use crate::{decode::get_str, Decode};
use byteorder::{BigEndian, ByteOrder};
use bytes::Bytes;

use std::{fmt, io, pin::Pin, ptr::NonNull};

pub struct NotificationResponse {
    #[used]
    storage: Pin<Bytes>,
    pid: u32,
    channel_name: NonNull<str>,
    message: NonNull<str>,
}

impl NotificationResponse {
    #[inline]
    pub fn pid(&self) -> u32 {
        self.pid
    }

    #[inline]
    pub fn channel_name(&self) -> &str {
        // SAFE: Memory is pinned
        unsafe { self.channel_name.as_ref() }
    }

    #[inline]
    pub fn message(&self) -> &str {
        // SAFE: Memory is pinned
        unsafe { self.message.as_ref() }
    }
}

// SAFE: Raw pointers point to pinned memory inside the struct
unsafe impl Send for NotificationResponse {}
unsafe impl Sync for NotificationResponse {}

impl fmt::Debug for NotificationResponse {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.debug_struct("NotificationResponse")
            .field("pid", &self.pid())
            .field("channel_name", &self.channel_name())
            .field("message", &self.message())
            .finish()
    }
}

impl Decode for NotificationResponse {
    fn decode(src: Bytes) -> io::Result<Self> {
        let storage = Pin::new(src);
        let pid = BigEndian::read_u32(&*storage);

        // offset from pid=4
        let channel_name = get_str(&storage[4..])?;

        // offset = pid + channel_name.len() + \0
        let message = get_str(&storage[(4 + channel_name.len() + 1)..])?;

        let channel_name = NonNull::from(channel_name);
        let message = NonNull::from(message);

        Ok(Self {
            storage,
            pid,
            channel_name,
            message,
        })
    }
}

#[cfg(test)]
mod tests {
    use super::NotificationResponse;
    use crate::Decode;
    use bytes::Bytes;
    use std::io;

    const NOTIFICATION_RESPONSE: &[u8] = b"\x34\x20\x10\x02TEST-CHANNEL\0THIS IS A TEST\0";

    #[test]
    fn it_decodes_notification_response() -> io::Result<()> {
        let src = Bytes::from_static(NOTIFICATION_RESPONSE);
        let message = NotificationResponse::decode(src)?;

        assert_eq!(message.pid(), 0x34201002);
        assert_eq!(message.channel_name(), "TEST-CHANNEL");
        assert_eq!(message.message(), "THIS IS A TEST");
        Ok(())
    }
}