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use crate::err::Result;
use byteorder::{ByteOrder, LittleEndian, ReadBytesExt};
use serde::Serialize;

/// Represents a MFT Reference struct
/// https://msdn.microsoft.com/en-us/library/bb470211(v=vs.85).aspx
/// https://jmharkness.wordpress.com/2011/01/27/mft-file-reference-number/
#[derive(Serialize, Debug, Hash, Eq, PartialEq, Copy, Clone)]
pub struct MftReference {
    pub entry: u64,
    pub sequence: u16,
}

use std::io::Read;

impl MftReference {
    pub fn new(entry: u64, sequence: u16) -> Self {
        MftReference { entry, sequence }
    }

    pub fn from_reader<R: Read>(reader: &mut R) -> Result<Self> {
        Ok(Self::from(reader.read_u64::<LittleEndian>()?))
    }
}

impl From<u64> for MftReference {
    fn from(mft_entry: u64) -> Self {
        let mut as_bytes: [u8; 8] = mft_entry.to_le_bytes();

        // Since the entry is a u64, but is only 6 bytes, we first read the sequence,
        // and then replace them with zeroes, since u64 are expected to be 8 bytes.
        let sequence = LittleEndian::read_u16(&as_bytes[6..8]);

        as_bytes[6] = 0;
        as_bytes[7] = 0;

        let entry = LittleEndian::read_u64(&as_bytes);

        MftReference { entry, sequence }
    }
}

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

    #[test]
    fn test_mft_reference() {
        let raw_reference = vec![0x73, 0x00, 0x00, 0x00, 0x00, 0x00, 0x68, 0x91];

        let mft_reference = MftReference::from_reader(&mut Cursor::new(raw_reference)).unwrap();
        assert_eq!(mft_reference.entry, 115);
        assert_eq!(mft_reference.sequence, 37224);
    }
}