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use super::xor::XorState;
use crate::error::Error;
use crate::Result;
/// Simple LZSS decompression with optional on-the-fly XOR decryption
pub fn lzss_decompress_simple(
data: &[u8],
expected_size: usize,
xor_key: Option<u16>,
) -> Result<Vec<u8>> {
let mut ring = [0x20u8; 0x1000];
let mut ring_pos = 0xFEEusize;
let mut out = Vec::with_capacity(expected_size);
let mut in_pos = 0usize;
let mut control = 0u8;
let mut bits_left = 0u8;
// XOR state for on-the-fly decryption
let mut xor_state = xor_key.map(XorState::new);
// Helper to read byte with optional XOR decryption
let read_byte = |pos: usize, state: &mut Option<XorState>| -> Option<u8> {
let encrypted = data.get(pos).copied()?;
Some(if let Some(ref mut s) = state {
s.decrypt_byte(encrypted)
} else {
encrypted
})
};
while out.len() < expected_size {
if bits_left == 0 {
let byte = read_byte(in_pos, &mut xor_state)
.ok_or(Error::DecompressionFailed("lzss-simple: unexpected EOF"))?;
control = byte;
in_pos += 1;
bits_left = 8;
}
if (control & 1) != 0 {
let byte = read_byte(in_pos, &mut xor_state)
.ok_or(Error::DecompressionFailed("lzss-simple: unexpected EOF"))?;
in_pos += 1;
out.push(byte);
ring[ring_pos] = byte;
ring_pos = (ring_pos + 1) & 0x0FFF;
} else {
let low = read_byte(in_pos, &mut xor_state)
.ok_or(Error::DecompressionFailed("lzss-simple: unexpected EOF"))?;
let high = read_byte(in_pos + 1, &mut xor_state)
.ok_or(Error::DecompressionFailed("lzss-simple: unexpected EOF"))?;
in_pos += 2;
let offset = usize::from(low) | (usize::from(high & 0xF0) << 4);
let length = usize::from((high & 0x0F) + 3);
for step in 0..length {
let byte = ring[(offset + step) & 0x0FFF];
out.push(byte);
ring[ring_pos] = byte;
ring_pos = (ring_pos + 1) & 0x0FFF;
if out.len() >= expected_size {
break;
}
}
}
control >>= 1;
bits_left -= 1;
}
if out.len() != expected_size {
return Err(Error::DecompressionFailed("lzss-simple"));
}
Ok(out)
}
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