#!/bin/bash

# remove the # on the following line to turn on debugging
# set -o xtrace

#==================
function initialize ()
{
trap 'summarize ; exit 0' INT     #  Handle user interrupts
num_ques=0                        #  Number of questions asked so far
num_correct=0                     #  Number answered correctly so far
first_time=true                   #  true until first question is asked
cd ${QUIZDIR:=~/quiz} || exit 2
}

#==================
function choose_subj ()
{
subjects=($(ls))
PS3="Choose a subject for the quiz from the preceding list: "
select Subject in ${subjects[*]}; do
     if [[ -z "$Subject" ]]; then
         echo "No subject chosen. Bye." >&2
         exit 1
     fi
     echo $Subject
     return 0
done
}

#==================
function exchange ()
{
temp_value=${questions[$1]}
questions[$1]=${questions[$2]}
questions[$2]=$temp_value
}

#==================
function scramble ()
{
typeset -i index quescount
questions=($(ls))
quescount=${#questions[*]}          # Number of elements
((index=quescount-1))
while [[ $index > 0 ]]; do
     ((target=RANDOM % index))
     exchange $target $index
     ((index -= 1))
done
}

#==================
function ask ()
{
exec 3<$1
read -u3 ques || exit 2
read -u3 num_opts || exit 2

index=0
choices=()
while (( index < num_opts )) ; do
     read -u3 next_choice || exit 2
     choices=("${choices[@]}" "$next_choice")
     ((index += 1))
done
read -u3 correct_answer || exit 2
exec 3<&-

if [[ $first_time = true ]]; then
     first_time=false
     echo -e "You may press the interrupt key at any time to quit.\n"
fi

PS3=$ques"    "                     # Make $ques the prompt for select
                                    # and add some spaces for legibility.

select answer in "${choices[@]}"; do
     if [[ -z "$answer" ]]; then
              echo Not a valid choice. Please choose again.
         elif [[ "$answer" = "$correct_answer" ]]; then
              echo "Correct!"
              return 1
         else
              echo "No, the answer is $correct_answer."
              return 0
     fi
done
}

#==================
function summarize ()
{
echo                               # Skip a line
if (( num_ques == 0 )); then
     echo "You did not answer any questions"
     exit 0
fi

(( percent=num_correct*100/num_ques ))
echo "You answered $num_correct questions correctly, out of \
$num_ques total questions."
echo "Your score is $percent percent."
}

#==================
# Main program
initialize                         # Step 1 in top-level design
subject=$(choose_subj)             # Step 2
[[ $? -eq 0 ]] || exit 2           # If no valid choice, exit
cd $subject || exit 2              # Step 3
echo                               # Skip a line
scramble                           # Step 4

for ques in ${questions[*]}; do    # Step 5
     ask $ques
     result=$?
     (( num_ques=num_ques+1 ))
     if [[ $result == 1 ]]; then
          (( num_correct += 1 ))
     fi
     echo                          # Skip a line between questions
     sleep ${QUIZDELAY:=1}
done

summarize                          # Step 6
exit 0