# The Mia! Accounting Flask Project.
# Author: imacat@mail.imacat.idv.tw (imacat), 2023/3/7

#  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 balance sheet.

"""
from decimal import Decimal

import sqlalchemy as sa
from flask import render_template, Response

from accounting import db
from accounting.locale import gettext
from accounting.models import Currency, BaseAccount, Account, JournalEntry, \
    JournalEntryLineItem
from accounting.report.period import Period, PeriodChooser
from accounting.report.utils.base_page_params import BasePageParams
from accounting.report.utils.base_report import BaseReport
from accounting.report.utils.csv_export import BaseCSVRow, csv_download, \
    period_spec
from accounting.report.utils.option_link import OptionLink
from accounting.report.utils.report_chooser import ReportChooser
from accounting.report.utils.report_type import ReportType
from accounting.report.utils.urls import ledger_url, balance_sheet_url, \
    income_statement_url


class ReportAccount:
    """An account in the report."""

    def __init__(self, account: Account, amount: Decimal, url: str):
        """Constructs an account in the report.

        :param account: The account.
        :param amount: The amount.
        :param url: The URL to the ledger of the account.
        """
        self.account: Account = account
        """The account."""
        self.amount: Decimal = amount
        """The amount of the account."""
        self.url: str = url
        """The URL to the ledger of the account."""


class Subsection:
    """A subsection."""

    def __init__(self, title: BaseAccount):
        """Constructs a subsection.

        :param title: The title account.
        """
        self.title: BaseAccount = title
        """The title account."""
        self.accounts: list[ReportAccount] = []
        """The accounts in the subsection."""

    @property
    def total(self) -> Decimal:
        """Returns the total of the subsection.

        :return: The total of the subsection.
        """
        return sum([x.amount for x in self.accounts])


class Section:
    """A section."""

    def __init__(self, title: BaseAccount):
        """Constructs a section.

        :param title: The title account.
        """
        self.title: BaseAccount = title
        """The title account."""
        self.subsections: list[Subsection] = []
        """The subsections in the section."""

    @property
    def total(self) -> Decimal:
        """Returns the total of the section.

        :return: The total of the section.
        """
        return sum([x.total for x in self.subsections])


class AccountCollector:
    """The balance sheet account collector."""

    def __init__(self, currency: Currency, period: Period):
        """Constructs the balance sheet account collector.

        :param currency: The currency.
        :param period: The period.
        """
        self.__currency: Currency = currency
        """The currency."""
        self.__period: Period = period
        """The period."""
        self.accounts: list[ReportAccount] = self.__query_balances()
        """The balance sheet accounts."""

    def __query_balances(self) -> list[ReportAccount]:
        """Queries and returns the balances.

        :return: The balances.
        """
        sub_conditions: list[sa.BinaryExpression] \
            = [Account.base_code.startswith(x) for x in {"1", "2", "3"}]
        conditions: list[sa.BinaryExpression] \
            = [JournalEntryLineItem.currency_code == self.__currency.code,
               sa.or_(*sub_conditions)]
        if self.__period.end is not None:
            conditions.append(JournalEntry.date <= self.__period.end)
        balance_func: sa.Function = sa.func.sum(sa.case(
            (JournalEntryLineItem.is_debit, JournalEntryLineItem.amount),
            else_=-JournalEntryLineItem.amount)).label("balance")
        select_balance: sa.Select \
            = sa.select(Account.id, Account.base_code, Account.no,
                        balance_func)\
            .join(JournalEntry).join(Account)\
            .filter(*conditions)\
            .group_by(Account.id, Account.base_code, Account.no)\
            .order_by(Account.base_code, Account.no)
        account_balances: list[sa.Row] \
            = db.session.execute(select_balance).all()
        self.__all_accounts: list[Account] = Account.query\
            .filter(sa.or_(Account.id.in_({x.id for x in account_balances}),
                           Account.base_code == "3351",
                           Account.base_code == "3353")).all()
        account_by_id: dict[int, Account] \
            = {x.id: x for x in self.__all_accounts}
        self.accounts: list[ReportAccount] \
            = [ReportAccount(account=account_by_id[x.id],
                             amount=x.balance,
                             url=ledger_url(self.__currency,
                                            account_by_id[x.id],
                                            self.__period))
               for x in account_balances]
        self.__add_accumulated()
        self.__add_current_period()
        self.accounts.sort(key=lambda x: (x.account.base_code, x.account.no))
        for balance in self.accounts:
            if not balance.account.base_code.startswith("1"):
                balance.amount = -balance.amount
        return self.accounts

    def __add_accumulated(self) -> None:
        """Adds the accumulated profit or loss to the balances.

        :return: None.
        """
        self.__add_owner_s_equity(Account.ACCUMULATED_CHANGE_CODE,
                                  self.__query_accumulated(),
                                  self.__period)

    def __query_accumulated(self) -> Decimal | None:
        """Queries and returns the accumulated profit or loss.

        :return: The accumulated profit or loss.
        """
        if self.__period.start is None:
            return None
        conditions: list[sa.BinaryExpression] \
            = [JournalEntryLineItem.currency_code == self.__currency.code,
               JournalEntry.date < self.__period.start]
        return self.__query_balance(conditions)

    def __add_current_period(self) -> None:
        """Adds the accumulated profit or loss to the balances.

        :return: None.
        """
        self.__add_owner_s_equity(Account.NET_CHANGE_CODE,
                                  self.__query_current_period(),
                                  self.__period)

    def __query_current_period(self) -> Decimal | None:
        """Queries and returns the net income or loss for current period.

        :return: The net income or loss for current period.
        """
        conditions: list[sa.BinaryExpression] \
            = [JournalEntryLineItem.currency_code == self.__currency.code]
        if self.__period.start is not None:
            conditions.append(JournalEntry.date >= self.__period.start)
        if self.__period.end is not None:
            conditions.append(JournalEntry.date <= self.__period.end)
        return self.__query_balance(conditions)

    @staticmethod
    def __query_balance(conditions: list[sa.BinaryExpression])\
            -> Decimal:
        """Queries the balance.

        :param conditions: The SQL conditions for the balance.
        :return: The balance.
        """
        conditions.extend([sa.not_(Account.base_code.startswith(x))
                           for x in {"1", "2", "3"}])
        balance_func: sa.Function = sa.func.sum(sa.case(
            (JournalEntryLineItem.is_debit, JournalEntryLineItem.amount),
            else_=-JournalEntryLineItem.amount))
        select_balance: sa.Select = sa.select(balance_func)\
            .join(JournalEntry).join(Account).filter(*conditions)
        return db.session.scalar(select_balance)

    def __add_owner_s_equity(self, code: str, amount: Decimal | None,
                             period: Period) -> None:
        """Adds an owner's equity balance.

        :param code: The code of the account to add.
        :param amount: The amount.
        :param period: The period.
        :return: None.
        """
        if amount is None:
            return
        url: str = income_statement_url(self.__currency, period)
        # There is an existing balance.
        account_balance_by_code: dict[str, ReportAccount] \
            = {x.account.code: x for x in self.accounts}
        if code in account_balance_by_code:
            balance: ReportAccount = account_balance_by_code[code]
            balance.amount = balance.amount + amount
            balance.url = url
            return
        # Add a new balance
        account_by_code: dict[str, Account] \
            = {x.code: x for x in self.__all_accounts}
        self.accounts.append(ReportAccount(account=account_by_code[code],
                                           amount=amount,
                                           url=url))


class CSVHalfRow:
    """A half row in the CSV."""

    def __init__(self, title: str | None, amount: Decimal | None):
        """The constructs a half row in the CSV.

        :param title: The title.
        :param amount: The amount.
        """
        self.title: str | None = title
        """The title."""
        self.amount: Decimal | None = amount
        """The amount."""


class CSVRow(BaseCSVRow):
    """A row in the CSV."""

    def __init__(self):
        """Constructs a row in the CSV."""
        self.asset_title: str | None = None
        """The title of the asset."""
        self.asset_amount: Decimal | None = None
        """The amount of the asset."""
        self.liability_title: str | None = None
        """The title of the liability."""
        self.liability_amount: Decimal | None = None
        """The amount of the liability."""

    @property
    def values(self) -> list[str | Decimal | None]:
        """Returns the values of the row.

        :return: The values of the row.
        """
        return [self.asset_title, self.asset_amount,
                self.liability_title, self.liability_amount]


class PageParams(BasePageParams):
    """The HTML page parameters."""

    def __init__(self, currency: Currency,
                 period: Period,
                 has_data: bool,
                 assets: Section,
                 liabilities: Section,
                 owner_s_equity: Section):
        """Constructs the HTML page parameters.

        :param currency: The currency.
        :param period: The period.
        :param has_data: True if there is any data, or False otherwise.
        :param assets: The assets.
        :param liabilities: The liabilities.
        :param owner_s_equity: The owner's equity.
        """
        self.currency: Currency = currency
        """The currency."""
        self.period: Period = period
        """The period."""
        self.__has_data: bool = has_data
        """True if there is any data, or False otherwise."""
        self.assets: Section = assets
        """The assets."""
        self.liabilities: Section = liabilities
        """The liabilities."""
        self.owner_s_equity: Section = owner_s_equity
        """The owner's equity."""
        self.period_chooser: PeriodChooser = PeriodChooser(
            lambda x: balance_sheet_url(currency, x))
        """The period chooser."""

    @property
    def has_data(self) -> bool:
        """Returns whether there is any data on the page.

        :return: True if there is any data, or False otherwise.
        """
        return self.__has_data

    @property
    def report_chooser(self) -> ReportChooser:
        """Returns the report chooser.

        :return: The report chooser.
        """
        return ReportChooser(ReportType.BALANCE_SHEET,
                             currency=self.currency,
                             period=self.period)

    @property
    def currency_options(self) -> list[OptionLink]:
        """Returns the currency options.

        :return: The currency options.
        """
        return self._get_currency_options(
            lambda x: balance_sheet_url(x, self.period), self.currency)


class BalanceSheet(BaseReport):
    """The balance sheet."""

    def __init__(self, currency: Currency, period: Period):
        """Constructs a balance sheet.

        :param currency: The currency.
        :param period: The period.
        """
        self.__currency: Currency = currency
        """The currency."""
        self.__period: Period = period
        """The period."""
        self.__has_data: bool
        """True if there is any data, or False otherwise."""
        self.__assets: Section
        """The assets."""
        self.__liabilities: Section
        """The liabilities."""
        self.__owner_s_equity: Section
        """The owner's equity."""
        self.__set_data()

    def __set_data(self) -> None:
        """Queries and sets assets, the liabilities, and the owner's equity
        sections in the balance sheet.

        :return: None.
        """
        balances: list[ReportAccount] = AccountCollector(
            self.__currency, self.__period).accounts

        titles: list[BaseAccount] = BaseAccount.query\
            .filter(BaseAccount.code.in_({"1", "2", "3"})).all()
        subtitles: list[BaseAccount] = BaseAccount.query\
            .filter(BaseAccount.code.in_({x.account.base_code[:2]
                                          for x in balances})).all()

        sections: dict[str, Section] = {x.code: Section(x) for x in titles}
        subsections: dict[str, Subsection] = {x.code: Subsection(x)
                                              for x in subtitles}
        for subsection in subsections.values():
            sections[subsection.title.code[0]].subsections.append(subsection)
        for balance in balances:
            subsections[balance.account.base_code[:2]].accounts.append(balance)

        self.__has_data = len(balances) > 0
        self.__assets = sections["1"]
        self.__liabilities = sections["2"]
        self.__owner_s_equity = sections["3"]

    def csv(self) -> Response:
        """Returns the report as CSV for download.

        :return: The response of the report for download.
        """
        filename: str = "balance-sheet-{currency}-{period}.csv"\
            .format(currency=self.__currency.code,
                    period=period_spec(self.__period))
        return csv_download(filename, self.__get_csv_rows())

    def __get_csv_rows(self) -> list[CSVRow]:
        """Composes and returns the CSV rows.

        :return: The CSV rows.
        """
        asset_rows: list[CSVHalfRow] = self.__section_csv_rows(self.__assets)
        liability_rows: list[CSVHalfRow] = []
        liability_rows.extend(self.__section_csv_rows(self.__liabilities))
        liability_rows.append(CSVHalfRow(gettext("Total"),
                                         self.__liabilities.total))
        liability_rows.append(CSVHalfRow(None, None))
        liability_rows.extend(self.__section_csv_rows(self.__owner_s_equity))
        liability_rows.append(CSVHalfRow(gettext("Total"),
                                         self.__owner_s_equity.total))
        rows: list[CSVRow] = [CSVRow() for _ in
                              range(max(len(asset_rows), len(liability_rows)))]
        for i in range(len(rows)):
            if i < len(asset_rows):
                rows[i].asset_title = asset_rows[i].title
                rows[i].asset_amount = asset_rows[i].amount
            if i < len(liability_rows) and liability_rows[i].title is not None:
                rows[i].liability_title = liability_rows[i].title
                rows[i].liability_amount = liability_rows[i].amount
        total: CSVRow = CSVRow()
        total.asset_title = gettext("Total")
        total.asset_amount = self.__assets.total
        total.liability_title = gettext("Total")
        total.liability_amount \
            = self.__liabilities.total + self.__owner_s_equity.total
        rows.append(total)
        return rows

    @staticmethod
    def __section_csv_rows(section: Section) -> list[CSVHalfRow]:
        """Gathers the CSV rows for a section.

        :param section: The section.
        :return: The CSV rows for the section.
        """
        rows: list[CSVHalfRow] \
            = [CSVHalfRow(section.title.title.title(), None)]
        for subsection in section.subsections:
            rows.append(CSVHalfRow(f" {subsection.title.title.title()}", None))
            for account in subsection.accounts:
                rows.append(CSVHalfRow(f"  {str(account.account).title()}",
                                       account.amount))
        return rows

    def html(self) -> str:
        """Composes and returns the report as HTML.

        :return: The report as HTML.
        """
        params: PageParams = PageParams(currency=self.__currency,
                                        period=self.__period,
                                        has_data=self.__has_data,
                                        assets=self.__assets,
                                        liabilities=self.__liabilities,
                                        owner_s_equity=self.__owner_s_equity)
        return render_template("accounting/report/balance-sheet.html",
                               report=params)