import sys, inspect

from django.http import (HttpResponse, Http404, HttpResponseNotAllowed,
    HttpResponseForbidden, HttpResponseServerError)
from django.views.debug import ExceptionReporter
from django.views.decorators.vary import vary_on_headers
from django.conf import settings
from django.core.mail import EmailMultiAlternatives
from django.db.models.query import QuerySet
from django.http import Http404

from emitters import Emitter
from handler import typemapper
from doc import HandlerMethod
from authentication import NoAuthentication
from utils import coerce_put_post, FormValidationError, HttpStatusCode
from utils import rc, format_error, translate_mime, MimerDataException
from utils import head_guard

CHALLENGE = object()

class Resource(object):
    """
    Resource. Create one for your URL mappings, just
    like you would with Django. Takes one argument,
    the handler. The second argument is optional, and
    is an authentication handler. If not specified,
    `NoAuthentication` will be used by default.
    """
    callmap = { 'GET': 'read', 'POST': 'create',
                'PUT': 'update', 'DELETE': 'delete',
                'HEAD': 'meta' }

    def __init__(self, handler, authentication=None):
        if not callable(handler):
            raise AttributeError, "Handler not callable."

        self.handler = handler()
        self.csrf_exempt = getattr(self.handler, 'csrf_exempt', True)

        if not authentication:
            self.authentication = (NoAuthentication(),)
        elif isinstance(authentication, (list, tuple)):
            self.authentication = authentication
        else:
            self.authentication = (authentication,)

        # Erroring
        self.email_errors = getattr(settings, 'PISTON_EMAIL_ERRORS', True)
        self.display_errors = getattr(settings, 'PISTON_DISPLAY_ERRORS', True)
        self.stream = getattr(settings, 'PISTON_STREAM_OUTPUT', False)

    def determine_emitter(self, request, *args, **kwargs):
        """
        Function for determening which emitter to use
        for output. It lives here so you can easily subclass
        `Resource` in order to change how emission is detected.

        You could also check for the `Accept` HTTP header here,
        since that pretty much makes sense. Refer to `Mimer` for
        that as well.
        """
        em = kwargs.pop('emitter_format', None)

        if not em:
            em = request.GET.get('format', 'json')

        return em

    def form_validation_response(self, e):
        """
        Method to return form validation error information. 
        You will probably want to override this in your own
        `Resource` subclass.
        """
        resp = rc.BAD_REQUEST
        resp.write(' '+str(e.form.errors))
        return resp

    @property
    def anonymous(self):
        """
        Gets the anonymous handler. Also tries to grab a class
        if the `anonymous` value is a string, so that we can define
        anonymous handlers that aren't defined yet (like, when
        you're subclassing your basehandler into an anonymous one.)
        """
        if hasattr(self.handler, 'anonymous'):
            anon = self.handler.anonymous

            if callable(anon):
                return anon

            for klass in typemapper.keys():
                if anon == klass.__name__:
                    return klass

        return None

    def authenticate(self, request, rm):
        actor, anonymous = False, True

        for authenticator in self.authentication:
            if not authenticator.is_authenticated(request):
                if self.anonymous and \
                    rm in self.anonymous.allowed_methods:

                    actor, anonymous = self.anonymous(), True
                else:
                    actor, anonymous = authenticator.challenge, CHALLENGE
            else:
                return self.handler, self.handler.is_anonymous

        return actor, anonymous

    @head_guard
    @vary_on_headers('Authorization')
    def __call__(self, request, *args, **kwargs):
        """
        NB: Sends a `Vary` header so we don't cache requests
        that are different (OAuth stuff in `Authorization` header.)
        """
        rm = request.method.upper()

        # Django's internal mechanism doesn't pick up
        # PUT request, so we trick it a little here.
        if rm == "PUT":
            coerce_put_post(request)

        actor, anonymous = self.authenticate(request, rm)

        if anonymous is CHALLENGE:
            return actor()
        else:
            handler = actor

        # Translate nested datastructs into `request.data` here.
        if rm in ('POST', 'PUT'):
            try:
                translate_mime(request)
            except MimerDataException:
                return rc.BAD_REQUEST
            if not hasattr(request, 'data'):
                if rm == 'POST':
                    request.data = request.POST
                else:
                    request.data = request.PUT

        if not rm in handler.allowed_methods:
            return HttpResponseNotAllowed(handler.allowed_methods)

        meth = getattr(handler, self.callmap.get(rm, ''), None)
        if not meth:
            raise Http404

        # Support emitter both through (?P<emitter_format>) and ?format=emitter.
        em_format = self.determine_emitter(request, *args, **kwargs)

        kwargs.pop('emitter_format', None)

        # Clean up the request object a bit, since we might
        # very well have `oauth_`-headers in there, and we
        # don't want to pass these along to the handler.
        request = self.cleanup_request(request)

        try:
            result = meth(request, *args, **kwargs)
        except Exception, e:
            result = self.error_handler(e, request, meth, em_format)

        try:
            emitter, ct = Emitter.get(em_format)
            fields = handler.fields

            if hasattr(handler, 'list_fields') and isinstance(result, (list, tuple, QuerySet)):
                fields = handler.list_fields
        except ValueError:
            result = rc.BAD_REQUEST
            result.content = "Invalid output format specified '%s'." % em_format
            return result

        status_code = 200

        # If we're looking at a response object which contains non-string
        # content, then assume we should use the emitter to format that 
        # content
        if isinstance(result, HttpResponse) and not result._is_string:
            status_code = result.status_code
            # Note: We can't use result.content here because that method attempts
            # to convert the content into a string which we don't want. 
            # when _is_string is False _container is the raw data
            result = result._container
     
        srl = emitter(result, typemapper, handler, fields, anonymous)

        try:
            """
            Decide whether or not we want a generator here,
            or we just want to buffer up the entire result
            before sending it to the client. Won't matter for
            smaller datasets, but larger will have an impact.
            """
            if self.stream: stream = srl.stream_render(request)
            else: stream = srl.render(request)

            if not isinstance(stream, HttpResponse):
                resp = HttpResponse(stream, mimetype=ct, status=status_code)
            else:
                resp = stream

            resp.streaming = self.stream

            return resp
        except HttpStatusCode, e:
            return e.response

    @staticmethod
    def cleanup_request(request):
        """
        Removes `oauth_` keys from various dicts on the
        request object, and returns the sanitized version.
        """
        for method_type in ('GET', 'PUT', 'POST', 'DELETE'):
            block = getattr(request, method_type, { })

            if True in [ k.startswith("oauth_") for k in block.keys() ]:
                sanitized = block.copy()

                for k in sanitized.keys():
                    if k.startswith("oauth_"):
                        sanitized.pop(k)

                setattr(request, method_type, sanitized)

        return request

    # --

    def email_exception(self, reporter):
        subject = "Piston crash report"
        html = reporter.get_traceback_html()

        email_text = "This message is only visible in HTML view."

        email = EmailMultiAlternatives(subject, email_text, settings.SERVER_EMAIL, [ admin[1] for admin in settings.ADMINS ])
        email.attach_alternative(html, "text/html")
        email.send(fail_silently=True)


    def error_handler(self, e, request, meth, em_format):
        """
        Override this method to add handling of errors customized for your 
        needs
        """
        if isinstance(e, FormValidationError):
            return self.form_validation_response(e)

        elif isinstance(e, TypeError):
            result = rc.BAD_REQUEST
            hm = HandlerMethod(meth)
            sig = hm.signature

            msg = 'Method signature does not match.\n\n'

            if sig:
                msg += 'Signature should be: %s' % sig
            else:
                msg += 'Resource does not expect any parameters.'

            if self.display_errors:
                msg += '\n\nException was: %s' % str(e)

            result.content = format_error(msg)
            return result
        elif isinstance(e, Http404):
            return rc.NOT_FOUND

        elif isinstance(e, HttpStatusCode):
            return e.response
 
        else: 
            """
            On errors (like code errors), we'd like to be able to
            give crash reports to both admins and also the calling
            user. There's two setting parameters for this:

            Parameters::
             - `PISTON_EMAIL_ERRORS`: Will send a Django formatted
               error email to people in `settings.ADMINS`.
             - `PISTON_DISPLAY_ERRORS`: Will return a simple traceback
               to the caller, so he can tell you what error they got.

            If `PISTON_DISPLAY_ERRORS` is not enabled, the caller will
            receive a basic "500 Internal Server Error" message.
            """
            exc_type, exc_value, tb = sys.exc_info()
            rep = ExceptionReporter(request, exc_type, exc_value, tb.tb_next)
            if self.email_errors:
                self.email_exception(rep)
            if self.display_errors:
                return HttpResponseServerError(
                    format_error('\n'.join(rep.format_exception())))
            else:
                raise
