From 950a12a0f99f0fa12e0e9041174e494bbd4c8dca Mon Sep 17 00:00:00 2001
From: Ingo Karkat <swdev@ingo-karkat.de>
Date: Thu, 25 May 2017 00:00:00 +0200
Subject: [PATCH]

---
 autoload/ingo/str/restricted.vim | 78 +++++++++++++++++++++++++++++++-
 1 file changed, 77 insertions(+), 1 deletion(-)

diff --git a/autoload/ingo/str/restricted.vim b/autoload/ingo/str/restricted.vim
index 6fcac57..9f94015 100644
--- a/autoload/ingo/str/restricted.vim
+++ b/autoload/ingo/str/restricted.vim
@@ -3,7 +3,7 @@
 " DEPENDENCIES:
 "   - ingo/compat.vim autoload script
 "
-" Copyright: (C) 2014 Ingo Karkat
+" Copyright: (C) 2014-2017 Ingo Karkat
 "   The VIM LICENSE applies to this script; see ':help copyright'.
 "
 " Maintainer:	Ingo Karkat <ingo@karkat.de>
@@ -35,4 +35,80 @@ function! ingo#str#restricted#ToShortCharacterwise( expr, ... )
     return (a:expr =~# '\n' || ingo#compat#strchars(a:expr) > l:maxCharacterNum ? l:default : a:expr)
 endfunction
 
+function! ingo#str#restricted#ToSafeIdentifier( expr, ...)
+"******************************************************************************
+"* PURPOSE:
+"   Restrict an arbitrary string a:expr to a short one that can be safely used
+"   in filenames, URLs, etc. without having to worry about quoting or escaping
+"   of special characters.
+"* ASSUMPTIONS / PRECONDITIONS:
+"   None.
+"* EFFECTS / POSTCONDITIONS:
+"   None.
+"* INPUTS:
+"   a:expr  Source text, or List of strings.
+"   a:options.replacementForSpecialCharacters	Replacement character; default "-".
+"   a:options.removeFrom    Which position has the lowest priority in case the
+"			    result is still too long, and is dropped. One of
+"			    "l", "m", "r"; default is "m", dropping from the
+"			    middle.
+"   a:options.maxCharacterNum   Maximum width. Defaults to 'textwidth' / 80
+"				screen cells.
+"* RETURN VALUES:
+"   Non-alphanumeric characters are replaced by
+"   a:options.replacementForSpecialCharacters (two between different List items); those
+"   at the front and end are dropped. If the text exceeds a:maxCharacterNum,
+"   List elements / alphanumeric sequences from the middle are dropped until it
+"   fits.
+"******************************************************************************
+    let l:options = (a:0 ? a:1 : {})
+    let l:repl = get(l:options, 'replacementForSpecialCharacters', '-')
+    let l:removeFrom = get(l:options, 'removeFrom', 'm')
+    let l:maxCharacterNum = get(l:options, 'maxCharacterNum', &textwidth > 0 ? &textwidth : 80)
+
+    if type(a:expr) == type([])
+	let l:source = map(a:expr, 'l:repl . join(split(v:val, "[^[:alnum:]]\\+"), l:repl) . l:repl')
+    else
+	let l:source = split(a:expr, "[^[:alnum:]]\\+")
+    endif
+
+    while ingo#compat#strchars(s:Render(l:source, l:repl)) > l:maxCharacterNum
+	if l:removeFrom ==# 'm' && len(l:source) == 2
+	    " Special case: take the larger one that still fits.
+	    let l:len0 = ingo#compat#strchars(s:Render([l:source[0]], l:repl))
+	    let l:len1 = ingo#compat#strchars(s:Render([l:source[1]], l:repl))
+
+	    if l:len0 >= l:len1 && l:len0 <= l:maxCharacterNum
+		let l:source = [l:source[0]]
+	    elseif l:len1 >= l:len0 && l:len1 <= l:maxCharacterNum
+		let l:source = [l:source[1]]
+	    else
+		let l:source = [l:source[(l:len0 > l:len1 ? 1 : 0)]]
+	    endif
+	elseif len(l:source) > 1
+	    if l:removeFrom ==# 'm'
+		let l:dropIdx = len(l:source) / 2
+	    elseif l:removeFrom ==# 'l'
+		let l:dropIdx = 0
+	    elseif l:removeFrom ==# 'r'
+		let l:dropIdx = -1
+	    else
+		throw 'ASSERT: Invalid a:options.removeFrom: ' . string(l:removeFrom)
+	    endif
+	    call remove(l:source, l:dropIdx)
+	elseif stridx(l:source[0], l:repl) != -1
+	    " The part can be broken into sub-parts.
+	    let l:source = split(l:source[0], '\V\C' . escape(l:repl, '\'))
+	else
+	    return matchstr(s:Render(l:source, l:repl), '^.\{' . l:maxCharacterNum . '}')
+	endif
+    endwhile
+    return s:Render(l:source, l:repl)
+endfunction
+function! s:Render( source, repl )
+    let l:render = join(a:source, a:repl)
+    let l:r = escape(a:repl, '\')
+    return substitute(l:render, printf('\V\C\^%s\+\|%s\+\$\|%s\{2}\zs%s\+', l:r, l:r, l:r, l:r), '', 'g')
+endfunction
+
 " vim: set ts=8 sts=4 sw=4 noexpandtab ff=unix fdm=syntax :