# The Mia! Accounting Project.
# Author: imacat@mail.imacat.idv.tw (imacat), 2023/4/8

#  Copyright (c) 2023 imacat.
#
#  Licensed under the Apache License, Version 2.0 (the "License");
#  you may not use this file except in compliance with the License.
#  You may obtain a copy of the License at
#
#      http://www.apache.org/licenses/LICENSE-2.0
#
#  Unless required by applicable law or agreed to in writing, software
#  distributed under the License is distributed on an "AS IS" BASIS,
#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
#  See the License for the specific language governing permissions and
#  limitations under the License.
"""The forms for the unmatched offset management.

"""
from decimal import Decimal

import sqlalchemy as sa
from sqlalchemy.orm import selectinload

from accounting import db
from accounting.models import Account, JournalEntry, JournalEntryLineItem
from accounting.utils.cast import be
from accounting.utils.offset_alias import offset_alias


class OffsetPair:
    """A pair of an original line item and its offset."""

    def __init__(self, original_line_item: JournalEntryLineItem,
                 offset: JournalEntryLineItem):
        """Constructs a pair of an original line item and its offset.

        :param original_line_item: The original line item.
        :param offset: The offset.
        """
        self.original_line_item: JournalEntryLineItem = original_line_item
        """The original line item."""
        self.offset: JournalEntryLineItem = offset
        """The offset."""


class OffsetMatcher:
    """The offset matcher."""

    def __init__(self, account: Account):
        """Constructs the offset matcher.

        :param account: The account.
        """
        self.account: Account = account
        """The account."""
        self.matched_pairs: list[OffsetPair] = []
        """A list of matched pairs."""
        self.is_having_matches: bool = False
        """Whether there is any matches."""
        self.total: int = 0
        """The total number of unapplied debits or credits."""
        self.unapplied: list[JournalEntryLineItem] = []
        """The unapplied debits or credits."""
        self.unmatched_offsets: list[JournalEntryLineItem] = []
        """The unmatched offsets."""
        self.__find_matches()

    def __find_matches(self) -> None:
        """Finds the matched original line items and their offsets.

        :return: None.
        """
        self.unapplied: list[JournalEntryLineItem] = self.__get_unapplied()
        self.total = len(self.unapplied)
        if self.total == 0:
            self.is_having_matches = False
            return
        self.unmatched_offsets = self.__get_unmatched_offsets()
        remains: list[JournalEntryLineItem] = self.unmatched_offsets.copy()
        for original_item in self.unapplied:
            offset_candidates: list[JournalEntryLineItem] \
                = [x for x in remains
                   if (x.journal_entry.date > original_item.journal_entry.date
                       or (x.journal_entry.date
                           == original_item.journal_entry.date
                           and x.journal_entry.no
                           > original_item.journal_entry.no))
                   and x.currency_code == original_item.currency_code
                   and x.description == original_item.description
                   and x.amount == original_item.net_balance]
            if len(offset_candidates) == 0:
                continue
            self.matched_pairs.append(
                OffsetPair(original_item, offset_candidates[0]))
            original_item.match = offset_candidates[0]
            offset_candidates[0].match = original_item
            remains.remove(offset_candidates[0])
        self.is_having_matches = len(self.matched_pairs) > 0

    def __get_unapplied(self) -> list[JournalEntryLineItem]:
        """Returns the unapplied original line items of the account.

        :return: The unapplied original line items of the account.
        """
        offset: sa.Alias = offset_alias()
        net_balance: sa.Label \
            = (JournalEntryLineItem.amount
               + sa.func.sum(sa.case(
                    (be(offset.c.is_debit == JournalEntryLineItem.is_debit),
                     offset.c.amount),
                    else_=-offset.c.amount))).label("net_balance")
        select_net_balances: sa.Select \
            = sa.select(JournalEntryLineItem.id, net_balance) \
            .join(Account) \
            .join(offset, be(JournalEntryLineItem.id
                             == offset.c.original_line_item_id),
                  isouter=True) \
            .filter(be(Account.id == self.account.id),
                    sa.or_(sa.and_(Account.base_code.startswith("2"),
                                   sa.not_(JournalEntryLineItem.is_debit)),
                           sa.and_(Account.base_code.startswith("1"),
                                   JournalEntryLineItem.is_debit))) \
            .group_by(JournalEntryLineItem.id) \
            .having(sa.or_(sa.func.count(offset.c.id) == 0, net_balance != 0))
        net_balances: dict[int, Decimal] \
            = {x.id: x.net_balance
               for x in db.session.execute(select_net_balances).all()}
        line_items: list[JournalEntryLineItem] = JournalEntryLineItem.query \
            .filter(JournalEntryLineItem.id.in_({x for x in net_balances})) \
            .join(JournalEntry) \
            .order_by(JournalEntry.date, JournalEntry.no,
                      JournalEntryLineItem.is_debit, JournalEntryLineItem.no) \
            .options(selectinload(JournalEntryLineItem.currency),
                     selectinload(JournalEntryLineItem.journal_entry)).all()
        for line_item in line_items:
            line_item.net_balance = line_item.amount \
                if net_balances[line_item.id] is None \
                else net_balances[line_item.id]
        return line_items

    def __get_unmatched_offsets(self) -> list[JournalEntryLineItem]:
        """Returns the unmatched offsets of an account.

        :return: The unmatched offsets of the account.
        """
        return JournalEntryLineItem.query.join(Account).join(JournalEntry)\
            .filter(Account.id == self.account.id,
                    JournalEntryLineItem.original_line_item_id.is_(None),
                    sa.or_(sa.and_(Account.base_code.startswith("2"),
                                   JournalEntryLineItem.is_debit),
                           sa.and_(Account.base_code.startswith("1"),
                                   sa.not_(JournalEntryLineItem.is_debit))))\
            .order_by(JournalEntry.date, JournalEntry.no,
                      JournalEntryLineItem.is_debit, JournalEntryLineItem.no)\
            .options(selectinload(JournalEntryLineItem.currency),
                     selectinload(JournalEntryLineItem.journal_entry)).all()

    @property
    def matches(self) -> int:
        """Returns the number of matches.

        :return: The number of matches.
        """
        return len(self.matched_pairs)

    def match(self) -> None:
        """Matches the original line items with offsets.

        :return: None.
        """
        for pair in self.matched_pairs:
            pair.offset.original_line_item_id = pair.original_line_item.id