from functools import partial

from django.db.models.loading import get_model
from django.utils import timezone
from django.utils.functional import cached_property
from django.utils.translation import ugettext_lazy as _

from orchestra import plugins

from . import methods


class ServiceBackend(plugins.Plugin):
    """
    Service management backend base class
    
    It uses the _unit of work_ design principle, which allows bulk operations to
    be conviniently supported. Each backend generates the configuration for all
    the changes of all modified objects, reloading the daemon just once.
    """
    model = None
    related_models = () # ((model, accessor__attribute),)
    script_method = methods.SSH
    script_executable = '/bin/bash'
    function_method = methods.Python
    type = 'task' # 'sync'
    ignore_fields = []
    actions = []
    
    __metaclass__ = plugins.PluginMount
    
    def __unicode__(self):
        return type(self).__name__
    
    def __str__(self):
        return unicode(self)
    
    def __init__(self):
        self.head = []
        self.content = []
        self.tail = []
    
    def __getattribute__(self, attr):
        """ Select head, content or tail section depending on the method name """
        IGNORE_ATTRS = (
            'append',
            'cmd_section',
            'head',
            'tail',
            'content',
            'script_method',
            'function_method'
        )
        if attr == 'prepare':
            self.cmd_section = self.head
        elif attr == 'commit':
            self.cmd_section = self.tail
        elif attr not in IGNORE_ATTRS:
            self.cmd_section = self.content
        return super(ServiceBackend, self).__getattribute__(attr)
    
    @classmethod
    def get_actions(cls):
        return [ action for action in cls.actions if action in dir(cls) ]
    
    @classmethod
    def get_name(cls):
        return cls.__name__
    
    @classmethod
    def is_main(cls, obj):
        opts = obj._meta
        return cls.model == '%s.%s' % (opts.app_label, opts.object_name)
    
    @classmethod
    def get_related(cls, obj):
        opts = obj._meta
        model = '%s.%s' % (opts.app_label, opts.object_name)
        for rel_model, field in cls.related_models:
            if rel_model == model:
                related = obj
                for attribute in field.split('__'):
                    related = getattr(related, attribute)
                return related
        return None
    
    @classmethod
    def get_backends(cls, instance=None, action=None):
        backends = cls.get_plugins()
        included = []
        # Filter for instance or action
        if instance or action:
            for backend in backends:
                include = True
                if instance:
                    opts = instance._meta
                    if backend.model != '.'.join((opts.app_label, opts.object_name)):
                        include = False
                if include and action:
                    if action not in backend.get_actions():
                        include = False
                if include:
                    included.append(backend)
            backends = included
        return backends
    
    @classmethod
    def get_backend(cls, name):
        return cls.get_plugin(name)
    
    @classmethod
    def model_class(cls):
        return get_model(cls.model)
    
    @property
    def scripts(self):
        """ group commands based on their method """
        if not self.content:
            return []
        scripts = {}
        for method, cmd in self.content:
            scripts[method] = []
        for method, commands in self.head + self.content + self.tail:
            try:
                scripts[method] += commands
            except KeyError:
                pass
        return list(scripts.iteritems())
    
    def get_banner(self):
        time = timezone.now().strftime("%h %d, %Y %I:%M:%S")
        return "Generated by Orchestra at %s" % time
    
    def execute(self, server, async=False):
        from .models import BackendLog
        scripts = self.scripts
        state = BackendLog.STARTED
        if not scripts:
            state = BackendLog.SUCCESS
        log = BackendLog.objects.create(backend=self.get_name(), state=state, server=server)
        for method, commands in scripts:
            method(log, server, commands, async)
            if log.state != BackendLog.SUCCESS:
                break
        return log
    
    def append(self, *cmd):
        # aggregate commands acording to its execution method
        if isinstance(cmd[0], basestring):
            method = self.script_method
            cmd = cmd[0]
        else:
            method = self.function_method
            cmd = partial(*cmd)
        if not self.cmd_section or self.cmd_section[-1][0] != method:
            self.cmd_section.append((method, [cmd]))
        else:
            self.cmd_section[-1][1].append(cmd)
    
    def prepare(self):
        """
        hook for executing something at the beging
        define functions or initialize state
        """
        self.append(
            'set -e\n'
            'set -o pipefail'
        )
    
    def commit(self):
        """
        hook for executing something at the end
        apply the configuration, usually reloading a service 
        reloading a service is done in a separated method in order to reload 
        the service once in bulk operations
        """
        self.append('exit 0')


class ServiceController(ServiceBackend):
    actions = ('save', 'delete')
    abstract = True
    
    @classmethod
    def get_verbose_name(cls):
        return _("[S] %s") % super(ServiceController, cls).get_verbose_name()
    
    @classmethod
    def get_backends(cls):
        """ filter controller classes """
        backends = super(ServiceController, cls).get_backends()
        return [
            backend for backend in backends if ServiceController in backend.__mro__
        ]