helix-plus/helix-term/src/line.rs

use termwiz::cell::AttributeChange;
use termwiz::color::{AnsiColor, ColorAttribute, RgbColor};
use termwiz::lineedit::*;

#[derive(Default)]
struct Host {
    history: BasicHistory,
}

impl LineEditorHost for Host {
    // Render the prompt with a darkslateblue background color if
    // the terminal supports true color, otherwise render it with
    // a navy blue ansi color.
    fn render_prompt(&self, prompt: &str) -> Vec<OutputElement> {
        vec![
            OutputElement::Attribute(AttributeChange::Background(
                ColorAttribute::TrueColorWithPaletteFallback(
                    RgbColor::from_named("darkslateblue").unwrap(),
                    AnsiColor::Navy.into(),
                ),
            )),
            OutputElement::Text(prompt.to_owned()),
        ]
    }

    fn history(&mut self) -> &mut dyn History {
        &mut self.history
    }

    /// Demo of the completion API for words starting with "h" or "he"
    fn complete(&self, line: &str, cursor_position: usize) -> Vec<CompletionCandidate> {
        let mut candidates = vec![];
        if let Some((range, word)) = word_at_cursor(line, cursor_position) {
            let words = &["hello", "help", "he-man"];

            for w in words {
                if w.starts_with(word) {
                    candidates.push(CompletionCandidate {
                        range: range.clone(),
                        text: w.to_string(),
                    });
                }
            }
        }
        candidates
    }
}

/// This is a conceptually simple function that computes the bounds
/// of the whitespace delimited word at the specified cursor position
/// in the supplied line string.
/// It returns the range and the corresponding slice out of the line.
/// This function is sufficient for example purposes; in a real application
/// the equivalent function would need to be aware of quoting and other
/// application specific context.
fn word_at_cursor(line: &str, cursor_position: usize) -> Option<(std::ops::Range<usize>, &str)> {
    let char_indices: Vec<(usize, char)> = line.char_indices().collect();
    if char_indices.is_empty() {
        return None;
    }
    let char_position = char_indices
        .iter()
        .position(|(idx, _)| *idx == cursor_position)
        .unwrap_or(char_indices.len());

    // Look back until we find whitespace
    let mut start_position = char_position;
    while start_position > 0
        && start_position <= char_indices.len()
        && !char_indices[start_position - 1].1.is_whitespace()
    {
        start_position -= 1;
    }

    // Look forwards until we find whitespace
    let mut end_position = char_position;
    while end_position < char_indices.len() && !char_indices[end_position].1.is_whitespace() {
        end_position += 1;
    }

    if end_position > start_position {
        let range = char_indices[start_position].0
            ..char_indices
                .get(end_position)
                .map(|c| c.0 + 1)
                .unwrap_or(line.len());
        Some((range.clone(), &line[range]))
    } else {
        None
    }
}

fn main() -> anyhow::Result<()> {
    println!("Type `exit` to quit this example, or start a word with `h` and press Tab.");
    let mut terminal = line_editor_terminal()?;
    let mut editor = LineEditor::new(&mut terminal);

    let mut host = Host::default();
    loop {
        if let Some(line) = editor.read_line(&mut host)? {
            println!("read line: {:?}", line);
            if line == "exit" {
                break;
            }

            host.history().add(&line);
        }
    }

    Ok(())
}