svpng 0.1.1

use std::fs::OpenOptions;
use std::io;
use std::io::prelude::*;
use std::path::Path;

const MAGIC_NUMBER: [u8; 8] = [137, 80, 78, 71, 13, 10, 26, 10];

/// `svpng` save pixels to png file,
/// color types 2 and 6 (truecolor and truecolor with alpha) are supported
/// ## Example:
/// ```no_run
/// // RGB
/// let mut pix = Vec::new();
/// for y in 0..=255 {
///     for x in 0..=255 {
///         pix.push(x);
///         pix.push(y);
///        pix.push(128);
///     }
/// }
/// svpng("rgb.png", 256, 256, &pix, false)?;
/// ```
pub fn svpng<P: AsRef<Path>>(
    path: P,
    w: u32,
    h: u32,
    pix: &[u8],
    is_alpha: bool,
) -> io::Result<()> {
    if w * h * if is_alpha { 4 } else { 3 } != pix.len() as u32 {
        return Err(io::Error::from(io::ErrorKind::InvalidData));
    }
    let mut file = OpenOptions::new()
        .write(true)
        .truncate(true)
        .create(true)
        .open(path)?;

    // Write magic number
    file.write_all(&MAGIC_NUMBER)?;

    // Write IHDR, see https://en.wikipedia.org/wiki/Portable_Network_Graphics#File_format
    {
        file.write_all(&be_u32(13))?; // LENGTH
        let mut buf = "IHDR".chars().map(|x| x as u8).collect::<Vec<u8>>(); // TYPE
                                                                            // DATA {
        buf.extend_from_slice(&be_u32(w)); // width (4 bytes)
        buf.extend_from_slice(&be_u32(h)); // height (4 bytes)
        buf.extend_from_slice(&[8u8]); // bit depth (1 byte)
        buf.extend_from_slice(&[if is_alpha { 6u8 } else { 2u8 }]); // color type (1 byte)
        buf.extend_from_slice(&[0u8, 0u8, 0u8]); // compression method (1 byte), filter method (1 byte), and interlace method (1 byte)
                                                 // }
        file.write_all(&buf)?;
        file.write_all(&be_u32(crc32(&buf)))?;
    }

    // IDAT
    {
        let p = w * if is_alpha { 4 } else { 3 };
        let mut buf = "IDAT".chars().map(|x| x as u8).collect::<Vec<u8>>();

        buf.extend_from_slice(&[0x78, 1u8]); // CM = 8, CINFO = 7 and FLG = 1, see https://www.ietf.org/rfc/rfc1950.txt 2.2. Data format
                                             // compressed data
        for i in 0..h {
            // each row is a comressed block
            // BFINAL BTYPE (3bits, and will omit 5 bits), see https://www.rfc-editor.org/rfc/rfc1951.txt 3.2.3
            buf.extend_from_slice(&[if i == h - 1 { 1u8 } else { 0u8 }]);
            buf.extend_from_slice(&le_u16((p + 1) as u16)); // LEN
            buf.extend_from_slice(&le_u16(!((p + 1) as u16))); // NLEN

            buf.extend_from_slice(&[0u8]); // Indicates no-filter
            for c in 0..p {
                let idx = i * p + c;
                buf.extend_from_slice(&[pix[idx as usize]])
            }
        }
        buf.extend_from_slice(&be_u32(adler32(pix)));
        file.write_all(&be_u32(buf.len() as u32 - 4))?; // LEN
        file.write_all(&buf)?; // TYPE + DATA
        file.write_all(&be_u32(crc32(&buf)))?;
    }

    // IEND
    {
        file.write_all(&be_u32(0))?;
        let buf = "IEND".chars().map(|x| x as u8).collect::<Vec<u8>>(); // TYPE
        file.write_all(&buf)?;
        file.write_all(&be_u32(crc32(&buf)))?;
    }
    Ok(())
}

fn be_u32(n: u32) -> [u8; 4] {
    [(n >> 24) as u8, (n >> 16) as u8, (n >> 8) as u8, n as u8]
}

fn le_u16(n: u16) -> [u8; 2] {
    [n as u8, (n >> 8) as u8]
}

fn adler32(pix: &[u8]) -> u32 {
    let mut s1 = 1u32;
    let mut s2 = 0u32;
    for p in pix.iter() {
        s1 += u32::from(*p);
        if s1 >= 65521 {
            s1 -= 65521
        }
        s2 += s1;
        if s2 >= 65521 {
            s2 -= 65521
        }
    }
    s2 * 65536 + s1
}

// CRC32

// Ref: http://web.mit.edu/freebsd/head/sys/libkern/crc32.c
#[allow(clippy::unreadable_literal)]
const CRC32_TAB: [u32; 256] = [
    0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419, 0x706af48f, 0xe963a535, 0x9e6495a3,
    0x0edb8832, 0x79dcb8a4, 0xe0d5e91e, 0x97d2d988, 0x09b64c2b, 0x7eb17cbd, 0xe7b82d07, 0x90bf1d91,
    0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de, 0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7,
    0x136c9856, 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec, 0x14015c4f, 0x63066cd9, 0xfa0f3d63, 0x8d080df5,
    0x3b6e20c8, 0x4c69105e, 0xd56041e4, 0xa2677172, 0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b,
    0x35b5a8fa, 0x42b2986c, 0xdbbbc9d6, 0xacbcf940, 0x32d86ce3, 0x45df5c75, 0xdcd60dcf, 0xabd13d59,
    0x26d930ac, 0x51de003a, 0xc8d75180, 0xbfd06116, 0x21b4f4b5, 0x56b3c423, 0xcfba9599, 0xb8bda50f,
    0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924, 0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d,
    0x76dc4190, 0x01db7106, 0x98d220bc, 0xefd5102a, 0x71b18589, 0x06b6b51f, 0x9fbfe4a5, 0xe8b8d433,
    0x7807c9a2, 0x0f00f934, 0x9609a88e, 0xe10e9818, 0x7f6a0dbb, 0x086d3d2d, 0x91646c97, 0xe6635c01,
    0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e, 0x6c0695ed, 0x1b01a57b, 0x8208f4c1, 0xf50fc457,
    0x65b0d9c6, 0x12b7e950, 0x8bbeb8ea, 0xfcb9887c, 0x62dd1ddf, 0x15da2d49, 0x8cd37cf3, 0xfbd44c65,
    0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2, 0x4adfa541, 0x3dd895d7, 0xa4d1c46d, 0xd3d6f4fb,
    0x4369e96a, 0x346ed9fc, 0xad678846, 0xda60b8d0, 0x44042d73, 0x33031de5, 0xaa0a4c5f, 0xdd0d7cc9,
    0x5005713c, 0x270241aa, 0xbe0b1010, 0xc90c2086, 0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,
    0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4, 0x59b33d17, 0x2eb40d81, 0xb7bd5c3b, 0xc0ba6cad,
    0xedb88320, 0x9abfb3b6, 0x03b6e20c, 0x74b1d29a, 0xead54739, 0x9dd277af, 0x04db2615, 0x73dc1683,
    0xe3630b12, 0x94643b84, 0x0d6d6a3e, 0x7a6a5aa8, 0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1,
    0xf00f9344, 0x8708a3d2, 0x1e01f268, 0x6906c2fe, 0xf762575d, 0x806567cb, 0x196c3671, 0x6e6b06e7,
    0xfed41b76, 0x89d32be0, 0x10da7a5a, 0x67dd4acc, 0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5,
    0xd6d6a3e8, 0xa1d1937e, 0x38d8c2c4, 0x4fdff252, 0xd1bb67f1, 0xa6bc5767, 0x3fb506dd, 0x48b2364b,
    0xd80d2bda, 0xaf0a1b4c, 0x36034af6, 0x41047a60, 0xdf60efc3, 0xa867df55, 0x316e8eef, 0x4669be79,
    0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236, 0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f,
    0xc5ba3bbe, 0xb2bd0b28, 0x2bb45a92, 0x5cb36a04, 0xc2d7ffa7, 0xb5d0cf31, 0x2cd99e8b, 0x5bdeae1d,
    0x9b64c2b0, 0xec63f226, 0x756aa39c, 0x026d930a, 0x9c0906a9, 0xeb0e363f, 0x72076785, 0x05005713,
    0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38, 0x92d28e9b, 0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21,
    0x86d3d2d4, 0xf1d4e242, 0x68ddb3f8, 0x1fda836e, 0x81be16cd, 0xf6b9265b, 0x6fb077e1, 0x18b74777,
    0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c, 0x8f659eff, 0xf862ae69, 0x616bffd3, 0x166ccf45,
    0xa00ae278, 0xd70dd2ee, 0x4e048354, 0x3903b3c2, 0xa7672661, 0xd06016f7, 0x4969474d, 0x3e6e77db,
    0xaed16a4a, 0xd9d65adc, 0x40df0b66, 0x37d83bf0, 0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,
    0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6, 0xbad03605, 0xcdd70693, 0x54de5729, 0x23d967bf,
    0xb3667a2e, 0xc4614ab8, 0x5d681b02, 0x2a6f2b94, 0xb40bbe37, 0xc30c8ea1, 0x5a05df1b, 0x2d02ef8d,
];

pub fn crc32(buf: &[u8]) -> u32 {
    let mut crc = !0u32;
    for x in buf.iter() {
        crc = CRC32_TAB[((crc ^ u32::from(*x)) & 0xFF) as usize] ^ (crc >> 8);
    }
    crc ^ !0u32
}

#[cfg(test)]
mod tests {
    use super::crc32;
    #[test]
    fn crc32_test() {
        assert_eq!(
            crc32(&"123456789".chars().map(|x| x as u8).collect::<Vec<u8>>()),
            0xCBF43926
        );
    }
}