preprocessor.rs

use std::fmt::Write;

use console::AnsiCodeIterator;

/// Expand tabs like an ANSI-enabled expand(1).
pub fn expand_tabs(line: &str, width: usize, cursor: &mut usize) -> String {
    let mut buffer = String::with_capacity(line.len() * 2);

    for chunk in AnsiCodeIterator::new(line) {
        match chunk {
            (text, true) => buffer.push_str(text),
            (mut text, false) => {
                while let Some(index) = text.find('\t') {
                    // Add previous text.
                    if index > 0 {
                        *cursor += index;
                        buffer.push_str(&text[0..index]);
                    }

                    // Add tab.
                    let spaces = width - (*cursor % width);
                    *cursor += spaces;
                    buffer.push_str(&*" ".repeat(spaces));

                    // Next.
                    text = &text[index + 1..text.len()];
                }

                *cursor += text.len();
                buffer.push_str(text);
            }
        }
    }

    buffer
}

fn try_parse_utf8_char(input: &[u8]) -> Option<(char, usize)> {
    let str_from_utf8 = |seq| std::str::from_utf8(seq).ok();

    let decoded = input
        .get(0..1)
        .and_then(str_from_utf8)
        .map(|c| (c, 1))
        .or_else(|| input.get(0..2).and_then(str_from_utf8).map(|c| (c, 2)))
        .or_else(|| input.get(0..3).and_then(str_from_utf8).map(|c| (c, 3)))
        .or_else(|| input.get(0..4).and_then(str_from_utf8).map(|c| (c, 4)));

    decoded.map(|(seq, n)| (seq.chars().next().unwrap(), n))
}

pub fn replace_nonprintable(input: &[u8], tab_width: usize) -> String {
    let mut output = String::new();

    let tab_width = if tab_width == 0 { 4 } else { tab_width };

    let mut idx = 0;
    let mut line_idx = 0;
    let len = input.len();
    while idx < len {
        if let Some((chr, skip_ahead)) = try_parse_utf8_char(&input[idx..]) {
            idx += skip_ahead;
            line_idx += 1;

            match chr {
                // space
                ' ' => output.push('·'),
                // tab
                '\t' => {
                    let tab_stop = tab_width - ((line_idx - 1) % tab_width);
                    line_idx = 0;
                    if tab_stop == 1 {
                        output.push('↹');
                    } else {
                        output.push('├');
                        output.push_str(&"─".repeat(tab_stop - 2));
                        output.push('┤');
                    }
                }
                // line feed
                '\x0A' => {
                    output.push_str("␊\x0A");
                    line_idx = 0;
                }
                // carriage return
                '\x0D' => output.push('␍'),
                // null
                '\x00' => output.push('␀'),
                // bell
                '\x07' => output.push('␇'),
                // backspace
                '\x08' => output.push('␈'),
                // escape
                '\x1B' => output.push('␛'),
                // printable ASCII
                c if c.is_ascii_alphanumeric()
                    || c.is_ascii_punctuation()
                    || c.is_ascii_graphic() =>
                {
                    output.push(c)
                }
                // everything else
                c => output.push_str(&c.escape_unicode().collect::<String>()),
            }
        } else {
            write!(output, "\\x{:02X}", input[idx]).ok();
            idx += 1;
        }
    }

    output
}

#[test]
fn test_try_parse_utf8_char() {
    assert_eq!(try_parse_utf8_char(&[0x20]), Some((' ', 1)));
    assert_eq!(try_parse_utf8_char(&[0x20, 0x20]), Some((' ', 1)));
    assert_eq!(try_parse_utf8_char(&[0x20, 0xef]), Some((' ', 1)));

    assert_eq!(try_parse_utf8_char(&[0x00]), Some(('\x00', 1)));
    assert_eq!(try_parse_utf8_char(&[0x1b]), Some(('\x1b', 1)));

    assert_eq!(try_parse_utf8_char(&[0xc3, 0xa4]), Some(('ä', 2)));
    assert_eq!(try_parse_utf8_char(&[0xc3, 0xa4, 0xef]), Some(('ä', 2)));
    assert_eq!(try_parse_utf8_char(&[0xc3, 0xa4, 0x20]), Some(('ä', 2)));

    assert_eq!(try_parse_utf8_char(&[0xe2, 0x82, 0xac]), Some(('€', 3)));
    assert_eq!(
        try_parse_utf8_char(&[0xe2, 0x82, 0xac, 0xef]),
        Some(('€', 3))
    );
    assert_eq!(
        try_parse_utf8_char(&[0xe2, 0x82, 0xac, 0x20]),
        Some(('€', 3))
    );

    assert_eq!(try_parse_utf8_char(&[0xe2, 0x88, 0xb0]), Some(('∰', 3)));

    assert_eq!(
        try_parse_utf8_char(&[0xf0, 0x9f, 0x8c, 0x82]),
        Some(('🌂', 4))
    );
    assert_eq!(
        try_parse_utf8_char(&[0xf0, 0x9f, 0x8c, 0x82, 0xef]),
        Some(('🌂', 4))
    );
    assert_eq!(
        try_parse_utf8_char(&[0xf0, 0x9f, 0x8c, 0x82, 0x20]),
        Some(('🌂', 4))
    );

    assert_eq!(try_parse_utf8_char(&[]), None);
    assert_eq!(try_parse_utf8_char(&[0xef]), None);
    assert_eq!(try_parse_utf8_char(&[0xef, 0x20]), None);
    assert_eq!(try_parse_utf8_char(&[0xf0, 0xf0]), None);
}