cursive/src/utils/mod.rs

//! Toolbox to make text layout easier.

use unicode_width::UnicodeWidthStr;
use unicode_segmentation::UnicodeSegmentation;

mod lines_iterator;
mod reader;

pub use self::lines_iterator::{LinesIterator, Row};
pub use self::reader::ProgressReader;

/// Computes the length of a prefix that fits in the given `width`.
///
/// Takes non-breakable elements from `iter`, while keeping the
/// string width under `width` (and adding the length of `delimiter`
/// between each element).
///
/// Given `total_text = iter.collect().join(delimiter)`, the result
/// is the length of the longest prefix of `width` or less cells,
/// without breaking inside an element.
///
/// Example:
///
/// ```
/// # extern crate cursive;
/// extern crate unicode_segmentation;
/// use unicode_segmentation::UnicodeSegmentation;
///
/// # use cursive::utils::prefix_length;
/// # fn main() {
/// let my_text = "blah...";
/// // This returns the number of bytes for a prefix of `my_text` that
/// // fits within 5 cells.
/// prefix_length(my_text.graphemes(true), 5, "");
/// # }
/// ```
pub fn prefix_length<'a, I: Iterator<Item = &'a str>>(iter: I, width: usize,
                                                      delimiter: &str)
                                                      -> usize {
    let delimiter_width = delimiter.width();
    let delimiter_len = delimiter.len();

    let sum = iter.scan(0, |w, token| {
            *w += token.width();
            if *w > width {
                None
            } else {
                // Add a space
                *w += delimiter_width;
                Some(token)
            }
        })
        .map(|token| token.len() + delimiter_len)
        .fold(0, |a, b| a + b);

    // We counted delimiter once too many times,
    // but only if the iterator was non empty.
    if sum == 0 {
        sum
    } else {
        sum - delimiter_len
    }
}

/// Computes the length of a suffix that fits in the given `width`.
///
/// Returns the number of bytes of the longest
/// suffix from `text` that fits in `width`.
pub fn suffix_length(text: &str, width: usize) -> usize {
    text.graphemes(true)
        .rev()
        .scan(0, |w, g| {
            *w += g.width();
            if *w > width {
                None
            } else {
                Some(g)
            }
        })
        .map(|g| g.len())
        .fold(0, |a, b| a + b)
}