use std::io;

use serde::{Serialize, de::DeserializeOwned};
use tokio::io::{AsyncRead, AsyncReadExt, AsyncWrite, AsyncWriteExt};

const MAX_FRAME_SIZE: usize = 1024 * 1024;

pub async fn write_frame<W, T>(writer: &mut W, value: &T) -> io::Result<()>
where
    W: AsyncWrite + Unpin,
    T: Serialize,
{
    let payload = serde_json::to_vec(value)
        .map_err(|e| io::Error::new(io::ErrorKind::InvalidData, e.to_string()))?;
    if payload.len() > MAX_FRAME_SIZE {
        return Err(io::Error::new(
            io::ErrorKind::InvalidInput,
            "frame exceeds max size",
        ));
    }
    writer.write_u32(payload.len() as u32).await?;
    writer.write_all(&payload).await?;
    writer.flush().await
}

pub async fn read_frame<R, T>(reader: &mut R) -> io::Result<T>
where
    R: AsyncRead + Unpin,
    T: DeserializeOwned,
{
    let len = reader.read_u32().await? as usize;
    if len > MAX_FRAME_SIZE {
        return Err(io::Error::new(
            io::ErrorKind::InvalidData,
            "frame too large",
        ));
    }
    let mut payload = vec![0u8; len];
    reader.read_exact(&mut payload).await?;
    serde_json::from_slice(&payload)
        .map_err(|e| io::Error::new(io::ErrorKind::InvalidData, e.to_string()))
}