fasrt 0.4.0

A blazing fast, zero-copy subtitle parser and writer for SRT and WebVTT in Rust.
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use core::num::ParseIntError;
use derive_more::{IsVariant, TryUnwrap, Unwrap};

/// The error type for parsing minute components of timestamps.
#[derive(Debug, Clone, PartialEq, Eq, IsVariant, Unwrap, TryUnwrap, thiserror::Error)]
#[unwrap(ref, ref_mut)]
#[try_unwrap(ref, ref_mut)]
pub enum ParseMinuteError {
  /// The minute component is not zero-padded to 2 digits.
  #[error("minute component is not zero-padded to 2 digits")]
  #[unwrap(ignore)]
  #[try_unwrap(ignore)]
  NotPadded,
  /// The minute component is out of range (not between 0-59).
  #[error("minute component must be between 0-59, but was {0}")]
  Overflow(u8),
  /// Not a valid number.
  #[error(transparent)]
  ParseInt(#[from] ParseIntError),
}

/// The error type for parsing second components of timestamps.
#[derive(Debug, Clone, PartialEq, Eq, IsVariant, Unwrap, TryUnwrap, thiserror::Error)]
#[unwrap(ref, ref_mut)]
#[try_unwrap(ref, ref_mut)]
pub enum ParseSecondError {
  /// The second component is not zero-padded to 2 digits.
  #[error("second component is not zero-padded to 2 digits")]
  #[unwrap(ignore)]
  #[try_unwrap(ignore)]
  NotPadded,
  /// The second component is out of range (not between 0-59).
  #[error("second component must be between 0-59, but was {0}")]
  Overflow(u8),
  /// Not a valid number.
  #[error(transparent)]
  ParseInt(#[from] ParseIntError),
}

/// The error type for parsing hour components of timestamps.
///
/// This enum is shared by the SRT, WebVTT and ASS/SSA parsers:
/// - **SRT** hours are 2–3 digits (0–999): uses [`NotPadded`](Self::NotPadded)
///   and [`Overflow(u16)`](Self::Overflow).
/// - **WebVTT** hours are unbounded (`u64`): uses [`NotPadded`](Self::NotPadded)
///   for non-digit input and [`HourOverflow`](Self::HourOverflow) when the
///   value exceeds `u64::MAX`.
/// - **ASS/SSA** hours are one or more digits and are *not* zero-padded
///   (`0:00:00.00`): uses [`NotPadded`](Self::NotPadded) for non-digit input
///   and [`HourOverflow`](Self::HourOverflow) when the value exceeds
///   `u64::MAX`.
#[derive(Debug, Clone, PartialEq, Eq, IsVariant, Unwrap, TryUnwrap, thiserror::Error)]
#[unwrap(ref, ref_mut)]
#[try_unwrap(ref, ref_mut)]
pub enum ParseHourError {
  /// The hour component is not zero-padded to 2 digits (SRT),
  /// or contains non-digit characters (VTT).
  #[error("hour component is not zero-padded to 2 digits or contains invalid characters")]
  #[unwrap(ignore)]
  #[try_unwrap(ignore)]
  NotPadded,
  /// The hour component is out of the SRT range (0–999).
  #[error("hour component must be between 0-999, but was {0}")]
  Overflow(u16),
  /// The hour component overflowed `u64` (VTT unbounded hours).
  #[error("hour component overflowed")]
  #[unwrap(ignore)]
  #[try_unwrap(ignore)]
  HourOverflow,
  /// Not a valid number.
  #[error(transparent)]
  ParseInt(#[from] ParseIntError),
}

/// The error type for parsing millisecond components of timestamps.
#[derive(Debug, Clone, PartialEq, Eq, IsVariant, Unwrap, TryUnwrap, thiserror::Error)]
#[unwrap(ref, ref_mut)]
#[try_unwrap(ref, ref_mut)]
pub enum ParseMillisecondError {
  /// The millisecond component is not zero-padded to 3 digits.
  #[error("millisecond component is not zero-padded to 3 digits")]
  #[unwrap(ignore)]
  #[try_unwrap(ignore)]
  NotPadded,
  /// The millisecond component is out of range (not between 0-999).
  #[error("millisecond component must be between 0-999, but was {0}")]
  Overflow(u16),
  /// Not a valid number.
  #[error(transparent)]
  ParseInt(#[from] ParseIntError),
}

/// The error type for parsing centisecond components of timestamps.
///
/// Centiseconds are the sub-second unit of ASS/SSA timestamps
/// (`H:MM:SS.cc`), where `cc` is always exactly two digits.
#[derive(Debug, Clone, PartialEq, Eq, IsVariant, Unwrap, TryUnwrap, thiserror::Error)]
#[unwrap(ref, ref_mut)]
#[try_unwrap(ref, ref_mut)]
pub enum ParseCentisecondError {
  /// The centisecond component is not zero-padded to 2 digits.
  #[error("centisecond component is not zero-padded to 2 digits")]
  #[unwrap(ignore)]
  #[try_unwrap(ignore)]
  NotPadded,
  /// The centisecond component is out of range (not between 0-99).
  #[error("centisecond component must be between 0-99, but was {0}")]
  Overflow(u8),
  /// Not a valid number.
  #[error(transparent)]
  ParseInt(#[from] ParseIntError),
}

/// Specific reason why a timestamp has invalid structure.
///
/// This covers structural validation errors only (length, separators, digits).
/// Component range errors (hours, minutes, seconds, milliseconds,
/// centiseconds) are represented by their dedicated error types
/// ([`ParseHourError`], [`ParseMinuteError`], [`ParseSecondError`],
/// [`ParseMillisecondError`], [`ParseCentisecondError`]) which are separate
/// variants of [`crate::vtt::ParseVttError`] and
/// [`crate::ass::ParseAssError`].
#[derive(Debug, Clone, Copy, PartialEq, Eq, thiserror::Error)]
pub enum TimestampError {
  /// The input is too short or has an invalid length for the timestamp form
  /// being parsed.
  #[error("invalid length")]
  InvalidLength,
  /// A separator (`.` or `:`) is not in the expected position.
  #[error("invalid format")]
  InvalidFormat,
  /// One or more digit positions contain non-digit bytes.
  #[error("invalid digits")]
  InvalidDigits,
}

/// The error returned when cue text nests deeper than the configured limit.
///
/// WebVTT places no bound on how deeply a cue payload may nest, and the depth
/// is chosen by the file rather than by the caller. A tree is walked
/// recursively by [`Clone`], [`PartialEq`], [`core::fmt::Debug`],
/// [`core::fmt::Display`] and by the compiler's own drop glue, so an unbounded
/// tree lets a hostile cue overflow the stack — an abort, which no caller can
/// catch. [`CueText::try_parse`] refuses such input instead.
///
/// [`CueText::try_parse`]: crate::vtt::cue::CueText::try_parse
#[cfg(any(feature = "alloc", feature = "std"))]
#[cfg_attr(docsrs, doc(cfg(any(feature = "alloc", feature = "std"))))]
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, thiserror::Error)]
#[error("cue text nests deeper than the maximum depth of {max_depth}")]
pub struct MaxDepthExceededError {
  max_depth: usize,
}

#[cfg(any(feature = "alloc", feature = "std"))]
impl MaxDepthExceededError {
  #[cfg_attr(not(tarpaulin), inline(always))]
  pub(crate) const fn new(max_depth: usize) -> Self {
    Self { max_depth }
  }

  /// Returns the maximum depth that the input exceeded.
  ///
  /// ```rust
  /// # #[cfg(any(feature = "alloc", feature = "std"))]
  /// # {
  /// use fasrt::vtt::cue::{CueText, Options};
  ///
  /// let deep = "<i>".repeat(4);
  /// let err = CueText::try_parse_with(&deep, Options::new().with_max_depth(2))
  ///   .unwrap_err();
  /// assert_eq!(err.max_depth(), 2);
  /// # }
  /// ```
  #[cfg_attr(not(tarpaulin), inline(always))]
  pub const fn max_depth(&self) -> usize {
    self.max_depth
  }
}

/// The error type for parsing index numbers of subtitles.
#[derive(Debug, Clone, PartialEq, Eq, IsVariant, Unwrap, TryUnwrap, thiserror::Error)]
#[unwrap(ref, ref_mut)]
#[try_unwrap(ref, ref_mut)]
pub enum ParseIndexNumberError {
  /// The index number is zero, which is invalid (must be between 1-18446744073709551615).
  #[error("index number cannot be zero")]
  Zero,
  /// The index number is out of range (not between 1-18446744073709551615).
  #[error("index number must be between 1-18446744073709551615")]
  Overflow,
  /// Not a valid index number.
  #[error(transparent)]
  ParseInt(#[from] ParseIntError),
}