brec 0.3.0

use crate::*;

impl ReadFrom for Slot {
    /// Reads a `Slot` from a stream, expecting the full structure to be available.
    ///
    /// This includes:
    /// - A `SlotHeader` (with capacity)
    /// - A sequence of `u64` length entries (`capacity` items)
    /// - A 4-byte CRC checksum
    ///
    /// # Validation
    /// After reading, the CRC is recomputed and compared with the stored one.
    ///
    /// # Errors
    /// - I/O errors during reading
    /// - `Error::SignatureDismatch` if header signature is invalid
    /// - `Error::CrcDismatch` if CRC check fails
    fn read<T: std::io::Read>(buf: &mut T) -> Result<Self, Error> {
        let header = SlotHeader::read(buf)?;

        let mut lenghts = Vec::with_capacity(header.capacity as usize);
        for _ in 0..header.capacity {
            let mut packet_len = [0u8; 8usize];
            buf.read_exact(&mut packet_len)?;
            lenghts.push(u64::from_le_bytes(packet_len));
        }

        let mut crc = [0u8; 4usize];
        buf.read_exact(&mut crc)?;

        let slot = Slot::new(lenghts, header.capacity, crc);
        if slot.crc == slot.crc() {
            Ok(slot)
        } else {
            Err(Error::CrcDismatch)
        }
    }
}

impl TryReadFrom for Slot {
    /// Attempts to read a `Slot` from a seekable stream, with partial-read awareness.
    ///
    /// This method:
    /// - Tries to read the `SlotHeader` using `try_read`
    /// - Calculates how many bytes are required for the rest of the slot
    /// - Returns `NotEnoughData` if the stream has insufficient bytes
    /// - Performs a CRC check after reading
    ///
    /// The stream is restored to its original position if not enough data is present.
    ///
    /// # Returns
    /// - `ReadStatus::Success(slot)` on success
    /// - `ReadStatus::NotEnoughData(missing)` if full data is not yet available
    /// - `Error::CrcDismatch` if CRC check fails
    fn try_read<T: std::io::Read + std::io::Seek>(buf: &mut T) -> Result<ReadStatus<Self>, Error> {
        let start_pos = buf.stream_position()?;
        let len = buf.seek(std::io::SeekFrom::End(0))? - start_pos;
        buf.seek(std::io::SeekFrom::Start(start_pos))?;

        let header = match SlotHeader::try_read(buf)? {
            ReadStatus::Success(header) => header,
            ReadStatus::NotEnoughData(needed) => return Ok(ReadStatus::NotEnoughData(needed)),
        };

        let needed = SlotHeader::ssize()
            + header.capacity * std::mem::size_of::<u64>() as u64
            + std::mem::size_of::<u32>() as u64;
        if len < needed {
            buf.seek(std::io::SeekFrom::Start(start_pos))?;
            return Ok(ReadStatus::NotEnoughData(PacketHeader::ssize() - needed));
        }

        let mut lenghts = Vec::with_capacity(header.capacity as usize);
        for _ in 0..header.capacity {
            let mut packet_len = [0u8; 8usize];
            buf.read_exact(&mut packet_len)?;
            lenghts.push(u64::from_le_bytes(packet_len));
        }

        let mut crc = [0u8; 4usize];
        buf.read_exact(&mut crc)?;

        let slot = Slot::new(lenghts, header.capacity, crc);
        if slot.crc == slot.crc() {
            Ok(ReadStatus::Success(slot))
        } else {
            Err(Error::CrcDismatch)
        }
    }
}