#!/usr/bin/env python
#
# save as .hg/check_whitespace.py and make executable

import re

def trailing_whitespace(difflines):
    # 
    linenum, header = 0, False

    for line in difflines:
        if header:
            # remember the name of the file that this diff affects
            m = re.match(r'(?:---|\+\+\+) ([^\t]+)', line)
            if m and m.group(1) != '/dev/null':
                filename = m.group(1).split('/', 1)[-1]
            if line.startswith('+++ '):
                header = False
            continue
        if line.startswith('diff '):
            header = True
            continue
        # hunk header - save the line number
        m = re.match(r'@@ -\d+,\d+ \+(\d+),', line)
        if m:
            linenum = int(m.group(1))
            continue
        # hunk body - check for an added line with trailing whitespace
        m = re.match(r'\+.*\s$', line)
        if m:
            yield filename, linenum
        if line and line[0] in ' +':
            linenum += 1

if __name__ == '__main__':
    import os, sys
    
    added = 0
    for filename, linenum in trailing_whitespace(os.popen('hg export tip')):
        print >> sys.stderr, ('%s, line %d: trailing whitespace added' %
                              (filename, linenum))
        added += 1
    if added:
        # save the commit message so we don't need to retype it
        os.system('hg tip --template "{desc}" > .hg/commit.save')
        print >> sys.stderr, 'commit message saved to .hg/commit.save'
        sys.exit(1)