from __future__ import unicode_literals

import datetime
import os
import subprocess

from django.utils.lru_cache import lru_cache


def get_version(version=None):
    "Returns a PEP 440-compliant version number from VERSION."
    version = get_complete_version(version)

    # Now build the two parts of the version number:
    # main = X.Y[.Z]
    # sub = .devN - for pre-alpha releases
    #     | {a|b|rc}N - for alpha, beta, and rc releases

    main = get_main_version(version)

    sub = ''
    if version[3] == 'alpha' and version[4] == 0:
        git_changeset = get_git_changeset()
        if git_changeset:
            sub = '.dev%s' % git_changeset

    elif version[3] != 'final':
        mapping = {'alpha': 'a', 'beta': 'b', 'rc': 'rc'}
        sub = mapping[version[3]] + str(version[4])

    return str(main + sub)


def get_main_version(version=None):
    "Returns main version (X.Y[.Z]) from VERSION."
    version = get_complete_version(version)
    parts = 2 if version[2] == 0 else 3
    return '.'.join(str(x) for x in version[:parts])


def get_complete_version(version=None):
    """Returns a tuple of the django version. If version argument is non-empty,
    then checks for correctness of the tuple provided.
    """
    if version is None:
        from django import VERSION as version
    else:
        assert len(version) == 5
        assert version[3] in ('alpha', 'beta', 'rc', 'final')

    return version


def get_docs_version(version=None):
    version = get_complete_version(version)
    if version[3] != 'final':
        return 'dev'
    else:
        return '%d.%d' % version[:2]


@lru_cache()
def get_git_changeset():
    """Returns a numeric identifier of the latest git changeset.

    The result is the UTC timestamp of the changeset in YYYYMMDDHHMMSS format.
    This value isn't guaranteed to be unique, but collisions are very unlikely,
    so it's sufficient for generating the development version numbers.
    """
    repo_dir = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
    git_log = subprocess.Popen(
        'git log --pretty=format:%ct --quiet -1 HEAD',
        stdout=subprocess.PIPE, stderr=subprocess.PIPE,
        shell=True, cwd=repo_dir, universal_newlines=True,
    )
    timestamp = git_log.communicate()[0]
    try:
        timestamp = datetime.datetime.utcfromtimestamp(int(timestamp))
    except ValueError:
        return None
    return timestamp.strftime('%Y%m%d%H%M%S')
