#!/bin/bash
cmd=$1
file=$2
#takes filename as argument and returns top and bottom result seperated by colon
topAndBotGrade() {
                #top is the highest grade
                highestGrade=`awk -F":" '{ print $3 }' $file| sort -nr | head -1`
                #bottom is the lowest grade
                lowestGrade=`awk -F":" '{ print $3 }' $file| sort -nr | tail -1`
                #echo $highestGrade
                echo $highestGrade":"$lowestGrade
}

#outputs the amount of students with grades below 50
Failed() {
                #failed is the number of students with grades below 50
                failed=`awk -F":" '$3<50' $file | awk '{print NR}' | tail -1`
                echo $failed
}

#shows all the students with the highest marks
Top() {
        top=`awk -F":" '{ print $3 }' $file | sort -nr | head -1`
        echo -e "`awk -F":" '($3 == top) { print $2 }' top=$top $1`"
}

#outputs the average mark
Avg(){
        total=0
        count=0
        mark=0
        while read line
        do
                #sets current mark the loop is looking at
                $mark=`echo $line | awk -F":" '{ print $3 }' $file`
                #echo $mark
                #adds mark to the total
                $total=`echo $(($total+$mark)) | bc`
  #echo $total
                #increases counter
                $count=$(($count+1))
                done <$file
                echo "scale=2; $total/$count" | bc

}

#make sure the input file exists
if [ ! -f $file ]
then
    echo "Input file [$file] not found - Aborting"
    exit
fi
if [ "$1" == m ]
then
        topAndBotGrade $file
elif [ "$1" == f ]
then
  Failed $file
elif [ "$1" == n ]
then
        Top $file
elif [ "$1" == a ]
then
        Avg $file
else
        #error trapping.
        echo "Invalid input."
fi