Development update – October 29, 2021

What we’ve done

In the past 6 months

This month

Core Data

I rewrote the app data store to use Core Data the right way. We were using some custom setup, like a local API, but this meant a lot of boilerplate code and a very bad integration with UIKit and SwiftUI. This was mainly done thanks to Donny Wals very complete book “Practical Core Data”. It’s a real goldmine, I learned the key Core Data concepts I was missing, it’s the click I needed.

Search parser

In the version presented on this website, we show a working search bar. The problem with it is that the code backing it was very ugly, and not reusable at all. Also, it was prone to performance issues as the app would grow, which will soon be fixed with the use of Core Data.

To fix those issues, I wrote a reusable search parser ( It uses parser combinators and a Parsing Expression Grammar (PEG) to make the code more performant, more robust and good-looking (really, I’m surprised how readable it is).

I wrote tests, described the grammar for users and setup workflows to ensure the parser works correctly on both Linux and macOS. Making it cross-platform was necessary, because I will use the same parser in the API that will serve all other platforms.

Website fixes

As you had probably noticed browsing this website, there were a few (enormous) bugs which occurred from time to time. I fixed them all, yay 🎉

  1. For some reason, clicking a link to a cached page (even with HTTPS link) would switch to an unsecure version of the website (HTTP). I don’t really know why this happened, but I added a trailing slash (/) to menu links and it fixed the issue 🤷🏻‍♂️
  2. The most problematic issue was that if you opened a cached page, it would load without the CSS style sheet 🤭 Surprise, this was also a cache problem 🤪 I had put an integrity field to the HTML tag loading the CSS file. Unfortunately, when the file was cached, it would resolve as a -1 size file, and the integrity check would fail. For security reasons, the browser would not load the cached file. I just removed it.
  3. The third one was quite weird too. Because of it, the website font (Nunito) would not load. I had seen the problem months ago, but I had no idea where it came from. I thought about different things:
    1. Font URL changed: The font is not stored locally in the website’s files, it’s loaded from a website. If this URL changed for some reason, which is not supposed to happen, it would break the link. Obviously, this was not the reason.
    2. CORS: Because of CORS, the server delivering the font could block my website from accessing this font. As the font comes from Google Fonts, it’s not subject to CORS restrictions. Another dead end.
    3. Quotas / subscriptions: When I chose the font, it was free. However, things could have changed, and after a quick check, it did not. That’s good because I can keep it, but bad because I had to dig deeper.
    4. PostCSS bug: Next I thought “maybe I used a wrong PostCSS tag to load the font”, but @import url(); is a regular CSS tag… which means it should be read correctly.
    5. No more idea, let’s try things: The problem only happened in the production website, not locally on my computer (i.e. when developing). I opened this website and inspected the CSS style sheet. To my surprise, there was a Tailwind warning written in plain text (not a comment) on the first line which is… the line that imports the font! Hurray, I have something 🎉
    6. When I improved this website a few months ago, I switched from Bootstrap to Tailwind. Now I knew the bug came from here. The warning said “warn - As of Tailwind CSS v2.2, `lightBlue` has been renamed to `sky`. warn - Please update your color palette to eliminate this warning.". I checked my code, and lightBlue was never used 🤔 I tried manually upgrading Tailwind from v2.1 to v2.2, but this did nothing. I still didn’t have the problem locally, and it stayed in production.
    7. I figured out the problematic line was …colors. It imported all of Tailwind’s colors, no matter if I used it or not. I chose to do this to keep all colors available, not just my custom colors, but for Tailwind this meant I was using it. What solved my problem is camiant’s comment in an issue on Tailwind’s repository. I added the temporary fix until Tailwind removes the color from its default palette and it solved the issue.
    8. Who would have thought the missing font came from a Tailwind warning in my CSS file, due to something I wasn’t using, put on the first line due to minification, and which would prevent browsers from reading the @import statement? 🤯
  4. While fixing those 3 issues, I realized I could improve something else: the color of the browser’s bar and page background (see Meta Theme Color and Trickery on to avoid white straps at the top of the page (and bottom when scrolling). I used the same color as the header and footer so now it should look gorgeous 🙂

What we’re doing

Switching back to UIKit

You may already know I spent hundreds of hours (yeah… this much) rewriting the Monki Map using different architectures to find the right fit. Well, after a long talk during a training session with traceurs from Nantes, I realized the version I was working on for nearly a year didn’t have the features it had in July 2020, and this was the most important.

It really clicked me that the most important is having a working app, something everyone can touch and feel. That’s why I made the hard choice to revert the app as it was back then. That’s the magic of git, a tool developers use everyday for its versioning capabilities.

This time, I didn’t start again from scratch, I just took the working year-old app to progressively include the new things I’ve been working on since then. If you’re familiar with iOS development, I switched back to a UIKit-based app, while I was working on a SwiftUI-focused one for almost a year.

I’m progressively transforming what was complex code from a year ago to new code using Core Data correctly and using more reusable structures (like the search parser).

Where we are

Well, it’s always hard to say, but to give you a very simple TODO list, here’s what’s done and remaining: