tuigram-cli 1.0.0

Telegram in your terminal: a fast, vim-style Telegram client built on TDLib
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//! Text from other people, made safe to show and copy.

/// Characters left out of text from Telegram:
/// - control characters other than line breaks and tabs. The screen drops
///   them anyway, but copied text keeps them, and a hidden `\r` or escape
///   can run a command when pasted into a shell or vim.
/// - bidi overrides and isolates, which can make text read backwards:
///   "invoice<U+202E>fdp.exe" shows as `invoiceexe.pdf` in some terminals,
///   and the bidi marks.
/// - invisible characters that terminals and the layout disagree on: the
///   layout counts them as no columns, while some terminals move the cursor
///   on, which pushes the rest of the row out of place. These are the Hangul
///   fillers of "invisible" Telegram names, the soft hyphen, zero-width
///   spaces and the like. Joiners and variation selectors stay, since emoji
///   need them.
/// - the private character kitty uses to place images, so text can't pose
///   as one.
pub fn is_hidden(c: char) -> bool {
    (c.is_control() && c != '\n' && c != '\t')
        || matches!(
            c,
            '\u{202A}'..='\u{202E}'
                | '\u{2066}'..='\u{2069}'
                | '\u{200E}'
                | '\u{200F}'
                | '\u{061C}'
                | '\u{00AD}'
                | '\u{034F}'
                | '\u{115F}'
                | '\u{1160}'
                | '\u{17B4}'
                | '\u{17B5}'
                | '\u{180E}'
                | '\u{200B}'
                | '\u{2060}'..='\u{2064}'
                | '\u{206A}'..='\u{206F}'
                | '\u{3164}'
                | '\u{FEFF}'
                | '\u{FFA0}'
                | '\u{FFF9}'..='\u{FFFB}'
                | '\u{1D173}'..='\u{1D17A}'
                | '\u{E0001}'
                | '\u{10EEEE}'
        )
}

/// `text` without the characters [`is_hidden`] leaves out.
pub fn clean(text: &str) -> String {
    text.chars().filter(|&c| !is_hidden(c)).collect()
}

/// The first `n` characters of `text`.
pub fn first_chars(text: &str, n: usize) -> &str {
    text.char_indices().nth(n).map_or(text, |(i, _)| &text[..i])
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn controls_and_bidi_overrides_are_dropped_but_line_breaks_and_tabs_stay() {
        assert_eq!(clean("invoice\u{202E}fdp.exe"), "invoicefdp.exe");
        assert_eq!(clean("a\u{1b}[2Jb\rc\u{7}d\u{9b}e"), "a[2Jbcde");
        assert_eq!(clean("one\ntwo\tthree"), "one\ntwo\tthree");
        assert_eq!(clean("עברית and العربية"), "עברית and العربية");
    }

    #[test]
    fn invisible_fillers_go_but_emoji_keep_their_joiners_and_selectors() {
        let filler = format!("x{}SPOOF", "\u{3164}".repeat(40));
        assert_eq!(clean(&filler), "xSPOOF");
        assert_eq!(clean("a\u{FFA0}\u{00AD}\u{200B}\u{FEFF}b"), "ab");
        let family = "👨\u{200D}👩\u{200D}👧";
        assert_eq!(clean(family), family);
        assert_eq!(clean("❤\u{FE0F}"), "❤\u{FE0F}");
        let england = "🏴\u{E0067}\u{E0062}\u{E0065}\u{E006E}\u{E0067}\u{E007F}";
        assert_eq!(clean(england), england);
    }

    #[test]
    fn first_chars_stops_on_a_character_boundary() {
        assert_eq!(first_chars("héllo", 2), "hé");
        assert_eq!(first_chars("hi", 5), "hi");
    }
}