#!/usr/bin/env python

"""Healthchecker for exabgp.

This program is to be used as a process for exabgp. It will announce
some VIP depending on the state of a check whose a third-party program
wrapped by this program.

To use, declare this program as a process in your
:file:`/etc/exabgp/exabgp.conf`::

    neighbor 192.0.2.1 {
       router-id 192.0.2.2;
       local-as 64496;
       peer-as 64497;
    }
    process watch-haproxy {
       run python -m exabgp healthcheck --cmd "curl -sf http://127.0.0.1/healthcheck" --label haproxy;
    }
    process watch-mysql {
       run python -m exabgp healthcheck --cmd "mysql -u check -e 'SELECT 1'" --label mysql;
    }

Use :option:`--help` to get options accepted by this program. A
configuration file is also possible. Such a configuration file looks
like this::

     debug
     name = haproxy
     interval = 10
     fast-interval = 1
     command = curl -sf http://127.0.0.1/healthcheck

The left-part of each line is the corresponding long option.

When using label for loopback selection, the provided value should
match the beginning of the label without the interface prefix. In the
example above, this means that you should have addresses on lo
labelled ``lo:haproxy1``, ``lo:haproxy2``, etc.

"""

from __future__ import print_function
from __future__ import unicode_literals

import sys
import os
import subprocess
import re
import logging
import logging.handlers
import argparse
import signal
import time
import collections

logger = logging.getLogger("healthcheck")

# Python 3.3+ or backport
from exabgp.vendoring.ipaddress import ip_network  # pylint: disable=F0401
from exabgp.vendoring.ipaddress import ip_address  # pylint: disable=F0401


def fix(f):
    def fixed(x):
        try:
            x = x.decode('ascii')
        except AttributeError:
            pass
        return f(x)

    return fixed


ip_network = fix(ip_network)
ip_address = fix(ip_address)


def enum(*sequential):
    """Create a simple enumeration."""
    return type(str("Enum"), (), dict(zip(sequential, sequential)))


def parse():
    """Parse arguments"""
    formatter = argparse.RawDescriptionHelpFormatter
    parser = argparse.ArgumentParser(description=sys.modules[__name__].__doc__, formatter_class=formatter)

    g = parser.add_mutually_exclusive_group()
    g.add_argument("--silent", "-s", action="store_true", default=False, help="don't log to console")
    g.add_argument(
        "--syslog-facility",
        "-sF",
        metavar="FACILITY",
        nargs='?',
        const="daemon",
        default="daemon",
        help=("log to syslog using FACILITY, " "default FACILITY is daemon"),
    )
    g.add_argument("--no-syslog", action="store_true", help="disable syslog logging")

    parser.add_argument(
        "--no-ack", "-a", action="store_true", default=False, help="set for exabgp 3.4 or 4.x when exabgp.api.ack=false"
    )
    parser.add_argument("--sudo", action="store_true", default=False, help="use sudo to setup ip addresses")
    parser.add_argument("--debug", "-d", action="store_true", default=False, help="enable debugging")

    parser.add_argument("--name", "-n", metavar="NAME", help="name for this healthchecker")
    parser.add_argument("--config", "-F", metavar="FILE", type=open, help="read configuration from a file")
    parser.add_argument(
        "--pid", "-p", metavar="FILE", type=argparse.FileType('w'), help="write PID to the provided file"
    )
    parser.add_argument("--user", metavar="USER", help="set user after setting loopback addresses")
    parser.add_argument("--group", metavar="GROUP", help="set group after setting loopback addresses")

    g = parser.add_argument_group("checking healthiness")
    g.add_argument(
        "--interval",
        "-i",
        metavar='N',
        default=5,
        type=float,
        help="wait N seconds between each healthcheck (zero to exit after first announcement)",
    )
    g.add_argument(
        "--fast-interval",
        "-f",
        metavar='N',
        default=1,
        type=float,
        dest="fast",
        help=("when a state change is about to occur, " "wait N seconds between each healthcheck"),
    )
    g.add_argument(
        "--timeout", "-t", metavar='N', default=5, type=int, help="wait N seconds for the check command to execute"
    )
    g.add_argument("--rise", metavar='N', default=3, type=int, help="check N times before considering the service up")
    g.add_argument("--fall", metavar='N', default=3, type=int, help="check N times before considering the service down")
    g.add_argument("--disable", metavar='FILE', type=str, help="if FILE exists, the service is considered disabled")
    g.add_argument("--command", "--cmd", "-c", metavar='CMD', type=str, help="command to use for healthcheck")

    g = parser.add_argument_group("advertising options")
    g.add_argument("--next-hop", "-N", metavar='IP', type=ip_address, help="self IP address to use as next hop")
    g.add_argument(
        "--ip",
        metavar='IP',
        type=ip_network,
        dest="ips",
        action="append",
        help="advertise this IP address or network (CIDR notation)",
    )
    g.add_argument("--local-preference", metavar='P', type=int, default=-1, help="advertise with local preference P")
    g.add_argument(
        "--deaggregate-networks",
        dest="deaggregate_networks",
        action="store_true",
        help="Deaggregate Networks specified in --ip",
    )
    g.add_argument("--no-ip-setup", action="store_false", dest="ip_setup", help="don't setup missing IP addresses")
    g.add_argument(
        "--dynamic-ip-setup",
        default=False,
        action="store_true",
        dest="ip_dynamic",
        help="delete existing loopback ips on state down and " "disabled, then restore loopback when up",
    )
    g.add_argument("--label", default=None, help="use the provided label to match loopback addresses")
    g.add_argument(
        "--start-ip", metavar='N', type=int, default=0, help="index of the first IP in the list of IP addresses"
    )
    g.add_argument(
        "--up-metric", metavar='M', type=int, default=100, help="first IP get the metric M when the service is up"
    )
    g.add_argument(
        "--down-metric", metavar='M', type=int, default=1000, help="first IP get the metric M when the service is down"
    )
    g.add_argument(
        "--disabled-metric",
        metavar='M',
        type=int,
        default=500,
        help=("first IP get the metric M " "when the service is disabled"),
    )
    g.add_argument(
        "--increase",
        metavar='M',
        type=int,
        default=1,
        help=("for each additional IP address, " "increase metric value by M"),
    )
    g.add_argument(
        "--community", metavar="COMMUNITY", type=str, default=None, help="announce IPs with the supplied community"
    )
    g.add_argument(
        "--extended-community",
        metavar="EXTENDEDCOMMUNITY",
        type=str,
        default=None,
        help="announce IPs with the supplied extended community",
    )
    g.add_argument(
        "--large-community",
        metavar="LARGECOMMUNITY",
        type=str,
        default=None,
        help="announce IPs with the supplied large community",
    )
    g.add_argument(
        "--disabled-community",
        metavar="DISABLEDCOMMUNITY",
        type=str,
        default=None,
        help="announce IPs with the supplied community when disabled",
    )
    g.add_argument("--as-path", metavar="ASPATH", type=str, default=None, help="announce IPs with the supplied as-path")
    g.add_argument("--up-as-path", metavar='ASPATH', type=str, default=None, help="announce IPs with the supplied as-path when the service is up")
    g.add_argument("--down-as-path", metavar='ASPATH', type=str, default=None, help="announce IPs with the supplied as-path when the service is down")
    g.add_argument("--disabled-as-path", metavar='ASPATH', type=str, default=None, help="announce IPs with the supplied as-path when the service is disabled")
    g.add_argument(
        "--withdraw-on-down",
        action="store_true",
        help=("Instead of increasing the metric on health failure, " "withdraw the route"),
    )
    g.add_argument("--path-id", metavar='PATHID', type=int, default=None, help="path ID to advertise for the route")
    g.add_argument("--neighbor", metavar='NEIGHBOR', type=str, dest="neighbors", action="append", help="advertise the route to the selected neigbors")

    g = parser.add_argument_group("reporting")
    g.add_argument("--execute", metavar='CMD', type=str, action="append", help="execute CMD on state change")
    g.add_argument(
        "--up-execute", metavar='CMD', type=str, action="append", help="execute CMD when the service becomes available"
    )
    g.add_argument(
        "--down-execute",
        metavar='CMD',
        type=str,
        action="append",
        help="execute CMD when the service becomes unavailable",
    )
    g.add_argument(
        "--disabled-execute", metavar='CMD', type=str, action="append", help="execute CMD when the service is disabled"
    )

    options = parser.parse_args()
    if options.config is not None:
        # A configuration file has been provided. Read each line and
        # build an equivalent command line.
        args = sum(
            [
                "--{0}".format(l.strip()).split("=", 1)
                for l in options.config.readlines()
                if not l.strip().startswith("#") and l.strip()
            ],
            [],
        )
        args = [x.strip() for x in args]
        args.extend(sys.argv[1:])
        options = parser.parse_args(args)
    return options


def setup_logging(debug, silent, name, syslog_facility, syslog):
    """Setup logger"""

    def syslog_address():
        """Return a sensible syslog address"""
        if sys.platform == "darwin":
            return "/var/run/syslog"
        if sys.platform.startswith("freebsd"):
            return "/var/run/log"
        if sys.platform.startswith("netbsd"):
            return "/var/run/log"
        if sys.platform.startswith("linux"):
            return "/dev/log"
        raise EnvironmentError("Unable to guess syslog address for your " "platform, try to disable syslog")

    logger.setLevel(debug and logging.DEBUG or logging.INFO)
    enable_syslog = syslog and not debug
    # To syslog
    if enable_syslog:
        facility = getattr(logging.handlers.SysLogHandler, "LOG_{0}".format(syslog_facility.upper()))
        sh = logging.handlers.SysLogHandler(address=str(syslog_address()), facility=facility)
        if name:
            healthcheck_name = "healthcheck-{0}".format(name)
        else:
            healthcheck_name = "healthcheck"
        sh.setFormatter(logging.Formatter("{0}[{1}]: %(message)s".format(healthcheck_name, os.getpid())))
        logger.addHandler(sh)
    # To console
    toconsole = hasattr(sys.stderr, "isatty") and sys.stderr.isatty() and not silent  # pylint: disable=E1101
    if toconsole:
        ch = logging.StreamHandler()
        ch.setFormatter(logging.Formatter("%(levelname)s[%(name)s] %(message)s"))
        logger.addHandler(ch)


def loopback_ips(label, label_only):
    """Retrieve loopback IP addresses"""
    logger.debug("Retrieve loopback IP addresses")
    addresses = []

    if sys.platform.startswith("linux"):
        # Use "ip" (ifconfig is not able to see all addresses)
        ipre = re.compile(r"^(?P<index>\d+):\s+(?P<name>\S+)\s+inet6?\s+" r"(?P<ip>[\da-f.:]+)/(?P<mask>\d+)\s+.*")
        labelre = re.compile(r".*\s+lo:(?P<label>\S+).*")
        cmd = subprocess.Popen("/sbin/ip -o address show dev lo".split(), shell=False, stdout=subprocess.PIPE)
    else:
        # Try with ifconfig
        ipre = re.compile(
            r"^inet6?\s+(alias\s+)?(?P<ip>[\da-f.:]+)\s+"
            r"(?:netmask 0x(?P<netmask>[0-9a-f]+)|"
            r"prefixlen (?P<mask>\d+)).*"
        )
        cmd = subprocess.Popen("/sbin/ifconfig lo0".split(), shell=False, stdout=subprocess.PIPE)
        labelre = re.compile(r"")
    for line in cmd.stdout:
        line = line.decode("ascii", "ignore").strip()
        mo = ipre.match(line)
        if not mo:
            continue
        if mo.group("mask"):
            mask = int(mo.group("mask"))
        else:
            mask = bin(int(mo.group("netmask"), 16)).count("1")
        try:
            ip = ip_network("{0}/{1}".format(mo.group("ip"), mask))
        except ValueError:
            continue
        if not ip.is_loopback:
            if label:
                lmo = labelre.match(line)
                if not lmo:
                    continue
                if lmo.groupdict().get("label", "").startswith(label):
                    addresses.append(ip)
            elif not label_only:
                addresses.append(ip)

    logger.debug("Loopback addresses: %s", addresses)
    return addresses


def loopback():
    lo = "lo0"
    if sys.platform.startswith("linux"):
        lo = "lo"
    return lo


def setup_ips(ips, label, sudo=False):
    """Setup missing IP on loopback interface"""

    existing = set(loopback_ips(label, False))
    toadd = set([ip_network(ip) for net in ips for ip in net]) - existing
    for ip in toadd:
        logger.debug("Setup loopback IP address %s", ip)
        with open(os.devnull, "w") as fnull:
            cmd = ["ip", "address", "add", str(ip), "dev", loopback()]
            if sudo:
                cmd.insert(0, "sudo")
            if label:
                cmd += ["label", "{0}:{1}".format(loopback(), label)]
            try:
                subprocess.check_call(cmd, stdout=fnull, stderr=fnull)
            except subprocess.CalledProcessError as e:
                # the IP address is already setup, ignoring
                if cmd[0] == "ip" and cmd[2] == "add" and e.returncode == 2:
                    continue
                raise e


def remove_ips(ips, label, sudo=False):
    """Remove added IP on loopback interface"""
    existing = set(loopback_ips(label, True))

    # Get intersection of IPs (ips setup, and IPs configured by ExaBGP)
    toremove = set([ip_network(ip) for net in ips for ip in net]) & existing
    for ip in toremove:
        logger.debug("Remove loopback IP address %s", ip)
        with open(os.devnull, "w") as fnull:
            cmd = ["ip", "address", "delete", str(ip), "dev", loopback()]
            if sudo:
                cmd.insert(0, "sudo")
            if label:
                cmd += ["label", "{0}:{1}".format(loopback(), label)]
            try:
                subprocess.check_call(cmd, stdout=fnull, stderr=fnull)
            except subprocess.CalledProcessError:
                logger.warn(
                    "Unable to remove loopback IP address %s - is \
                    healthcheck running as root?",
                    str(ip),
                )


def drop_privileges(user, group):
    """Drop privileges to specified user and group"""
    if group is not None:
        import grp

        gid = grp.getgrnam(group).gr_gid
        logger.debug("Dropping privileges to group {0}/{1}".format(group, gid))
        try:
            os.setresgid(gid, gid, gid)
        except AttributeError:
            os.setregid(gid, gid)
    if user is not None:
        import pwd

        uid = pwd.getpwnam(user).pw_uid
        logger.debug("Dropping privileges to user {0}/{1}".format(user, uid))
        try:
            os.setresuid(uid, uid, uid)
        except AttributeError:
            os.setreuid(uid, uid)


def check(cmd, timeout):
    """Check the return code of the given command.

    :param cmd: command to execute. If :keyword:`None`, no command is executed.
    :param timeout: how much time we should wait for command completion.
    :return: :keyword:`True` if the command was successful or
             :keyword:`False` if not or if the timeout was triggered.
    """
    if cmd is None:
        return True

    class Alarm(Exception):
        """Exception to signal an alarm condition."""

        pass

    def alarm_handler(number, frame):  # pylint: disable=W0613
        """Handle SIGALRM signal."""
        raise Alarm()

    logger.debug("Checking command %s", repr(cmd))
    p = subprocess.Popen(cmd, shell=True, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, preexec_fn=os.setpgrp)
    if timeout:
        signal.signal(signal.SIGALRM, alarm_handler)
        signal.alarm(timeout)
    try:
        stdout = None
        stdout, _ = p.communicate()
        if timeout:
            signal.alarm(0)
        if p.returncode != 0:
            logger.warn("Check command was unsuccessful: %s", p.returncode)
            if stdout.strip():
                logger.info("Output of check command: %s", stdout)
            return False
        logger.debug("Command was executed successfully %s %s", p.returncode, stdout)
        return True
    except Alarm:
        logger.warn("Timeout (%s) while running check command %s", timeout, cmd)
        os.killpg(p.pid, signal.SIGKILL)
        return False


def loop(options):
    """Main loop."""
    states = enum(
        "INIT",  # Initial state
        "DISABLED",  # Disabled state
        "RISING",  # Checks are currently succeeding.
        "FALLING",  # Checks are currently failing.
        "UP",  # Service is considered as up.
        "DOWN",  # Service is considered as down.
        "EXIT",  # Exit state
        "END",  # End state, exiting but without removing loopback and/or announced routes
    )

    def exabgp(target):
        """Communicate new state to ExaBGP"""
        if target not in (states.UP, states.DOWN, states.DISABLED, states.EXIT, states.END):
            return
        if target in (states.END,):
            return
        # if ips was deleted with dyn ip, re-setup them
        if target == states.UP and options.ip_dynamic:
            logger.info("service up, restoring loopback ips")
            setup_ips(options.ips, options.label, options.sudo)

        logger.info("send announces for %s state to ExaBGP", target)
        metric = vars(options).get("{0}_metric".format(str(target).lower()), 0)
        as_path = vars(options).get("{0}_as_path".format(str(target).lower()), None)
        if as_path is None:
            as_path = options.as_path
        for ip in options.ips:
            if options.withdraw_on_down or target is states.EXIT:
                command = "neighbor * announce" if target is states.UP else "neighbor * withdraw"
            else:
                command = "neighbor * announce"
            announce = "route {0} next-hop {1}".format(str(ip), options.next_hop or "self")

            if command == "neighbor * announce":
                announce = "{0} med {1}".format(announce, metric)
                if options.local_preference >= 0:
                    announce = "{0} local-preference {1}".format(announce, options.local_preference)
                if options.community or options.disabled_community:
                    community = options.community
                    if target in (states.DOWN, states.DISABLED):
                        if options.disabled_community:
                            community = options.disabled_community
                    if community:
                        announce = "{0} community [ {1} ]".format(announce, community)
                if options.extended_community:
                    announce = "{0} extended-community [ {1} ]".format(announce, options.extended_community)
                if options.large_community:
                    announce = "{0} large-community [ {1} ]".format(announce, options.large_community)
                if as_path:
                    announce = "{0} as-path [ {1} ]".format(announce, as_path)

            # append path ID if required
            if options.path_id:
                announce = "{0} path-information {1}".format(announce, options.path_id)

            # allow filtering neighbors that the route should be advertised to
            if options.neighbors:
                # routes are filtered to specific neighbors; format them and put into a list
                neighbors = ["neighbor {0}".format(neighbor) for neighbor in options.neighbors]
                # comma seperate the neighbor list and prepend to announcement command
                command = "{0} {1}".format(", ".join(neighbors), command)

            metric += options.increase

            # Send and flush command
            logger.debug("exabgp: {0} {1}".format(command, announce))
            print("{0} {1}".format(command, announce))
            sys.stdout.flush()

            # Wait for confirmation from ExaBGP if expected
            if options.no_ack:
                continue
            # if the program is not ran manually, do not read the input
            if hasattr(sys.stdout, "isatty") and sys.stdout.isatty():
                continue
            sys.stdin.readline()

        # dynamic ip management. When the service fail, remove the loopback
        if target in (states.EXIT,) and (options.ip_dynamic or options.ip_setup):
            logger.info("exiting, deleting loopback ips")
            remove_ips(options.ips, options.label, options.sudo)
        # dynamic ip management. When the service fail, remove the loopback
        if target in (states.DOWN, states.DISABLED) and options.ip_dynamic:
            logger.info("service down, deleting loopback ips")
            remove_ips(options.ips, options.label, options.sudo)

    def trigger(target):
        """Trigger a state change and execute the appropriate commands"""
        # Shortcut for RISING->UP and FALLING->UP
        if target == states.RISING and options.rise <= 1:
            target = states.UP
        elif target == states.FALLING and options.fall <= 1:
            target = states.DOWN

        # Log and execute commands
        logger.debug("Transition to %s", str(target))
        cmds = []
        cmds.extend(vars(options).get("{0}_execute".format(str(target).lower()), []) or [])
        cmds.extend(vars(options).get("execute", []) or [])
        for cmd in cmds:
            logger.debug("Transition to %s, execute `%s`", str(target), cmd)
            env = os.environ.copy()
            env.update({"STATE": str(target)})
            with open(os.devnull, "w") as fnull:
                subprocess.call(cmd, shell=True, stdout=fnull, stderr=fnull, env=env)

        return target

    def one(checks, state):
        """Execute one loop iteration."""
        disabled = options.disable is not None and os.path.exists(options.disable)
        successful = disabled or check(options.command, options.timeout)
        # FSM
        if state != states.DISABLED and disabled:
            state = trigger(states.DISABLED)
        elif state == states.INIT:
            if successful and options.rise <= 1:
                state = trigger(states.UP)
            elif successful:
                state = trigger(states.RISING)
                checks = 1
            else:
                state = trigger(states.FALLING)
                checks = 1
        elif state == states.DISABLED:
            if not disabled:
                state = trigger(states.INIT)
        elif state == states.RISING:
            if successful:
                checks += 1
                if checks >= options.rise:
                    state = trigger(states.UP)
            else:
                state = trigger(states.FALLING)
                checks = 1
        elif state == states.FALLING:
            if not successful:
                checks += 1
                if checks >= options.fall:
                    state = trigger(states.DOWN)
            else:
                state = trigger(states.RISING)
                checks = 1
        elif state == states.UP:
            if not successful:
                state = trigger(states.FALLING)
                checks = 1
        elif state == states.DOWN:
            if successful:
                state = trigger(states.RISING)
                checks = 1
        else:
            raise ValueError("Unhandled state: {0}".format(str(state)))

        # Send announces. We announce them on a regular basis in case
        # we lose connection with a peer and the adj-rib-out is disabled.
        exabgp(state)
        return checks, state

    checks = 0
    state = states.INIT
    # Do cleanups on SIGTERM
    def sigterm_handler(signum, frame):  # pylint: disable=W0612,W0613
        exabgp(states.EXIT)
        sys.exit(0)

    signal.signal(signal.SIGTERM, sigterm_handler)

    while os.getppid() != 1:
        checks, state = one(checks, state)

        try:
            # How much we should sleep?
            if state in (states.FALLING, states.RISING):
                time.sleep(options.fast)
            elif options.interval == 0:
                logger.info("interval set to zero, exiting after the announcement")
                exabgp(states.END)
                break
            else:
                time.sleep(options.interval)
        except KeyboardInterrupt:
            exabgp(states.EXIT)
            break


def main():
    """Entry point."""
    options = parse()
    setup_logging(options.debug, options.silent, options.name, options.syslog_facility, not options.no_syslog)
    if options.pid:
        options.pid.write("{0}\n".format(os.getpid()))
        options.pid.close()
    try:
        # Setup IP to use
        options.ips = options.ips or loopback_ips(options.label, False)
        if not options.ips:
            logger.error("No IP found")
            sys.exit(1)
        if options.ip_setup:
            setup_ips(options.ips, options.label, options.sudo)
        drop_privileges(options.user, options.group)

        # Parse defined networks into a list of IPs for advertisement
        if options.deaggregate_networks:
            options.ips = [ip_network(ip) for net in options.ips for ip in net]

        options.ips = collections.deque(options.ips)
        options.ips.rotate(-options.start_ip)
        options.ips = list(options.ips)
        # Main loop
        loop(options)
    except Exception as e:  # pylint: disable=W0703
        logger.exception("Uncaught exception: %s", e)
        sys.exit(1)


if __name__ == "__main__":
    main()
