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//! Operations on the WebTransport streams.

use core::future::Future;

use crate::utils::{maybe, Error};

/// Read the data from the stream.
pub trait Read: maybe::Send {
    /// An error that can occur while reading the stream.
    type Error: Error + maybe::Send + maybe::Sync + 'static;

    /// Read the data from the stream into a given buffer and return the amount
    /// of bytes filled in the buffer or `None` if the stream is closed and does
    /// not have any pending unread data.
    fn read(
        &mut self,
        buf: &mut [u8],
    ) -> impl Future<Output = Result<Option<usize>, Self::Error>> + maybe::Send;
}

/// Write the data to a stream.
pub trait Write: maybe::Send {
    /// An error that can occur while writing to the stream.
    type Error: Error + maybe::Send + maybe::Sync + 'static;

    /// Write the data from the given buffer into the stream, returning
    /// the amount of of bytes that were successfully written into the stream.
    /// If the returned amount is smaller than the size of the data that was
    /// being written, the user should try writing the remaining data again.
    fn write(
        &mut self,
        buf: &[u8],
    ) -> impl Future<Output = Result<usize, Self::Error>> + maybe::Send;
}

/// An chunk of data with an explicit offset in the stream.
#[derive(Debug)]
pub struct Chunk<Data> {
    /// The offset of the data in the stream.
    pub offset: u64,
    /// The data.
    pub data: Data,
}

/// Read a [`Chunk`] from a stream.
pub trait ReadChunk<ChunkType: ?Sized + ReadableChunk>: maybe::Send {
    /// An error that can occur while reading a chunk from the stream.
    type Error: Error + maybe::Send + maybe::Sync + 'static;

    /// Read the data with the offset information from a stream.
    fn read_chunk(
        &mut self,
        max_length: usize,
        ordered: bool,
    ) -> impl Future<
        Output = Result<Option<Chunk<<ChunkType as ReadableChunk>::Data<'_>>>, Self::Error>,
    > + maybe::Send;
}

/// Write a [`Chunk`] to a stream.
pub trait WriteChunk<ChunkType: ?Sized + WriteableChunk>: maybe::Send {
    /// An error that can occur while writing the chunk to a stream.
    type Error: Error + maybe::Send + maybe::Sync + 'static;

    /// Write the data with the offset information from a stream.
    fn write_chunk<'a>(
        &'a mut self,
        buf: <ChunkType as WriteableChunk>::Data<'a>,
    ) -> impl Future<Output = Result<(), Self::Error>> + 'a + maybe::Send;
}

/// Something that specifies the data type for a [`Chunk`] that can
/// be read from a stream.
pub trait ReadableChunk: maybe::Send {
    /// The type that will hold the read data.
    type Data<'a>: AsRef<[u8]>;
}

/// Something that specifies the data type for a [`Chunk`] that can
/// be written to a stream.
pub trait WriteableChunk: maybe::Send {
    /// The type that will hold the data to write.
    type Data<'a>: From<&'a [u8]>;
}

#[cfg(feature = "alloc")]
pub mod chunk {
    //! Provided [`ReadableChunk`] and [`WriteableChunk`] implementations.

    use super::*;

    /// A chunk type that represents operations that carry the data as [`u8`]
    /// [`slice`]s or [`alloc::vec::Vec`]s
    #[derive(Debug)]
    pub struct U8;

    impl WriteableChunk for U8 {
        type Data<'b> = &'b [u8];
    }

    impl ReadableChunk for U8 {
        type Data<'b> = alloc::vec::Vec<u8>;
    }
}