#!/usr/bin/python3


import asyncio
import collections
from   concurrent.futures   import ThreadPoolExecutor
import contextlib
import enum
import itertools
import json
import logging
import re
import os
import signal
import socket
import sys
import time
import threading
import traceback

import docker
import MySQLdb
from   sqlalchemy import desc
import sqlalchemy.orm.scoping

from database import *

HOST_PATH="/vol/host/"

##################################################
# default number of concurrent tasks

# pushing images from the sandbox to the registry
NB_PUSH_SANDBOX = 2

# pulling images from the registry to the sandbox
NB_PULL_SANDBOX = 2

# pulling images from the registry to the swarm
NB_PULL_SWARM   = 2

# sandbox actions (start, stop, commit, ...)
NB_SANDBOX_TASKS = 4

# jobs
NB_JOB_TASKS     = 4


# default thread pool (used by most of the tasks)
default_executor = ThreadPoolExecutor(10)

##################################################

log = logging.getLogger("controller")

assert MySQLdb.threadsafety >= 1


class Error(Exception):
    pass

class ShuttingDown(Exception):
    pass

def docker_check_error(func, *k, **kw):
    """Wrapper for docker-py methods that produce a stream

    Methods producing a stram (eg: push, build) do not report all errors
    by raising exceptions. Some errors are reported later in the stream.

    This function parses the stream and raise Error() if needed.
    """
    for elem in func(*k, stream=True, **kw):
        js = json.loads(elem.decode())
        if "error" in js:
            raise Error("push error: " + js["error"])

@contextlib.contextmanager
def docker_warning(msg, *k, ignore=None):
    """Catch docker errors and issue a warning instead"""
    try:
        yield
    except docker.errors.APIError as e:
        if ignore is None or not isinstance(e, ignore):
            k += e,
            log.warning(msg + " (%s)", *k)

@contextlib.contextmanager
def report_error(fmt, *k):
    try:
        yield
    except Exception as e:
        msg = fmt % k
        log_func = log.error if isinstance(e, Error) else log.exception
        log_func("%s (%s)", msg,
                traceback.format_exception_only(type(e), e)[-1].strip())
        raise

def auto_create_task(func):
    """Decorator for forcing the creation of a task when a coroutine function is called

    Return a wrappers that calls the function, create the task on the fly and
    return it. Also it installs a no-op callback to avoid warnings in case the
    result is not used.
    """
    assert asyncio.iscoroutinefunction(func)

    def wrapper(*k, **kw):
        tsk = asyncio.async(func(*k, **kw))
        # ignore warning about result not used
        tsk.add_done_callback(lambda f: f.exception())
        return tsk
    return wrapper

def cascade_future(src, dst):
    """propagate the result of a future to another future
    
    This function installs a callback to the future `src`, that propagates its
    result to the future `dst`.
    """
    def callback(fut):
        ex = fut.exception()
        if ex is None:
            dst.set_result(fut.result())
        else:
            dst.set_exception(ex)

    if src.done():
        callback(src)
    else:
        src.add_done_callback(callback)

class Manager:
    """A class for scheduling asynchronous jobs on a collection of keys

    (the one-line summary is not very helpful, sorry)
    

    Job submission

    The job is scheduled on key KEY by calling .process(KEY), the function
    returns an asyncio.Future object (which will receive the result)

    If .process(KEY) is called while a job is already running for KEY, then the
    manager arranges the job to be run a second time in a row for the same key


    Job implementation

    This is an abstract class. The job shall be implemented as the coroutine
    named ._process() in the inherited class.

    The manager guarantees that ._process() cannot be called multiple times
    concurrently for the same key

    In case a shutdown is requested (see .shutdown()):
     - all jobs that are not yet started are cancelled
     - running jobs continue until they return or until they try to acquire the
       internal semaphore (which raises ShuttingDown())


    Concurrency

    The job tasks are all started immediately (whatever the number of existing
    jobs)

    It is possible to limit the concurrency to a maximum number of parallel
    tasks. Manager provides an internal semaphore (the number of tokens is set
    in .__init__())

    The semaphore can be locked in two ways:
     - by locking the manager:

            with (yield from self): ... concurrency limited to `nb_tokens`
            tasks ...

     - by calling .run_in_executor (this is for running non-async code):

            yield from self.run_in_executor(func, args...)

    Shutdown

    When .shutdown() is called the Manager ensures that all jobs are properly
    terminated
     - it cancels all jobs that are not yet started
     - it prevents starting new jobs
     - it lets running pending jobs, but interrupts them if they when ther try
       to acquire the internal semaphore

    All cancel/interrupted tasks have their future raise ShuttingDown().

    .shutdown() returns after all pending jobs are terminated.


    Thread safety

    - Manager is *not* thread safe, all public methods must be called from the
      same thread
    """

    class _Handle:
        __slots__ = "key", "cur", "nxt"

    def __init__(self, nb_tokens=1, *, executor = default_executor):
        # {key: _TaskHandler}
        self._handles = {}
        self._semaphore = asyncio.Semaphore(nb_tokens)
        self._shutdown = None
        self._executor = executor

    def _create_task(self, hnd):
        assert hnd.nxt is None
        def reset():
            assert not hnd.cur.done()
            nxt = hnd.nxt
            if nxt is not None:
                cascade_future(hnd.cur, nxt)
                hnd.nxt = None

        hnd.cur = asyncio.async(self._process(hnd.key, reset))
        hnd.cur.add_done_callback(lambda fut: self._done(hnd))
        log.debug("task scheduled %r %r", self, hnd.key)
        return hnd.cur

    def process(self, key):
        """Schedule the job to be run on key `key`

        returns an asyncio.Future (that will provide the result of ._process())
        """
        if self._shutdown is not None:
            return self._shutdown

        hnd = self._handles.get(key)
        if hnd is None:
            # create handle
            self._handles[key] = hnd = self._Handle()
            hnd.key = key
            hnd.cur = None
            hnd.nxt = None

        if hnd.cur is None:
            # create task
            return self._create_task(hnd)
        else:
            # reschedule task
            if hnd.nxt is None:
                hnd.nxt = asyncio.Future()
            return hnd.nxt

    def _done(self, hnd):

        assert hnd is self._handles.get(hnd.key)
        assert hnd.cur.done()

        try:
            hnd.cur.result()
        except Exception:
            log.exception("task %r %r unhandled exception", self, hnd.key)

        nxt     = hnd.nxt
        hnd.cur = hnd.nxt = None
        if nxt is None:
            del self._handles[hnd.key]
        else:
            cascade_future(self._create_task(hnd), nxt)


    @asyncio.coroutine
    def __iter__(self):
        """Coroutine for locking the internal semaphore
        
        Usage:
            with (yield from manager):
              ...

        Warning:
            after a shutdown is initiated, this function will always raise
            ShuttingDown()
        """
        ctx = yield from iter(self._semaphore)
        if self._shutdown:
            with ctx:
                raise ShuttingDown()
        return ctx


    @asyncio.coroutine
    def run_in_executor(self, *k):
        """Run a function in a separate thread (with limited concurrency)

        This function locks the internal semaphore and runs the provided
        functionc call in a separate thread (using the executor)
        """
        with (yield from self):
            return (yield from asyncio.get_event_loop().run_in_executor(self._executor, *k))


    def _process(self, key, reset):
        """Actual implementation of the job (to be reimplemented in inherited classes)

        The Manager class guarantees that this function cannot be called
        multiple times concurrently on the same key (in case the same key is
        submitted multiple times, they Manager will call this function a second
        time after it has terminated).

        `reset` is a function that may be called to reset the 'dirty' state of
        this key (this is to avoid calling ._process() a second time if not
        necessary)
        """
        raise NotImplementedError()

    @asyncio.coroutine
    def shutdown(self):
        """Initiate a graceful shutdown

        This coroutine terminates once all tasks are properly terminated.
        """
        self._shutdown = asyncio.Future()
        self._shutdown.set_exception(ShuttingDown())
        self._shutdown.exception()  # to avoid asyncio warnings
        # cancel all 'next' tasks
        for hnd in self._handles.values():
            if hnd.nxt is not None:
                hnd.nxt.set_exception(self._shutdown)
                hnd.nxt = None

        yield from asyncio.gather(*(h.cur for h in self._handles.values() if h.cur is not None),
                return_exceptions=True)


class SandboxManager(Manager):
    """Manager for sandbox operation

    This manager handles all sandbox operations (start, stop, commit).

    Operations are requested asynchronously in the database:
     - Webapp.sandbox_state=starting (for starting a sandbox)
     - Webapp.sandbox_state=stopping (for stopping a sandbox)
     - WebappVersion with state=sandbox (for committing a new image)

    All state changes on Webapp.sandbox_state are atomic (e.g: if the user
    requests a stop while the sandbox is starting then the manager finishes
    with starting the sandbox but does not update the state, and it runs
    immediately again to stop the sandbox)

    Whatever is the value of Webapp.sandbox_state, the manager first examines
    commit requests and makes the commit if requested.

    If the container already exists before starting the webapp (not possible in
    normal operations), then a recovery image is committed first.

    When a commit is successful. The image manager is notified for pushing the
    image to the registry and (if it is not a recovery image) to pull it to the
    swarm (because this image will very likely be used soon).

    State changes:

     - sandbox start:
            starting->running     (normal case)
            starting->start_error (error case)

     - sandbox stop:
            stopping->idle        (normal case)
            stopping->stop_error  (error case)

     - image commit:
            sandbox->committed  (normal case)
            sandbox->error      (error case)
            (none)->committed   (recovery version) 
    """

    def __init__(self, ctrl, nb_threads = NB_SANDBOX_TASKS):
        super().__init__(nb_threads)
        self.ctrl = ctrl


    def inspect_sandbox(self, webapp):
        try:
            return self.ctrl.sandbox.inspect_container(
                    self.ctrl.gen_sandbox_name(webapp))
        except docker.errors.NotFound:
            return None

    @staticmethod
    def filter_sandbox_version(query, webapp_id):
        """Narrow a WebappVersion query to filter the version that must be started in the sandbox"""

        return (query.
                # filter the right webapp
                filter_by(webapp_id=webapp_id)
                # keep only versions whose state is 'ready' or 'committed'
                .filter(WebappVersion.state.in_((int(VersionState.committed), int(VersionState.ready))))
                # take the latest one
                .order_by(desc(WebappVersion.id)).limit(1))

    @staticmethod
    def filter_commit_version(query, webapp_id):
        """Narrow a WebappVersion query to select the candidate versions to be committed"""
        return (query.
                filter_by(webapp_id=webapp_id,
                         state = int(VersionState.sandbox))
                    )

    def _start(self, webapp, version):
        """Start a webapp sandbox

        (to be executed in a thread pool)
        """

        ctrl = self.ctrl
        ses  = ctrl.session

        # prepare sandbox parameters

        # docker image
        if version is None:
            image = "%s/factory/%s:%s" % (self.ctrl.registry,
                    webapp.docker_os.docker_name,
                    webapp.docker_os.version)
        else:
            image = "%s:%s" % (webapp.image_name, version.number)

        log.debug("sandbox %r: using image %r", webapp.docker_name, image)

        # safety checks
        # (because docker_name is used it the paths of the external volumes
        if ("/" in webapp.docker_name) or (webapp.docker_name in ("", ".", "..")):
            raise Error("malformatted docker_name")

        pipebin = os.path.join(ctrl.sandbox_path, "bin")
        pipedir = os.path.join(ctrl.sandbox_path, "srvdir", webapp.docker_name)

        uid = webapp.id + 2000
        if uid < 2000:
            # just for safety
            raise Error("bad webapp id")

        # remove stale container (if any)
        if self.inspect_sandbox(webapp) is not None:
            self._stop(webapp)

        container = webapp.sandbox_name
        try:
            # prepare the sandbox
            # (create files for pipesrv)
            ctrl.sandbox.create_container("busybox:latest", name=container,
                    command = ["/bin/sh", "-c", "set -x ;rm -rf -- /.pipedir/* && chmod 0700 /.pipedir && mkfifo -m 0600 /.pipedir/srv && chown -R %d:65534 /.pipedir" % uid],
                    host_config = ctrl.sandbox.create_host_config(
                        binds   = {pipedir: {"bind": "/.pipedir"}}
                    ))
            ctrl.sandbox.start(container)
            if ctrl.sandbox.wait(container):
                raise Error("sandbox preparation failed")
            ctrl.sandbox.remove_container(container)


            # create and start the sandbox
            ctrl.check_host_path("isdir", pipedir)
            ctrl.check_host_path("isdir", pipebin)
            command = ["/.pipebin/pipesrv", "-d", "/.pipedir"]

            if version is None and webapp.entrypoint:
                # prepend instructions to initialise a dummy entrypoint
                dn, bn = os.path.split(webapp.entrypoint)
                command = ["/bin/sh", "-c", """
                    {mkdir}
                    cat > {entrypoint!r} <<EOF
#!/bin/sh
echo
echo "This is app '{name}' called with parameters '\$@'"
echo
echo "The workdir contains:"
ls -l
EOF
                    chmod 0755 -- {entrypoint!r}
                    exec {cmd}
                """.format( entrypoint  = webapp.entrypoint,
                            name        = webapp.docker_name,
                            mkdir       = (("mkdir -p -- %r" % dn) if dn else ""),
                            cmd         = " ".join(map(repr, command)))]

            ctrl.sandbox.create_container(image, name=container, hostname=container,
                    command = command,
                    host_config = ctrl.sandbox.create_host_config(
                        binds = {
                            pipedir: {"bind": "/.pipedir", "mode": "ro"},
                            pipebin: {"bind": "/.pipebin", "mode": "ro"},
                            },
                        # TODO: maybe drop other caps
                        cap_drop = ["NET_RAW"],
                        ))

            ctrl.sandbox.start(container)

        except:
            with docker_warning("cleanup error: unable to remove container %r",
                    container, ignore=docker.errors.NotFound):
                ctrl.sandbox.remove_container(container, force=True)
            raise

    def _commit(self, webapp, versions):
        """Commit a webapp sandbox

        (to be executed in a thread pool)

        The image version is looked up in webapp_versions (where state==sandbox).
        
        In case of any error, a recovery version is committed instead (to avoid
        loosing the work done inside the sandbox) and the candidates are put in
        error state.
        """
        ctrl = self.ctrl
        ses  = ctrl.session

        # pre-commit checks
        # - ensure that there is exactly one candidate webapp_version with
        #   state=sandbox
        # - otherwise:
        #   - put all candidates in error state
        #   - create a recovery version

        # version be committed
        version = None
        
        # error msg (if any)
        error = None

        # version ids to be recovered
        recover = ()

        if len(versions) == 1:
            # normal case (sandbox commit)
            version = versions[0]
            if not version.number:
                error   = "empty version number"
                recover = version.id,

        elif not versions:
            # sandbox rollback (when user drops a sandbox without committing a new image)
            error     = "dangling sandbox"

        else:
            # multiple candidates (should never happen)
            error    = "multiple candidate versions (%s)" % (
                ", ".join(map(repr, sorted(v.number for v in versions))))
            recover = tuple(v.id for v in versions)

        # TODO: make 'sandbox' a reserved name

        if error:
            changelog = "pre-commit error: " + error
            log.error("sandbox %r version id %r: %s", webapp.docker_name, recover, changelog)

            with ses.begin():
                # put all candidates in 'error state'
                if recover:
                    ses.execute('''UPDATE webapp_versions
                            SET changelog=CONCAT(changelog, " [", :changelog, "]"), state=:state
                            WHERE id IN :ids''', dict(changelog=changelog, ids=recover,
                                state=int(VersionState.error)))

                # create a recovery version
                version = WebappVersion(
                        webapp_id = webapp.id,
                        number    = time.strftime("recovery-%Y%m%d-%H%M%S"),
                        changelog = changelog,
                        published = False,
                        state     = int(VersionState.sandbox))
                ses.add(version)
            ses.refresh(version)
            ses.expunge(version)

        assert version is not None

        # commit the docker image

        log.debug("dicts %r %r", webapp.__dict__, version.__dict__)
        log.info("commit sandbox %r version %r", webapp.docker_name, version.number)

        container = webapp.sandbox_name
        next_state = image_size = None
        try:
            # stop the container (if stopping or if creating a new sandbox)
            if webapp.sandbox_state in (SandboxState.stopping, SandboxState.starting):
               ctrl.sandbox.stop(container)
               ctrl.sandbox.wait(container)

            # commit
            cid = ctrl.sandbox.commit(container, webapp.image_name, version.number)
            next_state = VersionState.committed
            image_size = ctrl.sandbox.inspect_image(cid)["Size"]

            return version, error

        except docker.errors.NotFound:
            error = "commit error: container not found %r" % container
            log.error("%s", error)
            next_state = VersionState.error
            image_size = 0
            ses.execute('''UPDATE webapp_versions
                    SET changelog=CONCAT(changelog, " [commit error: sandbox is down]")
                    WHERE id=%d''' % version.id)

            # here we do not propagate the error to allow starting/stopping the
            # sandbox immediately (without going through sandbox_state=:error)
            return None, error

        except Exception as e:
            log.exception("sandbox %r version %r: unexpected commit error (sandbox may still be recovered)",
                    webapp.docker_name, version.number)
            raise

        finally:
            # NOTE: if anything unexpected happens, the version is
            # left in state 'sandbox' and we propagate the exception to
            # ensure the work done inside the sandbox is not dropped
            # and the sandbox is pute in 'error' state
            #
            # The error will not be reported to the user. If this is an issue,
            # then the solution would be to create another error state (to be
            # used when the sandbox is still there).
            # 
            if next_state is not None:
                with ses.begin():
                    ses.execute("UPDATE webapp_versions SET state=%d, docker_image_size=%d WHERE id=%d"
                            % (next_state, image_size, version.id))


    @asyncio.coroutine
    def _manage_commit(self, webapp, versions, *, force=False):
        """Manage sandbox commit (if needed) and notify the image manager

        The commit is performed if one of these conditions is fulfilled:
        - a commit was requested (there is at least one WebappVersion entry
          with state=sandbox for this app)
        - a docker container exists (for this sandbox) and force is true
        """

        if not (versions or (force and self.inspect_sandbox(webapp) is not None)):
            return
        
        # do the commit
        version, error = yield from self.run_in_executor(self._commit, webapp, versions)

        # trigger push/pull operations (but do not wait)
        if version is not None:

            # push to the registry
            self.ctrl.image_manager.push(version.id)

            if not error:
                # preemptive pull to the swarm
                # (the image may be needed soon)
                self.ctrl.image_manager.pull(version.id, swarm=True)


    def _stop(self, webapp):
        """Stop a webapp sandbox

        (to be executed in a thread pool)
        """
        try:
            # FIXME: remove volumes (v=True) too ?
            self.ctrl.sandbox.remove_container(webapp.sandbox_name, force=True)
        except docker.errors.NotFound:
            pass


    @asyncio.coroutine
    def _process(self, webapp_id, reset):
        ctrl = self.ctrl

        log.debug("process sandbox %d", webapp_id)

        ses = ctrl.session
        with ses.begin():
            # current state of the sandbox + load docker os
            webapp = ses.query(Webapp).filter_by(id=webapp_id).one()
            webapp.docker_os

            # version to be started
            sandbox_version = self.filter_sandbox_version(ses.query(WebappVersion), webapp_id).first()

            # requested commits
            commit_versions = self.filter_commit_version(ses.query(WebappVersion), webapp_id).all()

            ses.expunge_all()

        # docker name of the sandbox & image
        webapp.sandbox_name = ctrl.gen_sandbox_name(webapp)
        webapp.image_name   = ctrl.gen_image_name(webapp)

        phase = "inspect"
        next_state = fail_state = None
        try:
            if webapp.sandbox_state == SandboxState.starting:
                # start the sandbox
                phase = "start"
                next_state = SandboxState.running
                fail_state = SandboxState.start_error

                # commit (if a sandbox exists)
                yield from self._manage_commit(webapp, commit_versions, force=True)

                # pull requested image
                if sandbox_version is not None:
                    yield from ctrl.image_manager.pull(sandbox_version.id)

                # start sandbox
                yield from self.run_in_executor(self._start, webapp, sandbox_version)

            elif webapp.sandbox_state == SandboxState.stopping:
                # stop the sandbox
                phase = "stop"
                next_state = SandboxState.idle
                fail_state = SandboxState.stop_error

                # commit (if requested)
                yield from self._manage_commit(webapp, commit_versions)

                yield from self.run_in_executor(self._stop, webapp)

            else:
                # commit (if requested)
                phase = "commit"
                yield from self._manage_commit(webapp, commit_versions)

        except ShuttingDown:
            next_state = None
            log.info("sandbox %r %s aborted (controller shutdown)", webapp.docker_name, phase)

        except BaseException as e:
            next_state = fail_state

            log_func = log.error if isinstance(e, (docker.errors.APIError, Error)) else log.exception
            log_func ("sandbox %r %s error (%s)", webapp.docker_name, phase,
                    traceback.format_exception_only(type(e), e)[-1].strip())

        finally:
            if next_state is not None:
                # atomically update the sandbox state in the db
                # (in case another action is requested during the process, eg: the user
                #  stops the sandbox while it is not fully started)
                log.info("sandbox %r is now in state %r", webapp.docker_name, next_state.name)
                with ses.begin():
                    ses.execute("UPDATE webapps SET sandbox_state=%d WHERE id=%d AND sandbox_state=%d" %
                            (next_state, webapp_id, webapp.sandbox_state))

            log.debug("done    sandbox %d", webapp_id)



class JobManager(Manager):
    def __init__(self, ctrl, nb_jobs=NB_JOB_TASKS):
        super().__init__(nb_jobs)
        self.ctrl = ctrl

    def _run_job(self, job_id, ver_id):
        ctrl = self.ctrl
        ses  = ctrl.session
        ctr = tmp_img = start_time = None

        try:
            with ses.begin():
                job = ses.query(Job).filter_by(id=job_id).one()
                webapp = job.webapp
                if ver_id is None:
                    tag = "sandbox"
                else:
                    ver = ses.query(WebappVersion).filter_by(id=ver_id).one()
                    tag = ver.number

                log.info("start job %d (%s:%s)",
                        job_id, webapp.docker_name, tag)

                start_time = time.time()
                job.state = int(JobState.RUNNING)

            
            repo = ctrl.gen_image_name(webapp)
            image = "%s:%s" % (repo, tag)

            job_path = ctrl.gen_job_path(job)
            log.debug("job.path: %r", job_path)

            if ver_id is None:
                client = ctrl.sandbox
                image = tmp_img = client.commit(ctrl.gen_sandbox_name(webapp), repo, tag)["Id"]
            else:
                client = ctrl.swarm
            
            # TODO use another workdir
            # TODO use another uid

            ctrl.check_host_path("isdir", job_path)
            ctr = client.create_container(image, name=ctrl.gen_job_name(job),
                    working_dir = "/tmp",   # TODO use another dir
                    # TODO parse quotes in job.param (instead of a rough .split())
                    #
                    # NOTE: the command line is a little complex, but this is
                    #   to ensure that:
                    #   - no output is lost (we go though a pipe in case the
                    #     app has multiple processes writing to stdout/stderr
                    #     concurrently)
                    #   - we get the exit code of the app (not the exit code of
                    #     cat)
                    #   - we are failsafe (if fifo creation fails then the app
                    #     is run anyway, with the exit code of cat)
                    #   - we have no unusual dependencies (only sh, cat and
                    #     mkfifo)
                   command = ["/bin/sh", "-c", """
                                fifo=/tmp/.allgo.fifo
                                if mkfifo "$fifo"
                                then
                                    exec cat <"$fifo" >allgo.log &
                                    exec "$@" >"$fifo" 2>&1 &
                                    rm "$fifo"
                                    wait %1
                                    wait %2
                                else
                                    "$@" 2>&1 | cat >allgo.log
                                fi
                        """,
                        "job%d" % job.id, webapp.entrypoint] + job.param.split(),

                    host_config = ctrl.sandbox.create_host_config(
                        binds = {job_path: {"bind": "/tmp"}},
                        cap_drop = ["all"],
                        # FIXME: CAP_DAC_OVERRIDE needed because all nfs files have uid,gid=1000,1000
                        cap_add = ["dac_override"],
                    ))
            client.start(ctr)
            # TODO report exit code to the user
            client.wait(ctr)

        finally:
            # FIXME: if interrupted (power down) here, the job will remain in
            #        state RUNNING forever ==> do some periodic monitoring

            stop_time = time.time()

            log.info("stop  job %d (%s:%s)",
                        job_id, webapp.docker_name, tag)

            with ses.begin():
                job.state = int(JobState.DONE)

                if start_time is not None:
                    job.exec_time    = int(stop_time - start_time)
                    webapp.exec_time = (webapp.exec_time + job.exec_time) // 2


            if ctr is not None:
                with docker_warning("cleanup error: unable to remove container %r", ctr,
                        ignore=docker.errors.NotFound):

                    client.remove_container(ctr, force=True)

            if tmp_img is not None:
                with docker_warning("cleanup error: unable to remove image %r", ctr,
                        ignore=docker.errors.NotFound):

                    client.remove_image(tmp_img,)

    @asyncio.coroutine
    def _process(self, job_id, reset):
        ctrl = self.ctrl
        ses  = ctrl.session
        log.debug("process job id %d", job_id)
        

        with ses.begin():
            # query db
            job = ses.query(Job).filter_by(id=job_id).first()
            if job is None or job.state != JobState.WAITING:
                return

            if job.webapp is None:
                log.error("job %d: webapp id %r not found", job_id, job.webapp_id)

                job.state = JobState.DONE
                # TODO report error to the user
                return

            # select version
            if job.version == "sandbox":
                ver_id = None
            else:
                #TODO: replace version_id with webapp_version_id
                ver = ses.query(WebappVersion).filter_by(
                        webapp_id = job.webapp_id,
                        number    = job.version).filter(
                            WebappVersion.state != VersionState.error
                        ).order_by(WebappVersion.id.desc()).first()
                if ver is None:
                    log.error("job %d: webapp %r version %r not found",
                            job_id, job.webapp.docker_name, job.version)

                    job.state = int(JobState.DONE)
                    # TODO report error to the user
                    return
                ver_id = ver.id

        if ver_id is not None:
            # pull image to the swarm
            # FIXME: race condition: will fail if ver.state==sandbox
            yield from ctrl.image_manager.pull(ver_id, swarm=True)

        # run job
        yield from self.run_in_executor(self._run_job, job_id, ver_id)


class PullManager(Manager):
    def __init__(self, nb_threads, client, name):
        super().__init__(nb_threads)
        self.client    = client
        self.name      = name

    def _process(self, img, reset):
        image, version = img
        log.info("pull to the %-10s %s:%s", self.name, image, version)
        return self.run_in_executor(self.client.pull, image, version)


class PushManager(Manager):
    def __init__(self, nb_threads, ctrl):
        super().__init__(nb_threads)
        self.ctrl = ctrl

    def _process(self, version_id, reset):
        ses = self.ctrl.session

        with report_error("unable to push version id %d", version_id):

            with ses.begin():
                # get the version object and check its state
                version = ses.query(WebappVersion).filter_by(id=version_id).one()
                if version.state != VersionState.committed:
                    if version.state == VersionState.ready:
                        # already pushed
                        return
                    if version.state == VersionState.sandbox:
                        raise Error("unable to push (image not yet committed)")
                    raise Error("unable to push (invalid state: %s)" % version.state)

                # ensure that there is no other version with the same number in the pipeline
                # (to avoid a race condition)
                others = (ses.query(WebappVersion.id)
                        .filter_by(webapp_id=version.webapp_id, number=version.number)
                        .filter(WebappVersion.id     != version.id)
                        .filter(WebappVersion.state.in_((int(VersionState.sandbox), int(VersionState.committed)))))
                if others.count():
                    raise Error("unable to push (there are other pushable versions with the same number: %s)" % (
                        " ".join(map(str, itertools.chain(*others)))))

                image = self.ctrl.gen_image_name(version.webapp)
                tag   = version.number

            log.info("push from the %-8s %s:%s", "sandbox", image, tag)
            yield from self.run_in_executor(docker_check_error, self.ctrl.sandbox.push, image, tag)

            with ses.begin():
                prev = ses.query(WebappVersion).filter_by(
                        webapp_id = version.webapp_id,
                        number    = version.number,
                        state     = int(VersionState.ready)).scalar()
                log.debug("prev version id %r", (prev.id if prev else None))

                if prev is None:
                    # this is a new version
                    version.state = VersionState.ready
                else:
                    # overwrite an existing version
                    for key in "updated_at", "changelog", "published":
                        setattr(prev, key, getattr(version, key))

                    ses.delete(version)


class ImageManager:

    def __init__(self, ctrl,
            nb_push_sandbox = NB_PUSH_SANDBOX,
            nb_pull_sandbox = NB_PULL_SANDBOX,
            nb_pull_swarm   = NB_PULL_SWARM):

        self.ctrl = ctrl

        self.sandbox_push_manager = PushManager(nb_push_sandbox, ctrl)
        self.sandbox_pull_manager = PullManager(nb_pull_sandbox, ctrl.sandbox, "sandbox")
        self.swarm_pull_manager   = PullManager(nb_pull_swarm,   ctrl.swarm,   "swarm")

    # return a future
    @auto_create_task
    @asyncio.coroutine
    def pull(self, version_id: int, *, swarm=False):
        with report_error("unable to pull version id %d to %s", version_id,
                ("swarm" if swarm else "sandbox")):

            ses = self.ctrl.session
            with ses.begin():
                # get the version object and check its state
                version = ses.query(WebappVersion).filter_by(id=version_id).one()

                image = self.ctrl.gen_image_name(version.webapp)
                tag   = version.number


            if swarm:
                # pull to the swarm

                if version.state == VersionState.committed:
                    # must be pushed to the registry first
                    yield from self.push(version_id)
                    with ses.begin():
                        version = ses.query(WebappVersion).filter_by(id=version_id).one()

                if version.state != VersionState.ready:
                    raise Error("bad version state: %s" % version.state)

                yield from self.swarm_pull_manager.process((image, tag))

            else:
                # pull to the sandbox
                if version.state == VersionState.committed:
                    # do not pull!
                    return

                if version.state != VersionState.ready:
                    raise Error("bad version state: %s" % version.state)

                yield from self.sandbox_pull_manager.process((image, tag))


    # return a future
    def push(self, version_id: int):
        return self.sandbox_push_manager.process(version_id)

    @asyncio.coroutine
    def shutdown(self, **kw):
        yield from asyncio.gather(
                self.sandbox_pull_manager.shutdown(),
                self.sandbox_push_manager.shutdown(),
                self.swarm_pull_manager.shutdown(),
                return_exceptions=True)



class DockerController:
    def __init__(self, sandbox_host, swarm_host, mysql_host,
            port, registry, env, datastore_path, sandbox_path,
            max_jobs):

        self.sandbox = docker.Client(sandbox_host)
        self.swarm   = self.sandbox if sandbox_host == swarm_host else docker.Client(swarm_host)

        self._db_sessionmaker = sqlalchemy.orm.scoping.scoped_session(
                connect_db(mysql_host))
        self._thread_local = threading.local()

        self.sock = socket.socket()
        self.sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
        self.sock.bind(("0.0.0.0", port))
        self.sock.listen(32)
        self.sock.setblocking(False)

        self.image_manager   = ImageManager(self)
        self.sandbox_manager = SandboxManager(self)
        self.job_manager     = JobManager(self, max_jobs)

        self.registry       = registry
        self.env            = env
        self.datastore_path = datastore_path
        self.sandbox_path   = sandbox_path

        self._task               = None
        self._shutdown_requested = None

        img = "busybox:latest"
        try:
            self.sandbox.inspect_image(img)
        except docker.errors.NotFound:
            log.info("pulling docker image %s", img)
            self.sandbox.pull(img)

    def gen_sandbox_name(self, webapp):
        return "%s-sandbox-%s" % (self.env, webapp.docker_name)

    def gen_image_name(self, webapp):
        return "%s/webapp/%s" % (self.registry, webapp.docker_name)

    def gen_job_name(self, job):
        return "%s-job-%d-%s" % (self.env, job.id, job.webapp.docker_name)

    def gen_job_path(self, job):
        assert self.datastore_path.endswith("/")
        return "%s%d/%d/%s" % (
                self.datastore_path, job.user_id,
                job.webapp_id, job.access_token)


    def check_host_path(self, funcname, path, *, nolink=True):
        """Validate a path before using it as an external volume in docker

        - ensure the path is canonical:
            - it is absolute
            - it does not contain any '..' parts
            - it does not contain any symbolic link
        - ensure the path is of the right type (call os.path.`funcname`())
        """

        if not os.path.isabs(path):
            raise Error("host path %r is not absolute" % path)

        if path != os.path.normpath(path):
            raise Error("host path %r is not canonical (os.path.normpath())")

        ctrpath = "/vol/host" + path
        log.debug("ctrpath %r", ctrpath)

        
        func = getattr(os.path, funcname)
        if nolink and os.path.realpath(ctrpath) != os.path.normpath(ctrpath):
            raise Error("host path %r contains a symbolic link" % path)
        
        if not func(ctrpath):
            raise Error("host path %r not found (os.path.%s())" % (path, funcname))


    @property
    def session(self):
        """Return the thread-local sqlalchemy session
        
        WARNING: in async functions, db transaction must not span over any
                 'yield from' statements (to avoid interleaving)
        """
        return self._db_sessionmaker()


    def _sock_callback(self):
        try:
            while True:
                self.sock.accept()[0].close()
        except BlockingIOError:
            pass

        self.check_db()

    def check_db(self):
        log.debug("check_db")
        try:
            ses = self.session
            with ses.begin():
                for webapp_id, in ses.execute("""SELECT webapps.id FROM webapps
                        LEFT JOIN webapp_versions ON webapps.id=webapp_versions.webapp_id
                        WHERE sandbox_state IN (%d,%d) OR state=%d
                        GROUP BY webapps.id""" % (
                        SandboxState.starting, SandboxState.stopping, VersionState.sandbox)).fetchall():

                    self.sandbox_manager.process(webapp_id)

                for job_id, in ses.query(Job.id).filter_by(state = JobState.WAITING.value):
                    log.debug("schedule job %d", job_id)
                    self.job_manager.process(job_id)

                # TODO schedule the push of images versions in state 'committed'
        except sqlalchemy.exc.OperationalError as e:
            log.error("db error %s", e.orig.args)
            return

    def shutdown(self):
        if not self._shutdown_requested.done():
            self._shutdown_requested.set_result(None)
        return self._task


    @asyncio.coroutine
    def _run(self):
        assert self._shutdown_requested is None

        try:
            loop = asyncio.get_event_loop()

            self._shutdown_requested = asyncio.Future()

            loop.add_signal_handler(signal.SIGTERM, self.shutdown)
            loop.add_signal_handler(signal.SIGINT,  self.shutdown)
            loop.add_reader(self.sock, self._sock_callback)

            self.check_db()
            try:
                yield from self._shutdown_requested
            finally:
                # graceful shutdown

                # close socket (to disable incoming notifications)
                self.sock.close()

                # terminate all pending tasks
                yield from asyncio.gather(
                        self.image_manager.shutdown(),
                        self.sandbox_manager.shutdown(),
                        self.job_manager.shutdown(),
                        return_exceptions=True)
        finally:
            self.sock.close()
            self.sandbox.close()
            self.swarm.close()

    def run(self):
        asyncio.get_event_loop().run_until_complete(self._run())