## Saturday, November 9, 2013

### ChuckNorris is a Color

I just came across a fun question asking why does HTML think 'chucknorris' is a color on StackOverflow. This is called "Flex Hex" and is described in detail in a little rant about Microsoft Internet Explorer's color parsing.

It turns out these are all valid colors:

 chucknorris sick crap

I thought it would be fun to support parsing colors in this (arguably broken) format in Factor. The algorithm basically breaks down into three parts:

1. Convert non-hexadecimal digits to zero.

```: hex-only ( str -- str' )
[ dup hex-digit? [ drop CHAR: 0 ] unless ] map ;```
2. Group into three equal groups, padding on the right with zero if necessary.

```: pad-length ( str -- n )
length dup 3 mod [ 3 swap - + ] unless-zero ;

: three-groups ( str -- array )
dup pad-length [ CHAR: 0 pad-tail ] [ 3 / group ] bi ;```
3. Convert each segment into a two-digit hexadecimal value, shortening each segment first to eight chars from the right, padding on the left if only one character.

```: hex-rgb ( array -- array' )
[
8 short tail*
] map ;```

Putting that together, we have this word to parse "flex hex" colors (removing hash-marks from the left if present):

```: flex-hex ( str -- hex )
"#" ?head drop hex-only three-groups hex-rgb "" join ;```

And, of course, some tests to verify that we handle lots of different cases:

```{ "00b000" } [ "#zqbttv" flex-hex ] unit-test

{ "0f0000" } [ "f" flex-hex ] unit-test
{ "000f00" } [ "0f" flex-hex ] unit-test
{ "000f00" } [ "0f0" flex-hex ] unit-test
{ "0f0f00" } [ "0f0f" flex-hex ] unit-test
{ "0ff000" } [ "0f0f0f0" flex-hex ] unit-test