const ASSIGNMENT = 'assignment';
const ANSWER = 'answer';
const ALGORITHM_CHECKBOX = 'algorithm';
const ERROR_MESSAGE_INVALID_RANGE = "Invalid range, ";
const COMMA_CHARACTER = ',';
const NEWLINE_CHARACTER = '\n';
const RANGE_CHARACTER = '-';

/**
 * Main function
 */
window.onload = function() {
    document.getElementById(ASSIGNMENT).addEventListener("input", calculateAnswer);
    document.getElementById(ALGORITHM_CHECKBOX).addEventListener("click", calculateAnswer);
}

/**
 * Listener function for input in assignment field.
 * @param event the onInput event 
 */
function calculateAnswer(event) {
  console.info("Calculating answer for input...");
  let assignment = document.getElementById(ASSIGNMENT).value;
  let fullOverlap = document.getElementById(ALGORITHM_CHECKBOX).checked;
  let answer = algorithm(assignment, fullOverlap);

  document.getElementById(ANSWER).innerText = answer;
}

/**
 * Calculate the answer to assignment.
 * @param assignment the input from the assignment.
 * @param fullOverlap if input needs to fully overlap.
 * @return string the answer
 */
function algorithm(assignment, fullOverlap) {
    let lines = assignment.trim().split(NEWLINE_CHARACTER);
    console.info("Linecount:" + lines.length);

    let containedPairs = 0;
    for(let i=0; i<lines.length; i++) {
        let error = false;
        let ranges = lines[i].trim();
        // Search for separation charactes -,-
        let range1CharacterIndex = ranges.indexOf(RANGE_CHARACTER);
        let range1EndCharacterIndex = ranges.indexOf(COMMA_CHARACTER);
        let range2CharacterIndex = ranges.indexOf(RANGE_CHARACTER, range1CharacterIndex+1);

        // Get range substrings
        let range1LowerString = ranges.substring(0,range1CharacterIndex);
        let range1HigherString = ranges.substring(range1CharacterIndex+1, range1EndCharacterIndex);
        let range2LowerString = ranges.substring(range1EndCharacterIndex+1, range2CharacterIndex);
        let range2HigherString = ranges.substring(range2CharacterIndex+1);
        console.debug("Parsed values: " + range1LowerString + "-" + range1HigherString + "," + range2LowerString + "-" + range2HigherString);

        // Parse to int
        let range1Lower = parseInt(range1LowerString);
        let range1Higher = parseInt(range1HigherString);
        let range2Lower = parseInt(range2LowerString);
        let range2Higher = parseInt(range2HigherString);

        // Validation
        if(range1Lower > range1Higher) {
            console.error(ERROR_MESSAGE_INVALID_RANGE + range1Lower + "-" + range1Higher + " on line:" + i + " for range1");
            error = true;
        }
        if(range2Lower > range2Higher) {
            console.error(ERROR_MESSAGE_INVALID_RANGE + range2Lower + "-" + range2Higher + " on line:" + i + " for range2");
            error = true;
        }

        if(error) {
            continue;
        }

        // Check for overlap
        if(fullOverlap && doesRangeFullyOverlap(range1Lower, range1Higher, range2Lower, range2Higher) 
            || !fullOverlap && doesRangeOverlap(range1Lower, range1Higher, range2Lower, range2Higher)) {
            console.debug("Found overlapping range:" + range1Lower + "-" + range1Higher + "," + range2Lower + "-" + range2Higher);
            containedPairs++;
        }
    }

    return "Fully overlapping timeslot counts: " + containedPairs;
}

function doesRangeFullyOverlap(lower, higher, lower2, higher2) {
    console.debug("Compare range: " + lower + "-" + higher + " with " + lower2 + "-" + higher2);
    if(lower > higher || lower2 > higher2) {
        return false;
    } 
    return ((lower <= lower2 && higher >= higher2) || (lower2 <= lower && higher2 >= higher));
}

function doesRangeOverlap(lower, higher, lower2, higher2) {
    console.debug("Compare range: " + lower + "-" + higher + " with " + lower2 + "-" + higher2);
    if(lower > higher || lower2 > higher2) {
        return false;
    } 

    return higher2 >= lower && lower2 <= higher;
}