"""core.py - Common data classes for reporting functionality"""
# 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 abc
import collections
import datetime
import itertools
import operator
import re
import urllib.parse as urlparse

import babel.core  # type:ignore[import]
import babel.numbers  # type:ignore[import]

import odf.config  # type:ignore[import]
import odf.element  # type:ignore[import]
import odf.number  # type:ignore[import]
import odf.opendocument  # type:ignore[import]
import odf.style  # type:ignore[import]
import odf.table  # type:ignore[import]
import odf.text  # type:ignore[import]

from decimal import Decimal
from pathlib import Path

from beancount.core import amount as bc_amount

from .. import data
from .. import filters
from .. import rtutil

from typing import (
    cast,
    overload,
    Any,
    BinaryIO,
    Callable,
    Dict,
    Generic,
    Iterable,
    Iterator,
    List,
    Mapping,
    MutableMapping,
    Optional,
    Sequence,
    Set,
    Tuple,
    Type,
    TypeVar,
    Union,
)
from ..beancount_types import (
    MetaKey,
    MetaValue,
)

DecimalCompat = data.DecimalCompat
BalanceType = TypeVar('BalanceType', bound='Balance')
ElementType = Callable[..., odf.element.Element]
LinkType = Union[str, Tuple[str, Optional[str]]]
RelatedType = TypeVar('RelatedType', bound='RelatedPostings')
RT = TypeVar('RT', bound=Sequence)
ST = TypeVar('ST')
T = TypeVar('T')

class Balance(Mapping[str, data.Amount]):
    """A collection of amounts mapped by currency

    Each key is a Beancount currency string, and each value represents the
    balance in that currency.
    """
    __slots__ = ('_currency_map', 'tolerance')
    TOLERANCE = Decimal('0.01')

    def __init__(self,
                 source: Iterable[data.Amount]=(),
                 tolerance: Optional[Decimal]=None,
    ) -> None:
        if tolerance is None:
            tolerance = self.TOLERANCE
        self.tolerance = tolerance
        self._currency_map: Dict[str, data.Amount] = {}
        for amount in source:
            self._add_amount(self._currency_map, amount)

    def _add_amount(self,
                    currency_map: MutableMapping[str, data.Amount],
                    amount: data.Amount,
    ) -> None:
        code = amount.currency
        try:
            current_number = currency_map[code].number
        except KeyError:
            current_number = Decimal(0)
        currency_map[code] = data.Amount(current_number + amount.number, code)

    def _add_other(self,
                   currency_map: MutableMapping[str, data.Amount],
                   other: Union[data.Amount, 'Balance'],
    ) -> None:
        if isinstance(other, Balance):
            for amount in other.values():
                self._add_amount(currency_map, amount)
        else:
            self._add_amount(currency_map, other)

    def __repr__(self) -> str:
        values = [repr(amt) for amt in self.values()]
        return f"{type(self).__name__}({values!r})"

    def __str__(self) -> str:
        return self.format()

    def __abs__(self: BalanceType) -> BalanceType:
        return type(self)(bc_amount.abs(amt) for amt in self.values())

    def __add__(self: BalanceType, other: Union[data.Amount, 'Balance']) -> BalanceType:
        retval_map = self._currency_map.copy()
        self._add_other(retval_map, other)
        return type(self)(retval_map.values())

    def __sub__(self: BalanceType, other: Union[data.Amount, 'Balance']) -> BalanceType:
        return self.__add__(-other)

    def __eq__(self, other: Any) -> bool:
        if isinstance(other, Balance):
            clean_self = self.clean_copy()
            clean_other = other.clean_copy()
            return len(clean_self) == len(clean_other) and all(
                clean_self[key] == clean_other.get(key) for key in clean_self
            )
        else:
            return super().__eq__(other)

    def __neg__(self: BalanceType) -> BalanceType:
        return type(self)(-amt for amt in self.values())

    def __pos__(self: BalanceType) -> BalanceType:
        return self

    def __getitem__(self, key: str) -> data.Amount:
        return self._currency_map[key]

    def __iter__(self) -> Iterator[str]:
        return iter(self._currency_map)

    def __len__(self) -> int:
        return len(self._currency_map)

    def _all_amounts(self,
                     op_func: Callable[[DecimalCompat, DecimalCompat], bool],
                     operand: DecimalCompat,
    ) -> bool:
        return all(op_func(amt.number, operand) for amt in self.values())

    def copy(self: BalanceType) -> BalanceType:
        return type(self)(self.values())

    def clean_copy(self: BalanceType, tolerance: Optional[Decimal]=None) -> BalanceType:
        if tolerance is None:
            tolerance = self.tolerance
        return type(self)(
            (amount for amount in self.values() if abs(amount.number) >= tolerance),
            tolerance,
        )

    @staticmethod
    def within_tolerance(dec: DecimalCompat, tolerance: DecimalCompat) -> bool:
        dec = cast(Decimal, dec)
        return abs(dec) < tolerance

    def eq_zero(self) -> bool:
        """Returns true if all amounts in the balance == 0, within tolerance."""
        return self._all_amounts(self.within_tolerance, self.tolerance)

    is_zero = eq_zero

    def ge_zero(self) -> bool:
        """Returns true if all amounts in the balance >= 0, within tolerance."""
        op_func = operator.gt if self.tolerance else operator.ge
        return self._all_amounts(op_func, -self.tolerance)

    def le_zero(self) -> bool:
        """Returns true if all amounts in the balance <= 0, within tolerance."""
        op_func = operator.lt if self.tolerance else operator.le
        return self._all_amounts(op_func, self.tolerance)

    def format(self,
               fmt: Optional[str]='#,#00.00 ¤¤',
               sep: str=', ',
               empty: str="Zero balance",
               tolerance: Optional[Decimal]=None,
    ) -> str:
        """Formats the balance as a string with the given parameters

        If the balance is zero (within tolerance), returns ``empty``.
        Otherwise, returns a string with each amount in the balance formatted
        as ``fmt``, separated by ``sep``.

        If you set ``fmt`` to None, amounts will be formatted according to the
        user's locale. The default format is Beancount's input format.
        """
        amounts = list(self.clean_copy(tolerance).values())
        if not amounts:
            return empty
        amounts.sort(key=lambda amt: abs(amt.number), reverse=True)
        return sep.join(
            babel.numbers.format_currency(amt.number, amt.currency, fmt)
            for amt in amounts
        )


class MutableBalance(Balance):
    __slots__ = ()

    def __iadd__(self: BalanceType, other: Union[data.Amount, Balance]) -> BalanceType:
        self._add_other(self._currency_map, other)
        return self

    def __isub__(self: BalanceType, other: Union[data.Amount, Balance]) -> BalanceType:
        self._add_other(self._currency_map, -other)
        return self


class RelatedPostings(Sequence[data.Posting]):
    """Collect and query related postings

    This class provides common functionality for collecting related postings
    and running queries on them: iterating over them, tallying their balance,
    etc.

    This class doesn't know anything about how the postings are related. That's
    entirely up to the caller.

    A common pattern is to use this class with collections.defaultdict
    to organize postings based on some key. See the group_by_meta classmethod
    for an example.
    """
    __slots__ = ('_postings',)

    def __init__(self,
                 source: Iterable[data.Posting]=(),
                 *,
                 _can_own: bool=False,
    ) -> None:
        self._postings: List[data.Posting]
        if _can_own and isinstance(source, list):
            self._postings = source
        else:
            self._postings = list(source)

    @classmethod
    def _group_by(cls: Type[RelatedType],
                  postings: Iterable[data.Posting],
                  key: Callable[[data.Posting], T],
    ) -> Iterator[Tuple[T, RelatedType]]:
        mapping: Dict[T, List[data.Posting]] = collections.defaultdict(list)
        for post in postings:
            mapping[key(post)].append(post)
        for value, posts in mapping.items():
            yield value, cls(posts, _can_own=True)

    @classmethod
    def group_by_account(cls: Type[RelatedType],
                         postings: Iterable[data.Posting],
    ) -> Iterator[Tuple[data.Account, RelatedType]]:
        return cls._group_by(postings, operator.attrgetter('account'))

    @classmethod
    def group_by_meta(cls: Type[RelatedType],
                      postings: Iterable[data.Posting],
                      key: MetaKey,
                      default: Optional[MetaValue]=None,
    ) -> Iterator[Tuple[Optional[MetaValue], RelatedType]]:
        """Relate postings by metadata value

        This method takes an iterable of postings and returns a mapping.
        The keys of the mapping are the values of post.meta.get(key, default).
        The values are RelatedPostings instances that contain all the postings
        that had that same metadata value.
        """
        def key_func(post: data.Posting) -> Optional[MetaValue]:
            return post.meta.get(key, default)
        return cls._group_by(postings, key_func)

    @classmethod
    def group_by_first_meta_link(
            cls: Type[RelatedType],
            postings: Iterable[data.Posting],
            key: MetaKey,
    ) -> Iterator[Tuple[Optional[str], RelatedType]]:
        """Relate postings by the first link in metadata

        This method takes an iterable of postings and returns a mapping.
        The keys of the mapping are the values of
        post.meta.first_link(key, None).
        The values are RelatedPostings instances that contain all the postings
        that had that same first metadata link.
        """
        def key_func(post: data.Posting) -> Optional[MetaValue]:
            return post.meta.first_link(key, None)
        return cls._group_by(postings, key_func)

    def __repr__(self) -> str:
        return f'<{type(self).__name__} {self._postings!r}>'

    @overload
    def __getitem__(self: RelatedType, index: int) -> data.Posting: ...

    @overload
    def __getitem__(self: RelatedType, s: slice) -> RelatedType: ...

    def __getitem__(self: RelatedType,
                    index: Union[int, slice],
    ) -> Union[data.Posting, RelatedType]:
        if isinstance(index, slice):
            return type(self)(self._postings[index], _can_own=True)
        else:
            return self._postings[index]

    def __len__(self) -> int:
        return len(self._postings)

    def all_meta_links(self, key: MetaKey) -> Iterator[str]:
        return filters.iter_unique(
            link for post in self for link in post.meta.report_links(key)
        )

    @overload
    def first_meta_links(self, key: MetaKey, default: str='') -> Iterator[str]: ...

    @overload
    def first_meta_links(self, key: MetaKey, default: None) -> Iterator[Optional[str]]: ...

    def first_meta_links(self,
                         key: MetaKey,
                         default: Optional[str]='',
    ) -> Iterator[Optional[str]]:
        retval = filters.iter_unique(
            post.meta.first_link(key, default) for post in self
        )
        if default == '':
            retval = (s for s in retval if s)
        return retval

    def iter_with_balance(self) -> Iterator[Tuple[data.Posting, Balance]]:
        balance = MutableBalance()
        for post in self:
            balance += post.units
            yield post, balance

    def balance(self) -> Balance:
        return Balance(post.units for post in self)

    def balance_at_cost(self) -> Balance:
        return Balance(post.at_cost() for post in self)

    def balance_at_cost_by_date(self, date: datetime.date) -> Balance:
        for index, post in enumerate(self):
            if post.meta.date >= date:
                break
        else:
            index += 1
        return Balance(post.at_cost() for post in self._postings[:index])

    def meta_values(self,
                    key: MetaKey,
                    default: Optional[MetaValue]=None,
    ) -> Set[Optional[MetaValue]]:
        return {post.meta.get(key, default) for post in self}


class BaseSpreadsheet(Generic[RT, ST], metaclass=abc.ABCMeta):
    """Abstract base class to help write spreadsheets

    This class provides the very core logic to write an arbitrary set of data
    rows to arbitrary output. It calls hooks when it starts writing the
    spreadsheet, starts a new "section" of rows, ends a section, and ends the
    spreadsheet.

    RT is the type of the input data rows. ST is the type of the section
    identifier that you create from each row. If you don't want to use the
    section logic at all, set ST to None and define section_key to return None.
    """

    @abc.abstractmethod
    def section_key(self, row: RT) -> ST:
        """Return the section a row belongs to

        Given a data row, this method should return some identifier for the
        "section" the row belongs to. The write method uses this to
        determine when to call start_section and end_section.

        If your spreadsheet doesn't need sections, define this to return None.
        """
        ...

    @abc.abstractmethod
    def write_row(self, row: RT) -> None:
        """Write a data row to the output spreadsheet

        This method is called once for each data row in the input.
        """
        ...

    # The next four methods are all called by the write method when the name
    # says. You may override them to output headers or sums, record
    # state, etc. The default implementations are all noops.

    def start_spreadsheet(self) -> None:
        pass

    def start_section(self, key: ST) -> None:
        pass

    def end_section(self, key: ST) -> None:
        pass

    def end_spreadsheet(self) -> None:
        pass

    def write(self, rows: Iterable[RT]) -> None:
        prev_section: Optional[ST] = None
        self.start_spreadsheet()
        for row in rows:
            section = self.section_key(row)
            if section != prev_section:
                if prev_section is not None:
                    self.end_section(prev_section)
                self.start_section(section)
                prev_section = section
            self.write_row(row)
        try:
            should_end = section is not None
        except NameError:
            should_end = False
        if should_end:
            self.end_section(section)
        self.end_spreadsheet()


class BaseODS(BaseSpreadsheet[RT, ST], metaclass=abc.ABCMeta):
    """Abstract base class to help write OpenDocument spreadsheets

    This class provides the very core logic to write an arbitrary set of data
    rows to an OpenDocument spreadsheet. It provides helper methods for
    building sheets, rows, and cells.

    See also the BaseSpreadsheet base class for additional documentation about
    methods you must and can define, the definition of RT and ST, etc.
    """
    # Defined in the XSL spec, "Definitions of Units of Measure"
    MEASUREMENT_UNITS = frozenset([
        'cm',
        'em',
        'in',
        'mm',
        'pc',
        'pt',
        'px',
    ])
    MEASUREMENT_RE = re.compile(
        r'([-+]?(?:\d+\.?|\.\d+|\d+\.\d+))({})'.format('|'.join(MEASUREMENT_UNITS)),
        re.ASCII,
    )

    def __init__(self, rt_wrapper: Optional[rtutil.RT]=None) -> None:
        self.rt_wrapper = rt_wrapper
        self.locale = babel.core.Locale.default('LC_MONETARY')
        self.currency_fmt_key = 'accounting'
        self._name_counter = itertools.count(1)
        self._currency_style_cache: MutableMapping[str, odf.style.Style] = {}
        self.document = odf.opendocument.OpenDocumentSpreadsheet()
        self.init_settings()
        self.init_styles()
        self.sheet = self.use_sheet("Report")

    ### Low-level document tree manipulation
    # The *intent* is that you only need to use these if you're adding new
    # methods to manipulate document settings or styles.

    def copy_element(self, elem: odf.element.Element) -> odf.element.Element:
        qattrs = dict(self.iter_qattributes(elem))
        retval = odf.element.Element(qname=elem.qname, qattributes=qattrs)
        try:
            orig_name = retval.getAttribute('name')
        except ValueError:
            orig_name = None
        if orig_name is not None:
            retval.setAttribute('name', f'{orig_name}{next(self._name_counter)}')
        return retval

    def ensure_child(self,
                     parent: odf.element.Element,
                     child_type: ElementType,
                     **kwargs: Any,
    ) -> odf.element.Element:
        new_child = child_type(**kwargs)
        found_child = self.find_child(parent, new_child)
        if found_child is None:
            parent.addElement(new_child)
            return parent.lastChild
        else:
            return found_child

    def ensure_config_map_entry(self,
                                root: odf.element.Element,
                                map_name: str,
                                entry_name: str,
    ) -> odf.element.Element:
        """Return a ``ConfigItemMapEntry`` under ``root``

        This method ensures there's a ``ConfigItemMapNamed`` named ``map_name``
        under ``root``, and a ``ConfigItemMapEntry`` named ``entry_name`` under
        that. Return the ``ConfigItemMapEntry`` element.
        """
        config_map = self.ensure_child(root, odf.config.ConfigItemMapNamed, name=map_name)
        return self.ensure_child(config_map, odf.config.ConfigItemMapEntry, name=entry_name)

    def find_child(self,
                   parent: odf.element.Element,
                   child: odf.element.Element,
    ) -> Optional[odf.element.Element]:
        attrs = {k: v for k, v in self.iter_attributes(child)}
        if not attrs:
            return None
        for elem in parent.childNodes:
            if (elem.qname == child.qname
                and all(elem.getAttribute(k) == v for k, v in attrs.items())):
                return elem
        return None

    def iter_attributes(self, elem: odf.element.Element) -> Iterator[Tuple[str, str]]:
        for (_, key), value in self.iter_qattributes(elem):
            yield key.lower().replace('-', ''), value

    def iter_qattributes(self, elem: odf.element.Element) -> Iterator[Tuple[Tuple[str, str], str]]:
        if elem.attributes:
            yield from elem.attributes.items()

    def replace_child(self,
                     parent: odf.element.Element,
                     child_type: ElementType,
                     **kwargs: Any,
    ) -> odf.element.Element:
        new_child = child_type(**kwargs)
        found_child = self.find_child(parent, new_child)
        parent.insertBefore(new_child, found_child)
        if found_child is not None:
            parent.removeChild(found_child)
        return new_child

    def set_config(self,
                   root: odf.element.Element,
                   name: str,
                   value: Union[bool, int, str],
                   config_type: Optional[str]=None,
    ) -> None:
        """Ensure ``root`` has a ``ConfigItem`` with the given name, type, and value"""
        value_s = str(value)
        if isinstance(value, bool):
            value_s = str(value).lower()
            default_type = 'boolean'
        elif isinstance(value, str):
            default_type = 'string'
        if config_type is None:
            try:
                config_type = default_type
            except NameError:
                raise ValueError(
                    f"need config_type for {type(value).__name__} value",
                ) from None
        item = self.replace_child(
            root, odf.config.ConfigItem, name=name, type=config_type,
        )
        item.addText(value_s)

    ### Styles

    def column_style(self, width: Union[float, str], **attrs: Any) -> odf.style.Style:
        if not isinstance(width, str) or (width and not width[-1].isalpha()):
            width = f'{width}in'
        match = self.MEASUREMENT_RE.fullmatch(width)
        if match is None:
            raise ValueError(f"invalid width {width!r}")
        width_float = float(match.group(1))
        if width_float <= 0:
            # Per the OpenDocument spec, column-width is a positiveLength.
            raise ValueError(f"width {width!r} must be positive")
        width = '{:.3g}{}'.format(width_float, match.group(2))
        retval = self.ensure_child(
            self.document.automaticstyles,
            odf.style.Style,
            name=f'col_{width.replace(".", "_")}'
        )
        retval.setAttribute('family', 'table-column')
        if retval.firstChild is None:
            retval.addElement(odf.style.TableColumnProperties(
                columnwidth=width, **attrs
            ))
        return retval

    def _build_currency_style(
            self,
            root: odf.element.Element,
            locale: babel.core.Locale,
            code: str,
            fmt_index: int,
            properties: Optional[odf.style.TextProperties]=None,
            *,
            fmt_key: Optional[str]=None,
            volatile: bool=False,
            minintegerdigits: int=1,
    ) -> odf.element.Element:
        if fmt_key is None:
            fmt_key = self.currency_fmt_key
        pattern = locale.currency_formats[fmt_key]
        fmts = pattern.pattern.split(';')
        try:
            fmt = fmts[fmt_index]
        except IndexError:
            fmt = fmts[0]
            grouping = pattern.grouping[0]
        else:
            grouping = pattern.grouping[fmt_index]
        zero_s = babel.numbers.format_currency(0, code, '##0.0', locale)
        try:
            decimal_index = zero_s.rindex('.') + 1
        except ValueError:
            decimalplaces = 0
        else:
            decimalplaces = len(zero_s) - decimal_index
        style = self.replace_child(
            root,
            odf.number.CurrencyStyle,
            name=f'{code}{next(self._name_counter)}',
        )
        style.setAttribute('volatile', 'true' if volatile else 'false')
        if properties is not None:
            style.addElement(properties)
        for part in re.split(r"(¤+|[#0,.]+|'[^']+')", fmt):
            if not part:
                pass
            elif not part.strip('#0,.'):
                style.addElement(odf.number.Number(
                    decimalplaces=str(decimalplaces),
                    grouping='true' if grouping else 'false',
                    minintegerdigits=str(minintegerdigits),
                ))
            elif part == '¤':
                style.addElement(odf.number.CurrencySymbol(
                    country=locale.territory,
                    language=locale.language,
                    text=babel.numbers.get_currency_symbol(code, locale),
                ))
            elif part == '¤¤':
                style.addElement(odf.number.Text(text=code))
            else:
                style.addElement(odf.number.Text(text=part.strip("'")))
        return style

    def currency_style(
            self,
            code: str,
            locale: Optional[babel.core.Locale]=None,
            negative_properties: Optional[odf.style.TextProperties]=None,
            positive_properties: Optional[odf.style.TextProperties]=None,
            root: odf.element.Element=None,
    ) -> odf.style.Style:
        """Create and return a spreadsheet style to format currency data

        Given a currency code and a locale, this method will create all the
        styles necessary to format the currency according to the locale's
        rules, including rendering of decimal points and negative values.

        You may optionally pass in TextProperties to use for negative and
        positive amounts, respectively. If you don't, negative values will
        automatically be rendered in red (text color #f00).

        Results are cached. If you repeatedly call this method with the same
        arguments, you'll keep getting the same style returned, which will
        only be added to the document once.
        """
        if locale is None:
            locale = self.locale
        if negative_properties is None:
            negative_properties = odf.style.TextProperties(color='#ff0000')
        if root is None:
            root = self.document.styles
        cache_parts = [str(id(root)), code, str(locale)]
        for key, value in self.iter_attributes(negative_properties):
            cache_parts.append(f'{key}={value}')
        if positive_properties is not None:
            cache_parts.append('')
            for key, value in self.iter_attributes(positive_properties):
                cache_parts.append(f'{key}={value}')
        cache_key = '\0'.join(cache_parts)
        try:
            style = self._currency_style_cache[cache_key]
        except KeyError:
            pos_style = self._build_currency_style(
                root, locale, code, 0, positive_properties, volatile=True,
            )
            curr_style = self._build_currency_style(
                root, locale, code, 1, negative_properties,
            )
            curr_style.addElement(odf.style.Map(
                condition='value()>=0', applystylename=pos_style,
            ))
            style = self.ensure_child(
                self.document.styles,
                odf.style.Style,
                name=f'{curr_style.getAttribute("name")}Cell',
                family='table-cell',
                datastylename=curr_style,
            )
            self._currency_style_cache[cache_key] = style
        return style

    def _merge_style_iter_names(
            self,
            styles: Sequence[Union[str, odf.style.Style, None]],
    ) -> Iterator[str]:
        for source in styles:
            if source is None:
                continue
            elif not isinstance(source, str):
                source = source.getAttribute('name')
            if source.startswith('Merge_'):
                orig_names = iter(source.split('_'))
                next(orig_names)
                yield from orig_names
            else:
                yield source

    def _merge_styles(self,
                      new_style: odf.style.Style,
                      sources: Iterable[odf.style.Style],
    ) -> None:
        for elem in sources:
            for key, new_value in self.iter_attributes(elem):
                old_value = new_style.getAttribute(key)
                if (key == 'name'
                    or key == 'displayname'
                    or old_value == new_value):
                    pass
                elif old_value is None:
                    new_style.setAttribute(key, new_value)
                else:
                    raise ValueError(f"cannot merge styles with conflicting {key}")
            for child in elem.childNodes:
                new_style.addElement(self.copy_element(child))

    def merge_styles(self,
                     *styles: Union[str, odf.style.Style, None],
    ) -> Optional[odf.style.Style]:
        """Create a new style from multiple existing styles

        Given any number of existing styles, create a new style that combines
        all of those styles' attributes and properties, add it to the document
        styles, and return it.

        Styles can be specified by name, or by passing in their Style element.
        For convenience, you can also pass in None as an argument; None will
        simply be skipped.

        Results are cached. If you repeatedly call this method with the same
        arguments, you'll keep getting the same style returned, which will
        only be added to the document once.

        If you pass in zero real style arguments, returns None.
        If you pass in one style argument, returns that style unchanged.
        If you pass in a style that doesn't already exist in the document,
        or if you pass in styles that can't be merged (because they have
        conflicting attributes), raises ValueError.
        """
        name_map: Dict[str, odf.style.Style] = {}
        for name in self._merge_style_iter_names(styles):
            source = odf.style.Style(name=name)
            found = self.find_child(self.document.styles, source)
            if found is None:
                raise ValueError(f"no style named {name!r}")
            name_map[name] = found
        if not name_map:
            retval = None
        elif len(name_map) == 1:
            _, retval = name_map.popitem()
        else:
            new_name = f'Merge_{"_".join(sorted(name_map))}'
            retval = self.ensure_child(
                self.document.styles, odf.style.Style, name=new_name,
            )
            if retval.firstChild is None:
                self._merge_styles(retval, name_map.values())
        return retval

    ### Sheets

    def lock_first_row(self, sheet: Optional[odf.table.Table]=None) -> None:
        """Lock the first row of cells under the given sheet

        This method sets all the appropriate settings to "lock" the first row
        of cells in a sheet, so it stays in view even as the viewer scrolls
        through rows. If a sheet is not given, works on ``self.sheet``.
        """
        if sheet is None:
            sheet = self.sheet
        config_map = self.ensure_config_map_entry(
            self.view, 'Tables', sheet.getAttribute('name'),
        )
        self.set_config(config_map, 'PositionBottom', 1, 'int')
        self.set_config(config_map, 'VerticalSplitMode', 2, 'short')
        self.set_config(config_map, 'VerticalSplitPosition', 1, 'short')

    def use_sheet(self, name: str) -> odf.table.Table:
        """Switch the active sheet ``self.sheet`` to the one with the given name

        If there is no sheet with the given name, create it and append it to
        the spreadsheet first.

        If the current active sheet is empty when this method is called, it
        will be removed from the spreadsheet.
        """
        try:
            empty_sheet = not self.sheet.hasChildNodes()
        except AttributeError:
            empty_sheet = False
        if empty_sheet:
            self.document.spreadsheet.removeChild(self.sheet)
        self.sheet = self.ensure_child(
            self.document.spreadsheet, odf.table.Table, name=name,
        )
        return self.sheet

    ### Initialization hooks

    def init_settings(self) -> None:
        """Hook called to initialize settings

        This method is called by __init__ to populate
        ``self.document.settings``. This implementation creates the barest
        skeleton structure necessary to support other methods, in particular
        ``lock_first_row``.
        """
        view_settings = self.ensure_child(
            self.document.settings, odf.config.ConfigItemSet, name='ooo:view-settings',
        )
        views = self.ensure_child(
            view_settings, odf.config.ConfigItemMapIndexed, name='Views',
        )
        self.view = self.ensure_child(views, odf.config.ConfigItemMapEntry)
        self.set_config(self.view, 'ViewId', 'view1')

    def init_styles(self) -> None:
        """Hook called to initialize settings

        This method is called by __init__ to populate
        ``self.document.styles``. This implementation creates basic building
        block cell styles often used in financial reports.
        """
        styles = self.document.styles
        self.style_bold = self.ensure_child(
            styles, odf.style.Style, name='Bold', family='table-cell',
        )
        self.ensure_child(
            self.style_bold, odf.style.TextProperties, fontweight='bold',
        )
        self.style_dividerline = self.ensure_child(
            styles, odf.style.Style, name='DividerLine', family='table-cell',
        )
        self.ensure_child(
            self.style_dividerline,
            odf.style.TableCellProperties,
            borderbottom='1pt solid #0000ff',
        )

        date_style = self.replace_child(styles, odf.number.DateStyle, name='ISODate')
        date_style.addElement(odf.number.Year(style='long'))
        date_style.addElement(odf.number.Text(text='-'))
        date_style.addElement(odf.number.Month(style='long'))
        date_style.addElement(odf.number.Text(text='-'))
        date_style.addElement(odf.number.Day(style='long'))
        self.style_date = self.ensure_child(
            styles,
            odf.style.Style,
            name=f'{date_style.getAttribute("name")}Cell',
            family='table-cell',
            datastylename=date_style,
        )

        self.style_starttext: odf.style.Style
        self.style_centertext: odf.style.Style
        self.style_endtext: odf.style.Style
        for textalign in ['start', 'center', 'end']:
            aligned_style = self.replace_child(
                styles, odf.style.Style, name=f'{textalign.title()}Text',
            )
            aligned_style.setAttribute('family', 'table-cell')
            aligned_style.addElement(odf.style.ParagraphProperties(textalign=textalign))
            setattr(self, f'style_{textalign}text', aligned_style)

    ### Rows and cells

    def add_row(self, *cells: odf.table.TableCell, **attrs: Any) -> odf.table.TableRow:
        row = odf.table.TableRow(**attrs)
        for cell in cells:
            row.addElement(cell)
        self.sheet.addElement(row)
        return row

    def balance_cell(self, balance: Balance, **attrs: Any) -> odf.table.TableCell:
        balance = balance.clean_copy() or balance
        balance_currency_count = len(balance)
        if balance_currency_count == 0:
            return self.float_cell(0, **attrs)
        elif balance_currency_count == 1:
            amount = next(iter(balance.values()))
            attrs['stylename'] = self.merge_styles(
                attrs.get('stylename'), self.currency_style(amount.currency),
            )
            return self.currency_cell(amount, **attrs)
        else:
            lines = [babel.numbers.format_currency(
                number, currency, locale=self.locale, format_type=self.currency_fmt_key,
            ) for number, currency in balance.values()]
            attrs['stylename'] = self.merge_styles(
                attrs.get('stylename'), self.style_endtext,
            )
            return self.multiline_cell(lines, **attrs)

    def currency_cell(self, amount: data.Amount, **attrs: Any) -> odf.table.TableCell:
        if 'stylename' not in attrs:
            attrs['stylename'] = self.currency_style(amount.currency)
        number, currency = amount
        cell = odf.table.TableCell(valuetype='currency', value=number, **attrs)
        cell.addElement(odf.text.P(text=babel.numbers.format_currency(
            number, currency, locale=self.locale, format_type=self.currency_fmt_key,
        )))
        return cell

    def date_cell(self, date: datetime.date, **attrs: Any) -> odf.table.TableCell:
        attrs.setdefault('stylename', self.style_date)
        cell = odf.table.TableCell(valuetype='date', datevalue=date, **attrs)
        cell.addElement(odf.text.P(text=date.isoformat()))
        return cell

    def float_cell(self, value: Union[int, float, Decimal], **attrs: Any) -> odf.table.TableCell:
        cell = odf.table.TableCell(valuetype='float', value=value, **attrs)
        cell.addElement(odf.text.P(text=str(value)))
        return cell

    def _meta_link_pairs(self, links: Iterable[Optional[str]]) -> Iterator[Tuple[str, str]]:
        for href in links:
            if href is None:
                continue
            elif self.rt_wrapper is not None:
                rt_ids = self.rt_wrapper.parse(href)
                rt_href = rt_ids and self.rt_wrapper.url(*rt_ids)
            else:
                rt_ids = None
                rt_href = None
            if rt_ids is None or rt_href is None:
                # '..' pops the ODS filename off the link path. In other words,
                # make the link relative to the directory the ODS is in.
                href_path = Path('..', href)
                href = str(href_path)
                text = href_path.name
            else:
                rt_path = urlparse.urlparse(rt_href).path
                if rt_path.endswith('/Ticket/Display.html'):
                    text = rtutil.RT.unparse(*rt_ids)
                else:
                    text = urlparse.unquote(Path(rt_path).name)
                href = rt_href
            yield (href, text)

    def meta_links_cell(self, links: Iterable[Optional[str]], **attrs: Any) -> odf.table.TableCell:
        return self.multilink_cell(self._meta_link_pairs(links), **attrs)

    def multiline_cell(self, lines: Iterable[Any], **attrs: Any) -> odf.table.TableCell:
        cell = odf.table.TableCell(valuetype='string', **attrs)
        for line in lines:
            cell.addElement(odf.text.P(text=str(line)))
        return cell

    def multilink_cell(self, links: Iterable[LinkType], **attrs: Any) -> odf.table.TableCell:
        cell = odf.table.TableCell(valuetype='string', **attrs)
        for link in links:
            if isinstance(link, tuple):
                href, text = link
            else:
                href = link
                text = None
            cell.addElement(odf.text.P())
            cell.lastChild.addElement(odf.text.A(
                type='simple', href=href, text=text or href,
            ))
        return cell

    def string_cell(self, text: str, **attrs: Any) -> odf.table.TableCell:
        cell = odf.table.TableCell(valuetype='string', **attrs)
        cell.addElement(odf.text.P(text=text))
        return cell

    def write_row(self, row: RT) -> None:
        """Write a single row of input data to the spreadsheet

        This default implementation adds a single row to the spreadsheet,
        with one cell per element of the row. The type of each element
        determines what kind of cell is created.

        This implementation will help get you started, but you'll probably
        want to override it to specify styles.
        """
        out_row = odf.table.TableRow()
        for cell_source in row:
            if isinstance(cell_source, (int, float, Decimal)):
                cell = self.float_cell(cell_source)
            else:
                cell = self.string_cell(cell_source)
            out_row.addElement(cell)
        self.sheet.addElement(out_row)

    def save_file(self, out_file: BinaryIO) -> None:
        self.document.write(out_file)

    def save_path(self, path: Path, mode: str='w') -> None:
        with path.open(f'{mode}b') as out_file:
            out_file = cast(BinaryIO, out_file)
            self.save_file(out_file)


def normalize_amount_func(account_name: str) -> Callable[[T], T]:
    """Get a function to normalize amounts for reporting

    Given an account name, return a function that can be used on "amounts"
    under that account (including numbers, Amount objects, and Balance objects)
    to normalize them for reporting. Right now that means make flipping the
    sign for accounts where "normal" postings are negative.
    """
    if account_name.startswith(('Assets:', 'Expenses:')):
        # We can't just return operator.pos because Beancount's Amount class
        # doesn't implement __pos__.
        return lambda amt: amt
    elif account_name.startswith(('Equity:', 'Income:', 'Liabilities:')):
        return operator.neg
    else:
        raise ValueError(f"unrecognized account name {account_name!r}")