#!/usr/bin/env bash

# Get the number from the first argument passed
number=$1

# Check if input is valid. The input must be a number 
#  - greater than 1
#  - smaller than 5000
# I chose this max value of 5000 because nobody would 
# like to convert a very big number like below:
# 15001 = MMMMMMMMMMMMMMMI 

if ! [[ "$number" =~ ^[0-9]+$ ]] || [ "$number" -lt 1 ] || [ "$number" -gt 5000 ]; then
    echo "Usage: $0 <number between 1 and 5000>"
    exit 1
fi

# Arrays of values and corresponding Roman numerals
# 1000 = M ; 900 = CM etc.
values=(1000 900 500 400 100 90 50 40 10 9 5 4 1)
numerals=("M" "CM" "D" "CD" "C" "XC" "L" "XL" "X" "IX" "V" "IV" "I")

# Result starts as an empty string.
result=""

# Roman numerals get appended here using the greedy algorithm
for i in "${!values[@]}"; do
    while [ "$number" -ge "${values[$i]}" ]; do
        result+="${numerals[$i]}"
        ((number -= values[$i]))
    done
done

# Echo the roman numeral
echo "$result"