"""books - Tools for loading the books"""
# 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 datetime

from pathlib import Path

from typing import (
    Iterable,
    Mapping,
    NamedTuple,
    Optional,
    Union,
)

PathLike = Union[str, Path]
PluginsSpec = Mapping[str, Optional[str]]
Year = Union[int, datetime.date]

class FiscalYear(NamedTuple):
    month: int = 3
    day: int = 1

    def for_date(self, date: Optional[datetime.date]=None) -> int:
        if date is None:
            date = datetime.date.today()
        if (date.month, date.day) < self:
            return date.year - 1
        else:
            return date.year

    def range(self, from_fy: Year, to_fy: Optional[Year]=None) -> Iterable[int]:
        """Return a range of fiscal years

        Both arguments can be either a year (represented as an integer) or a
        date. Dates will be converted into a year by calling for_date() on
        them.

        If the first argument is negative or below 1000, it will be treated as
        an offset. You'll get a range of fiscal years between the second
        argument offset by this amount.

        If the second argument is omitted, it defaults to the current fiscal
        year.

        Note that unlike normal Python ranges, these ranges include the final
        fiscal year.

        Examples:

          range(2015)  # Iterate all fiscal years from 2015 to today, inclusive

          range(-1)  # Iterate the previous fiscal year and current fiscal year
        """
        if not isinstance(from_fy, int):
            from_fy = self.for_date(from_fy)
        if to_fy is None:
            to_fy = self.for_date()
        elif not isinstance(to_fy, int):
            to_fy = self.for_date(to_fy - datetime.timedelta(days=1))
        if from_fy < 1:
            from_fy += to_fy
        elif from_fy < 1000:
            from_fy, to_fy = to_fy, from_fy + to_fy
        return range(from_fy, to_fy + 1)


class Loader:
    """Load Beancount books organized by fiscal year"""

    DEFAULT_PLUGINS: PluginsSpec = {
        'conservancy_beancount.plugin': None,
    }

    def __init__(self,
                 books_root: Path,
                 fiscal_year: FiscalYear,
                 plugins: Optional[PluginsSpec]=None,
    ) -> None:
        """Set up a books loader

        Arguments:
        * books_root: A Path to a Beancount books checkout.
        * fiscal_year: A FiscalYear object, used to determine what books to
          load for a given date range.
        * plugins: A mapping that specifies what plugins should be loaded
          before any books. The keys are plugin names, and the values are the
          configuration parameters string to follow. A value of None means the
          plugin takes no configuration string. By default, the loader loads
          conservancy_beancount.plugin.
        """
        if plugins is None:
            plugins = self.DEFAULT_PLUGINS
        self.books_root = books_root
        self.fiscal_year = fiscal_year
        self.plugins = dict(plugins)

    def _format_include(self, year: int, subdir: PathLike='') -> str:
        file_path = Path(self.books_root, subdir, f'{year}.beancount')
        return f'include "{file_path}"'

    def _format_plugin(self, name: str, optstring: Optional[str]=None) -> str:
        if optstring is None:
            return f'plugin "{name}"'
        else:
            return f'plugin "{name}" "{optstring}"'

    def fy_range_string(self,
                        from_fy: Year,
                        to_fy: Optional[Year]=None,
                        plugins: Optional[PluginsSpec]=None,
    ) -> str:
        """Return a string to load books for a range of fiscal years

        This method generates a range of fiscal years by calling
        FiscalYear.range() with its first two arguments. It returns a string of
        Beancount directives to load all plugins and Beancount files for that
        range of fiscal years, suitable for passing to
        beancount.loader.load_string().

        You can specify what plugins to load with the plugins argument. If not
        specified, the string loads the plugins specified for this instance.
        See the __init__ docstring for details.
        """
        if plugins is None:
            plugins = self.plugins
        years = iter(self.fiscal_year.range(from_fy, to_fy))
        try:
            books_start = self._format_include(next(years), 'books')
        except StopIteration:
            return ''
        return '\n'.join([
            *(self._format_plugin(name, opts) for name, opts in plugins.items()),
            books_start,
            *(self._format_include(year) for year in years),
        ])