qubit-io 0.13.0

// =============================================================================
//    Copyright (c) 2026 Haixing Hu.
//
//    SPDX-License-Identifier: Apache-2.0
//
//    Licensed under the Apache License, Version 2.0.
// =============================================================================
use std::io::{
    Result,
    Seek,
    SeekFrom,
};

/// Extension methods for [`Seek`] values.
///
/// `SeekExt` provides stable, position-preserving helpers for seekable streams.
/// The methods are implemented for every type that implements [`Seek`],
/// including `dyn Seek` trait objects.
pub trait SeekExt: Seek {
    /// Gets the stream size without changing the final stream position.
    ///
    /// The original position is captured with [`Seek::stream_position`], then
    /// the stream is moved to the end to measure its size, and finally the
    /// original position is restored.
    ///
    /// # Compatibility
    /// If the standard library adds an equivalent `Seek::stream_size` method,
    /// this extension method may be deprecated in a future release.
    ///
    /// # Returns
    /// The stream size in bytes.
    ///
    /// # Errors
    /// Returns an error when reading the current position, seeking to the end,
    /// or restoring the original position fails. If restoring fails, the
    /// restore error is returned because the caller's stream position contract
    /// was not preserved.
    fn stream_size(&mut self) -> Result<u64>;
}

impl<T> SeekExt for T
where
    T: Seek + ?Sized,
{
    #[inline]
    fn stream_size(&mut self) -> Result<u64> {
        let position = self.stream_position()?;
        let size_result = self.seek(SeekFrom::End(0));
        let restore_result = self.seek(SeekFrom::Start(position));
        match (size_result, restore_result) {
            (Ok(size), Ok(_)) => Ok(size),
            (Err(error), Ok(_)) => Err(error),
            (_, Err(error)) => Err(error),
        }
    }
}