qubit-codec-text 0.1.0

// =============================================================================
//    Copyright (c) 2026 Haixing Hu.
//
//    SPDX-License-Identifier: Apache-2.0
//
//    Licensed under the Apache License, Version 2.0.
// =============================================================================
use core::fmt;
use std::error::Error;

use crate::{
    Charset,
    CharsetDecodeErrorKind,
};

/// Error reported by a charset decoder.
///
/// The error always carries the charset, error kind, and input unit index at
/// which the failure was detected. Errors that decode a raw numeric value, such
/// as invalid UTF-32 units, carry that value through [`Self::kind`] and
/// [`Self::value`]. Invalid-input errors may also carry a consumed-unit count
/// so buffered decoders can make progress without an extra status wrapper.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct CharsetDecodeError {
    /// Charset being decoded when this error was detected.
    charset: Charset,
    /// Failure category describing the decoding error.
    kind: CharsetDecodeErrorKind,
    /// Input unit index at which decoding failure occurred.
    index: usize,
    /// Units that may be consumed after invalid input.
    consumed: usize,
}

/// Result type returned by charset decoders.
///
/// # Type Parameters
///
/// - `T`: Successful value produced by a decoding operation.
pub type CharsetDecodeResult<T> = Result<T, CharsetDecodeError>;

impl CharsetDecodeError {
    /// Creates a decoding error.
    ///
    /// # Parameters
    ///
    /// - `charset`: The charset being decoded.
    /// - `kind`: The failure category.
    /// - `index`: The input unit index where the failure was detected.
    ///
    /// # Returns
    ///
    /// Returns a decoding error carrying the supplied context.
    #[inline(always)]
    pub const fn new(
        charset: Charset,
        kind: CharsetDecodeErrorKind,
        index: usize,
    ) -> Self {
        Self {
            charset,
            kind,
            index,
            consumed: 1,
        }
    }

    /// Returns a copy of this error with invalid-input consumption context.
    ///
    /// # Parameters
    ///
    /// - `consumed`: Number of units that may be consumed to make progress.
    ///
    /// # Returns
    ///
    /// Returns this error carrying the supplied consumption count.
    #[must_use]
    #[inline(always)]
    pub const fn with_consumed(self, consumed: usize) -> Self {
        Self {
            charset: self.charset,
            kind: self.kind,
            index: self.index,
            consumed,
        }
    }

    /// Returns the charset being decoded.
    ///
    /// # Returns
    ///
    /// Returns the stored [`Charset`].
    #[inline(always)]
    pub const fn charset(self) -> Charset {
        self.charset
    }

    /// Returns the decoding error kind.
    ///
    /// # Returns
    ///
    /// Returns the stored [`CharsetDecodeErrorKind`].
    #[inline(always)]
    pub const fn kind(self) -> CharsetDecodeErrorKind {
        self.kind
    }

    /// Returns the input unit index associated with this error.
    ///
    /// # Returns
    ///
    /// Returns the index at which the error was detected.
    #[inline(always)]
    pub const fn index(self) -> usize {
        self.index
    }

    /// Returns required input units for this decoding error, if reported.
    ///
    /// # Returns
    ///
    /// Returns `Some(required)` for
    /// [`CharsetDecodeErrorKind::IncompleteSequence`], otherwise `None`.
    #[inline(always)]
    pub const fn required(self) -> Option<usize> {
        self.kind.required()
    }

    /// Returns available input units for this decoding error, if reported.
    ///
    /// # Returns
    ///
    /// Returns `Some(available)` for
    /// [`CharsetDecodeErrorKind::IncompleteSequence`], otherwise `None`.
    #[inline(always)]
    pub const fn available(self) -> Option<usize> {
        self.kind.available()
    }

    /// Returns input length for this decoding error, if reported.
    ///
    /// # Returns
    ///
    /// Returns `Some(input_len)` for
    /// [`CharsetDecodeErrorKind::InvalidInputIndex`], otherwise `None`.
    #[inline(always)]
    pub const fn input_len(self) -> Option<usize> {
        self.kind.input_len()
    }

    /// Returns output length for this decoding error, if reported.
    ///
    /// # Returns
    ///
    /// Returns `Some(output_len)` for
    /// [`CharsetDecodeErrorKind::InvalidOutputIndex`], otherwise `None`.
    #[inline(always)]
    pub const fn output_len(self) -> Option<usize> {
        self.kind.output_len()
    }

    /// Returns the raw value associated with this error.
    ///
    /// # Returns
    ///
    /// Returns `Some(value)` when the error kind carries a raw unit or code
    /// point value, or `None` for kinds without an associated value.
    #[inline(always)]
    pub const fn value(self) -> Option<u32> {
        self.kind.value()
    }

    /// Returns units that may be consumed after this invalid-input error.
    ///
    /// # Returns
    ///
    /// Returns `Some(consumed)` for malformed and invalid-code-point input, or
    /// `None` for incomplete input and invalid caller indexes.
    #[inline(always)]
    pub const fn consumed(self) -> Option<usize> {
        match self.kind {
            CharsetDecodeErrorKind::MalformedSequence { .. }
            | CharsetDecodeErrorKind::InvalidCodePoint { .. } => {
                Some(self.consumed)
            }
            CharsetDecodeErrorKind::IncompleteSequence { .. }
            | CharsetDecodeErrorKind::InvalidInputIndex { .. }
            | CharsetDecodeErrorKind::InvalidOutputIndex { .. } => None,
        }
    }

    /// Offsets this error by a base unit index.
    ///
    /// # Parameters
    ///
    /// - `base`: The base index to add to the stored index.
    ///
    /// # Returns
    ///
    /// Returns a copy of this error with its index shifted by `base`.
    ///
    /// If the shifted index cannot be represented, it is saturated to
    /// [`usize::MAX`].
    #[inline(always)]
    pub const fn offset_by(self, base: usize) -> Self {
        Self {
            charset: self.charset,
            kind: self.kind,
            index: match self.index.checked_add(base) {
                Some(index) => index,
                None => usize::MAX,
            },
            consumed: self.consumed,
        }
    }
}

impl fmt::Display for CharsetDecodeError {
    /// Formats this decoding error.
    ///
    /// # Parameters
    ///
    /// - `formatter`: The formatter receiving the diagnostic message.
    ///
    /// # Errors
    ///
    /// Returns any formatting error reported by `formatter`.
    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
        if let Some(value) = self.kind.value() {
            write!(
                formatter,
                "{} decoding error at index {} for value 0x{:x}: {}",
                self.charset, self.index, value, self.kind,
            )
        } else {
            write!(
                formatter,
                "{} decoding error at index {}: {}",
                self.charset, self.index, self.kind,
            )
        }
    }
}

impl Error for CharsetDecodeError {}