from __future__ import annotations

from typing import TYPE_CHECKING, Generic, TypeVar

from narwhals._expression_parsing import ExprKind, ExprNode

if TYPE_CHECKING:
    from narwhals.expr import Expr
    from narwhals.typing import IntoExpr

ExprT = TypeVar("ExprT", bound="Expr")


class ExprStringNamespace(Generic[ExprT]):
    def __init__(self, expr: ExprT) -> None:
        self._expr = expr

    def len_chars(self) -> ExprT:
        r"""Return the length of each string as the number of characters.

        Examples:
            >>> import polars as pl
            >>> import narwhals as nw
            >>> df_native = pl.DataFrame({"words": ["foo", "345", None]})
            >>> df = nw.from_native(df_native)
            >>> df.with_columns(words_len=nw.col("words").str.len_chars())
            ┌─────────────────────┐
            | Narwhals DataFrame  |
            |---------------------|
            |shape: (3, 2)        |
            |┌───────┬───────────┐|
            |│ words ┆ words_len │|
            |│ ---   ┆ ---       │|
            |│ str   ┆ u32       │|
            |╞═══════╪═══════════╡|
            |│ foo   ┆ 3         │|
            |│ 345   ┆ 3         │|
            |│ null  ┆ null      │|
            |└───────┴───────────┘|
            └─────────────────────┘
        """
        return self._expr._append_node(ExprNode(ExprKind.ELEMENTWISE, "str.len_chars"))

    def replace(
        self, pattern: str, value: str | IntoExpr, *, literal: bool = False, n: int = 1
    ) -> ExprT:
        r"""Replace first matching regex/literal substring with a new string value.

        Arguments:
            pattern: A valid regular expression pattern.
            value: String that will replace the matched substring.
            literal: Treat `pattern` as a literal string.
            n: Number of matches to replace.

        Examples:
            >>> import pandas as pd
            >>> import narwhals as nw
            >>> df_native = pd.DataFrame({"foo": ["123abc", "abc abc123"]})
            >>> df = nw.from_native(df_native)
            >>> df.with_columns(replaced=nw.col("foo").str.replace("abc", ""))
            ┌──────────────────────┐
            |  Narwhals DataFrame  |
            |----------------------|
            |          foo replaced|
            |0      123abc      123|
            |1  abc abc123   abc123|
            └──────────────────────┘
        """
        return self._expr._append_node(
            ExprNode(
                ExprKind.ELEMENTWISE,
                "str.replace",
                value,
                pattern=pattern,
                literal=literal,
                n=n,
                str_as_lit=True,
            )
        )

    def replace_all(
        self, pattern: str, value: IntoExpr, *, literal: bool = False
    ) -> ExprT:
        r"""Replace all matching regex/literal substring with a new string value.

        Arguments:
            pattern: A valid regular expression pattern.
            value: String that will replace the matched substring.
            literal: Treat `pattern` as a literal string.

        Examples:
            >>> import pandas as pd
            >>> import narwhals as nw
            >>> df_native = pd.DataFrame({"foo": ["123abc", "abc abc123"]})
            >>> df = nw.from_native(df_native)
            >>> df.with_columns(replaced=nw.col("foo").str.replace_all("abc", ""))
            ┌──────────────────────┐
            |  Narwhals DataFrame  |
            |----------------------|
            |          foo replaced|
            |0      123abc      123|
            |1  abc abc123      123|
            └──────────────────────┘
        """
        return self._expr._append_node(
            ExprNode(
                ExprKind.ELEMENTWISE,
                "str.replace_all",
                value,
                pattern=pattern,
                literal=literal,
                str_as_lit=True,
            )
        )

    def strip_chars(self, characters: str | None = None) -> ExprT:
        r"""Remove leading and trailing characters.

        Arguments:
            characters: The set of characters to be removed. All combinations of this
                set of characters will be stripped from the start and end of the string.
                If set to None (default), all leading and trailing whitespace is removed
                instead.

        Examples:
            >>> import polars as pl
            >>> import narwhals as nw
            >>> df_native = pl.DataFrame({"fruits": ["apple", "\nmango"]})
            >>> df = nw.from_native(df_native)
            >>> df.with_columns(stripped=nw.col("fruits").str.strip_chars()).to_dict(
            ...     as_series=False
            ... )
            {'fruits': ['apple', '\nmango'], 'stripped': ['apple', 'mango']}
        """
        return self._expr._append_node(
            ExprNode(ExprKind.ELEMENTWISE, "str.strip_chars", characters=characters)
        )

    def starts_with(self, prefix: str) -> ExprT:
        r"""Check if string values start with a substring.

        Arguments:
            prefix: prefix substring

        Examples:
            >>> import pandas as pd
            >>> import narwhals as nw
            >>> df_native = pd.DataFrame({"fruits": ["apple", "mango", None]})
            >>> df = nw.from_native(df_native)
            >>> df.with_columns(has_prefix=nw.col("fruits").str.starts_with("app"))
            ┌───────────────────┐
            |Narwhals DataFrame |
            |-------------------|
            |  fruits has_prefix|
            |0  apple       True|
            |1  mango      False|
            |2   None       None|
            └───────────────────┘
        """
        return self._expr._append_node(
            ExprNode(ExprKind.ELEMENTWISE, "str.starts_with", prefix=prefix)
        )

    def ends_with(self, suffix: str) -> ExprT:
        r"""Check if string values end with a substring.

        Arguments:
            suffix: suffix substring

        Examples:
            >>> import pandas as pd
            >>> import narwhals as nw
            >>> df_native = pd.DataFrame({"fruits": ["apple", "mango", None]})
            >>> df = nw.from_native(df_native)
            >>> df.with_columns(has_suffix=nw.col("fruits").str.ends_with("ngo"))
            ┌───────────────────┐
            |Narwhals DataFrame |
            |-------------------|
            |  fruits has_suffix|
            |0  apple      False|
            |1  mango       True|
            |2   None       None|
            └───────────────────┘
        """
        return self._expr._append_node(
            ExprNode(ExprKind.ELEMENTWISE, "str.ends_with", suffix=suffix)
        )

    def contains(self, pattern: str, *, literal: bool = False) -> ExprT:
        r"""Check if string contains a substring that matches a pattern.

        Arguments:
            pattern: A Character sequence or valid regular expression pattern.
            literal: If True, treats the pattern as a literal string.
                     If False, assumes the pattern is a regular expression.

        Examples:
            >>> import pyarrow as pa
            >>> import narwhals as nw
            >>> df_native = pa.table({"pets": ["cat", "dog", "rabbit and parrot"]})
            >>> df = nw.from_native(df_native)
            >>> df.with_columns(
            ...     default_match=nw.col("pets").str.contains("cat|parrot"),
            ...     case_insensitive_match=nw.col("pets").str.contains("cat|(?i)parrot"),
            ... ).to_native()
            pyarrow.Table
            pets: string
            default_match: bool
            case_insensitive_match: bool
            ----
            pets: [["cat","dog","rabbit and parrot"]]
            default_match: [[true,false,true]]
            case_insensitive_match: [[true,false,true]]
        """
        return self._expr._append_node(
            ExprNode(
                ExprKind.ELEMENTWISE, "str.contains", pattern=pattern, literal=literal
            )
        )

    def slice(self, offset: int, length: int | None = None) -> ExprT:
        r"""Create subslices of the string values of an expression.

        Arguments:
            offset: Start index. Negative indexing is supported.
            length: Length of the slice. If set to `None` (default), the slice is taken to the
                end of the string.

        Examples:
            >>> import pandas as pd
            >>> import narwhals as nw
            >>> df_native = pd.DataFrame({"s": ["pear", None, "papaya"]})
            >>> df = nw.from_native(df_native)
            >>> df.with_columns(s_sliced=nw.col("s").str.slice(4, length=3))
            ┌──────────────────┐
            |Narwhals DataFrame|
            |------------------|
            |        s s_sliced|
            |0    pear         |
            |1    None     None|
            |2  papaya       ya|
            └──────────────────┘
        """
        return self._expr._append_node(
            ExprNode(ExprKind.ELEMENTWISE, "str.slice", offset=offset, length=length)
        )

    def split(self, by: str) -> ExprT:
        r"""Split the string values of an expression by a substring.

        Arguments:
            by: Substring to split by.

        Examples:
            >>> import polars as pl
            >>> import narwhals as nw
            >>> df_native = pl.DataFrame({"s": ["foo bar", "foo_bar"]})
            >>> df = nw.from_native(df_native)
            >>> df.with_columns(nw.col("s").str.split("_").alias("s_split"))
            ┌────────────────────────────┐
            |     Narwhals DataFrame     |
            |----------------------------|
            |shape: (2, 2)               |
            |┌─────────┬────────────────┐|
            |│ s       ┆ s_split        │|
            |│ ---     ┆ ---            │|
            |│ str     ┆ list[str]      │|
            |╞═════════╪════════════════╡|
            |│ foo bar ┆ ["foo bar"]    │|
            |│ foo_bar ┆ ["foo", "bar"] │|
            |└─────────┴────────────────┘|
            └────────────────────────────┘
        """
        return self._expr._append_node(ExprNode(ExprKind.ELEMENTWISE, "str.split", by=by))

    def head(self, n: int = 5) -> ExprT:
        r"""Take the first n elements of each string.

        Arguments:
            n: Number of elements to take. Negative indexing is **not** supported.

        Notes:
            If the length of the string has fewer than `n` characters, the full string is returned.

        Examples:
            >>> import pyarrow as pa
            >>> import narwhals as nw
            >>> df_native = pa.table({"lyrics": ["taata", "taatatata", "zukkyun"]})
            >>> df = nw.from_native(df_native)
            >>> df.with_columns(lyrics_head=nw.col("lyrics").str.head()).to_native()
            pyarrow.Table
            lyrics: string
            lyrics_head: string
            ----
            lyrics: [["taata","taatatata","zukkyun"]]
            lyrics_head: [["taata","taata","zukky"]]
        """
        return self._expr._append_node(
            ExprNode(ExprKind.ELEMENTWISE, "str.slice", offset=0, length=n)
        )

    def tail(self, n: int = 5) -> ExprT:
        r"""Take the last n elements of each string.

        Arguments:
            n: Number of elements to take. Negative indexing is **not** supported.

        Notes:
            If the length of the string has fewer than `n` characters, the full string is returned.

        Examples:
            >>> import pyarrow as pa
            >>> import narwhals as nw
            >>> df_native = pa.table({"lyrics": ["taata", "taatatata", "zukkyun"]})
            >>> df = nw.from_native(df_native)
            >>> df.with_columns(lyrics_tail=nw.col("lyrics").str.tail()).to_native()
            pyarrow.Table
            lyrics: string
            lyrics_tail: string
            ----
            lyrics: [["taata","taatatata","zukkyun"]]
            lyrics_tail: [["taata","atata","kkyun"]]
        """
        return self._expr._append_node(
            ExprNode(ExprKind.ELEMENTWISE, "str.slice", offset=-n, length=None)
        )

    def to_datetime(self, format: str | None = None) -> ExprT:
        """Convert to Datetime dtype.

        Notes:
            - pandas defaults to nanosecond time unit, Polars to microsecond.
              Prior to pandas 2.0, nanoseconds were the only time unit supported
              in pandas, with no ability to set any other one. The ability to
              set the time unit in pandas, if the version permits, will arrive.
            - timezone-aware strings are all converted to and parsed as UTC.

        Warning:
            As different backends auto-infer format in different ways, if `format=None`
            there is no guarantee that the result will be equal.

        Arguments:
            format: Format to use for conversion. If set to None (default), the format is
                inferred from the data.

        Examples:
            >>> import polars as pl
            >>> import narwhals as nw
            >>> df_native = pl.DataFrame({"a": ["2020-01-01", "2020-01-02"]})
            >>> df = nw.from_native(df_native)
            >>> df.select(nw.col("a").str.to_datetime(format="%Y-%m-%d"))
            ┌───────────────────────┐
            |  Narwhals DataFrame   |
            |-----------------------|
            |shape: (2, 1)          |
            |┌─────────────────────┐|
            |│ a                   │|
            |│ ---                 │|
            |│ datetime[μs]        │|
            |╞═════════════════════╡|
            |│ 2020-01-01 00:00:00 │|
            |│ 2020-01-02 00:00:00 │|
            |└─────────────────────┘|
            └───────────────────────┘
        """
        return self._expr._append_node(
            ExprNode(ExprKind.ELEMENTWISE, "str.to_datetime", format=format)
        )

    def to_date(self, format: str | None = None) -> ExprT:
        """Convert to date dtype.

        Warning:
            As different backends auto-infer format in different ways, if `format=None`
            there is no guarantee that the result will be equal.

        Arguments:
            format: Format to use for conversion. If set to None (default), the format is inferred from the data.

        Examples:
            >>> import pyarrow as pa
            >>> import narwhals as nw
            >>> df_native = pa.table({"a": ["2020-01-01", "2020-01-02"]})
            >>> df = nw.from_native(df_native)
            >>> df.select(nw.col("a").str.to_date(format="%Y-%m-%d"))
            ┌────────────────────────────┐
            |     Narwhals DataFrame     |
            |----------------------------|
            |pyarrow.Table               |
            |a: date32[day]              |
            |----                        |
            |a: [[2020-01-01,2020-01-02]]|
            └────────────────────────────┘
        """
        return self._expr._append_node(
            ExprNode(ExprKind.ELEMENTWISE, "str.to_date", format=format)
        )

    def to_uppercase(self) -> ExprT:
        r"""Transform string to uppercase variant.

        Notes:
            The PyArrow backend will convert 'ß' to 'ẞ' instead of 'SS'.
            For more info see [the related issue](https://github.com/apache/arrow/issues/34599).
            There may be other unicode-edge-case-related variations across implementations.

        Examples:
            >>> import pandas as pd
            >>> import narwhals as nw
            >>> df_native = pd.DataFrame({"fruits": ["apple", None]})
            >>> df = nw.from_native(df_native)
            >>> df.with_columns(upper_col=nw.col("fruits").str.to_uppercase())
            ┌──────────────────┐
            |Narwhals DataFrame|
            |------------------|
            |  fruits upper_col|
            |0  apple     APPLE|
            |1   None      None|
            └──────────────────┘
        """
        return self._expr._append_node(ExprNode(ExprKind.ELEMENTWISE, "str.to_uppercase"))

    def to_lowercase(self) -> ExprT:
        r"""Transform string to lowercase variant.

        Examples:
            >>> import pandas as pd
            >>> import narwhals as nw
            >>> df_native = pd.DataFrame({"fruits": ["APPLE", None]})
            >>> df = nw.from_native(df_native)
            >>> df.with_columns(lower_col=nw.col("fruits").str.to_lowercase())
            ┌──────────────────┐
            |Narwhals DataFrame|
            |------------------|
            |  fruits lower_col|
            |0  APPLE     apple|
            |1   None      None|
            └──────────────────┘
        """
        return self._expr._append_node(ExprNode(ExprKind.ELEMENTWISE, "str.to_lowercase"))

    def to_titlecase(self) -> ExprT:
        """Modify strings to their titlecase equivalent.

        Notes:
            This is a form of case transform where the first letter of each word is
            capitalized, with the rest of the word in lowercase.

            Word boundaries are defined by non-**alphabetic** characters, matching the
            behavior of [`str.title`](https://docs.python.org/3/library/stdtypes.html#str.title)

        Examples:
            >>> import polars as pl
            >>> import narwhals as nw
            >>> df_native = pl.DataFrame(
            ...     {
            ...         "quotes": [
            ...             "'e.t. phone home'",
            ...             "you talkin' to me?",
            ...             "to infinity,and BEYOND!",
            ...         ]
            ...     }
            ... )
            >>> df = nw.from_native(df_native)
            >>> df.with_columns(quotes_title=nw.col("quotes").str.to_titlecase())
            ┌─────────────────────────────────────────────────────┐
            |                 Narwhals DataFrame                  |
            |-----------------------------------------------------|
            |shape: (3, 2)                                        |
            |┌─────────────────────────┬─────────────────────────┐|
            |│ quotes                  ┆ quotes_title            │|
            |│ ---                     ┆ ---                     │|
            |│ str                     ┆ str                     │|
            |╞═════════════════════════╪═════════════════════════╡|
            |│ 'e.t. phone home'       ┆ 'E.T. Phone Home'       │|
            |│ you talkin' to me?      ┆ You Talkin' To Me?      │|
            |│ to infinity,and BEYOND! ┆ To Infinity,And Beyond! │|
            |└─────────────────────────┴─────────────────────────┘|
            └─────────────────────────────────────────────────────┘
        """
        return self._expr._append_node(ExprNode(ExprKind.ELEMENTWISE, "str.to_titlecase"))

    def zfill(self, width: int) -> ExprT:
        """Transform string to zero-padded variant.

        Arguments:
            width: The desired length of the string after padding. If the length of the
                string is greater than `width`, no padding is applied.
                If `width` is less than 0, no padding is applied.

        Examples:
            >>> import pandas as pd
            >>> import narwhals as nw
            >>> df_native = pd.DataFrame({"digits": ["+1", "-1", "1", None]})
            >>> df = nw.from_native(df_native)
            >>> df.with_columns(zfill_col=nw.col("digits").str.zfill(3))
            ┌──────────────────┐
            |Narwhals DataFrame|
            |------------------|
            |  digits zfill_col|
            |0     +1       +01|
            |1     -1       -01|
            |2      1       001|
            |3   None      None|
            └──────────────────┘
        """
        return self._expr._append_node(
            ExprNode(ExprKind.ELEMENTWISE, "str.zfill", width=width)
        )
