import asyncio
import logging
import sys
import tempfile
import traceback
from io import BytesIO

from asgiref.sync import sync_to_async

from django.conf import settings
from django.core import signals
from django.core.exceptions import RequestAborted, RequestDataTooBig
from django.core.handlers import base
from django.http import (
    FileResponse, HttpRequest, HttpResponse, HttpResponseBadRequest,
    HttpResponseServerError, QueryDict, parse_cookie,
)
from django.urls import set_script_prefix
from django.utils.functional import cached_property

logger = logging.getLogger('django.request')


class ASGIRequest(HttpRequest):
    """
    Custom request subclass that decodes from an ASGI-standard request dict
    and wraps request body handling.
    """
    # Number of seconds until a Request gives up on trying to read a request
    # body and aborts.
    body_receive_timeout = 60

    def __init__(self, scope, body_file):
        self.scope = scope
        self._post_parse_error = False
        self._read_started = False
        self.resolver_match = None
        self.script_name = self.scope.get('root_path', '')
        if self.script_name and scope['path'].startswith(self.script_name):
            # TODO: Better is-prefix checking, slash handling?
            self.path_info = scope['path'][len(self.script_name):]
        else:
            self.path_info = scope['path']
        # The Django path is different from ASGI scope path args, it should
        # combine with script name.
        if self.script_name:
            self.path = '%s/%s' % (
                self.script_name.rstrip('/'),
                self.path_info.replace('/', '', 1),
            )
        else:
            self.path = scope['path']
        # HTTP basics.
        self.method = self.scope['method'].upper()
        # Ensure query string is encoded correctly.
        query_string = self.scope.get('query_string', '')
        if isinstance(query_string, bytes):
            query_string = query_string.decode()
        self.META = {
            'REQUEST_METHOD': self.method,
            'QUERY_STRING': query_string,
            'SCRIPT_NAME': self.script_name,
            'PATH_INFO': self.path_info,
            # WSGI-expecting code will need these for a while
            'wsgi.multithread': True,
            'wsgi.multiprocess': True,
        }
        if self.scope.get('client'):
            self.META['REMOTE_ADDR'] = self.scope['client'][0]
            self.META['REMOTE_HOST'] = self.META['REMOTE_ADDR']
            self.META['REMOTE_PORT'] = self.scope['client'][1]
        if self.scope.get('server'):
            self.META['SERVER_NAME'] = self.scope['server'][0]
            self.META['SERVER_PORT'] = str(self.scope['server'][1])
        else:
            self.META['SERVER_NAME'] = 'unknown'
            self.META['SERVER_PORT'] = '0'
        # Headers go into META.
        for name, value in self.scope.get('headers', []):
            name = name.decode('latin1')
            if name == 'content-length':
                corrected_name = 'CONTENT_LENGTH'
            elif name == 'content-type':
                corrected_name = 'CONTENT_TYPE'
            else:
                corrected_name = 'HTTP_%s' % name.upper().replace('-', '_')
            # HTTP/2 say only ASCII chars are allowed in headers, but decode
            # latin1 just in case.
            value = value.decode('latin1')
            if corrected_name in self.META:
                value = self.META[corrected_name] + ',' + value
            self.META[corrected_name] = value
        # Pull out request encoding, if provided.
        self._set_content_type_params(self.META)
        # Directly assign the body file to be our stream.
        self._stream = body_file
        # Other bits.
        self.resolver_match = None

    @cached_property
    def GET(self):
        return QueryDict(self.META['QUERY_STRING'])

    def _get_scheme(self):
        return self.scope.get('scheme') or super()._get_scheme()

    def _get_post(self):
        if not hasattr(self, '_post'):
            self._load_post_and_files()
        return self._post

    def _set_post(self, post):
        self._post = post

    def _get_files(self):
        if not hasattr(self, '_files'):
            self._load_post_and_files()
        return self._files

    POST = property(_get_post, _set_post)
    FILES = property(_get_files)

    @cached_property
    def COOKIES(self):
        return parse_cookie(self.META.get('HTTP_COOKIE', ''))


class ASGIHandler(base.BaseHandler):
    """Handler for ASGI requests."""
    request_class = ASGIRequest
    # Size to chunk response bodies into for multiple response messages.
    chunk_size = 2 ** 16

    def __init__(self):
        super(ASGIHandler, self).__init__()
        self.load_middleware()

    async def __call__(self, scope, receive, send):
        """
        Async entrypoint - parses the request and hands off to get_response.
        """
        # Serve only HTTP connections.
        # FIXME: Allow to override this.
        if scope['type'] != 'http':
            raise ValueError(
                'Django can only handle ASGI/HTTP connections, not %s.'
                % scope['type']
            )
        # Receive the HTTP request body as a stream object.
        try:
            body_file = await self.read_body(receive)
        except RequestAborted:
            return
        # Request is complete and can be served.
        set_script_prefix(self.get_script_prefix(scope))
        await sync_to_async(signals.request_started.send)(sender=self.__class__, scope=scope)
        # Get the request and check for basic issues.
        request, error_response = self.create_request(scope, body_file)
        if request is None:
            await self.send_response(error_response, send)
            return
        # Get the response, using a threadpool via sync_to_async, if needed.
        if asyncio.iscoroutinefunction(self.get_response):
            response = await self.get_response(request)
        else:
            # If get_response is synchronous, run it non-blocking.
            response = await sync_to_async(self.get_response)(request)
        response._handler_class = self.__class__
        # Increase chunk size on file responses (ASGI servers handles low-level
        # chunking).
        if isinstance(response, FileResponse):
            response.block_size = self.chunk_size
        # Send the response.
        await self.send_response(response, send)

    async def read_body(self, receive):
        """Reads a HTTP body from an ASGI connection."""
        # Use the tempfile that auto rolls-over to a disk file as it fills up,
        # if a maximum in-memory size is set. Otherwise use a BytesIO object.
        if settings.FILE_UPLOAD_MAX_MEMORY_SIZE is None:
            body_file = BytesIO()
        else:
            body_file = tempfile.SpooledTemporaryFile(max_size=settings.FILE_UPLOAD_MAX_MEMORY_SIZE, mode='w+b')
        while True:
            message = await receive()
            if message['type'] == 'http.disconnect':
                # Early client disconnect.
                raise RequestAborted()
            # Add a body chunk from the message, if provided.
            if 'body' in message:
                body_file.write(message['body'])
            # Quit out if that's the end.
            if not message.get('more_body', False):
                break
        body_file.seek(0)
        return body_file

    def create_request(self, scope, body_file):
        """
        Create the Request object and returns either (request, None) or
        (None, response) if there is an error response.
        """
        try:
            return self.request_class(scope, body_file), None
        except UnicodeDecodeError:
            logger.warning(
                'Bad Request (UnicodeDecodeError)',
                exc_info=sys.exc_info(),
                extra={'status_code': 400},
            )
            return None, HttpResponseBadRequest()
        except RequestDataTooBig:
            return None, HttpResponse('413 Payload too large', status=413)

    def handle_uncaught_exception(self, request, resolver, exc_info):
        """Last-chance handler for exceptions."""
        # There's no WSGI server to catch the exception further up
        # if this fails, so translate it into a plain text response.
        try:
            return super().handle_uncaught_exception(request, resolver, exc_info)
        except Exception:
            return HttpResponseServerError(
                traceback.format_exc() if settings.DEBUG else 'Internal Server Error',
                content_type='text/plain',
            )

    async def send_response(self, response, send):
        """Encode and send a response out over ASGI."""
        # Collect cookies into headers. Have to preserve header case as there
        # are some non-RFC compliant clients that require e.g. Content-Type.
        response_headers = []
        for header, value in response.items():
            if isinstance(header, str):
                header = header.encode('ascii')
            if isinstance(value, str):
                value = value.encode('latin1')
            response_headers.append((bytes(header), bytes(value)))
        for c in response.cookies.values():
            response_headers.append(
                (b'Set-Cookie', c.output(header='').encode('ascii').strip())
            )
        # Initial response message.
        await send({
            'type': 'http.response.start',
            'status': response.status_code,
            'headers': response_headers,
        })
        # Streaming responses need to be pinned to their iterator.
        if response.streaming:
            # Access `__iter__` and not `streaming_content` directly in case
            # it has been overridden in a subclass.
            for part in response:
                for chunk, _ in self.chunk_bytes(part):
                    await send({
                        'type': 'http.response.body',
                        'body': chunk,
                        # Ignore "more" as there may be more parts; instead,
                        # use an empty final closing message with False.
                        'more_body': True,
                    })
            # Final closing message.
            await send({'type': 'http.response.body'})
        # Other responses just need chunking.
        else:
            # Yield chunks of response.
            for chunk, last in self.chunk_bytes(response.content):
                await send({
                    'type': 'http.response.body',
                    'body': chunk,
                    'more_body': not last,
                })
        response.close()

    @classmethod
    def chunk_bytes(cls, data):
        """
        Chunks some data up so it can be sent in reasonable size messages.
        Yields (chunk, last_chunk) tuples.
        """
        position = 0
        if not data:
            yield data, True
            return
        while position < len(data):
            yield (
                data[position:position + cls.chunk_size],
                (position + cls.chunk_size) >= len(data),
            )
            position += cls.chunk_size

    def get_script_prefix(self, scope):
        """
        Return the script prefix to use from either the scope or a setting.
        """
        if settings.FORCE_SCRIPT_NAME:
            return settings.FORCE_SCRIPT_NAME
        return scope.get('root_path', '') or ''
