// Copyright 2017 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'dart:async';

import 'package:meta/meta.dart';

import 'package:flutter/services.dart';
import 'package:flutter/foundation.dart';

/// Firebase Analytics API.
class FirebaseAnalytics {
  static final FirebaseAnalytics _instance =
      new FirebaseAnalytics.private(const MethodChannel('firebase_analytics'));

  /// Provides an instance of this class.
  factory FirebaseAnalytics() => _instance;

  /// We don't want people to extend this class, but implementing its interface,
  /// e.g. in tests, is OK.
  @visibleForTesting
  FirebaseAnalytics.private(MethodChannel platformChannel)
      : _channel = platformChannel,
        android = defaultTargetPlatform == TargetPlatform.android
            ? new FirebaseAnalyticsAndroid.private(platformChannel)
            : null;

  final MethodChannel _channel;

  /// Namespace for analytics API available on Android only.
  ///
  /// The value of this field is `null` on non-Android platforms. If you are
  /// writing cross-platform code, consider using null-aware operator when
  /// accessing it.
  ///
  /// Example:
  ///
  ///     FirebaseAnalytics analytics = new FirebaseAnalytics();
  ///     analytics.android?.setMinimumSessionDuration(200000);
  final FirebaseAnalyticsAndroid android;

  /// Logs a custom Flutter Analytics event with the given [name] and event [parameters].
  Future<Null> logEvent(
      {@required String name, Map<String, dynamic> parameters}) async {
    if (_reservedEventNames.contains(name)) {
      throw new ArgumentError.value(
          name, 'name', 'Event name is reserved and cannot be used');
    }

    const String kReservedPrefix = 'firebase_';

    if (name.startsWith(kReservedPrefix)) {
      throw new ArgumentError.value(name, 'name',
          'Prefix "$kReservedPrefix" is reserved and cannot be used.');
    }

    await _channel.invokeMethod('logEvent', <String, dynamic>{
      'name': name,
      'parameters': parameters,
    });
  }

  /// Sets the user ID property.
  ///
  /// This feature must be used in accordance with [Google's Privacy Policy][1].
  ///
  /// [1]: https://www.google.com/policies/privacy/
  Future<Null> setUserId(String id) async {
    if (id == null) {
      throw new ArgumentError.notNull('id');
    }

    await _channel.invokeMethod('setUserId', id);
  }

  /// Sets the current [screenName], which specifies the current visual context
  /// in your app.
  ///
  /// This helps identify the areas in your app where users spend their time
  /// and how they interact with your app.
  ///
  /// The class name can optionally be overridden by the [screenClassOverride]
  /// parameter.
  ///
  /// The [screenName] and [screenClassOverride] remain in effect until the
  /// current `Activity` (in Android) or `UIViewController` (in iOS) changes or
  /// a new call to [setCurrentScreen] is made.
  ///
  /// See also:
  ///
  /// https://firebase.google.com/docs/reference/android/com/google/firebase/analytics/FirebaseAnalytics.html#setCurrentScreen(android.app.Activity, java.lang.String, java.lang.String)
  /// https://firebase.google.com/docs/reference/ios/firebaseanalytics/api/reference/Classes/FIRAnalytics#setscreennamescreenclass
  Future<Null> setCurrentScreen(
      {@required String screenName,
      String screenClassOverride: 'Flutter'}) async {
    if (screenName == null) {
      throw new ArgumentError.notNull('screenName');
    }

    await _channel.invokeMethod('setCurrentScreen', <String, String>{
      'screenName': screenName,
      'screenClassOverride': screenClassOverride,
    });
  }

  static final RegExp _nonAlphaNumeric = new RegExp(r'[^a-zA-Z0-9_]');
  static final RegExp _alpha = new RegExp(r'[a-zA-Z]');

  /// Sets a user property to a given value.
  ///
  /// Up to 25 user property names are supported. Once set, user property
  /// values persist throughout the app lifecycle and across sessions.
  ///
  /// [name] is the name of the user property to set. Should contain 1 to 24
  /// alphanumeric characters or underscores and must start with an alphabetic
  /// character. The "firebase_" prefix is reserved and should not be used for
  /// user property names.
  Future<Null> setUserProperty(
      {@required String name, @required String value}) async {
    if (name == null) {
      throw new ArgumentError.notNull('name');
    }

    if (name.isEmpty ||
        name.length > 24 ||
        name.indexOf(_alpha) != 0 ||
        name.contains(_nonAlphaNumeric))
      throw new ArgumentError.value(
          name, 'name', 'must contain 1 to 24 alphanumeric characters.');

    if (name.startsWith('firebase_'))
      throw new ArgumentError.value(
          name, 'name', '"firebase_" prefix is reserved');

    await _channel.invokeMethod('setUserProperty', <String, String>{
      'name': name,
      'value': value,
    });
  }

  /// Logs the standard `add_payment_info` event.
  ///
  /// This event signifies that a user has submitted their payment information
  /// to your app.
  ///
  /// See: https://firebase.google.com/docs/reference/android/com/google/firebase/analytics/FirebaseAnalytics.Event.html#ADD_PAYMENT_INFO
  Future<Null> logAddPaymentInfo() {
    return logEvent(name: 'add_payment_info');
  }

  /// Logs the standard `add_to_cart` event.
  ///
  /// This event signifies that an item was added to a cart for purchase. Add
  /// this event to a funnel with [logEcommercePurchase] to gauge the
  /// effectiveness of your checkout process. Note: If you supply the
  /// [value] parameter, you must also supply the [currency] parameter so that
  /// revenue metrics can be computed accurately.
  ///
  /// See: https://firebase.google.com/docs/reference/android/com/google/firebase/analytics/FirebaseAnalytics.Event.html#ADD_TO_CART
  Future<Null> logAddToCart({
    @required String itemId,
    @required String itemName,
    @required String itemCategory,
    @required int quantity,
    double price,
    double value,
    String currency,
    String origin,
    String itemLocationId,
    String destination,
    String startDate,
    String endDate,
  }) {
    _requireValueAndCurrencyTogether(value, currency);

    return logEvent(
      name: 'add_to_cart',
      parameters: filterOutNulls(<String, dynamic>{
        _ITEM_ID: itemId,
        _ITEM_NAME: itemName,
        _ITEM_CATEGORY: itemCategory,
        _QUANTITY: quantity,
        _PRICE: price,
        _VALUE: value,
        _CURRENCY: currency,
        _ORIGIN: origin,
        _ITEM_LOCATION_ID: itemLocationId,
        _DESTINATION: destination,
        _START_DATE: startDate,
        _END_DATE: endDate,
      }),
    );
  }

  /// Logs the standard `add_to_wishlist` event.
  ///
  /// This event signifies that an item was added to a wishlist. Use this event
  /// to identify popular gift items in your app. Note: If you supply the
  /// [value] parameter, you must also supply the [currency] parameter so that
  /// revenue metrics can be computed accurately.
  ///
  /// See: https://firebase.google.com/docs/reference/android/com/google/firebase/analytics/FirebaseAnalytics.Event.html#ADD_TO_WISHLIST
  Future<Null> logAddToWishlist({
    @required String itemId,
    @required String itemName,
    @required String itemCategory,
    @required int quantity,
    double price,
    double value,
    String currency,
    String itemLocationId,
  }) {
    _requireValueAndCurrencyTogether(value, currency);

    return logEvent(
      name: 'add_to_wishlist',
      parameters: filterOutNulls(<String, dynamic>{
        _ITEM_ID: itemId,
        _ITEM_NAME: itemName,
        _ITEM_CATEGORY: itemCategory,
        _QUANTITY: quantity,
        _PRICE: price,
        _VALUE: value,
        _CURRENCY: currency,
        _ITEM_LOCATION_ID: itemLocationId,
      }),
    );
  }

  /// Logs the standard `app_open` event.
  ///
  /// See: https://firebase.google.com/docs/reference/android/com/google/firebase/analytics/FirebaseAnalytics.Event.html#APP_OPEN
  Future<Null> logAppOpen() {
    return logEvent(name: 'app_open');
  }

  /// Logs the standard `begin_checkout` event.
  ///
  /// This event signifies that a user has begun the process of checking out.
  /// Add this event to a funnel with your [logEcommercePurchase] event to
  /// gauge the effectiveness of your checkout process. Note: If you supply the
  /// [value] parameter, you must also supply the [currency] parameter so that
  /// revenue metrics can be computed accurately.
  ///
  /// See: https://firebase.google.com/docs/reference/android/com/google/firebase/analytics/FirebaseAnalytics.Event.html#BEGIN_CHECKOUT
  Future<Null> logBeginCheckout({
    double value,
    String currency,
    String transactionId,
    int numberOfNights,
    int numberOfRooms,
    int numberOfPassengers,
    String origin,
    String destination,
    String startDate,
    String endDate,
    String travelClass,
  }) {
    _requireValueAndCurrencyTogether(value, currency);

    return logEvent(
      name: 'begin_checkout',
      parameters: filterOutNulls(<String, dynamic>{
        _VALUE: value,
        _CURRENCY: currency,
        _TRANSACTION_ID: transactionId,
        _NUMBER_OF_NIGHTS: numberOfNights,
        _NUMBER_OF_ROOMS: numberOfRooms,
        _NUMBER_OF_PASSENGERS: numberOfPassengers,
        _ORIGIN: origin,
        _DESTINATION: destination,
        _START_DATE: startDate,
        _END_DATE: endDate,
        _TRAVEL_CLASS: travelClass,
      }),
    );
  }

  /// Logs the standard `campaign_details` event.
  ///
  /// Log this event to supply the referral details of a re-engagement campaign.
  ///
  /// See: https://firebase.google.com/docs/reference/android/com/google/firebase/analytics/FirebaseAnalytics.Event.html#CAMPAIGN_DETAILS
  Future<Null> logCampaignDetails({
    @required String source,
    @required String medium,
    @required String campaign,
    String term,
    String content,
    String aclid,
    String cp1,
  }) {
    return logEvent(
      name: 'campaign_details',
      parameters: filterOutNulls(<String, String>{
        _SOURCE: source,
        _MEDIUM: medium,
        _CAMPAIGN: campaign,
        _TERM: term,
        _CONTENT: content,
        _ACLID: aclid,
        _CP1: cp1,
      }),
    );
  }

  /// Logs the standard `earn_virtual_currency` event.
  ///
  /// This event tracks the awarding of virtual currency in your app. Log this
  /// along with [logSpendVirtualCurrency] to better understand your virtual
  /// economy.
  ///
  /// See: https://firebase.google.com/docs/reference/android/com/google/firebase/analytics/FirebaseAnalytics.Event.html#EARN_VIRTUAL_CURRENCY
  Future<Null> logEarnVirtualCurrency({
    @required String virtualCurrencyName,
    @required num value,
  }) {
    return logEvent(
      name: 'earn_virtual_currency',
      parameters: filterOutNulls(<String, dynamic>{
        _VIRTUAL_CURRENCY_NAME: virtualCurrencyName,
        _VALUE: value,
      }),
    );
  }

  /// Logs the standard `ecommerce_purchase` event.
  ///
  /// This event signifies that an item was purchased by a user. Note: This is
  /// different from the in-app purchase event, which is reported automatically
  /// for Google Play-based apps. Note: If you supply the [value] parameter,
  /// you must also supply the [currency] parameter so that revenue metrics can
  /// be computed accurately.
  ///
  /// See: https://firebase.google.com/docs/reference/android/com/google/firebase/analytics/FirebaseAnalytics.Event.html#ECOMMERCE_PURCHASE
  Future<Null> logEcommercePurchase({
    String currency,
    double value,
    String transactionId,
    double tax,
    double shipping,
    String coupon,
    String location,
    int numberOfNights,
    int numberOfRooms,
    int numberOfPassengers,
    String origin,
    String destination,
    String startDate,
    String endDate,
    String travelClass,
  }) {
    _requireValueAndCurrencyTogether(value, currency);

    return logEvent(
      name: 'ecommerce_purchase',
      parameters: filterOutNulls(<String, dynamic>{
        _CURRENCY: currency,
        _VALUE: value,
        _TRANSACTION_ID: transactionId,
        _TAX: tax,
        _SHIPPING: shipping,
        _COUPON: coupon,
        _LOCATION: location,
        _NUMBER_OF_NIGHTS: numberOfNights,
        _NUMBER_OF_ROOMS: numberOfRooms,
        _NUMBER_OF_PASSENGERS: numberOfPassengers,
        _ORIGIN: origin,
        _DESTINATION: destination,
        _START_DATE: startDate,
        _END_DATE: endDate,
        _TRAVEL_CLASS: travelClass,
      }),
    );
  }

  /// Logs the standard `generate_lead` event.
  ///
  /// Log this event when a lead has been generated in the app to understand
  /// the efficacy of your install and re-engagement campaigns. Note: If you
  /// supply the [value] parameter, you must also supply the [currency]
  /// parameter so that revenue metrics can be computed accurately.
  ///
  /// See: https://firebase.google.com/docs/reference/android/com/google/firebase/analytics/FirebaseAnalytics.Event.html#GENERATE_LEAD
  Future<Null> logGenerateLead({
    String currency,
    double value,
  }) {
    _requireValueAndCurrencyTogether(value, currency);

    return logEvent(
      name: 'generate_lead',
      parameters: filterOutNulls(<String, dynamic>{
        _CURRENCY: currency,
        _VALUE: value,
      }),
    );
  }

  /// Logs the standard `join_group` event.
  ///
  /// Log this event when a user joins a group such as a guild, team or family.
  /// Use this event to analyze how popular certain groups or social features
  /// are in your app.
  ///
  /// See: https://firebase.google.com/docs/reference/android/com/google/firebase/analytics/FirebaseAnalytics.Event.html#JOIN_GROUP
  Future<Null> logJoinGroup({
    @required String groupId,
  }) {
    return logEvent(
      name: 'join_group',
      parameters: filterOutNulls(<String, dynamic>{
        _GROUP_ID: groupId,
      }),
    );
  }

  /// Logs the standard `level_up` event.
  ///
  /// This event signifies that a player has leveled up in your gaming app. It
  /// can help you gauge the level distribution of your userbase and help you
  /// identify certain levels that are difficult to pass.
  ///
  /// See: https://firebase.google.com/docs/reference/android/com/google/firebase/analytics/FirebaseAnalytics.Event.html#LEVEL_UP
  Future<Null> logLevelUp({
    @required int level,
    String character,
  }) {
    return logEvent(
      name: 'level_up',
      parameters: filterOutNulls(<String, dynamic>{
        _LEVEL: level,
        _CHARACTER: character,
      }),
    );
  }

  /// Logs the standard `login` event.
  ///
  /// Apps with a login feature can report this event to signify that a user
  /// has logged in.
  ///
  /// See: https://firebase.google.com/docs/reference/android/com/google/firebase/analytics/FirebaseAnalytics.Event.html#LOGIN
  Future<Null> logLogin() {
    return logEvent(name: 'login');
  }

  /// Logs the standard `post_score` event.
  ///
  /// Log this event when the user posts a score in your gaming app. This event
  /// can help you understand how users are actually performing in your game
  /// and it can help you correlate high scores with certain audiences or
  /// behaviors.
  ///
  /// See: https://firebase.google.com/docs/reference/android/com/google/firebase/analytics/FirebaseAnalytics.Event.html#POST_SCORE
  Future<Null> logPostScore({
    @required int score,
    int level,
    String character,
  }) {
    return logEvent(
      name: 'post_score',
      parameters: filterOutNulls(<String, dynamic>{
        _SCORE: score,
        _LEVEL: level,
        _CHARACTER: character,
      }),
    );
  }

  /// Logs the standard `present_offer` event.
  ///
  /// This event signifies that the app has presented a purchase offer to a
  /// user. Add this event to a funnel with the [logAddToCart] and
  /// [logEcommercePurchase] to gauge your conversion process. Note: If you
  /// supply the [value] parameter, you must also supply the [currency]
  /// parameter so that revenue metrics can be computed accurately.
  ///
  /// See: https://firebase.google.com/docs/reference/android/com/google/firebase/analytics/FirebaseAnalytics.Event.html#PRESENT_OFFER
  Future<Null> logPresentOffer({
    @required String itemId,
    @required String itemName,
    @required String itemCategory,
    @required int quantity,
    double price,
    double value,
    String currency,
    String itemLocationId,
  }) {
    _requireValueAndCurrencyTogether(value, currency);

    return logEvent(
      name: 'present_offer',
      parameters: filterOutNulls(<String, dynamic>{
        _ITEM_ID: itemId,
        _ITEM_NAME: itemName,
        _ITEM_CATEGORY: itemCategory,
        _QUANTITY: quantity,
        _PRICE: price,
        _VALUE: value,
        _CURRENCY: currency,
        _ITEM_LOCATION_ID: itemLocationId,
      }),
    );
  }

  /// Logs the standard `purchase_refund` event.
  ///
  /// This event signifies that an item purchase was refunded. Note: If you
  /// supply the [value] parameter, you must also supply the [currency]
  /// parameter so that revenue metrics can be computed accurately.
  ///
  /// See: https://firebase.google.com/docs/reference/android/com/google/firebase/analytics/FirebaseAnalytics.Event.html#PURCHASE_REFUND
  Future<Null> logPurchaseRefund({
    String currency,
    double value,
    String transactionId,
  }) {
    _requireValueAndCurrencyTogether(value, currency);

    return logEvent(
      name: 'purchase_refund',
      parameters: filterOutNulls(<String, dynamic>{
        _CURRENCY: currency,
        _VALUE: value,
        _TRANSACTION_ID: transactionId,
      }),
    );
  }

  /// Logs the standard `search` event.
  ///
  /// Apps that support search features can use this event to contextualize
  /// search operations by supplying the appropriate, corresponding parameters.
  /// This event can help you identify the most popular content in your app.
  ///
  /// See: https://firebase.google.com/docs/reference/android/com/google/firebase/analytics/FirebaseAnalytics.Event.html#SEARCH
  Future<Null> logSearch({
    @required String searchTerm,
    int numberOfNights,
    int numberOfRooms,
    int numberOfPassengers,
    String origin,
    String destination,
    String startDate,
    String endDate,
    String travelClass,
  }) {
    return logEvent(
      name: 'search',
      parameters: filterOutNulls(<String, dynamic>{
        _SEARCH_TERM: searchTerm,
        _NUMBER_OF_NIGHTS: numberOfNights,
        _NUMBER_OF_ROOMS: numberOfRooms,
        _NUMBER_OF_PASSENGERS: numberOfPassengers,
        _ORIGIN: origin,
        _DESTINATION: destination,
        _START_DATE: startDate,
        _END_DATE: endDate,
        _TRAVEL_CLASS: travelClass,
      }),
    );
  }

  /// Logs the standard `select_content` event.
  ///
  /// This general purpose event signifies that a user has selected some
  /// content of a certain type in an app. The content can be any object in
  /// your app. This event can help you identify popular content and categories
  /// of content in your app.
  ///
  /// See: https://firebase.google.com/docs/reference/android/com/google/firebase/analytics/FirebaseAnalytics.Event.html#SELECT_CONTENT
  Future<Null> logSelectContent({
    @required String contentType,
    @required String itemId,
  }) {
    return logEvent(
      name: 'select_content',
      parameters: filterOutNulls(<String, dynamic>{
        _CONTENT_TYPE: contentType,
        _ITEM_ID: itemId,
      }),
    );
  }

  /// Logs the standard `share` event.
  ///
  /// Apps with social features can log the Share event to identify the most
  /// viral content.
  ///
  /// See: https://firebase.google.com/docs/reference/android/com/google/firebase/analytics/FirebaseAnalytics.Event.html#SHARE
  Future<Null> logShare({
    @required String contentType,
    @required String itemId,
  }) {
    return logEvent(
      name: 'share',
      parameters: filterOutNulls(<String, dynamic>{
        _CONTENT_TYPE: contentType,
        _ITEM_ID: itemId,
      }),
    );
  }

  /// Logs the standard `sign_up` event.
  ///
  /// This event indicates that a user has signed up for an account in your
  /// app. The parameter signifies the method by which the user signed up. Use
  /// this event to understand the different behaviors between logged in and
  /// logged out users.
  ///
  /// See: https://firebase.google.com/docs/reference/android/com/google/firebase/analytics/FirebaseAnalytics.Event.html#SIGN_UP
  Future<Null> logSignUp({
    @required String signUpMethod,
  }) {
    return logEvent(
      name: 'sign_up',
      parameters: filterOutNulls(<String, dynamic>{
        _SIGN_UP_METHOD: signUpMethod,
      }),
    );
  }

  /// Logs the standard `spend_virtual_currency` event.
  ///
  /// This event tracks the sale of virtual goods in your app and can help you
  /// identify which virtual goods are the most popular objects of purchase.
  ///
  /// See: https://firebase.google.com/docs/reference/android/com/google/firebase/analytics/FirebaseAnalytics.Event.html#SPEND_VIRTUAL_CURRENCY
  Future<Null> logSpendVirtualCurrency({
    @required String itemName,
    @required String virtualCurrencyName,
    @required num value,
  }) {
    return logEvent(
      name: 'spend_virtual_currency',
      parameters: filterOutNulls(<String, dynamic>{
        _ITEM_NAME: itemName,
        _VIRTUAL_CURRENCY_NAME: virtualCurrencyName,
        _VALUE: value,
      }),
    );
  }

  /// Logs the standard `tutorial_begin` event.
  ///
  /// This event signifies the start of the on-boarding process in your app.
  /// Use this in a funnel with [logTutorialComplete] to understand how many
  /// users complete this process and move on to the full app experience.
  ///
  /// See: https://firebase.google.com/docs/reference/android/com/google/firebase/analytics/FirebaseAnalytics.Event.html#TUTORIAL_BEGIN
  Future<Null> logTutorialBegin() {
    return logEvent(name: 'tutorial_begin');
  }

  /// Logs the standard `tutorial_complete` event.
  ///
  /// Use this event to signify the user's completion of your app's on-boarding
  /// process. Add this to a funnel with [logTutorialBegin] to gauge the
  /// completion rate of your on-boarding process.
  ///
  /// See: https://firebase.google.com/docs/reference/android/com/google/firebase/analytics/FirebaseAnalytics.Event.html#TUTORIAL_COMPLETE
  Future<Null> logTutorialComplete() {
    return logEvent(name: 'tutorial_complete');
  }

  /// Logs the standard `unlock_achievement` event with a given achievement
  /// [id].
  ///
  /// Log this event when the user has unlocked an achievement in your game.
  /// Since achievements generally represent the breadth of a gaming
  /// experience, this event can help you understand how many users are
  /// experiencing all that your game has to offer.
  ///
  /// See: https://firebase.google.com/docs/reference/android/com/google/firebase/analytics/FirebaseAnalytics.Event.html#UNLOCK_ACHIEVEMENT
  Future<Null> logUnlockAchievement({
    @required String id,
  }) {
    return logEvent(
      name: 'unlock_achievement',
      parameters: filterOutNulls(<String, dynamic>{
        _ACHIEVEMENT_ID: id,
      }),
    );
  }

  /// Logs the standard `view_item` event.
  ///
  /// This event signifies that some content was shown to the user. This
  /// content may be a product, a webpage or just a simple image or text. Use
  /// the appropriate parameters to contextualize the event. Use this event to
  /// discover the most popular items viewed in your app. Note: If you supply
  /// the [value] parameter, you must also supply the [currency] parameter so
  /// that revenue metrics can be computed accurately.
  ///
  /// See: https://firebase.google.com/docs/reference/android/com/google/firebase/analytics/FirebaseAnalytics.Event.html#VIEW_ITEM
  Future<Null> logViewItem({
    @required String itemId,
    @required String itemName,
    @required String itemCategory,
    String itemLocationId,
    double price,
    int quantity,
    String currency,
    double value,
    String flightNumber,
    int numberOfPassengers,
    int numberOfNights,
    int numberOfRooms,
    String origin,
    String destination,
    String startDate,
    String endDate,
    String searchTerm,
    String travelClass,
  }) {
    _requireValueAndCurrencyTogether(value, currency);

    return logEvent(
      name: 'view_item',
      parameters: filterOutNulls(<String, dynamic>{
        _ITEM_ID: itemId,
        _ITEM_NAME: itemName,
        _ITEM_CATEGORY: itemCategory,
        _ITEM_LOCATION_ID: itemLocationId,
        _PRICE: price,
        _QUANTITY: quantity,
        _CURRENCY: currency,
        _VALUE: value,
        _FLIGHT_NUMBER: flightNumber,
        _NUMBER_OF_PASSENGERS: numberOfPassengers,
        _NUMBER_OF_NIGHTS: numberOfNights,
        _NUMBER_OF_ROOMS: numberOfRooms,
        _ORIGIN: origin,
        _DESTINATION: destination,
        _START_DATE: startDate,
        _END_DATE: endDate,
        _SEARCH_TERM: searchTerm,
        _TRAVEL_CLASS: travelClass,
      }),
    );
  }

  /// Logs the standard `view_item_list` event.
  ///
  /// Log this event when the user has been presented with a list of items of a
  /// certain category.
  ///
  /// See: https://firebase.google.com/docs/reference/android/com/google/firebase/analytics/FirebaseAnalytics.Event.html#VIEW_ITEM_LIST
  Future<Null> logViewItemList({
    @required String itemCategory,
  }) {
    return logEvent(
      name: 'view_item_list',
      parameters: filterOutNulls(<String, dynamic>{
        _ITEM_CATEGORY: itemCategory,
      }),
    );
  }

  /// Logs the standard `view_search_results` event.
  ///
  /// Log this event when the user has been presented with the results of a
  /// search.
  ///
  /// See: https://firebase.google.com/docs/reference/android/com/google/firebase/analytics/FirebaseAnalytics.Event.html#VIEW_SEARCH_RESULTS
  Future<Null> logViewSearchResults({
    @required String searchTerm,
  }) {
    return logEvent(
      name: 'view_search_results',
      parameters: filterOutNulls(<String, dynamic>{
        _SEARCH_TERM: searchTerm,
      }),
    );
  }
}

/// Android-specific analytics API.
class FirebaseAnalyticsAndroid {
  final MethodChannel _channel;

  @visibleForTesting
  const FirebaseAnalyticsAndroid.private(this._channel);

  /// Sets whether analytics collection is enabled for this app on this device.
  ///
  /// This setting is persisted across app sessions. By default it is enabled.
  Future<Null> setAnalyticsCollectionEnabled(bool enabled) async {
    if (enabled == null) {
      throw new ArgumentError.notNull('enabled');
    }

    await _channel.invokeMethod('setAnalyticsCollectionEnabled', enabled);
  }

  /// Sets the minimum engagement time required before starting a session.
  ///
  /// The default value is 10000 (10 seconds).
  Future<Null> setMinimumSessionDuration(int milliseconds) async {
    if (milliseconds == null) {
      throw new ArgumentError.notNull('milliseconds');
    }

    await _channel.invokeMethod('setMinimumSessionDuration', milliseconds);
  }

  /// Sets the duration of inactivity that terminates the current session.
  ///
  /// The default value is 1800000 (30 minutes).
  Future<Null> setSessionTimeoutDuration(int milliseconds) async {
    if (milliseconds == null) {
      throw new ArgumentError.notNull('milliseconds');
    }

    await _channel.invokeMethod('setSessionTimeoutDuration', milliseconds);
  }
}

/// Creates a new map containing all of the key/value pairs from [parameters]
/// except those whose value is `null`.
@visibleForTesting
Map<String, dynamic> filterOutNulls(Map<String, dynamic> parameters) {
  final Map<String, dynamic> filtered = <String, dynamic>{};
  parameters.forEach((String key, dynamic value) {
    if (value != null) {
      filtered[key] = value;
    }
  });
  return filtered;
}

@visibleForTesting
const String valueAndCurrencyMustBeTogetherError = 'If you supply the "value" '
    'parameter, you must also supply the "currency" parameter.';

void _requireValueAndCurrencyTogether(double value, String currency) {
  if (value != null && currency == null) {
    throw new ArgumentError(valueAndCurrencyMustBeTogetherError);
  }
}

/// Reserved event names that cannot be used.
///
/// See: https://firebase.google.com/docs/reference/android/com/google/firebase/analytics/FirebaseAnalytics.Event.html
const List<String> _reservedEventNames = const <String>[
  'app_clear_data',
  'app_uninstall',
  'app_update',
  'error',
  'first_open',
  'in_app_purchase',
  'notification_dismiss',
  'notification_foreground',
  'notification_open',
  'notification_receive',
  'os_update',
  'session_start',
  'user_engagement',
];

// The following constants are defined in:
//
// https://firebase.google.com/docs/reference/android/com/google/firebase/analytics/FirebaseAnalytics.Param.html

/// Game achievement ID.
const String _ACHIEVEMENT_ID = 'achievement_id';

/// `CAMPAIGN_DETAILS` click ID.
const String _ACLID = 'aclid';

/// `CAMPAIGN_DETAILS` name; used for keyword analysis to identify a specific
/// product promotion or strategic campaign.
const String _CAMPAIGN = 'campaign';

/// Character used in game.
const String _CHARACTER = 'character';

/// `CAMPAIGN_DETAILS` content; used for A/B testing and content-targeted ads to
/// differentiate ads or links that point to the same URL.
const String _CONTENT = 'content';

/// Type of content selected.
const String _CONTENT_TYPE = 'content_type';

/// Coupon code for a purchasable item.
const String _COUPON = 'coupon';

/// `CAMPAIGN_DETAILS` custom parameter.
const String _CP1 = 'cp1';

/// Purchase currency in 3 letter ISO_4217 format.
const String _CURRENCY = 'currency';

/// Flight or Travel destination.
const String _DESTINATION = 'destination';

/// The arrival date, check-out date, or rental end date for the item.
const String _END_DATE = 'end_date';

/// Flight number for travel events.
const String _FLIGHT_NUMBER = 'flight_number';

/// Group/clan/guild id.
const String _GROUP_ID = 'group_id';

/// Item category.
const String _ITEM_CATEGORY = 'item_category';

/// Item ID.
const String _ITEM_ID = 'item_id';

/// The Google Place ID that corresponds to the associated item.
const String _ITEM_LOCATION_ID = 'item_location_id';

/// Item name.
const String _ITEM_NAME = 'item_name';

/// Level in game (long).
const String _LEVEL = 'level';

/// Location.
const String _LOCATION = 'location';

/// `CAMPAIGN_DETAILS` medium; used to identify a medium such as email or
/// cost-per-click (cpc).
const String _MEDIUM = 'medium';

/// Number of nights staying at hotel (long).
const String _NUMBER_OF_NIGHTS = 'number_of_nights';

/// Number of passengers traveling (long).
const String _NUMBER_OF_PASSENGERS = 'number_of_passengers';

/// Number of rooms for travel events (long).
const String _NUMBER_OF_ROOMS = 'number_of_rooms';

/// Flight or Travel origin.
const String _ORIGIN = 'origin';

/// Purchase price (double).
const String _PRICE = 'price';

/// Purchase quantity (long).
const String _QUANTITY = 'quantity';

/// Score in game (long).
const String _SCORE = 'score';

/// The search string/keywords used.
const String _SEARCH_TERM = 'search_term';

/// Shipping cost (double).
const String _SHIPPING = 'shipping';

/// Signup method.
const String _SIGN_UP_METHOD = 'sign_up_method';

/// `CAMPAIGN_DETAILS` source; used to identify a search engine, newsletter, or
/// other source.
const String _SOURCE = 'source';

/// The departure date, check-in date, or rental start date for the item.
const String _START_DATE = 'start_date';

/// Tax amount (double).
const String _TAX = 'tax';

/// `CAMPAIGN_DETAILS` term; used with paid search to supply the keywords for
/// ads.
const String _TERM = 'term';

/// A single ID for a ecommerce group transaction.
const String _TRANSACTION_ID = 'transaction_id';

/// Travel class.
const String _TRAVEL_CLASS = 'travel_class';

/// A context-specific numeric value which is accumulated automatically for
/// each event type.
const String _VALUE = 'value';

/// Name of virtual currency type.
const String _VIRTUAL_CURRENCY_NAME = 'virtual_currency_name';