ardupilot-binlog 0.2.0

use std::collections::HashMap;
use std::io::{BufReader, Read};
use std::sync::Arc;

use crate::entry::Entry;
use crate::error::BinlogError;
use crate::format::{parse_fmt_payload, MessageFormat};
use crate::{FMT_TYPE, HEADER_MAGIC};

const MAX_CONSECUTIVE_ERRORS: u32 = 256;

/// Streaming parser for DataFlash BIN data.
///
/// Reads from any `Read` source, discovers message schemas via FMT
/// messages, and yields parsed [`Entry`] values via the [`Iterator`] trait.
///
/// ```
/// use ardupilot_binlog::Reader;
/// use std::io::Cursor;
///
/// let data: Vec<u8> = vec![];
/// let reader = Reader::new(Cursor::new(data));
/// for result in reader {
///     let entry = result.unwrap();
///     println!("{}: {} fields", entry.name, entry.len());
/// }
/// ```
pub struct Reader<R: Read> {
    reader: BufReader<R>,
    formats: HashMap<u8, Arc<MessageFormat>>,
    consecutive_errors: u32,
}

impl<R: Read> Reader<R> {
    /// Create a new reader wrapping a byte source.
    pub fn new(reader: R) -> Self {
        let mut formats = HashMap::new();
        // Bootstrap: hardcode the FMT definition so we can parse the first FMT message
        formats.insert(
            FMT_TYPE,
            Arc::new(MessageFormat {
                msg_type: FMT_TYPE,
                msg_len: 89,
                name: "FMT".into(),
                format: "BBnNZ".into(),
                labels: Arc::from([
                    "Type".into(),
                    "Length".into(),
                    "Name".into(),
                    "Format".into(),
                    "Labels".into(),
                ]),
            }),
        );

        Reader {
            reader: BufReader::new(reader),
            formats,
            consecutive_errors: 0,
        }
    }

    fn next_inner(&mut self) -> Result<Option<Entry>, BinlogError> {
        if self.consecutive_errors >= MAX_CONSECUTIVE_ERRORS {
            return Ok(None);
        }

        // Read the 3-byte header
        let mut header = [0u8; 3];
        match self.read_exact_or_eof(&mut header) {
            Ok(true) => {}
            Ok(false) => return Ok(None), // EOF
            Err(_) => return Ok(None),
        }

        // Validate magic bytes
        if header[0] != HEADER_MAGIC[0] || header[1] != HEADER_MAGIC[1] {
            self.consecutive_errors += 1;
            return self.recover_and_retry();
        }

        let msg_type = header[2];
        self.parse_message(msg_type)
    }

    /// Return all message format definitions discovered so far.
    #[must_use]
    pub fn formats(&self) -> &HashMap<u8, Arc<MessageFormat>> {
        &self.formats
    }

    /// Parse a message given its type byte (header already consumed).
    fn parse_message(&mut self, msg_type: u8) -> Result<Option<Entry>, BinlogError> {
        // Clone the Arc so we own a handle and don't borrow self.formats
        let format = match self.formats.get(&msg_type) {
            Some(f) => Arc::clone(f),
            None => {
                self.consecutive_errors += 1;
                return self.recover_and_retry();
            }
        };

        // Read payload (no borrow on self.formats)
        let payload = match self.read_payload(&format) {
            Ok(p) => p,
            Err(_) => {
                self.consecutive_errors += 1;
                return self.recover_and_retry();
            }
        };

        let result = if msg_type == FMT_TYPE {
            build_fmt_entry(&format, &payload)
        } else {
            build_data_entry(&format, msg_type, &payload)
        };

        match result {
            Ok((entry, new_fmt)) => {
                if let Some(new_fmt) = new_fmt {
                    self.formats.insert(new_fmt.msg_type, Arc::new(new_fmt));
                }
                self.consecutive_errors = 0;
                Ok(Some(entry))
            }
            Err(_) => {
                self.consecutive_errors += 1;
                self.recover_and_retry()
            }
        }
    }

    /// Read the payload bytes for a message (everything after the 3-byte header).
    fn read_payload(&mut self, format: &MessageFormat) -> Result<Vec<u8>, BinlogError> {
        let payload_len = format.msg_len as usize - 3;
        let mut payload = vec![0u8; payload_len];
        match self.read_exact_or_eof(&mut payload) {
            Ok(true) => Ok(payload),
            Ok(false) => Err(BinlogError::UnexpectedEof),
            Err(e) => Err(e),
        }
    }

    /// Scan forward byte-by-byte looking for the magic header, then retry parsing.
    fn recover_and_retry(&mut self) -> Result<Option<Entry>, BinlogError> {
        if self.consecutive_errors >= MAX_CONSECUTIVE_ERRORS {
            return Ok(None);
        }
        match self.scan_for_header()? {
            Some(msg_type) => self.parse_message(msg_type),
            None => Ok(None),
        }
    }

    /// Scan byte-by-byte for the next 0xA3 0x95 sequence.
    /// Returns the msg_type byte that follows the magic, or None at EOF.
    fn scan_for_header(&mut self) -> Result<Option<u8>, BinlogError> {
        let mut prev = 0u8;
        loop {
            let mut byte = [0u8; 1];
            match self.reader.read(&mut byte) {
                Ok(0) => return Ok(None), // EOF
                Ok(_) => {
                    if prev == HEADER_MAGIC[0] && byte[0] == HEADER_MAGIC[1] {
                        // Found magic, read msg_type
                        let mut msg_type = [0u8; 1];
                        match self.reader.read(&mut msg_type) {
                            Ok(0) => return Ok(None),
                            Ok(_) => return Ok(Some(msg_type[0])),
                            Err(_) => return Ok(None),
                        }
                    }
                    prev = byte[0];
                }
                Err(_) => return Ok(None),
            }
        }
    }

    /// Read exactly `buf.len()` bytes. Returns Ok(true) on success, Ok(false) on EOF
    /// (zero bytes available), Err on partial read / IO error.
    fn read_exact_or_eof(&mut self, buf: &mut [u8]) -> Result<bool, BinlogError> {
        let mut total = 0;
        while total < buf.len() {
            match self.reader.read(&mut buf[total..]) {
                Ok(0) => {
                    if total == 0 {
                        return Ok(false); // Clean EOF
                    }
                    return Err(BinlogError::UnexpectedEof);
                }
                Ok(n) => total += n,
                Err(e) => return Err(BinlogError::Io(e)),
            }
        }
        Ok(true)
    }
}

fn build_fmt_entry(
    format: &MessageFormat,
    payload: &[u8],
) -> Result<(Entry, Option<MessageFormat>), BinlogError> {
    let new_fmt = parse_fmt_payload(payload)?;
    let values = format.decode_fields(payload)?;
    let entry = Entry {
        name: "FMT".into(),
        msg_type: FMT_TYPE,
        timestamp_usec: None,
        labels: format.labels.clone(),
        values,
    };
    Ok((entry, Some(new_fmt)))
}

fn build_data_entry(
    format: &MessageFormat,
    msg_type: u8,
    payload: &[u8],
) -> Result<(Entry, Option<MessageFormat>), BinlogError> {
    let values = format.decode_fields(payload)?;
    let timestamp_usec = format.extract_timestamp(payload);
    let entry = Entry {
        name: format.name.clone(),
        msg_type,
        timestamp_usec,
        labels: format.labels.clone(),
        values,
    };
    Ok((entry, None))
}

impl<R: Read> Iterator for Reader<R> {
    type Item = Result<Entry, BinlogError>;

    fn next(&mut self) -> Option<Self::Item> {
        self.next_inner().transpose()
    }
}

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

    /// Build a valid FMT message (89 bytes) that defines the FMT type itself.
    fn build_fmt_bootstrap() -> Vec<u8> {
        let mut msg = Vec::new();
        msg.extend_from_slice(&HEADER_MAGIC);
        msg.push(FMT_TYPE);
        // 86-byte payload
        let mut payload = [0u8; 86];
        payload[0] = FMT_TYPE; // type
        payload[1] = 89; // length
        payload[2..6].copy_from_slice(b"FMT\0"); // name
        payload[6..11].copy_from_slice(b"BBnNZ"); // format
        let labels = b"Type,Length,Name,Format,Labels";
        payload[22..22 + labels.len()].copy_from_slice(labels);
        msg.extend_from_slice(&payload);
        msg
    }

    /// Build a FMT message that defines a custom message type.
    fn build_fmt_for_type(
        msg_type: u8,
        msg_len: u8,
        name: &[u8; 4],
        format: &str,
        labels: &str,
    ) -> Vec<u8> {
        let mut msg = Vec::new();
        msg.extend_from_slice(&HEADER_MAGIC);
        msg.push(FMT_TYPE);
        let mut payload = [0u8; 86];
        payload[0] = msg_type;
        payload[1] = msg_len;
        payload[2..6].copy_from_slice(name);
        let fmt_bytes = format.as_bytes();
        payload[6..6 + fmt_bytes.len()].copy_from_slice(fmt_bytes);
        let lbl_bytes = labels.as_bytes();
        payload[22..22 + lbl_bytes.len()].copy_from_slice(lbl_bytes);
        msg.extend_from_slice(&payload);
        msg
    }

    /// Build a data message with a given type and raw payload.
    fn build_data_message(msg_type: u8, payload: &[u8]) -> Vec<u8> {
        let mut msg = Vec::new();
        msg.extend_from_slice(&HEADER_MAGIC);
        msg.push(msg_type);
        msg.extend_from_slice(payload);
        msg
    }

    #[test]
    fn parse_empty_input() {
        let reader = Reader::new(std::io::Cursor::new(Vec::new()));
        let entries: Vec<_> = reader.collect::<Result<Vec<_>, _>>().unwrap();
        assert!(entries.is_empty());
    }

    #[test]
    fn parse_fmt_bootstrap_only() {
        let data = build_fmt_bootstrap();
        let reader = Reader::new(std::io::Cursor::new(data));
        let entries: Vec<_> = reader.collect::<Result<Vec<_>, _>>().unwrap();
        assert_eq!(entries.len(), 1);
        assert_eq!(entries[0].name, "FMT");
        assert_eq!(entries[0].msg_type, FMT_TYPE);
        assert!(entries[0].timestamp_usec.is_none());
    }

    #[test]
    fn parse_data_message() {
        let mut data = Vec::new();
        // Bootstrap FMT
        data.extend(build_fmt_bootstrap());
        // payload size: 8 + 2 + 2 = 12, total = 15
        data.extend(build_fmt_for_type(
            0x81,
            15,
            b"ATT\0",
            "Qhh",
            "TimeUS,Roll,Pitch",
        ));
        let mut payload = Vec::new();
        payload.extend_from_slice(&1_000_000u64.to_le_bytes());
        payload.extend_from_slice(&4500i16.to_le_bytes()); // Roll
        payload.extend_from_slice(&(-200i16).to_le_bytes()); // Pitch
        data.extend(build_data_message(0x81, &payload));

        let reader = Reader::new(std::io::Cursor::new(data));
        let entries: Vec<_> = reader.collect::<Result<Vec<_>, _>>().unwrap();
        assert_eq!(entries.len(), 3); // FMT(FMT), FMT(ATT), ATT

        let att = &entries[2];
        assert_eq!(att.name, "ATT");
        assert_eq!(att.msg_type, 0x81);
        assert_eq!(att.timestamp_usec, Some(1_000_000));
        assert_eq!(att.get("Roll"), Some(&FieldValue::Int(4500)));
        assert_eq!(att.get("Pitch"), Some(&FieldValue::Int(-200)));
    }

    #[test]
    fn error_recovery_with_garbage() {
        let mut data = Vec::new();
        data.extend(build_fmt_bootstrap());
        // Define a simple type
        data.extend(build_fmt_for_type(
            0x81, 11, // 3 + 8
            b"TST\0", "Q", "TimeUS",
        ));
        // First valid data message
        data.extend(build_data_message(0x81, &100u64.to_le_bytes()));
        // Garbage bytes
        data.extend_from_slice(&[0xFF; 50]);
        // Second valid data message
        data.extend(build_data_message(0x81, &200u64.to_le_bytes()));

        let reader = Reader::new(std::io::Cursor::new(data));
        let entries: Vec<_> = reader.collect::<Result<Vec<_>, _>>().unwrap();

        // Should have: FMT(FMT), FMT(TST), TST(100), TST(200)
        let tst_entries: Vec<_> = entries.iter().filter(|e| e.name == "TST").collect();
        assert_eq!(tst_entries.len(), 2);
        assert_eq!(tst_entries[0].timestamp_usec, Some(100));
        assert_eq!(tst_entries[1].timestamp_usec, Some(200));
    }

    #[test]
    fn truncated_final_message() {
        let mut data = Vec::new();
        data.extend(build_fmt_bootstrap());
        data.extend(build_fmt_for_type(0x81, 11, b"TST\0", "Q", "TimeUS"));
        // Valid message
        data.extend(build_data_message(0x81, &100u64.to_le_bytes()));
        // Truncated message: header + partial payload
        data.extend_from_slice(&HEADER_MAGIC);
        data.push(0x81);
        data.extend_from_slice(&[0; 3]); // only 3 of 8 payload bytes

        let reader = Reader::new(std::io::Cursor::new(data));
        let entries: Vec<_> = reader.collect::<Result<Vec<_>, _>>().unwrap();

        let tst_entries: Vec<_> = entries.iter().filter(|e| e.name == "TST").collect();
        assert_eq!(tst_entries.len(), 1);
        assert_eq!(tst_entries[0].timestamp_usec, Some(100));
    }

    #[test]
    fn unknown_type_recovery() {
        let mut data = Vec::new();
        data.extend(build_fmt_bootstrap());
        data.extend(build_fmt_for_type(0x81, 11, b"TST\0", "Q", "TimeUS"));
        // Message with unknown type 0x99
        data.extend_from_slice(&HEADER_MAGIC);
        data.push(0x99);
        data.extend_from_slice(&[0; 20]); // some bytes
                                          // Valid message after
        data.extend(build_data_message(0x81, &300u64.to_le_bytes()));

        let reader = Reader::new(std::io::Cursor::new(data));
        let entries: Vec<_> = reader.collect::<Result<Vec<_>, _>>().unwrap();

        let tst_entries: Vec<_> = entries.iter().filter(|e| e.name == "TST").collect();
        assert_eq!(tst_entries.len(), 1);
        assert_eq!(tst_entries[0].timestamp_usec, Some(300));
    }

    #[test]
    fn max_consecutive_errors_boundary() {
        let mut data = Vec::new();
        data.extend(build_fmt_bootstrap());
        data.extend(build_fmt_for_type(0x81, 11, b"TST\0", "Q", "TimeUS"));

        // Each unknown-type header chains: parse_message → recover_and_retry →
        // scan_for_header → parse_message, incrementing consecutive_errors each time.
        let error_count = MAX_CONSECUTIVE_ERRORS + 10;
        for _ in 0..error_count {
            data.extend_from_slice(&HEADER_MAGIC);
            data.push(0x99);
        }

        data.extend(build_data_message(0x81, &999u64.to_le_bytes()));

        let reader = Reader::new(std::io::Cursor::new(data));
        let entries: Vec<_> = reader.collect::<Result<Vec<_>, _>>().unwrap();

        let tst_entries: Vec<_> = entries.iter().filter(|e| e.name == "TST").collect();
        assert!(
            tst_entries.is_empty(),
            "reader should stop before reaching the valid message after {} errors",
            MAX_CONSECUTIVE_ERRORS
        );
    }

    #[test]
    fn recovery_just_below_max_errors() {
        let mut data = Vec::new();
        data.extend(build_fmt_bootstrap());
        data.extend(build_fmt_for_type(0x81, 11, b"TST\0", "Q", "TimeUS"));

        // 255 unknown-type headers: one below the limit, so the final
        // recover_and_retry still scans forward and finds the valid message.
        for _ in 0..(MAX_CONSECUTIVE_ERRORS - 1) {
            data.extend_from_slice(&HEADER_MAGIC);
            data.push(0x99);
        }

        data.extend(build_data_message(0x81, &777u64.to_le_bytes()));

        let reader = Reader::new(std::io::Cursor::new(data));
        let entries: Vec<_> = reader.collect::<Result<Vec<_>, _>>().unwrap();

        let tst_entries: Vec<_> = entries.iter().filter(|e| e.name == "TST").collect();
        assert_eq!(
            tst_entries.len(),
            1,
            "recovery should still work at {} consecutive errors",
            MAX_CONSECUTIVE_ERRORS - 1
        );
        assert_eq!(tst_entries[0].timestamp_usec, Some(777));
    }

    #[test]
    fn formats_accessible() {
        let data = build_fmt_bootstrap();
        let mut reader = Reader::new(std::io::Cursor::new(data));
        let _ = reader.next(); // parse the FMT
        assert!(reader.formats().contains_key(&FMT_TYPE));
        assert_eq!(reader.formats().get(&FMT_TYPE).unwrap().name, "FMT");
    }
}