Tweetium suspend handling

SuspendHandlingExamples.js

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// Excerpt of Tweetium suspend handling code as an example 
// Note most of this code is from several years ago,  
// thus light on modern ES6+ usage and uses WinJS promises and such.

// In my default.js, using WinJS's Application object (optional),
// it wraps the system suspend event and calls it "oncheckpoint"
var app = WinJS.Application;
app.oncheckpoint = function (args) {
    try {
        var localSettings = Settings.getLocalSettings();
        localSettings.insert("LastSuspendTime", Date.now());
        // This lets the current page that the window is navigated to do its own handling
        // Tweetium really only has one "page" though...
        if (AppInstance.currentPage && AppInstance.currentPage.onSuspend) {
            AppInstance.currentPage.onSuspend();
        }
        var tweetMarkerPromise = Settings.isTweetMarkerEnabled() ? 
                                    TweetMarker.uploadLastReadMarkersForInvalidatedScopes() : WinJS.Promise.as(null);
        var stopMonitoringPromise = TweetRT.SyncEngine.StopMonitoring();
        
        // I found that Phone is less forgiving about the time you can take to suspend,
        // so use a more aggressive timeout there
        var timeout = Globals.isPhoneHost ? 1500 : 3000;
        var suspendPromises = WinJS.Promise.join([tweetMarkerPromise, stopMonitoringPromise]);
        
        var promise = WinJS.Promise.timeout(timeout).then(function ()
        {
            localSettings.insert("LastSuccessfulSuspendTime", Date.now());
        },
        function (error) {
            debugger;
            // We really don't want to return an error here, even canceled!
        });

        window.CollectGarbage();
        args.setPromise(promise);
    }
    catch (ex) {
        debugger;
    }
};

// In the main page class
class MainPage
{    
    onSuspend() {
        if (this.resumeTimeout) {
            clearTimeout(this.resumeTimeout);
            this.resumeTimeout = null;
        }

        this.lastHiddenTime = Date.now();
        var localSettings = Settings.getLocalSettings();
        var scopeDetails = {
            accountId: TwitterAPI.getCurrentUserId(),
            scopeName: this.currentScope,
        };

        if (!this.loading) {
            this._saveViewState();
        }
        localSettings.insert("LastScope", JSON.stringify(scopeDetails));
        localSettings.insert("LastViewState", JSON.stringify(nav.state));

        this.pivotScroller.style.visibility = "hidden";

        if (Globals.isPhoneHost) {
            // Need to kill inertia or weirdness can happen on phone.
            this.pivotScroller.style.overflow = "hidden";
            this.scrollViewer.style.overflow = "hidden";
        }

        if (this.loading) {
            this.wasLoadingLastSuspend = true;
        }

        // If we're still navigating to the current view, cancel that
        if (this.loadPromise) {
            this.loadPromise.cancel();
        }

        // If we were loading more tweets because the user scrolled
        // close to the bottom, cancel that
        if (this.loadMorePromise) {
            this.loadMorePromise.cancel();
            this.loadMorePromise = null;
        }

        // Kill timer used to batch tweets sent from the worker thread
        if (this._pendingTweetsInterval) {
            clearInterval(this._pendingTweetsInterval);
            this._pendingTweetsInterval = null;
        }

        // Free up some memory by dropping UI elements and cached tweets other than
        // those for the current view and near the current scroll position
        this._compactLists();
        this.loading = false;
    }

    onVisibilityChange () {
        Debug.log("HomePage onVisibilityChange: " + (document.hidden ? "hidden" : "visible"));
        if (document.hidden) {
            this.lastHiddenTime = Date.now();
        }
        else if (!this.firstLoad) {
            this.pivotScroller.style.visibility = "";
            this.lastVisibleNotificationTime = Date.now();
            this.timelineControl.updateAgeIndicators();
            // Make extra sure we know the correct connectivity state.
            if (!Utils.isInternetConnectivityAvailable()) {
                if (this.networkAvailable) {
                    this.onNetworkStatusChanged();
                }
            }
            else {
                this.networkAvailable = true;
            }
        }
    }
}

// Over in worker thread
const cachedScopeDataMaxAge = 5 * 60 * 1000; // 5 minutes
class TweetMonitor {
    stopMonitoring() {
        Debug.log("stopMonitoring called");
        this._isMonitoring = false;

        // Cancel requests for all scopes (e.g. Timeline, Connect, lists, etc)
        var promisesToCancel = [];
        var dataByScope = this._dataByScope;
        Object.keys(dataByScope).forEach(function (scopeName) {
            var scopeData = dataByScope[scopeName];
            if (scopeData.pendingRequestPromise) {
                promisesToCancel.push(scopeData.pendingRequestPromise);
                scopeData.pendingRequestPromise = null;
            }
        });

        // Clears per-scope state
        this._initScopeData();
        var promise = WinJS.Promise.as(null);
        if (this._currentStreamPromise) {
            Debug.log("stopMonitoring canceling stream promise");
            var streamPromise = this._currentStreamPromise;
            this._currentStreamPromise = null;
            var cancelPromise = streamPromise.then(function () { return null; },
                function (error) { return null; });
            var timeoutPromise = WinJS.Promise.timeout(600).then(function () { return null; },
                function (error) { return null; }); // Give <1 second to cancel, don't return errors. Using _currentStreamPromise here is unreliable.
            promise = WinJS.Promise.any([cancelPromise, timeoutPromise]);
            streamPromise.cancel();
        }

        promisesToCancel.forEach(function (promiseToCancel) {
            promiseToCancel.cancel();
        });

        return promise;
    }

    compactLists(options) {
        if (!options) { debugger; }
        for (var scopeName in this._dataByScope) {
            var scopeData = this._dataByScope[scopeName];
            if (!scopeData.noCompaction) {
                var isCurrentScope = (scopeName == options.currentScope);
                // Revisit this...
                // Don't clear recently sync'd data to help the back button to be able to restore position quickly and easily.
                var scopeCacheExpired = (scopeData.lastRequestTime && ((Date.now() - scopeData.lastRequestTime) > cachedScopeDataMaxAge));
                var isOtherScopeAndExpired = !isCurrentScope && scopeCacheExpired && !scopeData.builtin;
                if (isCurrentScope) {
                    var countToKeep = 50;
                    if (options.preserveToTweetId) {
                        for (var i = 0; i < scopeData.tweets.length; i++) {
                            if (scopeData.tweets[i].id == options.preserveToTweetId) {
                                countToKeep = i;
                                break;
                            }
                        }
                    }

                    if (scopeData.tweets.length > countToKeep) {
                        var removed = scopeData.tweets.slice(countToKeep);
                        if (removed.length > 0) {
                            scopeData.endReached = false;
                            removed.forEach(function (removedTweet) {
                                delete scopeData.tweetIds[removedTweet.id];
                            });
                        }
                        scopeData.tweets = scopeData.tweets.slice(0, countToKeep);
                    }
                }
                else if (isOtherScopeAndExpired) {
                    // Non-builtin scopes get purged (unless we're looking at it)
                    this._resetScopeData(scopeData);
                }
            }
        }

        self.CollectGarbage();
    }
}