# Copyright 2013 The Chromium Authors
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

# pylint: disable=W0702

import os
import signal
import subprocess
import sys
import time


def _IsLinux():
    """Return True if on Linux; else False."""
    return sys.platform.startswith('linux')


class Xvfb:
    """Class to start and stop Xvfb if relevant.  Nop if not Linux."""

    def __init__(self):
        self._pid = 0

    def Start(self):
        """Start Xvfb and set an appropriate DISPLAY environment.  Linux only.

        Copied from tools/code_coverage/coverage_posix.py
        """
        if not _IsLinux():
            return
        proc = subprocess.Popen(
            ['Xvfb', ':9', '-screen', '0', '1024x768x24', '-ac'],
            stdout=subprocess.PIPE,
            stderr=subprocess.STDOUT,
        )
        self._pid = proc.pid
        if not self._pid:
            raise Exception('Could not start Xvfb')
        os.environ['DISPLAY'] = ':9'

        # Now confirm, giving a chance for it to start if needed.
        for _ in range(10):
            proc = subprocess.Popen('xdpyinfo >/dev/null', shell=True)
            _, retcode = os.waitpid(proc.pid, 0)
            if retcode == 0:
                break
            time.sleep(0.25)
        if retcode != 0:
            raise Exception('Could not confirm Xvfb happiness')

    def Stop(self):
        """Stop Xvfb if needed.  Linux only."""
        if self._pid:
            try:
                os.kill(self._pid, signal.SIGKILL)
            except:
                pass
            del os.environ['DISPLAY']
            self._pid = 0