// SPF Smart Gateway - Message Framing Protocol
// Copyright 2026 Joseph Stone - All Rights Reserved
//
// Length-prefixed message framing for persistent bidirectional streams.
// Replaces one-shot read_to_end/finish pattern in mesh transport.
// Supports 8 stream types: TOOL_RPC, CHAT, VOICE, PIPELINE, BRAIN_SYNC, WEIGHT_SYNC, CONTROL
//
// Frame format: [1-byte type][4-byte length BE][payload bytes]
// Max frame size: 10MB (matches existing mesh limit)
//
// Depends on: nothing (Layer 2 protocol definition)

use std::io;

// ============================================================================
// STREAM TYPES
// ============================================================================

/// Stream type identifiers — first byte of every frame
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
#[repr(u8)]
pub enum StreamType {
    /// Tool RPC calls (existing mesh functionality) — JSON-RPC format
    ToolRpc = 0x01,
    /// Text chat messages (user ↔ user, user ↔ agent, agent ↔ agent)
    ChatText = 0x02,
    /// Voice audio frames (Opus codec)
    VoiceAudio = 0x03,
    /// Pipeline task assignment (orchestrator → worker)
    PipelineTask = 0x04,
    /// Pipeline result (worker → orchestrator)
    PipelineResult = 0x05,
    /// Brain knowledge sync between nodes
    BrainSync = 0x06,
    /// Transformer weight sharing / delta sync
    WeightSync = 0x07,
    /// Control messages: heartbeat, status, peer management
    Control = 0x08,
}

impl StreamType {
    /// Convert byte to StreamType
    pub fn from_byte(b: u8) -> Option<Self> {
        match b {
            0x01 => Some(Self::ToolRpc),
            0x02 => Some(Self::ChatText),
            0x03 => Some(Self::VoiceAudio),
            0x04 => Some(Self::PipelineTask),
            0x05 => Some(Self::PipelineResult),
            0x06 => Some(Self::BrainSync),
            0x07 => Some(Self::WeightSync),
            0x08 => Some(Self::Control),
            _ => None,
        }
    }

    /// Convert StreamType to byte
    pub fn as_byte(self) -> u8 {
        self as u8
    }

    /// Human-readable name for logging
    pub fn name(self) -> &'static str {
        match self {
            Self::ToolRpc => "TOOL_RPC",
            Self::ChatText => "CHAT_TEXT",
            Self::VoiceAudio => "VOICE_AUDIO",
            Self::PipelineTask => "PIPELINE_TASK",
            Self::PipelineResult => "PIPELINE_RESULT",
            Self::BrainSync => "BRAIN_SYNC",
            Self::WeightSync => "WEIGHT_SYNC",
            Self::Control => "CONTROL",
        }
    }

    /// Whether this stream type carries real-time data (low latency required)
    pub fn is_realtime(self) -> bool {
        matches!(self, Self::VoiceAudio | Self::ChatText | Self::Control)
    }

    /// Whether this stream type carries bulk data (high throughput preferred)
    pub fn is_bulk(self) -> bool {
        matches!(self, Self::BrainSync | Self::WeightSync | Self::PipelineTask | Self::PipelineResult)
    }
}

// ============================================================================
// FRAME FORMAT
// ============================================================================

/// Maximum frame payload size: 10MB (matches mesh.rs MAX_MSG_SIZE)
pub const MAX_FRAME_SIZE: u32 = 10_485_760;

/// Frame header size: 1 (type) + 4 (length) = 5 bytes
pub const FRAME_HEADER_SIZE: usize = 5;

/// A single framed message ready for transmission
#[derive(Debug, Clone)]
pub struct Frame {
    /// Stream type identifier
    pub stream_type: StreamType,
    /// Payload bytes (JSON, audio, binary, etc.)
    pub payload: Vec<u8>,
}

impl Frame {
    /// Create a new frame
    pub fn new(stream_type: StreamType, payload: Vec<u8>) -> Self {
        Self { stream_type, payload }
    }

    /// Create a Tool RPC frame from JSON string
    pub fn tool_rpc(json: &str) -> Self {
        Self::new(StreamType::ToolRpc, json.as_bytes().to_vec())
    }

    /// Create a Chat frame from text
    pub fn chat(text: &str) -> Self {
        Self::new(StreamType::ChatText, text.as_bytes().to_vec())
    }

    /// Create a Control frame from JSON
    pub fn control(json: &str) -> Self {
        Self::new(StreamType::Control, json.as_bytes().to_vec())
    }

    /// Create a Pipeline Task frame
    pub fn pipeline_task(payload: Vec<u8>) -> Self {
        Self::new(StreamType::PipelineTask, payload)
    }

    /// Create a Pipeline Result frame
    pub fn pipeline_result(payload: Vec<u8>) -> Self {
        Self::new(StreamType::PipelineResult, payload)
    }

    /// Serialize frame to wire format: [type:1][length:4 BE][payload:N]
    pub fn to_bytes(&self) -> Vec<u8> {
        let len = self.payload.len() as u32;
        let mut buf = Vec::with_capacity(FRAME_HEADER_SIZE + self.payload.len());
        buf.push(self.stream_type.as_byte());
        buf.extend_from_slice(&len.to_be_bytes());
        buf.extend_from_slice(&self.payload);
        buf
    }

    /// Payload as UTF-8 string (for JSON/text frames)
    pub fn payload_str(&self) -> Result<&str, std::str::Utf8Error> {
        std::str::from_utf8(&self.payload)
    }
}

// ============================================================================
// FRAME READER / WRITER — for use with any Read/Write stream
// ============================================================================

/// Read a single frame from a byte stream.
/// Returns None on clean EOF (stream closed by peer).
/// Returns Err on protocol violations or I/O errors.
pub fn read_frame(reader: &mut dyn io::Read) -> io::Result<Option<Frame>> {
    // Read header: 5 bytes [type:1][length:4]
    let mut header = [0u8; FRAME_HEADER_SIZE];
    match reader.read_exact(&mut header) {
        Ok(()) => {},
        Err(e) if e.kind() == io::ErrorKind::UnexpectedEof => return Ok(None),
        Err(e) => return Err(e),
    }

    let type_byte = header[0];
    let length = u32::from_be_bytes([header[1], header[2], header[3], header[4]]);

    // Validate stream type
    let stream_type = StreamType::from_byte(type_byte).ok_or_else(|| {
        io::Error::new(io::ErrorKind::InvalidData, format!("Unknown stream type: 0x{:02x}", type_byte))
    })?;

    // Validate frame size
    if length > MAX_FRAME_SIZE {
        return Err(io::Error::new(
            io::ErrorKind::InvalidData,
            format!("Frame too large: {} bytes (max {})", length, MAX_FRAME_SIZE),
        ));
    }

    // Read payload
    let mut payload = vec![0u8; length as usize];
    reader.read_exact(&mut payload)?;

    Ok(Some(Frame { stream_type, payload }))
}

/// Write a single frame to a byte stream.
pub fn write_frame(writer: &mut dyn io::Write, frame: &Frame) -> io::Result<()> {
    let len = frame.payload.len();
    if len > MAX_FRAME_SIZE as usize {
        return Err(io::Error::new(
            io::ErrorKind::InvalidInput,
            format!("Frame payload too large: {} bytes (max {})", len, MAX_FRAME_SIZE),
        ));
    }

    writer.write_all(&[frame.stream_type.as_byte()])?;
    writer.write_all(&(len as u32).to_be_bytes())?;
    writer.write_all(&frame.payload)?;
    writer.flush()?;
    Ok(())
}

// ============================================================================
// ASYNC FRAME READER / WRITER — for tokio AsyncRead/AsyncWrite
// ============================================================================

/// Read a frame from an async byte stream (iroh SendStream/RecvStream).
/// This operates on raw byte slices for compatibility with iroh's API.
///
/// For iroh streams: caller reads bytes into buffer, passes to parse_frame.
/// iroh RecvStream doesn't implement AsyncRead directly — we work with
/// the bytes it gives us.

/// Parse a frame from a complete byte buffer.
/// Returns (frame, bytes_consumed) on success.
/// Returns None if buffer doesn't contain a complete frame yet.
pub fn parse_frame(buf: &[u8]) -> Result<Option<(Frame, usize)>, io::Error> {
    if buf.len() < FRAME_HEADER_SIZE {
        return Ok(None); // Need more data
    }

    let type_byte = buf[0];
    let length = u32::from_be_bytes([buf[1], buf[2], buf[3], buf[4]]);

    let stream_type = StreamType::from_byte(type_byte).ok_or_else(|| {
        io::Error::new(io::ErrorKind::InvalidData, format!("Unknown stream type: 0x{:02x}", type_byte))
    })?;

    if length > MAX_FRAME_SIZE {
        return Err(io::Error::new(
            io::ErrorKind::InvalidData,
            format!("Frame too large: {} bytes (max {})", length, MAX_FRAME_SIZE),
        ));
    }

    let total_len = FRAME_HEADER_SIZE + length as usize;
    if buf.len() < total_len {
        return Ok(None); // Need more data
    }

    let payload = buf[FRAME_HEADER_SIZE..total_len].to_vec();
    Ok(Some((Frame { stream_type, payload }, total_len)))
}

/// Serialize a frame into a byte buffer for writing to iroh SendStream.
/// Same as Frame::to_bytes() but takes components directly.
pub fn encode_frame(stream_type: StreamType, payload: &[u8]) -> Result<Vec<u8>, io::Error> {
    if payload.len() > MAX_FRAME_SIZE as usize {
        return Err(io::Error::new(
            io::ErrorKind::InvalidInput,
            format!("Payload too large: {} bytes", payload.len()),
        ));
    }
    let mut buf = Vec::with_capacity(FRAME_HEADER_SIZE + payload.len());
    buf.push(stream_type.as_byte());
    buf.extend_from_slice(&(payload.len() as u32).to_be_bytes());
    buf.extend_from_slice(payload);
    Ok(buf)
}

// ============================================================================
// LEGACY DETECTION
// ============================================================================

/// Detect whether incoming data is legacy JSON-RPC or new framed protocol.
/// Legacy mesh messages start with '{' (0x7B) — raw JSON.
/// New framed messages start with 0x01-0x08 — stream type byte.
///
/// Call this on the first byte(s) of a new stream to determine protocol version.
pub fn is_legacy_jsonrpc(first_byte: u8) -> bool {
    // ASCII '{' = 0x7B. All stream types are 0x01-0x08.
    // No overlap — clean detection.
    first_byte == b'{'
}

/// Detect protocol from first byte
#[derive(Debug, Clone, Copy, PartialEq)]
pub enum Protocol {
    /// Legacy one-shot JSON-RPC (existing mesh behavior)
    LegacyJsonRpc,
    /// New framed protocol with persistent streams
    Framed(StreamType),
    /// Unknown protocol
    Unknown(u8),
}

pub fn detect_protocol(first_byte: u8) -> Protocol {
    if first_byte == b'{' {
        Protocol::LegacyJsonRpc
    } else if let Some(st) = StreamType::from_byte(first_byte) {
        Protocol::Framed(st)
    } else {
        Protocol::Unknown(first_byte)
    }
}

// ============================================================================
// CONTROL MESSAGES
// ============================================================================

/// Well-known control message types (sent as JSON in Control frames)
pub mod control {
    /// Heartbeat — sent periodically to keep stream alive
    pub const HEARTBEAT: &str = r#"{"type":"heartbeat"}"#;

    /// Status request
    pub const STATUS_REQUEST: &str = r#"{"type":"status_request"}"#;

    /// Peer closing stream gracefully
    pub const STREAM_CLOSE: &str = r#"{"type":"stream_close"}"#;

    /// Peer requesting stream type upgrade/change
    pub const STREAM_UPGRADE: &str = r#"{"type":"stream_upgrade"}"#;

    /// Initial role/team/version exchange on persistent stream connect.
    pub const HANDSHAKE: &str = r#"{"type":"handshake"}"#;

    /// Build a handshake frame JSON string from role/team/name/version.
    pub fn build_handshake(role: &str, name: &str, version: &str) -> String {
        format!(r#"{{"type":"handshake","role":"{}","name":"{}","version":"{}"}}"#, role, name, version)
    }

    /// Parse role from a handshake frame payload. Returns None if not a handshake.
    pub fn parse_role(payload: &str) -> Option<String> {
        if payload.contains(r#""type":"handshake""#) || payload.contains(r#""type": "handshake""#) {
            let start = payload.find(r#""role":"#)?;
            let role_start = start + 8;
            payload[role_start..].find('"').map(|end| payload[role_start..role_start + end].to_string())
        } else {
            None
        }
    }

    /// Parse name from a handshake frame payload.
    pub fn parse_name(payload: &str) -> Option<String> {
        let start = payload.find(r#""name":"#)?;
        let name_start = start + 8;
        payload[name_start..].find('"').map(|end| payload[name_start..name_start + end].to_string())
    }
}

// ============================================================================
// TESTS
// ============================================================================

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

    #[test]
    fn test_stream_type_roundtrip() {
        for byte in 0x01..=0x08 {
            let st = StreamType::from_byte(byte).unwrap();
            assert_eq!(st.as_byte(), byte);
        }
        assert!(StreamType::from_byte(0x00).is_none());
        assert!(StreamType::from_byte(0x0A).is_none());
        assert!(StreamType::from_byte(0xFF).is_none());
    }

    #[test]
    fn test_frame_to_bytes_and_parse() {
        let frame = Frame::tool_rpc(r#"{"method":"spf_status"}"#);
        let bytes = frame.to_bytes();

        // Verify header
        assert_eq!(bytes[0], 0x01); // TOOL_RPC
        let len = u32::from_be_bytes([bytes[1], bytes[2], bytes[3], bytes[4]]);
        assert_eq!(len as usize, frame.payload.len());

        // Parse back
        let (parsed, consumed) = parse_frame(&bytes).unwrap().unwrap();
        assert_eq!(parsed.stream_type, StreamType::ToolRpc);
        assert_eq!(parsed.payload, frame.payload);
        assert_eq!(consumed, bytes.len());
    }

    #[test]
    fn test_read_write_frame_sync() {
        let original = Frame::chat("Hello from SPF mesh!");
        let mut buffer = Vec::new();

        write_frame(&mut buffer, &original).unwrap();

        let mut cursor = Cursor::new(&buffer);
        let read_back = read_frame(&mut cursor).unwrap().unwrap();

        assert_eq!(read_back.stream_type, StreamType::ChatText);
        assert_eq!(read_back.payload_str().unwrap(), "Hello from SPF mesh!");
    }

    #[test]
    fn test_multiple_frames() {
        let frames = vec![
            Frame::tool_rpc(r#"{"method":"test1"}"#),
            Frame::chat("message two"),
            Frame::control(control::HEARTBEAT),
        ];

        let mut buffer = Vec::new();
        for f in &frames {
            write_frame(&mut buffer, f).unwrap();
        }

        let mut cursor = Cursor::new(&buffer);
        for expected in &frames {
            let read = read_frame(&mut cursor).unwrap().unwrap();
            assert_eq!(read.stream_type, expected.stream_type);
            assert_eq!(read.payload, expected.payload);
        }

        // Next read should return None (EOF)
        let eof = read_frame(&mut cursor).unwrap();
        assert!(eof.is_none());
    }

    #[test]
    fn test_parse_frame_incomplete() {
        // Only header, no payload
        let bytes = vec![0x01, 0x00, 0x00, 0x00, 0x05]; // type=TOOL_RPC, len=5
        let result = parse_frame(&bytes).unwrap();
        assert!(result.is_none()); // Needs 5 more bytes

        // Too short for header
        let result2 = parse_frame(&[0x01, 0x00]).unwrap();
        assert!(result2.is_none());
    }

    #[test]
    fn test_oversized_frame_rejected() {
        let mut header = vec![0x01]; // TOOL_RPC
        let big_len = MAX_FRAME_SIZE + 1;
        header.extend_from_slice(&big_len.to_be_bytes());
        header.extend_from_slice(&[0u8; 100]); // some payload bytes

        let result = parse_frame(&header);
        assert!(result.is_err());
    }

    #[test]
    fn test_unknown_stream_type_rejected() {
        let bytes = vec![0xFF, 0x00, 0x00, 0x00, 0x01, 0x42]; // type=0xFF
        let result = parse_frame(&bytes);
        assert!(result.is_err());
    }

    #[test]
    fn test_legacy_detection() {
        assert!(is_legacy_jsonrpc(b'{'));
        assert!(!is_legacy_jsonrpc(0x01));
        assert!(!is_legacy_jsonrpc(0x08));

        assert_eq!(detect_protocol(b'{'), Protocol::LegacyJsonRpc);
        assert_eq!(detect_protocol(0x01), Protocol::Framed(StreamType::ToolRpc));
        assert_eq!(detect_protocol(0x08), Protocol::Framed(StreamType::Control));
        assert_eq!(detect_protocol(0x09), Protocol::Unknown(0x09));
        assert_eq!(detect_protocol(0xAA), Protocol::Unknown(0xAA));
    }

    #[test]
    fn test_stream_type_properties() {
        assert!(StreamType::VoiceAudio.is_realtime());
        assert!(StreamType::ChatText.is_realtime());
        assert!(!StreamType::BrainSync.is_realtime());

        assert!(StreamType::BrainSync.is_bulk());
        assert!(StreamType::WeightSync.is_bulk());
        assert!(!StreamType::ChatText.is_bulk());
    }

    #[test]
    fn test_encode_frame() {
        let payload = b"test payload";
        let bytes = encode_frame(StreamType::PipelineTask, payload).unwrap();
        assert_eq!(bytes[0], 0x04);
        let len = u32::from_be_bytes([bytes[1], bytes[2], bytes[3], bytes[4]]);
        assert_eq!(len, payload.len() as u32);
        assert_eq!(&bytes[5..], payload);
    }

    #[test]
    fn test_empty_frame() {
        let frame = Frame::new(StreamType::Control, vec![]);
        let bytes = frame.to_bytes();
        assert_eq!(bytes.len(), FRAME_HEADER_SIZE); // Just header, no payload

        let (parsed, consumed) = parse_frame(&bytes).unwrap().unwrap();
        assert_eq!(parsed.payload.len(), 0);
        assert_eq!(consumed, FRAME_HEADER_SIZE);
    }
}