qubit-io 0.19.4

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

use std::io::Result;
use std::pin::Pin;
use std::task::Context;
use std::task::Poll;

use futures_io::AsyncRead;

use crate::AsyncInput;
use crate::traits::normalize_async_error;
use crate::util::UncheckedSlice;

/// Adapts a futures-io [`AsyncRead`] value to Qubit's [`AsyncInput`].
///
/// # Type Parameters
///
/// - `T`: Futures-io reader type.
///
/// # Examples
///
/// ```
/// use futures_io::AsyncRead;
/// use qubit_io::AsyncInput;
/// use qubit_io::FuturesInput;
/// use std::io::Result;
/// use std::pin::Pin;
/// use std::sync::Arc;
/// use std::task::Context;
/// use std::task::Poll;
/// use std::task::Wake;
/// use std::task::Waker;
///
/// struct OneByteReader;
///
/// impl AsyncRead for OneByteReader {
///     fn poll_read(
///         self: Pin<&mut Self>,
///         _cx: &mut Context<'_>,
///         output: &mut [u8],
///     ) -> Poll<Result<usize>> {
///         output[0] = b'x';
///         Poll::Ready(Ok(1))
///     }
/// }
///
/// struct NoopWake;
///
/// impl Wake for NoopWake {
///     fn wake(self: Arc<Self>) {}
/// }
///
/// let mut input = FuturesInput::new(OneByteReader);
/// let waker = Waker::from(Arc::new(NoopWake));
/// let mut context = Context::from_waker(&waker);
/// let mut output = [0; 1];
/// assert!(matches!(
///     unsafe {
///         AsyncInput::poll_read_unchecked(
///             Pin::new(&mut input),
///             &mut context,
///             &mut output,
///             0,
///             1,
///         )
///     },
///     Poll::Ready(Ok(1)),
/// ));
/// assert_eq!(output, [b'x']);
/// ```
#[must_use]
#[repr(transparent)]
pub struct FuturesInput<T> {
    /// Futures-io reader adapted as a Qubit input.
    inner: T,
}

impl<T> FuturesInput<T> {
    /// Creates an adapter around a futures-io reader.
    ///
    /// # Parameters
    ///
    /// - `inner`: Futures-io reader to adapt.
    ///
    /// # Returns
    ///
    /// Returns a Qubit input adapter that owns `inner`.
    #[inline(always)]
    pub const fn new(inner: T) -> Self {
        Self { inner }
    }

    /// Returns a shared reference to the wrapped reader.
    ///
    /// # Returns
    ///
    /// Returns the wrapped futures-io reader.
    #[inline(always)]
    #[must_use = "the wrapped reader reference must be used"]
    pub const fn get_ref(&self) -> &T {
        &self.inner
    }

    /// Returns a mutable reference to the wrapped reader.
    ///
    /// # Returns
    ///
    /// Returns the wrapped futures-io reader with mutable access.
    #[inline(always)]
    #[must_use = "the wrapped reader reference must be used"]
    pub const fn get_mut(&mut self) -> &mut T {
        &mut self.inner
    }

    /// Projects a pinned adapter to its pinned wrapped reader.
    ///
    /// # Returns
    ///
    /// Returns a pinned mutable reference to the wrapped reader without moving
    /// it.
    #[inline(always)]
    #[must_use = "the pinned reader reference must be used"]
    pub fn get_pin_mut(self: Pin<&mut Self>) -> Pin<&mut T> {
        // SAFETY: The projection does not move `inner`, and the transparent
        // adapter never exposes a way to replace a pinned inner value.
        unsafe { self.map_unchecked_mut(|this| &mut this.inner) }
    }

    /// Consumes the adapter and returns the wrapped reader.
    ///
    /// # Returns
    ///
    /// Returns the owned futures-io reader.
    #[inline(always)]
    #[must_use = "the wrapped reader must be used"]
    pub fn into_inner(self) -> T {
        self.inner
    }
}

impl<T> AsyncInput for FuturesInput<T>
where
    T: AsyncRead,
{
    /// Byte item produced by a futures-io reader.
    type Item = u8;

    /// Polls an indexed read through the wrapped futures-io reader.
    ///
    /// A zero-length request completes immediately without polling `inner`.
    ///
    /// # Parameters
    ///
    /// - `cx`: Task context used to register a wake-up.
    /// - `output`: Destination byte slice.
    /// - `index`: Starting destination index.
    /// - `count`: Maximum number of bytes to read.
    ///
    /// # Returns
    ///
    /// Returns [`Poll::Pending`] when the reader is not ready. A ready result
    /// contains the number of bytes read.
    ///
    /// # Errors
    ///
    /// Returns an I/O error reported by the wrapped reader. Invalid
    /// asynchronous error kinds are normalized to
    /// [`std::io::ErrorKind::InvalidData`].
    ///
    /// # Panics
    ///
    /// Panics in debug builds if the requested output range does not fit.
    ///
    /// # Safety
    ///
    /// The range `index..index + count` must be valid for `output`.
    #[inline]
    unsafe fn poll_read_unchecked(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        output: &mut [u8],
        index: usize,
        count: usize,
    ) -> Poll<Result<usize>> {
        if count == 0 {
            return Poll::Ready(Ok(0));
        }
        // SAFETY: The caller guarantees that the destination range is valid.
        let target = unsafe { UncheckedSlice::subslice_mut(output, index, count) };
        AsyncRead::poll_read(self.get_pin_mut(), cx, target).map(|result| result.map_err(normalize_async_error))
    }
}