#!/usr/bin/python
# The contents of this file are subject to the Common Public Attribution
# License Version 1.0. (the "License"); you may not use this file except in
# compliance with the License. You may obtain a copy of the License at
# http://code.reddit.com/LICENSE. The License is based on the Mozilla Public
# License Version 1.1, but Sections 14 and 15 have been added to cover use of
# software over a computer network and provide for limited attribution for the
# Original Developer. In addition, Exhibit A has been modified to be consistent
# with Exhibit B.
#
# Software distributed under the License is distributed on an "AS IS" basis,
# WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License for
# the specific language governing rights and limitations under the License.
#
# The Original Code is reddit.
#
# The Original Developer is the Initial Developer.  The Initial Developer of
# the Original Code is reddit Inc.
#
# All portions of the code written by reddit are Copyright (c) 2006-2012 reddit
# Inc. All Rights Reserved.
###############################################################################
"""Check for new style guide violations in the current branch.

This script is meant to be used in a CI process to ensure that new changes
do not violate PEP-8, PEP-257, or any of the validity checks of pyflakes.

"""

import difflib
import os
import subprocess
import sys


DEVNULL = open("/dev/null", "w")
TOOLS = [
    ["pep8", "--repeat", "-q"],
    ["pep257"],
    ["pyflakes"],
]


def assert_tools_available():
    """Check if the external binaries needed are available or exit."""
    for tool in TOOLS:
        binary = tool[0]
        try:
            subprocess.check_call(["which", binary], stdout=DEVNULL)
        except subprocess.CalledProcessError:
            print >> sys.stderr, ("command %r not found. "
                                  "please install it!" % binary)
            sys.exit(1)


def assert_not_dirty():
    """Check if there are uncommitted changes in the repo and exit if so."""
    try:
        subprocess.check_call(["git", "diff",
                               "--no-ext-diff", "--quiet", "--exit-code"])
    except subprocess.CalledProcessError:
        print >> sys.stderr, ("you have uncommitted changes. "
                              "please commit them!")
        sys.exit(1)


def _parse_ref(ref):
    """Return the result of git rev-parse on the given ref."""
    ref = subprocess.check_output(["git", "rev-parse", ref])
    return ref.strip()


def get_current_ref():
    """Return the most descriptive name possible of the current HEAD."""
    try:
        ref = subprocess.check_output(["git", "symbolic-ref", "HEAD"]).strip()
        return ref[len("refs/heads/"):]
    except subprocess.CalledProcessError:
        return _parse_ref("HEAD")


def get_upstream_ref():
    """Return the ref that this topic branch is based on."""
    return _parse_ref("master@{upstream}")


def get_root():
    """Return the root directory of this git project."""
    return os.path.dirname(_parse_ref("--git-dir"))


def check_ref_out(ref):
    """Ask git to check out the specified ref."""
    try:
        subprocess.check_call(
            ["git", "checkout", ref],
            stdout=DEVNULL,
            stderr=DEVNULL,
        )
    except subprocess.CalledProcessError:
        print >> sys.stderr, "failed to check out %s" % ref
        sys.exit(1)


def generate_report(ref, changed_files):
    """Run the tools on the specified files and return errors / warnings."""
    check_ref_out(ref)

    report = []
    for filepath in changed_files:
        for tool in TOOLS:
            command = tool + [filepath]
            print >> sys.stderr, " ".join(command)
            process = subprocess.Popen(
                command,
                stdout=subprocess.PIPE,
                stderr=subprocess.STDOUT,
            )

            lines = process.communicate()[0].splitlines()
            for line in lines:
                # if present, get rid of file/line number markings which will
                # cause false positives.
                pref, sep, suf = line.partition(" ")
                line = pref if not sep else suf
                report.append(line)
    return report


def get_changed_files(old_ref, new_ref):
    """Return a list of files that have changed from one ref to another."""
    root = get_root()
    changed_files_text = subprocess.check_output(["git", "diff", "--name-only",
                                                  old_ref, new_ref])
    changed_files = changed_files_text.splitlines()
    return [os.path.join(root, x) for x in changed_files]


def main():
    assert_tools_available()
    assert_not_dirty()

    current_ref = get_current_ref()
    base_ref = get_upstream_ref()
    changed_files = get_changed_files(base_ref, current_ref)

    try:
        new_report = generate_report(current_ref, changed_files)
        old_report = generate_report(base_ref, changed_files)
    finally:
        check_ref_out(current_ref)

    added, removed = 0, 0
    for line in difflib.unified_diff(old_report, new_report):
        line = line.strip()
        if line == "+++" or line == "---":
            continue
        if line.startswith("+"):
            added += 1
        elif line.startswith("-"):
            removed += 1

    if added:
        print "added %d issues" % added
    if removed:
        print "removed %d issues!" % removed

    return 1 if added else 0


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