kcode-k1-transaction 0.1.0

use kcode_k1_transaction_store::TxId;

pub const SUBSYSTEM_BYTES: usize = 20;
pub const PUBLIC_KEY_BYTES: usize = 32;
pub const SIGNATURE_BYTES: usize = 64;
pub const MIN_TRANSACTION_BYTES: usize = 136;
pub const GENESIS_PARENT: TxId = TxId::from_bytes([0xff; 12]);

#[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
pub struct SubsystemId {
    bytes: [u8; SUBSYSTEM_BYTES],
}

impl SubsystemId {
    pub fn from_bytes(bytes: [u8; SUBSYSTEM_BYTES]) -> Result<Self, String> {
        std::str::from_utf8(&bytes).map_err(|error| error.to_string())?;
        Ok(Self { bytes })
    }

    #[allow(clippy::should_implement_trait)]
    pub fn from_str(value: &str) -> Result<Self, String> {
        let bytes: [u8; SUBSYSTEM_BYTES] = value
            .as_bytes()
            .try_into()
            .map_err(|_| "subsystem ID must contain exactly 20 bytes".to_string())?;
        Self::from_bytes(bytes)
    }

    pub const fn as_bytes(&self) -> &[u8; SUBSYSTEM_BYTES] {
        &self.bytes
    }

    pub fn as_str(&self) -> &str {
        std::str::from_utf8(&self.bytes).expect("SubsystemId always contains valid UTF-8")
    }
}

pub struct Transaction<'a> {
    bytes: &'a [u8],
    subsystem: SubsystemId,
}

impl<'a> Transaction<'a> {
    pub fn parse(bytes: &'a [u8]) -> Result<Self, String> {
        if bytes.len() < MIN_TRANSACTION_BYTES {
            return Err(format!(
                "transaction must contain at least {MIN_TRANSACTION_BYTES} bytes"
            ));
        }
        let subsystem_bytes = bytes[52..72]
            .try_into()
            .map_err(|_| "invalid subsystem ID".to_string())?;
        let subsystem = SubsystemId::from_bytes(subsystem_bytes)?;
        Ok(Self { bytes, subsystem })
    }

    pub fn parent(&self) -> TxId {
        TxId::from_bytes(self.bytes[..12].try_into().expect("fixed parent range"))
    }

    pub fn timestamp(&self) -> u64 {
        u64::from_le_bytes(
            self.bytes[12..20]
                .try_into()
                .expect("fixed timestamp range"),
        )
    }

    pub fn creator(&self) -> &[u8; PUBLIC_KEY_BYTES] {
        self.bytes[20..52].try_into().expect("fixed creator range")
    }

    pub fn subsystem(&self) -> SubsystemId {
        self.subsystem
    }

    pub fn payload(&self) -> &'a [u8] {
        &self.bytes[72..self.bytes.len() - SIGNATURE_BYTES]
    }

    pub fn signature(&self) -> &'a [u8; SIGNATURE_BYTES] {
        self.bytes[self.bytes.len() - SIGNATURE_BYTES..]
            .try_into()
            .expect("fixed signature range")
    }

    pub fn signing_bytes(&self) -> &'a [u8] {
        &self.bytes[..self.bytes.len() - SIGNATURE_BYTES]
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    fn transaction(payload: &[u8], subsystem: [u8; SUBSYSTEM_BYTES]) -> Vec<u8> {
        let mut bytes = Vec::new();
        bytes.extend_from_slice(&[1; 12]);
        bytes.extend_from_slice(&0x0102_0304_0506_0708_u64.to_le_bytes());
        bytes.extend_from_slice(&[2; PUBLIC_KEY_BYTES]);
        bytes.extend_from_slice(&subsystem);
        bytes.extend_from_slice(payload);
        bytes.extend_from_slice(&[3; SIGNATURE_BYTES]);
        bytes
    }

    #[test]
    fn parses_exact_fields_and_empty_payload() {
        let subsystem = *b"12345678901234567890";
        let bytes = transaction(&[], subsystem);
        let parsed = Transaction::parse(&bytes).unwrap();

        assert_eq!(parsed.parent().into_bytes(), [1; 12]);
        assert_eq!(parsed.timestamp(), 0x0102_0304_0506_0708);
        assert_eq!(parsed.creator(), &[2; PUBLIC_KEY_BYTES]);
        assert_eq!(parsed.subsystem().as_bytes(), &subsystem);
        assert_eq!(parsed.payload(), &[]);
        assert_eq!(parsed.signature(), &[3; SIGNATURE_BYTES]);
        assert_eq!(parsed.signing_bytes(), &bytes[..72]);
        assert_eq!(bytes.len(), MIN_TRANSACTION_BYTES);
    }

    #[test]
    fn preserves_payload_signature_and_signing_prefix() {
        let bytes = transaction(b"payload", *b"abcdefghijklmnopqrst");
        let parsed = Transaction::parse(&bytes).unwrap();

        assert_eq!(parsed.payload(), b"payload");
        assert_eq!(parsed.signature(), &[3; SIGNATURE_BYTES]);
        assert_eq!(
            parsed.signing_bytes(),
            &bytes[..bytes.len() - SIGNATURE_BYTES]
        );
    }

    #[test]
    fn rejects_short_transactions() {
        assert!(Transaction::parse(&[0; MIN_TRANSACTION_BYTES - 1]).is_err());
    }

    #[test]
    fn accepts_exact_multibyte_utf8_subsystem() {
        let value = "éééééééééé";
        let subsystem = SubsystemId::from_str(value).unwrap();

        assert_eq!(subsystem.as_str(), value);
        assert_eq!(subsystem.as_bytes().len(), SUBSYSTEM_BYTES);
    }

    #[test]
    fn rejects_wrong_subsystem_byte_length() {
        assert!(SubsystemId::from_str("short").is_err());
        assert!(SubsystemId::from_str("123456789012345678901").is_err());
    }

    #[test]
    fn rejects_invalid_subsystem_utf8() {
        assert!(SubsystemId::from_bytes([0xff; SUBSYSTEM_BYTES]).is_err());
    }

    #[test]
    fn rejects_transaction_with_invalid_subsystem_utf8() {
        let bytes = transaction(&[], [0xff; SUBSYSTEM_BYTES]);

        assert!(Transaction::parse(&bytes).is_err());
    }

    #[test]
    fn exposes_genesis_sentinel() {
        assert_eq!(GENESIS_PARENT.into_bytes(), [0xff; 12]);
    }
}