upstream-zulip/zerver/data_import/sequencer.py

from collections.abc import Callable
from typing import Generic, TypeVar

"""
This module helps you set up a bunch
of sequences, similar to how database
sequences work.

You need to be a bit careful here, since
you're dealing with a big singleton, but
for data imports that's usually easy to
manage.
"""

T = TypeVar("T")


def _seq() -> Callable[[], int]:
    i = 0

    def next_one() -> int:
        nonlocal i
        i += 1
        return i

    return next_one


def sequencer() -> Callable[[str], int]:
    """
    Use like this:

    NEXT_ID = sequencer()
    message_id = NEXT_ID('message')
    """
    seq_dict: dict[str, Callable[[], int]] = {}

    def next_one(name: str) -> int:
        if name not in seq_dict:
            seq_dict[name] = _seq()
        seq = seq_dict[name]
        return seq()

    return next_one


"""
NEXT_ID is a singleton used by an entire process, which is
almost always reasonable.  If you want to have two parallel
sequences, just use different `name` values.

This object gets created once and only once during the first
import of the file.
"""

NEXT_ID = sequencer()


class IdMapper(Generic[T]):
    def __init__(self) -> None:
        self.map: dict[T, int] = {}
        self.cnt = 0

    def has(self, their_id: T) -> bool:
        return their_id in self.map

    def get(self, their_id: T) -> int:
        if their_id in self.map:
            return self.map[their_id]

        self.cnt += 1
        our_id = self.cnt
        self.map[their_id] = our_id
        return our_id