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from azure.core.pipeline import PipelineRequest, PipelineResponse
from azure.core.pipeline.policies import SansIOHTTPPolicy

class SyncToken(object):
    """The sync token structure
    """
    def __init__(self, token_id, value, sequence_number):
        self.token_id = token_id
        self.value = value
        self.sequence_number = sequence_number

    def __str__(self):
        return "{}={}".format(self.token_id, self.value)

    @classmethod
    def from_sync_token_string(cls, sync_token):
        try:
            position = sync_token.index(';sn=')
            sequence_number = int(sync_token[position+4:])
            id_value = sync_token[:position]
            position = id_value.index('=')
            token_id = id_value[:position]
            value = id_value[position+1:]
            return SyncToken(token_id, value, sequence_number)
        except ValueError:
            return None

class SyncTokenPolicy(SansIOHTTPPolicy):
    """A simple policy that enable the given callback
    with the response.

    :keyword callback raw_response_hook: Callback function. Will be invoked on response.
    """
    def __init__(self, **kwargs): # pylint: disable=unused-argument,super-init-not-called
        self._sync_token_header = "Sync-Token"
        self._sync_tokens = dict()

    def on_request(self, request): # type: ignore # pylint: disable=arguments-differ
        # type: (PipelineRequest) -> None
        """This is executed before sending the request to the next policy.

        :param request: The PipelineRequest object.
        :type request: ~azure.core.pipeline.PipelineRequest
        """
        sync_token_header = ",".join(str(x) for x in self._sync_tokens.values())
        if sync_token_header:
            request.http_request.headers.update({self._sync_token_header: sync_token_header})

    def on_response(self, request, response): # type: ignore # pylint: disable=arguments-differ
        # type: (PipelineRequest, PipelineResponse) -> None
        """This is executed after the request comes back from the policy.

        :param request: The PipelineRequest object.
        :type request: ~azure.core.pipeline.PipelineRequest
        :param response: The PipelineResponse object.
        :type response: ~azure.core.pipeline.PipelineResponse
        """
        sync_token_header = response.http_response.headers.get(self._sync_token_header)
        if not sync_token_header:
            return
        sync_token_strings = sync_token_header.split(',')
        if not sync_token_strings:
            return
        for sync_token_string in sync_token_strings:
            sync_token = SyncToken.from_sync_token_string(sync_token_string)
            if not sync_token:
                continue
            existing_token = self._sync_tokens.get(sync_token.token_id, None)
            if not existing_token:
                self._sync_tokens[sync_token.token_id] = sync_token
                continue
            if existing_token.sequence_number < sync_token.sequence_number:
                self._sync_tokens[sync_token.token_id] = sync_token
