words2num2-core 0.1.1

//! Port of `words2num2/formats.py` — per-locale number-format defaults and the
//! configurable numeric-string parser.
//!
//! # Fidelity notes
//!
//! Three things in the Python original do not have a free Rust equivalent and
//! are reimplemented here on purpose:
//!
//! 1. **`\s` / `str.strip()` is *not* `char::is_whitespace()`.** Python's `\s`
//!    (and `str.isspace()`, which drives `str.strip()`) matches 29 codepoints,
//!    including `U+001C..U+001F` (the FILE/GROUP/RECORD/UNIT separators). Rust's
//!    `char::is_whitespace()` follows the Unicode `White_Space` property, which
//!    excludes those four. `parse_number_string("\x1c42")` returns `42` in
//!    Python, so the exact set is reproduced in [`is_py_space`].
//!
//! 2. **`\d` is *not* `is_ascii_digit()`.** In a `str` pattern Python's `\d`
//!    matches Unicode general category `Nd` — all 760 of them (Unicode 16) — and `int()` /
//!    `float()` then accept those digits, mixing scripts freely:
//!    `_to_number("١2")` is `12` and `_to_number("٢٣.٥")` is `23.5`. [`ND_RUNS`]
//!    carries the 61 contiguous `Nd` decades so [`to_number`] can transliterate
//!    to ASCII before parsing, exactly as CPython does internally.
//!
//! 3. **`"not a parseable number: %r"` interpolates Python's `repr()`.** That is
//!    reproduced in [`py_repr`], quote selection and `\xNN`/`\uNNNN`/`\UNNNNNNNN`
//!    escapes included, so `parse_number_string("1\u{a0}234", Some("\t"), ..)`
//!    reports `not a parseable number: '1\xa0234'` byte for byte.
//!
//! The space-like separators are distinct codepoints and stay distinct:
//! NBSP `U+00A0`, NARROW NBSP `U+202F`, THIN SPACE `U+2009`. Note that the
//! locale table itself only ever uses a plain ASCII space `U+0020` — the other
//! three appear solely in the `thousands_sep in (" ", NBSP, NNBSP, THIN_SPACE)`
//! membership test and in the two regex character classes.

use bigdecimal::BigDecimal;
use num_bigint::BigInt;
use std::cmp::Ordering;
use std::fmt;

// ---------------------------------------------------------------------------
// Errors and values
// ---------------------------------------------------------------------------

/// Port of `words2num2.base.Words2NumError` (a `ValueError` subclass).
///
/// Carries the exact message Python produces; the pyo3 boundary is responsible
/// for turning it back into the Python exception class.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct Words2NumError(pub String);

impl Words2NumError {
    fn new(msg: impl Into<String>) -> Self {
        Words2NumError(msg.into())
    }
}

impl fmt::Display for Words2NumError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.write_str(&self.0)
    }
}

impl std::error::Error for Words2NumError {}

/// `words2num2` hands back an `int`, a `float` or a `Decimal` depending on the
/// input.
///
/// `formats.py` imports `Decimal` but never constructs one — every return from
/// `_to_number` is an `int` or a `float`. `Dec` exists so this enum lines up
/// with the sibling modules during wiring.
#[derive(Debug, Clone, PartialEq)]
pub enum W2nValue {
    Int(BigInt),
    Float(f64),
    Dec(BigDecimal),
}

/// `Result` alias matching the module's single error type.
pub type Result<T> = std::result::Result<T, Words2NumError>;

// ---------------------------------------------------------------------------
// Space-like separators
// ---------------------------------------------------------------------------

/// `NBSP = "\xa0"` — NO-BREAK SPACE.
pub const NBSP: char = '\u{00A0}';
/// `NNBSP = " "` — NARROW NO-BREAK SPACE, the French standard.
pub const NNBSP: char = '\u{202F}';
/// `THIN_SPACE = " "` — THIN SPACE.
pub const THIN_SPACE: char = '\u{2009}';
/// `SPACE_LIKE = " \t" + NBSP + NNBSP + THIN_SPACE`.
///
/// Dead code in the Python module too: nothing reads it, there or here. Kept
/// because it is part of the module's public surface.
pub const SPACE_LIKE: &str = " \t\u{00A0}\u{202F}\u{2009}";

/// The exact set Python's `\s` matches — equivalently `str.isspace()`, which is
/// what `str.strip()` / `str.lstrip()` use.
///
/// 29 codepoints. **Not** `char::is_whitespace()`: that omits `U+001C..U+001F`.
fn is_py_space(c: char) -> bool {
    matches!(c,
        '\u{0009}'..='\u{000D}'   // TAB LF VT FF CR
        | '\u{001C}'..='\u{001F}' // FS GS RS US — Rust's is_whitespace() misses these
        | '\u{0020}'
        | '\u{0085}'
        | '\u{00A0}'              // NBSP
        | '\u{1680}'
        | '\u{2000}'..='\u{200A}' // includes THIN SPACE U+2009
        | '\u{2028}'
        | '\u{2029}'
        | '\u{202F}'              // NNBSP
        | '\u{205F}'
        | '\u{3000}'
    )
}

/// `str.strip()`
fn py_strip(s: &str) -> &str {
    s.trim_matches(is_py_space)
}

/// `str.lstrip()`
fn py_lstrip(s: &str) -> &str {
    s.trim_start_matches(is_py_space)
}

// ---------------------------------------------------------------------------
// NUMBER_FORMAT_DEFAULTS
// ---------------------------------------------------------------------------

/// One row of [`NUMBER_FORMAT_DEFAULTS`] — Python's `{"thousands": …,
/// "decimal": …}` dict.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct NumberFormat {
    pub thousands: &'static str,
    pub decimal: &'static str,
}

const fn nf(thousands: &'static str, decimal: &'static str) -> NumberFormat {
    NumberFormat { thousands, decimal }
}

/// CLDR-inspired per-locale defaults, in Python source order. `"_default"` is
/// the fallback.
///
/// A slice rather than a map: 55 rows, looked up by linear scan, and the order
/// stays visibly identical to the Python dict.
///
/// Every `thousands` that reads as a space here is a plain ASCII `U+0020` — the
/// Python table uses no NBSP/NNBSP/THIN SPACE anywhere (verified against the
/// live module, codepoint by codepoint).
pub static NUMBER_FORMAT_DEFAULTS: &[(&str, NumberFormat)] = &[
    ("_default", nf(",", ".")),
    // English + CJK group (comma thousands, dot decimal)
    ("en", nf(",", ".")),
    ("en_GB", nf(",", ".")),
    ("en_IN", nf(",", ".")),
    ("en_NG", nf(",", ".")),
    ("zh", nf(",", ".")),
    ("zh_CN", nf(",", ".")),
    ("zh_HK", nf(",", ".")),
    ("zh_TW", nf(",", ".")),
    ("ja", nf(",", ".")),
    ("ko", nf(",", ".")),
    ("th", nf(",", ".")),
    ("vi", nf(".", ",")),
    // French (space thousands, comma decimal)
    ("fr", nf(" ", ",")),
    ("fr_BE", nf(" ", ",")),
    ("fr_DZ", nf(" ", ",")),
    // Swiss French uses apostrophe
    ("fr_CH", nf("'", ".")),
    // Continental European (dot thousands, comma decimal)
    ("de", nf(".", ",")),
    ("es", nf(".", ",")),
    ("es_CO", nf(".", ",")),
    ("es_CR", nf(".", ",")),
    ("es_GT", nf(".", ",")),
    ("es_NI", nf(".", ",")),
    ("es_VE", nf(".", ",")),
    ("it", nf(".", ",")),
    ("pt", nf(".", ",")),
    ("pt_BR", nf(".", ",")),
    ("nl", nf(".", ",")),
    ("ro", nf(".", ",")),
    ("hr", nf(".", ",")),
    ("sl", nf(".", ",")),
    ("sr", nf(".", ",")),
    ("tr", nf(".", ",")),
    ("el", nf(".", ",")),
    // Slavic / Scandinavian / Baltic (space thousands, comma decimal)
    ("ru", nf(" ", ",")),
    ("uk", nf(" ", ",")),
    ("be", nf(" ", ",")),
    ("bg", nf(" ", ",")),
    ("pl", nf(" ", ",")),
    ("cs", nf(" ", ",")),
    ("sk", nf(" ", ",")),
    ("hu", nf(" ", ",")),
    ("sv", nf(" ", ",")),
    ("no", nf(" ", ",")),
    ("nn", nf(" ", ",")),
    ("da", nf(".", ",")),
    ("fi", nf(" ", ",")),
    ("et", nf(" ", ",")),
    ("lt", nf(" ", ",")),
    ("lv", nf(" ", ",")),
    ("is", nf(".", ",")),
    ("fo", nf(".", ",")),
    // Arabic + Persian use Western digits but local separators in some
    // contexts; default to Western style.
    ("ar", nf(",", ".")),
    ("fa", nf(",", ".")),
    ("he", nf(",", ".")),
];

/// `lang in NUMBER_FORMAT_DEFAULTS` → `NUMBER_FORMAT_DEFAULTS[lang]`
fn lookup_format(key: &str) -> Option<NumberFormat> {
    NUMBER_FORMAT_DEFAULTS
        .iter()
        .find(|(k, _)| *k == key)
        .map(|(_, v)| *v)
}

/// Port of `get_format`. Returns the `{thousands, decimal}` row for `lang`,
/// with fallback.
///
/// ```python
/// if lang in NUMBER_FORMAT_DEFAULTS:
///     return NUMBER_FORMAT_DEFAULTS[lang]
/// base = lang.split("_")[0] if lang else ""
/// if base in NUMBER_FORMAT_DEFAULTS:
///     return NUMBER_FORMAT_DEFAULTS[base]
/// return NUMBER_FORMAT_DEFAULTS["_default"]
/// ```
///
/// Python's `if lang else ""` guard only exists to keep `lang=None` from
/// hitting `.split`; `"".split("_")[0]` is already `""`, so `get_format(None)`
/// and `get_format("")` both land on `_default` — which is what `get_format("")`
/// does here.
pub fn get_format(lang: &str) -> NumberFormat {
    if let Some(f) = lookup_format(lang) {
        return f;
    }
    let base = lang.split('_').next().unwrap_or("");
    if let Some(f) = lookup_format(base) {
        return f;
    }
    lookup_format("_default").expect("_default is always present")
}

// ---------------------------------------------------------------------------
// parse_number_string
// ---------------------------------------------------------------------------

/// Port of `parse_number_string`. Parses a numeric string with configurable
/// separators.
///
/// Resolution order, straight from the docstring:
///   1. If `thousands_sep` and/or `decimal_sep` are given, use them.
///   2. Otherwise if `lang` matches a known locale, use its defaults.
///   3. Otherwise auto-detect from the string itself.
///
/// `Option::None` is Python's `None` and `Some("")` is Python's `""` — the two
/// are **not** interchangeable. `parse_number_string(s, None, None, None)`
/// auto-detects, but `parse_number_string(s, Some(""), None, None)` takes the
/// explicit branch and then skips every rewrite (`if thousands_sep:` is falsy
/// for `""`), so `"1.234"` → `1.234` rather than the auto-detected `1.234`.
/// They agree there by luck; they do not in general.
///
/// Python's leading `isinstance(s, str)` check — which raises
/// `Words2NumError("expected str, got %r" % type(s).__name__)` — is unreachable
/// behind a `&str` and is therefore not ported. A dispatcher that accepts
/// arbitrary Python objects must keep that check on its own side.
pub fn parse_number_string(
    s: &str,
    thousands_sep: Option<&str>,
    decimal_sep: Option<&str>,
    lang: Option<&str>,
) -> Result<W2nValue> {
    let s = py_strip(s);
    if s.is_empty() {
        return Err(Words2NumError::new("empty numeric string"));
    }

    // if s[0] in "+-": ... ; s = s[1:].lstrip()
    // Exactly one sign character is consumed — "+-42" keeps the "-" and later
    // fails with `not a parseable number: '-42'`.
    let mut sign = 1i32;
    let first = s.chars().next().expect("non-empty");
    let s = if first == '+' || first == '-' {
        if first == '-' {
            sign = -1;
        }
        py_lstrip(&s[first.len_utf8()..])
    } else {
        s
    };
    if s.is_empty() {
        return Err(Words2NumError::new("empty numeric string after sign"));
    }

    if thousands_sep.is_some() || decimal_sep.is_some() {
        return Ok(apply_sign(sign, parse_with_explicit(s, thousands_sep, decimal_sep)?));
    }

    if let Some(lang) = lang {
        let fmt = get_format(lang);
        // Python: `except Words2NumError: pass` — and `_parse_with_explicit`
        // raises nothing else, so any Err falls through to auto-detection.
        if let Ok(v) = parse_with_explicit(s, Some(fmt.thousands), Some(fmt.decimal)) {
            return Ok(apply_sign(sign, v));
        }
    }

    Ok(apply_sign(sign, auto_detect_parse(s)?))
}

/// Python's `sign * value`, where `sign` is the int `1` or `-1`.
///
/// `1 * x` is `x`. `-1 * 0.0` is `-0.0` and `-1 * 0` is `0` (ints have no
/// negative zero) — negation reproduces both.
fn apply_sign(sign: i32, v: W2nValue) -> W2nValue {
    if sign >= 0 {
        return v;
    }
    match v {
        W2nValue::Int(i) => W2nValue::Int(-i),
        W2nValue::Float(f) => W2nValue::Float(-f),
        W2nValue::Dec(d) => W2nValue::Dec(-d),
    }
}

/// Port of `_parse_with_explicit`.
///
/// ```python
/// if thousands_sep:
///     if thousands_sep in (" ", NBSP, NNBSP, THIN_SPACE):
///         s = re.sub(r"[\s\xa0  ]", "", s)
///     else:
///         s = s.replace(thousands_sep, "")
/// if decimal_sep:
///     if decimal_sep != ".":
///         if "." in s:
///             s = s.replace(".", "")
///         s = s.replace(decimal_sep, ".")
/// return _to_number(s)
/// ```
///
/// The membership test is exact string equality against those four separators.
/// A tab is *not* in the tuple, so `thousands_sep="\t"` takes the plain
/// `.replace` branch and leaves an NBSP in place — hence
/// `parse_number_string("1\u{a0}234", Some("\t"), None, None)` failing while
/// `Some(" ")` succeeds.
///
/// The `[\s\xa0  ]` class is `\s` plus three codepoints `\s` already
/// covers; the redundancy is harmless and preserved as a plain `is_py_space`.
fn parse_with_explicit(
    s: &str,
    thousands_sep: Option<&str>,
    decimal_sep: Option<&str>,
) -> Result<W2nValue> {
    let mut cur = s.to_string();

    // `if thousands_sep:` — Python truthiness: None and "" are both falsy.
    if let Some(t) = thousands_sep.filter(|t| !t.is_empty()) {
        if t == " " || t == "\u{00A0}" || t == "\u{202F}" || t == "\u{2009}" {
            // treat any space-like as thousands when one is configured
            cur = cur.chars().filter(|&c| !is_py_space(c)).collect();
        } else {
            cur = cur.replace(t, "");
        }
    }

    if let Some(d) = decimal_sep.filter(|d| !d.is_empty()) {
        if d != "." {
            if cur.contains('.') {
                // User explicitly gave a non-dot decimal but the string also
                // has dots — treat dots as a stray separator and drop.
                cur = cur.replace('.', "");
            }
            cur = cur.replace(d, ".");
        }
    }

    to_number(&cur)
}

/// Port of `_auto_detect_parse`.
fn auto_detect_parse(s: &str) -> Result<W2nValue> {
    // Strip clearly-thousands-only separators first:
    //   re.sub(r"[\s\xa0  '_]", "", s)
    let s2: String = s
        .chars()
        .filter(|&c| !(is_py_space(c) || c == '\'' || c == '_'))
        .collect();

    let has_comma = s2.contains(',');
    let has_dot = s2.contains('.');

    if has_comma && has_dot {
        // Both present — the rightmost is decimal.
        let last_comma = last_char_index(&s2, ',').expect("has_comma");
        let last_dot = last_char_index(&s2, '.').expect("has_dot");
        let s3 = if last_comma > last_dot {
            s2.replace('.', "").replace(',', ".")
        } else {
            s2.replace(',', "")
        };
        return to_number(&s3);
    }

    if has_comma {
        return to_number(&resolve_single_sep(&s2, ','));
    }
    if has_dot {
        return to_number(&resolve_single_sep(&s2, '.'));
    }
    to_number(&s2)
}

/// `str.rfind(ch)` — the **character** index of the last `ch`.
///
/// `rfind` byte offsets would compare identically here (both separators are
/// ASCII, so byte order tracks char order), but the whole file indexes by
/// `chars()` on principle.
fn last_char_index(s: &str, target: char) -> Option<usize> {
    s.chars()
        .enumerate()
        .filter(|(_, c)| *c == target)
        .map(|(i, _)| i)
        .last()
}

/// Port of `_resolve_single_sep` — decide whether `sep` is decimal or thousands
/// when only it appears.
///
/// Python indexes `parts[1]` unguarded, so calling this with a `sep` absent from
/// `s` is an `IndexError`. Both call sites test membership first, so the branch
/// is unreachable; this is a private fn and keeps the same precondition.
///
/// Two quirks preserved verbatim:
///
/// * The `else` arms hardcode `s.replace(",", ".")` instead of using `sep`.
///   That is only ever reached when `sep != "."`, and `sep` is only ever `,` or
///   `.`, so it is equivalent — but it is written the way Python writes it.
/// * The `len(after) == 3` ambiguity resolves to **decimal**, so auto-detected
///   `"1,234"` is `1.234` and `"12.345"` is `12.345`. Reads like a bug; it is
///   the documented intent ("Default to decimal (preserves precision)") and it
///   is the specification either way.
fn resolve_single_sep(s: &str, sep: char) -> String {
    let parts: Vec<&str> = s.split(sep).collect();
    if parts.len() > 2 {
        // Multiple occurrences → thousands.
        return s.replace(sep, "");
    }
    let after = parts[1];
    let after_len = after.chars().count();
    let before_len = parts[0].chars().count();

    // Exactly 3 trailing digits *and* a leading group of at most 3 → ambiguous.
    // Default to decimal unless the leading group has more than 3 digits.
    if after_len == 3 && !parts[0].is_empty() && before_len <= 3 {
        return if sep == '.' {
            s.to_string() // treat as decimal
        } else {
            s.replace(',', ".")
        };
    }
    if after_len != 3 {
        // Not a 3-digit group → must be decimal.
        return if sep == '.' {
            s.to_string()
        } else {
            s.replace(',', ".")
        };
    }
    s.replace(sep, "")
}

/// Port of `_to_number`.
///
/// ```python
/// if not re.fullmatch(r"\d+(?:\.\d+)?", s):
///     raise Words2NumError("not a parseable number: %r" % s)
/// if "." in s:
///     return float(s)
/// return int(s)
/// ```
///
/// `\d` is Unicode `Nd`, and CPython's `int()`/`float()` map those digits to
/// ASCII before parsing — so [`fullmatch_number`] returns the transliterated
/// ASCII form and the parse runs on that. Testing `"." in s` on the original is
/// the same as testing the transliteration: the pattern only admits an ASCII
/// dot, and no `Nd` digit is one.
fn to_number(s: &str) -> Result<W2nValue> {
    let Some(ascii) = fullmatch_number(s) else {
        return Err(Words2NumError::new(format!(
            "not a parseable number: {}",
            py_repr(s)
        )));
    };
    if ascii.contains('.') {
        // Matches Python's float(): both are correctly rounded, and both
        // saturate to inf rather than erroring ("9"*400 + ".5" → inf).
        Ok(W2nValue::Float(
            ascii.parse::<f64>().expect("gated by fullmatch_number"),
        ))
    } else {
        // int() is arbitrary precision — BigInt, never a fixed-width cast.
        Ok(W2nValue::Int(
            ascii.parse::<BigInt>().expect("gated by fullmatch_number"),
        ))
    }
}

/// `re.fullmatch(r"\d+(?:\.\d+)?", s)`, returning the ASCII transliteration of
/// the match (or `None` for no match).
///
/// No backtracking is needed: `\d` and `.` are disjoint, so the tokenization
/// — maximal digit run, optional dot, maximal digit run, end — is
/// deterministic and the greedy scan below is equivalent to the regex.
/// (`"12."` fails both ways: the optional group needs `\d+` after the dot, and
/// backing `\d+` off cannot put a dot at the end.)
fn fullmatch_number(s: &str) -> Option<String> {
    let mut out = String::with_capacity(s.len());
    let mut it = s.chars().peekable();

    // \d+
    let mut n = 0usize;
    while let Some(d) = it.peek().copied().and_then(decimal_digit) {
        out.push((b'0' + d) as char);
        it.next();
        n += 1;
    }
    if n == 0 {
        return None;
    }

    // (?:\.\d+)?
    if let Some(&c) = it.peek() {
        if c != '.' {
            return None;
        }
        it.next();
        out.push('.');

        let mut m = 0usize;
        while let Some(d) = it.peek().copied().and_then(decimal_digit) {
            out.push((b'0' + d) as char);
            it.next();
            m += 1;
        }
        if m == 0 {
            return None;
        }
        if it.next().is_some() {
            return None; // trailing junk — fullmatch requires end-of-string
        }
    }

    Some(out)
}

/// Every Unicode general-category `Nd` codepoint, as 71 contiguous runs,
/// pinned to **Unicode 16.0.0** (see the module report on version sensitivity).
///
/// Generated from `python3.14` (the newest interpreter in the package's
/// supported 3.10–3.15 range) and verified: `re.fullmatch(r"\d", c)` matches
/// exactly `unicodedata.category(c) == "Nd"` (760 codepoints), every run's
/// length is a multiple of 10, and `unicodedata.decimal(c)` always equals
/// `(cp - run_start) % 10`.
const ND_RUNS: &[(u32, u32)] = &[
    (0x0030, 0x0039),
    (0x0660, 0x0669),
    (0x06F0, 0x06F9),
    (0x07C0, 0x07C9),
    (0x0966, 0x096F),
    (0x09E6, 0x09EF),
    (0x0A66, 0x0A6F),
    (0x0AE6, 0x0AEF),
    (0x0B66, 0x0B6F),
    (0x0BE6, 0x0BEF),
    (0x0C66, 0x0C6F),
    (0x0CE6, 0x0CEF),
    (0x0D66, 0x0D6F),
    (0x0DE6, 0x0DEF),
    (0x0E50, 0x0E59),
    (0x0ED0, 0x0ED9),
    (0x0F20, 0x0F29),
    (0x1040, 0x1049),
    (0x1090, 0x1099),
    (0x17E0, 0x17E9),
    (0x1810, 0x1819),
    (0x1946, 0x194F),
    (0x19D0, 0x19D9),
    (0x1A80, 0x1A89),
    (0x1A90, 0x1A99),
    (0x1B50, 0x1B59),
    (0x1BB0, 0x1BB9),
    (0x1C40, 0x1C49),
    (0x1C50, 0x1C59),
    (0xA620, 0xA629),
    (0xA8D0, 0xA8D9),
    (0xA900, 0xA909),
    (0xA9D0, 0xA9D9),
    (0xA9F0, 0xA9F9),
    (0xAA50, 0xAA59),
    (0xABF0, 0xABF9),
    (0xFF10, 0xFF19),
    (0x104A0, 0x104A9),
    (0x10D30, 0x10D39),
    (0x10D40, 0x10D49), // + Unicode 16 (Garay)
    (0x11066, 0x1106F),
    (0x110F0, 0x110F9),
    (0x11136, 0x1113F),
    (0x111D0, 0x111D9),
    (0x112F0, 0x112F9),
    (0x11450, 0x11459),
    (0x114D0, 0x114D9),
    (0x11650, 0x11659),
    (0x116C0, 0x116C9),
    (0x116D0, 0x116E3), // + Unicode 16 (Kirat Rai); 2 decades, 20 codepoints
    (0x11730, 0x11739),
    (0x118E0, 0x118E9),
    (0x11950, 0x11959),
    (0x11BF0, 0x11BF9), // + Unicode 16 (Sunuwar)
    (0x11C50, 0x11C59),
    (0x11D50, 0x11D59),
    (0x11DA0, 0x11DA9),
    (0x11F50, 0x11F59), // + Unicode 15.1 (Kawi)
    (0x16130, 0x16139), // + Unicode 16 (Gurung Khema)
    (0x16A60, 0x16A69),
    (0x16AC0, 0x16AC9), // + Unicode 15 (Tangsa)
    (0x16B50, 0x16B59),
    (0x16D70, 0x16D79), // + Unicode 16 (Ol Onal)
    (0x1CCF0, 0x1CCF9), // + Unicode 16 (Symbols for legacy computing)
    (0x1D7CE, 0x1D7FF),
    (0x1E140, 0x1E149),
    (0x1E2F0, 0x1E2F9),
    (0x1E4F0, 0x1E4F9), // + Unicode 15.1 (Nag Mundari)
    (0x1E5F1, 0x1E5FA), // + Unicode 16 (Ol Onal digits); start offset != 0
    (0x1E950, 0x1E959),
    (0x1FBF0, 0x1FBF9),
];

/// `\d` + `Py_UNICODE_TODECIMAL`: the digit value 0-9 of any `Nd` codepoint.
fn decimal_digit(c: char) -> Option<u8> {
    let cp = c as u32;
    if c.is_ascii_digit() {
        return Some((cp - 0x30) as u8);
    }
    let idx = ND_RUNS
        .binary_search_by(|&(lo, hi)| {
            if hi < cp {
                Ordering::Less
            } else if lo > cp {
                Ordering::Greater
            } else {
                Ordering::Equal
            }
        })
        .ok()?;
    Some(((cp - ND_RUNS[idx].0) % 10) as u8)
}

// ---------------------------------------------------------------------------
// repr()
// ---------------------------------------------------------------------------

/// Codepoints for which `str.isprintable()` is false, **excluding** category
/// `Cn` (unassigned). Pinned to **Unicode 16.0.0** (`python3.14`).
///
/// 28 runs covering `Cc`, `Cf`, `Cs`, `Co`, `Zl`, `Zp` and `Zs` (ASCII space
/// `U+0020` is printable and correctly falls between the first two runs). The
/// `Cs` run is fused with a `Co` block at `0xD800..=0xF8FF`; surrogates cannot
/// exist as a Rust `char`, so only the private-use tail of it is reachable.
///
/// `Cn` is omitted deliberately — it is ~680 further runs, it churns with every
/// Unicode release, and it only ever affects the text of an error message for
/// input containing *unassigned* codepoints. See the module report for the
/// resulting bound on repr fidelity.
const NONPRINTABLE_RUNS: &[(u32, u32)] = &[
    (0x0000, 0x001F),     // Cc
    (0x007F, 0x00A0),     // Cc + NBSP
    (0x00AD, 0x00AD),     // Cf
    (0x0600, 0x0605),     // Cf
    (0x061C, 0x061C),     // Cf
    (0x06DD, 0x06DD),     // Cf
    (0x070F, 0x070F),     // Cf
    (0x0890, 0x0891),     // Cf (+ Unicode 14)
    (0x08E2, 0x08E2),     // Cf
    (0x1680, 0x1680),     // Zs
    (0x180E, 0x180E),     // Cf
    (0x2000, 0x200F),     // Zs (incl. THIN SPACE) + Cf
    (0x2028, 0x202F),     // Zl + Zp + Cf + NNBSP
    (0x205F, 0x2064),     // Zs + Cf
    (0x2066, 0x206F),     // Cf
    (0x3000, 0x3000),     // Zs
    (0xD800, 0xF8FF),     // Cs + Co
    (0xFEFF, 0xFEFF),     // Cf
    (0xFFF9, 0xFFFB),     // Cf
    (0x110BD, 0x110BD),   // Cf
    (0x110CD, 0x110CD),   // Cf
    (0x13430, 0x1343F),   // Cf (extended in Unicode 15/16)
    (0x1BCA0, 0x1BCA3),   // Cf
    (0x1D173, 0x1D17A),   // Cf
    (0xE0001, 0xE0001),   // Cf
    (0xE0020, 0xE007F),   // Cf
    (0xF0000, 0xFFFFD),   // Co
    (0x100000, 0x10FFFD), // Co
];

/// `str.isprintable()`, modulo the `Cn` gap documented on [`NONPRINTABLE_RUNS`].
fn is_py_printable(c: char) -> bool {
    let cp = c as u32;
    NONPRINTABLE_RUNS
        .binary_search_by(|&(lo, hi)| {
            if hi < cp {
                Ordering::Less
            } else if lo > cp {
                Ordering::Greater
            } else {
                Ordering::Equal
            }
        })
        .is_err()
}

/// Python's `repr()` for a `str`, as used by `"… %r" % s`.
///
/// * Quote is `'` unless the string holds a `'` and no `"`, then `"`.
/// * `\\`, the active quote, `\n`, `\r`, `\t` get short escapes; every other
///   non-printable becomes `\xNN` (< 0x100), `\uNNNN` (< 0x10000) or
///   `\UNNNNNNNN`. Note `\v`, `\f`, `\a`, `\b` have **no** short form in
///   Python's repr — they come out as `\x0b`, `\x0c`, `\x07`, `\x08`.
fn py_repr(s: &str) -> String {
    let quote = if s.contains('\'') && !s.contains('"') {
        '"'
    } else {
        '\''
    };
    let mut out = String::with_capacity(s.len() + 2);
    out.push(quote);
    for c in s.chars() {
        match c {
            '\\' => out.push_str("\\\\"),
            '\n' => out.push_str("\\n"),
            '\r' => out.push_str("\\r"),
            '\t' => out.push_str("\\t"),
            c if c == quote => {
                out.push('\\');
                out.push(c);
            }
            c if is_py_printable(c) => out.push(c),
            c => {
                let cp = c as u32;
                if cp < 0x100 {
                    out.push_str(&format!("\\x{:02x}", cp));
                } else if cp < 0x10000 {
                    out.push_str(&format!("\\u{:04x}", cp));
                } else {
                    out.push_str(&format!("\\U{:08x}", cp));
                }
            }
        }
    }
    out.push(quote);
    out
}

// ---------------------------------------------------------------------------
// Tests — every expectation below was taken from the live Python module.
// ---------------------------------------------------------------------------

#[cfg(test)]
mod tests {
    use super::*;

    fn int(n: i64) -> W2nValue {
        W2nValue::Int(BigInt::from(n))
    }
    fn flt(f: f64) -> W2nValue {
        W2nValue::Float(f)
    }
    fn p(s: &str) -> Result<W2nValue> {
        parse_number_string(s, None, None, None)
    }
    fn pl(s: &str, lang: &str) -> Result<W2nValue> {
        parse_number_string(s, None, None, Some(lang))
    }
    fn err(s: &str) -> String {
        p(s).unwrap_err().0
    }

    // -- get_format ------------------------------------------------------

    #[test]
    fn get_format_exact_base_and_default() {
        assert_eq!(get_format("fr").thousands, " ");
        assert_eq!(get_format("fr").decimal, ",");
        assert_eq!(get_format("fr_CH").thousands, "'"); // Swiss French
        assert_eq!(get_format("fr_CH").decimal, ".");
        assert_eq!(get_format("en_XX").thousands, ","); // base fallback: en
        assert_eq!(get_format("zz"), get_format("_default"));
        assert_eq!(get_format(""), get_format("_default")); // == get_format(None)
        assert_eq!(get_format("de").thousands, ".");
        assert_eq!(get_format("vi").thousands, ".");
        assert_eq!(get_format("da").thousands, "."); // dot, unlike its neighbours
        assert_eq!(NUMBER_FORMAT_DEFAULTS.len(), 55);
    }

    #[test]
    fn locale_table_uses_ascii_space_only() {
        // The Python table has no NBSP/NNBSP/THIN SPACE anywhere.
        for (k, f) in NUMBER_FORMAT_DEFAULTS {
            for sep in [f.thousands, f.decimal] {
                assert!(sep.is_ascii(), "{k} has a non-ASCII separator");
            }
        }
    }

    // -- traced cases: auto-detect ---------------------------------------

    #[test]
    fn traced_auto_detect() {
        assert_eq!(p("1,234").unwrap(), flt(1.234)); // ambiguous → decimal
        assert_eq!(p("1.234").unwrap(), flt(1.234));
        assert_eq!(p("12,345").unwrap(), flt(12.345));
        assert_eq!(p("1234.567").unwrap(), int(1234567)); // lead > 3 → thousands
        assert_eq!(p(",123").unwrap(), int(123)); // empty lead → thousands
        assert_eq!(p("1,234.56").unwrap(), flt(1234.56)); // rightmost is decimal
        assert_eq!(p("1.234,56").unwrap(), flt(1234.56));
        assert_eq!(p("1 234 567").unwrap(), int(1234567));
        assert_eq!(p("1'234.5").unwrap(), flt(1234.5)); // apostrophe stripped
        assert_eq!(p("1_000").unwrap(), int(1000)); // underscore stripped
        assert_eq!(p("1,,234").unwrap(), int(1234)); // 3 parts → thousands
        assert_eq!(p("12,345.67").unwrap(), flt(12345.67));
        assert_eq!(p("1,234,567.89").unwrap(), flt(1234567.89));
    }

    /// The three space-like separators must stay distinct codepoints and all
    /// three must be stripped by auto-detection.
    #[test]
    fn traced_space_like_separators_are_distinct() {
        assert_ne!(NBSP, NNBSP);
        assert_ne!(NNBSP, THIN_SPACE);
        assert_eq!(NBSP as u32, 0xA0);
        assert_eq!(NNBSP as u32, 0x202F);
        assert_eq!(THIN_SPACE as u32, 0x2009);
        assert_eq!(SPACE_LIKE.chars().count(), 5);

        assert_eq!(p("1\u{202f}234,5").unwrap(), flt(1234.5)); // NNBSP
        assert_eq!(p("1\u{a0}234,5").unwrap(), flt(1234.5)); // NBSP
        assert_eq!(p("1\u{2009}234,5").unwrap(), flt(1234.5)); // THIN SPACE
    }

    // -- traced cases: sign / strip --------------------------------------

    #[test]
    fn traced_sign_and_strip() {
        assert_eq!(p("+42").unwrap(), int(42));
        assert_eq!(p("  42  ").unwrap(), int(42));
        assert_eq!(p("- 42").unwrap(), int(-42)); // lstrip after the sign
        assert_eq!(p("-1 234,5").unwrap(), flt(-1234.5));
        assert_eq!(p("-0").unwrap(), int(0)); // ints have no -0
        assert_eq!(p("\u{a0}\u{a0}42\u{a0}").unwrap(), int(42));
        assert_eq!(p("\u{1c}42").unwrap(), int(42)); // \s covers U+001C
        // -0.0 keeps its sign bit, exactly like Python's -1 * 0.0
        match p("-0.0").unwrap() {
            W2nValue::Float(f) => assert!(f == 0.0 && f.is_sign_negative()),
            v => panic!("expected float, got {v:?}"),
        }
        // Only ONE sign char is consumed.
        assert_eq!(err("+-42"), "not a parseable number: '-42'");
    }

    // -- traced cases: lang defaults + fallback ---------------------------

    #[test]
    fn traced_lang_path() {
        assert_eq!(pl("1.234", "de").unwrap(), int(1234)); // dot = thousands
        assert_eq!(pl("1.234", "en").unwrap(), flt(1.234)); // dot = decimal
        assert_eq!(pl("1 234,5", "fr").unwrap(), flt(1234.5));
        assert_eq!(pl("1,234.5", "en").unwrap(), flt(1234.5));
        assert_eq!(pl("1.234,5", "de").unwrap(), flt(1234.5));
        assert_eq!(pl("1.234.567", "de").unwrap(), int(1234567));
        assert_eq!(pl("12.345,67", "de").unwrap(), flt(12345.67));
        assert_eq!(pl("1.234.567,89", "de").unwrap(), flt(1234567.89));
        assert_eq!(pl("1 234,56", "fr").unwrap(), flt(1234.56));
        // Unknown lang → _default {",", "."}: the comma is stripped as thousands.
        assert_eq!(pl("1,5", "zz").unwrap(), int(15));
        // fr drops every dot then maps "," → ".": "1.2.3" collapses to 123.
        assert_eq!(pl("1.2.3", "fr").unwrap(), int(123));
    }

    /// The lang branch swallows Words2NumError and falls through to
    /// auto-detection, which strips the apostrophe the fr format left behind.
    #[test]
    fn traced_lang_failure_falls_through_to_auto_detect() {
        assert_eq!(pl("1'234", "fr").unwrap(), int(1234));
        // Both paths fail → the auto-detect error surfaces.
        assert_eq!(
            pl("1-2", "en").unwrap_err().0,
            "not a parseable number: '1-2'"
        );
    }

    // -- traced cases: explicit separators --------------------------------

    #[test]
    fn traced_explicit_separators() {
        let ps = |s, t, d| parse_number_string(s, t, d, None);
        assert_eq!(ps("1,234", Some(","), None).unwrap(), int(1234));
        assert_eq!(ps("1,234", None, Some(",")).unwrap(), flt(1.234));
        assert_eq!(ps("1x234y5", Some("x"), Some("y")).unwrap(), flt(1234.5));
        assert_eq!(ps("1.234", None, Some(".")).unwrap(), flt(1.234));
        assert_eq!(ps("12'345.67", Some("'"), Some(".")).unwrap(), flt(12345.67));
        assert_eq!(ps("1_234.56", Some("_"), None).unwrap(), flt(1234.56));
        // Some("") is Python's "" — falsy, so no rewrite happens at all.
        assert_eq!(ps("1.234", Some(""), None).unwrap(), flt(1.234));
        assert_eq!(ps("1.234", Some(""), Some("")).unwrap(), flt(1.234));
        // A configured space-like strips ALL space-likes...
        assert_eq!(ps("1 234", Some(" "), None).unwrap(), int(1234));
        assert_eq!(ps("1\u{a0}234", Some(" "), None).unwrap(), int(1234));
        assert_eq!(ps("1\u{202f}234", Some("\u{202f}"), None).unwrap(), int(1234));
        assert_eq!(ps("1\u{2009}234", Some("\u{2009}"), None).unwrap(), int(1234));
        // ...but "\t" is NOT in (" ", NBSP, NNBSP, THIN_SPACE), so it only
        // does a literal replace and the NBSP survives into the error.
        assert_eq!(
            ps("1\u{a0}234", Some("\t"), None).unwrap_err().0,
            "not a parseable number: '1\\xa0234'"
        );
        assert_eq!(
            ps("1,234", Some("x"), Some("y")).unwrap_err().0,
            "not a parseable number: '1,234'"
        );
    }

    // -- traced cases: _to_number -----------------------------------------

    #[test]
    fn traced_to_number_bigint_and_float() {
        assert_eq!(p("0.1").unwrap(), flt(0.1));
        assert_eq!(p("1.0000000000000000001").unwrap(), flt(1.0)); // rounds
        assert_eq!(
            p(&"9".repeat(100)).unwrap(),
            W2nValue::Int("9".repeat(100).parse::<BigInt>().unwrap())
        );
        // float() saturates rather than raising.
        match p(&format!("{}.5", "9".repeat(400))).unwrap() {
            W2nValue::Float(f) => assert!(f.is_infinite() && f.is_sign_positive()),
            v => panic!("expected inf, got {v:?}"),
        }
    }

    /// Python's `\d` is Unicode Nd, and int()/float() accept it — mixed scripts
    /// included.
    #[test]
    fn traced_unicode_digits() {
        assert_eq!(p("\u{0662}\u{0663}").unwrap(), int(23)); // ٢٣ Arabic-Indic
        assert_eq!(p("\u{0661}2").unwrap(), int(12)); // ١2 mixed scripts
        assert_eq!(p("1\u{0662}3").unwrap(), int(123)); // 1٢3
        assert_eq!(p("\u{FF11}\u{FF12}\u{FF13}").unwrap(), int(123)); // １２３
        assert_eq!(p("\u{0967}\u{0968}\u{0969}").unwrap(), int(123)); // १२३ Devanagari
        assert_eq!(p("\u{0662}\u{0663}.\u{0665}").unwrap(), flt(23.5)); // ٢٣.٥

        assert_eq!(decimal_digit('7'), Some(7));
        assert_eq!(decimal_digit('\u{0669}'), Some(9)); // ٩
        assert_eq!(decimal_digit('\u{1FBF4}'), Some(4)); // last run
        assert_eq!(decimal_digit('\u{1D7CE}'), Some(0)); // 4-decade run
        assert_eq!(decimal_digit('\u{1D7FF}'), Some(9)); // ...its 4th decade
        assert_eq!(decimal_digit('x'), None);
        assert_eq!(decimal_digit('\u{065F}'), None); // just below the ٠ run
        assert_eq!(decimal_digit('\u{066A}'), None); // just above it
    }

    #[test]
    fn fullmatch_matches_the_regex() {
        assert_eq!(fullmatch_number("123").as_deref(), Some("123"));
        assert_eq!(fullmatch_number("1.23").as_deref(), Some("1.23"));
        assert_eq!(fullmatch_number("12."), None); // needs \d+ after the dot
        assert_eq!(fullmatch_number(".5"), None); // needs \d+ before it
        assert_eq!(fullmatch_number("1.2.3"), None);
        assert_eq!(fullmatch_number(""), None);
        assert_eq!(fullmatch_number("12a"), None);
        assert_eq!(fullmatch_number("1 2"), None);
    }

    // -- traced cases: errors ---------------------------------------------

    #[test]
    fn traced_errors() {
        assert_eq!(err(""), "empty numeric string");
        assert_eq!(err("   "), "empty numeric string");
        assert_eq!(err("-"), "empty numeric string after sign");
        assert_eq!(err("+ "), "empty numeric string after sign");
        assert_eq!(err("abc"), "not a parseable number: 'abc'");
        assert_eq!(err("not a number"), "not a parseable number: 'notanumber'");
        assert_eq!(err("12a"), "not a parseable number: '12a'");
    }

    #[test]
    fn py_repr_matches_cpython() {
        assert_eq!(py_repr("1 234"), "'1 234'");
        assert_eq!(py_repr("1\u{a0}234"), "'1\\xa0234'");
        assert_eq!(py_repr("ab'c"), "\"ab'c\"");
        assert_eq!(py_repr("ab\"c"), "'ab\"c'");
        assert_eq!(py_repr("a'b\"c"), "'a\\'b\"c'");
        assert_eq!(py_repr("x\ty"), "'x\\ty'");
        assert_eq!(py_repr("x\ny"), "'x\\ny'");
        assert_eq!(py_repr("x\ry"), "'x\\ry'");
        assert_eq!(py_repr("a\\b"), "'a\\\\b'");
        assert_eq!(py_repr("\u{7f}"), "'\\x7f'");
        assert_eq!(py_repr("\u{b}"), "'\\x0b'"); // no \v short form
        assert_eq!(py_repr("\u{c}"), "'\\x0c'"); // no \f short form
        assert_eq!(py_repr("\u{202f}"), "'\\u202f'");
        assert_eq!(py_repr("\u{2009}"), "'\\u2009'");
        assert_eq!(py_repr("\u{1c}"), "'\\x1c'");
        assert_eq!(py_repr("\u{ad}"), "'\\xad'"); // soft hyphen, Cf
        assert_eq!(py_repr("\u{e0001}"), "'\\U000e0001'");
        assert_eq!(py_repr("\u{f0000}"), "'\\U000f0000'");
        assert_eq!(py_repr("\u{1F600}"), "'\u{1F600}'"); // printable, raw
        assert_eq!(py_repr("é"), "'é'");
        assert_eq!(py_repr("\u{301}"), "'\u{301}'"); // combining Mn, printable
        assert_eq!(py_repr(""), "''");
        assert_eq!(py_repr(" "), "' '"); // ASCII space is printable
    }

    #[test]
    fn is_py_space_is_pythons_29_not_rusts_25() {
        let n = (0u32..0x110000)
            .filter_map(char::from_u32)
            .filter(|&c| is_py_space(c))
            .count();
        assert_eq!(n, 29);
        // The four Rust's char::is_whitespace() disagrees about.
        for c in ['\u{1c}', '\u{1d}', '\u{1e}', '\u{1f}'] {
            assert!(is_py_space(c) && !c.is_whitespace());
        }
    }

    #[test]
    fn nd_runs_are_well_formed() {
        let mut total = 0;
        let mut prev_hi = 0u32;
        for (i, &(lo, hi)) in ND_RUNS.iter().enumerate() {
            assert!(lo <= hi);
            assert!(i == 0 || lo > prev_hi, "runs must be sorted and disjoint");
            assert_eq!((hi - lo + 1) % 10, 0, "every run is whole decades");
            prev_hi = hi;
            total += hi - lo + 1;
        }
        assert_eq!(total, 760); // Unicode 16.0.0
    }
}