Educative fun Rust snippets.

christmas_carols.rs

use std::io;
use std::str::FromStr;

const MAX_VERSE_COUNT: usize = 12;
const NUMBER_WORDS: [&str; MAX_VERSE_COUNT] = [
    "a", "two", "three", "four", "five", "six",
    "seven", "eight", "nine", "ten", "eleven", "twelve",
];
const NUMBER_COUNT_WORDS: [&str; MAX_VERSE_COUNT] = [
    "first", "second", "third", "fourth", "fifth", "sixth",
    "seventh", "eighth", "ninth", "tenth", "eleventh", "twelfth",
];
const ITEMS: [&str; MAX_VERSE_COUNT] = [
    "partridge", "turtle doves", "French Hens", "calling birds",
    "gold rings", "geese a laying", "swans a swimming",
    "maids a milking", "ladies dancing", "lords a leaping",
    "pipers piping", "drummers drumming",
];

fn upper_str(s: &str) -> String {
    let mut c = s.chars();
    match c.next() {
        None => String::new(),
        Some(f) => f.to_uppercase().collect::<String>() + c.as_str(),
    }
}

fn fetch_input<T: FromStr>(question: &str) -> T {
    loop {
        let mut input = String::new();
        println!("{}", question);
        match io::stdin().read_line(&mut input) {
            Ok(_) => (),
            Err(msg) => {
                println!("failed to read from STDIN: {}", msg);
                continue;
            },
        };
        return match input.trim().parse::<T>() {
            Ok(r) => r,
            Err(_) => {
                println!("failed to parse input '{}'", input.trim());
                continue;
            },
        };
    }
}

fn main() {
    let verse_count: u8 = {
        let mut n: u8;
        loop {
            n = fetch_input("How many verses would you like (min 1, max 12)?");
            if n >= 1 && n <= MAX_VERSE_COUNT as u8 {
                break;
            }
            println!("Invalid verse count given....");
        }
        n
    };

    println!("Generating your christmas carol with {} verse(s):", verse_count);
    println!("");

    for verse in 0..verse_count {
        println!("On the {} day of Christmas my true love gave to me",
            upper_str(NUMBER_COUNT_WORDS[verse as usize]));
        for i in 0..verse+1 {
            let mut count_word = String::from_str(NUMBER_WORDS[(verse -i ) as usize]).expect("failed to turn into String");
            if i == 0 {
                count_word = upper_str(&count_word);
            }
            print!("{} {}{}",
                count_word, ITEMS[(verse - i) as usize],
                if i == verse { " in a tree" } else { "" });
            if i != verse {
                print!("{}", if i < verse-1 { "," } else { " and" });
                let mut u = i;
                if (verse+1)%2 == 1 {
                    if u < 2 {
                        print!(" ");
                        continue;
                    } else if u == 2 {
                        print!("\r\n");
                        continue;
                    }
                    u -= 3;
                }
                if u%2 == 1 {
                    print!("\r\n");
                } else {
                    print!(" ");
                }
            }
        }
        println!("\r\n");
    }
}