#!/bin/bash

# convertatemp--Temperature conversion script that lets the user enter
# a temperature in Farenheit, Celsius, or Kelvin and receive the
# equivalent temperature in the other two units as the output

# Usage Examples:
# convertatemp 212 # default behavior, farenheit conversion
# convertatemp 100C # celsius conversion
# convertatemp 100K # kelvin conversion

# just a test of debugging mode using set (comment out later)
#set -n

if [ $# -eq 0 ] ; then # if no arguments are passed
    # then redirect from EOF (End of FILE) the string until another EOF caps off the string.
    # essentially, this just prints a message to the user about how to use the script.
    cat << EOF >&2
Usage: $0 temperature[F|C|K]
where the suffix:
    F   indicates input is in Fahrenheit (default)
    C   indicates input is in Celsius
    K   indicates input is in Kelvin
EOF
    exit 1 # and exit with an error status
fi

# the variable, $unit is assigned the echoed first argument, which is piped to sed, which takes a regular expression that expects any amount of digits
# the '-' means to include anything but the following, which essentially means unit becomes just the letter passed (f,c,k)
# this is then piped to tr (transform), which takes strings and converts them, in this case all lowercase is converted to uppercase
unit="$(echo $1|sed -e 's/[-[:digit:]]*//g' | tr '[:lower:]' '[:upper:]' )"
# the $temp variable is assigned the first parameter's digits only
temp="$(echo $1|sed -e 's/[^-[:digit:]]*//g')"

case ${unit:=F} # if the unit's final character is F...
in
F ) # Farenheit to Celsius formula:  Tc = (F - 32) / 1.8
    farn="$temp"
    cels="$(echo "scale=2;($farn - 32) / 1.8" | bc)"
    kelv="$(echo "scale=2;$cels + 273.15" | bc)"
    ;;

C ) # Celsius to Fahrenheit formula: Tf = (9/5)*Tc+32
    cels="$temp"
    kelv="$(echo "scale=2;$cels + 273.15" | bc)"
    farn="$(echo "scale=2;(1.8 * $cels) + 32" | bc)"
    ;;

K ) # Celsius = Kelvin - 273.15, then use Celsius -> Fahrenheit formula
   kelv="$temp" 
   cels="$(echo "scale=2;($kelv - 32) / 1.8" | bc)"
    farn="$(echo "scale=2;(1.8 * $cels) + 32" | bc)"
    ;;

    *) # otherwise, if F,C, or K are not passed, then...
    echo "Given temperature unit is not supported"
    exit 1 # and exit with an error status.
esac

#Finally, we simply print back the results
echo "Fahrenheit = $farn"
echo "Celsius = $cels"
echo "Kelvin = $kelv"

# and exit with a success/ok status
exit 0