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

/**
 * 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 getHighestScenicScore = document.getElementById(ALGORITHM_CHECKBOX).checked;
  let answer = algorithm(assignment, getHighestScenicScore);

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

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

  let visibleTreeCount = 0;
  let highestScenicScore = 0;

  for (let i = 0; i < lines.length; i++) {
    let row = lines[i].trim();

    for (let j = 0; j < row.length; j++) {
      if (i <= 0 || i >= lines.length - 1 || j <= 0 || j >= row.length - 1) { // Edge node
        //console.debug("Edge node found.");
        visibleTreeCount++;
        continue;
      }

      let height = parseInt(lines[i].charAt(j));
      if (!walkRowVisible(height, j, row) && !walkColumnVisible(height, i, j, lines)) {
        console.log("Found invisible tree, height:" + height + ", i:" + i + ", j:" + j);
        visibleTreeCount--;
      }

      if (getHighestScenicScore) {
        let scenicScore = walkRowCount(height, j, row) * walkColumnCount(height, i, j, lines);
        if (scenicScore > highestScenicScore) {
          console.debug("Found new highest scenic score: " + scenicScore);
          highestScenicScore = scenicScore;
        }
      }

      // Tree is on edge.
      visibleTreeCount++;
    }
  }

  if (getHighestScenicScore) {
    return "Highest scenic score: " + highestScenicScore;
  }

  return "Amount of visible trees in the grid: " + visibleTreeCount;
}

function walkColumnCount(height, index, rowIndex, column) {
  return walkCount(height, index, column, false, rowIndex);
}

function walkRowCount(height, index, row) {
  return walkCount(height, index, row, true, -1);
}

function walkColumnVisible(height, index, rowIndex, column) {
  return walkVisible(height, index, column, false, rowIndex);
}

function walkRowVisible(height, index, row) {
  return walkVisible(height, index, row, true, -1);
}

function walkCount(height, index, line, isRow, rowIndex) {
  let visibleLeftCount = __walkHelper(height, index, line, isRow, -1, rowIndex, 0);
  let visibleRightCount = __walkHelper(height, index, line, isRow, 1, rowIndex, 0);

  return visibleLeftCount * visibleRightCount;
}

function walkVisible(height, index, line, isRow, rowIndex) {
  let visibleLeft = __walkHelper(height, index, line, isRow, -1, rowIndex);
  let visibleRight = __walkHelper(height, index, line, isRow, 1, rowIndex);

  return visibleLeft || visibleRight;
}

function __walkHelper(height, index, line, isRow, direction, rowIndex, count) {
  if (direction == 0) {
    console.error("Invalid direction 0 in __walkhelper");
    return -1;
  }

  direction = direction / Math.abs(direction);

  // Edge reached
  if ((direction < 0 && index <= 0) || (direction > 0 && index >= line.length - 1)) {
    return (count == undefined) ? true : count;
  }

  let nextIndex = index + direction;
  let nextHeightCharacter = (isRow) ? line.charAt(nextIndex) : line[nextIndex].trim().charAt(rowIndex);
  let nextHeight = parseInt(nextHeightCharacter);

  if (isNaN(height) || isNaN(nextHeightCharacter)) {
    console.error("Invalid height found, height:" + height + ", nextHeight: " + nextHeightCharacter);
    return -1;
  }

  if (height <= nextHeight) {
    if (count == undefined)
      return false;
    return count + 1;
  }

  return __walkHelper(height, nextIndex, line, isRow, direction, rowIndex, (count !=undefined)? count + 1 : undefined);
}