正则表达式将包含字符串的缩写转换为标题案例

Question

As part of a simple URL cleaning/slugging function I'm extending, I need to make conversions such as the following:

Original               Converted
---------------------------------------------
USAMarch               UsaMarch
FETExaminations        FetExaminations      *
AnotherABBRString      AnotherAbbrString
LastONE                LastOne

(These are just examples, except for the second, which is what got me to doing this in the first place.)

I'm assuming I need to use preg_replace_callback to determine the position of any abbreviations and case them appropriately.

I haven't the foggiest of where to begin. Does anyone know what I can do to get this right?

Update

Okay, I have this so far:

$input = preg_replace_callback("~([A-Z])([A-Z]+)([^a-z])([a-z]|)~",
function ($captures) {
   return $captures[1].strtolower($captures[2]).$captures[3].$captures[4];
},
$input);

Unfortunately, however, it doesn't work with strings where the abbreviation is last:

This                   Becomes
---------------------------------------------
LastONE                LastOnE

So I'm checking the end incorrectly, I assume. Also, this attempt isn't recursive. How would I do that?

Answer 1

These work with your examples.

Even finds stand alone caps.

 # Find:  '/([A-Z])([A-Z]+)(?=[A-Z]|\b)/'
 # Replace:  $1 . tolower($2)

 ( [A-Z] )                     # (1), Upper case
 ( [A-Z]+ )                    # (2), 1 or more upper case
 (?=                           # Lookahead assertion
      [A-Z]                         # Upper case
   |                              # or,
      \b                            # Word boundry
 )

Or, requires a lower case before possible end caps

 # Find:  '/([a-z])?([A-Z])([A-Z]+)(?=[A-Z]|(?(1)\b|(?!)))/'
 # Replace:  $1$2 . tolower($3)

 ( [a-z] )?                    # (1), optional lower case
 ( [A-Z] )                     # (2), Upper case
 ( [A-Z]+ )                    # (3), 1 or more upper case
 (?=                           # Lookahead assertion
      [A-Z]                         # Upper case
   |                              # or
      (?(1)                         # Conditional, does lower case precede this ?
           \b                            # yes, match boundry
        |  (?!)                          # or fail, this is a stand alone cap's
      )
 )