#!/usr/bin/env python
# License: GPLv3 Copyright: 2017, Kovid Goyal <kovid at kovidgoyal.net>

import atexit
import errno
import os
import stat
import tempfile
import time
from functools import partial

from calibre.constants import (
    __appname__, filesystem_encoding, islinux, ismacos, iswindows
)
from calibre_extensions import speedup
from calibre.utils.monotonic import monotonic

if iswindows:
    import msvcrt
    from calibre.constants import get_windows_username
    from calibre_extensions import winutil
    excl_file_mode = stat.S_IREAD | stat.S_IWRITE
else:
    excl_file_mode = stat.S_IRUSR | stat.S_IWUSR | stat.S_IRGRP | stat.S_IROTH
    import fcntl


def unix_open(path):
    flags = os.O_RDWR | os.O_CREAT
    has_cloexec = False
    if hasattr(speedup, 'O_CLOEXEC'):
        try:
            fd = os.open(path, flags | speedup.O_CLOEXEC, excl_file_mode)
            has_cloexec = True
        except OSError as err:
            # Kernel may not support O_CLOEXEC
            if err.errno != errno.EINVAL:
                raise

    if not has_cloexec:
        fd = os.open(path, flags, excl_file_mode)
        fcntl.fcntl(fd, fcntl.F_SETFD, fcntl.FD_CLOEXEC)
    return os.fdopen(fd, 'r+b')


def unix_retry(err):
    return err.errno in (errno.EACCES, errno.EAGAIN, errno.ENOLCK, errno.EINTR)


def windows_open(path):
    if isinstance(path, bytes):
        path = os.fsdecode(path)
    h = winutil.create_file(
        path,
        winutil.GENERIC_READ |
        winutil.GENERIC_WRITE,  # Open for reading and writing
        0,  # Open exclusive
        winutil.OPEN_ALWAYS,  # If file does not exist, create it
        winutil.FILE_ATTRIBUTE_NORMAL,  # Normal attributes
    )
    fd = msvcrt.open_osfhandle(int(h), 0)
    ans = os.fdopen(fd, 'r+b')
    h.detach()
    return ans


def windows_retry(err):
    return err.winerror in (
        winutil.ERROR_SHARING_VIOLATION, winutil.ERROR_LOCK_VIOLATION
    )


def retry_for_a_time(timeout, sleep_time, func, error_retry, *args):
    limit = monotonic() + timeout
    while True:
        try:
            return func(*args)
        except OSError as err:
            if not error_retry(err) or monotonic() > limit:
                raise
        time.sleep(sleep_time)


def lock_file(path, timeout=15, sleep_time=0.2):
    if iswindows:
        return retry_for_a_time(
            timeout, sleep_time, windows_open, windows_retry, path
        )
    f = unix_open(path)
    try:
        retry_for_a_time(
            timeout, sleep_time, fcntl.flock, unix_retry,
            f.fileno(), fcntl.LOCK_EX | fcntl.LOCK_NB
        )
    except Exception:
        f.close()
        raise
    return f


class ExclusiveFile:

    def __init__(self, path, timeout=15, sleep_time=0.2):
        if iswindows and isinstance(path, bytes):
            path = path.decode(filesystem_encoding)
        self.path = path
        self.timeout = timeout
        self.sleep_time = sleep_time

    def __enter__(self):
        self.file = lock_file(self.path, self.timeout, self.sleep_time)
        return self.file

    def __exit__(self, type, value, traceback):
        self.file.close()


def _clean_lock_file(file_obj):
    try:
        os.remove(file_obj.name)
    except OSError:
        pass
    try:
        file_obj.close()
    except OSError:
        pass


if iswindows:
    def create_single_instance_mutex(name, per_user=True):
        mutexname = '{}-singleinstance-{}-{}'.format(
            __appname__, (get_windows_username() if per_user else ''), name
        )
        try:
            mutex = winutil.create_mutex(mutexname, False)
        except FileExistsError:
            return
        return mutex.close

elif islinux:

    def create_single_instance_mutex(name, per_user=True):
        import socket
        from calibre.utils.ipc import eintr_retry_call
        name = '{}-singleinstance-{}-{}'.format(
            __appname__, (os.geteuid() if per_user else ''), name
        )
        name = name
        address = '\0' + name.replace(' ', '_')
        sock = socket.socket(family=socket.AF_UNIX)
        try:
            eintr_retry_call(sock.bind, address)
        except OSError as err:
            sock.close()
            if getattr(err, 'errno', None) == errno.EADDRINUSE:
                return
            raise
        fd = sock.fileno()
        old_flags = fcntl.fcntl(fd, fcntl.F_GETFD)
        fcntl.fcntl(fd, fcntl.F_SETFD, old_flags | fcntl.FD_CLOEXEC)
        return sock.close

else:

    def singleinstance_path(name, per_user=True):
        name = '{}-singleinstance-{}-{}.lock'.format(
            __appname__, (os.geteuid() if per_user else ''), name
        )
        home = os.path.expanduser('~')
        locs = ['/var/lock', home, tempfile.gettempdir()]
        if ismacos:
            locs.insert(0, '/Library/Caches')
        for loc in locs:
            if os.access(loc, os.W_OK | os.R_OK | os.X_OK):
                return os.path.join(loc, ('.' if loc is home else '') + name)
        raise OSError(
            'Failed to find a suitable filesystem location for the lock file'
        )

    def create_single_instance_mutex(name, per_user=True):
        from calibre.utils.ipc import eintr_retry_call
        path = singleinstance_path(name, per_user)
        f = open(path, 'w')
        try:
            eintr_retry_call(fcntl.lockf, f.fileno(), fcntl.LOCK_EX | fcntl.LOCK_NB)
            return partial(_clean_lock_file, f)
        except OSError as err:
            f.close()
            if err.errno not in (errno.EAGAIN, errno.EACCES):
                raise


class SingleInstance:

    def __init__(self, name):
        self.name = name
        self.release_mutex = None

    def __enter__(self):
        self.release_mutex = create_single_instance_mutex(self.name)
        return self.release_mutex is not None

    def __exit__(self, *a):
        if self.release_mutex is not None:
            self.release_mutex()
            self.release_mutex = None


def singleinstance(name):
    ' Ensure that only a single process exists with the specified mutex key '
    release_mutex = create_single_instance_mutex(name)
    if release_mutex is None:
        return False
    atexit.register(release_mutex)
    return True
