//! CSS property types for time durations (`s`, `ms`, `t`).

use alloc::string::{String, ToString};

use crate::corety::AzString;

use crate::props::formatter::PrintAsCssValue;

/// Nominal engine tick (frame) rate, in ticks per second.

///

/// The CSS `t` unit — and `azul_core::task::Duration::Tick` behind it — counts

/// FRAMES, not wall time. Nothing needs a real clock to advance a tick; that is

/// the entire point of the unit. But a tick span still has to be COMPARABLE

/// against a wall-clock one, because the engine's interval constants are

/// milliseconds (`Duration::System`) and a comparison between the two variants

/// has to answer something truthful rather than "not yet, forever".

///

/// This constant is the single exchange rate between the two scales, shared by

/// `azul-css` (parsing/printing) and `azul-core` (`Duration` arithmetic). It is

/// NOT a clock: nothing reads it to decide *when* a frame happens, only how many

/// nanoseconds a frame is worth when the two units must be put side by side.

///

/// 60 Hz because that is the frame budget the renderer already targets (see the

/// `16_666_667`ns scroll-animation step in `azul-layout`), so `1t` is one frame

/// at the target rate and `60t` is exactly one second.

pub const TICKS_PER_SECOND: u64 = 60;

/// The unit a [`CssDuration`]'s magnitude is expressed in.

///

/// `Milliseconds` is the CSS `ms` / `s` family (wall time). `Ticks` is the CSS

/// `t` unit: engine frames, which advance because the engine rendered, not

/// because a clock ticked. `t` was chosen over `fr` because `fr` is already

/// taken by CSS grid (`grid-template-columns: 1fr`) and would collide in

/// dimension parsing.

#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Default)]

#[repr(C)]

pub enum CssDurationUnit {

    /// Wall-clock milliseconds (parsed from `ms` and `s`).

    #[default]

    Milliseconds,

    /// Engine ticks / frames (parsed from `t`).

    Ticks,

}

impl PrintAsCssValue for CssDurationUnit {

        }

}

impl crate::codegen::format::FormatAsRustCode for CssDurationUnit {

        }

}

/// A CSS time duration: a magnitude plus the unit it is counted in.

///

/// `inner` is NOT unconditionally milliseconds — read it together with `unit`,

/// or go through [`CssDuration::millis`] / [`CssDuration::ticks`], which convert.

///

/// The derived `Ord` compares `inner` first and only then `unit`, so it is a

/// total order for storage/dedup purposes but is NOT a chronological comparison

/// across units (`5ms` sorts below `5t` purely by field order). Compare

/// durations chronologically by converting them first, or by handing them to

/// `azul_core::task::Duration`, which compares on a canonical scale.

#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]

#[repr(C)]

#[derive(Default)]

pub struct CssDuration {

    /// Magnitude, counted in `unit`.

    pub inner: u32,

    /// The unit `inner` is counted in.

    pub unit: CssDurationUnit,

}

impl CssDuration {

    /// A duration of `ms` wall-clock milliseconds.

    #[must_use]

    /// A duration of `ticks` engine frames (the CSS `t` unit).

    #[must_use]

    /// This duration in whole milliseconds, converting ticks at

    /// [`TICKS_PER_SECOND`] and truncating toward zero.

    ///

    /// Saturates at `u32::MAX` rather than wrapping: `u32::MAX` ticks is ~828

    /// days, which does not fit `u32` milliseconds.

    // `as` rather than `From`/`TryFrom`: this is a `const fn`. The widening is

    // lossless and the narrowing is range-checked immediately above it.

    #[allow(clippy::cast_lossless, clippy::cast_possible_truncation)]

    #[must_use]

            CssDurationUnit::Ticks => {

                // `* 1000` first, then divide: 60t is exactly 1000ms, not 996ms.

                } else {

                }

            }

        }

    /// This duration in whole ticks, converting milliseconds at

    /// [`TICKS_PER_SECOND`] and truncating toward zero.

    ///

    /// Truncation means a sub-frame duration (`10ms` at 60Hz) is **zero** ticks,

    /// not one — "how many whole frames fit in this span".

    // `as` rather than `From`/`TryFrom`: this is a `const fn`. `u32::MAX * 60 /

    // 1000` is ~2.6e8, comfortably inside u32, so the narrowing cannot truncate.

    #[allow(clippy::cast_lossless, clippy::cast_possible_truncation)]

    #[must_use]

            CssDurationUnit::Milliseconds => {

                // Cannot overflow: u32::MAX ms * 60 / 1000 < u32::MAX.

            }

        }

}

impl PrintAsCssValue for CssDuration {

}

impl crate::codegen::format::FormatAsRustCode for CssDuration {

        use crate::codegen::format::FormatAsRustCode;

            self.inner,

        )

}

/// Error returned when parsing a CSS duration string fails.

#[cfg(feature = "parser")]

#[derive(Clone, PartialEq, Eq)]

pub enum DurationParseError<'a> {

    InvalidValue(&'a str),

    ParseFloat(core::num::ParseFloatError),

}

#[cfg(feature = "parser")]

impl_debug_as_display!(DurationParseError<'a>);

#[cfg(feature = "parser")]

impl_display! { DurationParseError<'a>, {

    InvalidValue(v) => format!("Invalid time value: \"{}\"", v),

    ParseFloat(e) => format!("Invalid number for time value: {}", e),

}}

/// Owned version of [`DurationParseError`] for FFI and storage.

#[cfg(feature = "parser")]

#[derive(Debug, Clone, PartialEq, Eq)]

#[repr(C, u8)]

pub enum DurationParseErrorOwned {

    InvalidValue(AzString),

    ParseFloat(AzString),

}

#[cfg(feature = "parser")]

impl DurationParseError<'_> {

        }

}

#[cfg(feature = "parser")]

impl DurationParseErrorOwned {

        }

}

/// Parses a CSS duration string (e.g. `"200ms"`, `"1.5s"`, `"5t"`) into a

/// [`CssDuration`].

///

/// Three units are accepted:

///

/// * `ms` — milliseconds

/// * `s`  — seconds (stored as milliseconds)

/// * `t`  — engine ticks / frames, kept as ticks (see [`CssDurationUnit::Ticks`])

///

/// `t` is deliberately NOT normalised to milliseconds here: the whole reason the

/// unit exists is that a tick count survives to the timer as an exact frame

/// count, so a test can advance N ticks and assert the Nth frame — and only the

/// Nth — flipped. Converting at parse time would throw that away and reintroduce

/// the wall-clock rounding the unit is meant to escape.

#[cfg(feature = "parser")]

/// # Errors

///

/// Returns an error if `input` is not a valid CSS `duration` value.

    // Suffix order matters: `ms` must be stripped before the bare `s`, otherwise

    // "5ms" reads as 5 *seconds*. `t` shares no suffix with either, so it can sit

    // anywhere in the chain.

    } else {

    }

#[cfg(test)]

#[allow(clippy::unreadable_literal)]

mod autotest_generated {

    use super::*;

    use crate::codegen::format::FormatAsRustCode;

    use crate::props::formatter::PrintAsCssValue;

    /// Largest integer an `f32` represents exactly (`2^24`). Above this, the

    /// spacing between neighbouring `f32`s exceeds 1ms, so `parse_duration`

    /// (which round-trips through `f32`) can no longer be lossless.

    #[cfg(feature = "parser")]

    const TWO_POW_24: u32 = 16_777_216;

    /// Convenience: parse, assert the result is in milliseconds, and unwrap to

    /// the raw millisecond count.

    #[cfg(feature = "parser")]

    fn ms(input: &str) -> u32 {

        let d = parse_duration(input)

            .unwrap_or_else(|e| panic!("expected {input:?} to parse, got {e}"));

        assert_eq!(

            d.unit,

            CssDurationUnit::Milliseconds,

            "{input:?} parsed as {:?}, not milliseconds",

            d.unit

        );

        d.inner

    }

    /// Convenience: parse, assert the result is in ticks, and unwrap to the raw

    /// tick count.

    #[cfg(feature = "parser")]

    fn ticks(input: &str) -> u32 {

        let d = parse_duration(input)

            .unwrap_or_else(|e| panic!("expected {input:?} to parse, got {e}"));

        assert_eq!(

            d.unit,

            CssDurationUnit::Ticks,

            "{input:?} parsed as {:?}, not ticks",

            d.unit

        );

        d.inner

    }

    // ------------------------------------------------------ positive control ---

    #[cfg(feature = "parser")]

    #[test]

    fn valid_minimal_inputs_parse_to_expected_values() {

        assert_eq!(ms("0"), 0);

        assert_eq!(ms("0ms"), 0);

        assert_eq!(ms("0s"), 0);

        assert_eq!(ms("200ms"), 200);

        assert_eq!(ms("1s"), 1000);

        assert_eq!(ms("1.5s"), 1500);

        assert_eq!(ms("0.5s"), 500);

        assert_eq!(ms(".25s"), 250);

        assert_eq!(ms("5e2ms"), 500);

        assert_eq!(ms("+5ms"), 5);

    }

    /// The `ms` suffix must be stripped before the bare `s` suffix, otherwise

    /// `"5ms"` would be read as 5 *seconds* (a 1000x error).

    #[cfg(feature = "parser")]

    #[test]

    fn ms_suffix_wins_over_s_suffix() {

        assert_eq!(ms("5ms"), 5);

        assert_ne!(ms("5ms"), ms("5s"));

        assert_eq!(ms("5s"), 5000);

    }

    #[cfg(feature = "parser")]

    #[test]

    fn units_are_case_insensitive() {

        assert_eq!(ms("200MS"), 200);

        assert_eq!(ms("200Ms"), 200);

        assert_eq!(ms("1S"), 1000);

        assert_eq!(ms("1.5E1S"), 15000);

        assert_eq!(ticks("5T"), 5);

    }

    // ---------------------------------------------------------- tick unit ---

    /// `t` counts FRAMES and must survive parsing as a frame count. If this ever

    /// starts returning milliseconds, every "advance exactly N ticks" test

    /// silently becomes a wall-clock test again.

    #[cfg(feature = "parser")]

    #[test]

    fn the_t_unit_parses_to_a_tick_count_and_is_not_normalised_to_millis() {

        assert_eq!(parse_duration("5t"), Ok(CssDuration::from_ticks(5)));

        assert_eq!(ticks("0t"), 0);

        assert_eq!(ticks("1t"), 1);

        assert_eq!(ticks("60t"), 60);

        assert_eq!(ticks("4294967295t"), u32::MAX);

        // Not milliseconds, and not silently multiplied by anything.

        assert_ne!(parse_duration("5t"), parse_duration("5ms"));

        assert_ne!(parse_duration("60t"), parse_duration("1s"));

    }

    /// `t` is only ever the *last* suffix tried, so it must not steal values that

    /// belong to `ms` / `s`, and it must not accept unit-ish garbage.

    #[cfg(feature = "parser")]

    #[test]

    fn the_t_unit_does_not_collide_with_the_other_units_or_swallow_garbage() {

        assert_eq!(ms("5ms"), 5);

        assert_eq!(ms("5s"), 5000);

        // Suffixes that merely END in `t` are not durations.

        for garbage in ["5pt", "5t5", "t", "5tt", "5mst", "5st", "5 t", "-5t"] {

            assert!(

                parse_duration(garbage).is_err(),

                "expected {garbage:?} to be rejected"

            );

        }

    }

    /// Truncation across units is exact at the boundaries that matter: 60 ticks

    /// is one whole second, and a sub-frame millisecond span is zero frames (not

    /// one) — "how many whole frames fit", never "round up so something happens".

    #[test]

    fn millis_and_ticks_convert_at_the_nominal_frame_rate() {

        assert_eq!(TICKS_PER_SECOND, 60);

        assert_eq!(CssDuration::from_ticks(60).millis(), 1000);

        assert_eq!(CssDuration::from_ticks(30).millis(), 500);

        assert_eq!(CssDuration::from_ticks(1).millis(), 16);

        assert_eq!(CssDuration::from_ticks(0).millis(), 0);

        assert_eq!(CssDuration::from_millis(1000).ticks(), 60);

        assert_eq!(CssDuration::from_millis(500).ticks(), 30);

        assert_eq!(CssDuration::from_millis(16).ticks(), 0, "sub-frame is 0 frames");

        assert_eq!(CssDuration::from_millis(17).ticks(), 1);

        assert_eq!(CssDuration::from_millis(0).ticks(), 0);

        // Same-unit conversions are the identity, not a round-trip through the

        // other scale (which would lose precision).

        assert_eq!(CssDuration::from_millis(7).millis(), 7);

        assert_eq!(CssDuration::from_ticks(7).ticks(), 7);

    }

    /// `u32::MAX` ticks is ~828 days, which does not fit in `u32` milliseconds.

    /// It must clamp, not wrap.

    #[test]

    fn tick_to_milli_conversion_saturates_instead_of_wrapping() {

        assert_eq!(CssDuration::from_ticks(u32::MAX).millis(), u32::MAX);

        // The largest tick count that still fits: floor(u32::MAX * 60 / 1000).

        let last_exact = (u64::from(u32::MAX) * TICKS_PER_SECOND / 1000) as u32;

        assert!(CssDuration::from_ticks(last_exact).millis() < u32::MAX);

        // ...and the reverse direction cannot overflow at all.

        assert_eq!(

            CssDuration::from_millis(u32::MAX).ticks(),

            (u64::from(u32::MAX) * TICKS_PER_SECOND / 1000) as u32

        );

    }

    // ----------------------------------------------------------- truncation ---

    /// Fractional milliseconds are truncated toward zero, never rounded.

    #[cfg(feature = "parser")]

    #[test]

    fn sub_millisecond_values_truncate_toward_zero() {

        assert_eq!(ms("5.9ms"), 5);

        assert_eq!(ms("0.9ms"), 0);

        assert_eq!(ms("0.0009s"), 0); // 0.9ms

        assert_eq!(ms("0.0015s"), 1); // 1.5ms

    }

    // ------------------------------------------------------- empty / blank ---

    #[cfg(feature = "parser")]

    #[test]

    fn empty_input_is_rejected_without_panicking() {

        assert_eq!(parse_duration(""), Err(DurationParseError::InvalidValue("")));

    }

    #[cfg(feature = "parser")]

    #[test]

    fn whitespace_only_input_is_rejected_and_error_keeps_the_raw_input() {

        // The input is trimmed for parsing but the *error* carries the original

        // (untrimmed) slice, so callers can point at the offending source text.

        assert_eq!(

            parse_duration("   "),

            Err(DurationParseError::InvalidValue("   "))

        );

        assert_eq!(

            parse_duration("\t\n"),

            Err(DurationParseError::InvalidValue("\t\n"))

        );

    }

    // ---------------------------------------------------------- malformed ---

    #[cfg(feature = "parser")]

    #[test]

    fn a_bare_unit_with_no_number_is_a_parse_float_error_not_a_panic() {

        assert!(matches!(

            parse_duration("ms"),

            Err(DurationParseError::ParseFloat(_))

        ));

        assert!(matches!(

            parse_duration("s"),

            Err(DurationParseError::ParseFloat(_))

        ));

    }

    #[cfg(feature = "parser")]

    #[test]

    fn unitless_numbers_other_than_literal_zero_are_rejected() {

        // Only the exact string "0" is accepted without a unit.

        assert_eq!(ms("0"), 0);

        assert_eq!(

            parse_duration("200"),

            Err(DurationParseError::InvalidValue("200"))

        );

        assert_eq!(

            parse_duration("1.5"),

            Err(DurationParseError::InvalidValue("1.5"))

        );

        assert_eq!(

            parse_duration("0.0"),

            Err(DurationParseError::InvalidValue("0.0"))

        );

        assert_eq!(

            parse_duration("00"),

            Err(DurationParseError::InvalidValue("00"))

        );

        assert_eq!(

            parse_duration("-0"),

            Err(DurationParseError::InvalidValue("-0"))

        );

    }

    #[cfg(feature = "parser")]

    #[test]

    fn garbage_and_junk_never_panic() {

        for garbage in [

            "abc", "!!!", "\0\0\0", "ms ms", "1,5s", "1 ms", "--5ms", "5mss", "5sms", "0x10ms",

            "1e", "1e+", ".s", "-.ms", "s1", "ms200", "200ms;garbage", "200ms !important",

        ] {

            // The only contract is: never panic, and never silently succeed with

            // a value we did not ask for. Every one of these is an error.

            assert!(

                parse_duration(garbage).is_err(),

                "expected {garbage:?} to be rejected"

            );

        }

    }

    #[cfg(feature = "parser")]

    #[test]

    fn leading_and_trailing_whitespace_is_trimmed_but_interior_space_is_not() {

        assert_eq!(ms("   200ms   "), 200);

        assert_eq!(ms("\t\n1.5s\r\n"), 1500);

        // Interior whitespace stays inside the number and kills the float parse.

        assert!(matches!(

            parse_duration("200 ms"),

            Err(DurationParseError::ParseFloat(_))

        ));

        assert!(matches!(

            parse_duration("2 0 0ms"),

            Err(DurationParseError::ParseFloat(_))

        ));

    }

    #[cfg(feature = "parser")]

    #[test]

    fn trailing_junk_after_a_valid_value_is_rejected_not_silently_accepted() {

        assert!(parse_duration("200ms;").is_err());

        assert!(parse_duration("200msx").is_err());

        // ...but note "200msms" strips one "ms" and then fails the float parse.

        assert!(matches!(

            parse_duration("200msms"),

            Err(DurationParseError::ParseFloat(_))

        ));

    }

    // ------------------------------------------------------------ negative ---

    #[cfg(feature = "parser")]

    #[test]

    fn negative_durations_are_rejected_in_both_units() {

        assert_eq!(

            parse_duration("-1ms"),

            Err(DurationParseError::InvalidValue("-1ms"))

        );

        assert_eq!(

            parse_duration("-0.5s"),

            Err(DurationParseError::InvalidValue("-0.5s"))

        );

        assert_eq!(

            parse_duration("-1e-30s"),

            Err(DurationParseError::InvalidValue("-1e-30s"))

        );

    }

    #[cfg(feature = "parser")]

    #[test]

    fn the_invalid_value_error_reports_the_original_untrimmed_uncased_input() {

        // Not the lowercased/trimmed copy used internally.

        assert_eq!(

            parse_duration("  -1MS  "),

            Err(DurationParseError::InvalidValue("  -1MS  "))

        );

    }

    /// `-0.0 < 0.0` is false, so signed zero slips past the negativity check —

    /// but the cast lands on `0`, so the result is still sane.

    #[cfg(feature = "parser")]

    #[test]

    fn negative_zero_is_accepted_and_clamps_to_zero() {

        assert_eq!(ms("-0ms"), 0);

        assert_eq!(ms("-0.0s"), 0);

        assert_eq!(ms("-0e10ms"), 0);

    }

    // ---------------------------------------------- overflow / saturation ---

    #[cfg(feature = "parser")]

    #[test]

    fn values_beyond_u32_max_saturate_instead_of_wrapping_or_panicking() {

        assert_eq!(ms("4294967296ms"), u32::MAX); // 2^32 exactly

        assert_eq!(ms("99999999999ms"), u32::MAX);

        assert_eq!(ms("1e30s"), u32::MAX);

        assert_eq!(ms("5000000s"), u32::MAX); // 5e6 * 1000 = 5e9 > u32::MAX

    }

    /// A float literal too large for `f32` parses to `+inf` (not an error), and

    /// `inf as u32` saturates. Assert the whole chain lands on `u32::MAX`.

    #[cfg(feature = "parser")]

    #[test]

    fn float_overflow_to_infinity_saturates_to_u32_max() {

        assert_eq!(ms("1e39ms"), u32::MAX); // > f32::MAX

        assert_eq!(ms("1e999999ms"), u32::MAX);

        assert_eq!(ms("infms"), u32::MAX);

        assert_eq!(ms("infinityms"), u32::MAX);

        assert_eq!(ms("INFms"), u32::MAX);

        assert_eq!(ms("infs"), u32::MAX);

    }

    #[cfg(feature = "parser")]

    #[test]

    fn negative_infinity_is_rejected_as_a_negative_duration() {

        assert_eq!(

            parse_duration("-infms"),

            Err(DurationParseError::InvalidValue("-infms"))

        );

        assert_eq!(

            parse_duration("-infinitys"),

            Err(DurationParseError::InvalidValue("-infinitys"))

        );

    }

    /// `NaN < 0.0` is false, so `"nan"` is *accepted* rather than rejected; the

    /// saturating cast then turns it into `0ms`. Documented here so that any

    /// future change to reject NaN outright is a visible, intentional change.

    #[cfg(feature = "parser")]

    #[test]

    fn nan_is_accepted_and_degrades_to_zero_rather_than_panicking() {

        assert_eq!(ms("nanms"), 0);

        assert_eq!(ms("NaNms"), 0);

        assert_eq!(ms("-nanms"), 0);

        assert_eq!(ms("nans"), 0); // NaN * 1000.0 is still NaN

    }

    #[cfg(feature = "parser")]

    #[test]

    fn underflow_to_zero_is_not_an_error() {

        assert_eq!(ms("1e-30ms"), 0);

        assert_eq!(ms("1e-999999s"), 0);

    }

    #[cfg(feature = "parser")]

    #[test]

    fn u32_max_and_f32_max_boundary_strings_are_handled() {

        assert_eq!(ms("4294967295ms"), u32::MAX); // u32::MAX, rounds up in f32 then saturates back

        assert_eq!(ms("4294967040ms"), 4294967040); // 2^32 - 256: exactly representable in f32

        let f32_max = format!("{}ms", f32::MAX);

        assert_eq!(ms(&f32_max), u32::MAX);

        let i64_max = format!("{}ms", i64::MAX);

        assert_eq!(ms(&i64_max), u32::MAX);

    }

    // ------------------------------------------------------------ huge input ---

    #[cfg(feature = "parser")]

    #[test]

    fn extremely_long_digit_string_saturates_without_hanging() {

        let mut input = "9".repeat(100_000);

        input.push_str("ms");

        assert_eq!(ms(&input), u32::MAX);

    }

    #[cfg(feature = "parser")]

    #[test]

    fn extremely_long_run_of_leading_zeros_still_parses_exactly() {

        let mut input = "0".repeat(100_000);

        input.push_str("1ms");

        assert_eq!(ms(&input), 1);

    }

    #[cfg(feature = "parser")]

    #[test]

    fn extremely_long_garbage_is_rejected_without_hanging() {

        let input = "x".repeat(100_000);

        assert!(parse_duration(&input).is_err());

        // Long, *trimmable* padding around a valid value.

        let padded = format!("{}200ms{}", " ".repeat(50_000), " ".repeat(50_000));

        assert_eq!(ms(&padded), 200);

    }

    #[cfg(feature = "parser")]

    #[test]

    fn deeply_nested_brackets_do_not_stack_overflow() {

        // The parser is not recursive; prove it by feeding it 10k nesting levels.

        let nested = format!("{}{}", "(".repeat(10_000), ")".repeat(10_000));

        assert!(parse_duration(&nested).is_err());

        let nested_with_unit = format!("{nested}s");

        assert!(parse_duration(&nested_with_unit).is_err());

    }

    // -------------------------------------------------------------- unicode ---

    #[cfg(feature = "parser")]

    #[test]

    fn non_ascii_input_is_rejected_without_panicking() {

        for input in [

            "\u{1F600}",       // emoji

            "\u{1F600}ms",     // emoji + valid unit

            "1\u{FF53}",       // FULLWIDTH LATIN SMALL LETTER S is not "s"

            "1s\u{0301}",      // combining acute after the unit

            "２００ms",        // fullwidth digits

            "\u{202E}200ms",   // RTL override prefix

            "1\u{00A0}s",      // NBSP *inside* the value

        ] {

            assert!(

                parse_duration(input).is_err(),

                "expected {input:?} to be rejected"

            );

        }

    }

    /// `str::trim` strips Unicode whitespace, not just ASCII.

    #[cfg(feature = "parser")]

    #[test]

    fn unicode_whitespace_around_a_valid_value_is_trimmed() {

        assert_eq!(ms("\u{00A0}200ms\u{00A0}"), 200); // NBSP

        assert_eq!(ms("\u{3000}1.5s\u{3000}"), 1500); // ideographic space

    }

    /// `to_lowercase` can *grow* the string (`İ` -> `i` + combining dot), which

    /// would corrupt any byte-index-based suffix logic. Suffix stripping here is

    /// char-safe, so this must merely fail to parse.

    #[cfg(feature = "parser")]

    #[test]

    fn lowercasing_that_changes_the_byte_length_does_not_panic() {

        assert!(parse_duration("\u{0130}ms").is_err()); // LATIN CAPITAL I WITH DOT ABOVE

        assert!(parse_duration("1\u{0130}s").is_err());

    }

    // ----------------------------------------------------------- round-trip ---

    #[cfg(feature = "parser")]

    #[test]

    fn print_as_css_value_round_trips_through_parse_duration() {

        for inner in [

            0,

            1,

            2,

            17,

            999,

            1000,

            65_535,

            1_000_000,

            TWO_POW_24,      // last exactly-representable integer in f32

            4_294_967_040,   // 2^32 - 256: still exact (a multiple of the f32 ulp there)

            u32::MAX,        // rounds up to 2^32 in f32, then the cast saturates back down

        ] {

            let duration = CssDuration::from_millis(inner);

            let printed = duration.print_as_css_value();

            assert_eq!(

                parse_duration(&printed),

                Ok(duration),

                "round-trip failed for {inner}ms (printed as {printed:?})"

            );

        }

    }

    /// A tick duration must print back as `t` and reparse as the SAME tick count.

    /// A printer that emitted `ms` here would silently convert every stylesheet

    /// round-trip from frames to wall time.

    #[cfg(feature = "parser")]

    #[test]

    fn print_as_css_value_round_trips_tick_durations_as_ticks() {

        for inner in [0, 1, 5, 60, 999, TWO_POW_24, u32::MAX] {

            let duration = CssDuration::from_ticks(inner);

            let printed = duration.print_as_css_value();

            assert_eq!(printed, format!("{inner}t"));

            assert_eq!(

                parse_duration(&printed),

                Ok(duration),

                "round-trip failed for {inner}t (printed as {printed:?})"

            );

        }

    }

    #[test]

    fn print_as_css_value_always_emits_the_unit_it_was_built_with() {

        for inner in [0, 1, u32::MAX] {

            let printed = CssDuration::from_millis(inner).print_as_css_value();

            assert!(printed.ends_with("ms"), "{printed:?} lacks a unit");

            assert_eq!(printed, format!("{inner}ms"));

            let printed = CssDuration::from_ticks(inner).print_as_css_value();

            assert!(printed.ends_with('t'), "{printed:?} lacks a unit");

            assert!(!printed.ends_with("ms"), "{printed:?} lost the tick unit");

            assert_eq!(printed, format!("{inner}t"));

        }

    }

    /// Above `2^24` the millisecond count no longer survives an `f32`, so the

    /// round-trip is lossy. This is a real precision limit of the parser, pinned

    /// here so it cannot regress further (the error must stay within one ulp).

    #[cfg(feature = "parser")]

    #[test]

    fn round_trip_above_two_pow_24_is_lossy_but_bounded() {

        let duration = CssDuration::from_millis(TWO_POW_24 + 1);

        let reparsed = parse_duration(&duration.print_as_css_value()).unwrap();

        assert_ne!(reparsed.inner, duration.inner);

        assert_eq!(reparsed.inner, TWO_POW_24);

        assert!(reparsed.inner.abs_diff(duration.inner) <= 1);

    }

    #[cfg(feature = "parser")]

    #[test]

    fn seconds_and_milliseconds_agree_for_the_same_duration() {

        assert_eq!(ms("2s"), ms("2000ms"));

        assert_eq!(ms("0.001s"), ms("1ms"));

        assert_eq!(ms("0s"), ms("0ms"));

    }

    // ------------------------------------------------------- CssDuration ---

    /// The default unit is milliseconds, not ticks: every pre-existing

    /// `CssDuration::default()` in the tree means "0ms", and a default that

    /// silently meant frames would reinterpret all of them.

    #[test]

    fn default_duration_is_zero_milliseconds() {

        assert_eq!(CssDuration::default(), CssDuration::from_millis(0));

        assert_eq!(CssDuration::default().inner, 0);

        assert_eq!(CssDuration::default().unit, CssDurationUnit::Milliseconds);

        assert_eq!(CssDurationUnit::default(), CssDurationUnit::Milliseconds);

    }

    #[test]

    fn ordering_and_equality_follow_the_inner_count_within_one_unit() {

        let a = CssDuration::from_millis(1);

        let b = CssDuration::from_millis(2);

        let max = CssDuration::from_millis(u32::MAX);

        assert!(a < b);

        assert!(b < max);

        assert_eq!(a, CssDuration::from_millis(1));

        assert_eq!(a.max(b), b);

        assert_eq!(CssDuration::default(), CssDuration::from_millis(0));

        // Same magnitude, different unit: NOT equal. `5ms` and `5t` are

        // different durations and must never compare equal, or a stylesheet

        // dedup/cache would collapse them into one.

        assert_ne!(CssDuration::from_millis(5), CssDuration::from_ticks(5));

    }

    #[test]

    fn format_as_rust_code_emits_a_constructor_and_ignores_indentation() {

        let d = CssDuration::from_millis(42);

        assert_eq!(

            d.format_as_rust_code(0),

            "CssDuration { inner: 42, unit: CssDurationUnit::Milliseconds }"

        );

        assert_eq!(d.format_as_rust_code(7), d.format_as_rust_code(0));

        assert_eq!(

            CssDuration::from_millis(u32::MAX).format_as_rust_code(0),

            "CssDuration { inner: 4294967295, unit: CssDurationUnit::Milliseconds }"

        );

        assert_eq!(

            CssDuration::from_ticks(5).format_as_rust_code(0),

            "CssDuration { inner: 5, unit: CssDurationUnit::Ticks }"

        );

        assert_eq!(

            CssDurationUnit::Ticks.format_as_rust_code(0),

            "CssDurationUnit::Ticks"

        );

    }

    // --------------------------------------------------- error conversions ---

    #[cfg(feature = "parser")]

    fn parse_float_error() -> core::num::ParseFloatError {

        "not-a-float".parse::<f32>().unwrap_err()

    }

    #[cfg(feature = "parser")]

    #[test]

    fn to_contained_preserves_an_invalid_value_payload() {

        let owned = DurationParseError::InvalidValue("10px").to_contained();

        match owned {

            DurationParseErrorOwned::InvalidValue(s) => assert_eq!(s.as_str(), "10px"),

            DurationParseErrorOwned::ParseFloat(_) => panic!("variant changed"),

        }

    }

    #[cfg(feature = "parser")]

    #[test]

    fn to_contained_stringifies_the_float_error() {

        let owned = DurationParseError::ParseFloat(parse_float_error()).to_contained();

        match owned {

            DurationParseErrorOwned::ParseFloat(s) => {

                assert!(!s.as_str().is_empty(), "float error message was empty");

                assert_eq!(s.as_str(), parse_float_error().to_string());

            }

            DurationParseErrorOwned::InvalidValue(_) => panic!("variant changed"),

        }

    }

    #[cfg(feature = "parser")]

    #[test]

    fn to_contained_handles_empty_and_extreme_payloads() {

        assert_eq!(

            DurationParseError::InvalidValue("").to_contained(),

            DurationParseErrorOwned::InvalidValue(String::new().into())

        );

        let huge = "x".repeat(100_000);

        let owned = DurationParseError::InvalidValue(&huge).to_contained();

        match owned {

            DurationParseErrorOwned::InvalidValue(s) => assert_eq!(s.as_str().len(), 100_000),

            DurationParseErrorOwned::ParseFloat(_) => panic!("variant changed"),

        }

        // Non-UTF8-boundary-unsafe payloads must survive the copy intact.

        let unicode = "\u{1F600}\u{0301}";

        assert_eq!(

            DurationParseError::InvalidValue(unicode).to_contained(),

            DurationParseErrorOwned::InvalidValue(unicode.to_string().into())

        );

    }

    #[cfg(feature = "parser")]

    #[test]

    fn to_shared_preserves_an_invalid_value_payload() {

        let owned = DurationParseErrorOwned::InvalidValue("garbage".to_string().into());

        assert_eq!(owned.to_shared(), DurationParseError::InvalidValue("garbage"));

    }

    /// `DurationParseErrorOwned::to_shared` maps `ParseFloat(msg)` onto

    /// `DurationParseError::InvalidValue(msg)` — the variant is *not* preserved,

    /// so the error message ("invalid float literal") ends up in the slot that

    /// normally holds the offending source text. Pinned as the current behaviour;

    /// see the report accompanying this test module.

    #[cfg(feature = "parser")]

    #[test]

    fn to_shared_downgrades_parse_float_to_invalid_value() {

        let msg = parse_float_error().to_string();

        let owned = DurationParseErrorOwned::ParseFloat(msg.clone().into());

        let shared = owned.to_shared();

        assert!(!matches!(shared, DurationParseError::ParseFloat(_)));

        assert_eq!(shared, DurationParseError::InvalidValue(msg.as_str()));

    }

    #[cfg(feature = "parser")]

    #[test]

    fn to_shared_does_not_panic_on_empty_or_extreme_payloads() {

        assert_eq!(

            DurationParseErrorOwned::InvalidValue(String::new().into()).to_shared(),

            DurationParseError::InvalidValue("")

        );

        let huge = "y".repeat(100_000);

        let owned = DurationParseErrorOwned::InvalidValue(huge.clone().into());

        assert_eq!(owned.to_shared(), DurationParseError::InvalidValue(&huge));

        let empty_float = DurationParseErrorOwned::ParseFloat(String::new().into());

        assert_eq!(empty_float.to_shared(), DurationParseError::InvalidValue(""));

    }

    /// A real error straight out of the parser must survive the owned round-trip

    /// (this is the FFI path: borrow -> own -> borrow).

    #[cfg(feature = "parser")]

    #[test]

    fn invalid_value_survives_a_full_shared_owned_shared_round_trip() {

        let input = "10px";

        let err = parse_duration(input).unwrap_err();

        assert_eq!(err, DurationParseError::InvalidValue(input));

        let owned = err.to_contained();

        assert_eq!(owned.to_shared(), DurationParseError::InvalidValue(input));

    }

    /// `"200 nanoseconds"` ends in `s`, so it goes down the *seconds* branch and

    /// fails in the float parse — not the "unknown unit" branch. Pinning this

    /// keeps the two error variants from being swapped by accident.

    #[cfg(feature = "parser")]

    #[test]

    fn a_word_ending_in_s_is_treated_as_a_seconds_value() {

        assert!(matches!(

            parse_duration("200 nanoseconds"),

            Err(DurationParseError::ParseFloat(_))

        ));

        assert!(matches!(

            parse_duration("always"),

            Err(DurationParseError::ParseFloat(_))

        ));

        // ...whereas a word *not* ending in s/ms is an unknown-unit error.

        assert_eq!(

            parse_duration("200 nanosecond"),

            Err(DurationParseError::InvalidValue("200 nanosecond"))

        );

    }

    #[cfg(feature = "parser")]

    #[test]

    fn error_display_never_panics_and_mentions_the_offender() {

        let invalid = DurationParseError::InvalidValue("\u{1F600}");

        let printed = format!("{invalid}");

        assert!(printed.contains('\u{1F600}'), "{printed:?}");

        let float = DurationParseError::ParseFloat(parse_float_error());

        assert!(!format!("{float}").is_empty());

        // Debug is wired to Display; both must work on both variants.

        assert!(!format!("{invalid:?}").is_empty());

        assert!(!format!("{float:?}").is_empty());

    }

}