#!/bin/bash

get_fraction() {
    st=$(date --date "$1" +%s)
    en=$(date --date "$2" +%s)
    now=$(date +%s)

    total=$(( en - st ))
    already_done=$(( now - st ))
    passed=$(echo "$already_done * 100 / $total" | bc -l)
    onesec=$(echo "1/$total" | bc -l)
}

determine_auto_precision() {
    mapfile -t digits < <(echo "$onesec" | cut -d'.' -f2 | grep -o .)
    for i in "${!digits[@]}"; do
        if [[ ${digits[i]} -ne 0 ]]; then
            echo $(( i + 1 ))
            return
        fi
    done
    echo 0
}

main() {
    start_time=$(date +'%Y-%m-%d %H:%M:%S' -d "January 1")
    end_time=$(date +'%Y-%m-%d %H:%M:%S' -d "January 1 next year")
    precision="auto"
    format="%\n"

    while [[ $# -gt 0 ]]; do
        case $1 in
            -h|--help)
                echo "Usage: percentages [-s START] [-e END] [-p PRECISION] [-f FORMAT]"
                echo ""
                echo "Print how far through a time interval you are as a percentage."
                echo "Defaults to the current calendar year."
                echo ""
                echo "Options:"
                echo "  -s, --start START        Start datetime (default: Jan 1 this year)"
                echo "  -e, --end END            End datetime (default: Jan 1 next year)"
                echo "  -p, --precision DIGITS   Decimal places (default: auto)"
                echo "  -f, --format SUFFIX      String appended after the number (default: '%\n')"
                echo "  -h, --help               Show this help message"
                exit 0
                ;;
            -s|--start)
                start_time=$2
                shift 2
                ;;
            -e|--end)
                end_time=$2
                shift 2
                ;;
            -p|--precision)
                precision=$2
                shift 2
                ;;
            -f|--format)
                format=$2
                shift 2
                ;;
            *)
                shift
                ;;
        esac
    done

    get_fraction "$start_time" "$end_time"
    [[ $precision == "auto" ]] && precision=$(determine_auto_precision)
    string=$(printf "%.${precision}f\n" $passed)
    echo -e -n "${string}${format}"
}

main "$@"