Shorten grep/ag/ack results to look nicer in Vim

grepsnip.py

#!/usr/bin/env python2
# Extracted from the "Vim-Holmes" plugin by Daan Bakker
# Example: ag --column function | ./grepsnip.py

import fileinput
import re
import os

GUESS_SIZE = 10
COLUMNS = os.environ.get('COLUMNS', 120)
SNIP_BEFORE = '... '
SNIP_AFTER = ' ...'
REGEX = re.compile(r'([^:]+):(\d+):(\d+):(.*)$')


def create_snippet(line, start, end, message_size, message_lead=None):
    size = end - start
    if message_lead is None:
        message_lead = (message_size - size) / 5

    orig = line

    line = re.sub('^\s+', '', line)
    index = max([0, start - (len(orig) - len(line))])

    line = re.sub('\s+$', '', line)

    if len(line) > message_size and index > message_lead:
        reduction = min([len(line) - message_size + len(SNIP_BEFORE), index - message_lead])

        line = SNIP_BEFORE + line[reduction:]
        index = index - reduction + len(SNIP_BEFORE)
        if index < 0:
            index = 0

    if len(line) > message_size:
        line = line[:message_size - len(SNIP_AFTER)] + SNIP_AFTER

    return line

if __name__ == '__main__':
    for line in fileinput.input('-'):
        filename, linenumber, start, content = REGEX.match(line).groups()

        content = create_snippet(line=content,
                                 start=int(start),
                                 end=int(start) + GUESS_SIZE,
                                 message_size=COLUMNS)

        print('{}:{}:{}:{}'.format(filename, linenumber, start, content))