qubit-io 0.14.1

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

use std::pin::Pin;
use std::task::{
    Context,
    Poll,
};

use futures_io::AsyncWrite;

use crate::{
    AsyncClose,
    traits::normalize_async_error,
};

/// Exposes a Qubit byte [`crate::AsyncOutput`] as a futures-io [`AsyncWrite`].
///
/// # Type Parameters
///
/// - `O`: Qubit byte output type.
#[must_use]
#[repr(transparent)]
pub struct FuturesAsyncWrite<O> {
    /// Qubit byte output exposed through futures-io.
    inner: O,
}

impl<O> FuturesAsyncWrite<O> {
    /// Creates a futures-io writer around a Qubit byte output.
    ///
    /// # Parameters
    ///
    /// - `inner`: Qubit byte output to expose.
    ///
    /// # Returns
    ///
    /// Returns a futures-io writer adapter that owns `inner`.
    #[inline(always)]
    pub const fn new(inner: O) -> Self {
        Self { inner }
    }

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

    /// Returns a mutable reference to the wrapped output.
    ///
    /// # Returns
    ///
    /// Returns the wrapped Qubit output with mutable access.
    #[inline(always)]
    #[must_use]
    pub const fn get_mut(&mut self) -> &mut O {
        &mut self.inner
    }

    /// Projects a pinned adapter to its pinned wrapped output.
    ///
    /// # Returns
    ///
    /// Returns a pinned mutable reference to the wrapped Qubit output without
    /// moving it.
    #[inline(always)]
    #[must_use]
    pub fn get_pin_mut(self: Pin<&mut Self>) -> Pin<&mut O> {
        // 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 output.
    ///
    /// # Returns
    ///
    /// Returns the owned Qubit output.
    #[inline(always)]
    #[must_use]
    pub fn into_inner(self) -> O {
        self.inner
    }
}

impl<O> AsyncWrite for FuturesAsyncWrite<O>
where
    O: AsyncClose<Item = u8>,
{
    /// Polls one futures-io write through the wrapped Qubit output.
    ///
    /// # Parameters
    ///
    /// - `cx`: Task context used to register a wake-up.
    /// - `input`: Source byte slice.
    ///
    /// # Returns
    ///
    /// Returns [`Poll::Pending`] when the output is not ready. A ready result
    /// contains the number of bytes accepted.
    ///
    /// # Errors
    ///
    /// Returns an I/O error reported by the wrapped output.
    #[inline(always)]
    fn poll_write(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        input: &[u8],
    ) -> Poll<std::io::Result<usize>> {
        self.get_pin_mut().poll_write(cx, input)
    }

    /// Polls flushing through the wrapped Qubit output.
    ///
    /// # 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 I/O error reported by the wrapped output. Invalid
    /// asynchronous error kinds are normalized to
    /// [`std::io::ErrorKind::InvalidData`].
    #[inline(always)]
    fn poll_flush(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
    ) -> Poll<std::io::Result<()>> {
        self.get_pin_mut()
            .poll_flush(cx)
            .map(|result| result.map_err(normalize_async_error))
    }

    /// Polls closing through the wrapped Qubit 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 I/O error reported by the wrapped output. Invalid
    /// asynchronous error kinds are normalized to
    /// [`std::io::ErrorKind::InvalidData`].
    #[inline(always)]
    fn poll_close(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
    ) -> Poll<std::io::Result<()>> {
        self.get_pin_mut()
            .poll_close(cx)
            .map(|result| result.map_err(normalize_async_error))
    }
}