calculate the max debug/display width of items in an iterator

width.rs

use std::fmt::{Debug, Display, Write};
use std::ops::Deref;

/// The output width from a write statement
#[derive(Default, Eq, PartialEq, Ord, PartialOrd)]
struct Width(usize);

impl Width {
    /// reset the stored width
    fn reset(&mut self) {
        self.0 = 0;
    }
}

impl Deref for Width {
    type Target = usize;

    fn deref(&self) -> &Self::Target {
        &self.0
    }
}

/// Capture the width of a write statement
impl Write for Width {
    fn write_str(&mut self, s: &str) -> std::fmt::Result {
        self.0 += s.len();
        Ok(())
    }
}

/// Calculated the maximum debug print width of items in an Iterator
#[inline]
pub fn max_debug_width<T: Debug>(source: impl Iterator<Item=T>) -> usize {
    let mut width = Width::default();

    // unwrap ok, width write always returns ok
    source.map(|v| {
        width.reset();
        write!(width, "{:?}", v).unwrap();
        *width
    }).max().unwrap_or_default()
}

/// Calculated the maximum display  print width of items in an Iterator
#[inline]
pub fn max_display_width<T: Display>(source: impl Iterator<Item=T>) -> usize {
    let mut width = Width::default();

    // unwrap ok, width write always returns ok
    source.map(|v| {
        width.reset();
        write!(width, "{}", v).unwrap();
        *width
    }).max().unwrap_or_default()
}

#[cfg(test)]
mod tests {
    use crate::utils::width::{max_debug_width, max_display_width};

    #[test]
    fn given_a_collection_of_one_value_you_should_be_able_to_calc_max_debug_width() {
        let values = vec!["EF"];
        let acutal = max_debug_width(values.iter());
        let expected = 4;

        assert_eq!(expected, acutal);
    }

    #[test]
    fn given_a_collection_of_one_value_you_should_be_able_to_calc_max_display_width() {
        let values = vec!["EF"];
        let acutal = max_display_width(values.iter());
        let expected = 2;

        assert_eq!(expected, acutal);
    }

    #[test]
    fn given_a_collection_of_values_you_should_be_able_to_calc_max_debug_width() {
        let values = vec!["A", "BCD", "EF", "G", "HIJ", "KL"];
        let acutal = max_debug_width(values.iter());
        let expected = 5;

        assert_eq!(expected, acutal);
    }

    #[test]
    fn given_a_collection_of_values_you_should_be_able_to_calc_max_display_width() {
        let values = vec!["A", "BCD", "EF", "G", "HIJ", "KL"];
        let acutal = max_display_width(values.iter());
        let expected = 3;

        assert_eq!(expected, acutal);
    }

    #[test]
    fn given_an_empty_collection_of_values_you_should_be_able_to_calc_max_debug_width() {
        let values = <Vec<&str>>::new();
        let acutal = max_debug_width(values.iter());
        let expected = 0;

        assert_eq!(expected, acutal);
    }

    #[test]
    fn given_an_empty_collection_of_values_you_should_be_able_to_calc_max_display_width() {
        let values = <Vec<&str>>::new();
        let acutal = max_display_width(values.iter());
        let expected = 0;

        assert_eq!(expected, acutal);
    }
}