
# Authors: William Fagan
# Copyright (c) 2013-2017 William Fagan
# License: The MIT License (MIT)

import sys
import functools
from gzip import GzipFile
import zlib
from io import BytesIO

from collections import defaultdict

import brotli
from flask import request, after_this_request, current_app


if sys.version_info[:2] == (2, 6):
    class GzipFile(GzipFile):
        """ Backport of context manager support for python 2.6"""
        def __enter__(self):
            if self.fileobj is None:
                raise ValueError("I/O operation on closed GzipFile object")
            return self

        def __exit__(self, *args):
            self.close()


class DictCache(object):

    def __init__(self):
        self.data = {}

    def get(self, key):
        return self.data.get(key)

    def set(self, key, value):
        self.data[key] = value


class Compress(object):
    """
    The Compress object allows your application to use Flask-Compress.

    When initialising a Compress object you may optionally provide your
    :class:`flask.Flask` application object if it is ready. Otherwise,
    you may provide it later by using the :meth:`init_app` method.

    :param app: optional :class:`flask.Flask` application object
    :type app: :class:`flask.Flask` or None
    """
    def __init__(self, app=None):
        """
        An alternative way to pass your :class:`flask.Flask` application
        object to Flask-Compress. :meth:`init_app` also takes care of some
        default `settings`_.

        :param app: the :class:`flask.Flask` application object.
        """
        self.app = app
        if app is not None:
            self.init_app(app)

    def init_app(self, app):
        defaults = [
            ('COMPRESS_MIMETYPES', ['text/html', 'text/css', 'text/xml',
                                    'application/json',
                                    'application/javascript']),
            ('COMPRESS_LEVEL', 6),
            ('COMPRESS_BR_LEVEL', 4),
            ('COMPRESS_BR_MODE', 0),
            ('COMPRESS_BR_WINDOW', 22),
            ('COMPRESS_BR_BLOCK', 0),
            ('COMPRESS_DEFLATE_LEVEL', -1),
            ('COMPRESS_MIN_SIZE', 500),
            ('COMPRESS_CACHE_KEY', None),
            ('COMPRESS_CACHE_BACKEND', None),
            ('COMPRESS_REGISTER', True),
            ('COMPRESS_ALGORITHM', ['br', 'gzip', 'deflate']),
        ]

        for k, v in defaults:
            app.config.setdefault(k, v)

        backend = app.config['COMPRESS_CACHE_BACKEND']
        self.cache = backend() if backend else None
        self.cache_key = app.config['COMPRESS_CACHE_KEY']

        algo = app.config['COMPRESS_ALGORITHM']
        if isinstance(algo, str):
            self.enabled_algorithms = [i.strip() for i in algo.split(',')]
        else:
            self.enabled_algorithms = list(algo)

        if (app.config['COMPRESS_REGISTER'] and
                app.config['COMPRESS_MIMETYPES']):
            app.after_request(self.after_request)

    def _choose_compress_algorithm(self, accept_encoding_header):
        """
        Determine which compression algorithm we're going to use based on the
        client request. The `Accept-Encoding` header may list one or more desired
        algorithms, together with a "quality factor" for each one (higher quality
        means the client prefers that algorithm more).

        :param accept_encoding_header: Content of the `Accept-Encoding` header
        :return: name of a compression algorithm (`gzip`, `deflate`, `br`) or `None` if
            the client and server don't agree on any.
        """
        # A flag denoting that client requested using any (`*`) algorithm,
        # in case a specific one is not supported by the server
        fallback_to_any = False

        # Map quality factors to requested algorithm names.
        algos_by_quality = defaultdict(set)

        # Set of supported algorithms
        server_algos_set = set(self.enabled_algorithms)

        for part in accept_encoding_header.lower().split(','):
            part = part.strip()
            if ';q=' in part:
                # If the client associated a quality factor with an algorithm,
                # try to parse it. We could do the matching using a regex, but
                # the format is so simple that it would be overkill.
                algo = part.split(';')[0].strip()
                try:
                    quality = float(part.split('=')[1].strip())
                except ValueError:
                    quality = 1.0
            else:
                # Otherwise, use the default quality
                algo = part
                quality = 1.0

            if algo == '*':
                if quality > 0:
                    fallback_to_any = True
            elif algo == 'identity':  # identity means 'no compression asked'
                algos_by_quality[quality].add(None)
            elif algo in server_algos_set:
                algos_by_quality[quality].add(algo)

        # Choose the algorithm with the highest quality factor that the server supports.
        #
        # If there are multiple equally good options, choose the first supported algorithm
        # from server configuration.
        #
        # If the server doesn't support any algorithm that the client requested but
        # there's a special wildcard algorithm request (`*`), choose the first supported
        # algorithm.
        for _, viable_algos in sorted(algos_by_quality.items(), reverse=True):
            if len(viable_algos) == 1:
                return viable_algos.pop()
            elif len(viable_algos) > 1:
                for server_algo in self.enabled_algorithms:
                    if server_algo in viable_algos:
                        return server_algo

        if fallback_to_any:
            return self.enabled_algorithms[0]
        return None

    def after_request(self, response):
        app = self.app or current_app

        vary = response.headers.get('Vary')
        if not vary:
            response.headers['Vary'] = 'Accept-Encoding'
        elif 'accept-encoding' not in vary.lower():
            response.headers['Vary'] = '{}, Accept-Encoding'.format(vary)

        accept_encoding = request.headers.get('Accept-Encoding', '')
        chosen_algorithm = self._choose_compress_algorithm(accept_encoding)

        if (chosen_algorithm is None or
            response.mimetype not in app.config["COMPRESS_MIMETYPES"] or
            response.status_code < 200 or
            response.status_code >= 300 or
            response.is_streamed or
            "Content-Encoding" in response.headers or
            (response.content_length is not None and
             response.content_length < app.config["COMPRESS_MIN_SIZE"])):
            return response

        response.direct_passthrough = False

        if self.cache is not None:
            key = self.cache_key(request)
            compressed_content = self.cache.get(key)
            if compressed_content is None:
                compressed_content = self.compress(app, response, chosen_algorithm)
            self.cache.set(key, compressed_content)
        else:
            compressed_content = self.compress(app, response, chosen_algorithm)

        response.set_data(compressed_content)

        response.headers['Content-Encoding'] = chosen_algorithm
        response.headers['Content-Length'] = response.content_length

        # "123456789"   => "123456789:gzip"   - A strong ETag validator
        # W/"123456789" => W/"123456789:gzip" - A weak ETag validator
        etag = response.headers.get('ETag')
        if etag:
            response.headers['ETag'] = '{0}:{1}"'.format(etag[:-1], chosen_algorithm)

        return response

    def compressed(self):
        def decorator(f):
            @functools.wraps(f)
            def decorated_function(*args, **kwargs):
                @after_this_request
                def compressor(response):
                    return self.after_request(response)
                return f(*args, **kwargs)
            return decorated_function
        return decorator

    def compress(self, app, response, algorithm):
        if algorithm == 'gzip':
            gzip_buffer = BytesIO()
            with GzipFile(mode='wb',
                          compresslevel=app.config['COMPRESS_LEVEL'],
                          fileobj=gzip_buffer) as gzip_file:
                gzip_file.write(response.get_data())
            return gzip_buffer.getvalue()
        elif algorithm == 'deflate':
            return zlib.compress(response.get_data(),
                                 app.config['COMPRESS_DEFLATE_LEVEL'])
        elif algorithm == 'br':
            return brotli.compress(response.get_data(),
                                   mode=app.config['COMPRESS_BR_MODE'],
                                   quality=app.config['COMPRESS_BR_LEVEL'],
                                   lgwin=app.config['COMPRESS_BR_WINDOW'],
                                   lgblock=app.config['COMPRESS_BR_BLOCK'])
