cursive/src/utils/mod.rs

//! Toolbox to make text layout easier.

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

mod lines_iterator;
mod reader;

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

/// The length and width of a part of a string.
pub struct Prefix {
    /// The length (in bytes) of the string.
    pub length: usize,
    /// The unicode-width of the string.
    pub width: usize,
}

/// Computes the length (number of bytes) and width 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;
/// # fn main() {
/// let my_text = "blah...";
/// // This returns the number of bytes for a prefix of `my_text` that
/// // fits within 5 cells.
/// prefix(my_text.graphemes(true), 5, "");
/// # }
/// ```
pub fn prefix<'a, I>(
    iter: I, available_width: usize, delimiter: &str
) -> Prefix
where
    I: Iterator<Item = &'a str>,
{
    let delimiter_width = delimiter.width();
    let delimiter_len = delimiter.len();

    // `current_width` is the width of everything
    // before the next token, including any space.
    let mut current_width = 0;
    let sum: usize = iter.take_while(|token| {
        let width = token.width();
        if current_width + width > available_width {
            false
        } else {
            // Include the delimiter after this token.
            current_width += width;
            current_width += delimiter_width;
            true
        }
    }).map(|token| token.len() + delimiter_len)
        .sum();

    // We counted delimiter once too many times,
    // but only if the iterator was non empty.
    let length = sum.saturating_sub(delimiter_len);

    // `current_width` includes a delimiter after the last token
    debug_assert!(current_width <= available_width + delimiter_width);

    Prefix {
        length: length,
        width: current_width,
    }
}

/// Computes the length (number of bytes) and width of a suffix that fits in the given `width`.
///
/// Doesn't break inside elements returned by `iter`.
///
/// Returns the number of bytes of the longest
/// suffix from `text` that fits in `width`.
///
/// This is a shortcut for `prefix_length(iter.rev(), width, delimiter)`
pub fn suffix<'a, I>(iter: I, width: usize, delimiter: &str) -> Prefix
where
    I: DoubleEndedIterator<Item = &'a str>,
{
    prefix(iter.rev(), width, delimiter)
}

/// Computes the length (number of bytes) and width of a suffix that fits in the given `width`.
///
/// Breaks between any two graphemes.
pub fn simple_suffix(text: &str, width: usize) -> Prefix {
    suffix(text.graphemes(true), width, "")
}

#[cfg(test)]
mod tests {
    use utils;

    #[test]
    fn test_prefix() {
        assert_eq!(utils::prefix(" abra ".split(' '), 5, " ").length, 5);
        assert_eq!(utils::prefix("abra a".split(' '), 5, " ").length, 4);
        assert_eq!(utils::prefix("a a br".split(' '), 5, " ").length, 3);
    }
}