Calendar example

format_year.rs

use chrono::{NaiveDate, Datelike, Duration};
use std::cmp;

fn format_year(y: i32, cols: usize) -> String {
    let mut day: Vec<_> = (0..12).into_iter().map(|i| {
        let first = NaiveDate::from_ymd(y, i+1, 1);
        (first, first - Duration::days(first.weekday().num_days_from_sunday() as i64))
    }).collect();

    let mut s = String::new();
    let mut startm = 0; 
    loop {
        let endm = cmp::min(startm+cols, 12);
        for c in startm..endm { s += &format!("{}{:^21}", if c > startm {" "} else {""}, MONTH_NAMES[c]); }
        s += "\n";

        loop {
            let mut moredays = false;
            for c in startm..endm {
                if c > startm { s += " "; }
                let d = &mut day[c];
                for _ in 0..7 {
                     s += if d.0.month() == d.1.month() { &format!("{:>3}", d.1.day()) } else {"   "};
                     d.1 = d.1 + Duration::days(1);
                }
                moredays |= d.0.month() == d.1.month() || d.1 < d.0;
            }
            s += "\n";
            if !moredays { break; }
        }
        startm += cols;
        if startm >= 12 { return s; }
        s += "\n";
    }
}