## January 17, 2021 — Adding support for comments, mathjax, emojis and syntax highlighting

I wanted to include commentars and Mathjax support in my posts.

1. There is various ways to include commentars in a static website hosted on GitHub. One way is to use an external web application and database like Disqus and an other way is to use an external script Staticman, which simulates the dynamic behaviour by processing and pushing user input to GitHub automatically.

Nevertheless, there is also Utterances which works on a similar principle as Staticman, but instead of storing comments in new files in the repository, it creates an Issue in the native GitHub discussion system and puts the commentaries there! This is seemingly the best solution, and hence I decided to use Utterances. Staticman might be useful in the future when I need, e.g., input forms.

2. A disadvange of the GitHub’s issues and comments system is that it does not support Mathjax. In order to insert formulas in the comments, internet people (:= people on the internet) recommend to use
<img src="https://latex.codecogs.com/svg.latex?f(x)=\pi^2+x+\sum_{i=1}^ka_i"/>


which renders the formula $$f(x)=\pi^2+x+\sum_{i=1}^ka_i$$ as an image on the fly. If your formula contains a space or some special characters, please, test the URL before posting your comment. For instance, the white space can be written as %20 in the URL.

3. Github comments support a ton of emoji’s, which are listed for instance here. Emojis can be also inserted in my posts. The recommended plugin jemoji, which uses GitHub’s emojis, is mentioned in the documentation. The corresponding gem is installed on the local machine via Bundler by adding gem "jemoji" in Gemfile and running bundler.ruby2.5 install in the project directory. In order to tell jekyll to use it, one has to add jemoji to the list of plugins in _config.yml. Writing

:blush: :bowtie: :hankey: :+1:


in Markdown produces , , , . Unfortunately, it seems like that there is not the :vomiting_face: emoji, which can be used normally in the comments.

4. I wanted to modify the default layout for a post so that comments and mathjax can be turned on and off liquidly by setting the variables comments and mathjax in the YAML front matter of a post (the header between --- ... ---). Internet people claim that it can not be done easily and one has to copy the default layouts of the jekyll theme in use to the project folder and modify those.
I use the mimina theme, which is installed as a gem. I ran bundler.ruby2.5 info minima to get the path to the gem, which is /usr/lib64/ruby/gems/2.5.0/gems/minima-2.5.1 in my case. I displayed the directory structure using the tree command and had a look at what is in _includes (HTML snippets to be included), _layouts (page layouts) and _sass (some CSS related things). Because I wanted to modify the layout for posts, I copied _layouts/post.html to the project directory. I then created the files _includes/mathjax-support.html and _includes/comments-utterances.html with the following content in the project directory.

File _includes/mathjax-support.html:

<!-- for mathjax support -->
<script type="text/x-mathjax-config">
MathJax.Hub.Config({
TeX: { equationNumbers: { autoNumber: "AMS" } }
});
</script>
<script type="text/javascript" async src="https://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML">
</script>


File _includes/comments-utterances:

<!-- for comment section -->
<script src="https://utteranc.es/client.js"
repo="p135246/p135246.github.io"
issue-term="title"
label="comment"
theme="preferred-color-scheme"
crossorigin="anonymous"
async>
</script>


These snippets can be found in the documentation of Mathjax and of Utterances, respectively.

Finally, I modified _layouts/post.html by including

{%- if page.mathjax -%}
{%- include mathjax-support.html -%}
{%- endif -%}


{%- if page.comments -%}
{%- endif -%}


at the end of the article tag, which is where I want the comments to be displayed. Note that I quote the liquid syntax by enclosing it in the raw and endraw liquid commands.

In _config.yml, I put the following

markdown: kramdown
math_engine: mathjax
input: GFM
highlighter: rouge


The first option tells jekyll which Markdown interpreter to use and the second enables mathjax. The third option tells to use GitHub flavored Markdown and the fourth to use the syntax highlighter rogue. See the official documentation of GitHub Pages about jekyll here.

Now, Mathjax support and the comment section, which appears on the bottom of the page, can be turned on and off in the header as in the example of this post:

---
layout: post
title:  "Notes about maintaing this website (constantly updated)"
date:   2020-02-02 15:36:00 -0000
categories: changelog
mathjax: true
---

5. A note on Mathjax. Formulas are enclosed in $$...$$ and whether they are inline, like $$\sqrt{45\pi}$$, or displayed, like

\begin{aligned} a_1 &= 16\pi e^2, \\ a_2 &= 5.3534, \\ a_3 &= \ldots, \end{aligned} \qquad A = \begin{pmatrix} 4 & 8 & 5 \\ 2 & 1 & 0 \\ 3 & 9 & 6 \end{pmatrix},

is decided by the markdown indentation.

6. In order to enable syntax highlighting, one has to add rogue to _config.yml as above. The following construction, where md can be replaced by html, ruby, … highlihts the code:
md
Some markdown **code** here.



Note that in order to render this code block with three ticks, I had to enclose it in four ticks, and so on (the following was enclosed in five ticks):

md

Some markdown **code** here.




Internet people say that in order to highliht inline code, the following construction has to be used

x = 4{:.ruby}


However, it produces x = 4, which does not seem to work on my local machine.

## January 15, 2021 — Upload of a CV

After a year of not doing anything on the website, I decided to upload my CV. Unfortunately, it was not that straightforward and I had to recall some knowledge of Jekyll, Ruby, OpenSuse and Markdown. I also had to think about the whole concept to confirm my choices from a year ago.

1. There are two mainstream static website generators: Jekyll and Hugo. An advantage of Jekyll over Hugo is supposedly its bigger extensibility by plugins and a disadvantage the necessity to have a working installation of Ruby.

I decided to use Jekyll.

2. My system is openSUSE Leap 15.2, which I obtain by running cat /usr/lib/os-release.

The interpreter (or compiler) of Ruby was probably installed a long time ago by running sudo zypper in ruby. It provides the command ruby, and running ruby -v gives ruby 2.5.8p224. The package (or gem in Ruby terms) manager RubyGem is probably packed in one *.rpm together with Ruby or is installed automatically as a dependency (?). It provides the command gem, and running gem -v gives 3.1.2.

Bundler, the “consistent environment for Ruby projects by tracking and installing the exact gems and versions that are needed”, is installed by running sudo gem install bundler. Using Bundler, one can specify the required gems and versions in the file Gemfile in the project directory and Bundler automatically takes care of their download and configuration. For some reason, the correct bundler executable on my system is /usr/bin/bundle.ruby2.5 and not /usr/bin/bundle. The latter also exists on my system, but running it gives a RubyGem version error (?). This is probably related to an automatic zypper update to a new version of Ruby during the last year and an effort of the system to keep both the new and old version (?). Running bundler.ruby2.5 -v gives Bundler version 2.2.5.

Information about the current Ruby and RubyGem installation can be displayed by running gem environment. It shows that the gems are installed to /usr/lib64/ruby/gems/2.5.0/. Some people on the internet suggest that it is better to install gems in a hidden folder in ~ (the “user installation directory” in gem environment). However, because the zypper installation is configured to put gems in /usr/... by default, and I do not want to fiddle with that, I decided to install everything globally using sudo. Some people propose to remove the zypper installation of Ruby and install everything locally using RVM. However, running sudo zypper rm ruby on my system would lead to removal of many, seemingly important, packages (?), which I don’t want. Therefore, I will stick to the global installation as root.

Jekyll was installed by running sudo gem install jekyll. Running bundler.ruby2.5 exec jekyll -v gives jekyll 3.8.5. The correct executable is again jekyll.ruby2.5 and not jekyll, but it is suggested to run jekyll via bundler.ruby2.5 exec jekyll anyway. It is namely the purpose of Bundler to create a neat environment for Ruby programs.

3. In order to convert the project to a website, run bundler.ruby2.5 exec jekyll build in the project directory. This produces a static website consisting of HTML, CSS and possibly JavaScript (?) in the directory _site/. The website can be tested on the local machine by running bundler.ruby2.5 exec jekyll serve and then opening http://localhost:4000/ in a web browser, in my case Google Chrome.

4. I encountered a problem when adding the static file academic-cv.pdf to the website. I created a directory assets/pdf/ in the project folder and copied academic-cv.pdf to it. I referred to it by defining [CV]:https://p135246.github.io/assets/pdf/academic-cv.pdf and writing [Academic CV][CV] in about.markdown. However, the link was not working either locally or on GitHub because bundler.ruby2.5 exec jekyll build did not copy assets/pdf/academic-cv.pdf to _site/. The solution was to add the following to _config.yml:
include:
- assets/


Also note that I first created academic-cv.pdf as a symlink, but it was not copied to _site/ and was not working on GitHub Pages even after modifying _config.yml as above. This is strange because Git should replace symlinks by copies of the actual files in a commit, and hence it should have worked at least on GitHub Pages (?).

5. After making my changes to the project, I ran the standard triple git add *, git commit -m "message" and git push master origin to push the changes to GitHub. As soon as the commit arrives to GitHub, it should be automatically processed by the engine of GitHub Pages and within seconds published on the given URL, provided that it is properly configured in GitHub/Settings. If this process takes too long, there is probably an error while running jekyll on the server side, and an error message appears in GitHub/Settings. Before modifying _config.yml, I was getting an error which said that the link to academic-cv.pdf was not working. After that, I was getting another error which sad that I was trying to publish sensitive data. This was solved by removing Gemfile.lock, which seems to contain informations about versions of gems on the machine, from the commit. Before I discovered and corrected these issues, GitHub Pages had been silently refusing to publish the website and it took me a while to find out that there were error messages in GitHub/Settings. I discovered much later that GitHub was sending build errors and error messages via email!

6. I should be using the folder _drafts/ which contains posts under construction which are not incorporated by Jekyll in the final website. Weirdly, this directory seems not to be included in a git commit even if it is not in .gitignore (?). However, I put it in .gitignore just to be sure that the drafts do not leak to public. The files in _drafts/ have names in the form name.markdown, i.e., not yyyy-mm-dd-name.markdown as the files in drafts.

## February 2, 2020 — Website created!

My first post after setting up the website using jekyll (see jekyll-docs).