fax 0.2.7

Decoder and Encoder for CCITT Group 3 and 4 bi-level image encodings used by fax machines TIFF and PDF.
Documentation 
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use fax::{decoder, decoder::pels, BitWriter, Bits, Color, VecWriter};
use std::fs::{self, File};
use std::io::Write;

fn split_once_byte(data: &[u8], needle: u8) -> Option<(&[u8], &[u8])> {
    let pos = data.iter().position(|&b| b == needle)?;
    Some((&data[..pos], &data[pos + 1..]))
}

fn main() {
    let mut args = std::env::args().skip(1);
    let input: String = args.next().unwrap();
    let reference = args.next().unwrap();

    let ref_data = std::fs::read(&reference).unwrap();
    let (header1, data) = split_once_byte(&ref_data, b'\n').unwrap();
    assert_eq!(header1, b"P4");
    let (header2, ref_image) = split_once_byte(data, b'\n').unwrap();
    let header2 = std::str::from_utf8(header2).unwrap();
    dbg!(header2);
    let (w, h) = header2.split_once(" ").unwrap();
    let width: u16 = w.parse().unwrap();
    let h: u16 = h.parse().unwrap();

    let mut ref_lines = ref_image.chunks_exact((width as usize + 7) / 8);

    let data;
    let inverted;
    if input.ends_with(".tiff") {
        use tiff::{decoder::Decoder, tags::Tag};
        let tiff = std::fs::read(&input).unwrap();
        let reader = std::io::Cursor::new(tiff.as_slice());
        let mut decoder = Decoder::new(reader).unwrap();
        let (w, h) = decoder.chunk_dimensions();
        let mut buf = vec![0; w as usize * h as usize];
        let strip_offset = decoder
            .get_tag(Tag::StripOffsets)
            .unwrap()
            .into_u32()
            .unwrap() as usize;
        let strip_bytes = decoder
            .get_tag(Tag::StripByteCounts)
            .unwrap()
            .into_u32()
            .unwrap() as usize;

        let interpr = decoder
            .get_tag(Tag::PhotometricInterpretation)
            .unwrap()
            .into_u16()
            .unwrap();

        data = tiff[strip_offset..strip_offset + strip_bytes].to_vec();
        inverted = interpr != 0;
    } else {
        data = fs::read(&input).unwrap();
        inverted = false;
    }
    let mut height = 0;
    let (black, white) = match inverted {
        false => (Bits { data: 1, len: 1 }, Bits { data: 0, len: 1 }),
        true => (Bits { data: 0, len: 1 }, Bits { data: 1, len: 1 }),
    };
    decoder::decode_g4(data.iter().cloned(), width, None, |transitions| {
        let mut writer = VecWriter::new();
        for c in pels(transitions, width) {
            let bit = match c {
                Color::Black => black,
                Color::White => white,
            };
            writer.write(bit);
        }
        writer.pad();
        let data = writer.finish();
        let ref_line = ref_lines.next().unwrap();
        println!("{height:3} dec: {}", Line(&data));
        if ref_line != data {
            println!("    ref: {}", Line(ref_line));
            'a: for (byte, (&r, &v)) in ref_line.iter().zip(data.iter()).enumerate() {
                if r != v {
                    for i in (0..8).rev() {
                        if r & (1 << i) != v & (1 << i) {
                            println!("mismatch at pos {}", (8 * byte) + 7 - i);
                            break 'a;
                        }
                    }
                }
            }
            panic!("decode error");
        }
        height += 1;
    });
}

struct Line<'a>(&'a [u8]);
impl<'a> std::fmt::Display for Line<'a> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        let codes = [' ', '▐', '▌', '█'];
        for b in self
            .0
            .iter()
            .flat_map(|b| [b >> 6, (b >> 4) & 3, (b >> 2) & 3, b & 3])
        {
            write!(f, "{}", codes[b as usize])?;
        }
        Ok(())
    }
}