#! /usr/bin/env python

# Change the #! line occurring in Python scripts.  The new interpreter

# pathname must be given with a -i option.

#

# Command line arguments are files or directories to be processed.

# Directories are searched recursively for files whose name looks

# like a python module.

# Symbolic links are always ignored (except as explicit directory

# arguments).  Of course, the original file is kept as a back-up

# (with a "~" attached to its name).

#

# Undoubtedly you can do this using find and sed or perl, but this is

# a nice example of Python code that recurses down a directory tree

# and uses regular expressions.  Also note several subtleties like

# preserving the file's mode and avoiding to even write a temp file

# when no changes are needed for a file.

#

# NB: by changing only the function fixfile() you can turn this

# into a program for a different change to Python programs...

import sys

import re

import os

from stat import *

import getopt

err = sys.stderr.write

dbg = err

rep = sys.stdout.write

new_interpreter = None

def main():

    global new_interpreter

    usage = ('usage: %s -i /interpreter file-or-directory ...\n' %

             sys.argv[0])

    try:

        opts, args = getopt.getopt(sys.argv[1:], 'i:')

    except getopt.error, msg:

        err(msg + '\n')

        err(usage)

        sys.exit(2)

    for o, a in opts:

        if o == '-i':

            new_interpreter = a

    if not new_interpreter or new_interpreter[0] != '/' or not args:

        err('-i option or file-or-directory missing\n')

        err(usage)

        sys.exit(2)

    bad = 0

    for arg in args:

        if os.path.isdir(arg):

            if recursedown(arg): bad = 1

        elif os.path.islink(arg):

            err(arg + ': will not process symbolic links\n')

            bad = 1

        else:

            if fix(arg): bad = 1

    sys.exit(bad)

ispythonprog = re.compile('^[a-zA-Z0-9_]+\.py$')

def ispython(name):

    return ispythonprog.match(name) >= 0

def recursedown(dirname):

    dbg('recursedown(%r)\n' % (dirname,))

    bad = 0

    try:

        names = os.listdir(dirname)

    except os.error, msg:

        err('%s: cannot list directory: %r\n' % (dirname, msg))

        return 1

    names.sort()

    subdirs = []

    for name in names:

        if name in (os.curdir, os.pardir): continue

        fullname = os.path.join(dirname, name)

        if os.path.islink(fullname): pass

        elif os.path.isdir(fullname):

            subdirs.append(fullname)

        elif ispython(name):

            if fix(fullname): bad = 1

    for fullname in subdirs:

        if recursedown(fullname): bad = 1

    return bad

def fix(filename):

##  dbg('fix(%r)\n' % (filename,))

    try:

        f = open(filename, 'r')

    except IOError, msg:

        err('%s: cannot open: %r\n' % (filename, msg))

        return 1

    line = f.readline()

    fixed = fixline(line)

    if line == fixed:

        rep(filename+': no change\n')

        f.close()

        return

    head, tail = os.path.split(filename)

    tempname = os.path.join(head, '@' + tail)

    try:

        g = open(tempname, 'w')

    except IOError, msg:

        f.close()

        err('%s: cannot create: %r\n' % (tempname, msg))

        return 1

    rep(filename + ': updating\n')

    g.write(fixed)

    BUFSIZE = 8*1024

    while 1:

        buf = f.read(BUFSIZE)

        if not buf: break

        g.write(buf)

    g.close()

    f.close()

    # Finishing touch -- move files

    # First copy the file's mode to the temp file

    try:

        statbuf = os.stat(filename)

        os.chmod(tempname, statbuf[ST_MODE] & 07777)

    except os.error, msg:

        err('%s: warning: chmod failed (%r)\n' % (tempname, msg))

    # Then make a backup of the original file as filename~

    try:

        os.rename(filename, filename + '~')

    except os.error, msg:

        err('%s: warning: backup failed (%r)\n' % (filename, msg))

    # Now move the temp file to the original file

    try:

        os.rename(tempname, filename)

    except os.error, msg:

        err('%s: rename failed (%r)\n' % (filename, msg))

        return 1

    # Return succes

    return 0

def fixline(line):

    if not line.startswith('#!'):

        return line

    if "python" not in line:

        return line

    return '#! %s\n' % new_interpreter

if __name__ == '__main__':

    main()