#! /usr/bin/env python

import subprocess
import difflib
import time
import sys
import os
import os.path
import optparse


def changed_lines(oldlines, newlines):
    markers = { 'replace': ' ', 'insert': '+', 'delete': '-' }
    if oldlines is None:
        markers['insert'] = ' '
        oldlines = []
    sm = difflib.SequenceMatcher(None, oldlines, newlines)
    for (type, ostart, oend, nstart, nend) in sm.get_opcodes():
        if type == 'replace':
            for i in xrange(nstart, nend):
                yield markers[type], i, newlines[i]
        elif type == 'insert':
            for i in xrange(nstart, nend):
                yield markers[type], i, newlines[i]
        elif type == 'delete':
            for i in xrange(ostart, oend):
                yield markers[type], i, oldlines[i]
        else:
            pass
    return


def main(argv):
    op = optparse.OptionParser(
        usage="%prog [options] command...",
        description=("Run a command at regular intervals and show the lines"
                     " that have changed between each run, with a timestamp"))
    op.add_option("-i", "--interval", type='float', default=10.0,
                  help="Seconds between each command run [%default]")
    op.add_option("-f", "--timeformat", type='string', default="%H:%M:%S",
                  help="strftime style format string for timestamp [%default]")
    op.add_option("-s", "--separator", type='string', default=" %c ",
                  help="separator between timestamp and line [\"%default\"]")
    op.disable_interspersed_args()

    try:
        (opts, command) = op.parse_args(argv[1:])
    except SystemExit:
        return os.EX_USAGE
    command = " ".join(command).strip()
    if not command:
        sys.stderr.write(os.path.basename(argv[0])
                         + ": Command must not be empty.\n")
        op.print_usage()
        return os.EX_USAGE

    prev = None
    while True:
        now = time.strftime(opts.timeformat)
        cmd = subprocess.Popen(command, shell=True, stdout=subprocess.PIPE)
        this = cmd.communicate()[0].split("\n")
        if this[-1] == "":
            del this[-1]
        changes = list(changed_lines(prev, this))
        for marker,lineo,line in changes:
            print now + (opts.separator % (marker,)) + line
        prev = this
        time.sleep(opts.interval)


if __name__ == "__main__":
    retval = main(sys.argv)
    sys.exit(retval)