use strict;

# Constants used to define the type of question being asked
use constant TYPE_MULTIPLE_CHOICE => 1;     # multiple choice question
use constant TYPE_FREE_TEXT       => 2;     # free response question

# Some constants used internally 
use constant INDEX_MAGIC   => 0;
use constant INDEX_TYPE    => 1;
use constant INDEX_PROMPT  => 2;
use constant INDEX_CHOICES => 3;
use constant INDEX_CORRECTVALUE => 4;
use constant INDEX_POINTS  => 5;

# DEBUG: This magic number is stored in the first index of the question array.
# Each function will check that the magic number is valid -- if not, then something
# was gone wrong -- most likely this means you called the function wrong.
use constant QUESTION_MAGIC_NUMBER => 23498234;

use constant NO_CORRECT_ANSWER => -1;

# This file define functions to read and write different elements of a particular question.
# The whole element is stored in array as follows:
#   array[INDEX_MAGIC] holds a magic number used for debugging
#   array[INDEX_TYPE] holds the type of the question  
#   array[INDEX_PROMPT] holds the prompt for the question, e.g. "When did Columbus discover America?"
#   array[INDEX_CHOICES] holds a reference to another array, with the possible answers to choose from, if any (empty array)
#   array[INDEX_CORRECTVALUE]] holds the index of the correct answer, or NO_CORRECT_ANSWER if none
#   array[INDEX_POINTS} holds the number of points for a question, if any

# Internal debug function -- if this complains then you probably called the original function wrong
sub questionCheckMagic {
  my ($question, $functionName, $caller_package, $caller_filename, $caller_line) = @_;
  if ($$question[INDEX_MAGIC] != QUESTION_MAGIC_NUMBER) {
     print "\n\n\n<h1>ERROR! Bad question magic number in call to $functionName from $caller_filename, line $caller_line.\n " .
           "This probably means you called $functionName wrong.</h1>\n\n\n";
     exit(1);
  }   
}


# Inputs: none
# Returns: a new survey.  Internally, this is just a reference to an empty array
# 
sub questionCreateNew {
  my @anArray = ();
  $anArray[INDEX_MAGIC] = QUESTION_MAGIC_NUMBER;
  
  my $question = \@anArray;
  questionSetChoices($question, () );    # set to initially empty
  questionSetCorrectValue($question, NO_CORRECT_ANSWER());

  return $question;
}

# Inputs: a question
# Returns: the type of that question
sub questionGetType {
  my($question) = @_;              # get the input parameter
  questionCheckMagic($question, "questionGetType()", caller());
  return $$question[INDEX_TYPE];
}

# Inputs: (question, type) 
#   where 'question' is the question to modify
#   and 'type' is the question type to be set
# Returns: nothing (but modifies the question that was provided,
#   setting the type of that question))
sub questionSetType {
  my($question, $type) = @_;
  questionCheckMagic($question, "questionSetType()", caller());
  $$question[INDEX_TYPE] = $type;
}

# Inputs: a question
# Returns: the prompt of that question
sub questionGetPrompt {
  my($question) = @_;              # get the input parameter
  questionCheckMagic($question, "questionGetPrompt()", caller());
  return $$question[INDEX_PROMPT];
}

# Inputs: (question, prompt) 
#   where 'question' is the question to modify
#   and 'prompt' is the question prompt to be set
# Returns: nothing (but modifies the question that was provided,
#   setting the prompt of that question))
sub questionSetPrompt() {
  my($question, $prompt) = @_;
  questionCheckMagic($question, "questionSetPrompt()", caller());
  $$question[INDEX_PROMPT] = $prompt;
}

# Inputs: a question
# Returns: the choices of that question (an array of strings)
sub questionGetChoices {
  my($question) = @_;              # get the input parameter
  questionCheckMagic($question, "questionGetChoices()", caller());
  my $array_ref = $$question[INDEX_CHOICES];   # get reference to the choices array
  return @$array_ref;                          # return copy of the array
}

# Inputs: (question, choices) 
#   where 'question' is the question to modify
#   and 'choices' is the question choices to be set (an array of strings)
# Returns: nothing (but modifies the question that was provided,
#   setting the choices of that question))
sub questionSetChoices() {
  my($question, @choices) = @_;
  questionCheckMagic($question, "questionSetChoices()", caller());
  my @arrayCopy = @choices;
  $$question[INDEX_CHOICES] = \@arrayCopy;;
}

# Inputs: a question
# Returns: the correctValue of that question
sub questionGetCorrectValue {
  my($question) = @_;              # get the input parameter
  questionCheckMagic($question, "questionGetCorrectChoice()", caller());
  return $$question[INDEX_CORRECTVALUE];
}

# Inputs: (question, correctValue) 
#   where 'question' is the question to modify
#   and 'correctValue' is the question correctValue to be set
# Returns: nothing (but modifies the question that was provided,
#   setting the correctValue of that question))
sub questionSetCorrectValue() {
  my($question, $correctValue) = @_;
  questionCheckMagic($question, "questionSetCorrectChoice()", caller());
  $$question[INDEX_CORRECTVALUE] = $correctValue;
}


# Inputs: a question
# Returns: the points of that question
sub questionGetPoints {
  my($question) = @_;              # get the input parameter
  questionCheckMagic($question, "questionGetPoints()", caller());
  return $$question[INDEX_POINTS];
}

# Inputs: (question, points) 
#   where 'question' is the question to modify
#   and 'points' is the question points to be set
# Returns: nothing (but modifies the question that was provided,
#   setting the points of that question))
sub questionSetPoints() {
  my($question, $points) = @_;
  questionCheckMagic($question, "questionSetPoints()", caller());
  $$question[INDEX_POINTS] = $points;
}


1;