qubit-io 0.11.1

// =============================================================================
//    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,
    Write,
};

/// Extension methods for values that implement both [`Write`] and [`Seek`].
///
/// `WriteSeekExt` provides position-preserving write helpers for random-access
/// output use cases such as patching headers, offsets, and indexes after a
/// stream has already been written.
pub trait WriteSeekExt: Write + Seek {
    /// Writes all bytes at `offset` and restores the original position.
    ///
    /// This method seeks to `offset`, delegates to [`Write::write_all`], and
    /// then restores the position that was current before the call.
    ///
    /// # Parameters
    /// - `offset`: Absolute byte offset from the start of the stream.
    /// - `buffer`: Bytes to write.
    ///
    /// # Errors
    /// Returns an error when reading the current position, seeking to `offset`,
    /// writing bytes, or restoring the original position fails. If restoration
    /// fails, the restoration error is returned.
    fn write_all_at_preserving_position(
        &mut self,
        offset: u64,
        buffer: &[u8],
    ) -> Result<()>;
}

impl<T> WriteSeekExt for T
where
    T: Write + Seek + ?Sized,
{
    #[inline]
    fn write_all_at_preserving_position(
        &mut self,
        offset: u64,
        buffer: &[u8],
    ) -> Result<()> {
        let position = self.stream_position()?;
        let write_result = match self.seek(SeekFrom::Start(offset)) {
            Ok(_) => self.write_all(buffer),
            Err(error) => Err(error),
        };
        let restore_result = self.seek(SeekFrom::Start(position));
        match (write_result, restore_result) {
            (Ok(()), Ok(_)) => Ok(()),
            (Err(error), Ok(_)) => Err(error),
            (_, Err(error)) => Err(error),
        }
    }
}