Source code for azure.core.paging

# --------------------------------------------------------------------------
#
# Copyright (c) Microsoft Corporation. All rights reserved.
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# The MIT License (MIT)
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# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the ""Software""), to
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# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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# --------------------------------------------------------------------------
import itertools
from typing import (  # pylint: disable=unused-import
    Callable,
    Optional,
    TypeVar,
    Iterator,
    Iterable,
    Tuple,
)
import logging


_LOGGER = logging.getLogger(__name__)

ReturnType = TypeVar("ReturnType")
ResponseType = TypeVar("ResponseType")


class PageIterator(Iterator[Iterator[ReturnType]]):
    def __init__(
        self,
        get_next,  # type: Callable[[Optional[str]], ResponseType]
        extract_data,  # type: Callable[[ResponseType], Tuple[str, Iterable[ReturnType]]]
        continuation_token=None,  # type: Optional[str]
    ):
        """Return an iterator of pages.

        :param get_next: Callable that take the continuation token and return a HTTP response
        :param extract_data: Callable that take an HTTP response and return a tuple continuation token,
         list of ReturnType
        :param str continuation_token: The continuation token needed by get_next
        """
        self._get_next = get_next
        self._extract_data = extract_data
        self.continuation_token = continuation_token
        self._did_a_call_already = False
        self._response = None  # type: Optional[ResponseType]
        self._current_page = None  # type: Optional[Iterable[ReturnType]]

    def __iter__(self):
        """Return 'self'."""
        return self

    def __next__(self):
        # type: () -> Iterator[ReturnType]
        if self.continuation_token is None and self._did_a_call_already:
            raise StopIteration("End of paging")

        self._response = self._get_next(self.continuation_token)
        self._did_a_call_already = True

        self.continuation_token, self._current_page = self._extract_data(self._response)

        return iter(self._current_page)

    next = __next__  # Python 2 compatibility.


class ItemPaged(Iterator[ReturnType]):
    def __init__(self, *args, **kwargs):
        """Return an iterator of items.

        args and kwargs will be passed to the PageIterator constructor directly,
        except page_iterator_class
        """
        self._args = args
        self._kwargs = kwargs
        self._page_iterator = None
        self._page_iterator_class = self._kwargs.pop(
            "page_iterator_class", PageIterator
        )

    def by_page(self, continuation_token=None):
        # type: (Optional[str]) -> Iterator[Iterator[ReturnType]]
        """Get an iterator of pages of objects, instead of an iterator of objects.

        :param str continuation_token:
            An opaque continuation token. This value can be retrieved from the
            continuation_token field of a previous generator object. If specified,
            this generator will begin returning results from this point.
        :returns: An iterator of pages (themselves iterator of objects)
        """
        return self._page_iterator_class(
            continuation_token=continuation_token, *self._args, **self._kwargs
        )

    def __repr__(self):
        return "<iterator object azure.core.paging.ItemPaged at {}>".format(hex(id(self)))

    def __iter__(self):
        """Return 'self'."""
        return self

    def __next__(self):
        if self._page_iterator is None:
            self._page_iterator = itertools.chain.from_iterable(self.by_page())
        return next(self._page_iterator)

    next = __next__  # Python 2 compatibility.