# This file is part of PRAW.
#
# PRAW 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, either version 3 of the License, or (at your option) any later
# version.
#
# PRAW 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
# PRAW.  If not, see <http://www.gnu.org/licenses/>.

"""
Decorators.

They mainly do two things: ensure API guidelines are followed and
prevent unnecessary failed API requests by testing that the call can be made
first. Also, they can limit the length of output strings and parse json
response for certain errors.
"""

from __future__ import print_function, unicode_literals

import decorator
import inspect
import six
import sys
from functools import wraps
from praw.decorator_helpers import _get_captcha, _is_mod_of_all
from praw import errors
from warnings import simplefilter, warn


# Enable deprecation warnings
simplefilter('default')


def alias_function(function, class_name):
    """Create a RedditContentObject function mapped to a BaseReddit function.

    The BaseReddit classes define the majority of the API's functions. The
    first argument for many of these functions is the RedditContentObject that
    they operate on. This factory returns functions appropriate to be called on
    a RedditContent object that maps to the corresponding BaseReddit function.

    """
    @wraps(function)
    def wrapped(self, *args, **kwargs):
        func_args = inspect.getargspec(function).args
        if 'subreddit' in func_args and func_args.index('subreddit') != 1:
            # Only happens for search
            kwargs['subreddit'] = self
            return function(self.reddit_session, *args, **kwargs)
        else:
            return function(self.reddit_session, self, *args, **kwargs)
    # Only grab the short-line doc and add a link to the complete doc
    if wrapped.__doc__ is not None:
        wrapped.__doc__ = wrapped.__doc__.split('\n', 1)[0]
        wrapped.__doc__ += ('\n\nSee :meth:`.{0}.{1}` for complete usage. '
                            'Note that you should exclude the subreddit '
                            'parameter when calling this convenience method.'
                            .format(class_name, function.__name__))
    # Don't hide from sphinx as this is a parameter modifying decorator
    return wrapped


def deprecated(msg=''):
    """Deprecate decorated method."""
    @decorator.decorator
    def wrap(function, *args, **kwargs):
        if not kwargs.pop('disable_warning', False):
            warn(msg, DeprecationWarning)
        return function(*args, **kwargs)
    return wrap


@decorator.decorator
def limit_chars(function, *args, **kwargs):
    """Truncate the string returned from a function and return the result."""
    output_chars_limit = args[0].reddit_session.config.output_chars_limit
    output_string = function(*args, **kwargs)
    if -1 < output_chars_limit < len(output_string):
        output_string = output_string[:output_chars_limit - 3] + '...'
    return output_string


@decorator.decorator
def oauth_generator(function, *args, **kwargs):
    """Set the _use_oauth keyword argument to True when appropriate.

    This is needed because generator functions may be called at anytime, and
    PRAW relies on the Reddit._use_oauth value at original call time to know
    when to make OAuth requests.

    Returned data is not modified.

    """
    if getattr(args[0], '_use_oauth', False):
        kwargs['_use_oauth'] = True
    return function(*args, **kwargs)


@decorator.decorator
def raise_api_exceptions(function, *args, **kwargs):
    """Raise client side exception(s) when present in the API response.

    Returned data is not modified.

    """
    try:
        return_value = function(*args, **kwargs)
    except errors.HTTPException as exc:
        if exc._raw.status_code != 400:  # pylint: disable=W0212
            raise  # Unhandled HTTPErrors
        try:  # Attempt to convert v1 errors into older format (for now)
            data = exc._raw.json()  # pylint: disable=W0212
            assert len(data) == 2
            return_value = {'errors': [(data['reason'],
                                        data['explanation'], '')]}
        except Exception:
            raise exc
    if isinstance(return_value, dict):
        if return_value.get('error') == 304:  # Not modified exception
            raise errors.NotModified(return_value)
        elif return_value.get('errors'):
            error_list = []
            for error_type, msg, value in return_value['errors']:
                if error_type in errors.ERROR_MAPPING:
                    if error_type == 'RATELIMIT':
                        args[0].evict(args[1])
                    error_class = errors.ERROR_MAPPING[error_type]
                else:
                    error_class = errors.APIException
                error_list.append(error_class(error_type, msg, value,
                                              return_value))
            if len(error_list) == 1:
                raise error_list[0]
            else:
                raise errors.ExceptionList(error_list)
    return return_value


@decorator.decorator
def require_captcha(function, *args, **kwargs):
    """Return a decorator for methods that require captchas."""
    raise_captcha_exception = kwargs.pop('raise_captcha_exception', False)
    captcha_id = None

    # Get a handle to the reddit session
    if hasattr(args[0], 'reddit_session'):
        reddit_session = args[0].reddit_session
    else:
        reddit_session = args[0]

    while True:
        try:
            if captcha_id:
                captcha_answer = _get_captcha(reddit_session, captcha_id)

                # When the method is being decorated, all of its default
                # parameters become part of this *args tuple. This means that
                # *args currently contains a None where the captcha answer
                # needs to go. If we put the captcha in the **kwargs,
                # we get a TypeError for having two values of the same param.
                func_args = inspect.getargspec(function)
                if 'captcha' in func_args.args:
                    captcha_index = func_args.args.index('captcha')
                    args = list(args)
                    args[captcha_index] = captcha_answer
                else:
                    kwargs['captcha'] = captcha_answer
            return function(*args, **kwargs)
        except errors.InvalidCaptcha as exception:
            if raise_captcha_exception or \
                    not hasattr(sys.stdin, 'closed') or sys.stdin.closed:
                raise
            captcha_id = exception.response['captcha']


def restrict_access(scope, mod=None, login=None, oauth_only=False):
    """Restrict function access unless the user has the necessary permissions.

    Raises one of the following exceptions when appropriate:
      * LoginRequired
      * LoginOrOAuthRequired
        * the scope attribute will provide the necessary scope name
      * ModeratorRequired
      * ModeratorOrOAuthRequired
        * the scope attribute will provide the necessary scope name

    :param scope: Indicate the scope that is required for the API call. None or
        False must be passed to indicate that no scope handles the API call.
        All scopes save for `read` imply login=True. Scopes with 'mod' in their
        name imply mod=True.
    :param mod: Indicate that a moderator is required. Implies login=True.
    :param login: Indicate that a login is required.
    :param oauth_only: Indicate that only OAuth is supported for the function.

    Returned data is not modified.

    This decorator assumes that all mod required functions fit one of these
    categories:

      * have the subreddit as the first argument (Reddit instance functions) or
        have a subreddit keyword argument
      * are called upon a subreddit object (Subreddit RedditContentObject)
      * are called upon a RedditContent object with attribute subreddit

    """
    if not scope and oauth_only:
        raise TypeError('`scope` must be set when `oauth_only` is set')

    mod = mod is not False and (mod or scope and 'mod' in scope)
    login = login is not False and (login or mod or scope and scope != 'read')

    @decorator.decorator
    def wrap(function, *args, **kwargs):
        if args[0] is None:  # Occurs with (un)friend
            assert login
            raise errors.LoginRequired(function.__name__)
        # This segment of code uses hasattr to determine what instance type
        # the function was called on. We could use isinstance if we wanted
        # to import the types at runtime (decorators is used by all the
        # types).
        if mod:
            if hasattr(args[0], 'reddit_session'):
                # Defer access until necessary for RedditContentObject.
                # This is because scoped sessions may not require this
                # attribute to exist, thus it might not be set.
                from praw.objects import Subreddit
                subreddit = args[0] if isinstance(args[0], Subreddit) \
                    else False
            else:
                subreddit = kwargs.get(
                    'subreddit', args[1] if len(args) > 1 else None)
                if subreddit is None:  # Try the default value
                    defaults = six.get_function_defaults(function)
                    subreddit = defaults[0] if defaults else None
        else:
            subreddit = None

        obj = getattr(args[0], 'reddit_session', args[0])
        # This function sets _use_oauth for one time use only.
        # Verify that statement is actually true.
        assert not obj._use_oauth  # pylint: disable=W0212

        if scope and obj.has_scope(scope):
            obj._use_oauth = True  # pylint: disable=W0212
        elif oauth_only:
            raise errors.OAuthScopeRequired(function.__name__, scope)
        elif login and obj.is_logged_in():
            if subreddit is False:
                # Now fetch the subreddit attribute. There is no good
                # reason for it to not be set during a logged in session.
                subreddit = args[0].subreddit
            if mod and not _is_mod_of_all(obj.user, subreddit):
                if scope:
                    raise errors.ModeratorOrScopeRequired(
                        function.__name__, scope)
                raise errors.ModeratorRequired(function.__name__)
        elif login:
            if scope:
                raise errors.LoginOrScopeRequired(function.__name__, scope)
            raise errors.LoginRequired(function.__name__)
        try:
            return function(*args, **kwargs)
        finally:
            obj._use_oauth = False  # pylint: disable=W0212
    return wrap


@decorator.decorator
def require_oauth(function, *args, **kwargs):
    """Verify that the OAuth functions can be used prior to use.

    Returned data is not modified.

    """
    if not args[0].has_oauth_app_info:
        err_msg = ("The OAuth app config parameters client_id, client_secret "
                   "and redirect_url must be specified to use this function.")
        raise errors.OAuthAppRequired(err_msg)
    return function(*args, **kwargs)
