Ask HN: What's the hardest problem you've ever solved?

Creating a user customizeable webportal in ACT3 as my first real programming job. An undocumented template engine that grew into a full fledged programming language that compiled down to into a perl-dialect which inturn compiled down into native C. (ACT3 was used by just 2 companies APA and DPA)

Nearly every (but not all) instruction began and ended like HTML comments. It mixed HTML with code logic and code logic with HTML. Oh, I mean DHTML. Target plattforms: IE 5.5. & IE 6. and Netscape

No stack traces, no debugging tools other than alert().

In the end I had a whole meetingroom as my office as ever wall was full of print out sheets and hand written dependency & inheritance graphs. It was a procedural language, nearly functional but every function had mandatory side-effects (as it started as a template engine) with object oriented approaches sprinkeled in.

The project was a major success, but as the aspect of maintanance came up we switched to something sane: PHP 3 at that time.

These 9 months, it changed me & my brain.

Missing notifications for Android I was the lead for Flock Android, a team messaging app which competes with the likes of Slack. We started receiving some weird complaints from users about missing notifications. Now since it was a business messaging app, notifications were critical. We tried out everything to reproduce this issue, including bombarding devices with notifications, trying out different networks but we just could not reproduce the issue. Worse we had a couple of incidents with devices in our team but logs showed absolutely nothing. Google GCM said that the notification was sent but there was no trace of the notification in the app's logs, it was as the the OS was swallowing notifications. And somehow popular apps like whatsapp, facebook were immune to these issues. The final nail in the coffin was the CEO himself missing notifications on some occassions. Google was unhelpful as usual with their non existent dev customer support. We were able to find a bunch of support articles on the internet where other apps had essentially listed down steps to turn off battery optimizations and that seemed to work ( Interestly whatsapp, facebook are usually added by default in these lists). But there was no way to do it automatically and we could also do it in response to a support ticket, which is painful for users.

After a couple of days we were able to encounter a few missed notifications on a oneplus device which we had connected to a machine taking system logs. And voila we got a few lines of what was happening.

01-12 09:05:23.649 2719 2839 I ActivityManager: [BgDetect]chkExcessCpu level: 0 doKills: true auto_mode: false uptime: 183054

01-12 09:05:23.661 2719 2839 I ActivityManager: [BgDetect]detect excessive cpu on process to.talk(pid : 13406) level 0 usage 29

01-12 09:05:23.892 2719 2839 I ActivityManager: [BgDetect]force stop to.talk (uid 10151) level 0

01-12 09:05:23.893 2719 2839 I ActivityManager: Force stopping to.talk appid=10151 user=0: from pid 2719

01-12 09:05:23.893 2719 2839 I ActivityManager: Killing 13406:to.talk/u0a151 (adj 200): stop to.talk

Apparently some process called BgDetect figured out that our app was taking too much CPU and decided to kill it. Android being open source, we figured that we should be able to get source for it. But not only could we not find BgDetect in Android sources, it was non existent on oneplus sources too. We then got in touch with the marketing team and reached out to some contacts at oneplus, who directed us to their dev team. They asked for our apk and voila , in a week we were whitelisted along with the likes of Whatsapp and Facebook.

But the issue persisted on Xiaomi, Oppo and a bunch of chinese manufacturers and for those we still had to dish out steps to whitelist Flock in battery optimizations. We eventually figured out that moving from http to xmpp for android fcm notifications gave us delivery receipts for push notifications on device. On google phones and reputable manufacturers these delivery receipts also meant that app received the notification. On affected devices apparently the OS would give us a delivery receipt but not deliver it to the application. We built a double ack mechanism which also sent delivery receipts from the app. Based on the time difference between app delivery receipts and fcm delivery receipts we were able to figure out affected devices and send them directed bot messages to preemptively ask users to whitelist flock. You can read more about the double ack mechanism architechture here: https://hackernoon.com/notifications-in-android-are-horribly....

Google still refuses to even acknowledge the issue while problems like these are widespread: https://bit.ly/2QSzTKK

For our to-do app, Matterlist (https://matterlist.com), we went with the first approach: we represent a recurring task as a separate entity. Here's a quick explanation: https://matterlist.com/recurring.html

Matterlist's recurring task descriptors ("Schedule Items") essentialy define infinite sequences of recurring events, which are not represented in the database, but are visible and editable via the same UI, just as the regular, non-recurring tasks.

Here's how we deal with the problems you outlined:

1) When a user deletes a specific instance, we create an "exclusion" record for that day, so that the function that generates an endless sequence of recurrences doesn't generate one for that day.

2) When a user edits a specific instance of a recurring task, we also create an "exclusion" record for that day (because otherwise we would have two tasks on that day, the edited instance, now with a database record, and the virtual instance), and we create a database record for the edited instance, so it just becomes a regular task.

3) We don't have shared tasks yet, but that would be handled via the same framework, as outlined in 1 and 2 above. We'd just de-virtualize an instance and add/remove users to it.

Creating a database entry for each instance of a recurring task was unacceptable for us, because we wanted infinite forward visibility, and because when a user edits the parameters of a recurring task (e.g. changes it from daily to weekly), we'd have to delete all the old records and create the new records.

BTW, we have finally released an Android app, so you can see our recurring tasks in action: https://matterlist.com/#apps

I wrote a system that managed class assignments for a school.

Of course `Class` was a reserved constant and it most of a week before I settled on `TeachingGroup` as a feasible alternative.

You can't beat naming things for sheer hand-wringing difficulty.

That’s the thing. I miss being broken by a game. I miss that struggle. I’ve tried to experience it again but maybe nostalgia is superior. I’m hoping for pantheon to bring that feeling back. I genuinely miss being addicted to the struggle and joy Everquest was. It helped mold me into who I am today and I love it.