# -*- coding: utf-8 -*-
# Part of Odoo, Flectra. See LICENSE file for full copyright and licensing details.

""" This module provides the elements for managing two different API styles,
    namely the "traditional" and "record" styles.

    In the "traditional" style, parameters like the database cursor, user id,
    context dictionary and record ids (usually denoted as ``cr``, ``uid``,
    ``context``, ``ids``) are passed explicitly to all methods. In the "record"
    style, those parameters are hidden into model instances, which gives it a
    more object-oriented feel.

    For instance, the statements::

        model = self.pool.get(MODEL)
        ids = model.search(cr, uid, DOMAIN, context=context)
        for rec in model.browse(cr, uid, ids, context=context):
            print rec.name
        model.write(cr, uid, ids, VALUES, context=context)

    may also be written as::

        env = Environment(cr, uid, context) # cr, uid, context wrapped in env
        model = env[MODEL]                  # retrieve an instance of MODEL
        recs = model.search(DOMAIN)         # search returns a recordset
        for rec in recs:                    # iterate over the records
            print rec.name
        recs.write(VALUES)                  # update all records in recs

    Methods written in the "traditional" style are automatically decorated,
    following some heuristics based on parameter names.
"""

__all__ = [
    'Environment',
    'Meta', 'guess', 'noguess',
    'model', 'multi', 'one',
    'model_cr', 'model_cr_context',
    'cr', 'cr_context',
    'cr_uid', 'cr_uid_context',
    'cr_uid_id', 'cr_uid_id_context',
    'cr_uid_ids', 'cr_uid_ids_context',
    'cr_uid_records', 'cr_uid_records_context',
    'constrains', 'depends', 'onchange', 'returns',
    'call_kw',
]

import logging
from collections import defaultdict, Mapping
from contextlib import contextmanager
from inspect import currentframe, getargspec
from pprint import pformat
from weakref import WeakSet

from decorator import decorate, decorator
from werkzeug.local import Local, release_local

from flectra.tools import frozendict, classproperty, StackMap
from flectra.exceptions import CacheMiss

_logger = logging.getLogger(__name__)

# The following attributes are used, and reflected on wrapping methods:
#  - method._constrains: set by @constrains, specifies constraint dependencies
#  - method._depends: set by @depends, specifies compute dependencies
#  - method._returns: set by @returns, specifies return model
#  - method._onchange: set by @onchange, specifies onchange fields
#  - method.clear_cache: set by @ormcache, used to clear the cache
#
# On wrapping method only:
#  - method._api: decorator function, used for re-applying decorator
#  - method._orig: original method
#

WRAPPED_ATTRS = ('__module__', '__name__', '__doc__', '_constrains',
                 '_depends', '_onchange', '_returns', 'clear_cache')

INHERITED_ATTRS = ('_returns',)


class Params(object):
    def __init__(self, args, kwargs):
        self.args = args
        self.kwargs = kwargs
    def __str__(self):
        params = []
        for arg in self.args:
            params.append(repr(arg))
        for item in sorted(self.kwargs.items()):
            params.append("%s=%r" % item)
        return ', '.join(params)


class Meta(type):
    """ Metaclass that automatically decorates traditional-style methods by
        guessing their API. It also implements the inheritance of the
        :func:`returns` decorators.
    """

    def __new__(meta, name, bases, attrs):
        # dummy parent class to catch overridden methods decorated with 'returns'
        parent = type.__new__(meta, name, bases, {})

        for key, value in list(attrs.items()):
            if not key.startswith('__') and callable(value):
                # make the method inherit from decorators
                value = propagate(getattr(parent, key, None), value)

                # guess calling convention if none is given
                if not hasattr(value, '_api'):
                    try:
                        value = guess(value)
                    except TypeError:
                        pass

                if (getattr(value, '_api', None) or '').startswith('cr'):
                    _logger.warning("Deprecated method %s.%s in module %s", name, key, attrs.get('__module__'))

                attrs[key] = value

        return type.__new__(meta, name, bases, attrs)


def attrsetter(attr, value):
    """ Return a function that sets ``attr`` on its argument and returns it. """
    return lambda method: setattr(method, attr, value) or method

def propagate(method1, method2):
    """ Propagate decorators from ``method1`` to ``method2``, and return the
        resulting method.
    """
    if method1:
        for attr in INHERITED_ATTRS:
            if hasattr(method1, attr) and not hasattr(method2, attr):
                setattr(method2, attr, getattr(method1, attr))
    return method2


def constrains(*args):
    """ Decorates a constraint checker. Each argument must be a field name
    used in the check::

        @api.one
        @api.constrains('name', 'description')
        def _check_description(self):
            if self.name == self.description:
                raise ValidationError("Fields name and description must be different")

    Invoked on the records on which one of the named fields has been modified.

    Should raise :class:`~flectra.exceptions.ValidationError` if the
    validation failed.

    .. warning::

        ``@constrains`` only supports simple field names, dotted names
        (fields of relational fields e.g. ``partner_id.customer``) are not
        supported and will be ignored

        ``@constrains`` will be triggered only if the declared fields in the
        decorated method are included in the ``create`` or ``write`` call.
        It implies that fields not present in a view will not trigger a call
        during a record creation. A override of ``create`` is necessary to make
        sure a constraint will always be triggered (e.g. to test the absence of
        value).

    """
    return attrsetter('_constrains', args)


def onchange(*args):
    """ Return a decorator to decorate an onchange method for given fields.
        Each argument must be a field name::

            @api.onchange('partner_id')
            def _onchange_partner(self):
                self.message = "Dear %s" % (self.partner_id.name or "")

        In the form views where the field appears, the method will be called
        when one of the given fields is modified. The method is invoked on a
        pseudo-record that contains the values present in the form. Field
        assignments on that record are automatically sent back to the client.

        The method may return a dictionary for changing field domains and pop up
        a warning message, like in the old API::

            return {
                'domain': {'other_id': [('partner_id', '=', partner_id)]},
                'warning': {'title': "Warning", 'message': "What is this?"},
            }


        .. warning::

            ``@onchange`` only supports simple field names, dotted names
            (fields of relational fields e.g. ``partner_id.tz``) are not
            supported and will be ignored
    """
    return attrsetter('_onchange', args)


def depends(*args):
    """ Return a decorator that specifies the field dependencies of a "compute"
        method (for new-style function fields). Each argument must be a string
        that consists in a dot-separated sequence of field names::

            pname = fields.Char(compute='_compute_pname')

            @api.one
            @api.depends('partner_id.name', 'partner_id.is_company')
            def _compute_pname(self):
                if self.partner_id.is_company:
                    self.pname = (self.partner_id.name or "").upper()
                else:
                    self.pname = self.partner_id.name

        One may also pass a single function as argument. In that case, the
        dependencies are given by calling the function with the field's model.
    """
    if args and callable(args[0]):
        args = args[0]
    elif any('id' in arg.split('.') for arg in args):
        raise NotImplementedError("Compute method cannot depend on field 'id'.")
    return attrsetter('_depends', args)


def returns(model, downgrade=None, upgrade=None):
    """ Return a decorator for methods that return instances of ``model``.

        :param model: a model name, or ``'self'`` for the current model

        :param downgrade: a function ``downgrade(self, value, *args, **kwargs)``
            to convert the record-style ``value`` to a traditional-style output

        :param upgrade: a function ``upgrade(self, value, *args, **kwargs)``
            to convert the traditional-style ``value`` to a record-style output

        The arguments ``self``, ``*args`` and ``**kwargs`` are the ones passed
        to the method in the record-style.

        The decorator adapts the method output to the api style: ``id``, ``ids`` or
        ``False`` for the traditional style, and recordset for the record style::

            @model
            @returns('res.partner')
            def find_partner(self, arg):
                ...     # return some record

            # output depends on call style: traditional vs record style
            partner_id = model.find_partner(cr, uid, arg, context=context)

            # recs = model.browse(cr, uid, ids, context)
            partner_record = recs.find_partner(arg)

        Note that the decorated method must satisfy that convention.

        Those decorators are automatically *inherited*: a method that overrides
        a decorated existing method will be decorated with the same
        ``@returns(model)``.
    """
    return attrsetter('_returns', (model, downgrade, upgrade))


def downgrade(method, value, self, args, kwargs):
    """ Convert ``value`` returned by ``method`` on ``self`` to traditional style. """
    spec = getattr(method, '_returns', None)
    if not spec:
        return value
    _, convert, _ = spec
    if convert and len(getargspec(convert).args) > 1:
        return convert(self, value, *args, **kwargs)
    elif convert:
        return convert(value)
    else:
        return value.ids


def aggregate(method, value, self):
    """ Aggregate record-style ``value`` for a method decorated with ``@one``. """
    spec = getattr(method, '_returns', None)
    if spec:
        # value is a list of instances, concatenate them
        model, _, _ = spec
        if model == 'self':
            return sum(value, self.browse())
        elif model:
            return sum(value, self.env[model])
    return value


def split_context(method, args, kwargs):
    """ Extract the context from a pair of positional and keyword arguments.
        Return a triple ``context, args, kwargs``.
    """
    pos = len(getargspec(method).args) - 1
    if pos < len(args):
        return args[pos], args[:pos], kwargs
    else:
        return kwargs.pop('context', None), args, kwargs


def model(method):
    """ Decorate a record-style method where ``self`` is a recordset, but its
        contents is not relevant, only the model is. Such a method::

            @api.model
            def method(self, args):
                ...

        may be called in both record and traditional styles, like::

            # recs = model.browse(cr, uid, ids, context)
            recs.method(args)

            model.method(cr, uid, args, context=context)

        Notice that no ``ids`` are passed to the method in the traditional style.
    """
    if method.__name__ == 'create':
        return model_create_single(method)
    method._api = 'model'
    return method


def multi(method):
    """ Decorate a record-style method where ``self`` is a recordset. The method
        typically defines an operation on records. Such a method::

            @api.multi
            def method(self, args):
                ...

        may be called in both record and traditional styles, like::

            # recs = model.browse(cr, uid, ids, context)
            recs.method(args)

            model.method(cr, uid, ids, args, context=context)
    """
    method._api = 'multi'
    return method


def one(method):
    """ Decorate a record-style method where ``self`` is expected to be a
        singleton instance. The decorated method automatically loops on records,
        and makes a list with the results. In case the method is decorated with
        :func:`returns`, it concatenates the resulting instances. Such a
        method::

            @api.one
            def method(self, args):
                return self.name

        may be called in both record and traditional styles, like::

            # recs = model.browse(cr, uid, ids, context)
            names = recs.method(args)

            names = model.method(cr, uid, ids, args, context=context)

        .. deprecated:: 9.0

            :func:`~.one` often makes the code less clear and behaves in ways
            developers and readers may not expect.

            It is strongly recommended to use :func:`~.multi` and either
            iterate on the ``self`` recordset or ensure that the recordset
            is a single record with :meth:`~flectra.models.Model.ensure_one`.
    """
    def loop(method, self, *args, **kwargs):
        result = [method(rec, *args, **kwargs) for rec in self]
        return aggregate(method, result, self)

    wrapper = decorator(loop, method)
    wrapper._api = 'one'
    return wrapper


def model_cr(method):
    """ Decorate a record-style method where ``self`` is a recordset, but its
        contents is not relevant, only the model is. Such a method::

            @api.model_cr
            def method(self, args):
                ...

        may be called in both record and traditional styles, like::

            # recs = model.browse(cr, uid, ids, context)
            recs.method(args)

            model.method(cr, args)

        Notice that no ``uid``, ``ids``, ``context`` are passed to the method in
        the traditional style.
    """
    method._api = 'model_cr'
    return method


def model_cr_context(method):
    """ Decorate a record-style method where ``self`` is a recordset, but its
        contents is not relevant, only the model is. Such a method::

            @api.model_cr_context
            def method(self, args):
                ...

        may be called in both record and traditional styles, like::

            # recs = model.browse(cr, uid, ids, context)
            recs.method(args)

            model.method(cr, args, context=context)

        Notice that no ``uid``, ``ids`` are passed to the method in the
        traditional style.
    """
    method._api = 'model_cr_context'
    return method


_create_logger = logging.getLogger(__name__ + '.create')


def _model_create_single(create, self, arg):
    # 'create' expects a dict and returns a record
    if isinstance(arg, Mapping):
        return create(self, arg)
    if len(arg) > 1:
        _create_logger.debug("%s.create() called with %d dicts", self, len(arg))
    return self.browse().concat(*(create(self, vals) for vals in arg))


def model_create_single(method):
    """ Decorate a method that takes a dictionary and creates a single record.
        The method may be called with either a single dict or a list of dicts::

            record = model.create(vals)
            records = model.create([vals, ...])
    """
    wrapper = decorate(method, _model_create_single)
    wrapper._api = 'model_create'
    return wrapper


def _model_create_multi(create, self, arg):
    # 'create' expects a list of dicts and returns a recordset
    if isinstance(arg, Mapping):
        return create(self, [arg])
    return create(self, arg)


def model_create_multi(method):
    """ Decorate a method that takes a list of dictionaries and creates multiple
        records. The method may be called with either a single dict or a list of
        dicts::

            record = model.create(vals)
            records = model.create([vals, ...])
    """
    wrapper = decorate(method, _model_create_multi)
    wrapper._api = 'model_create'
    return wrapper


def cr(method):
    """ Decorate a traditional-style method that takes ``cr`` as a parameter.
        Such a method may be called in both record and traditional styles, like::

            # recs = model.browse(cr, uid, ids, context)
            recs.method(args)

            model.method(cr, args)
    """
    method._api = 'cr'
    return method


def cr_context(method):
    """ Decorate a traditional-style method that takes ``cr``, ``context`` as parameters. """
    method._api = 'cr_context'
    return method


def cr_uid(method):
    """ Decorate a traditional-style method that takes ``cr``, ``uid`` as parameters. """
    method._api = 'cr_uid'
    return method


def cr_uid_context(method):
    """ Decorate a traditional-style method that takes ``cr``, ``uid``, ``context`` as
        parameters. Such a method may be called in both record and traditional
        styles, like::

            # recs = model.browse(cr, uid, ids, context)
            recs.method(args)

            model.method(cr, uid, args, context=context)
    """
    method._api = 'cr_uid_context'
    return method


def cr_uid_id(method):
    """ Decorate a traditional-style method that takes ``cr``, ``uid``, ``id`` as
        parameters. Such a method may be called in both record and traditional
        styles. In the record style, the method automatically loops on records.
    """
    method._api = 'cr_uid_id'
    return method


def cr_uid_id_context(method):
    """ Decorate a traditional-style method that takes ``cr``, ``uid``, ``id``,
        ``context`` as parameters. Such a method::

            @api.cr_uid_id
            def method(self, cr, uid, id, args, context=None):
                ...

        may be called in both record and traditional styles, like::

            # rec = model.browse(cr, uid, id, context)
            rec.method(args)

            model.method(cr, uid, id, args, context=context)
    """
    method._api = 'cr_uid_id_context'
    return method


def cr_uid_ids(method):
    """ Decorate a traditional-style method that takes ``cr``, ``uid``, ``ids`` as
        parameters. Such a method may be called in both record and traditional
        styles.
    """
    method._api = 'cr_uid_ids'
    return method


def cr_uid_ids_context(method):
    """ Decorate a traditional-style method that takes ``cr``, ``uid``, ``ids``,
        ``context`` as parameters. Such a method::

            @api.cr_uid_ids_context
            def method(self, cr, uid, ids, args, context=None):
                ...

        may be called in both record and traditional styles, like::

            # recs = model.browse(cr, uid, ids, context)
            recs.method(args)

            model.method(cr, uid, ids, args, context=context)

        It is generally not necessary, see :func:`guess`.
    """
    method._api = 'cr_uid_ids_context'
    return method


def cr_uid_records(method):
    """ Decorate a traditional-style method that takes ``cr``, ``uid``, a
        recordset of model ``self`` as parameters. Such a method::

            @api.cr_uid_records
            def method(self, cr, uid, records, args):
                ...

        may be called in both record and traditional styles, like::

            # records = model.browse(cr, uid, ids, context)
            records.method(args)

            model.method(cr, uid, records, args)
    """
    method._api = 'cr_uid_records'
    return method


def cr_uid_records_context(method):
    """ Decorate a traditional-style method that takes ``cr``, ``uid``, a
        recordset of model ``self``, ``context`` as parameters. Such a method::

            @api.cr_uid_records_context
            def method(self, cr, uid, records, args, context=None):
                ...

        may be called in both record and traditional styles, like::

            # records = model.browse(cr, uid, ids, context)
            records.method(args)

            model.method(cr, uid, records, args, context=context)
    """
    method._api = 'cr_uid_records_context'
    return method


def v7(method_v7):
    """ Decorate a method that supports the old-style api only. A new-style api
        may be provided by redefining a method with the same name and decorated
        with :func:`~.v8`::

            @api.v7
            def foo(self, cr, uid, ids, context=None):
                ...

            @api.v8
            def foo(self):
                ...

        Special care must be taken if one method calls the other one, because
        the method may be overridden! In that case, one should call the method
        from the current class (say ``MyClass``), for instance::

            @api.v7
            def foo(self, cr, uid, ids, context=None):
                # Beware: records.foo() may call an overriding of foo()
                records = self.browse(cr, uid, ids, context)
                return MyClass.foo(records)

        Note that the wrapper method uses the docstring of the first method.
    """
    # retrieve method_v8 from the caller's frame
    frame = currentframe().f_back
    return frame.f_locals.get(method_v7.__name__, method_v7)


def v8(method_v8):
    """ Decorate a method that supports the new-style api only. An old-style api
        may be provided by redefining a method with the same name and decorated
        with :func:`~.v7`::

            @api.v8
            def foo(self):
                ...

            @api.v7
            def foo(self, cr, uid, ids, context=None):
                ...

        Note that the wrapper method uses the docstring of the first method.
    """
    if method_v8.__name__ == 'read':
        return multi(method_v8)
    method_v8._api = 'v8'
    return method_v8


def noguess(method):
    """ Decorate a method to prevent any effect from :func:`guess`. """
    method._api = None
    return method


def guess(method):
    """ Decorate ``method`` to make it callable in both traditional and record
        styles. This decorator is applied automatically by the model's
        metaclass, and has no effect on already-decorated methods.

        The API style is determined by heuristics on the parameter names: ``cr``
        or ``cursor`` for the cursor, ``uid`` or ``user`` for the user id,
        ``id`` or ``ids`` for a list of record ids, and ``context`` for the
        context dictionary. If a traditional API is recognized, one of the
        decorators :func:`cr`, :func:`cr_context`, :func:`cr_uid`,
        :func:`cr_uid_context`, :func:`cr_uid_id`, :func:`cr_uid_id_context`,
        :func:`cr_uid_ids`, :func:`cr_uid_ids_context` is applied on the method.

        Method calls are considered traditional style when their first parameter
        is a database cursor.
    """
    if hasattr(method, '_api'):
        return method

    # introspection on argument names to determine api style
    args, vname, kwname, defaults = getargspec(method)
    names = tuple(args) + (None,) * 4

    if names[0] == 'self':
        if names[1] in ('cr', 'cursor'):
            if names[2] in ('uid', 'user'):
                if names[3] == 'ids':
                    if 'context' in names or kwname:
                        return cr_uid_ids_context(method)
                    else:
                        return cr_uid_ids(method)
                elif names[3] == 'id' or names[3] == 'res_id':
                    if 'context' in names or kwname:
                        return cr_uid_id_context(method)
                    else:
                        return cr_uid_id(method)
                elif 'context' in names or kwname:
                    return cr_uid_context(method)
                else:
                    return cr_uid(method)
            elif 'context' in names:
                return cr_context(method)
            else:
                return cr(method)

    # no wrapping by default
    return noguess(method)


def expected(decorator, func):
    """ Decorate ``func`` with ``decorator`` if ``func`` is not wrapped yet. """
    return decorator(func) if not hasattr(func, '_api') else func


def _call_kw_model(method, self, args, kwargs):
    context, args, kwargs = split_context(method, args, kwargs)
    recs = self.with_context(context or {})
    _logger.debug("call %s.%s(%s)", recs, method.__name__, Params(args, kwargs))
    result = method(recs, *args, **kwargs)
    return downgrade(method, result, recs, args, kwargs)


def _call_kw_model_create(method, self, args, kwargs):
    # special case for method 'create'
    context, args, kwargs = split_context(method, args, kwargs)
    recs = self.with_context(context or {})
    _logger.debug("call %s.%s(%s)", recs, method.__name__, Params(args, kwargs))
    result = method(recs, *args, **kwargs)
    return result.id if isinstance(args[0], Mapping) else result.ids


def _call_kw_multi(method, self, args, kwargs):
    ids, args = args[0], args[1:]
    context, args, kwargs = split_context(method, args, kwargs)
    recs = self.with_context(context or {}).browse(ids)
    _logger.debug("call %s.%s(%s)", recs, method.__name__, Params(args, kwargs))
    result = method(recs, *args, **kwargs)
    return downgrade(method, result, recs, args, kwargs)


def call_kw(model, name, args, kwargs):
    """ Invoke the given method ``name`` on the recordset ``model``. """
    method = getattr(type(model), name)
    api = getattr(method, '_api', None)
    if api == 'model':
        return _call_kw_model(method, model, args, kwargs)
    elif api == 'model_create':
        return _call_kw_model_create(method, model, args, kwargs)
    else:
        return _call_kw_multi(method, model, args, kwargs)


class Environment(Mapping):
    """ An environment wraps data for ORM records:

        - :attr:`cr`, the current database cursor;
        - :attr:`uid`, the current user id;
        - :attr:`context`, the current context dictionary.

        It provides access to the registry by implementing a mapping from model
        names to new api models. It also holds a cache for records, and a data
        structure to manage recomputations.
    """
    _local = Local()

    @classproperty
    def envs(cls):
        return cls._local.environments

    @classmethod
    @contextmanager
    def manage(cls):
        """ Context manager for a set of environments. """
        if hasattr(cls._local, 'environments'):
            yield
        else:
            try:
                cls._local.environments = Environments()
                yield
            finally:
                release_local(cls._local)

    @classmethod
    def reset(cls):
        """ Clear the set of environments.
            This may be useful when recreating a registry inside a transaction.
        """
        cls._local.environments = Environments()

    def __new__(cls, cr, uid, context):
        assert context is not None
        args = (cr, uid, context)

        # if env already exists, return it
        env, envs = None, cls.envs
        for env in envs:
            if env.args == args:
                return env

        # otherwise create environment, and add it in the set
        self = object.__new__(cls)
        self.cr, self.uid, self.context = self.args = (cr, uid, frozendict(context))
        self.registry = Registry(cr.dbname)
        self.cache = envs.cache
        self._protected = StackMap()                # {field: ids, ...}
        self.dirty = defaultdict(set)               # {record: set(field_name), ...}
        self.all = envs
        envs.add(self)
        return self

    #
    # Mapping methods
    #

    def __contains__(self, model_name):
        """ Test whether the given model exists. """
        return model_name in self.registry

    def __getitem__(self, model_name):
        """ Return an empty recordset from the given model. """
        return self.registry[model_name]._browse((), self)

    def __iter__(self):
        """ Return an iterator on model names. """
        return iter(self.registry)

    def __len__(self):
        """ Return the size of the model registry. """
        return len(self.registry)

    def __eq__(self, other):
        return self is other

    def __ne__(self, other):
        return self is not other

    def __hash__(self):
        return object.__hash__(self)

    def __call__(self, cr=None, user=None, context=None):
        """ Return an environment based on ``self`` with modified parameters.

            :param cr: optional database cursor to change the current cursor
            :param user: optional user/user id to change the current user
            :param context: optional context dictionary to change the current context
        """
        cr = self.cr if cr is None else cr
        uid = self.uid if user is None else int(user)
        context = self.context if context is None else context
        return Environment(cr, uid, context)

    def ref(self, xml_id, raise_if_not_found=True):
        """ return the record corresponding to the given ``xml_id`` """
        return self['ir.model.data'].xmlid_to_object(xml_id, raise_if_not_found=raise_if_not_found)

    @property
    def user(self):
        """ return the current user (as an instance) """
        return self(user=SUPERUSER_ID)['res.users'].browse(self.uid)

    @property
    def lang(self):
        """ return the current language code """
        return self.context.get('lang')

    @contextmanager
    def _do_in_mode(self, mode):
        if self.all.mode:
            yield
        else:
            try:
                self.all.mode = mode
                yield
            finally:
                self.all.mode = False
                self.dirty.clear()

    def do_in_draft(self):
        """ Context-switch to draft mode, where all field updates are done in
            cache only.
        """
        return self._do_in_mode(True)

    @property
    def in_draft(self):
        """ Return whether we are in draft mode. """
        return bool(self.all.mode)

    def do_in_onchange(self):
        """ Context-switch to 'onchange' draft mode, which is a specialized
            draft mode used during execution of onchange methods.
        """
        return self._do_in_mode('onchange')

    @property
    def in_onchange(self):
        """ Return whether we are in 'onchange' draft mode. """
        return self.all.mode == 'onchange'

    def clear(self):
        """ Clear all record caches, and discard all fields to recompute.
            This may be useful when recovering from a failed ORM operation.
        """
        self.cache.invalidate()
        self.all.todo.clear()

    @contextmanager
    def clear_upon_failure(self):
        """ Context manager that clears the environments (caches and fields to
            recompute) upon exception.
        """
        try:
            yield
        except Exception:
            self.clear()
            raise

    def protected(self, field):
        """ Return the recordset for which ``field`` should not be invalidated or recomputed. """
        return self[field.model_name].browse(self._protected.get(field, ()))

    @contextmanager
    def protecting(self, what, records=None):
        """ Prevent the invalidation or recomputation of fields on records.
            The parameters are either:
             - ``what`` a collection of fields and ``records`` a recordset, or
             - ``what`` a collection of pairs ``(fields, records)``.
        """
        protected = self._protected
        try:
            protected.pushmap()
            what = what if records is None else [(what, records)]
            for fields, records in what:
                for field in fields:
                    ids = protected.get(field, frozenset())
                    protected[field] = ids.union(records._ids)
            yield
        finally:
            protected.popmap()

    def field_todo(self, field):
        """ Return a recordset with all records to recompute for ``field``. """
        ids = {rid for recs in self.all.todo.get(field, ()) for rid in recs.ids}
        return self[field.model_name].browse(ids)

    def check_todo(self, field, record):
        """ Check whether ``field`` must be recomputed on ``record``, and if so,
            return the corresponding recordset to recompute.
        """
        for recs in self.all.todo.get(field, []):
            if recs & record:
                return recs

    def add_todo(self, field, records):
        """ Mark ``field`` to be recomputed on ``records``. """
        recs_list = self.all.todo.setdefault(field, [])
        for i, recs in enumerate(recs_list):
            if recs.env == records.env:
                # only add records if not already in the recordset, much much
                # cheaper in case recs is big and records is a singleton
                # already present
                if not records <= recs:
                    recs_list[i] |= records
                break
        else:
            recs_list.append(records)

    def remove_todo(self, field, records):
        """ Mark ``field`` as recomputed on ``records``. """
        recs_list = [recs - records for recs in self.all.todo.pop(field, [])]
        recs_list = [r for r in recs_list if r]
        if recs_list:
            self.all.todo[field] = recs_list

    def has_todo(self):
        """ Return whether some fields must be recomputed. """
        return bool(self.all.todo)

    def get_todo(self):
        """ Return a pair ``(field, records)`` to recompute.
            The field is such that none of its dependencies must be recomputed.
        """
        field = min(self.all.todo, key=self.registry.field_sequence)
        return field, self.all.todo[field][0]

    @property
    def recompute(self):
        return self.all.recompute

    @contextmanager
    def norecompute(self):
        tmp = self.all.recompute
        self.all.recompute = False
        try:
            yield
        finally:
            self.all.recompute = tmp


class Environments(object):
    """ A common object for all environments in a request. """
    def __init__(self):
        self.envs = WeakSet()           # weak set of environments
        self.cache = Cache()            # cache for all records
        self.todo = {}                  # recomputations {field: [records]}
        self.mode = False               # flag for draft/onchange
        self.recompute = True

    def add(self, env):
        """ Add the environment ``env``. """
        self.envs.add(env)

    def __iter__(self):
        """ Iterate over environments. """
        return iter(self.envs)


class Cache(object):
    """ Implementation of the cache of records. """
    def __init__(self):
        # {field: {record_id: {key: value}}}
        self._data = defaultdict(lambda: defaultdict(dict))

    def contains(self, record, field):
        """ Return whether ``record`` has a value for ``field``. """
        key = field.cache_key(record)
        return key in self._data[field].get(record.id, ())

    def get(self, record, field):
        """ Return the value of ``field`` for ``record``. """
        key = field.cache_key(record)
        try:
            value = self._data[field][record.id][key]
        except KeyError:
            raise CacheMiss(record, field)

        return value.get() if isinstance(value, SpecialValue) else value

    def set(self, record, field, value):
        """ Set the value of ``field`` for ``record``. """
        key = field.cache_key(record)
        self._data[field][record.id][key] = value

    def remove(self, record, field):
        """ Remove the value of ``field`` for ``record``. """
        key = field.cache_key(record)
        del self._data[field][record.id][key]

    def contains_value(self, record, field):
        """ Return whether ``record`` has a regular value for ``field``. """
        key = field.cache_key(record)
        value = self._data[field][record.id].get(key, SpecialValue(None))
        return not isinstance(value, SpecialValue)

    def get_value(self, record, field, default=None):
        """ Return the regular value of ``field`` for ``record``. """
        key = field.cache_key(record)
        value = self._data[field][record.id].get(key, SpecialValue(None))
        return default if isinstance(value, SpecialValue) else value

    def set_special(self, record, field, getter):
        """ Set the value of ``field`` for ``record`` to return ``getter()``. """
        key = field.cache_key(record)
        self._data[field][record.id][key] = SpecialValue(getter)

    def set_failed(self, records, fields, exception):
        """ Mark ``fields`` on ``records`` with the given exception. """
        def getter():
            raise exception
        for field in fields:
            for record in records:
                self.set_special(record, field, getter)

    def get_fields(self, record):
        """ Return the fields with a value for ``record``. """
        for name, field in record._fields.items():
            key = field.cache_key(record)
            if name != 'id' and key in self._data[field].get(record.id, ()):
                yield field

    def get_records(self, model, field):
        """ Return the records of ``model`` that have a value for ``field``. """
        key = field.cache_key(model)
        # optimization: do not field.cache_key(record) for each record in cache
        ids = [
            record_id
            for record_id, field_record_cache in self._data[field].items()
            if key in field_record_cache
        ]
        return model.browse(ids)

    def get_missing_ids(self, records, field):
        """ Return the ids of ``records`` that have no value for ``field``. """
        key = field.cache_key(records)
        field_cache = self._data[field]
        for record_id in records._ids:
            if key not in field_cache.get(record_id, ()):
                yield record_id

    def copy(self, records, env):
        """ Copy the cache of ``records`` to ``env``. """
        src = records
        dst = records.with_env(env)
        for field, field_cache in self._data.items():
            src_key = field.cache_key(src)
            dst_key = field.cache_key(dst)
            for record_cache in field_cache.values():
                if src_key in record_cache and not isinstance(record_cache[src_key], SpecialValue):
                    # But not if it's a SpecialValue, which often is an access error
                    # because the other environment (eg. sudo()) is well expected to have access.
                    record_cache[dst_key] = record_cache[src_key]

    def invalidate(self, spec=None):
        """ Invalidate the cache, partially or totally depending on ``spec``. """
        if spec is None:
            self._data.clear()
        elif spec:
            data = self._data
            for field, ids in spec:
                if ids is None:
                    data.pop(field, None)
                else:
                    field_cache = data[field]
                    for id in ids:
                        field_cache.pop(id, None)

    def check(self, env):
        """ Check the consistency of the cache for the given environment. """
        # make a full copy of the cache, and invalidate it
        dump = defaultdict(dict)
        for field, field_cache in self._data.items():
            browse = env[field.model_name].browse
            for record_id, field_record_cache in field_cache.items():
                if record_id:
                    key = field.cache_key(browse(record_id))
                    if key in field_record_cache:
                        dump[field][record_id] = field_record_cache[key]

        self.invalidate()

        # re-fetch the records, and compare with their former cache
        invalids = []
        for field, field_dump in dump.items():
            records = env[field.model_name].browse(field_dump)
            for record in records:
                try:
                    cached = field_dump[record.id]
                    cached = cached.get() if isinstance(cached, SpecialValue) else cached
                    value = field.convert_to_record(cached, record)
                    fetched = record[field.name]
                    if fetched != value:
                        info = {'cached': value, 'fetched': fetched}
                        invalids.append((record, field, info))
                except (AccessError, MissingError):
                    pass

        if invalids:
            raise UserError('Invalid cache for fields\n' + pformat(invalids))


class SpecialValue(object):
    """ Wrapper for a function to get the cached value of a field. """
    __slots__ = ['get']

    def __init__(self, getter):
        self.get = getter


# keep those imports here in order to handle cyclic dependencies correctly
from flectra import SUPERUSER_ID
from flectra.exceptions import UserError, AccessError, MissingError
from flectra.modules.registry import Registry