metric

#!/bin/bash

set -e
set -o pipefail


################################################################################

function usage {
    cat <<EOM

Usage: $(basename "${0}") [-h | --help] <#UN|# UNIT>

  -h, --help    Show this help message.

EOM
}

function error {
    echo "ERROR: ${*}" >/dev/stderr
}

function metric-unit {
    case "${unit}" in
        mi|mile|miles)        echo "km"    ;;
        mph|"miles per hour") echo "kph"   ;;
        mi/h)                 echo "km/h"  ;;
        in|inch|inches)       echo "cm"    ;;
        ft|feet|foots)        echo "m"     ;;
        yd|yard|yards)        echo "m"     ;;
        ac|acre|acres)        echo "m2"    ;;
        gal|gallon|gallons)   echo "l"     ;;
        lbs|pounds)           echo "kg"    ;;
        *)
            error "Unknown unit!"
            return 2
            ;;
    esac
}

function split {
    local val group

    val="${1}"
    group="${2}"

    sed -E 's/([0-9]*)([a-z][a-z0-9]+)/'"\\${group}"'/' <<< "${val}"
}

function main {
    local val unit result metric

    case "${#}" in
        0) usage; exit 2 ;;
        1) val="$(split  "${1}" 1)"
           unit="$(split "${1}" 2)"
           ;;
        *) val="${1}"
           shift
           unit="${*}"
    esac

    metric="$(metric-unit "${unit}")"

    result="$(/bin/units -t -o "%.${#val}f" "${val} ${unit}" "${metric}")"

    echo "${result} ${metric}"
}

main "${@}"; exit