polytrack_codes/tools/

mod.rs

#![allow(clippy::cast_possible_truncation, clippy::cast_sign_loss)]
#[cfg(test)]
mod tests;

pub mod prelude {
    pub use super::{Track, read::*, write::*};
}

use std::io::Read as _;

use flate2::{Compression, FlushCompress, read::ZlibDecoder};

const ENCODE_VALUES: [char; 62] = [
    'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S',
    'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l',
    'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4',
    '5', '6', '7', '8', '9',
];

const DECODE_VALUES: [i32; 123] = [
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8,
    9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1, -1, 26,
    27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50,
    51,
];

#[must_use]
/// Encode the given byte buffer into base62 encoded text according to Polytrack's base62 implementation.
/// Returns [`None`] if something failed in the process.
pub fn encode(input: &[u8]) -> Option<String> {
    let mut bit_pos = 0;
    let mut res = String::new();

    while bit_pos < 8 * input.len() {
        let mut char_value = encode_chars(input, bit_pos)?;
        // if char_num ends with 11110, shorten it to 5 bits
        // (getting rid of value 62 and 63, which are too big for base62)
        if (char_value & 0b11110) == 0b11110 {
            char_value &= 0b11111;
            bit_pos += 5;
        } else {
            bit_pos += 6;
        }
        res.push(*ENCODE_VALUES.get(char_value)?);
    }

    Some(res)
}

#[must_use]
/// Decode the given string as base62 text according to Polytrack's base62 implementation.
/// Returns [`None`] if any character isn't valid for base62 encoded text.
pub fn decode(input: &str) -> Option<Vec<u8>> {
    let mut out_pos = 0;
    let mut bytes_out: Vec<u8> = Vec::new();

    for (i, ch) in input.chars().enumerate() {
        let char_code = ch as usize;
        let char_value = *DECODE_VALUES.get(char_code)?;
        if char_value == -1 {
            return None;
        }
        // 5 if char_value is 30 or 31, 6 otherwise (see encode for explanation)
        let value_len = if (char_value & 0b11110) == 0b11110 {
            5
        } else {
            6
        };
        decode_chars(
            &mut bytes_out,
            out_pos,
            value_len,
            char_value,
            i == input.len() - 1,
        );
        out_pos += value_len;
    }

    Some(bytes_out)
}

fn encode_chars(bytes: &[u8], bit_index: usize) -> Option<usize> {
    if bit_index >= 8 * bytes.len() {
        return None;
    }

    let byte_index = bit_index / 8;
    let current_byte = *bytes.get(byte_index)? as usize;
    let offset = bit_index - 8 * byte_index;
    if offset <= 2 || byte_index >= bytes.len() - 1 {
        // move mask into right position, get only offset bits of current_byte, move back
        Some((current_byte & (63 << offset)) >> offset)
    } else {
        let next_byte = *bytes.get(byte_index + 1)? as usize;
        // same concept as above, move mask into right position,
        // get correct bits of current and next byte, move back, combine the two
        Some(
            ((current_byte & (63 << offset)) >> offset)
                | ((next_byte & (63 >> (8 - offset))) << (8 - offset)),
        )
    }
}

fn decode_chars(
    bytes: &mut Vec<u8>,
    bit_index: usize,
    value_len: usize,
    char_value: i32,
    is_last: bool,
) {
    let byte_index = bit_index / 8;
    while byte_index >= bytes.len() {
        bytes.push(0);
    }

    // offset in current byte
    let offset = bit_index - 8 * byte_index;

    // writes value into byte (only part that fits)
    bytes[byte_index] |= ((char_value << offset) & 0xFF) as u8;

    // in case of value going into next byte add that part
    if offset > 8 - value_len && !is_last {
        let byte_index_next = byte_index + 1;
        if byte_index_next >= bytes.len() {
            bytes.push(0);
        }

        // write rest of value into next byte
        bytes[byte_index_next] |= (char_value >> (8 - offset)) as u8;
    }
}

#[must_use]
pub fn decompress(data: &[u8]) -> Option<Vec<u8>> {
    let mut decoder = ZlibDecoder::new(data);
    let mut decompressed_data = Vec::new();
    decoder.read_to_end(&mut decompressed_data).ok()?;
    Some(decompressed_data)
}

#[must_use]
pub fn compress_first(data: &[u8]) -> Option<Vec<u8>> {
    deflate_with_window(data, 9)
}

#[must_use]
pub fn compress_final(data: &[u8]) -> Option<Vec<u8>> {
    deflate_with_window(data, 15)
}

fn deflate_with_window(input: &[u8], window_bits: u8) -> Option<Vec<u8>> {
    let mut compressor =
        flate2::Compress::new_with_window_bits(Compression::best(), true, window_bits);
    let mut output = Vec::new();
    let mut buffer = [0u8; 65536];
    let mut input_offset = 0;
    loop {
        let before_in = compressor.total_in();
        let before_out = compressor.total_out();
        let flush = if input_offset >= input.len() {
            FlushCompress::Finish
        } else {
            FlushCompress::None
        };
        let status = compressor
            .compress(&input[input_offset..], &mut buffer, flush)
            .ok()?;
        let consumed = (compressor.total_in() - before_in) as usize;
        let produced = (compressor.total_out() - before_out) as usize;
        input_offset += consumed;
        output.extend_from_slice(&buffer[..produced]);
        if status == flate2::Status::StreamEnd {
            break;
        }
    }
    Some(output)
}

#[must_use]
pub fn hash_vec(track_data: Vec<u8>) -> String {
    sha256::digest(track_data)
}

#[derive(Debug, PartialEq, Eq, Clone)]
pub struct Track {
    pub name: String,
    pub author: Option<String>,
    pub last_modified: Option<u32>,
    pub track_data: Vec<u8>,
}

pub(crate) mod read {
    #[inline]
    pub fn read_u8(buf: &[u8], offset: &mut usize) -> Option<u8> {
        let res = buf.get(*offset).copied();
        *offset += 1;
        res
    }
    #[inline]
    pub fn read_u16(buf: &[u8], offset: &mut usize) -> Option<u16> {
        let res = Some(u16::from(*buf.get(*offset)?) | (u16::from(*buf.get(*offset + 1)?) << 8));
        *offset += 2;
        res
    }
    #[inline]
    pub fn read_i24(buf: &[u8], offset: &mut usize) -> Option<i32> {
        let res = Some(
            i32::from(*buf.get(*offset)?)
                | (i32::from(*buf.get(*offset + 1)?) << 8)
                | (i32::from(*buf.get(*offset + 2)?) << 16),
        );
        *offset += 3;
        res
    }
    #[inline]
    pub fn read_u32(buf: &[u8], offset: &mut usize) -> Option<u32> {
        let res = Some(
            u32::from(*buf.get(*offset)?)
                | (u32::from(*buf.get(*offset + 1)?) << 8)
                | (u32::from(*buf.get(*offset + 2)?) << 16)
                | (u32::from(*buf.get(*offset + 3)?) << 24),
        );
        *offset += 4;
        res
    }
}

pub(crate) mod write {
    #[inline]
    pub fn write_u8(data: &mut Vec<u8>, value: u32) {
        data.push((value & 0xFF) as u8);
    }
    #[inline]
    pub fn write_u16(data: &mut Vec<u8>, value: u32) {
        data.push((value & 0xFF) as u8);
        data.push((value >> 8 & 0xFF) as u8);
    }
    #[inline]
    pub fn write_u24(data: &mut Vec<u8>, value: u32) {
        data.push((value & 0xFF) as u8);
        data.push((value >> 8 & 0xFF) as u8);
        data.push((value >> 16 & 0xFF) as u8);
    }
    #[inline]
    pub fn write_u32(data: &mut Vec<u8>, value: u32) {
        data.push((value & 0xFF) as u8);
        data.push((value >> 8 & 0xFF) as u8);
        data.push((value >> 16 & 0xFF) as u8);
        data.push((value >> 24 & 0xFF) as u8);
    }
}