Added feature isHSL

[ayala-io]

As suggested in #1156, I made an isHSL validator. It accepts padded zeroes and white spaces. I basically tried playing around with https://www.w3schools.com/colors/tryit.asp?filename=trycolors_hsl and checked what worked and what didn't work.

Summary of changes:

• src/lib/isHSL.js: Source of validator
• src/index.js: Modified to recognize newly created isHSL
• test/validators.js: Added test cases for isHSL
• README.md: Added short description of isHSL

[ezkemboi]

@kurisu-gh, I will review this PR.
Also, try run tests and push the changes.

[ghost]

Should values greater than 360 and lesser than 0 be invalid as the first parameter (hue)? Since it's a circle, you just have to account turns in order to get the right value. If you try this out in chrome devtools you'll see that the browser handles turns in the circle.

[ayala-io]

Should values greater than 360 and lesser than 0 be invalid as the first parameter (hue)? Since it's a circle, you just have to account turns in order to get the right value. If you try this out in chrome devtools you'll see that the browser handles turns in the circle.

You're right. I confirmed this myself in https://www.w3schools.com/colors/tryit.asp?filename=trycolors_hsl

I just pushed some modifications to this PR that allows hue values larger than 360 and less than 0. +/- signs are also validated. I added some more test cases considering that modulo 360 is possible.

[profnandaa]

LGTM, thanks for the PR 🎉

[profnandaa]

@ezkemboi -- please have a look at this again.

[ezkemboi]

Alright, checking @profnandaa

[ezkemboi]

I left my feedback here @kurisu-gh, @GuiSchafer, and @profnandaa.

[profnandaa]

@kurisu-gh -- ping!

[ayala-io]

Sorry for the delay! Was bogged down with work.

I've pushed some updates and synced with upstream. This PR now handles the test cases that @ezkemboi brought up. But upon further reviewing of the MDM documentation, validating HSL is a bit more involved than I thought. To summarize:

• HSL actually supports the alpha parameter (optionally) previously mentioned in Added feature isHSL #1159 (comment) and I see there is now a feature request Add isHSLA() #1245. As of CSS Colors Level 4, hsla() is merely an alias to hsl(). If you use hsla() without the alpha parameter, it would still work fine due to hsl() alias. In other words, isHSL() needs to validate the optional 4th parameter. In this PR, I added the 4th parameter check. I think we no longer need an isHSLA() validator because hsla() is really hsl() or we can have isHSLA() as alias to isHSL().
• There is a comma-separated and a space-separated way to express hsl(). Comma-separated is straight forward, but space-separated adds the 4th parameter (alpha) with a / delimiter. Space-separated can actually have no spaces at all like: hsl(200grad+.1%62%/1) . It gets complicated when taking into account that the optional +/- is like a space separator. My PR doesn't fully capture all the cases.
• Percentage values and alpha values [0,1] (or percentage) can be actually be set to values beyond their normal bounds. They will just saturate to 0% (0.0) or 100% (1.0) in practice. This PR now allows values beyond the normal bounds.
• My regex patterns are a bit brute force right now. It would be nicer to break them down into reusable pieces. Many parts of my patterns are repeated. For example, checking for a CSS <number> which has an optional +/-, an integer followed by an optional scientific notation portion; or it can be a (+/- optional) float with optional leading 0's before the decimal, followed by an optional scientific notion portion. I think there are definitely smarter, more modular ways to express the patterns here.
• More test cases should be considered.

So in short, the PR handles the additional checks requested by @ezkemboi as well as the optional alpha parameter. More work is needed to handle space-separated validation. I can continue development of this feature but it will be slow. If anyone wants to take over development of this, feel free. Also open to suggestions on simplifying my regex patterns.

[profnandaa]

@ezkemboi -- ping ^

[ezkemboi]

This is good @profnandaa. @kurisu-gh has done even extra research and work which is amazing.
Good work @kurisu-gh and thanks once again.

[ayala-io]

Thank you for reviewing @ezkemboi and @profnandaa. Let me just update the readme in a little bit to note that an optional alpha parameter is also supported.

[ayala-io]

@ezkemboi @profnandaa, updated the README.md appropriately and synced up the PR as well. Thank you for the efforts!