WIP: Add file backend

[matthiasbeyer]

Closes #574

Something along those lines?

I am not sure whether the feature works, it just compiles for now and I didn't test it. Lets see what you think! 😄

[AmmarAbouZor]

Very thanks for the suggestion and the implementation. I had a short look and it's looking really good already 👍

I'll try to get it to it with more detailed review once I've got some free time, but for now I just wanted to tell you that this is looking really good and you can continue working on it for sure 🙏

Quick Note: I would consider adding some integration tests for the backend where we create a temp file and create the file and test all the API calls for them (Something similar to the current tests for the other backends).

Hopefully, I'll get back with more detailed review in the next couple days

[matthiasbeyer]

Take your time! I am doing this in my free time as well and I am not sure how fast I can continue on this. We will see! 😉

[matthiasbeyer]

Just to note this: I do not want to keep the one-json-file-per-entry scheme, but want to transition to something like the following format:

+++
<TOML Header>
+++

<Text content>

So that files are also trivially editable with $EDITOR.

[AmmarAbouZor]

Just to note this: I do not want to keep the one-json-file-per-entry scheme, but want to transition to something like the following format

Sure you can experiment with different formats. Here are my initial thoughts about that:

• Using a well tested serialization is a safe and easy choice. The project has already dependencies for json and toml serde.
• TOML format seems a good fit but we may need to test it with journals with multiple break lines and special characters.
• You can still for sure introduce a new format, but in this case we would need to invest some time to ensure that this is working in all edge cases

[matthiasbeyer]

No need to review at this time. I continued, but did not finish anything, just pushing as a backup 😉

[matthiasbeyer]

I did not forget this, but I am very busy atm, so I don't know when I can continue. If someone wants to pick up where I left off, I am of course not offended! 😉 👍

[AmmarAbouZor]

No problem, let's keep this PR open until you have time again or if someone else is willing to pick it up.
Thanks again for the idea and the initial implementation