"""Enhanced Beancount data structures for Conservancy

The classes in this module are interface-compatible with Beancount's core data

structures, and provide additional business logic that we want to use

throughout Conservancy tools.

"""

# Copyright © 2020  Brett Smith

#

# This program is free software: you can redistribute it and/or modify

# it under the terms of the GNU Affero General Public License as published by

# the Free Software Foundation, either version 3 of the License, or

# (at your option) any later version.

#

# This program is distributed in the hope that it will be useful,

# but WITHOUT ANY WARRANTY; without even the implied warranty of

# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

# GNU Affero General Public License for more details.

#

# You should have received a copy of the GNU Affero General Public License

# along with this program.  If not, see <https://www.gnu.org/licenses/>.

import collections

import datetime

import decimal

import functools

from beancount.core import account as bc_account

from beancount.core import amount as bc_amount

from beancount.core import convert as bc_convert

from typing import (

    cast,

    Callable,

    Hashable,

    Iterable,

    Iterator,

    MutableMapping,

    Optional,

    Sequence,

    TypeVar,

    Union,

)

from .beancount_types import (

    Directive,

    MetaKey,

    MetaValue,

    Posting as BasePosting,

    Transaction,

)

DecimalCompat = Union[decimal.Decimal, int]

LINK_METADATA = frozenset([

    'approval',

    'check',

    'contract',

    'invoice',

    'purchase-order',

    'receipt',

    'rt-id',

            super().__setitem__(key, value)

    def __delitem__(self, key: MetaKey) -> None:

        if self.post.meta is None:

            raise KeyError(key)

        else:

            super().__delitem__(key)

    # This is arguably cheating a litttle bit, but I'd argue the date of

    # the parent transaction still qualifies as posting metadata, and

    # it's something we want to access so often it's good to have it

    # within easy reach.

    @property

    def date(self) -> datetime.date:

        return self.txn.date

class Posting(BasePosting):

    """Enhanced Posting objects

    This class is a subclass of Beancount's native Posting class where

    specific fields are replaced with enhanced versions:

    * The `account` field is an Account object

    * The `units` field is our Amount object (which simply declares that the

      number is always a Decimal—see that docstring for details)

    * The `meta` field is a PostingMeta object

    """

    __slots__ = ()

    account: Account

    units: Amount

    # mypy correctly complains that our MutableMapping is not compatible

    # with Beancount's meta type declaration of Optional[Dict]. IMO

    # Beancount's type declaration is a smidge too specific: I think its type

    # declaration should also use MutableMapping, because it would be very

    # unusual for code to specifically require a Dict over that.

    # If it did, this declaration would pass without issue.

    meta: PostingMeta  # type:ignore[assignment]

    @classmethod

    def from_beancount(cls,

                       txn: Transaction,

                       index: int,

                       post: Optional[BasePosting]=None,

    ) -> 'Posting':

        if post is None:

            post = txn.postings[index]

        return cls(

            Account(post.account),

            *post[1:5],

            # see rationale above about Posting.meta

            PostingMeta(txn, index, post), # type:ignore[arg-type]

        )

    @classmethod

    def from_txn(cls, txn: Transaction) -> Iterator['Posting']:

        """Yield an enhanced Posting object for every posting in the transaction"""

        for index, post in enumerate(txn.postings):

            yield cls.from_beancount(txn, index, post)

    @classmethod

    def from_entries(cls, entries: Iterable[Directive]) -> Iterator['Posting']:

        """Yield an enhanced Posting object for every posting in these entries"""