use anyhow::{bail, Result};
use tokio::io::{AsyncRead, AsyncReadExt as _};

#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum RequestKind {
    Signal,
    Command,
}

#[derive(Debug)]
pub struct Request<'a> {
    pub kind: RequestKind,
    body: &'a str,
}

impl<'a> Request<'a> {
    pub async fn read<R: AsyncRead + Unpin>(
        reader: &mut R,
        buffer: &'a mut Vec<u8>,
    ) -> Result<Self> {
        buffer.clear();

        let mut char = reader.read_u8().await?;
        while char == b'+' {
            // just ignore positive acks
            char = reader.read_u8().await?;
        }
        if char == b'-' {
            bail!("no support for negative acks");
        }
        if char == 0x03 {
            // This is how the client "cancels an in-flight request"
            buffer.push(char);
            let body = std::str::from_utf8(buffer)?;
            return Ok(Self {
                kind: RequestKind::Signal,
                body,
            });
        }
        if char != b'$' {
            // Messages are supposed to start with a dollar sign
            bail!("malformed message");
        }

        // now read the body
        let mut checksum = 0u8;
        char = reader.read_u8().await?;
        while char != b'#' {
            if char == b'}' {
                // escape character
                checksum = checksum.wrapping_add(char);
                char = reader.read_u8().await?;
                checksum = checksum.wrapping_add(char);
                buffer.push(char ^ 0x20);
            } else {
                checksum = checksum.wrapping_add(char);
                buffer.push(char);
            }
            char = reader.read_u8().await?;
        }

        let mut checksum_bytes = [b'0'; 2];
        reader.read_exact(&mut checksum_bytes).await?;
        let checksum_str = std::str::from_utf8(&checksum_bytes)?;
        let real_checksum = u8::from_str_radix(checksum_str, 16)?;
        if checksum != real_checksum {
            bail!("invalid checksum");
        }

        let body = std::str::from_utf8(buffer)?;
        Ok(Self {
            kind: RequestKind::Command,
            body,
        })
    }

    pub fn match_str(&mut self, prefix: &str) -> bool {
        if let Some(new_body) = self.body.strip_prefix(prefix) {
            self.body = new_body;
            return true;
        }
        false
    }
}