from __future__ import annotations

from functools import partial
from typing import TYPE_CHECKING
from typing import Any
from typing import Collection
from typing import Iterator
from typing import Literal
from typing import Mapping
from typing import Sequence
from typing import cast
from typing import overload

import pyarrow as pa
import pyarrow.compute as pc

from narwhals._arrow.series import ArrowSeries
from narwhals._arrow.utils import align_series_full_broadcast
from narwhals._arrow.utils import native_to_narwhals_dtype
from narwhals._compliant import EagerDataFrame
from narwhals._expression_parsing import ExprKind
from narwhals.dependencies import is_numpy_array_1d
from narwhals.exceptions import ShapeError
from narwhals.utils import Implementation
from narwhals.utils import Version
from narwhals.utils import check_column_exists
from narwhals.utils import check_column_names_are_unique
from narwhals.utils import convert_str_slice_to_int_slice
from narwhals.utils import generate_temporary_column_name
from narwhals.utils import not_implemented
from narwhals.utils import parse_columns_to_drop
from narwhals.utils import parse_version
from narwhals.utils import scale_bytes
from narwhals.utils import supports_arrow_c_stream
from narwhals.utils import validate_backend_version

if TYPE_CHECKING:
    from io import BytesIO
    from pathlib import Path
    from types import ModuleType

    import pandas as pd
    import polars as pl
    from typing_extensions import Self
    from typing_extensions import TypeAlias
    from typing_extensions import TypeIs

    from narwhals._arrow.expr import ArrowExpr
    from narwhals._arrow.group_by import ArrowGroupBy
    from narwhals._arrow.namespace import ArrowNamespace
    from narwhals._arrow.typing import ChunkedArrayAny
    from narwhals._arrow.typing import Mask  # type: ignore[attr-defined]
    from narwhals._arrow.typing import Order  # type: ignore[attr-defined]
    from narwhals._compliant.typing import CompliantDataFrameAny
    from narwhals._compliant.typing import CompliantLazyFrameAny
    from narwhals._translate import IntoArrowTable
    from narwhals.dtypes import DType
    from narwhals.schema import Schema
    from narwhals.typing import JoinStrategy
    from narwhals.typing import SizedMultiIndexSelector
    from narwhals.typing import SizedMultiNameSelector
    from narwhals.typing import SizeUnit
    from narwhals.typing import UniqueKeepStrategy
    from narwhals.typing import _1DArray
    from narwhals.typing import _2DArray
    from narwhals.typing import _SliceIndex
    from narwhals.typing import _SliceName
    from narwhals.utils import Version
    from narwhals.utils import _FullContext

    JoinType: TypeAlias = Literal[
        "left semi",
        "right semi",
        "left anti",
        "right anti",
        "inner",
        "left outer",
        "right outer",
        "full outer",
    ]
    PromoteOptions: TypeAlias = Literal["none", "default", "permissive"]


class ArrowDataFrame(
    EagerDataFrame["ArrowSeries", "ArrowExpr", "pa.Table", "ChunkedArrayAny"]
):
    def __init__(
        self,
        native_dataframe: pa.Table,
        *,
        backend_version: tuple[int, ...],
        version: Version,
        validate_column_names: bool,
    ) -> None:
        if validate_column_names:
            check_column_names_are_unique(native_dataframe.column_names)
        self._native_frame = native_dataframe
        self._implementation = Implementation.PYARROW
        self._backend_version = backend_version
        self._version = version
        validate_backend_version(self._implementation, self._backend_version)

    @classmethod
    def from_arrow(cls, data: IntoArrowTable, /, *, context: _FullContext) -> Self:
        backend_version = context._backend_version
        if cls._is_native(data):
            native = data
        elif backend_version >= (14,) or isinstance(data, Collection):
            native = pa.table(data)
        elif supports_arrow_c_stream(data):  # pragma: no cover
            msg = f"'pyarrow>=14.0.0' is required for `from_arrow` for object of type {type(data).__name__!r}."
            raise ModuleNotFoundError(msg)
        else:  # pragma: no cover
            msg = f"`from_arrow` is not supported for object of type {type(data).__name__!r}."
            raise TypeError(msg)
        return cls.from_native(native, context=context)

    @classmethod
    def from_dict(
        cls,
        data: Mapping[str, Any],
        /,
        *,
        context: _FullContext,
        schema: Mapping[str, DType] | Schema | None,
    ) -> Self:
        from narwhals.schema import Schema

        pa_schema = Schema(schema).to_arrow() if schema is not None else schema
        native = pa.Table.from_pydict(data, schema=pa_schema)
        return cls.from_native(native, context=context)

    @staticmethod
    def _is_native(obj: pa.Table | Any) -> TypeIs[pa.Table]:
        return isinstance(obj, pa.Table)

    @classmethod
    def from_native(cls, data: pa.Table, /, *, context: _FullContext) -> Self:
        return cls(
            data,
            backend_version=context._backend_version,
            version=context._version,
            validate_column_names=True,
        )

    @classmethod
    def from_numpy(
        cls,
        data: _2DArray,
        /,
        *,
        context: _FullContext,
        schema: Mapping[str, DType] | Schema | Sequence[str] | None,
    ) -> Self:
        from narwhals.schema import Schema

        arrays = [pa.array(val) for val in data.T]
        if isinstance(schema, (Mapping, Schema)):
            native = pa.Table.from_arrays(arrays, schema=Schema(schema).to_arrow())
        else:
            native = pa.Table.from_arrays(arrays, cls._numpy_column_names(data, schema))
        return cls.from_native(native, context=context)

    def __narwhals_namespace__(self) -> ArrowNamespace:
        from narwhals._arrow.namespace import ArrowNamespace

        return ArrowNamespace(
            backend_version=self._backend_version, version=self._version
        )

    def __native_namespace__(self) -> ModuleType:
        if self._implementation is Implementation.PYARROW:
            return self._implementation.to_native_namespace()

        msg = f"Expected pyarrow, got: {type(self._implementation)}"  # pragma: no cover
        raise AssertionError(msg)

    def __narwhals_dataframe__(self) -> Self:
        return self

    def __narwhals_lazyframe__(self) -> Self:
        return self

    def _with_version(self, version: Version) -> Self:
        return self.__class__(
            self.native,
            backend_version=self._backend_version,
            version=version,
            validate_column_names=False,
        )

    def _with_native(self, df: pa.Table, *, validate_column_names: bool = True) -> Self:
        return self.__class__(
            df,
            backend_version=self._backend_version,
            version=self._version,
            validate_column_names=validate_column_names,
        )

    @property
    def shape(self) -> tuple[int, int]:
        return self.native.shape

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

    def row(self, index: int) -> tuple[Any, ...]:
        return tuple(col[index] for col in self.native.itercolumns())

    @overload
    def rows(self, *, named: Literal[True]) -> list[dict[str, Any]]: ...

    @overload
    def rows(self, *, named: Literal[False]) -> list[tuple[Any, ...]]: ...

    @overload
    def rows(self, *, named: bool) -> list[tuple[Any, ...]] | list[dict[str, Any]]: ...

    def rows(self, *, named: bool) -> list[tuple[Any, ...]] | list[dict[str, Any]]:
        if not named:
            return list(self.iter_rows(named=False, buffer_size=512))  # type: ignore[return-value]
        return self.native.to_pylist()

    def iter_columns(self) -> Iterator[ArrowSeries]:
        for name, series in zip(self.columns, self.native.itercolumns()):
            yield ArrowSeries.from_native(series, context=self, name=name)

    _iter_columns = iter_columns

    def iter_rows(
        self, *, named: bool, buffer_size: int
    ) -> Iterator[tuple[Any, ...]] | Iterator[dict[str, Any]]:
        df = self.native
        num_rows = df.num_rows

        if not named:
            for i in range(0, num_rows, buffer_size):
                rows = df[i : i + buffer_size].to_pydict().values()
                yield from zip(*rows)
        else:
            for i in range(0, num_rows, buffer_size):
                yield from df[i : i + buffer_size].to_pylist()

    def get_column(self, name: str) -> ArrowSeries:
        if not isinstance(name, str):
            msg = f"Expected str, got: {type(name)}"
            raise TypeError(msg)
        return ArrowSeries.from_native(self.native[name], context=self, name=name)

    def __array__(self, dtype: Any, *, copy: bool | None) -> _2DArray:
        return self.native.__array__(dtype, copy=copy)

    def _gather(self, rows: SizedMultiIndexSelector[ChunkedArrayAny]) -> Self:
        if len(rows) == 0:
            return self._with_native(self.native.slice(0, 0))
        if self._backend_version < (18,) and isinstance(rows, tuple):
            rows = list(rows)
        return self._with_native(self.native.take(rows))

    def _gather_slice(self, rows: _SliceIndex | range) -> Self:
        start = rows.start or 0
        stop = rows.stop if rows.stop is not None else len(self.native)
        if start < 0:
            start = len(self.native) + start
        if stop < 0:
            stop = len(self.native) + stop
        if rows.step is not None and rows.step != 1:
            msg = "Slicing with step is not supported on PyArrow tables"
            raise NotImplementedError(msg)
        return self._with_native(self.native.slice(start, stop - start))

    def _select_slice_name(self, columns: _SliceName) -> Self:
        start, stop, step = convert_str_slice_to_int_slice(columns, self.columns)
        return self._with_native(self.native.select(self.columns[start:stop:step]))

    def _select_slice_index(self, columns: _SliceIndex | range) -> Self:
        return self._with_native(
            self.native.select(self.columns[columns.start : columns.stop : columns.step])
        )

    def _select_multi_index(
        self, columns: SizedMultiIndexSelector[ChunkedArrayAny]
    ) -> Self:
        selector: Sequence[int]
        if isinstance(columns, pa.ChunkedArray):
            # TODO @dangotbanned: Fix upstream with `pa.ChunkedArray.to_pylist(self) -> list[Any]:`
            selector = cast("Sequence[int]", columns.to_pylist())
        # TODO @dangotbanned: Fix upstream, it is actually much narrower
        # **Doesn't accept `ndarray`**
        elif is_numpy_array_1d(columns):
            selector = columns.tolist()
        else:
            selector = columns
        return self._with_native(self.native.select(selector))

    def _select_multi_name(
        self, columns: SizedMultiNameSelector[ChunkedArrayAny]
    ) -> Self:
        selector: Sequence[str] | _1DArray
        if isinstance(columns, pa.ChunkedArray):
            # TODO @dangotbanned: Fix upstream with `pa.ChunkedArray.to_pylist(self) -> list[Any]:`
            selector = cast("Sequence[str]", columns.to_pylist())
        else:
            selector = columns
        # NOTE: Fixed in https://github.com/zen-xu/pyarrow-stubs/pull/221
        return self._with_native(self.native.select(selector))  # pyright: ignore[reportArgumentType]

    @property
    def schema(self) -> dict[str, DType]:
        schema = self.native.schema
        return {
            name: native_to_narwhals_dtype(dtype, self._version)
            for name, dtype in zip(schema.names, schema.types)
        }

    def collect_schema(self) -> dict[str, DType]:
        return self.schema

    def estimated_size(self, unit: SizeUnit) -> int | float:
        sz = self.native.nbytes
        return scale_bytes(sz, unit)

    explode = not_implemented()

    @property
    def columns(self) -> list[str]:
        return self.native.column_names

    def simple_select(self, *column_names: str) -> Self:
        return self._with_native(
            self.native.select(list(column_names)), validate_column_names=False
        )

    def select(self: ArrowDataFrame, *exprs: ArrowExpr) -> ArrowDataFrame:
        new_series = self._evaluate_into_exprs(*exprs)
        if not new_series:
            # return empty dataframe, like Polars does
            return self._with_native(
                self.native.__class__.from_arrays([]), validate_column_names=False
            )
        names = [s.name for s in new_series]
        reshaped = align_series_full_broadcast(*new_series)
        df = pa.Table.from_arrays([s.native for s in reshaped], names=names)
        return self._with_native(df, validate_column_names=True)

    def _extract_comparand(self, other: ArrowSeries) -> ChunkedArrayAny:
        length = len(self)
        if not other._broadcast:
            if (len_other := len(other)) != length:
                msg = f"Expected object of length {length}, got: {len_other}."
                raise ShapeError(msg)
            return other.native

        import numpy as np  # ignore-banned-import

        value = other.native[0]
        if self._backend_version < (13,) and hasattr(value, "as_py"):
            value = value.as_py()
        return pa.chunked_array([np.full(shape=length, fill_value=value)])

    def with_columns(self: ArrowDataFrame, *exprs: ArrowExpr) -> ArrowDataFrame:
        # NOTE: We use a faux-mutable variable and repeatedly "overwrite" (native_frame)
        # All `pyarrow` data is immutable, so this is fine
        native_frame = self.native
        new_columns = self._evaluate_into_exprs(*exprs)
        columns = self.columns

        for col_value in new_columns:
            col_name = col_value.name
            column = self._extract_comparand(col_value)
            native_frame = (
                native_frame.set_column(columns.index(col_name), col_name, column=column)
                if col_name in columns
                else native_frame.append_column(col_name, column=column)
            )

        return self._with_native(native_frame, validate_column_names=False)

    def group_by(
        self, keys: Sequence[str] | Sequence[ArrowExpr], *, drop_null_keys: bool
    ) -> ArrowGroupBy:
        from narwhals._arrow.group_by import ArrowGroupBy

        return ArrowGroupBy(self, keys, drop_null_keys=drop_null_keys)

    def join(
        self,
        other: Self,
        *,
        how: JoinStrategy,
        left_on: Sequence[str] | None,
        right_on: Sequence[str] | None,
        suffix: str,
    ) -> Self:
        how_to_join_map: dict[str, JoinType] = {
            "anti": "left anti",
            "semi": "left semi",
            "inner": "inner",
            "left": "left outer",
            "full": "full outer",
        }

        if how == "cross":
            plx = self.__narwhals_namespace__()
            key_token = generate_temporary_column_name(
                n_bytes=8, columns=[*self.columns, *other.columns]
            )

            return self._with_native(
                self.with_columns(
                    plx.lit(0, None).alias(key_token).broadcast(ExprKind.LITERAL)
                )
                .native.join(
                    other.with_columns(
                        plx.lit(0, None).alias(key_token).broadcast(ExprKind.LITERAL)
                    ).native,
                    keys=key_token,
                    right_keys=key_token,
                    join_type="inner",
                    right_suffix=suffix,
                )
                .drop([key_token])
            )

        coalesce_keys = how != "full"  # polars full join does not coalesce keys
        return self._with_native(
            self.native.join(
                other.native,
                keys=left_on or [],  # type: ignore[arg-type]
                right_keys=right_on,  # type: ignore[arg-type]
                join_type=how_to_join_map[how],
                right_suffix=suffix,
                coalesce_keys=coalesce_keys,
            ),
        )

    join_asof = not_implemented()

    def drop(self, columns: Sequence[str], *, strict: bool) -> Self:
        to_drop = parse_columns_to_drop(
            compliant_frame=self, columns=columns, strict=strict
        )
        return self._with_native(self.native.drop(to_drop), validate_column_names=False)

    def drop_nulls(self: ArrowDataFrame, subset: Sequence[str] | None) -> ArrowDataFrame:
        if subset is None:
            return self._with_native(self.native.drop_null(), validate_column_names=False)
        plx = self.__narwhals_namespace__()
        return self.filter(~plx.any_horizontal(plx.col(*subset).is_null()))

    def sort(
        self,
        *by: str,
        descending: bool | Sequence[bool],
        nulls_last: bool,
    ) -> Self:
        if isinstance(descending, bool):
            order: Order = "descending" if descending else "ascending"
            sorting: list[tuple[str, Order]] = [(key, order) for key in by]
        else:
            sorting = [
                (key, "descending" if is_descending else "ascending")
                for key, is_descending in zip(by, descending)
            ]

        null_placement = "at_end" if nulls_last else "at_start"

        return self._with_native(
            self.native.sort_by(sorting, null_placement=null_placement),
            validate_column_names=False,
        )

    def to_pandas(self) -> pd.DataFrame:
        return self.native.to_pandas()

    def to_polars(self) -> pl.DataFrame:
        import polars as pl  # ignore-banned-import

        return pl.from_arrow(self.native)  # type: ignore[return-value]

    def to_numpy(self, dtype: Any = None, *, copy: bool | None = None) -> _2DArray:
        import numpy as np  # ignore-banned-import

        arr: Any = np.column_stack([col.to_numpy() for col in self.native.columns])
        return arr

    @overload
    def to_dict(self, *, as_series: Literal[True]) -> dict[str, ArrowSeries]: ...

    @overload
    def to_dict(self, *, as_series: Literal[False]) -> dict[str, list[Any]]: ...

    def to_dict(
        self, *, as_series: bool
    ) -> dict[str, ArrowSeries] | dict[str, list[Any]]:
        it = self.iter_columns()
        if as_series:
            return {ser.name: ser for ser in it}
        return {ser.name: ser.to_list() for ser in it}

    def with_row_index(self, name: str) -> Self:
        df = self.native
        cols = self.columns

        row_indices = pa.array(range(df.num_rows))
        return self._with_native(
            df.append_column(name, row_indices).select([name, *cols])
        )

    def filter(
        self: ArrowDataFrame, predicate: ArrowExpr | list[bool | None]
    ) -> ArrowDataFrame:
        if isinstance(predicate, list):
            mask_native: Mask | ChunkedArrayAny = predicate
        else:
            # `[0]` is safe as the predicate's expression only returns a single column
            mask_native = self._evaluate_into_exprs(predicate)[0].native
        return self._with_native(
            self.native.filter(mask_native), validate_column_names=False
        )

    def head(self, n: int) -> Self:
        df = self.native
        if n >= 0:
            return self._with_native(df.slice(0, n), validate_column_names=False)
        else:
            num_rows = df.num_rows
            return self._with_native(
                df.slice(0, max(0, num_rows + n)), validate_column_names=False
            )

    def tail(self, n: int) -> Self:
        df = self.native
        if n >= 0:
            num_rows = df.num_rows
            return self._with_native(
                df.slice(max(0, num_rows - n)), validate_column_names=False
            )
        else:
            return self._with_native(df.slice(abs(n)), validate_column_names=False)

    def lazy(self, *, backend: Implementation | None = None) -> CompliantLazyFrameAny:
        if backend is None:
            return self
        elif backend is Implementation.DUCKDB:
            import duckdb  # ignore-banned-import

            from narwhals._duckdb.dataframe import DuckDBLazyFrame

            df = self.native  # noqa: F841
            return DuckDBLazyFrame(
                duckdb.table("df"),
                backend_version=parse_version(duckdb),
                version=self._version,
            )
        elif backend is Implementation.POLARS:
            import polars as pl  # ignore-banned-import

            from narwhals._polars.dataframe import PolarsLazyFrame

            return PolarsLazyFrame(
                cast("pl.DataFrame", pl.from_arrow(self.native)).lazy(),
                backend_version=parse_version(pl),
                version=self._version,
            )
        elif backend is Implementation.DASK:
            import dask  # ignore-banned-import
            import dask.dataframe as dd  # ignore-banned-import

            from narwhals._dask.dataframe import DaskLazyFrame

            return DaskLazyFrame(
                dd.from_pandas(self.native.to_pandas()),
                backend_version=parse_version(dask),
                version=self._version,
            )
        raise AssertionError  # pragma: no cover

    def collect(
        self, backend: Implementation | None, **kwargs: Any
    ) -> CompliantDataFrameAny:
        if backend is Implementation.PYARROW or backend is None:
            from narwhals._arrow.dataframe import ArrowDataFrame

            return ArrowDataFrame(
                self.native,
                backend_version=self._backend_version,
                version=self._version,
                validate_column_names=False,
            )

        if backend is Implementation.PANDAS:
            import pandas as pd  # ignore-banned-import

            from narwhals._pandas_like.dataframe import PandasLikeDataFrame

            return PandasLikeDataFrame(
                self.native.to_pandas(),
                implementation=Implementation.PANDAS,
                backend_version=parse_version(pd),
                version=self._version,
                validate_column_names=False,
            )

        if backend is Implementation.POLARS:
            import polars as pl  # ignore-banned-import

            from narwhals._polars.dataframe import PolarsDataFrame

            return PolarsDataFrame(
                cast("pl.DataFrame", pl.from_arrow(self.native)),
                backend_version=parse_version(pl),
                version=self._version,
            )

        msg = f"Unsupported `backend` value: {backend}"  # pragma: no cover
        raise AssertionError(msg)  # pragma: no cover

    def clone(self) -> Self:
        return self._with_native(self.native, validate_column_names=False)

    def item(self, row: int | None, column: int | str | None) -> Any:
        from narwhals._arrow.series import maybe_extract_py_scalar

        if row is None and column is None:
            if self.shape != (1, 1):
                msg = (
                    "can only call `.item()` if the dataframe is of shape (1, 1),"
                    " or if explicit row/col values are provided;"
                    f" frame has shape {self.shape!r}"
                )
                raise ValueError(msg)
            return maybe_extract_py_scalar(self.native[0][0], return_py_scalar=True)

        elif row is None or column is None:
            msg = "cannot call `.item()` with only one of `row` or `column`"
            raise ValueError(msg)

        _col = self.columns.index(column) if isinstance(column, str) else column
        return maybe_extract_py_scalar(self.native[_col][row], return_py_scalar=True)

    def rename(self, mapping: Mapping[str, str]) -> Self:
        names: dict[str, str] | list[str]
        if self._backend_version >= (17,):
            names = cast("dict[str, str]", mapping)
        else:  # pragma: no cover
            names = [mapping.get(c, c) for c in self.columns]
        return self._with_native(self.native.rename_columns(names))

    def write_parquet(self, file: str | Path | BytesIO) -> None:
        import pyarrow.parquet as pp

        pp.write_table(self.native, file)

    @overload
    def write_csv(self, file: None) -> str: ...

    @overload
    def write_csv(self, file: str | Path | BytesIO) -> None: ...

    def write_csv(self, file: str | Path | BytesIO | None) -> str | None:
        import pyarrow.csv as pa_csv

        if file is None:
            csv_buffer = pa.BufferOutputStream()
            pa_csv.write_csv(self.native, csv_buffer)
            return csv_buffer.getvalue().to_pybytes().decode()
        pa_csv.write_csv(self.native, file)
        return None

    def is_unique(self) -> ArrowSeries:
        col_token = generate_temporary_column_name(n_bytes=8, columns=self.columns)
        row_index = pa.array(range(len(self)))
        keep_idx = (
            self.native.append_column(col_token, row_index)
            .group_by(self.columns)
            .aggregate([(col_token, "min"), (col_token, "max")])
        )
        native = pa.chunked_array(
            pc.and_(
                pc.is_in(row_index, keep_idx[f"{col_token}_min"]),
                pc.is_in(row_index, keep_idx[f"{col_token}_max"]),
            )
        )
        return ArrowSeries.from_native(native, context=self)

    def unique(
        self: ArrowDataFrame,
        subset: Sequence[str] | None,
        *,
        keep: UniqueKeepStrategy,
        maintain_order: bool | None = None,
    ) -> ArrowDataFrame:
        # The param `maintain_order` is only here for compatibility with the Polars API
        # and has no effect on the output.
        import numpy as np  # ignore-banned-import

        check_column_exists(self.columns, subset)
        subset = list(subset or self.columns)

        if keep in {"any", "first", "last"}:
            from narwhals._arrow.group_by import ArrowGroupBy

            agg_func = ArrowGroupBy._REMAP_UNIQUE[keep]
            col_token = generate_temporary_column_name(n_bytes=8, columns=self.columns)
            keep_idx_native = (
                self.native.append_column(col_token, pa.array(np.arange(len(self))))
                .group_by(subset)
                .aggregate([(col_token, agg_func)])
                .column(f"{col_token}_{agg_func}")
            )
            return self._with_native(
                self.native.take(keep_idx_native), validate_column_names=False
            )

        keep_idx = self.simple_select(*subset).is_unique()
        plx = self.__narwhals_namespace__()
        return self.filter(plx._expr._from_series(keep_idx))

    def gather_every(self, n: int, offset: int) -> Self:
        return self._with_native(self.native[offset::n], validate_column_names=False)

    def to_arrow(self) -> pa.Table:
        return self.native

    def sample(
        self,
        n: int | None,
        *,
        fraction: float | None,
        with_replacement: bool,
        seed: int | None,
    ) -> Self:
        import numpy as np  # ignore-banned-import

        num_rows = len(self)
        if n is None and fraction is not None:
            n = int(num_rows * fraction)
        rng = np.random.default_rng(seed=seed)
        idx = np.arange(0, num_rows)
        mask = rng.choice(idx, size=n, replace=with_replacement)
        return self._with_native(self.native.take(mask), validate_column_names=False)

    def unpivot(
        self,
        on: Sequence[str] | None,
        index: Sequence[str] | None,
        variable_name: str,
        value_name: str,
    ) -> Self:
        n_rows = len(self)
        index_ = [] if index is None else index
        on_ = [c for c in self.columns if c not in index_] if on is None else on
        concat = (
            partial(pa.concat_tables, promote_options="permissive")
            if self._backend_version >= (14, 0, 0)
            else pa.concat_tables
        )
        names = [*index_, variable_name, value_name]
        return self._with_native(
            concat(
                [
                    pa.Table.from_arrays(
                        [
                            *(self.native.column(idx_col) for idx_col in index_),
                            cast(
                                "ChunkedArrayAny",
                                pa.array([on_col] * n_rows, pa.string()),
                            ),
                            self.native.column(on_col),
                        ],
                        names=names,
                    )
                    for on_col in on_
                ]
            )
        )
        # TODO(Unassigned): Even with promote_options="permissive", pyarrow does not
        # upcast numeric to non-numeric (e.g. string) datatypes

    pivot = not_implemented()