# This file is part of beets.
# Copyright 2016, Adrian Sampson.
#
# Permission is hereby granted, free of charge, to any person obtaining
# a copy of this software and associated documentation files (the
# "Software"), to deal in the Software without restriction, including
# without limitation the rights to use, copy, modify, merge, publish,
# distribute, sublicense, and/or sell copies of the Software, and to
# permit persons to whom the Software is furnished to do so, subject to
# the following conditions:
#
# The above copyright notice and this permission notice shall be
# included in all copies or substantial portions of the Software.

"""The Query type hierarchy for DBCore."""

from __future__ import annotations

import re
import unicodedata
from abc import ABC, abstractmethod
from collections.abc import Iterator, MutableSequence, Sequence
from datetime import datetime, timedelta
from functools import reduce
from operator import mul, or_
from re import Pattern
from typing import TYPE_CHECKING, Any, Generic, TypeVar, Union

from beets import util

if TYPE_CHECKING:
    from beets.dbcore import Model
    from beets.dbcore.db import AnyModel

    P = TypeVar("P", default=Any)
else:
    P = TypeVar("P")


class ParsingError(ValueError):
    """Abstract class for any unparsable user-requested album/query
    specification.
    """


class InvalidQueryError(ParsingError):
    """Represent any kind of invalid query.

    The query should be a unicode string or a list, which will be space-joined.
    """

    def __init__(self, query, explanation):
        if isinstance(query, list):
            query = " ".join(query)
        message = f"'{query}': {explanation}"
        super().__init__(message)


class InvalidQueryArgumentValueError(ParsingError):
    """Represent a query argument that could not be converted as expected.

    It exists to be caught in upper stack levels so a meaningful (i.e. with the
    query) InvalidQueryError can be raised.
    """

    def __init__(self, what, expected, detail=None):
        message = f"'{what}' is not {expected}"
        if detail:
            message = f"{message}: {detail}"
        super().__init__(message)


class Query(ABC):
    """An abstract class representing a query into the database."""

    @property
    def field_names(self) -> set[str]:
        """Return a set with field names that this query operates on."""
        return set()

    def clause(self) -> tuple[str | None, Sequence[Any]]:
        """Generate an SQLite expression implementing the query.

        Return (clause, subvals) where clause is a valid sqlite
        WHERE clause implementing the query and subvals is a list of
        items to be substituted for ?s in the clause.

        The default implementation returns None, falling back to a slow query
        using `match()`.
        """
        return None, ()

    @abstractmethod
    def match(self, obj: Model):
        """Check whether this query matches a given Model. Can be used to
        perform queries on arbitrary sets of Model.
        """
        ...

    def __and__(self, other: Query) -> AndQuery:
        return AndQuery([self, other])

    def __repr__(self) -> str:
        return f"{self.__class__.__name__}()"

    def __eq__(self, other) -> bool:
        return type(self) is type(other)

    def __hash__(self) -> int:
        """Minimalistic default implementation of a hash.

        Given the implementation if __eq__ above, this is
        certainly correct.
        """
        return hash(type(self))


SQLiteType = Union[str, bytes, float, int, memoryview, None]
AnySQLiteType = TypeVar("AnySQLiteType", bound=SQLiteType)
FieldQueryType = type["FieldQuery"]


class FieldQuery(Query, Generic[P]):
    """An abstract query that searches in a specific field for a
    pattern. Subclasses must provide a `value_match` class method, which
    determines whether a certain pattern string matches a certain value
    string. Subclasses may also provide `col_clause` to implement the
    same matching functionality in SQLite.
    """

    @property
    def field(self) -> str:
        return (
            f"{self.table}.{self.field_name}" if self.table else self.field_name
        )

    @property
    def field_names(self) -> set[str]:
        """Return a set with field names that this query operates on."""
        return {self.field_name}

    def __init__(self, field_name: str, pattern: P, fast: bool = True):
        self.table, _, self.field_name = field_name.rpartition(".")
        self.pattern = pattern
        self.fast = fast

    def col_clause(self) -> tuple[str, Sequence[SQLiteType]]:
        return self.field, ()

    def clause(self) -> tuple[str | None, Sequence[SQLiteType]]:
        if self.fast:
            return self.col_clause()
        else:
            # Matching a flexattr. This is a slow query.
            return None, ()

    @classmethod
    def value_match(cls, pattern: P, value: Any):
        """Determine whether the value matches the pattern."""
        raise NotImplementedError()

    def match(self, obj: Model) -> bool:
        return self.value_match(self.pattern, obj.get(self.field_name))

    def __repr__(self) -> str:
        return (
            f"{self.__class__.__name__}({self.field_name!r}, {self.pattern!r}, "
            f"fast={self.fast})"
        )

    def __eq__(self, other) -> bool:
        return (
            super().__eq__(other)
            and self.field_name == other.field_name
            and self.pattern == other.pattern
        )

    def __hash__(self) -> int:
        return hash((self.field_name, hash(self.pattern)))


class MatchQuery(FieldQuery[AnySQLiteType]):
    """A query that looks for exact matches in an Model field."""

    def col_clause(self) -> tuple[str, Sequence[SQLiteType]]:
        return self.field + " = ?", [self.pattern]

    @classmethod
    def value_match(cls, pattern: AnySQLiteType, value: Any) -> bool:
        return pattern == value


class NoneQuery(FieldQuery[None]):
    """A query that checks whether a field is null."""

    def __init__(self, field, fast: bool = True):
        super().__init__(field, None, fast)

    def col_clause(self) -> tuple[str, Sequence[SQLiteType]]:
        return self.field + " IS NULL", ()

    def match(self, obj: Model) -> bool:
        return obj.get(self.field_name) is None

    def __repr__(self) -> str:
        return f"{self.__class__.__name__}({self.field_name!r}, {self.fast})"


class StringFieldQuery(FieldQuery[P]):
    """A FieldQuery that converts values to strings before matching
    them.
    """

    @classmethod
    def value_match(cls, pattern: P, value: Any):
        """Determine whether the value matches the pattern. The value
        may have any type.
        """
        return cls.string_match(pattern, util.as_string(value))

    @classmethod
    def string_match(
        cls,
        pattern: P,
        value: str,
    ) -> bool:
        """Determine whether the value matches the pattern. Both
        arguments are strings. Subclasses implement this method.
        """
        raise NotImplementedError()


class StringQuery(StringFieldQuery[str]):
    """A query that matches a whole string in a specific Model field."""

    def col_clause(self) -> tuple[str, Sequence[SQLiteType]]:
        search = (
            self.pattern.replace("\\", "\\\\")
            .replace("%", "\\%")
            .replace("_", "\\_")
        )
        clause = self.field + " like ? escape '\\'"
        subvals = [search]
        return clause, subvals

    @classmethod
    def string_match(cls, pattern: str, value: str) -> bool:
        return pattern.lower() == value.lower()


class SubstringQuery(StringFieldQuery[str]):
    """A query that matches a substring in a specific Model field."""

    def col_clause(self) -> tuple[str, Sequence[SQLiteType]]:
        pattern = (
            self.pattern.replace("\\", "\\\\")
            .replace("%", "\\%")
            .replace("_", "\\_")
        )
        search = "%" + pattern + "%"
        clause = self.field + " like ? escape '\\'"
        subvals = [search]
        return clause, subvals

    @classmethod
    def string_match(cls, pattern: str, value: str) -> bool:
        return pattern.lower() in value.lower()


class RegexpQuery(StringFieldQuery[Pattern[str]]):
    """A query that matches a regular expression in a specific Model field.

    Raises InvalidQueryError when the pattern is not a valid regular
    expression.
    """

    def __init__(self, field_name: str, pattern: str, fast: bool = True):
        pattern = self._normalize(pattern)
        try:
            pattern_re = re.compile(pattern)
        except re.error as exc:
            # Invalid regular expression.
            raise InvalidQueryArgumentValueError(
                pattern, "a regular expression", format(exc)
            )

        super().__init__(field_name, pattern_re, fast)

    def col_clause(self) -> tuple[str, Sequence[SQLiteType]]:
        return f" regexp({self.field}, ?)", [self.pattern.pattern]

    @staticmethod
    def _normalize(s: str) -> str:
        """Normalize a Unicode string's representation (used on both
        patterns and matched values).
        """
        return unicodedata.normalize("NFC", s)

    @classmethod
    def string_match(cls, pattern: Pattern[str], value: str) -> bool:
        return pattern.search(cls._normalize(value)) is not None


class BooleanQuery(MatchQuery[int]):
    """Matches a boolean field. Pattern should either be a boolean or a
    string reflecting a boolean.
    """

    def __init__(
        self,
        field_name: str,
        pattern: bool,
        fast: bool = True,
    ):
        if isinstance(pattern, str):
            pattern = util.str2bool(pattern)

        pattern_int = int(pattern)

        super().__init__(field_name, pattern_int, fast)


class BytesQuery(FieldQuery[bytes]):
    """Match a raw bytes field (i.e., a path). This is a necessary hack
    to work around the `sqlite3` module's desire to treat `bytes` and
    `unicode` equivalently in Python 2. Always use this query instead of
    `MatchQuery` when matching on BLOB values.
    """

    def __init__(self, field_name: str, pattern: bytes | str | memoryview):
        # Use a buffer/memoryview representation of the pattern for SQLite
        # matching. This instructs SQLite to treat the blob as binary
        # rather than encoded Unicode.
        if isinstance(pattern, (str, bytes)):
            if isinstance(pattern, str):
                bytes_pattern = pattern.encode("utf-8")
            else:
                bytes_pattern = pattern
            self.buf_pattern = memoryview(bytes_pattern)
        elif isinstance(pattern, memoryview):
            self.buf_pattern = pattern
            bytes_pattern = bytes(pattern)
        else:
            raise ValueError("pattern must be bytes, str, or memoryview")

        super().__init__(field_name, bytes_pattern)

    def col_clause(self) -> tuple[str, Sequence[SQLiteType]]:
        return self.field + " = ?", [self.buf_pattern]

    @classmethod
    def value_match(cls, pattern: bytes, value: Any) -> bool:
        return pattern == value


class NumericQuery(FieldQuery[str]):
    """Matches numeric fields. A syntax using Ruby-style range ellipses
    (``..``) lets users specify one- or two-sided ranges. For example,
    ``year:2001..`` finds music released since the turn of the century.

    Raises InvalidQueryError when the pattern does not represent an int or
    a float.
    """

    def _convert(self, s: str) -> float | int | None:
        """Convert a string to a numeric type (float or int).

        Return None if `s` is empty.
        Raise an InvalidQueryError if the string cannot be converted.
        """
        # This is really just a bit of fun premature optimization.
        if not s:
            return None
        try:
            return int(s)
        except ValueError:
            try:
                return float(s)
            except ValueError:
                raise InvalidQueryArgumentValueError(s, "an int or a float")

    def __init__(self, field_name: str, pattern: str, fast: bool = True):
        super().__init__(field_name, pattern, fast)

        parts = pattern.split("..", 1)
        if len(parts) == 1:
            # No range.
            self.point = self._convert(parts[0])
            self.rangemin = None
            self.rangemax = None
        else:
            # One- or two-sided range.
            self.point = None
            self.rangemin = self._convert(parts[0])
            self.rangemax = self._convert(parts[1])

    def match(self, obj: Model) -> bool:
        if self.field_name not in obj:
            return False
        value = obj[self.field_name]
        if isinstance(value, str):
            value = self._convert(value)

        if self.point is not None:
            return value == self.point
        else:
            if self.rangemin is not None and value < self.rangemin:
                return False
            if self.rangemax is not None and value > self.rangemax:
                return False
            return True

    def col_clause(self) -> tuple[str, Sequence[SQLiteType]]:
        if self.point is not None:
            return self.field + "=?", (self.point,)
        else:
            if self.rangemin is not None and self.rangemax is not None:
                return (
                    "{0} >= ? AND {0} <= ?".format(self.field),
                    (self.rangemin, self.rangemax),
                )
            elif self.rangemin is not None:
                return f"{self.field} >= ?", (self.rangemin,)
            elif self.rangemax is not None:
                return f"{self.field} <= ?", (self.rangemax,)
            else:
                return "1", ()


class InQuery(Generic[AnySQLiteType], FieldQuery[Sequence[AnySQLiteType]]):
    """Query which matches values in the given set."""

    field_name: str
    pattern: Sequence[AnySQLiteType]
    fast: bool = True

    @property
    def subvals(self) -> Sequence[SQLiteType]:
        return self.pattern

    def col_clause(self) -> tuple[str, Sequence[SQLiteType]]:
        placeholders = ", ".join(["?"] * len(self.subvals))
        return f"{self.field_name} IN ({placeholders})", self.subvals

    @classmethod
    def value_match(
        cls, pattern: Sequence[AnySQLiteType], value: AnySQLiteType
    ) -> bool:
        return value in pattern


class CollectionQuery(Query):
    """An abstract query class that aggregates other queries. Can be
    indexed like a list to access the sub-queries.
    """

    @property
    def field_names(self) -> set[str]:
        """Return a set with field names that this query operates on."""
        return reduce(or_, (sq.field_names for sq in self.subqueries))

    def __init__(self, subqueries: Sequence[Query] = ()):
        self.subqueries = subqueries

    # Act like a sequence.

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

    def __getitem__(self, key):
        return self.subqueries[key]

    def __iter__(self) -> Iterator[Query]:
        return iter(self.subqueries)

    def __contains__(self, subq) -> bool:
        return subq in self.subqueries

    def clause_with_joiner(
        self,
        joiner: str,
    ) -> tuple[str | None, Sequence[SQLiteType]]:
        """Return a clause created by joining together the clauses of
        all subqueries with the string joiner (padded by spaces).
        """
        clause_parts = []
        subvals: list[SQLiteType] = []
        for subq in self.subqueries:
            subq_clause, subq_subvals = subq.clause()
            if not subq_clause:
                # Fall back to slow query.
                return None, ()
            clause_parts.append("(" + subq_clause + ")")
            subvals += subq_subvals
        clause = (" " + joiner + " ").join(clause_parts)
        return clause, subvals

    def __repr__(self) -> str:
        return f"{self.__class__.__name__}({self.subqueries!r})"

    def __eq__(self, other) -> bool:
        return super().__eq__(other) and self.subqueries == other.subqueries

    def __hash__(self) -> int:
        """Since subqueries are mutable, this object should not be hashable.
        However and for conveniences purposes, it can be hashed.
        """
        return reduce(mul, map(hash, self.subqueries), 1)


class MutableCollectionQuery(CollectionQuery):
    """A collection query whose subqueries may be modified after the
    query is initialized.
    """

    subqueries: MutableSequence[Query]

    def __setitem__(self, key, value):
        self.subqueries[key] = value

    def __delitem__(self, key):
        del self.subqueries[key]


class AndQuery(MutableCollectionQuery):
    """A conjunction of a list of other queries."""

    def clause(self) -> tuple[str | None, Sequence[SQLiteType]]:
        return self.clause_with_joiner("and")

    def match(self, obj: Model) -> bool:
        return all(q.match(obj) for q in self.subqueries)


class OrQuery(MutableCollectionQuery):
    """A conjunction of a list of other queries."""

    def clause(self) -> tuple[str | None, Sequence[SQLiteType]]:
        return self.clause_with_joiner("or")

    def match(self, obj: Model) -> bool:
        return any(q.match(obj) for q in self.subqueries)


class NotQuery(Query):
    """A query that matches the negation of its `subquery`, as a shortcut for
    performing `not(subquery)` without using regular expressions.
    """

    @property
    def field_names(self) -> set[str]:
        """Return a set with field names that this query operates on."""
        return self.subquery.field_names

    def __init__(self, subquery):
        self.subquery = subquery

    def clause(self) -> tuple[str | None, Sequence[SQLiteType]]:
        clause, subvals = self.subquery.clause()
        if clause:
            return f"not ({clause})", subvals
        else:
            # If there is no clause, there is nothing to negate. All the logic
            # is handled by match() for slow queries.
            return clause, subvals

    def match(self, obj: Model) -> bool:
        return not self.subquery.match(obj)

    def __repr__(self) -> str:
        return f"{self.__class__.__name__}({self.subquery!r})"

    def __eq__(self, other) -> bool:
        return super().__eq__(other) and self.subquery == other.subquery

    def __hash__(self) -> int:
        return hash(("not", hash(self.subquery)))


class TrueQuery(Query):
    """A query that always matches."""

    def clause(self) -> tuple[str, Sequence[SQLiteType]]:
        return "1", ()

    def match(self, obj: Model) -> bool:
        return True


class FalseQuery(Query):
    """A query that never matches."""

    def clause(self) -> tuple[str, Sequence[SQLiteType]]:
        return "0", ()

    def match(self, obj: Model) -> bool:
        return False


# Time/date queries.


def _parse_periods(pattern: str) -> tuple[Period | None, Period | None]:
    """Parse a string containing two dates separated by two dots (..).
    Return a pair of `Period` objects.
    """
    parts = pattern.split("..", 1)
    if len(parts) == 1:
        instant = Period.parse(parts[0])
        return (instant, instant)
    else:
        start = Period.parse(parts[0])
        end = Period.parse(parts[1])
        return (start, end)


class Period:
    """A period of time given by a date, time and precision.

    Example: 2014-01-01 10:50:30 with precision 'month' represents all
    instants of time during January 2014.
    """

    precisions = ("year", "month", "day", "hour", "minute", "second")
    date_formats = (
        ("%Y",),  # year
        ("%Y-%m",),  # month
        ("%Y-%m-%d",),  # day
        ("%Y-%m-%dT%H", "%Y-%m-%d %H"),  # hour
        ("%Y-%m-%dT%H:%M", "%Y-%m-%d %H:%M"),  # minute
        ("%Y-%m-%dT%H:%M:%S", "%Y-%m-%d %H:%M:%S"),  # second
    )
    relative_units = {"y": 365, "m": 30, "w": 7, "d": 1}
    relative_re = (
        "(?P<sign>[+|-]?)(?P<quantity>[0-9]+)" + "(?P<timespan>[y|m|w|d])"
    )

    def __init__(self, date: datetime, precision: str):
        """Create a period with the given date (a `datetime` object) and
        precision (a string, one of "year", "month", "day", "hour", "minute",
        or "second").
        """
        if precision not in Period.precisions:
            raise ValueError(f"Invalid precision {precision}")
        self.date = date
        self.precision = precision

    @classmethod
    def parse(cls: type[Period], string: str) -> Period | None:
        """Parse a date and return a `Period` object or `None` if the
        string is empty, or raise an InvalidQueryArgumentValueError if
        the string cannot be parsed to a date.

        The date may be absolute or relative. Absolute dates look like
        `YYYY`, or `YYYY-MM-DD`, or `YYYY-MM-DD HH:MM:SS`, etc. Relative
        dates have three parts:

        - Optionally, a ``+`` or ``-`` sign indicating the future or the
          past. The default is the future.
        - A number: how much to add or subtract.
        - A letter indicating the unit: days, weeks, months or years
          (``d``, ``w``, ``m`` or ``y``). A "month" is exactly 30 days
          and a "year" is exactly 365 days.
        """

        def find_date_and_format(
            string: str,
        ) -> tuple[None, None] | tuple[datetime, int]:
            for ord, format in enumerate(cls.date_formats):
                for format_option in format:
                    try:
                        date = datetime.strptime(string, format_option)
                        return date, ord
                    except ValueError:
                        # Parsing failed.
                        pass
            return (None, None)

        if not string:
            return None

        date: datetime | None

        # Check for a relative date.
        match_dq = re.match(cls.relative_re, string)
        if match_dq:
            sign = match_dq.group("sign")
            quantity = match_dq.group("quantity")
            timespan = match_dq.group("timespan")

            # Add or subtract the given amount of time from the current
            # date.
            multiplier = -1 if sign == "-" else 1
            days = cls.relative_units[timespan]
            date = (
                datetime.now()
                + timedelta(days=int(quantity) * days) * multiplier
            )
            return cls(date, cls.precisions[5])

        # Check for an absolute date.
        date, ordinal = find_date_and_format(string)
        if date is None or ordinal is None:
            raise InvalidQueryArgumentValueError(
                string, "a valid date/time string"
            )
        precision = cls.precisions[ordinal]
        return cls(date, precision)

    def open_right_endpoint(self) -> datetime:
        """Based on the precision, convert the period to a precise
        `datetime` for use as a right endpoint in a right-open interval.
        """
        precision = self.precision
        date = self.date
        if "year" == self.precision:
            return date.replace(year=date.year + 1, month=1)
        elif "month" == precision:
            if date.month < 12:
                return date.replace(month=date.month + 1)
            else:
                return date.replace(year=date.year + 1, month=1)
        elif "day" == precision:
            return date + timedelta(days=1)
        elif "hour" == precision:
            return date + timedelta(hours=1)
        elif "minute" == precision:
            return date + timedelta(minutes=1)
        elif "second" == precision:
            return date + timedelta(seconds=1)
        else:
            raise ValueError(f"unhandled precision {precision}")


class DateInterval:
    """A closed-open interval of dates.

    A left endpoint of None means since the beginning of time.
    A right endpoint of None means towards infinity.
    """

    def __init__(self, start: datetime | None, end: datetime | None):
        if start is not None and end is not None and not start < end:
            raise ValueError(
                "start date {} is not before end date {}".format(start, end)
            )
        self.start = start
        self.end = end

    @classmethod
    def from_periods(
        cls,
        start: Period | None,
        end: Period | None,
    ) -> DateInterval:
        """Create an interval with two Periods as the endpoints."""
        end_date = end.open_right_endpoint() if end is not None else None
        start_date = start.date if start is not None else None
        return cls(start_date, end_date)

    def contains(self, date: datetime) -> bool:
        if self.start is not None and date < self.start:
            return False
        if self.end is not None and date >= self.end:
            return False
        return True

    def __str__(self) -> str:
        return f"[{self.start}, {self.end})"


class DateQuery(FieldQuery[str]):
    """Matches date fields stored as seconds since Unix epoch time.

    Dates can be specified as ``year-month-day`` strings where only year
    is mandatory.

    The value of a date field can be matched against a date interval by
    using an ellipsis interval syntax similar to that of NumericQuery.
    """

    def __init__(self, field_name: str, pattern: str, fast: bool = True):
        super().__init__(field_name, pattern, fast)
        start, end = _parse_periods(pattern)
        self.interval = DateInterval.from_periods(start, end)

    def match(self, obj: Model) -> bool:
        if self.field_name not in obj:
            return False
        timestamp = float(obj[self.field_name])
        date = datetime.fromtimestamp(timestamp)
        return self.interval.contains(date)

    _clause_tmpl = "{0} {1} ?"

    def col_clause(self) -> tuple[str, Sequence[SQLiteType]]:
        clause_parts = []
        subvals = []

        # Convert the `datetime` objects to an integer number of seconds since
        # the (local) Unix epoch using `datetime.timestamp()`.
        if self.interval.start:
            clause_parts.append(self._clause_tmpl.format(self.field, ">="))
            subvals.append(int(self.interval.start.timestamp()))

        if self.interval.end:
            clause_parts.append(self._clause_tmpl.format(self.field, "<"))
            subvals.append(int(self.interval.end.timestamp()))

        if clause_parts:
            # One- or two-sided interval.
            clause = " AND ".join(clause_parts)
        else:
            # Match any date.
            clause = "1"
        return clause, subvals


class DurationQuery(NumericQuery):
    """NumericQuery that allow human-friendly (M:SS) time interval formats.

    Converts the range(s) to a float value, and delegates on NumericQuery.

    Raises InvalidQueryError when the pattern does not represent an int, float
    or M:SS time interval.
    """

    def _convert(self, s: str) -> float | None:
        """Convert a M:SS or numeric string to a float.

        Return None if `s` is empty.
        Raise an InvalidQueryError if the string cannot be converted.
        """
        if not s:
            return None
        try:
            return util.raw_seconds_short(s)
        except ValueError:
            try:
                return float(s)
            except ValueError:
                raise InvalidQueryArgumentValueError(
                    s, "a M:SS string or a float"
                )


# Sorting.


class Sort:
    """An abstract class representing a sort operation for a query into
    the database.
    """

    def order_clause(self) -> str | None:
        """Generates a SQL fragment to be used in a ORDER BY clause, or
        None if no fragment is used (i.e., this is a slow sort).
        """
        return None

    def sort(self, items: list[AnyModel]) -> list[AnyModel]:
        """Sort the list of objects and return a list."""
        return sorted(items)

    def is_slow(self) -> bool:
        """Indicate whether this query is *slow*, meaning that it cannot
        be executed in SQL and must be executed in Python.
        """
        return False

    def __hash__(self) -> int:
        return 0

    def __eq__(self, other) -> bool:
        return type(self) is type(other)

    def __repr__(self):
        return f"{self.__class__.__name__}()"


class MultipleSort(Sort):
    """Sort that encapsulates multiple sub-sorts."""

    def __init__(self, sorts: list[Sort] | None = None):
        self.sorts = sorts or []

    def add_sort(self, sort: Sort):
        self.sorts.append(sort)

    def order_clause(self) -> str:
        """Return the list SQL clauses for those sub-sorts for which we can be
        (at least partially) fast.

        A contiguous suffix of fast (SQL-capable) sub-sorts are
        executable in SQL. The remaining, even if they are fast
        independently, must be executed slowly.
        """
        order_strings = []
        for sort in reversed(self.sorts):
            clause = sort.order_clause()
            if clause is None:
                break
            order_strings.append(clause)
        order_strings.reverse()

        return ", ".join(order_strings)

    def is_slow(self) -> bool:
        for sort in self.sorts:
            if sort.is_slow():
                return True
        return False

    def sort(self, items):
        slow_sorts = []
        switch_slow = False
        for sort in reversed(self.sorts):
            if switch_slow:
                slow_sorts.append(sort)
            elif sort.order_clause() is None:
                switch_slow = True
                slow_sorts.append(sort)
            else:
                pass

        for sort in slow_sorts:
            items = sort.sort(items)
        return items

    def __repr__(self):
        return f"{self.__class__.__name__}({self.sorts!r})"

    def __hash__(self):
        return hash(tuple(self.sorts))

    def __eq__(self, other):
        return super().__eq__(other) and self.sorts == other.sorts


class FieldSort(Sort):
    """An abstract sort criterion that orders by a specific field (of
    any kind).
    """

    def __init__(
        self,
        field: str,
        ascending: bool = True,
        case_insensitive: bool = True,
    ):
        self.field = field
        self.ascending = ascending
        self.case_insensitive = case_insensitive

    def sort(self, objs: list[AnyModel]) -> list[AnyModel]:
        # TODO: Conversion and null-detection here. In Python 3,
        # comparisons with None fail. We should also support flexible
        # attributes with different types without falling over.

        def key(obj: Model) -> Any:
            field_val = obj.get(self.field, None)
            if field_val is None:
                if _type := obj._types.get(self.field):
                    # If the field is typed, use its null value.
                    field_val = obj._types[self.field].null
                else:
                    # If not, fall back to using an empty string.
                    field_val = ""
            if self.case_insensitive and isinstance(field_val, str):
                field_val = field_val.lower()
            return field_val

        return sorted(objs, key=key, reverse=not self.ascending)

    def __repr__(self) -> str:
        return (
            f"{self.__class__.__name__}"
            f"({self.field!r}, ascending={self.ascending!r})"
        )

    def __hash__(self) -> int:
        return hash((self.field, self.ascending))

    def __eq__(self, other) -> bool:
        return (
            super().__eq__(other)
            and self.field == other.field
            and self.ascending == other.ascending
        )


class FixedFieldSort(FieldSort):
    """Sort object to sort on a fixed field."""

    def order_clause(self) -> str:
        order = "ASC" if self.ascending else "DESC"
        if self.case_insensitive:
            field = (
                "(CASE "
                "WHEN TYPEOF({0})='text' THEN LOWER({0}) "
                "WHEN TYPEOF({0})='blob' THEN LOWER({0}) "
                "ELSE {0} END)".format(self.field)
            )
        else:
            field = self.field
        return f"{field} {order}"


class SlowFieldSort(FieldSort):
    """A sort criterion by some model field other than a fixed field:
    i.e., a computed or flexible field.
    """

    def is_slow(self) -> bool:
        return True


class NullSort(Sort):
    """No sorting. Leave results unsorted."""

    def sort(self, items: list[AnyModel]) -> list[AnyModel]:
        return items

    def __nonzero__(self) -> bool:
        return self.__bool__()

    def __bool__(self) -> bool:
        return False

    def __eq__(self, other) -> bool:
        return type(self) is type(other) or other is None

    def __hash__(self) -> int:
        return 0


class SmartArtistSort(FieldSort):
    """Sort by artist (either album artist or track artist),
    prioritizing the sort field over the raw field.
    """

    def order_clause(self):
        order = "ASC" if self.ascending else "DESC"
        collate = "COLLATE NOCASE" if self.case_insensitive else ""
        field = self.field

        return f"COALESCE(NULLIF({field}_sort, ''), {field}) {collate} {order}"

    def sort(self, objs: list[AnyModel]) -> list[AnyModel]:
        def key(o):
            val = o[f"{self.field}_sort"] or o[self.field]
            return val.lower() if self.case_insensitive else val

        return sorted(objs, key=key, reverse=not self.ascending)
