//! DEFLATE loader.

use crate::durandal::err::*;

/// Loads a GZIP file header.
pub fn load_gzip_header(b: &[u8]) -> ResultS<usize>
{
   const FHCRC:    u8 = 1 << 1;
   const FEXTRA:   u8 = 1 << 2;
   const FNAME:    u8 = 1 << 3;
   const FCOMMENT: u8 = 1 << 4;

   read_data! {
      10, LE in b =>
      id = u16[0];
      cm =  u8[2];
      fl =  u8[3];
   }

   if id != 0x8B1F || cm != 8 {
      bail!("not gzip format");
   }

   let mut p = 10;

   if fl & FEXTRA != 0 {
      read_data!(p + 2, LE in b => xlen = u16[p] usize;);

      if p + 2 + xlen > b.len() {
         bail!("not enough data");
      }

      p += xlen;
   }

   if fl & FNAME != 0 {
      p = skip_zero_terminated_item(&b[p..])?;
   }

   if fl & FCOMMENT != 0 {
      p = skip_zero_terminated_item(&b[p..])?;
   }

   if fl & FHCRC != 0 {
      read_data!(p + 2, LE in b => _crc = u16[p];);

      p += 2;
   }

   Ok(p)
}

fn skip_zero_terminated_item(b: &[u8]) -> ResultS<usize>
{
   if let Some(i) = b.iter().position(|&n| n == 0) {
      Ok(i)
   } else {
      bail!("no end of zero terminated item");
   }
}

// EOF