"""
Miscellaneous utility functions and classes.

.. testsetup:: *

    from wizard.util import *
"""

import os.path
import os
import subprocess
import pwd
import sys

import wizard
from wizard import shell

class ChangeDirectory(object):
    """
    Context for temporarily changing the working directory.

        >>> with ChangeDirectory("/tmp"):
        ...    print os.getcwd()
        /tmp
    """
    def __init__(self, dir):
        self.dir = dir
        self.olddir = None
    def __enter__(self):
        self.olddir = os.getcwd()
        os.chdir(self.dir)
    def __exit__(self, *args):
        os.chdir(self.olddir)

class Counter(object):
    """
    Object for counting different values when you don't know what
    they are a priori.  Supports index access and iteration.

        >>> counter = Counter()
        >>> counter.count("foo")
        >>> print counter["foo"]
        1
    """
    def __init__(self):
        self.dict = {}
    def count(self, value):
        """Increments count for ``value``."""
        self.dict.setdefault(value, 0)
        self.dict[value] += 1
    def __getitem__(self, key):
        return self.dict[key]
    def __iter__(self):
        return self.dict.__iter__()

def dictmap(f, d):
    """
    A map function for dictionaries.  Only changes values.

        >>> dictmap(lambda x: x + 2, {'a': 1, 'b': 2})
        {'a': 3, 'b': 4}
    """
    return dict((k,f(v)) for k,v in d.items())

def get_exception_name(output):
    """
    Reads the traceback from a Python program and grabs the
    fully qualified exception name.
    """
    lines = output.split("\n")
    for line in lines[1:]: # skip the "traceback" line
        line = line.rstrip()
        if line[0] == ' ': continue
        if line[-1] == ":":
            return line[:-1]
        else:
            return line

def get_dir_uid(dir):
    """Finds the uid of the person who owns this directory."""
    return os.stat(dir).st_uid

def get_dir_owner(dir = "."):
    """
    Finds the name of the locker this directory is in.

    .. note::

        This function uses the passwd database and thus
        only works on scripts servers.
    """
    return pwd.getpwuid(get_dir_uid(dir)).pw_name

def get_dir_tag():
    """Finds the output of git describe --tags of the current directory."""
    return shell.Shell().safeCall("git", "describe", "--tags")[0].rstrip()

def get_revision():
    """Returns the commit ID of the current Wizard install."""
    wizard_git = os.path.join(os.path.dirname(os.path.dirname(os.path.abspath(__file__))), ".git")
    return subprocess.Popen(["git", "--git-dir=" + wizard_git, "rev-parse", "HEAD"], stdout=subprocess.PIPE).communicate()[0].rstrip()

def get_operator_info():
    """
    Returns tuple of ``(realname, email)`` from Hesiod about the
    this operator of this script from :func:`get_operator_name`.
    Useful when generating commit messages.
    """
    username = get_operator_name()
    hesinfo = subprocess.Popen(["hesinfo", username, "passwd"],stdout=subprocess.PIPE).communicate()[0]
    fields = hesinfo.partition(",")[0]
    realname = fields.rpartition(":")[2]
    return realname, username + "@mit.edu"

def get_operator_git():
    """
    Returns ``Real Name <username@mit.edu>`` suitable for use in
    Git ``Something-by:`` string.
    """
    return "%s <%s>" % get_operator_info()

def get_operator_name():
    """
    Returns username of the person operating this script based
    off of the :envvar:`SSH_GSSAPI_NAME` environment variable.  Throws
    :exc:`NoOperatorInfo` if environment variable is not available.

    .. note::

        :envvar:`SSH_GSSAPI_NAME` is not set by a vanilla OpenSSH
        distributions.  Scripts servers are patched to support this
        environment variable.
    """
    principal = os.getenv("SSH_GSSAPI_NAME")
    if not principal: raise NoOperatorInfo
    instance, _, _ = principal.partition("@")
    if instance.endswith("/root"):
        username, _, _ = principal.partition("/")
    else:
        username = instance
    return username

def set_operator_env():
    """
    Sets :envvar:`GIT_COMMITTER_NAME` and :envvar:`GIT_COMMITTER_EMAIL`
    environment variables if applicable.  Does nothing if
    :func:`get_operator_info` throws :exc:`NoOperatorInfo`.
    """
    try:
        op_realname, op_email = get_operator_info()
        os.putenv("GIT_COMMITTER_NAME", op_realname)
        os.putenv("GIT_COMMITTER_EMAIL", op_email)
    except NoOperatorInfo:
        pass

def set_author_env():
    """
    Sets :envvar:`GIT_AUTHOR_NAME` and :envvar:`GIT_AUTHOR_EMAIL` environment
    variables if applicable. Does nothing if :func:`get_dir_owner` fails.
    """
    try:
        lockername = get_dir_owner()
        os.putenv("GIT_AUTHOR_NAME", "%s locker" % lockername)
        os.putenv("GIT_AUTHOR_EMAIL", "%s@scripts.mit.edu" % lockername)
    except KeyError: # XXX: This doesn't actually make sense
        pass

def set_git_env():
    """Sets all appropriate environment variables for Git commits."""
    set_operator_env()
    set_author_env()

def get_git_footer():
    """Returns strings for placing in Git log info about Wizard."""
    return "\n".join(["Wizard-revision: %s" % get_revision()
        ,"Wizard-args: %s" % " ".join(sys.argv)
        ])

class NoOperatorInfo(wizard.Error):
    """No information could be found about the operator from Kerberos."""
    pass