Mini Shell

import contextlib
import itertools
import logging
import sys
import time
from typing import IO, Generator, Optional

from pip._internal.utils.compat import WINDOWS
from pip._internal.utils.logging import get_indentation

logger = logging.getLogger(__name__)


class SpinnerInterface:
    def spin(self) -> None:
        raise NotImplementedError()

    def finish(self, final_status: str) -> None:
        raise NotImplementedError()


class InteractiveSpinner(SpinnerInterface):
    def __init__(
        self,
        message: str,
        file: Optional[IO[str]] = None,
        spin_chars: str = "-\\|/",
        # Empirically, 8 updates/second looks nice
        min_update_interval_seconds: float = 0.125,
    ):
        self._message = message
        if file is None:
            file = sys.stdout
        self._file = file
        self._rate_limiter = RateLimiter(min_update_interval_seconds)
        self._finished = False

        self._spin_cycle = itertools.cycle(spin_chars)

        self._file.write(" " * get_indentation() + self._message + " ... ")
        self._width = 0

    def _write(self, status: str) -> None:
        assert not self._finished
        # Erase what we wrote before by backspacing to the beginning, writing
        # spaces to overwrite the old text, and then backspacing again
        backup = "\b" * self._width
        self._file.write(backup + " " * self._width + backup)
        # Now we have a blank slate to add our status
        self._file.write(status)
        self._width = len(status)
        self._file.flush()
        self._rate_limiter.reset()

    def spin(self) -> None:
        if self._finished:
            return
        if not self._rate_limiter.ready():
            return
        self._write(next(self._spin_cycle))

    def finish(self, final_status: str) -> None:
        if self._finished:
            return
        self._write(final_status)
        self._file.write("\n")
        self._file.flush()
        self._finished = True


# Used for dumb terminals, non-interactive installs (no tty), etc.
# We still print updates occasionally (once every 60 seconds by default) to
# act as a keep-alive for systems like Travis-CI that take lack-of-output as
# an indication that a task has frozen.
class NonInteractiveSpinner(SpinnerInterface):
    def __init__(self, message: str, min_update_interval_seconds: float = 60.0) -> None:
        self._message = message
        self._finished = False
        self._rate_limiter = RateLimiter(min_update_interval_seconds)
        self._update("started")

    def _update(self, status: str) -> None:
        assert not self._finished
        self._rate_limiter.reset()
        logger.info("%s: %s", self._message, status)

    def spin(self) -> None:
        if self._finished:
            return
        if not self._rate_limiter.ready():
            return
        self._update("still running...")

    def finish(self, final_status: str) -> None:
        if self._finished:
            return
        self._update(f"finished with status '{final_status}'")
        self._finished = True


class RateLimiter:
    def __init__(self, min_update_interval_seconds: float) -> None:
        self._min_update_interval_seconds = min_update_interval_seconds
        self._last_update: float = 0

    def ready(self) -> bool:
        now = time.time()
        delta = now - self._last_update
        return delta >= self._min_update_interval_seconds

    def reset(self) -> None:
        self._last_update = time.time()


@contextlib.contextmanager
def open_spinner(message: str) -> Generator[SpinnerInterface, None, None]:
    # Interactive spinner goes directly to sys.stdout rather than being routed
    # through the logging system, but it acts like it has level INFO,
    # i.e. it's only displayed if we're at level INFO or better.
    # Non-interactive spinner goes through the logging system, so it is always
    # in sync with logging configuration.
    if sys.stdout.isatty() and logger.getEffectiveLevel() <= logging.INFO:
        spinner: SpinnerInterface = InteractiveSpinner(message)
    else:
        spinner = NonInteractiveSpinner(message)
    try:
        with hidden_cursor(sys.stdout):
            yield spinner
    except KeyboardInterrupt:
        spinner.finish("canceled")
        raise
    except Exception:
        spinner.finish("error")
        raise
    else:
        spinner.finish("done")


HIDE_CURSOR = "\x1b[?25l"
SHOW_CURSOR = "\x1b[?25h"


@contextlib.contextmanager
def hidden_cursor(file: IO[str]) -> Generator[None, None, None]:
    # The Windows terminal does not support the hide/show cursor ANSI codes,
    # even via colorama. So don't even try.
    if WINDOWS:
        yield
    # We don't want to clutter the output with control characters if we're
    # writing to a file, or if the user is running with --quiet.
    # See https://github.com/pypa/pip/issues/3418
    elif not file.isatty() or logger.getEffectiveLevel() > logging.INFO:
        yield
    else:
        file.write(HIDE_CURSOR)
        try:
            yield
        finally:
            file.write(SHOW_CURSOR)