""" An utility to load modules and objects in DIRAC and extensions, being sure that the extensions are considered
"""
from __future__ import absolute_import
from __future__ import division
from __future__ import print_function

__RCSID__ = "$Id$"

import six
import re
import pkgutil
import collections

from DIRAC import gLogger, S_OK, S_ERROR
from DIRAC.Core.Utilities import DErrno
from DIRAC.Core.Utilities import DIRACSingleton
from DIRAC.Core.Utilities.Extensions import extensionsByPriority, recurseImport


@six.add_metaclass(DIRACSingleton.DIRACSingleton)
class ObjectLoader(object):
  """ Class for loading objects. Example:

      from DIRAC.Core.Utilities.ObjectLoader import ObjectLoader
      ol = ObjectLoader()
      ol.loadObject('TransformationSystem.Client.TransformationClient')
  """
  def __init__(self, baseModules=False):
    """ init
    """
    # We save the original arguments in case
    # we need to reinitialize the rootModules
    # CAUTION: we cant do it after doing
    # baseModules = ['DIRAC']
    # because then baseModules, self.baseModules, and __rootModules
    # are the same and edited in place by __generateRootModules !!
    # (Think of it, it's a binding to a list)
    self.originalBaseModules = baseModules
    self._init(baseModules)

  def _init(self, baseModules):
    """ Actually performs the initialization """
    if not baseModules:
      baseModules = ['DIRAC']
    self.__rootModules = baseModules
    self.__objs = {}
    self.__generateRootModules(baseModules)

  def reloadRootModules(self):
    """ Retrigger the initialization of the rootModules.

        This should be used with care.
        Currently, its only use is (and should stay) to retrigger
        the initialization after the CS has been fully initialized in
        LocalConfiguration.enableCS
    """
    # Load the original baseModule argument that was given
    # to the constructor
    baseModules = self.originalBaseModules
    # and replay the init sequence
    self._init(baseModules)

  def __rootImport(self, modName, hideExceptions=False):
    """ Auto search which root module has to be used
    """
    for rootModule in self.__rootModules:
      impName = modName
      if rootModule:
        impName = "%s.%s" % (rootModule, impName)
      gLogger.debug("Trying to load %s" % impName)
      result = recurseImport(impName, hideExceptions=hideExceptions)
      if not result['OK']:
        return result
      if result['Value']:
        return S_OK((impName, result['Value']))
    return S_OK()

  def __generateRootModules(self, baseModules):
    """ Iterate over all the possible root modules
    """
    self.__rootModules = baseModules
    for rootModule in reversed(extensionsByPriority()):
      if rootModule not in self.__rootModules:
        self.__rootModules.append(rootModule)
    self.__rootModules.append("")

    # Reversing the order because we want first to look in the extension(s)
    self.__rootModules.reverse()

  def loadModule(self, importString, hideExceptions=False):
    """ Load a module from an import string
    """
    result = self.__rootImport(importString, hideExceptions=hideExceptions)
    if not result['OK']:
      return result
    if not result['Value']:
      return S_ERROR(DErrno.EIMPERR, "No module %s found" % importString)
    return S_OK(result['Value'][1])

  def loadObject(self, importString, objName=False, hideExceptions=False):
    """ Load an object from inside a module
    """
    if not objName:
      objName = importString.split(".")[-1]

    result = self.loadModule(importString, hideExceptions=hideExceptions)
    if not result['OK']:
      return result
    modObj = result['Value']
    try:
      result = S_OK(getattr(modObj, objName))
      result['ModuleFile'] = modObj.__file__
      return result
    except AttributeError:
      return S_ERROR(DErrno.EIMPERR, "%s does not contain a %s object" % (importString, objName))

  def getObjects(self, modulePath, reFilter=None, parentClass=None, recurse=False, continueOnError=False):
    """ Search for modules under a certain path

        modulePath is the import string needed to access the parent module.
        Root modules will be included automatically (like DIRAC). For instance "ConfigurationSystem.Service"

        reFilter is a regular expression to filter what to load. For instance ".*Handler"
        parentClass is a class object from which the loaded modules have to import from. For instance RequestHandler

        :param continueOnError: if True, continue loading further module even if one fails
    """
    modules = collections.OrderedDict()
    if isinstance(reFilter, six.string_types):
      reFilter = re.compile(reFilter)

    for rootModule in self.__rootModules:
      impPath = modulePath
      if rootModule:
        impPath = "%s.%s" % (rootModule, impPath)
      gLogger.debug("Trying to load %s" % impPath)

      result = recurseImport(impPath)
      if not result['OK']:
        return result
      if not result['Value']:
        continue
      parentModule = result['Value']
      gLogger.verbose("Loaded module %s at %s" % (impPath, parentModule.__path__))

      for _modLoader, modName, isPkg in pkgutil.walk_packages(parentModule.__path__):
        if reFilter and not reFilter.match(modName):
          continue
        if isPkg:
          if recurse:
            result = self.getObjects("%s.%s" % (modulePath, modName), reFilter=reFilter,
                                     parentClass=parentClass, recurse=recurse)
            if not result['OK']:
              return result
            modules.update(result['Value'])
          continue
        modKeyName = "%s.%s" % (modulePath, modName)
        if modKeyName in modules:
          continue
        fullName = "%s.%s" % (impPath, modName)
        result = recurseImport(fullName)
        if not result['OK']:
          if continueOnError:
            gLogger.error("Error loading module but continueOnError is true", "module %s error %s" % (fullName, result))
            continue
          return result
        if not result['Value']:
          continue

        modClass = getattr(result['Value'], modName, None)
        if not modClass:
          gLogger.warn("%s does not contain a %s object" % (fullName, modName))
          continue

        if parentClass and not issubclass(modClass, parentClass):
          continue

        modules[modKeyName] = modClass

    return S_OK(modules)
