#!/usr/bin/env python
# -*- coding: utf-8 -*-

USAGE = """
## Example

For any existing app

Create File: app/models/scheduler.py ======
from gluon.scheduler import Scheduler

def demo1(*args,**vars):
    print 'you passed args=%s and vars=%s' % (args, vars)
    return 'done!'

def demo2():
    1/0

scheduler = Scheduler(db,dict(demo1=demo1,demo2=demo2))
## run worker nodes with:

   cd web2py
   python web2py.py -K myapp
or
   python gluon/scheduler.py -u sqlite://storage.sqlite \
                             -f applications/myapp/databases/ \
                             -t mytasks.py
(-h for info)
python scheduler.py -h

## schedule jobs using
http://127.0.0.1:8000/myapp/appadmin/insert/db/scheduler_task

## monitor scheduled jobs
http://127.0.0.1:8000/myapp/appadmin/select/db?query=db.scheduler_task.id>0

## view completed jobs
http://127.0.0.1:8000/myapp/appadmin/select/db?query=db.scheduler_run.id>0

## view workers
http://127.0.0.1:8000/myapp/appadmin/select/db?query=db.scheduler_worker.id>0

## To install the scheduler as a permanent daemon on Linux (w/ Upstart), put the
## following into /etc/init/web2py-scheduler.conf:
## (This assumes your web2py instance is installed in <user>'s home directory,
## running as <user>, with app <myapp>, on network interface eth0.)

description "web2py task scheduler"
start on (local-filesystems and net-device-up IFACE=eth0)
stop on shutdown
respawn limit 8 60 # Give up if restart occurs 8 times in 60 seconds.
exec sudo -u <user> python /home/<user>/web2py/web2py.py -K <myapp>
respawn

## You can then start/stop/restart/check status of the daemon with:
sudo start web2py-scheduler
sudo stop web2py-scheduler
sudo restart web2py-scheduler
sudo status web2py-scheduler
"""

import os
import time
import multiprocessing
import sys
import cStringIO
import threading
import traceback
import signal
import socket
import datetime
import logging
import optparse
import types
import Queue

if 'WEB2PY_PATH' in os.environ:
    sys.path.append(os.environ['WEB2PY_PATH'])
else:
    os.environ['WEB2PY_PATH'] = os.getcwd()

if not os.environ['WEB2PY_PATH'] in sys.path:
    sys.path.append(os.environ['WEB2PY_PATH'])

try:
    from gluon.contrib.simplejson import loads, dumps
except:
    from simplejson import loads, dumps


from gluon import DAL, Field, IS_NOT_EMPTY, IS_IN_SET, IS_NOT_IN_DB, IS_INT_IN_RANGE
from gluon.utils import web2py_uuid


QUEUED = 'QUEUED'
ASSIGNED = 'ASSIGNED'
RUNNING = 'RUNNING'
COMPLETED = 'COMPLETED'
FAILED = 'FAILED'
TIMEOUT = 'TIMEOUT'
STOPPED = 'STOPPED'
ACTIVE = 'ACTIVE'
TERMINATE = 'TERMINATE'
DISABLED = 'DISABLED'
KILL = 'KILL'
EXPIRED = 'EXPIRED'
SECONDS = 1
HEARTBEAT = 3*SECONDS
MAXHIBERNATION = 10
CLEAROUT = '!clear!'

CALLABLETYPES = (types.LambdaType, types.FunctionType,
                 types.BuiltinFunctionType,
                 types.MethodType, types.BuiltinMethodType)

class Task(object):
    def __init__(self,app,function,timeout,args='[]',vars='{}',**kwargs):
        logging.debug(' new task allocated: %s.%s' % (app,function))
        self.app = app
        self.function = function
        self.timeout = timeout
        self.args = args # json
        self.vars = vars # json
        self.__dict__.update(kwargs)
    def __str__(self):
        return '<Task: %s>' % self.function

class TaskReport(object):
    def __init__(self,status,result=None,output=None,tb=None):
        logging.debug('    new task report: %s' % status)
        if tb:
            logging.debug('   traceback: %s' % tb)
        else:
            logging.debug('   result: %s' % result)
        self.status = status
        self.result = result
        self.output = output
        self.tb = tb
    def __str__(self):
        return '<TaskReport: %s>' % self.status

def demo_function(*argv,**kwargs):
    """ test function """
    for i in range(argv[0]):
        print 'click',i
        time.sleep(1)
    return 'done'

#the two functions below deal with simplejson decoding as unicode, esp for the dict decode
#and subsequent usage as function Keyword arguments unicode variable names won't work!
#borrowed from http://stackoverflow.com/questions/956867/how-to-get-string-objects-instead-unicode-ones-from-json-in-python
def _decode_list(lst):
    newlist = []
    for i in lst:
        if isinstance(i, unicode):
            i = i.encode('utf-8')
        elif isinstance(i, list):
            i = _decode_list(i)
        newlist.append(i)
    return newlist

def _decode_dict(dct):
    newdict = {}
    for k, v in dct.iteritems():
        if isinstance(k, unicode):
            k = k.encode('utf-8')
        if isinstance(v, unicode):
             v = v.encode('utf-8')
        elif isinstance(v, list):
            v = _decode_list(v)
        newdict[k] = v
    return newdict

def executor(queue,task, out):
    """ the background process """
    logging.debug('    task started')

    class LogOutput(object):
        """Facility to log output at intervals"""
        def __init__(self, out_queue):
            self.out_queue = out_queue
            self.stdout = sys.stdout
            sys.stdout = self
        def __del__(self):
            sys.stdout = self.stdout
        def flush(self):
            pass
        def write(self,data):
            self.out_queue.put(data)

    stdout = LogOutput(out)
    try:
        if task.app:
            os.chdir(os.environ['WEB2PY_PATH'])
            from gluon.shell import env, parse_path_info
            from gluon.dal import BaseAdapter
            from gluon import current
            level = logging.getLogger().getEffectiveLevel()
            logging.getLogger().setLevel(logging.WARN)
            # Get controller-specific subdirectory if task.app is of
            # form 'app/controller'
            (a,c,f) = parse_path_info(task.app)
            _env = env(a=a,c=c,import_models=True)
            logging.getLogger().setLevel(level)
            scheduler = current._scheduler
            f = task.function
            functions = current._scheduler.tasks
            if not functions:
                #look into env
                _function = _env.get(f)
            else:
                _function = functions.get(f)
            if not isinstance(_function, CALLABLETYPES):
                raise NameError("name '%s' not found in scheduler's environment" % f)
            globals().update(_env)
            args = loads(task.args)
            vars = loads(task.vars, object_hook=_decode_dict)
            result = dumps(_function(*args,**vars))
        else:
            ### for testing purpose only
            result = eval(task.function)(
                *loads(task.args, object_hook=_decode_dict),
                 **loads(task.vars, object_hook=_decode_dict))
        queue.put(TaskReport(COMPLETED, result=result))
    except BaseException,e:
        tb = traceback.format_exc()
        queue.put(TaskReport(FAILED,tb=tb))
    del stdout

class MetaScheduler(threading.Thread):
    def __init__(self):
        threading.Thread.__init__(self)
        self.process = None     # the background process
        self.have_heartbeat = True   # set to False to kill
        self.empty_runs = 0

    def async(self,task):
        """
        starts the background process and returns:
        ('ok',result,output)
        ('error',exception,None)
        ('timeout',None,None)
        ('terminated',None,None)
        """
        db = self.db
        sr = db.scheduler_run
        out = multiprocessing.Queue()
        queue = multiprocessing.Queue(maxsize=1)
        p = multiprocessing.Process(target=executor,args=(queue,task,out))
        self.process = p
        logging.debug('   task starting')
        p.start()

        task_output = ""
        tout = ""

        try:
            if task.sync_output > 0:
                run_timeout = task.sync_output
            else:
                run_timeout = task.timeout

            start = time.time()

            while p.is_alive() and (
                not task.timeout or time.time()-start < task.timeout):
                if tout:
                    try:
                        logging.debug(' partial output saved')
                        db(sr.id==task.run_id).update(output = task_output)
                        db.commit()
                    except:
                        pass
                p.join(timeout=run_timeout)
                tout = ""
                while not out.empty():
                    tout += out.get()
                if tout:
                    logging.debug(' partial output: "%s"' % str(tout))
                    if CLEAROUT in tout:
                        task_output = tout[tout.rfind(CLEAROUT)+len(CLEAROUT):]
                    else:
                        task_output += tout
        except:
            p.terminate()
            p.join()
            self.have_heartbeat = False
            logging.debug('    task stopped by general exception')
            tr = TaskReport(STOPPED)
        else:
            if p.is_alive():
                p.terminate()
                logging.debug('    task timeout')
                try:
                    # we try to get a traceback here
                    tr = queue.get(timeout=2)
                    tr.status = TIMEOUT
                    tr.output = task_output
                except Queue.Empty:
                    tr = TaskReport(TIMEOUT)
            elif queue.empty():
                self.have_heartbeat = False
                logging.debug('    task stopped')
                tr = TaskReport(STOPPED)
            else:
                logging.debug('  task completed or failed')
                tr = queue.get()
        tr.output = task_output
        return tr

    def die(self):
        logging.info('die!')
        self.have_heartbeat = False
        self.terminate_process()

    def give_up(self):
        logging.info('Giving up as soon as possible!')
        self.have_heartbeat = False

    def terminate_process(self):
        try:
            self.process.terminate()
        except:
            pass # no process to terminate

    def run(self):
        """ the thread that sends heartbeat """
        counter = 0
        while self.have_heartbeat:
            self.send_heartbeat(counter)
            counter += 1

    def start_heartbeats(self):
        self.start()

    def send_heartbeat(self,counter):
        print 'thum'
        time.sleep(1)

    def pop_task(self):
        return Task(
            app = None,
            function = 'demo_function',
            timeout = 7,
            args = '[2]',
            vars = '{}')

    def report_task(self,task,task_report):
        print 'reporting task'
        pass

    def sleep(self):
        pass

    def loop(self):
        try:
            self.start_heartbeats()
            while True and self.have_heartbeat:
                logging.debug('looping...')
                task = self.pop_task()
                if task:
                    self.empty_runs = 0
                    self.report_task(task,self.async(task))
                else:
                    self.empty_runs += 1
                    logging.debug('sleeping...')
                    if self.max_empty_runs != 0:
                        logging.debug('empty runs %s/%s', self.empty_runs, self.max_empty_runs)
                        if self.empty_runs >= self.max_empty_runs:
                            logging.info('empty runs limit reached, killing myself')
                            self.die()
                    self.sleep()
        except KeyboardInterrupt:
            self.die()


TASK_STATUS = (QUEUED, RUNNING, COMPLETED, FAILED, TIMEOUT, STOPPED, EXPIRED)
RUN_STATUS = (RUNNING, COMPLETED, FAILED, TIMEOUT, STOPPED)
WORKER_STATUS = (ACTIVE, DISABLED, TERMINATE, KILL)

class TYPE(object):
    """
    validator that check whether field is valid json and validate its type
    """

    def __init__(self,myclass=list,parse=False):
        self.myclass = myclass
        self.parse=parse

    def __call__(self,value):
        from gluon import current
        try:
            obj = loads(value)
        except:
            return (value,current.T('invalid json'))
        else:
            if isinstance(obj,self.myclass):
                if self.parse:
                    return (obj,None)
                else:
                    return (value,None)
            else:
                return (value,current.T('Not of type: %s') % self.myclass)

class Scheduler(MetaScheduler):
    def __init__(self,db,tasks=None,migrate=True,
                 worker_name=None,group_names=None,heartbeat=HEARTBEAT,
                 max_empty_runs=0, discard_results=False, utc_time=False):

        MetaScheduler.__init__(self)

        self.db = db
        self.db_thread = None
        self.tasks = tasks
        self.group_names = group_names or ['main']
        self.heartbeat = heartbeat
        self.worker_name = worker_name or socket.gethostname()+'#'+str(os.getpid())
        self.worker_status = RUNNING, 1 #tuple containing status as recorded in
                                        #the table, plus a boost parameter for
                                        #hibernation (i.e. when someone stop the
                                        #worker acting on the scheduler_worker table)
        self.max_empty_runs = max_empty_runs
        self.discard_results = discard_results
        self.is_a_ticker = False
        self.do_assign_tasks = False
        self.utc_time = utc_time

        from gluon import current
        current._scheduler = self

        self.define_tables(db,migrate=migrate)

    def now(self):
        return self.utc_time and datetime.datetime.utcnow() or datetime.datetime.now()

    def define_tables(self,db,migrate):
        from gluon import current
        from gluon.dal import DEFAULT
        logging.debug('defining tables (migrate=%s)' % migrate)
        now = self.now()
        db.define_table(
            'scheduler_task',
            Field('application_name',requires=IS_NOT_EMPTY(),
                  default=None,writable=False),
            Field('task_name',default=None),
            Field('group_name',default='main',writable=False),
            Field('status',requires=IS_IN_SET(TASK_STATUS),
                  default=QUEUED,writable=False),
            Field('function_name',
                  requires=IS_IN_SET(sorted(self.tasks.keys()))
                  if self.tasks else DEFAULT),
            Field('uuid', requires=IS_NOT_IN_DB(db, 'scheduler_task.uuid'),
                  unique=True, default=web2py_uuid),
            Field('args','text',default='[]',requires=TYPE(list)),
            Field('vars','text',default='{}',requires=TYPE(dict)),
            Field('enabled','boolean',default=True),
            Field('start_time','datetime',default=now, requires=IS_NOT_EMPTY()),
            Field('next_run_time','datetime',default=now),
            Field('stop_time','datetime'),
            Field('repeats','integer',default=1,comment="0=unlimited",
                  requires=IS_INT_IN_RANGE(0, None)),
            Field('retry_failed', 'integer', default=0, comment="-1=unlimited",
                  requires=IS_INT_IN_RANGE(-1, None)),
            Field('period','integer',default=60,comment='seconds',
                  requires=IS_INT_IN_RANGE(0, None)),
            Field('timeout','integer',default=60,comment='seconds',
                  requires=IS_INT_IN_RANGE(0, None)),
            Field('sync_output', 'integer', default=0,
                  comment="update output every n sec: 0=never",
                  requires=IS_INT_IN_RANGE(0, None)),
            Field('times_run','integer',default=0,writable=False),
            Field('times_failed','integer',default=0,writable=False),
            Field('last_run_time','datetime',writable=False,readable=False),
            Field('assigned_worker_name',default='',writable=False),
            migrate=migrate,format='%(task_name)s')
        if hasattr(current,'request'):
            db.scheduler_task.application_name.default= '%s/%s' % (
                current.request.application, current.request.controller
            )

        db.define_table(
            'scheduler_run',
            Field('scheduler_task','reference scheduler_task'),
            Field('status',requires=IS_IN_SET(RUN_STATUS)),
            Field('start_time','datetime'),
            Field('stop_time','datetime'),
            Field('output','text'),
            Field('result','text'),
            Field('traceback','text'),
            Field('worker_name',default=self.worker_name),
            migrate=migrate)

        db.define_table(
            'scheduler_worker',
            Field('worker_name', unique=True),
            Field('first_heartbeat','datetime'),
            Field('last_heartbeat','datetime'),
            Field('status',requires=IS_IN_SET(WORKER_STATUS)),
            Field('is_ticker', 'boolean', default=False, writable=False),
            Field('group_names', 'list:string', default=self.group_names),
            migrate=migrate)
        db.commit()

    def loop(self,worker_name=None):
        signal.signal(signal.SIGTERM, lambda signum, stack_frame: sys.exit(1))
        try:
            self.start_heartbeats()
            while True and self.have_heartbeat:
                if self.worker_status[0] == DISABLED:
                    logging.debug('Someone stopped me, sleeping until better times come (%s)' % self.worker_status[1])
                    self.sleep()
                    continue
                logging.debug('looping...')
                task = self.pop_task()
                if task:
                    self.empty_runs = 0
                    self.report_task(task,self.async(task))
                else:
                    self.empty_runs += 1
                    logging.debug('sleeping...')
                    if self.max_empty_runs != 0:
                        logging.debug('empty runs %s/%s', self.empty_runs, self.max_empty_runs)
                        if self.empty_runs >= self.max_empty_runs:
                            logging.info('empty runs limit reached, killing myself')
                            self.die()
                    self.sleep()
        except (KeyboardInterrupt, SystemExit):
            logging.info('catched')
            self.die()

    def pop_task(self):
        now = self.now()
        db, ts = self.db, self.db.scheduler_task
        if self.is_a_ticker and self.do_assign_tasks:
            #I'm a ticker, and 5 loops passed without reassigning tasks, let's do
            #that and loop again
            db.commit() #?don't know if it's useful, let's be completely sure
            while True:
                try:
                    self.assign_tasks()
                    db.commit()
                    break
                except:
                    db.rollback()
                    logging.error('TICKER: error assigning tasks')
            return None
        db.commit()
        grabbed = db(ts.assigned_worker_name==self.worker_name)\
            (ts.status==ASSIGNED)

        task = grabbed.select(limitby=(0,1), orderby=ts.next_run_time).first()
        if task:
            task.update_record(status=RUNNING,last_run_time=now)
            #noone will touch my task!
            db.commit()
            logging.debug('   work to do %s' % task.id)
        else:
            logging.debug('nothing to do')
            return None
        next_run_time = task.last_run_time + datetime.timedelta(seconds=task.period)
        times_run = task.times_run + 1
        if times_run < task.repeats or task.repeats==0:
            run_again = True
        else:
            run_again = False
        run_id = 0
        while True and not self.discard_results:
            logging.debug('    new scheduler_run record')
            try:
                run_id = db.scheduler_run.insert(
                    scheduler_task = task.id,
                    status=RUNNING,
                    start_time=now,
                    worker_name=self.worker_name)
                db.commit()
                break
            except:
                db.rollback()
        logging.info('new task %(id)s "%(task_name)s" %(application_name)s.%(function_name)s' % task)
        return Task(
            app = task.application_name,
            function = task.function_name,
            timeout = task.timeout,
            args = task.args, #in json
            vars = task.vars, #in json
            task_id = task.id,
            run_id = run_id,
            run_again = run_again,
            next_run_time=next_run_time,
            times_run = times_run,
            stop_time = task.stop_time,
            retry_failed = task.retry_failed,
            times_failed = task.times_failed,
            sync_output = task.sync_output)

    def report_task(self,task,task_report):
        db = self.db
        now = self.now()
        while True:
            try:
                if not self.discard_results:
                    if task_report.result != 'null' or task_report.tb:
                        #result is 'null' as a string if task completed
                        #if it's stopped it's None as NoneType, so we record
                        #the STOPPED "run" anyway
                        logging.debug(' recording task report in db (%s)' % task_report.status)
                        db(db.scheduler_run.id==task.run_id).update(
                            status = task_report.status,
                            stop_time = now,
                            result = task_report.result,
                            output = task_report.output,
                            traceback = task_report.tb)
                    else:
                        logging.debug(' deleting task report in db because of no result')
                        db(db.scheduler_run.id==task.run_id).delete()
                is_expired = (task.stop_time
                              and task.next_run_time > task.stop_time
                              and True or False)
                status = (task.run_again and is_expired and EXPIRED
                          or task.run_again and not is_expired
                          and QUEUED or COMPLETED)
                if task_report.status == COMPLETED:
                    d = dict(status = status,
                             next_run_time = task.next_run_time,
                             times_run = task.times_run,
                             times_failed = 0
                             )
                    db(db.scheduler_task.id==task.task_id)\
                        (db.scheduler_task.status==RUNNING).update(**d)
                else:
                    st_mapping = {'FAILED':'FAILED',
                                  'TIMEOUT':'TIMEOUT',
                                  'STOPPED':'QUEUED'}[task_report.status]
                    status = (task.retry_failed
                              and task.times_failed < task.retry_failed
                              and QUEUED or task.retry_failed==-1
                              and QUEUED or st_mapping)
                    db(db.scheduler_task.id==task.task_id)\
                        (db.scheduler_task.status==RUNNING).update(
                            times_failed=db.scheduler_task.times_failed+1,
                            next_run_time = task.next_run_time,
                            status=status)
                db.commit()
                logging.info('task completed (%s)' % task_report.status)
                break
            except:
                db.rollback()

    def adj_hibernation(self):
        if self.worker_status[0] == DISABLED:
            hibernation = self.worker_status[1] + 1 if self.worker_status[1] < MAXHIBERNATION else MAXHIBERNATION
            self.worker_status = DISABLED, hibernation

    def send_heartbeat(self,counter):
        if not self.db_thread:
            logging.debug('thread building own DAL object')
            self.db_thread = DAL(self.db._uri,folder = self.db._adapter.folder)
            self.define_tables(self.db_thread,migrate=False)
        try:
            db = self.db_thread
            sw, st = db.scheduler_worker, db.scheduler_task
            now = self.now()
            expiration = now-datetime.timedelta(seconds=self.heartbeat*3)
            departure = now-datetime.timedelta(seconds=self.heartbeat*3*MAXHIBERNATION)
            # record heartbeat
            mybackedstatus = db(sw.worker_name==self.worker_name).select().first()
            if not mybackedstatus:
                sw.insert(status = ACTIVE,worker_name = self.worker_name,
                          first_heartbeat = now,last_heartbeat = now,
                          group_names = self.group_names)
                self.worker_status = ACTIVE, 1       #activating the process
            else:
                if mybackedstatus.status == DISABLED:
                    self.worker_status = DISABLED, self.worker_status[1]#keep sleeping
                    if self.worker_status[1] == MAXHIBERNATION:
                        logging.debug('........recording heartbeat')
                        db(sw.worker_name==self.worker_name).update(
                            last_heartbeat = now)

                elif mybackedstatus.status == TERMINATE:
                    self.worker_status = TERMINATE, self.worker_status[1]
                    logging.debug("Waiting to terminate the current task")
                    self.give_up()
                    return
                elif mybackedstatus.status == KILL:
                    self.worker_status = KILL, self.worker_status[1]
                    self.die()

                else:
                    logging.debug('........recording heartbeat')
                    db(sw.worker_name==self.worker_name).update(
                        last_heartbeat = now, status = ACTIVE)
                    self.worker_status = ACTIVE, 1  #re-activating the process

            self.do_assign_tasks = False
            if counter % 5 == 0:
                try:
                    # delete inactive workers
                    logging.debug('    freeing workers that have not sent heartbeat')
                    inactive_workers = db(
                        ((sw.last_heartbeat<expiration) & (sw.status == ACTIVE)) |
                        ((sw.last_heartbeat<departure) & (sw.status != ACTIVE))
                        )
                    db(st.assigned_worker_name.belongs(
                        inactive_workers._select(sw.worker_name)))\
                        (st.status == RUNNING)\
                        .update(assigned_worker_name='',status=QUEUED)
                    inactive_workers.delete()
                    self.is_a_ticker = self.being_a_ticker()
                    if self.worker_status[0] == ACTIVE:
                        self.do_assign_tasks = True
                except:
                    pass
            db.commit()
        except:
            db.rollback()
        self.adj_hibernation()
        self.sleep()

    def being_a_ticker(self):
        db = self.db_thread
        sw = db.scheduler_worker
        ticker = db((sw.worker_name != self.worker_name) & (sw.is_ticker == True) & (sw.status == ACTIVE)).select().first()
        if not ticker:
            db(sw.worker_name == self.worker_name).update(is_ticker = True)
            db(sw.worker_name != self.worker_name).update(is_ticker = False)
            logging.info("TICKER: I'm a ticker (%s)" % self.worker_name)
            db.commit()
            return True
        else:
            logging.info("%s is a ticker, I'm a poor worker" % ticker.worker_name)
            return False

    def assign_tasks(self):
        db = self.db
        sw, ts = db.scheduler_worker, db.scheduler_task
        now = self.now()
        all_workers = db(sw.status == ACTIVE).select()
        #build workers as dict of groups
        wkgroups = {}
        for w in all_workers:
            group_names = w.group_names
            for gname in group_names:
                if gname not in wkgroups:
                    wkgroups[gname] = dict(workers=[{'name' : w.worker_name, 'c' : 0}])
                else:
                    wkgroups[gname]['workers'].append({'name' : w.worker_name, 'c' : 0})
        #set queued tasks that expired between "runs" (i.e., you turned off)
        #the scheduler and then it wasn't expired, but now it is
        db(ts.status.belongs((QUEUED,ASSIGNED)))(ts.stop_time<now).update(status=EXPIRED)

        all_available = db(ts.status.belongs((QUEUED,ASSIGNED)))\
                ((ts.times_run<ts.repeats)|(ts.repeats==0))\
                (ts.start_time<=now)\
                ((ts.stop_time==None) | (ts.stop_time>now))\
                (ts.next_run_time<=now)\
                (ts.enabled==True)

        limit = len(all_workers) * 50
        #if there are a moltitude of tasks, let's assign a maximum of 50 tasks per worker.
        #this can be adjusted with some added intelligence (like esteeming how many tasks will
        #a worker complete before the ticker reassign them around, but the gain is quite small
        #50 is quite a sweet spot also for fast tasks, with sane heartbeat values
        #NB: ticker reassign tasks every 5 cycles, so if a worker completes his 50 tasks in less
        #than heartbeat*5 seconds, it won't pick new tasks until heartbeat*5 seconds pass.
        tasks = all_available.select(limitby=(0,limit), orderby=ts.next_run_time)
        #everything until now is going fine. If a worker is currently elaborating a long task,
        #all other tasks assigned to him needs to be reassigned "freely" to other workers, that may be free.
        #this shuffles up things a bit, in order to maintain the idea of a semi-linear scalability
        #let's freeze it up
        db.commit()
        #let's break up the queue evenly among workers

        for task in tasks:
            gname = task.group_name
            ws = wkgroups.get(gname)
            if ws:
                counter = 0
                myw = 0
                for i, w in enumerate(ws['workers']):
                    if w['c'] < counter:
                        myw = i
                    counter = w['c']
                d = dict(status=ASSIGNED,
                         assigned_worker_name=wkgroups[gname]['workers'][myw]['name'])
                if not task.task_name:
                    d['task_name'] = task.function_name
                task.update_record(**d)
                wkgroups[gname]['workers'][myw]['c'] += 1

        db.commit()
        #I didn't report tasks but I'm working nonetheless!!!!
        if len(tasks) > 0:
            self.empty_runs = 0
        logging.info('TICKER: workers are %s' % len(all_workers))
        logging.info('TICKER: tasks are %s' % len(tasks))

    def sleep(self):
        time.sleep(self.heartbeat*self.worker_status[1]) # should only sleep until next available task

def main():
    """
    allows to run worker without python web2py.py .... by simply python this.py
    """
    parser = optparse.OptionParser()
    parser.add_option(
        "-w", "--worker_name", dest="worker_name", default=None,
        help="start a worker with name")
    parser.add_option(
        "-b", "--heartbeat",dest="heartbeat", default = 10,
        type='int', help="heartbeat time in seconds (default 10)")
    parser.add_option(
        "-L", "--logger_level",dest="logger_level",
        default=30,
        type='int',
        help="set debug output level (0-100, 0 means all, 100 means none;default is 30)")
    parser.add_option("-E", "--empty-runs",
        dest="max_empty_runs",
        type='int',
        default = 0,
        help="max loops with no grabbed tasks permitted (0 for never check)")
    parser.add_option(
        "-g", "--group_names",dest="group_names",
        default = 'main',
        help="comma separated list of groups to be picked by the worker")
    parser.add_option(
        "-f", "--db_folder",dest="db_folder",
        default = '/Users/mdipierro/web2py/applications/scheduler/databases',
        help="location of the dal database folder")
    parser.add_option(
        "-u", "--db_uri",dest="db_uri",
        default = 'sqlite://storage.sqlite',
        help="database URI string (web2py DAL syntax)")
    parser.add_option(
        "-t", "--tasks",dest="tasks",default=None,
        help="file containing task files, must define" + \
            "tasks = {'task_name':(lambda: 'output')} or similar set of tasks")
    parser.add_option(
        "-U", "--utc-time", dest="utc_time", default=False,
        help="work with UTC timestamps"
    )
    (options, args) = parser.parse_args()
    if not options.tasks or not options.db_uri:
        print USAGE
    if options.tasks:
        path,filename = os.path.split(options.tasks)
        if filename.endswith('.py'):
            filename = filename[:-3]
        sys.path.append(path)
        print 'importing tasks...'
        tasks = __import__(filename, globals(), locals(), [], -1).tasks
        print 'tasks found: '+', '.join(tasks.keys())
    else:
        tasks = {}
    group_names = [x.strip() for x in options.group_names.split(',')]

    logging.getLogger().setLevel(options.logger_level)

    print 'groups for this worker: '+', '.join(group_names)
    print 'connecting to database in folder: ' + options.db_folder or './'
    print 'using URI: '+options.db_uri
    db = DAL(options.db_uri,folder=options.db_folder)
    print 'instantiating scheduler...'
    scheduler=Scheduler(db = db,
                        worker_name = options.worker_name,
                        tasks = tasks,
                        migrate = True,
                        group_names = group_names,
                        heartbeat = options.heartbeat,
                        max_empty_runs = options.max_empty_runs,
                        utc_time = options.utc_time)
    signal.signal(signal.SIGTERM, lambda signum, stack_frame: sys.exit(1))
    print 'starting main worker loop...'
    scheduler.loop()

if __name__=='__main__':
    main()