#!/usr/bin/env python3
#
# byteify-strings.py - transform string literals to be Python 3 safe
#
# Copyright 2015 Gregory Szorc <gregory.szorc@gmail.com>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.

from __future__ import absolute_import

import argparse
import contextlib
import errno
import os
import sys
import tempfile
import token
import tokenize

if True:
    def replacetokens(tokens, opts):
        """Transform a stream of tokens from raw to Python 3.

        Returns a generator of possibly rewritten tokens.

        The input token list may be mutated as part of processing. However,
        its changes do not necessarily match the output token stream.
        """
        sysstrtokens = set()

        # The following utility functions access the tokens list and i index of
        # the for i, t enumerate(tokens) loop below
        def _isop(j, *o):
            """Assert that tokens[j] is an OP with one of the given values"""
            try:
                return tokens[j].type == token.OP and tokens[j].string in o
            except IndexError:
                return False

        def _findargnofcall(n):
            """Find arg n of a call expression (start at 0)

            Returns index of the first token of that argument, or None if
            there is not that many arguments.

            Assumes that token[i + 1] is '('.

            """
            nested = 0
            for j in range(i + 2, len(tokens)):
                if _isop(j, ')', ']', '}'):
                    # end of call, tuple, subscription or dict / set
                    nested -= 1
                    if nested < 0:
                        return None
                elif n == 0:
                    # this is the starting position of arg
                    return j
                elif _isop(j, '(', '[', '{'):
                    nested += 1
                elif _isop(j, ',') and nested == 0:
                    n -= 1

            return None

        def _ensuresysstr(j):
            """Make sure the token at j is a system string

            Remember the given token so the string transformer won't add
            the byte prefix.

            Ignores tokens that are not strings. Assumes bounds checking has
            already been done.

            """
            st = tokens[j]
            if st.type == token.STRING and st.string.startswith(("'", '"')):
                sysstrtokens.add(st)

        for i, t in enumerate(tokens):
            # Convert most string literals to byte literals. String literals
            # in Python 2 are bytes. String literals in Python 3 are unicode.
            # Most strings in Mercurial are bytes and unicode strings are rare.
            # Rather than rewrite all string literals to use ``b''`` to indicate
            # byte strings, we apply this token transformer to insert the ``b``
            # prefix nearly everywhere.
            if t.type == token.STRING and t not in sysstrtokens:
                s = t.string

                # Preserve docstrings as string literals. This is inconsistent
                # with regular unprefixed strings. However, the
                # "from __future__" parsing (which allows a module docstring to
                # exist before it) doesn't properly handle the docstring if it
                # is b''' prefixed, leading to a SyntaxError. We leave all
                # docstrings as unprefixed to avoid this. This means Mercurial
                # components touching docstrings need to handle unicode,
                # unfortunately.
                if s[0:3] in ("'''", '"""'):
                    yield t
                    continue

                # If the first character isn't a quote, it is likely a string
                # prefixing character (such as 'b', 'u', or 'r'. Ignore.
                if s[0] not in ("'", '"'):
                    yield t
                    continue

                # String literal. Prefix to make a b'' string.
                yield t._replace(string='b%s' % t.string)
                continue

            # This looks like a function call.
            if t.type == token.NAME and _isop(i + 1, '('):
                fn = t.string

                # *attr() builtins don't accept byte strings to 2nd argument.
                if (fn in ('getattr', 'setattr', 'hasattr', 'safehasattr') and
                        not _isop(i - 1, '.')):
                    arg1idx = _findargnofcall(1)
                    if arg1idx is not None:
                        _ensuresysstr(arg1idx)

                # .encode() and .decode() on str/bytes/unicode don't accept
                # byte strings on Python 3.
                elif fn in ('encode', 'decode') and _isop(i - 1, '.'):
                    for argn in range(2):
                        argidx = _findargnofcall(argn)
                        if argidx is not None:
                            _ensuresysstr(argidx)

                # It changes iteritems/values to items/values as they are not
                # present in Python 3 world.
                elif opts['dictiter'] and fn in ('iteritems', 'itervalues'):
                    yield t._replace(string=fn[4:])
                    continue

            # Emit unmodified token.
            yield t

def process(fin, fout, opts):
    tokens = tokenize.tokenize(fin.readline)
    tokens = replacetokens(list(tokens), opts)
    fout.write(tokenize.untokenize(tokens))

def tryunlink(fname):
    try:
        os.unlink(fname)
    except OSError as err:
        if err.errno != errno.ENOENT:
            raise

@contextlib.contextmanager
def editinplace(fname):
    n = os.path.basename(fname)
    d = os.path.dirname(fname)
    fp = tempfile.NamedTemporaryFile(prefix='.%s-' % n, suffix='~', dir=d,
                                     delete=False)
    try:
        yield fp
        fp.close()
        if os.name == 'nt':
            tryunlink(fname)
        os.rename(fp.name, fname)
    finally:
        fp.close()
        tryunlink(fp.name)

def main():
    ap = argparse.ArgumentParser()
    ap.add_argument('-i', '--inplace', action='store_true', default=False,
                    help='edit files in place')
    ap.add_argument('--dictiter', action='store_true', default=False,
                    help='rewrite iteritems() and itervalues()'),
    ap.add_argument('files', metavar='FILE', nargs='+', help='source file')
    args = ap.parse_args()
    opts = {
        'dictiter': args.dictiter,
    }
    for fname in args.files:
        if args.inplace:
            with editinplace(fname) as fout:
                with open(fname, 'rb') as fin:
                    process(fin, fout, opts)
        else:
            with open(fname, 'rb') as fin:
                fout = sys.stdout.buffer
                process(fin, fout, opts)

if __name__ == '__main__':
    main()