import base64
import io
import json
import zlib

import msgpack
from requests.structures import CaseInsensitiveDict

from .compat import HTTPResponse, pickle, text_type


def _b64_decode_bytes(b):
    return base64.b64decode(b.encode("ascii"))


def _b64_decode_str(s):
    return _b64_decode_bytes(s).decode("utf8")


class Serializer(object):

    def dumps(self, request, response, body=None):
        response_headers = CaseInsensitiveDict(response.headers)

        if body is None:
            body = response.read(decode_content=False)

            # NOTE: 99% sure this is dead code. I'm only leaving it
            #       here b/c I don't have a test yet to prove
            #       it. Basically, before using
            #       `cachecontrol.filewrapper.CallbackFileWrapper`,
            #       this made an effort to reset the file handle. The
            #       `CallbackFileWrapper` short circuits this code by
            #       setting the body as the content is consumed, the
            #       result being a `body` argument is *always* passed
            #       into cache_response, and in turn,
            #       `Serializer.dump`.
            response._fp = io.BytesIO(body)

        # NOTE: This is all a bit weird, but it's really important that on
        #       Python 2.x these objects are unicode and not str, even when
        #       they contain only ascii. The problem here is that msgpack
        #       understands the difference between unicode and bytes and we
        #       have it set to differentiate between them, however Python 2
        #       doesn't know the difference. Forcing these to unicode will be
        #       enough to have msgpack know the difference.
        data = {
            u"response": {
                u"body": body,
                u"headers": dict(
                    (text_type(k), text_type(v)) for k, v in response.headers.items()
                ),
                u"status": response.status,
                u"version": response.version,
                u"reason": text_type(response.reason),
                u"strict": response.strict,
                u"decode_content": response.decode_content,
            }
        }

        # Construct our vary headers
        data[u"vary"] = {}
        if u"vary" in response_headers:
            varied_headers = response_headers[u"vary"].split(",")
            for header in varied_headers:
                header = text_type(header).strip()
                header_value = request.headers.get(header, None)
                if header_value is not None:
                    header_value = text_type(header_value)
                data[u"vary"][header] = header_value

        return b",".join([b"cc=4", msgpack.dumps(data, use_bin_type=True)])

    def loads(self, request, data):
        # Short circuit if we've been given an empty set of data
        if not data:
            return

        # Determine what version of the serializer the data was serialized
        # with
        try:
            ver, data = data.split(b",", 1)
        except ValueError:
            ver = b"cc=0"

        # Make sure that our "ver" is actually a version and isn't a false
        # positive from a , being in the data stream.
        if ver[:3] != b"cc=":
            data = ver + data
            ver = b"cc=0"

        # Get the version number out of the cc=N
        ver = ver.split(b"=", 1)[-1].decode("ascii")

        # Dispatch to the actual load method for the given version
        try:
            return getattr(self, "_loads_v{}".format(ver))(request, data)

        except AttributeError:
            # This is a version we don't have a loads function for, so we'll
            # just treat it as a miss and return None
            return

    def prepare_response(self, request, cached):
        """Verify our vary headers match and construct a real urllib3
        HTTPResponse object.
        """
        # Special case the '*' Vary value as it means we cannot actually
        # determine if the cached response is suitable for this request.
        # This case is also handled in the controller code when creating
        # a cache entry, but is left here for backwards compatibility.
        if "*" in cached.get("vary", {}):
            return

        # Ensure that the Vary headers for the cached response match our
        # request
        for header, value in cached.get("vary", {}).items():
            if request.headers.get(header, None) != value:
                return

        body_raw = cached["response"].pop("body")

        headers = CaseInsensitiveDict(data=cached["response"]["headers"])
        if headers.get("transfer-encoding", "") == "chunked":
            headers.pop("transfer-encoding")

        cached["response"]["headers"] = headers

        try:
            body = io.BytesIO(body_raw)
        except TypeError:
            # This can happen if cachecontrol serialized to v1 format (pickle)
            # using Python 2. A Python 2 str(byte string) will be unpickled as
            # a Python 3 str (unicode string), which will cause the above to
            # fail with:
            #
            #     TypeError: 'str' does not support the buffer interface
            body = io.BytesIO(body_raw.encode("utf8"))

        return HTTPResponse(body=body, preload_content=False, **cached["response"])

    def _loads_v0(self, request, data):
        # The original legacy cache data. This doesn't contain enough
        # information to construct everything we need, so we'll treat this as
        # a miss.
        return

    def _loads_v1(self, request, data):
        try:
            cached = pickle.loads(data)
        except ValueError:
            return

        return self.prepare_response(request, cached)

    def _loads_v2(self, request, data):
        try:
            cached = json.loads(zlib.decompress(data).decode("utf8"))
        except (ValueError, zlib.error):
            return

        # We need to decode the items that we've base64 encoded
        cached["response"]["body"] = _b64_decode_bytes(cached["response"]["body"])
        cached["response"]["headers"] = dict(
            (_b64_decode_str(k), _b64_decode_str(v))
            for k, v in cached["response"]["headers"].items()
        )
        cached["response"]["reason"] = _b64_decode_str(cached["response"]["reason"])
        cached["vary"] = dict(
            (_b64_decode_str(k), _b64_decode_str(v) if v is not None else v)
            for k, v in cached["vary"].items()
        )

        return self.prepare_response(request, cached)

    def _loads_v3(self, request, data):
        # Due to Python 2 encoding issues, it's impossible to know for sure
        # exactly how to load v3 entries, thus we'll treat these as a miss so
        # that they get rewritten out as v4 entries.
        return

    def _loads_v4(self, request, data):
        try:
            cached = msgpack.loads(data, raw=False)
        except ValueError:
            return

        return self.prepare_response(request, cached)
