use anyhow::{bail, Result};

pub const CODE: &[u8] = b"61";

/// [Certificate authorization](https://geminiprotocol.net/docs/protocol-specification.gmi#status-61-certificate-not-authorized)
pub struct NotAuthorized {
    pub message: Option<String>,
}

impl NotAuthorized {
    /// Build `Self` from UTF-8 header bytes
    /// * expected buffer includes leading status code, message, CRLF
    pub fn from_bytes(buffer: &[u8]) -> Result<Self> {
        // calculate length once
        let len = buffer.len();
        // validate headers for this response type
        if !(3..=1024).contains(&len) {
            bail!("Unexpected header length")
        }
        if buffer
            .get(..2)
            .is_none_or(|c| c[0] != CODE[0] || c[1] != CODE[1])
        {
            bail!("Invalid status code")
        }
        // collect data bytes
        let mut m = Vec::with_capacity(len);
        for b in buffer[3..].iter() {
            if *b == b'\r' {
                continue;
            }
            if *b == b'\n' {
                break;
            }
            m.push(*b)
        }
        Ok(Self {
            message: String::from_utf8(m).map(|m| if m.is_empty() { None } else { Some(m) })?,
        })
    }

    /// Convert `Self` into UTF-8 bytes presentation
    pub fn into_bytes(self) -> Vec<u8> {
        match self.message {
            Some(message) => {
                let mut bytes = Vec::with_capacity(message.len() + 5);
                bytes.extend(CODE);
                bytes.push(b' ');
                bytes.extend(message.into_bytes());
                bytes.extend([b'\r', b'\n']);
                bytes
            }
            None => {
                let mut bytes = Vec::with_capacity(4);
                bytes.extend(CODE);
                bytes.extend([b'\r', b'\n']);
                bytes
            }
        }
    }
}

#[test]
fn test() {
    let request = format!("61 message\r\n");
    let source = NotAuthorized::from_bytes(request.as_bytes()).unwrap();

    assert_eq!(source.message, Some("message".to_string()));
    assert_eq!(source.into_bytes(), request.as_bytes());
}