Implement LZSS decompression with optional XOR decryption

- Added `lzss_decompress_simple` function for LZSS decompression in `lzss.rs`.
- Introduced `XorState` struct and `xor_stream` function for XOR decryption in `xor.rs`.
- Updated `mod.rs` to include new LZSS and XOR modules.
- Refactored `parse_library` function in `parse.rs` to utilize the new XOR decryption functionality.
- Cleaned up and organized code in `lib.rs` by removing redundant functions and structures.
- Added tests for new functionality in `tests.rs`.

1 files changed, 292 insertions, 0 deletions

diff --git a/crates/rsli/src/compress/lzh.rs b/crates/rsli/src/compress/lzh.rs
new file mode 100644
index 0000000..93f2267
--- /dev/null
+++ b/crates/rsli/src/compress/lzh.rs
@@ -0,0 +1,292 @@
+use super::xor::xor_stream;
+use crate::error::Error;
+use crate::Result;
+
+pub(crate) const LZH_N: usize = 4096;
+pub(crate) const LZH_F: usize = 60;
+pub(crate) const LZH_THRESHOLD: usize = 2;
+pub(crate) const LZH_N_CHAR: usize = 256 - LZH_THRESHOLD + LZH_F;
+pub(crate) const LZH_T: usize = LZH_N_CHAR * 2 - 1;
+pub(crate) const LZH_R: usize = LZH_T - 1;
+pub(crate) const LZH_MAX_FREQ: u16 = 0x8000;
+
+/// LZSS-Huffman decompression with optional XOR pre-decryption
+pub fn lzss_huffman_decompress(
+    data: &[u8],
+    expected_size: usize,
+    xor_key: Option<u16>,
+) -> Result<Vec<u8>> {
+    // TODO: Full optimization for Huffman variant (rare in practice)
+    // For now, fallback to separate XOR step for Huffman
+    if let Some(key) = xor_key {
+        let decrypted = xor_stream(data, key);
+        let mut decoder = LzhDecoder::new(&decrypted);
+        decoder.decode(expected_size)
+    } else {
+        let mut decoder = LzhDecoder::new(data);
+        decoder.decode(expected_size)
+    }
+}
+
+struct LzhDecoder<'a> {
+    bit_reader: BitReader<'a>,
+    text: [u8; LZH_N],
+    freq: [u16; LZH_T + 1],
+    parent: [usize; LZH_T + LZH_N_CHAR],
+    son: [usize; LZH_T],
+    d_code: [u8; 256],
+    d_len: [u8; 256],
+    ring_pos: usize,
+}
+
+impl<'a> LzhDecoder<'a> {
+    fn new(data: &'a [u8]) -> Self {
+        let mut decoder = Self {
+            bit_reader: BitReader::new(data),
+            text: [0x20u8; LZH_N],
+            freq: [0u16; LZH_T + 1],
+            parent: [0usize; LZH_T + LZH_N_CHAR],
+            son: [0usize; LZH_T],
+            d_code: [0u8; 256],
+            d_len: [0u8; 256],
+            ring_pos: LZH_N - LZH_F,
+        };
+        decoder.init_tables();
+        decoder.start_huff();
+        decoder
+    }
+
+    fn decode(&mut self, expected_size: usize) -> Result<Vec<u8>> {
+        let mut out = Vec::with_capacity(expected_size);
+
+        while out.len() < expected_size {
+            let c = self.decode_char();
+            if c < 256 {
+                let byte = c as u8;
+                out.push(byte);
+                self.text[self.ring_pos] = byte;
+                self.ring_pos = (self.ring_pos + 1) & (LZH_N - 1);
+            } else {
+                let mut offset = self.decode_position();
+                offset = (self.ring_pos.wrapping_sub(offset).wrapping_sub(1)) & (LZH_N - 1);
+                let mut length = c.saturating_sub(253);
+
+                while length > 0 && out.len() < expected_size {
+                    let byte = self.text[offset];
+                    out.push(byte);
+                    self.text[self.ring_pos] = byte;
+                    self.ring_pos = (self.ring_pos + 1) & (LZH_N - 1);
+                    offset = (offset + 1) & (LZH_N - 1);
+                    length -= 1;
+                }
+            }
+        }
+
+        if out.len() != expected_size {
+            return Err(Error::DecompressionFailed("lzss-huffman"));
+        }
+        Ok(out)
+    }
+
+    fn init_tables(&mut self) {
+        let d_code_group_counts = [1usize, 3, 8, 12, 24, 16];
+        let d_len_group_counts = [32usize, 48, 64, 48, 48, 16];
+
+        let mut group_index = 0u8;
+        let mut idx = 0usize;
+        let mut run = 32usize;
+        for count in d_code_group_counts {
+            for _ in 0..count {
+                for _ in 0..run {
+                    self.d_code[idx] = group_index;
+                    idx += 1;
+                }
+                group_index = group_index.wrapping_add(1);
+            }
+            run >>= 1;
+        }
+
+        let mut len = 3u8;
+        idx = 0;
+        for count in d_len_group_counts {
+            for _ in 0..count {
+                self.d_len[idx] = len;
+                idx += 1;
+            }
+            len = len.saturating_add(1);
+        }
+    }
+
+    fn start_huff(&mut self) {
+        for i in 0..LZH_N_CHAR {
+            self.freq[i] = 1;
+            self.son[i] = i + LZH_T;
+            self.parent[i + LZH_T] = i;
+        }
+
+        let mut i = 0usize;
+        let mut j = LZH_N_CHAR;
+        while j <= LZH_R {
+            self.freq[j] = self.freq[i].saturating_add(self.freq[i + 1]);
+            self.son[j] = i;
+            self.parent[i] = j;
+            self.parent[i + 1] = j;
+            i += 2;
+            j += 1;
+        }
+
+        self.freq[LZH_T] = u16::MAX;
+        self.parent[LZH_R] = 0;
+    }
+
+    fn decode_char(&mut self) -> usize {
+        let mut node = self.son[LZH_R];
+        while node < LZH_T {
+            let bit = usize::from(self.bit_reader.read_bit_or_zero());
+            node = self.son[node + bit];
+        }
+
+        let c = node - LZH_T;
+        self.update(c);
+        c
+    }
+
+    fn decode_position(&mut self) -> usize {
+        let i = self.bit_reader.read_bits_or_zero(8) as usize;
+        let mut c = usize::from(self.d_code[i]) << 6;
+        let mut j = usize::from(self.d_len[i]).saturating_sub(2);
+
+        while j > 0 {
+            j -= 1;
+            c |= usize::from(self.bit_reader.read_bit_or_zero()) << j;
+        }
+
+        c | (i & 0x3F)
+    }
+
+    fn update(&mut self, c: usize) {
+        if self.freq[LZH_R] == LZH_MAX_FREQ {
+            self.reconstruct();
+        }
+
+        let mut current = self.parent[c + LZH_T];
+        loop {
+            self.freq[current] = self.freq[current].saturating_add(1);
+            let freq = self.freq[current];
+
+            if current + 1 < self.freq.len() && freq > self.freq[current + 1] {
+                let mut swap_idx = current + 1;
+                while swap_idx + 1 < self.freq.len() && freq > self.freq[swap_idx + 1] {
+                    swap_idx += 1;
+                }
+
+                self.freq.swap(current, swap_idx);
+
+                let left = self.son[current];
+                let right = self.son[swap_idx];
+                self.son[current] = right;
+                self.son[swap_idx] = left;
+
+                self.parent[left] = swap_idx;
+                if left < LZH_T {
+                    self.parent[left + 1] = swap_idx;
+                }
+
+                self.parent[right] = current;
+                if right < LZH_T {
+                    self.parent[right + 1] = current;
+                }
+
+                current = swap_idx;
+            }
+
+            current = self.parent[current];
+            if current == 0 {
+                break;
+            }
+        }
+    }
+
+    fn reconstruct(&mut self) {
+        let mut j = 0usize;
+        for i in 0..LZH_T {
+            if self.son[i] >= LZH_T {
+                self.freq[j] = (self.freq[i].saturating_add(1)) / 2;
+                self.son[j] = self.son[i];
+                j += 1;
+            }
+        }
+
+        let mut i = 0usize;
+        let mut current = LZH_N_CHAR;
+        while current < LZH_T {
+            let sum = self.freq[i].saturating_add(self.freq[i + 1]);
+            self.freq[current] = sum;
+
+            let mut insert_at = current;
+            while insert_at > 0 && sum < self.freq[insert_at - 1] {
+                insert_at -= 1;
+            }
+
+            for move_idx in (insert_at..current).rev() {
+                self.freq[move_idx + 1] = self.freq[move_idx];
+                self.son[move_idx + 1] = self.son[move_idx];
+            }
+
+            self.freq[insert_at] = sum;
+            self.son[insert_at] = i;
+
+            i += 2;
+            current += 1;
+        }
+
+        for idx in 0..LZH_T {
+            let node = self.son[idx];
+            self.parent[node] = idx;
+            if node < LZH_T {
+                self.parent[node + 1] = idx;
+            }
+        }
+
+        self.freq[LZH_T] = u16::MAX;
+        self.parent[LZH_R] = 0;
+    }
+}
+
+struct BitReader<'a> {
+    data: &'a [u8],
+    byte_pos: usize,
+    bit_mask: u8,
+}
+
+impl<'a> BitReader<'a> {
+    fn new(data: &'a [u8]) -> Self {
+        Self {
+            data,
+            byte_pos: 0,
+            bit_mask: 0x80,
+        }
+    }
+
+    fn read_bit_or_zero(&mut self) -> u8 {
+        let Some(byte) = self.data.get(self.byte_pos).copied() else {
+            return 0;
+        };
+
+        let bit = if (byte & self.bit_mask) != 0 { 1 } else { 0 };
+        self.bit_mask >>= 1;
+        if self.bit_mask == 0 {
+            self.bit_mask = 0x80;
+            self.byte_pos = self.byte_pos.saturating_add(1);
+        }
+        bit
+    }
+
+    fn read_bits_or_zero(&mut self, bits: usize) -> u32 {
+        let mut value = 0u32;
+        for _ in 0..bits {
+            value = (value << 1) | u32::from(self.read_bit_or_zero());
+        }
+        value
+    }
+}