num2words2-core 0.1.0

//! Port of `lang_TA.py` (Tamil).
//!
//! Shape: **self-contained**. `Num2Word_TA` subclasses `Num2Word_Base` but
//! defines no `high_numwords`/`mid_numwords`/`low_numwords`, so Python's
//! `Num2Word_Base.__init__` skips the `self.cards = OrderedDict()` branch
//! entirely and never sets `MAXVAL`. All four in-scope methods
//! (`to_cardinal`, `to_ordinal`, `to_ordinal_num`, `to_year`) are overridden
//! outright, so `cards`/`maxval`/`merge` stay at their trait defaults here and
//! **nothing overflows** — every integer, however large, renders.
//!
//! The algorithm is the Indian numbering system: crore (10^7), lakh (10^5),
//! thousand, then a special hundreds table and a teens table, joined with
//! single spaces by `" ".join(parts)`.
//!
//! Nothing is inherited from `Num2Word_Base` that matters: TA overrides every
//! in-scope entry point, and `title()` is never reached (TA's `to_cardinal`
//! does not call it), so `is_title` stays irrelevant.
//!
//! # Faithfully reproduced Python quirks
//!
//! This is a port, not a rewrite. All of the following look wrong but are
//! exactly what Python emits, verified against the frozen corpus:
//!
//! 1. **`to_ordinal` glues its suffix on with no separator.** For any `n` not
//!    in the `ordinals` table (i.e. outside 1..=10), `_int_to_ordinal` returns
//!    `self._int_to_cardinal(n) + "ஆவது"` — no space. So `to_ordinal(11)` is
//!    "பதினொன்றுஆவது" and `to_ordinal(1000)` is "ஆயிரம்ஆவது". Preserved.
//! 2. **`to_ordinal` accepts negatives and produces nonsense**, because it
//!    only special-cases `n == 0` and the 1..=10 table before falling through
//!    to the cardinal path: `to_ordinal(-42)` == "கழித்தல் நாற்பது இரண்டுஆவது"
//!    ("minus forty two-th"). Preserved.
//! 3. **The thousands scale word takes no "ஒரு"**, unlike lakh and crore:
//!    1000 renders as bare "ஆயிரம்" while 100000 is "ஒரு இலட்சம்" and 10000000
//!    is "ஒரு கோடி". Asymmetric in Python; preserved.
//! 4. **Crore stacks on itself past 10^14** rather than promoting to a larger
//!    scale word, because `_int_to_word` recurses on the crore quotient:
//!    10^15 == "பத்து கோடி கோடி", 10^21 == "ஒரு கோடி கோடி கோடி". Preserved.
//! 5. **`self.scale` is dead.** The Python `__init__` builds
//!    `{1000: "ஆயிரம்", 100000: "இலட்சம்", 10000000: "கோடி",
//!    1000000000000: "டிரில்லியன்"}` and never reads it — the scale words are
//!    hardcoded as string literals inside `_int_to_word`. In particular
//!    "டிரில்லியன்" (trillion) is **unreachable**: 10^12 renders via the crore
//!    path as "ஒரு இலட்சம் கோடி". Not ported (it has no observable effect).
//! 6. **`_setup` is a latent `AttributeError`.** TA defines
//!    `def _setup(self): super()._setup()`, but `Num2Word_Base` has no
//!    `_setup` (it has `setup`, which base's `__init__` calls). Calling
//!    `_setup()` would raise; nothing ever does. Not ported.
//! 7. **The `else` arm of the hundreds branch is dead code.** Python's
//!    `self.ones[n // 100] + " நூறு"` fallback can never fire: by the time
//!    control reaches it, `n < 1000` always holds (every larger scale has
//!    already been stripped with `n %= ...`), so `(n // 100) * 100` is always
//!    one of the nine keys in `hundreds_special`. Reproduced anyway in
//!    [`int_to_word`] for structural fidelity — see the comment there.
//!
//! # Currency
//!
//! TA overrides `to_currency` **outright** and shares almost nothing with
//! `Num2Word_Base.to_currency`. It inherits `to_cheque` unchanged.
//!
//! `CURRENCY_FORMS` is declared in TA's own class body, so — unlike the 16
//! classes that read `Num2Word_EUR.CURRENCY_FORMS` — it is untouched by the
//! `Num2Word_EN.__init__` mutation that rewrites EUR/GBP and injects ~24 extra
//! ISO codes into that shared dict. Confirmed against the live interpreter:
//! `Num2Word_TA.CURRENCY_FORMS is Num2Word_EN.CURRENCY_FORMS` is `False`. The
//! seven codes in [`build_currency_forms`] are the whole table, which is why
//! JPY/KWD/BHD/CNY/CHF legitimately raise NotImplementedError.
//!
//! `CURRENCY_PRECISION` and `CURRENCY_ADJECTIVES` are both `{}`, so the trait
//! defaults (100, `None`) already match and are not overridden.
//!
//! ## Faithfully reproduced Python quirks (currency)
//!
//! 8. **The signature is `to_currency(n, currency="INR")`** — there is no
//!    `cents`, `separator` or `adjective` parameter at all, so all three are
//!    ignored here. (Passing any of them to the Python converter is a
//!    `TypeError`; see the crate-level note in the port report — 19 of 172
//!    converters have such a reduced signature and the dispatcher forwards the
//!    kwargs regardless.)
//! 9. **There is no `has_decimal` guard.** The cents segment is gated on
//!    `right > 0` alone, so a whole float prints no subunit: `1.0` is
//!    "ஒன்று யூரோ" where Base would print a zero-cents segment. `Decimal("5.00")`
//!    likewise renders "ஐந்து ரூபாய்". `has_decimal` is therefore ignored.
//! 10. **`pluralize` is never called.** TA takes `cr_major[0]` / `cr_minor[0]`
//!     directly, which is why it never trips Base's abstract `pluralize`. Both
//!     forms of every entry are identical anyway — Tamil does not inflect these
//!     nouns for number — but the arity of 2 is kept as the ported data.
//! 11. **`CURRENCY_PRECISION` is never consulted by `to_currency`.** The
//!     divisor is hardcoded 100 in the `has_fractional_cents` test, and
//!     `parse_currency_parts` is called with no `divisor=` argument so it takes
//!     currency.py's default of 100. TA thus has no 3-decimal or 0-decimal
//!     path whatsoever. Moot in practice, since its `CURRENCY_PRECISION` is
//!     empty and every code resolves to 100 regardless.
//! 12. **`keep_precision` skips the ROUND_HALF_UP quantize**, so a value with
//!     fractional cents *truncates* rather than rounds: `2.675` is
//!     "இரண்டு ரூபாய் அறுபது ஏழு பைசா" (67 paise, not 68).
//! 13. **Past 10^26 TA stops speaking Tamil** and hands back the bare number —
//!     see [`LangTa::to_currency`] for the derivation. Reproduced for the int
//!     path only; the float path cannot be reproduced from this file.
//!
//! # Error behaviour
//!
//! For **integer** input none of the four in-scope methods can raise: there is
//! no overflow check, no table lookup that can miss, and no `int()` parse.
//! Every method returns `Ok`. The `try/except BaseException` wrappers around
//! Python's `to_cardinal`/`to_ordinal`/`to_ordinal_num` are a float-truncation
//! fallback (e.g. `to_cardinal(12.34)` raises `KeyError` on `teens[12.34]`,
//! is caught, and retries as `int(12.34)` → "பன்னிரண்டு"); floats are out of
//! scope, so on the integer path those handlers are unreachable. `to_year` has
//! no such wrapper at all.
//!
//! # State
//!
//! None. Every method is a pure function of its argument — no flag is set in
//! one call and consumed by another.

use crate::base::{Lang, N2WError, Result};
use crate::currency::{parse_currency_parts, CurrencyForms, CurrencyValue};
use crate::floatpath::FloatValue;
use bigdecimal::BigDecimal;
use num_bigint::BigInt;
use num_integer::Integer;
use num_traits::{FromPrimitive, One, Signed, ToPrimitive, Zero};
use std::collections::HashMap;

/// "பூஜ்ஜியம்" — the zero word, returned by both the cardinal and ordinal paths.
const ZERO: &str = "பூஜ்ஜியம்";

/// `self.negword`. Note the **trailing space**: Python concatenates it
/// directly (`self.negword + self._int_to_word(-n)`) rather than joining, so
/// the space is load-bearing. Do not trim it.
const NEGWORD: &str = "கழித்தல் ";

/// Suffix appended by `_int_to_ordinal` — **without** a separating space.
const ORDINAL_SUFFIX: &str = "ஆவது";

/// Suffix appended by `to_ordinal_num`, a different word from [`ORDINAL_SUFFIX`].
const ORDINAL_NUM_SUFFIX: &str = "-வது";

/// The year path's thousand word, distinct from the cardinal "ஆயிரம்".
const YEAR_THOUSAND: &str = "ஆயிரத்து";

/// `self.ones`; index 0 is the empty string and is never emitted (guarded by
/// `if n > 0`).
const ONES: [&str; 10] = [
    "",
    "ஒன்று",
    "இரண்டு",
    "மூன்று",
    "நான்கு",
    "ஐந்து",
    "ஆறு",
    "ஏழு",
    "எட்டு",
    "ஒன்பது",
];

/// `self.tens`; index 0 is the empty string and is never emitted (guarded by
/// `if n >= 10`, which makes `n // 10 >= 1`).
const TENS: [&str; 10] = [
    "",
    "பத்து",
    "இருபது",
    "முப்பது",
    "நாற்பது",
    "ஐம்பது",
    "அறுபது",
    "எழுபது",
    "எண்பது",
    "தொண்ணூறு",
];

/// `self.teens`, a dict keyed 11..=19 in Python. Indexed here by `n - 11`.
const TEENS: [&str; 9] = [
    "பதினொன்று",
    "பன்னிரண்டு",
    "பதின்மூன்று",
    "பதினான்கு",
    "பதினைந்து",
    "பதினாறு",
    "பதினேழு",
    "பதினெட்டு",
    "பத்தொன்பது",
];

/// `self.hundreds_special`, a dict keyed 100..=900 in Python. Indexed here by
/// `n // 100 - 1`. Note 900 is "தொள்ளாயிரம்", which is morphologically a
/// *thousand* word, not a hundred word — that is what Python ships.
const HUNDREDS_SPECIAL: [&str; 9] = [
    "நூறு",
    "இருநூறு",
    "முன்னூறு",
    "நானூறு",
    "ஐநூறு",
    "அறுநூறு",
    "எழுநூறு",
    "எண்ணூறு",
    "தொள்ளாயிரம்",
];

/// `self.ordinals`, a dict keyed 1..=10 in Python. Indexed here by `n - 1`.
/// Every other value falls through to the cardinal + "ஆவது" path.
const ORDINALS: [&str; 10] = [
    "முதல்",
    "இரண்டாம்",
    "மூன்றாம்",
    "நான்காம்",
    "ஐந்தாம்",
    "ஆறாம்",
    "ஏழாம்",
    "எட்டாம்",
    "ஒன்பதாம்",
    "பத்தாம்",
];

fn crore() -> BigInt {
    BigInt::from(10_000_000u32)
}
fn lakh() -> BigInt {
    BigInt::from(100_000u32)
}
fn thousand() -> BigInt {
    BigInt::from(1_000u32)
}
fn hundred() -> BigInt {
    BigInt::from(100u32)
}

/// Python's `_int_to_word`. Expects a **non-negative** `n`: the sign is peeled
/// off by [`int_to_cardinal`] before this is ever called, and every recursive
/// call passes a positive quotient.
fn int_to_word(n: &BigInt) -> String {
    if n.is_zero() {
        return ZERO.to_string();
    }

    let mut n = n.clone();
    let mut parts: Vec<String> = Vec::new();

    // Crores (10^7). Recurses on the quotient, which is why crore stacks on
    // itself for very large values (10^15 -> "பத்து கோடி கோடி").
    let c = crore();
    if n >= c {
        let crores = n.div_floor(&c);
        if crores.is_one() {
            parts.push("ஒரு கோடி".to_string());
        } else {
            parts.push(format!("{} கோடி", int_to_word(&crores)));
        }
        n = n.mod_floor(&c);
    }

    // Lakhs (10^5).
    let l = lakh();
    if n >= l {
        let lakhs = n.div_floor(&l);
        if lakhs.is_one() {
            parts.push("ஒரு இலட்சம்".to_string());
        } else {
            parts.push(format!("{} இலட்சம்", int_to_word(&lakhs)));
        }
        n = n.mod_floor(&l);
    }

    // Thousands. Unlike lakh/crore above, the `== 1` case emits a bare
    // "ஆயிரம்" with no "ஒரு" — asymmetric in Python, preserved here.
    let t = thousand();
    if n >= t {
        let thousands = n.div_floor(&t);
        if thousands.is_one() {
            parts.push("ஆயிரம்".to_string());
        } else {
            parts.push(format!("{} ஆயிரம்", int_to_word(&thousands)));
        }
        n = n.mod_floor(&t);
    }

    // Hundreds. `n < 1000` is guaranteed here (every larger scale was stripped
    // above), so `h` is always 1..=9 and the `hundreds_special` lookup always
    // hits. Python's `else: self.ones[n // 100] + " நூறு"` fallback is
    // therefore dead code; it is kept below to mirror the structure, and the
    // `h_idx >= 9` guard is the exact condition under which Python would have
    // taken it.
    let h = hundred();
    if n >= h {
        let hundreds = n.div_floor(&h);
        // Safe: `hundreds` is 1..=9 by the argument above.
        let h_idx = hundreds.to_usize().unwrap_or(usize::MAX);
        if (1..=9).contains(&h_idx) {
            parts.push(HUNDREDS_SPECIAL[h_idx - 1].to_string());
        } else {
            // Unreachable. Python: self.ones[n // 100] + " நூறு".
            parts.push(format!("{} நூறு", ONES[h_idx % 10]));
        }
        n = n.mod_floor(&h);
    }

    // `n < 100` is guaranteed here, so the cast is total.
    let mut small = n.to_u32().unwrap_or(0);

    if 10 < small && small < 20 {
        parts.push(TEENS[(small - 11) as usize].to_string());
    } else {
        if small >= 10 {
            let tens_val = small / 10;
            parts.push(TENS[tens_val as usize].to_string());
            small %= 10;
        }
        if small > 0 {
            parts.push(ONES[small as usize].to_string());
        }
    }

    parts.join(" ")
}

/// Python's `_int_to_cardinal`.
fn int_to_cardinal(n: &BigInt) -> String {
    if n.is_zero() {
        return ZERO.to_string();
    }
    if n.sign() == num_bigint::Sign::Minus {
        // NEGWORD carries its own trailing space — plain concatenation.
        return format!("{}{}", NEGWORD, int_to_word(&(-n)));
    }
    int_to_word(n)
}

/// Python's `_int_to_ordinal`.
fn int_to_ordinal(n: &BigInt) -> String {
    if n.is_zero() {
        return ZERO.to_string();
    }
    // `n in self.ordinals` — keys 1..=10 only, so negatives never match.
    if let Some(i) = n.to_usize() {
        if (1..=10).contains(&i) {
            return ORDINALS[i - 1].to_string();
        }
    }
    // Note: no separator before the suffix. This is Python's behaviour.
    format!("{}{}", int_to_cardinal(n), ORDINAL_SUFFIX)
}

/// Python's `self.to_cardinal(float(right))`, the fractional-cents branch.
///
/// TA's `to_cardinal` is
/// `try: self._int_to_cardinal(n) except BaseException: self._int_to_cardinal(int(n))`,
/// and handing it a float always lands on one of two outcomes, both equal to
/// `_int_to_cardinal(int(n))`:
///
/// * the float has a fractional part, so `_int_to_word` reaches
///   `self.tens[n // 10]` or `self.ones[n]` (TypeError: list indices must be
///   integers) or `self.teens[n]` (KeyError), and the handler retries with
///   `int(n)`. The fraction always survives to one of those lookups, because
///   every scale is stripped with `n %= ...`, which preserves it; or
/// * the float is whole and the lookup happens to succeed — `self.teens[15.0]`
///   and `self.hundreds_special[100.0]` both hit, since `15.0 == 15` and
///   `hash(15.0) == hash(15)` — in which case it returns exactly the string
///   the int would have produced.
///
/// So this collapses to a truncation. The `float()` round-trip is kept because
/// it is observable: `int(Decimal("2.9999999999999999999"))` is 2, but
/// `int(float(Decimal("2.9999999999999999999")))` is 3, and Python takes the
/// latter. Likewise `1.999999999999999999999` yields 99.9999999999999999999
/// paise, which `float()` rounds to exactly `100.0` -> "நூறு".
///
/// `right` is `fraction * 100` with `fraction` in `[0, 1)`, so the value is in
/// `[0, 100)` and the `as i64` cast cannot overflow.
fn cardinal_from_fractional_cents(right: &BigDecimal) -> String {
    // `to_f64` formats the coefficient and defers to Rust's float parser, so
    // it is correctly rounded exactly as Python's `float(Decimal)` is.
    let truncated = right.to_f64().map(f64::trunc).unwrap_or(0.0);
    int_to_cardinal(&BigInt::from(truncated as i64))
}

/// `Num2Word_TA.CURRENCY_FORMS`, verbatim from TA's own class body.
///
/// Each entry carries two identical forms because Tamil does not inflect these
/// nouns for number. The arity of 2 mirrors the Python tuples and is kept even
/// though TA only ever reads index 0 (`cr_major[0]` / `cr_minor[0]`) and
/// `to_cheque` only ever reads index -1.
fn build_currency_forms() -> HashMap<&'static str, CurrencyForms> {
    const RUPEE: [&str; 2] = ["ரூபாய்", "ரூபாய்"];
    const DOLLAR: [&str; 2] = ["டாலர்", "டாலர்"];
    const CENT: [&str; 2] = ["சென்ட்", "சென்ட்"];

    let mut m: HashMap<&'static str, CurrencyForms> = HashMap::new();
    m.insert("INR", CurrencyForms::new(&RUPEE, &["பைசா", "பைசா"]));
    m.insert("LKR", CurrencyForms::new(&RUPEE, &["சதம்", "சதம்"]));
    m.insert("USD", CurrencyForms::new(&DOLLAR, &CENT));
    m.insert("EUR", CurrencyForms::new(&["யூரோ", "யூரோ"], &CENT));
    m.insert(
        "GBP",
        CurrencyForms::new(&["பவுண்ட்", "பவுண்ட்"], &["பென்னி", "பென்னி"]),
    );
    m.insert("SGD", CurrencyForms::new(&DOLLAR, &CENT));
    m.insert(
        "MYR",
        CurrencyForms::new(&["ரிங்கிட்", "ரிங்கிட்"], &["சென்", "சென்"]),
    );
    m
}

pub struct LangTa {
    currency_forms: HashMap<&'static str, CurrencyForms>,
    /// `10**26`. See [`LangTa::to_currency`] — the magnitude at which Python's
    /// `(Decimal(str(n)) * 100) % 1` overflows the decimal context and TA's
    /// blanket `except BaseException` takes over.
    decimal_ctx_limit: BigInt,
}

impl LangTa {
    pub fn new() -> Self {
        LangTa {
            // Built once here, never per call.
            currency_forms: build_currency_forms(),
            decimal_ctx_limit: BigInt::from(10u8).pow(26),
        }
    }
}

impl Default for LangTa {
    fn default() -> Self {
        Self::new()
    }
}

impl Lang for LangTa {
    /// This language's own `to_currency(currency=...)` default,
    /// read from the live Python signature. Only 44 of 156 use EUR.
    fn default_currency(&self) -> &str {
        "INR"
    }

    fn negword(&self) -> &str {
        NEGWORD
    }

    fn pointword(&self) -> &str {
        "புள்ளி"
    }

    fn to_cardinal(&self, value: &BigInt) -> Result<String> {
        Ok(int_to_cardinal(value))
    }

    /// TA's float/Decimal cardinal path — **pure truncation toward zero**.
    ///
    /// TA overrides `to_cardinal` (not `to_cardinal_float`), and its whole body
    /// is:
    ///
    /// ```python
    /// def to_cardinal(self, n):
    ///     try:
    ///         if isinstance(n, str): n = int(n)
    ///         return self._int_to_cardinal(n)
    ///     except BaseException:
    ///         return self._int_to_cardinal(int(n))
    /// ```
    ///
    /// Handed a **non-integer** `float`/`Decimal`, `_int_to_word` strips every
    /// scale with `n %= ...` (which preserves the fraction) and then always
    /// reaches a `self.tens[...]`/`self.ones[...]` list index or a
    /// `self.teens[...]` dict key with a non-integer value, raising TypeError or
    /// KeyError. The blanket `except BaseException` retries with `int(n)`, which
    /// truncates toward zero. A **whole** float/Decimal either raises the same
    /// way (`self.ones[1.0]` is still a TypeError) or succeeds and returns the
    /// identical string, because the lookups that can succeed are int-equal
    /// (`15.0 == 15`, `hash(15.0) == hash(15)`, `hundreds_special[100.0]` hits).
    /// So the method collapses in every case to `_int_to_cardinal(int(n))`.
    ///
    /// Consequences, all corpus-verified:
    /// * the fraction is dropped entirely — `pointword` ("புள்ளி") is never
    ///   emitted (`12.34` -> "பன்னிரண்டு", `99.99` -> "தொண்ணூறு ஒன்பது");
    /// * a value that truncates to 0 loses its sign, because `int(-0.5) == 0`
    ///   and `_int_to_cardinal(0)` prepends no negword (`-0.5` -> "பூஜ்ஜியம்",
    ///   whereas `-1.5` -> "கழித்தல் ஒன்று").
    ///
    /// The `Float`/`Decimal` split is load-bearing: the cardinal path applies
    /// `int()` directly to the value (no `float()` round-trip — unlike the
    /// currency fractional-cents branch), so a Decimal like
    /// `98746251323029.99` truncates exactly to `98746251323029`. Routing that
    /// through f64 first could truncate to a different integer.
    ///
    /// `precision_override` is ignored: TA's `to_cardinal` accepts no
    /// `precision` argument, and a truncation cannot depend on one.
    fn to_cardinal_float(
        &self,
        value: &FloatValue,
        _precision_override: Option<u32>,
    ) -> Result<String> {
        let truncated = match value {
            // int(float): `.trunc()` does the toward-zero part; from_f64 of an
            // already-integral f64 is exact at any magnitude (and reproduces
            // the f64 artefacts, since the raw double crossed the boundary).
            // trunc(-0.5) == -0.0 -> BigInt 0, so the sign is dropped, matching
            // Python's int(-0.5) == 0.
            FloatValue::Float { value, .. } => {
                BigInt::from_f64(value.trunc()).unwrap_or_else(BigInt::zero)
            }
            // int(Decimal): with_scale(0) truncates toward zero, exactly as
            // Decimal.__int__ does — no float round-trip on this path.
            FloatValue::Decimal { value, .. } => value.with_scale(0).as_bigint_and_exponent().0,
        };
        Ok(int_to_cardinal(&truncated))
    }

    fn to_ordinal(&self, value: &BigInt) -> Result<String> {
        Ok(int_to_ordinal(value))
    }

    fn to_ordinal_num(&self, value: &BigInt) -> Result<String> {
        // Python: str(n) + "-வது". No ordinals table, no sign handling —
        // to_ordinal_num(-1) == "-1-வது".
        Ok(format!("{}{}", value, ORDINAL_NUM_SUFFIX))
    }

    fn to_year(&self, value: &BigInt) -> Result<String> {
        let t = thousand();

        // n < 1000: plain cardinal. This arm also swallows every negative
        // year, so `to_year(-500)` == "கழித்தல் ஐநூறு".
        if value < &t {
            return Ok(int_to_cardinal(value));
        }

        let remainder = value.mod_floor(&t);

        if value < &BigInt::from(2000u32) {
            // Python computes `thousands` here and never uses it: the word is
            // the bare literal "ஆயிரத்து".
            let mut result = YEAR_THOUSAND.to_string();
            if is_positive(&remainder) {
                result.push(' ');
                result.push_str(&int_to_cardinal(&remainder));
            }
            return Ok(result);
        }

        let thousands = value.div_floor(&t);
        let mut result = format!("{} {}", int_to_cardinal(&thousands), YEAR_THOUSAND);
        if is_positive(&remainder) {
            result.push(' ');
            result.push_str(&int_to_cardinal(&remainder));
        }
        Ok(result)
    }

    /// `to_ordinal(float/Decimal)` — collapses to
    /// `_int_to_ordinal(int(n))`, exactly like the cardinal path.
    ///
    /// Python's `to_ordinal` wraps `_int_to_ordinal(n)` in
    /// `except BaseException: return self._int_to_ordinal(int(n))`. A whole
    /// float/Decimal either hits a hash-equal dict key (`5.0 in
    /// self.ordinals`, `teens[11.0]`, `hundreds_special[100.0]`) and returns
    /// the identical string, or raises on a list index
    /// (`self.tens[2.0]` → TypeError) and retries with `int(n)` — same
    /// string either way. A fractional value always raises somewhere
    /// (`ordinals`/`teens` miss, or list index) and retries with the
    /// truncation: `to_ordinal(1.5)` → `_int_to_ordinal(1)` → "முதல்",
    /// `to_ordinal(-1.5)` → `_int_to_ordinal(-1)` → "கழித்தல் ஒன்றுஆவது".
    fn ordinal_float_entry(&self, value: &FloatValue) -> Result<String> {
        Ok(int_to_ordinal(&ta_trunc(value)))
    }

    /// `to_ordinal_num(float/Decimal)` — `str(n) + "-வது"` for every numeric
    /// input (the `int(n)` in the try-block only fires for `str` input, which
    /// never reaches this hook). `repr_str` is Python's `str(value)`, so
    /// `5.00` keeps its trailing zeros and `1E+2` its exponent form.
    fn ordinal_num_float_entry(&self, _value: &FloatValue, repr_str: &str) -> Result<String> {
        Ok(format!("{}{}", repr_str, ORDINAL_NUM_SUFFIX))
    }

    /// `to_year(float/Decimal)` — **no** try/except wrapper in Python, so
    /// the non-int value walks `_int_to_cardinal`/`_int_to_word` live and
    /// the list-index lookups raise TypeError uncaught. Only values whose
    /// residual digits are absorbed entirely by dict lookups
    /// (`hundreds_special`, `teens`) or by `== 1` scale quotients survive:
    /// `to_year(1000.0)` → "ஆயிரத்து", `to_year(1e20)` →
    /// "ஆயிரம் கோடி கோடி ஆயிரத்து", but `to_year(5.0)`,
    /// `to_year(1234.0)`, `to_year(-3.0)` all raise TypeError on
    /// `self.ones[...]`/`self.tens[...]`. See [`ta_year_sim`].
    fn year_float_entry(&self, value: &FloatValue) -> Result<String> {
        let (x, is_decimal) = match value {
            FloatValue::Float { value, .. } => (
                BigDecimal::from_f64(*value).ok_or_else(|| {
                    // NaN/inf never reach the year hook (the shim keeps
                    // non-finite input on the Python side).
                    N2WError::Value(format!("cannot convert {} to Decimal", value))
                })?,
                false,
            ),
            FloatValue::Decimal { value, .. } => (value.clone(), true),
        };
        ta_year_sim(&x, is_decimal)
    }

    // ---- currency -------------------------------------------------------
    //
    // TA overrides `to_currency` wholesale and inherits `to_cheque` from
    // `Num2Word_Base` unchanged, so only the class name, the forms table and
    // `to_currency` itself are language-specific here.
    //
    // Deliberately NOT overridden, because the trait defaults already match:
    //   * `currency_precision` — TA's CURRENCY_PRECISION is `{}`, so
    //     `.get(code, 100)` is 100 for every code, which is the default.
    //   * `currency_adjective` — CURRENCY_ADJECTIVES is `{}` -> None.
    //   * `pluralize` — TA never calls it; Base's is abstract and the default
    //     raises NotImplemented, which is the faithful behaviour if reached.
    //   * `money_verbose` — Base's `_money_verbose` is `self.to_cardinal(n)`,
    //     and the default routes to `to_cardinal` -> `int_to_cardinal`. That
    //     is what `to_cheque` needs.
    //   * `cardinal_from_decimal` — unreachable: TA's own `to_currency` never
    //     delegates to `default_to_currency`, and its fractional-cents branch
    //     goes through [`cardinal_from_fractional_cents`] instead.

    fn lang_name(&self) -> &str {
        "Num2Word_TA"
    }

    fn currency_forms(&self, code: &str) -> Option<&CurrencyForms> {
        self.currency_forms.get(code)
    }

    /// Python's `Num2Word_TA.to_currency(n, currency="INR")`.
    ///
    /// `cents`, `separator` and `adjective` do not exist on the Python
    /// signature, so they are ignored (quirk 8). `has_decimal` is ignored too:
    /// the cents segment is gated on `right > 0` alone (quirk 9).
    fn to_currency(
        &self,
        val: &CurrencyValue,
        currency: &str,
        _cents: bool,
        _separator: Option<&str>,
        _adjective: bool,
    ) -> Result<String> {
        // Python opens the method with
        //
        //     decimal_val = Decimal(str(n))
        //     has_fractional_cents = (decimal_val * 100) % 1 != 0
        //
        // inside a `try:` whose `except BaseException` returns
        // `str(n) + " " + currency`. For |n| >= 10**26 that arithmetic
        // *raises*: `decimal_val * 100` is then >= 10**28, and decimal's
        // default context precision is 28, so the `% 1` remainder — whose
        // integer quotient would need 29+ digits — signals InvalidOperation.
        // The handler swallows it and TA hands back the bare number:
        //
        //     to_currency(10**26 - 1, "INR") == "தொண்ணூறு ஒன்பது ஆயிரம் ..."
        //     to_currency(10**26,     "INR") == "100000000000000000000000000 INR"
        //
        // The threshold is exact for ints: below it the product needs at most
        // 28 digits and is computed exactly, at or above it the product is
        // rounded to 28 significant digits and still lands >= 10**28.
        //
        // This runs *before* the CURRENCY_FORMS lookup because Python's does
        // too — the raise happens on the first line of the `try`, so the
        // fallback beats the NotImplementedError:
        //
        //     to_currency(10**30, "JPY") == "1000000000000000000000000000000 JPY"
        //
        // Reproduced for the int path only, where `str(n)` is exactly BigInt's
        // Display (sign included). The float/Decimal path hits the same limit,
        // but there `str(n)` is `repr(float)` — "1e+30", or "1E+26" for a
        // Decimal — which is not recoverable from the parsed BigDecimal. See
        // the port report's `concerns`.
        if let CurrencyValue::Int(v) = val {
            if v.abs() >= self.decimal_ctx_limit {
                return Ok(format!("{} {}", v, currency));
            }
        }

        // `(decimal_val * 100) % 1 != 0`. An int can never have fractional
        // cents — the product is integral — which is also why the arm above is
        // the only place the context limit can bite the int path.
        let has_fractional_cents = match val {
            CurrencyValue::Int(_) => false,
            CurrencyValue::Decimal { value, .. } => {
                let scaled = value * BigDecimal::from(100);
                // with_scale(0) truncates toward zero, matching Decimal's
                // sign-of-dividend `%`; either way this only tests != 0.
                &scaled - scaled.with_scale(0) != BigDecimal::zero()
            }
        };

        // divisor 100, not `self.currency_precision(currency)`: Python calls
        // `parse_currency_parts(n, is_int_with_cents=False,
        // keep_precision=has_fractional_cents)` and lets currency.py's
        // `divisor=100` default stand (quirk 11).
        let (left, right, is_negative) =
            parse_currency_parts(val, false, has_fractional_cents, 100);

        let forms = self.currency_forms.get(currency).ok_or_else(|| {
            N2WError::NotImplemented(format!(
                "Currency code \"{}\" not implemented for \"{}\"",
                currency,
                self.lang_name()
            ))
        })?;

        let mut result: Vec<String> = Vec::new();

        // Python appends `self.negword.strip()`: the trailing space is
        // stripped here and put back by the `" ".join(result)` below. `left`
        // is already the absolute value (parse_currency_parts abs()es it), so
        // `int_to_cardinal` cannot prepend a second negword.
        if is_negative {
            result.push(NEGWORD.trim().to_string());
        }
        result.push(int_to_cardinal(&left));
        result.push(forms.unit[0].clone());

        // Python: `if right > 0`. This is the *only* cents guard, so a whole
        // float (1.0) or a scaled Decimal ("5.00") prints no subunit.
        if right > BigDecimal::zero() {
            // Python: `if isinstance(right, Decimal)`. `right` is a Decimal
            // exactly when parse_currency_parts kept precision, i.e. exactly
            // when has_fractional_cents — otherwise it returned a plain int.
            let right_words = if has_fractional_cents {
                cardinal_from_fractional_cents(&right)
            } else {
                // Safe: !keep_precision leaves `cents` at scale 0, so the
                // coefficient is the value.
                int_to_cardinal(&right.as_bigint_and_exponent().0)
            };
            result.push(right_words);
            result.push(forms.subunit[0].clone());
        }

        Ok(result.join(" "))
    }
}

/// Mirrors Python's `if remainder > 0` on the year path. `remainder` there is
/// always non-negative (the branch is guarded by `value >= 1000`), so this is
/// effectively `!= 0`.
fn is_positive(n: &BigInt) -> bool {
    n.sign() == num_bigint::Sign::Plus
}

/// `int(n)` for a float/Decimal — truncation toward zero, the value both
/// `except BaseException` retries feed to `_int_to_cardinal`/`_int_to_ordinal`.
fn ta_trunc(value: &FloatValue) -> BigInt {
    match value {
        // trunc(-0.5) == -0.0 -> BigInt 0, so the sign is dropped, matching
        // Python's int(-0.5) == 0.
        FloatValue::Float { value, .. } => {
            BigInt::from_f64(value.trunc()).unwrap_or_else(BigInt::zero)
        }
        FloatValue::Decimal { value, .. } => value.with_scale(0).as_bigint_and_exponent().0,
    }
}

/// `self.ones[<float/Decimal>]` / `self.tens[<float/Decimal>]` — CPython's
/// message for a list indexed with a non-int. Only the exception *type* is
/// corpus-observable.
fn ta_type_error(is_decimal: bool) -> N2WError {
    N2WError::Type(format!(
        "list indices must be integers or slices, not {}",
        if is_decimal {
            "decimal.Decimal"
        } else {
            "float"
        }
    ))
}

/// Positive floor division, all operands positive: Python's `//` on
/// float/Decimal truncates here. Exact for every corpus value (the floats
/// are powers of ten or small, so the f64 ops Python performs are exact and
/// agree with this arbitrary-precision replay).
fn ta_floordiv(a: &BigDecimal, b: &BigDecimal) -> BigInt {
    (a / b).with_scale(0).as_bigint_and_exponent().0
}

/// Positive `a % b`, consistent with [`ta_floordiv`].
fn ta_mod(a: &BigDecimal, b: &BigDecimal) -> BigDecimal {
    a - BigDecimal::from(ta_floordiv(a, b)) * b
}

/// `_int_to_word(n)` replayed with a **non-int-typed** `n` (float or
/// Decimal), as `to_year` runs it — live, with no `except BaseException`
/// safety net:
///
/// * dict lookups (`teens`, `hundreds_special`) succeed by hash equality
///   whenever the value is whole (`teens[12.0]` hits);
/// * list indexing (`self.tens[n // 10]`, `self.ones[n]`) raises
///   **TypeError** for any non-int index — whole or not;
/// * a fractional value in the open teens interval misses the dict:
///   **KeyError**;
/// * scale quotients recurse through this same function (they are
///   floats/Decimals themselves), and `== 1` comparisons are numeric, so
///   `1000.0 // 1000 == 1` takes the bare-"ஆயிரம்" arm without indexing.
///
/// Net effect: only values whose residue at every level is 0, a whole teen,
/// or absorbed by `hundreds_special`/`== 1` produce words; everything else
/// raises exactly where Python does.
fn ta_word_sim(n: &BigDecimal, is_decimal: bool) -> Result<String> {
    if n.is_zero() {
        return Ok(ZERO.to_string());
    }

    let mut n = n.clone();
    let mut parts: Vec<String> = Vec::new();

    // Crores (10^7): `crores = n // 10000000` recurses on the quotient.
    let crore_bd = BigDecimal::from(10_000_000u32);
    if n >= crore_bd {
        let crores = BigDecimal::from(ta_floordiv(&n, &crore_bd));
        if crores == BigDecimal::from(1u32) {
            parts.push("ஒரு கோடி".to_string());
        } else {
            parts.push(format!("{} கோடி", ta_word_sim(&crores, is_decimal)?));
        }
        n = ta_mod(&n, &crore_bd);
    }

    // Lakhs (10^5).
    let lakh_bd = BigDecimal::from(100_000u32);
    if n >= lakh_bd {
        let lakhs = BigDecimal::from(ta_floordiv(&n, &lakh_bd));
        if lakhs == BigDecimal::from(1u32) {
            parts.push("ஒரு இலட்சம்".to_string());
        } else {
            parts.push(format!("{} இலட்சம்", ta_word_sim(&lakhs, is_decimal)?));
        }
        n = ta_mod(&n, &lakh_bd);
    }

    // Thousands — the `== 1` case is the bare "ஆயிரம்", as in the int path.
    let thousand_bd = BigDecimal::from(1000u32);
    if n >= thousand_bd {
        let thousands = BigDecimal::from(ta_floordiv(&n, &thousand_bd));
        if thousands == BigDecimal::from(1u32) {
            parts.push("ஆயிரம்".to_string());
        } else {
            parts.push(format!("{} ஆயிரம்", ta_word_sim(&thousands, is_decimal)?));
        }
        n = ta_mod(&n, &thousand_bd);
    }

    // Hundreds: `(n // 100) * 100` is a whole 100..=900 whenever this branch
    // runs, and Python's dict lookup hits it by hash equality — so this arm
    // never raises, even for a fractional n.
    let hundred_bd = BigDecimal::from(100u32);
    if n >= hundred_bd {
        let h = ta_floordiv(&n, &hundred_bd);
        let h_idx = h.to_usize().unwrap_or(0);
        debug_assert!((1..=9).contains(&h_idx));
        parts.push(HUNDREDS_SPECIAL[h_idx - 1].to_string());
        n = ta_mod(&n, &hundred_bd);
    }

    let ten_bd = BigDecimal::from(10u32);
    let twenty_bd = BigDecimal::from(20u32);
    if n > ten_bd && n < twenty_bd {
        // `self.teens[n]` — dict: whole values hit by hash equality,
        // fractional ones raise KeyError.
        if n.is_integer() {
            let i = n
                .with_scale(0)
                .as_bigint_and_exponent()
                .0
                .to_usize()
                .expect("teens index 11..=19 fits usize");
            parts.push(TEENS[i - 11].to_string());
        } else {
            return Err(N2WError::Key(format!("{}", n)));
        }
    } else {
        if n >= ten_bd {
            // `self.tens[n // 10]` — list index with a float/Decimal.
            return Err(ta_type_error(is_decimal));
        }
        if n > BigDecimal::from(0u32) {
            // `self.ones[n]` — same.
            return Err(ta_type_error(is_decimal));
        }
    }

    Ok(parts.join(" "))
}

/// `_int_to_cardinal(n)` over a non-int-typed `n`, no safety net.
fn ta_cardinal_sim(n: &BigDecimal, is_decimal: bool) -> Result<String> {
    if n.is_zero() {
        // `-0.0 == 0` is true, so negative zero lands here and loses its sign.
        return Ok(ZERO.to_string());
    }
    if n.is_negative() {
        let pos = -n.clone();
        return Ok(format!("{}{}", NEGWORD, ta_word_sim(&pos, is_decimal)?));
    }
    ta_word_sim(n, is_decimal)
}

/// `to_year(<float/Decimal>)` replayed live (see
/// [`Lang::year_float_entry`] on [`LangTa`]).
fn ta_year_sim(n: &BigDecimal, is_decimal: bool) -> Result<String> {
    let thousand_bd = BigDecimal::from(1000u32);
    if *n < thousand_bd {
        // Also swallows every negative year; the cardinal sim raises the
        // TypeError itself where the digits demand it.
        return ta_cardinal_sim(n, is_decimal);
    }

    // n >= 1000 here, so `//`/`%` are plain truncation.
    let remainder = ta_mod(n, &thousand_bd);
    if *n < BigDecimal::from(2000u32) {
        // Python computes `thousands` and never uses it on this branch.
        let mut result = YEAR_THOUSAND.to_string();
        if remainder > BigDecimal::from(0u32) {
            result.push(' ');
            result.push_str(&ta_cardinal_sim(&remainder, is_decimal)?);
        }
        return Ok(result);
    }

    let thousands = BigDecimal::from(ta_floordiv(n, &thousand_bd));
    let mut result = format!(
        "{} {}",
        ta_cardinal_sim(&thousands, is_decimal)?,
        YEAR_THOUSAND
    );
    if remainder > BigDecimal::from(0u32) {
        result.push(' ');
        result.push_str(&ta_cardinal_sim(&remainder, is_decimal)?);
    }
    Ok(result)
}

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

    /// Drives the same entry point the corpus harness does. `arg` is Python's
    /// `repr(value)`, so "100" is an int and "12.34" a float.
    fn cur(arg: &str, currency: &str) -> Result<String> {
        let is_int = !arg.contains('.') && !arg.to_lowercase().contains('e');
        let val = CurrencyValue::parse(arg, is_int, !is_int, !is_int).unwrap();
        LangTa::new().to_currency(&val, currency, true, None, false)
    }

    fn cheque(arg: &str, currency: &str) -> Result<String> {
        use std::str::FromStr;
        LangTa::new().to_cheque(&BigDecimal::from_str(arg).unwrap(), currency)
    }

    /// Frozen-corpus rows, verbatim.
    #[test]
    fn corpus_currency() {
        for (arg, want) in [
            ("0", "பூஜ்ஜியம் யூரோ"),
            ("1", "ஒன்று யூரோ"),
            ("2", "இரண்டு யூரோ"),
            ("100", "நூறு யூரோ"),
            ("12.34", "பன்னிரண்டு யூரோ முப்பது நான்கு சென்ட்"),
            ("0.01", "பூஜ்ஜியம் யூரோ ஒன்று சென்ட்"),
            // A whole float still prints no cents: TA has no has_decimal guard.
            ("1.0", "ஒன்று யூரோ"),
            ("99.99", "தொண்ணூறு ஒன்பது யூரோ தொண்ணூறு ஒன்பது சென்ட்"),
            ("1234.56", "ஆயிரம் இருநூறு முப்பது நான்கு யூரோ ஐம்பது ஆறு சென்ட்"),
            ("-12.34", "கழித்தல் பன்னிரண்டு யூரோ முப்பது நான்கு சென்ட்"),
            ("1000000", "பத்து இலட்சம் யூரோ"),
            ("0.5", "பூஜ்ஜியம் யூரோ ஐம்பது சென்ட்"),
        ] {
            assert_eq!(cur(arg, "EUR").unwrap(), want, "EUR {}", arg);
        }
        assert_eq!(
            cur("12.34", "INR").unwrap(),
            "பன்னிரண்டு ரூபாய் முப்பது நான்கு பைசா"
        );
        assert_eq!(
            cur("12.34", "USD").unwrap(),
            "பன்னிரண்டு டாலர் முப்பது நான்கு சென்ட்"
        );
        assert_eq!(
            cur("12.34", "GBP").unwrap(),
            "பன்னிரண்டு பவுண்ட் முப்பது நான்கு பென்னி"
        );
        assert_eq!(cur("1.05", "LKR").unwrap(), "ஒன்று ரூபாய் ஐந்து சதம்");
        assert_eq!(cur("1.05", "MYR").unwrap(), "ஒன்று ரிங்கிட் ஐந்து சென்");
        assert_eq!(cur("1.05", "SGD").unwrap(), "ஒன்று டாலர் ஐந்து சென்ட்");
    }

    /// TA's table has seven codes and nothing else; JPY/KWD/BHD/CNY/CHF are
    /// corpus NotImplementedError rows.
    #[test]
    fn corpus_currency_not_implemented() {
        for code in ["JPY", "KWD", "BHD", "CNY", "CHF"] {
            match cur("12.34", code) {
                Err(N2WError::NotImplemented(m)) => assert_eq!(
                    m,
                    format!(
                        "Currency code \"{}\" not implemented for \"Num2Word_TA\"",
                        code
                    )
                ),
                other => panic!("{}: expected NotImplemented, got {:?}", code, other),
            }
        }
    }

    #[test]
    fn corpus_cheque() {
        for (code, want) in [
            ("EUR", "ஆயிரம் இருநூறு முப்பது நான்கு AND 56/100 யூரோ"),
            ("USD", "ஆயிரம் இருநூறு முப்பது நான்கு AND 56/100 டாலர்"),
            ("GBP", "ஆயிரம் இருநூறு முப்பது நான்கு AND 56/100 பவுண்ட்"),
            ("INR", "ஆயிரம் இருநூறு முப்பது நான்கு AND 56/100 ரூபாய்"),
        ] {
            assert_eq!(cheque("1234.56", code).unwrap(), want, "cheque {}", code);
        }
        for code in ["JPY", "KWD", "BHD", "CNY", "CHF"] {
            assert!(matches!(
                cheque("1234.56", code),
                Err(N2WError::NotImplemented(_))
            ));
        }
        assert_eq!(
            cheque("-1234.56", "INR").unwrap(),
            "MINUS ஆயிரம் இருநூறு முப்பது நான்கு AND 56/100 ரூபாய்"
        );
        assert_eq!(cheque("1.05", "INR").unwrap(), "ஒன்று AND 05/100 ரூபாய்");
    }

    #[test]
    fn negatives_take_one_stripped_negword() {
        assert_eq!(cur("-0.5", "INR").unwrap(), "கழித்தல் பூஜ்ஜியம் ரூபாய் ஐம்பது பைசா");
        assert_eq!(cur("-5", "INR").unwrap(), "கழித்தல் ஐந்து ரூபாய்");
        assert_eq!(cur("-1.0", "INR").unwrap(), "கழித்தல் ஒன்று ரூபாய்");
        assert_eq!(cur("-0.01", "INR").unwrap(), "கழித்தல் பூஜ்ஜியம் ரூபாய் ஒன்று பைசா");
    }

    /// keep_precision skips the ROUND_HALF_UP quantize, so fractional cents
    /// truncate. All values checked against the live Python converter.
    #[test]
    fn fractional_cents_truncate() {
        assert_eq!(cur("2.675", "INR").unwrap(), "இரண்டு ரூபாய் அறுபது ஏழு பைசா");
        assert_eq!(cur("0.655", "INR").unwrap(), "பூஜ்ஜியம் ரூபாய் அறுபது ஐந்து பைசா");
        assert_eq!(
            cur("12.345", "INR").unwrap(),
            "பன்னிரண்டு ரூபாய் முப்பது நான்கு பைசா"
        );
        // 15.5 paise -> teens[15.5] KeyError -> int(15.5).
        assert_eq!(cur("1.155", "INR").unwrap(), "ஒன்று ரூபாய் பதினைந்து பைசா");
        // 0.5 paise -> ones[0.5] TypeError -> int(0.5) == 0.
        assert_eq!(cur("1.005", "INR").unwrap(), "ஒன்று ரூபாய் பூஜ்ஜியம் பைசா");
        assert_eq!(cur("1.00001", "INR").unwrap(), "ஒன்று ரூபாய் பூஜ்ஜியம் பைசா");
    }

    /// Python does `int(float(right))`, not `int(right)`, and the difference
    /// is observable.
    #[test]
    fn fractional_cents_go_through_float() {
        // 2.9999999999999999999 paise: float() rounds to 3.0, so "மூன்று" —
        // int(Decimal(...)) would have truncated to 2.
        assert_eq!(
            cur("1.029999999999999999999", "INR").unwrap(),
            "ஒன்று ரூபாய் மூன்று பைசா"
        );
        // 99.9999999999999999999 paise: float() rounds to exactly 100.0, and
        // _int_to_word(100.0) succeeds outright via hundreds_special[100.0].
        assert_eq!(
            cur("1.999999999999999999999", "INR").unwrap(),
            "ஒன்று ரூபாய் நூறு பைசா"
        );
    }

    /// Past 10**26 the decimal context blows up and TA's `except
    /// BaseException` returns the bare number. Boundary verified against the
    /// live Python converter.
    #[test]
    fn int_decimal_context_limit() {
        let below = "99999999999999999999999999"; // 10**26 - 1
        assert!(cur(below, "INR")
            .unwrap()
            .starts_with("தொண்ணூறு ஒன்பது ஆயிரம்"));
        assert_eq!(
            cur("100000000000000000000000000", "INR").unwrap(),
            "100000000000000000000000000 INR"
        );
        assert_eq!(
            cur("-100000000000000000000000000", "INR").unwrap(),
            "-100000000000000000000000000 INR"
        );
        assert!(cur("-99999999999999999999999999", "INR")
            .unwrap()
            .starts_with("கழித்தல்"));
        // The fallback beats the NotImplementedError: Python raises on the
        // first line of the try, before the CURRENCY_FORMS lookup.
        assert_eq!(
            cur("1000000000000000000000000000000", "JPY").unwrap(),
            "1000000000000000000000000000000 JPY"
        );
        // ... but a value under the limit still raises for an unknown code.
        assert!(matches!(
            cur("10000000000000000000000000", "JPY"),
            Err(N2WError::NotImplemented(_))
        ));
    }

    /// Float cardinal path == truncation toward zero. Every row is a frozen
    /// corpus `"to": "cardinal"` float row (arg has a dot).
    #[test]
    fn corpus_cardinal_float() {
        let l = LangTa::new();
        // (raw f64, repr-derived precision, expected)
        let cases: &[(f64, u32, &str)] = &[
            (0.0, 1, "பூஜ்ஜியம்"),
            (0.5, 1, "பூஜ்ஜியம்"),
            (1.0, 1, "ஒன்று"),
            (1.5, 1, "ஒன்று"),
            (2.25, 2, "இரண்டு"),
            (3.14, 2, "மூன்று"),
            (0.01, 2, "பூஜ்ஜியம்"),
            (0.1, 1, "பூஜ்ஜியம்"),
            (0.99, 2, "பூஜ்ஜியம்"),
            (1.01, 2, "ஒன்று"),
            (12.34, 2, "பன்னிரண்டு"),
            (99.99, 2, "தொண்ணூறு ஒன்பது"),
            (100.5, 1, "நூறு"),
            (1234.56, 2, "ஆயிரம் இருநூறு முப்பது நான்கு"),
            (-0.5, 1, "பூஜ்ஜியம்"),
            (-1.5, 1, "கழித்தல் ஒன்று"),
            (-12.34, 2, "கழித்தல் பன்னிரண்டு"),
            (1.005, 3, "ஒன்று"),
            (2.675, 3, "இரண்டு"),
        ];
        for (v, p, want) in cases {
            let fv = FloatValue::Float {
                value: *v,
                precision: *p,
            };
            assert_eq!(
                l.to_cardinal_float(&fv, None).unwrap(),
                *want,
                "float {}",
                v
            );
        }
    }

    /// Decimal cardinal path (`"to": "cardinal_dec"` corpus rows) — exact
    /// truncation toward zero, never routed through f64.
    #[test]
    fn corpus_cardinal_decimal() {
        use std::str::FromStr;
        let l = LangTa::new();
        let cases: &[(&str, u32, &str)] = &[
            ("0.01", 2, "பூஜ்ஜியம்"),
            ("1.10", 2, "ஒன்று"),
            ("12.345", 3, "பன்னிரண்டு"),
            (
                "98746251323029.99",
                2,
                "தொண்ணூறு எட்டு இலட்சம் எழுபது நான்கு ஆயிரம் அறுநூறு இருபது ஐந்து கோடி பதின்மூன்று இலட்சம் இருபது மூன்று ஆயிரம் இருபது ஒன்பது",
            ),
            ("0.001", 3, "பூஜ்ஜியம்"),
            // Negative Decimal truncates toward zero: int(Decimal("-1.5")) == -1.
            ("-1.5", 1, "கழித்தல் ஒன்று"),
            // Truncates to zero -> no negword, like the float -0.5 row.
            ("-0.5", 1, "பூஜ்ஜியம்"),
        ];
        for (s, p, want) in cases {
            let fv = FloatValue::Decimal {
                value: BigDecimal::from_str(s).unwrap(),
                precision: *p,
            };
            assert_eq!(
                l.to_cardinal_float(&fv, None).unwrap(),
                *want,
                "decimal {}",
                s
            );
        }
    }

    /// `cents` / `separator` / `adjective` do not exist on TA's Python
    /// signature, so nothing may react to them.
    #[test]
    fn extra_kwargs_are_inert() {
        let l = LangTa::new();
        let v = CurrencyValue::parse("12.34", false, true, true).unwrap();
        let want = "பன்னிரண்டு ரூபாய் முப்பது நான்கு பைசா";
        assert_eq!(l.to_currency(&v, "INR", true, None, false).unwrap(), want);
        assert_eq!(
            l.to_currency(&v, "INR", false, Some(" X"), true).unwrap(),
            want
        );
    }
}