//! Macintosh archived format header utilities.

use durandal::bin::*;

/// Checks for an AppleSingle header. Returns offset to the resource fork.
pub fn check_apple_single(b: &[u8]) -> usize
{
   if b_u32b(&b[0..4]) != 0x51600 || b_u32b(&b[4..8]) != 0x20000
      {return 0}

   let num = b_u16b(&b[24..26]) as usize;

   for i in 0..num
   {
      let p   = 26 + (12 * i);
      let fid = b_u32b(&b[p+0..p+ 4]);
      let ofs = b_u32b(&b[p+4..p+ 8]) as usize;
      let len = b_u32b(&b[p+8..p+12]) as usize;

      if fid == 1 {return if ofs + len > b.len() {0} else {ofs}}
   }

   0
}

/// Checks for a MacBin header. Returns offset to the resource fork.
pub fn check_mac_bin(b: &[u8]) -> usize
{
   if b[0] != 0 || b[1] > 63 || b[74] != 0 || b[123] > 0x81 {return 0}

   let mut crc = 0;

   for i in 0..124 {
      for j in 8..16
      {
         let d = b[i] as (u16) << j;
         if (d ^ crc) & 0x8000 != 0 {crc = crc << 1 ^ 0x1021}
         else                       {crc <<= 1}
      }
   }

   if crc == b_u16b(&b[124..126]) {128} else {0}
}

/// Reads a MacBin or AppleSingle header if there is one and returns the
/// offset from the start of the header to the resource fork (if one is found.)
pub fn try_mac_header(b: &[u8]) -> usize
{
   let ofs = check_mac_bin(b);
   if ofs != 0 {ofs} else {check_apple_single(b)}
}

// EOF