bandsaunter/tests/terminal.py

"""A real terminal, for tests that have to see what a resize leaves behind.

Rendering to a wide `Console` and reading the text back cannot show this class
of bug at all.  Live rendering works by moving the cursor over the frame it
drew last time and overwriting it, and whether that lands where it should is a
property of the terminal, not of the renderable.  So the program is run in a
pty, the window is resized underneath it the way a window manager would, and
the bytes it writes are fed to a terminal emulator whose screen is then read.
"""
import codecs
import fcntl
import os
import pty
import select
import signal
import struct
import termios
import time


class Terminal:
    """One program running in a pty, with a screen that can be read back."""

    def __init__(self, argv, cols=100, rows=30, env=None):
        """``env`` is added to the child's environment, not substituted for it.

        It was accepted and silently ignored until a test that pointed the
        program at a throwaway settings directory wrote to the real one
        instead.
        """
        import pyte

        self.cols, self.rows = cols, rows
        self.screen = pyte.Screen(cols, rows)
        self.stream = pyte.Stream(self.screen)
        # Incremental, because a read can land in the middle of a multi-byte
        # character: decoding each chunk on its own turns the second half of a
        # box-drawing character into a replacement character, which then looks
        # exactly like the debris these tests are here to find.
        self._decoder = codecs.getincrementaldecoder("utf8")("replace")
        self.pid, self.fd = pty.fork()
        if self.pid == 0:                       # pragma: no cover -- the child
            child = dict(os.environ, TERM="xterm-256color",
                         PYTHONUNBUFFERED="1", **(env or {}))
            # rich reads COLUMNS and LINES in preference to asking the
            # terminal, so leaving them set would make every resize invisible
            # and every one of these tests pass for the wrong reason.
            child.pop("COLUMNS", None)
            child.pop("LINES", None)
            os.execvpe(argv[0], argv, child)
        self._set_size(cols, rows)

    def _set_size(self, cols: int, rows: int) -> None:
        fcntl.ioctl(self.fd, termios.TIOCSWINSZ,
                    struct.pack("HHHH", rows, cols, 0, 0))

    def resize(self, cols: int, rows: int) -> None:
        """Resize the window, exactly as a window manager does."""
        self.cols, self.rows = cols, rows
        self._set_size(cols, rows)
        os.kill(self.pid, signal.SIGWINCH)
        self.screen.resize(rows, cols)

    def pump(self, seconds: float = 1.0) -> None:
        """Read whatever the program writes for a while."""
        end = time.time() + seconds
        while time.time() < end:
            ready, _, _ = select.select([self.fd], [], [], 0.05)
            if not ready:
                continue
            try:
                data = os.read(self.fd, 65536)
            except OSError:
                break
            if not data:
                break
            self.stream.feed(self._decoder.decode(data))

    def send(self, text: str) -> None:
        os.write(self.fd, text.encode())

    def display(self) -> list[str]:
        return [line.rstrip() for line in self.screen.display]

    def text(self) -> str:
        return "\n".join(self.display())

    def close(self) -> None:
        for action in (lambda: os.kill(self.pid, signal.SIGKILL),
                       lambda: os.close(self.fd),
                       lambda: os.waitpid(self.pid, 0)):
            try:
                action()
            except OSError:
                pass

    def __enter__(self):
        return self

    def __exit__(self, *exc):
        self.close()
        return False


def stray_rows(lines: list[str], width: int) -> list[str]:
    """Rows that belong to a frame drawn for some other window size.

    A panel drawn at the current width starts and ends at the edges of the
    screen.  A row carrying box-drawing characters that does neither is a
    piece of a frame drawn when the window was a different shape -- the debris
    a resize leaves when nothing erases it.
    """
    out = []
    for line in lines:
        stripped = line.strip()
        if not stripped or not any(c in line for c in "╭╮╰╯│─"):
            continue
        starts = stripped[0] in "╭╰│─"
        ends = stripped[-1] in "╮╯│─"
        if not (starts and ends) or len(line) > width:
            out.append(line)
    return out