is used as an
michael@0:  *     identifier to distinguish providers from each other.
michael@0:  *
michael@0:  *   measurementTypes
michael@0:  *     This must be an array of `Measurement`-derived types. Note that elements
michael@0:  *     in the array are the type functions, not instances. Instances of the
michael@0:  *     `Measurement` are created at run-time by the `Provider` and are bound
michael@0:  *     to the provider and to a specific storage backend.
michael@0:  */
michael@0: this.Provider = function () {
michael@0:   if (!this.name) {
michael@0:     throw new Error("Provider must define a name.");
michael@0:   }
michael@0: 
michael@0:   if (!Array.isArray(this.measurementTypes)) {
michael@0:     throw new Error("Provider must define measurement types.");
michael@0:   }
michael@0: 
michael@0:   this._log = Log.repository.getLogger("Services.Metrics.Provider." + this.name);
michael@0: 
michael@0:   this.measurements = null;
michael@0:   this.storage = null;
michael@0: }
michael@0: 
michael@0: Provider.prototype = Object.freeze({
michael@0:   /**
michael@0:    * Whether the provider only pulls data from other sources.
michael@0:    *
michael@0:    * If this is true, the provider pulls data from other sources. By contrast,
michael@0:    * "push-based" providers subscribe to foreign sources and record/react to
michael@0:    * external events as they happen.
michael@0:    *
michael@0:    * Pull-only providers likely aren't instantiated until a data collection
michael@0:    * is performed. Thus, implementations cannot rely on a provider instance
michael@0:    * always being alive. This is an optimization so provider instances aren't
michael@0:    * dead weight while the application is running.
michael@0:    *
michael@0:    * This must be set on the prototype to have an effect.
michael@0:    */
michael@0:   pullOnly: false,
michael@0: 
michael@0:   /**
michael@0:    * Obtain a `Measurement` from its name and version.
michael@0:    *
michael@0:    * If the measurement is not found, an Error is thrown.
michael@0:    */
michael@0:   getMeasurement: function (name, version) {
michael@0:     if (!Number.isInteger(version)) {
michael@0:       throw new Error("getMeasurement expects an integer version. Got: " + version);
michael@0:     }
michael@0: 
michael@0:     let m = this.measurements.get([name, version].join(":"));
michael@0: 
michael@0:     if (!m) {
michael@0:       throw new Error("Unknown measurement: " + name + " v" + version);
michael@0:     }
michael@0: 
michael@0:     return m;
michael@0:   },
michael@0: 
michael@0:   init: function (storage) {
michael@0:     if (this.storage !== null) {
michael@0:       throw new Error("Provider() not called. Did the sub-type forget to call it?");
michael@0:     }
michael@0: 
michael@0:     if (this.storage) {
michael@0:       throw new Error("Provider has already been initialized.");
michael@0:     }
michael@0: 
michael@0:     this.measurements = new Map();
michael@0:     this.storage = storage;
michael@0: 
michael@0:     let self = this;
michael@0:     return Task.spawn(function init() {
michael@0:       let pre = self.preInit();
michael@0:       if (!pre || typeof(pre.then) != "function") {
michael@0:         throw new Error("preInit() does not return a promise.");
michael@0:       }
michael@0:       yield pre;
michael@0: 
michael@0:       for (let measurementType of self.measurementTypes) {
michael@0:         let measurement = new measurementType();
michael@0: 
michael@0:         measurement.provider = self;
michael@0:         measurement.storage = self.storage;
michael@0: 
michael@0:         let id = yield storage.registerMeasurement(self.name, measurement.name,
michael@0:                                                    measurement.version);
michael@0: 
michael@0:         measurement.id = id;
michael@0: 
michael@0:         yield measurement._configureStorage();
michael@0: 
michael@0:         self.measurements.set([measurement.name, measurement.version].join(":"),
michael@0:                               measurement);
michael@0:       }
michael@0: 
michael@0:       let post = self.postInit();
michael@0:       if (!post || typeof(post.then) != "function") {
michael@0:         throw new Error("postInit() does not return a promise.");
michael@0:       }
michael@0:       yield post;
michael@0:     });
michael@0:   },
michael@0: 
michael@0:   shutdown: function () {
michael@0:     let promise = this.onShutdown();
michael@0: 
michael@0:     if (!promise || typeof(promise.then) != "function") {
michael@0:       throw new Error("onShutdown implementation does not return a promise.");
michael@0:     }
michael@0: 
michael@0:     return promise;
michael@0:   },
michael@0: 
michael@0:   /**
michael@0:    * Hook point for implementations to perform pre-initialization activity.
michael@0:    *
michael@0:    * This method will be called before measurement registration.
michael@0:    *
michael@0:    * Implementations should return a promise which is resolved when
michael@0:    * initialization activities have completed.
michael@0:    */
michael@0:   preInit: function () {
michael@0:     return CommonUtils.laterTickResolvingPromise();
michael@0:   },
michael@0: 
michael@0:   /**
michael@0:    * Hook point for implementations to perform post-initialization activity.
michael@0:    *
michael@0:    * This method will be called after `preInit` and measurement registration,
michael@0:    * but before initialization is finished.
michael@0:    *
michael@0:    * If a `Provider` instance needs to register observers, etc, it should
michael@0:    * implement this function.
michael@0:    *
michael@0:    * Implementations should return a promise which is resolved when
michael@0:    * initialization activities have completed.
michael@0:    */
michael@0:   postInit: function () {
michael@0:     return CommonUtils.laterTickResolvingPromise();
michael@0:   },
michael@0: 
michael@0:   /**
michael@0:    * Hook point for shutdown of instances.
michael@0:    *
michael@0:    * This is the opposite of `onInit`. If a `Provider` needs to unregister
michael@0:    * observers, etc, this is where it should do it.
michael@0:    *
michael@0:    * Implementations should return a promise which is resolved when
michael@0:    * shutdown activities have completed.
michael@0:    */
michael@0:   onShutdown: function () {
michael@0:     return CommonUtils.laterTickResolvingPromise();
michael@0:   },
michael@0: 
michael@0:   /**
michael@0:    * Collects data that doesn't change during the application's lifetime.
michael@0:    *
michael@0:    * Implementations should return a promise that resolves when all data has
michael@0:    * been collected and storage operations have been finished.
michael@0:    *
michael@0:    * @return Promise<>
michael@0:    */
michael@0:   collectConstantData: function () {
michael@0:     return CommonUtils.laterTickResolvingPromise();
michael@0:   },
michael@0: 
michael@0:   /**
michael@0:    * Collects data approximately every day.
michael@0:    *
michael@0:    * For long-running applications, this is called approximately every day.
michael@0:    * It may or may not be called every time the application is run. It also may
michael@0:    * be called more than once per day.
michael@0:    *
michael@0:    * Implementations should return a promise that resolves when all data has
michael@0:    * been collected and storage operations have completed.
michael@0:    *
michael@0:    * @return Promise<>
michael@0:    */
michael@0:   collectDailyData: function () {
michael@0:     return CommonUtils.laterTickResolvingPromise();
michael@0:   },
michael@0: 
michael@0:   /**
michael@0:    * Queue a deferred storage operation.
michael@0:    *
michael@0:    * Deferred storage operations are the preferred method for providers to
michael@0:    * interact with storage. When collected data is to be added to storage,
michael@0:    * the provider creates a function that performs the necessary storage
michael@0:    * interactions and then passes that function to this function. Pending
michael@0:    * storage operations will be executed sequentially by a coordinator.
michael@0:    *
michael@0:    * The passed function should return a promise which will be resolved upon
michael@0:    * completion of storage interaction.
michael@0:    */
michael@0:   enqueueStorageOperation: function (func) {
michael@0:     return this.storage.enqueueOperation(func);
michael@0:   },
michael@0: 
michael@0:   /**
michael@0:    * Obtain persisted provider state.
michael@0:    *
michael@0:    * Provider state consists of key-value pairs of string names and values.
michael@0:    * Providers can stuff whatever they want into state. They are encouraged to
michael@0:    * store as little as possible for performance reasons.
michael@0:    *
michael@0:    * State is backed by storage and is robust.
michael@0:    *
michael@0:    * These functions do not enqueue on storage automatically, so they should
michael@0:    * be guarded by `enqueueStorageOperation` or some other mutex.
michael@0:    *
michael@0:    * @param key
michael@0:    *        (string) The property to retrieve.
michael@0:    *
michael@0:    * @return Promise<string|null> String value on success. null if no state
michael@0:    *         is available under this key.
michael@0:    */
michael@0:   getState: function (key) {
michael@0:     return this.storage.getProviderState(this.name, key);
michael@0:   },
michael@0: 
michael@0:   /**
michael@0:    * Set state for this provider.
michael@0:    *
michael@0:    * This is the complementary API for `getState` and obeys the same
michael@0:    * storage restrictions.
michael@0:    */
michael@0:   setState: function (key, value) {
michael@0:     return this.storage.setProviderState(this.name, key, value);
michael@0:   },
michael@0: 
michael@0:   _dateToDays: function (date) {
michael@0:     return Math.floor(date.getTime() / MILLISECONDS_PER_DAY);
michael@0:   },
michael@0: 
michael@0:   _daysToDate: function (days) {
michael@0:     return new Date(days * MILLISECONDS_PER_DAY);
michael@0:   },
michael@0: });
michael@0: