//! Macintosh archived format header utilities.

use crate::durandal::bin::*;

/// Checks for an AppleSingle header. Returns offset to the resource fork.
pub fn check_apple_single(b: &[u8]) -> Option<usize>
{
   // check magic numbers
   if b[0..8] != [0, 5, 22, 0, 0, 2, 0, 0] {return None;}

   // get the resource fork (entity 1)
   let num = b.o_u16b(24)? as usize;
   for i in 0..num {
      let p   = 26 + 12 * i;
      let ent = b.o_u32b(p  )?;
      let ofs = b.o_u32b(p+4)? as usize;
      let len = b.o_u32b(p+8)? as usize;

      if ent == 1 {return if ofs + len > b.len() {None} else {Some(ofs)};}
   }

   // no resource fork
   None
}

/// Checks for a MacBinary II header. Returns offset to the resource fork.
pub fn check_macbin(b: &[u8]) -> Option<usize>
{
   // check legacy version, length, zero fill, and macbin2 version
   if b[0] != 0 || b[1] > 63 || b[74] != 0 || b[123] > 129 {return None;}

   let mut crc = 0;

   // check header crc
   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 ok, resource fork follows
   if crc == b.o_u16b(124)? {Some(128)} else {None}
}

/// 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
{
   if let Some(ofs) = check_macbin(b) {ofs}
   else {check_apple_single(b).unwrap_or(0)}
}

// EOF