Make percentage input consistent

[s3cur3]

This makes the Percentage feature more consistent, such that the input is accepted as a value between 0 and 100. Previously the input was required to be a ratio (between 0 and 1), but it was then displayed as a percentage (effectively "#{ratio / 100}%"). With this change, the formatting of the input and later display match.

Before	After

Resolves tompave/fun_with_flags#188

[tompave]

Thank you for submitting the PR, and for describing the issue in tompave/fun_with_flags#188. As I said there, I closed that issue in order to avoid duplication. We can discuss this here in the PR.

[tompave]

I see where you're coming from but, to be honest, I think I prefer dealing with floats between 0 and 1, rather than having to manage percentages expressed the "humanized" way in the range 0...100.

Asking users to enter a 0..1 float was a deliberate choice because I find it simpler on two regards:

1. It's easier to reason about. I admit this is subjective, and I mainly have anecdotal evidence to support this, based on the observation that software developers are mostly used to think of percentages as floats in 0..1.
2. It's easier to maintain, because the flag and gate model represent these percentages as a 0..1 float. We might argue that it's a leaky abstraction, but at least it's one that removes complexity from the system. For example, in your code changes you are forced to divide the input by 100.

I admit that displaying "30%" in the UI might be confusing, but that's what the next bit of UI is for, the one that says: "raw value: 0.1234". The layout is ugly though, I admit that. 😆

So I think I'm going to reject this PR as it is now, sorry.

However, I welcome a PR that tidies up the UI to make it easier to understand, provided that the input accepts the same 0..1 values that does right now.

[s3cur3]

If you're set on keeping it as a ratio, can we change the text and input labels to say "ratio" or "fraction" instead of "percentage"? I think it's perfectly understandable as a ratio... the confusion comes from labeling what is actually a ratio as a percentage. Entering 0.42 in the input field is not a percentage of time or percentage of actors at all.

[tompave]

In hindsight, I'd agree that cramming all that info into the placeholder attribute of the form input was a poor choice: "e.g. 0.421337 for 42.1337%". That short example should be phrased better, and should be more readable.

But I stand by the idea that "percentage" is the right word there. I wouldn't change it to say "ratio" in the UI because the package API uses "percentage", and I wouldn't change the input to accept a 0..100 float because the Elixir API accepts 0..1 floats.

Another point to keep in mind is that the current wording hasn't been a problem so far; at least I've not heard anyone complain. That doesn't necessarily mean that things cannot be improved (they always can), but at the very least it means that I must consider consistency and predictability in both the API and the web UI.

Therefore, I'm still inclined to reject the PR, sorry.

[s3cur3]

Fair enough! We'll continue using our fork. 👍

[tompave]

Very well, at least I'm glad you're unblocked! 👍 Thanks for using the (main? 😆) package!

[s3cur3]

Thank you for all your work on FWF!