# Authors:
#   Martin Nagy <mnagy@redhat.com>
#
# Copyright (C) 2008  Red Hat
# see file 'COPYING' for use and warranty information
#
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU General Public License as
# published by the Free Software Foundation; version 2 only
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA

"""
Basic configuration management.

This module handles the reading and representation of basic local settings.
It will also take care of settings that can be discovered by different
methods, such as DNS.
"""

from ConfigParser import RawConfigParser, ParsingError
from types import NoneType
import os
from os import path
import sys

from base import check_name
from constants import CONFIG_SECTION
from constants import TYPE_ERROR, OVERRIDE_ERROR, SET_ERROR, DEL_ERROR


class Env(object):
    """
    Store and retrieve environment variables.

    First an foremost, the `Env` class provides a handy container for
    environment variables.  These variables can be both set *and* retrieved
    either as attributes *or* as dictionary items.

    For example, you can set a variable as an attribute:

    >>> env = Env()
    >>> env.attr = 'I was set as an attribute.'
    >>> env.attr
    'I was set as an attribute.'
    >>> env['attr']  # Also retrieve as a dictionary item
    'I was set as an attribute.'

    Or you can set a variable as a dictionary item:

    >>> env['item'] = 'I was set as a dictionary item.'
    >>> env['item']
    'I was set as a dictionary item.'
    >>> env.item  # Also retrieve as an attribute
    'I was set as a dictionary item.'

    The variable values can be ``str`` or ``int`` instances, or the ``True``,
    ``False``, or ``None`` constants.  When the value provided is an ``str``
    instance, some limited automatic type conversion is performed, which allows
    values of specific types to be set easily from configuration files or
    command-line options.

    So in addition to their actual values, the ``True``, ``False``, and ``None``
    constants can be specified with an ``str`` equal to what ``repr()`` would
    return.  For example:

    >>> env.true = True
    >>> env.also_true = 'True'  # Equal to repr(True)
    >>> env.true
    True
    >>> env.also_true
    True

    Note that the automatic type conversion is case sensitive.  For example:

    >>> env.false = 'false'  # Not equal to repr(False)!
    >>> env.false
    'false'

    If an ``str`` value looks like an integer, it's automatically converted to
    the ``int`` type.  For example:

    >>> env.lucky = '7'
    >>> env.lucky
    7

    Leading and trailing white-space is automatically stripped from ``str``
    values.  For example:

    >>> env.message = '  Hello!  '  # Surrounded by double spaces
    >>> env.message
    'Hello!'
    >>> env.number = ' 42 '  # Still converted to an int
    >>> env.number
    42
    >>> env.actually_false = ' False '  # Still equal to repr(False)
    >>> env.actually_false
    False

    Also, empty ``str`` instances are converted to ``None``.  For example:

    >>> env.empty = ''
    >>> env.empty is None
    True

    `Env` variables are all set-once (first-one-wins).  Once a variable has been
    set, trying to override it will raise an ``AttributeError``.  For example:

    >>> env.date = 'First'
    >>> env.date = 'Second'
    Traceback (most recent call last):
      ...
    AttributeError: cannot override Env.date value 'First' with 'Second'

    An `Env` instance can be *locked*, after which no further variables can be
    set.  Trying to set variables on a locked `Env` instance will also raise
    an ``AttributeError``.  For example:

    >>> env = Env()
    >>> env.okay = 'This will work.'
    >>> env.__lock__()
    >>> env.nope = 'This wont work!'
    Traceback (most recent call last):
      ...
    AttributeError: locked: cannot set Env.nope to 'This wont work!'

    `Env` instances also provide standard container emulation for membership
    testing, counting, and iteration.  For example:

    >>> env = Env()
    >>> 'key1' in env  # Has key1 been set?
    False
    >>> env.key1 = 'value 1'
    >>> 'key1' in env
    True
    >>> env.key2 = 'value 2'
    >>> len(env)  # How many variables have been set?
    2
    >>> list(env)  # What variables have been set?
    ['key1', 'key2']

    Lastly, in addition to all the handy container functionality, the `Env`
    class provides high-level methods for bootstraping a fresh `Env` instance
    into one containing all the run-time and configuration information needed
    by the built-in freeIPA plugins.

    These are the `Env` bootstraping methods, in the order they must be called:

        1. `Env._bootstrap()` - initialize the run-time variables and then
           merge-in variables specified on the command-line.

        2. `Env._finalize_core()` - merge-in variables from the configuration
           files and then merge-in variables from the internal defaults, after
           which at least all the standard variables will be set.  After this
           method is called, the plugins will be loaded, during which 3rd-party
           plugins can set additional variables they may need.

        3. `Env._finalize()` - one last chance to merge-in variables and then
           the instance is locked.  After this method is called, no more
           environment variables can be set during the remaining life of the
           process.

    However, normally none of the above methods are called directly and instead
    only `plugable.API.bootstrap()` is called, which itself takes care of
    correctly calling the `Env` bootstrapping methods.
    """

    __locked = False

    def __init__(self):
        object.__setattr__(self, '_Env__d', {})
        object.__setattr__(self, '_Env__done', set())

    def __lock__(self):
        """
        Prevent further changes to environment.
        """
        if self.__locked is True:
            raise StandardError(
                '%s.__lock__() already called' % self.__class__.__name__
            )
        object.__setattr__(self, '_Env__locked', True)

    def __islocked__(self):
        """
        Return ``True`` if locked.
        """
        return self.__locked

    def __setattr__(self, name, value):
        """
        Set the attribute named ``name`` to ``value``.

        This just calls `Env.__setitem__()`.
        """
        self[name] = value

    def __setitem__(self, key, value):
        """
        Set ``key`` to ``value``.
        """
        if self.__locked:
            raise AttributeError(
                SET_ERROR % (self.__class__.__name__, key, value)
            )
        check_name(key)
        if key in self.__d:
            raise AttributeError(OVERRIDE_ERROR %
                (self.__class__.__name__, key, self.__d[key], value)
            )
        assert not hasattr(self, key)
        if isinstance(value, basestring):
            value = str(value.strip())
            m = {
                'True': True,
                'False': False,
                'None': None,
                '': None,
            }
            if value in m:
                value = m[value]
            elif value.isdigit():
                value = int(value)
        assert type(value) in (str, int, bool, NoneType)
        object.__setattr__(self, key, value)
        self.__d[key] = value

    def __getitem__(self, key):
        """
        Return the value corresponding to ``key``.
        """
        return self.__d[key]

    def __delattr__(self, name):
        """
        Raise AttributeError (deletion is never allowed).
        """
        raise AttributeError(
            DEL_ERROR % (self.__class__.__name__, name)
        )

    def __contains__(self, key):
        """
        Return True if instance contains ``key``; otherwise return False.
        """
        return key in self.__d

    def __len__(self):
        """
        Return number of variables currently set.
        """
        return len(self.__d)

    def __iter__(self):
        """
        Iterate through keys in ascending order.
        """
        for key in sorted(self.__d):
            yield key

    def _merge(self, **kw):
        """
        Merge variables in ``kw`` into environment.

        Any variables in ``kw`` that have already been set will be skipped
        (which means this method will not try to override them).

        This method returns a (set, total) tuple contained the number of
        variables actually set and the number of variables requested to be set.

        For example:

        >>> env = Env()
        >>> env._merge(first=1, second=2)
        (2, 2)
        >>> env._merge(first=1, third=3)
        (1, 2)
        >>> env._merge(first=1, second=2, third=3)
        (0, 3)
        """
        i = 0
        for (key, value) in kw.iteritems():
            if key not in self:
                self[key] = value
                i += 1
        return (i, len(kw))

    def _merge_from_file(self, conf_file):
        """
        Merge values from ``conf_file`` into this `Env`.
        """
        if not path.isfile(conf_file):
            return
        parser = RawConfigParser()
        try:
            parser.read(conf_file)
        except ParsingError:
            return
        if not parser.has_section(CONFIG_SECTION):
            parser.add_section(CONFIG_SECTION)
        items = parser.items(CONFIG_SECTION)
        if len(items) == 0:
            return
        i = 0
        for (key, value) in items:
            if key not in self:
                self[key] = value
                i += 1
        return (i, len(items))

    def __doing(self, name):
        if name in self.__done:
            raise StandardError(
                '%s.%s() already called' % (self.__class__.__name__, name)
            )
        self.__done.add(name)

    def __do_if_not_done(self, name):
        if name not in self.__done:
            getattr(self, name)()

    def _isdone(self, name):
        return name in self.__done

    def _bootstrap(self, **overrides):
        """
        Initialize basic environment.

        In addition to certain run-time information, this method will
        initialize only enough environment information to determine whether
        IPA is running in-tree, what the context is, and the location of the
        configuration file.
        """
        self.__doing('_bootstrap')

        # Set run-time variables:
        self.ipalib = path.dirname(path.abspath(__file__))
        self.site_packages = path.dirname(self.ipalib)
        self.script = path.abspath(sys.argv[0])
        self.bin = path.dirname(self.script)
        self.home = path.abspath(os.environ['HOME'])
        self.dot_ipa = path.join(self.home, '.ipa')

        for (key, value) in overrides.iteritems():
            self[key] = value
        if 'in_tree' not in self:
            if self.bin == self.site_packages and \
                    path.isfile(path.join(self.bin, 'setup.py')):
                self.in_tree = True
            else:
                self.in_tree = False
        if 'context' not in self:
            self.context = 'default'
        if self.in_tree:
            base = self.dot_ipa
        else:
            base = path.join('/', 'etc', 'ipa')
        if 'conf' not in self:
            self.conf = path.join(base, '%s.conf' % self.context)
        if 'conf_default' not in self:
            self.conf_default = path.join(base, 'default.conf')
        if 'conf_dir' not in self:
            self.conf_dir = base

    def _finalize_core(self, **defaults):
        """
        Complete initialization of standard IPA environment.

        After this method is called, the all environment variables
        used by all the built-in plugins will be available.

        This method should be called before loading any plugins.  It will
        automatically call `Env._bootstrap()` if it has not yet been called.

        After this method has finished, the `Env` instance is still writable
        so that 3rd-party plugins can set variables they may require as the
        plugins are registered.
        """
        self.__doing('_finalize_core')
        self.__do_if_not_done('_bootstrap')
        if self.__d.get('mode', None) != 'dummy':
            self._merge_from_file(self.conf)
            self._merge_from_file(self.conf_default)
        if 'in_server' not in self:
            self.in_server = (self.context == 'server')
        if 'log' not in self:
            name = '%s.log' % self.context
            if self.in_tree or self.context == 'cli':
                self.log = path.join(self.dot_ipa, 'log', name)
            else:
                self.log = path.join('/', 'var', 'log', 'ipa', name)
        self._merge(**defaults)

    def _finalize(self, **lastchance):
        """
        Finalize and lock environment.

        This method should be called after all plugins have been loaded and
        after `plugable.API.finalize()` has been called.  This method will
        automatically call `Env._finalize_core()` if it hasn't been called
        already, but in normal operation this would result in an exception
        being raised because the internal default values will not have been
        merged-in.

        After this method finishes, the `Env` instance will be locked and no
        more environment variables can be set.  Aside from unit-tests and
        example code, normally only one `Env` instance is created, which means
        no more variables can be set during the remaining life of the process.
        """
        self.__doing('_finalize')
        self.__do_if_not_done('_finalize_core')
        for (key, value) in lastchance.iteritems():
            if key not in self:
                self[key] = value
        self.__lock__()