qubit-io 0.17.0

// =============================================================================
//    Copyright (c) 2026 Haixing Hu.
//
//    SPDX-License-Identifier: Apache-2.0
//
//    Licensed under the Apache License, Version 2.0.
// =============================================================================

use std::hash::Hasher;
use std::io;
use std::pin::Pin;
use std::task::Context;
use std::task::Poll;

use crate::AsyncClose;
use crate::AsyncOutput;
use crate::traits::normalize_async_error;

/// Asynchronous byte output that hashes successfully accepted bytes.
///
/// Pending and failed writes do not change the hasher. The checksum algorithm
/// and stability guarantees are those of the supplied [`Hasher`].
///
/// # Type Parameters
///
/// - `O`: Wrapped asynchronous byte output type.
/// - `H`: Checksum hasher type.
#[must_use]
#[derive(Debug)]
pub struct AsyncChecksumOutput<O, H> {
    /// Output whose successful writes are hashed.
    inner: O,
    /// Hasher tracking accepted bytes.
    hasher: H,
}

impl<O, H> AsyncClose for AsyncChecksumOutput<O, H>
where
    O: AsyncClose<Item = u8>,
    H: Hasher,
{
    /// Polls closing through the wrapped output.
    ///
    /// # Parameters
    ///
    /// - `cx`: Task context used to register a wake-up.
    ///
    /// # Returns
    ///
    /// Returns [`Poll::Pending`] while closing is incomplete, otherwise a
    /// ready success result.
    ///
    /// # Errors
    ///
    /// Returns an error reported by the wrapped output. Invalid asynchronous
    /// error kinds are normalized to [`io::ErrorKind::InvalidData`].
    #[inline(always)]
    fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
        // SAFETY: `inner` is never moved while projecting this pinned wrapper.
        let this = unsafe { self.get_unchecked_mut() };
        // SAFETY: The pinned wrapper keeps `inner` at a stable address.
        unsafe { Pin::new_unchecked(&mut this.inner) }
            .poll_close(cx)
            .map(|result| result.map_err(normalize_async_error))
    }
}

impl<O, H> AsyncChecksumOutput<O, H>
where
    H: Hasher,
{
    /// Creates a checksum-tracking asynchronous output.
    ///
    /// # Parameters
    ///
    /// - `inner`: Asynchronous byte output to wrap.
    /// - `hasher`: Hasher updated after successful writes.
    ///
    /// # Returns
    ///
    /// Returns an output with the supplied initial hasher state.
    #[inline(always)]
    pub const fn new(inner: O, hasher: H) -> Self {
        Self { inner, hasher }
    }

    /// Returns the current checksum value.
    ///
    /// # Returns
    ///
    /// Returns [`Hasher::finish`] for the current state.
    #[inline(always)]
    #[must_use]
    pub fn checksum(&self) -> u64 {
        self.hasher.finish()
    }

    /// Returns a shared reference to the wrapped output.
    ///
    /// # Returns
    ///
    /// Returns the wrapped asynchronous byte output.
    #[inline(always)]
    #[must_use]
    pub const fn inner(&self) -> &O {
        &self.inner
    }

    /// Returns a mutable reference to the wrapped output.
    ///
    /// Writes performed directly on the returned output do not update this
    /// wrapper's hasher.
    ///
    /// # Returns
    ///
    /// Returns the wrapped asynchronous byte output.
    #[inline(always)]
    #[must_use]
    pub fn inner_mut(&mut self) -> &mut O {
        &mut self.inner
    }

    /// Returns a shared reference to the hasher.
    ///
    /// # Returns
    ///
    /// Returns the current hasher state.
    #[inline(always)]
    #[must_use]
    pub const fn hasher(&self) -> &H {
        &self.hasher
    }

    /// Returns a mutable reference to the hasher.
    ///
    /// Mutating the returned hasher changes the checksum independently of
    /// bytes written through this wrapper.
    ///
    /// # Returns
    ///
    /// Returns the current hasher state mutably.
    #[inline(always)]
    #[must_use]
    pub fn hasher_mut(&mut self) -> &mut H {
        &mut self.hasher
    }

    /// Consumes this wrapper without flushing the wrapped output.
    ///
    /// This method does not call [`AsyncOutput::flush_async`] and performs no
    /// asynchronous I/O. Any buffering owned by the returned output remains
    /// pending and unchanged.
    ///
    /// # Returns
    ///
    /// Returns the wrapped output and final hasher state.
    #[inline(always)]
    #[must_use]
    pub fn into_parts(self) -> (O, H) {
        (self.inner, self.hasher)
    }
}

impl<O, H> AsyncOutput for AsyncChecksumOutput<O, H>
where
    O: AsyncOutput<Item = u8>,
    H: Hasher,
{
    /// Byte item hashed after successful writes.
    type Item = u8;

    /// Preserves the wrapped output's buffering declaration.
    ///
    /// # Returns
    ///
    /// Returns the wrapped output's buffering declaration.
    #[inline(always)]
    fn is_buffered(&self) -> bool {
        self.inner.is_buffered()
    }

    /// Polls a write and hashes only bytes in a successful ready result.
    ///
    /// # Parameters
    ///
    /// - `cx`: Task context used to register a wake-up.
    /// - `input`: Source byte slice.
    /// - `index`: Starting source index.
    /// - `count`: Maximum number of bytes to write.
    ///
    /// # Returns
    ///
    /// Returns [`Poll::Pending`] when the output is not ready. A ready success
    /// contains the number of bytes accepted and hashed.
    ///
    /// # Errors
    ///
    /// Returns an I/O error reported by the wrapped output without changing the
    /// hasher.
    ///
    /// # Safety
    ///
    /// The range `index..index + count` must be valid for `input`.
    unsafe fn poll_write_unchecked(
        mut self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        input: &[u8],
        index: usize,
        count: usize,
    ) -> Poll<io::Result<usize>> {
        // SAFETY: `inner` is never moved while projecting this pinned wrapper.
        let this = unsafe { self.as_mut().get_unchecked_mut() };
        let source = &input[index..index + count];
        // SAFETY: The pinned wrapper keeps `inner` at a stable address.
        let inner = unsafe { Pin::new_unchecked(&mut this.inner) };
        match inner.poll_write(cx, source) {
            Poll::Ready(Ok(written)) => {
                this.hasher.write(&input[index..index + written]);
                Poll::Ready(Ok(written))
            }
            Poll::Ready(Err(error)) => Poll::Ready(Err(error)),
            Poll::Pending => Poll::Pending,
        }
    }

    /// Polls the wrapped output's flush operation.
    ///
    /// # Parameters
    ///
    /// - `cx`: Task context used to register a wake-up.
    ///
    /// # Returns
    ///
    /// Returns [`Poll::Pending`] while flushing is incomplete, otherwise a
    /// ready success result.
    ///
    /// # Errors
    ///
    /// Returns an error reported by the wrapped output. Invalid asynchronous
    /// error kinds are normalized to [`io::ErrorKind::InvalidData`].
    #[inline(always)]
    fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
        // SAFETY: `inner` is never moved while projecting this pinned wrapper.
        let this = unsafe { self.get_unchecked_mut() };
        // SAFETY: The pinned wrapper keeps `inner` at a stable address.
        unsafe { Pin::new_unchecked(&mut this.inner) }
            .poll_flush(cx)
            .map(|result| result.map_err(normalize_async_error))
    }
}