const ASSIGNMENT = 'assignment';
const ANSWER = 'answer';
const NEWLINE_CHARACTER = '\n';

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

const DIRECTIONS  = {
  UP: 'U',
  DOWN: 'D',
  LEFT: 'L',
  RIGHT: 'R'
};

class Knot {
  constructor(x, y) {
    this.x=x;
    this.y=y;
  }
}
/*class Rope {
  constructor(headX, headY, tailX, tailY) {
    this.headX = headX;
    this.headY = headY;
    this.tailX = tailX;
    this.tailY = tailY;
    console.info("Created Rope with head:" + headX + "," + headY + " and tail: " + tailX + "," + tailY);
  }

  step = function (direction) {
    let oldHeadX = this.headX;
    let oldHeadY = this.headY;
    switch (direction) {
      case DIRECTIONS.UP:
        this.headY++;
        break;
      case DIRECTIONS.DOWN:
        this.headY--;
        break;
      case DIRECTIONS.LEFT:
        this.headX--;
        break;
      case DIRECTIONS.RIGHT:
        this.headX++;
        break;
      default:
        console.error("Invalid direction given: " + direction);
    }
    this.__correctTail(oldHeadX, oldHeadY);
  }

  getTailPosition = function () {
    return "" + this.tailX + "," + this.tailY;
  }

  __correctTail = function (oldHeadX, oldHeadY) {
    let absoluteDifferenceX = Math.abs(this.headX - this.tailX);
    let absoluteDifferenceY = Math.abs(this.headY - this.tailY);

    if (absoluteDifferenceX > 1 || absoluteDifferenceY > 1) {
      this.tailX = oldHeadX;
      this.tailY = oldHeadY;
      console.debug("Corrected tail Position: (" + this.tailX + ", " + this.tailY + "), head position: (" + this.headX + ", " + this.headY + ")");
    }
  }
};*/
class Rope {
  constructor(count) {
    if(count < 2) {
      console.error("Rope needs at least 2 knots.");
      return;
    }

    let knots = [];
    while(count > 0) {
      knots.push(new Knot(0,0));
      count--;
    }

    this.head = knots[0];
    this.knots = Array.from(knots).slice(1);
    this.tail = this.knots[this.knots.length-1];
    console.info("Created Rope with " + knots.length + " knots.");
  }

  step = function(direction) {
    let oldHeadX = this.head.x;
    let oldHeadY = this.head.y;
    switch(direction) {
      case DIRECTIONS.UP:
        this.head.y++;
        break;
      case DIRECTIONS.DOWN:
        this.head.y--;
        break;
      case DIRECTIONS.LEFT:
        this.head.x--;
        break;
      case DIRECTIONS.RIGHT:
        this.head.x++;
        break;
      default:
        console.error("Invalid direction given: " + direction);
    }
    this.__correctTails(oldHeadX, oldHeadY, this.head, this.knots[0], this.knots.slice(1));
  }

  getTailPosition = function() {
    return "" + this.tail.x + "," + this.tail.y;
  }

  __correctTails = function(oldHeadX, oldHeadY, head, tail, tails) {
    let absoluteDifferenceX = Math.abs(head.x - tail.x);
    let absoluteDifferenceY = Math.abs(head.y - tail.y);
    let oldTailX = tail.x;
    let oldTailY = tail.y;

    if(absoluteDifferenceX > 1 || absoluteDifferenceY > 1) {
      tail.x = oldHeadX;
      tail.y = oldHeadY;
      console.debug("Corrected tail Position: (" + this.tail.x + ", " + this.tail.y + "), head position: (" + this.head.x + ", " + this.head.y + ")");
    }
    
    if(tails.length > 0)
      this.__correctTails(oldTailX, oldTailY, tail, tails[0], tails.slice(1));
  }
};

/**
 * Listener function for input in assignment field.
 * @param event the onInput event 
 */
function calculateAnswer(event) {
  console.info("Calculating answer for input...");
  let answer = algorithm(event.target.value);

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

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

    let rope = new Rope(10);
    let visitedPositions = [rope.getTailPosition()];

    for(let i=0; i<lines.length; i++) {
      let line = lines[i].replace(/\s/g, ''); // Remove all whitespace
      let direction = line[0];
      let count = parseInt(line.substring(1));
      
      if(isNaN(count)) { // Validate count
        console.error("Invalid number in line: " + lines[i]);
      }

      while(count > 0) {
        rope.step(direction);
        let tailPosition = rope.getTailPosition();

        if(!visitedPositions.includes(tailPosition) ) { // Add only unique tailpositions
          visitedPositions.push(tailPosition);
        }

        count--;
      }
    }

    console.log(visitedPositions);
    return "Amount of positions for tail: " + visitedPositions.length;
}