//! 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>
{
   if b.o_u32b(0)? != 0x51600 || b.o_u32b(4)? != 0x20000 {return None}

   let num = b.o_u16b(24)? as usize;

   for i in 0..num {
      let p   = 26 + (12 * i);
      let fid = b.o_u32b(p  )?;
      let ofs = b.o_u32b(p+4)? as usize;
      let len = b.o_u32b(p+8)? as usize;

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

   None
}

/// Checks for a MacBin header. Returns offset to the resource fork.
pub fn check_mac_bin(b: &[u8]) -> Option<usize>
{
   if b[0] != 0 || b[1] > 63 || b[74] != 0 || b[123] > 0x81 {return None}

   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.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
{
   let ofs = check_mac_bin(b).unwrap_or(0);
   if ofs != 0 {ofs} else {check_apple_single(b).unwrap_or(0)}
}

// EOF