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

import wizard

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

def get_exception_name(output):
    """Reads the stderr output of another Python command 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."""
    return pwd.getpwuid(get_dir_uid(dir)).pw_name

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) of person who is operating
    this script, as told to use by the Kerberos principal name.
    Useful for 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."""
    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():
    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():
    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:
        pass

def set_git_env():
    set_operator_env()
    set_author_env()

def get_git_footer():
    return "\n".join(["Wizard-revision: %s" % get_revision()
        ,"Wizard-args: %s" % " ".join(sys.argv)
        ])

class Error(wizard.Error):
    pass

class NoOperatorInfo(Error):
    pass