script.js

function generateSudoku() {
  // Initialize an empty Sudoku grid
  const grid = new Array(9).fill().map(() => new Array(9).fill(0));

  // Fill the grid with random values using backtracking
  solveSudoku(grid, 0, 0);

  // Convert the grid to a string
  const sudokuStr = grid.flat().join('');

  return sudokuStr;
}

function solveSudoku(grid, row, col) {
  // If we have reached the end of the grid, the Sudoku puzzle is solved
  if (row === 9) {
    return true;
  }

  // Calculate the next row and column
  const [nextRow, nextCol] = col < 8 ? [row, col + 1] : [row + 1, 0];

  // If the current cell is already filled, move on to the next cell
  if (grid[row][col] !== 0) {
    return solveSudoku(grid, nextRow, nextCol);
  }

  // Try different values for the current cell
  const values = shuffle([1, 2, 3, 4, 5, 6, 7, 8, 9]);
  for (const value of values) {
    if (isValid(grid, row, col, value)) {
      grid[row][col] = value;
      if (solveSudoku(grid, nextRow, nextCol)) {
        return true;
      }
      grid[row][col] = 0;
    }
  }

  // If no value works, backtrack
  return false;
}

function isValid(grid, row, col, value) {
  // Check if the value is already in the same row or column
  if (grid[row].includes(value) || grid.some(rowValues => rowValues[col] === value)) {
    return false;
  }

  // Check if the value is already in the same 3x3 box
  const boxRow = Math.floor(row / 3) * 3;
  const boxCol = Math.floor(col / 3) * 3;
  for (let i = boxRow; i < boxRow + 3; i++) {
    for (let j = boxCol; j < boxCol + 3; j++) {
      if (grid[i][j] === value) {
        return false;
      }
    }
  }

  return true;
}

function shuffle(array) {
  // Fisher-Yates shuffle algorithm
  for (let i = array.length - 1; i > 0; i--) {
    const j = Math.floor(Math.random() * (i + 1));
    [array[i], array[j]] = [array[j], array[i]];
  }
  return array;
}


function hideRandomDigits(inputString, numToHide) {
  // Find all digit positions in the input string
  const digitPositions = [];
  for (let i = 0; i < inputString.length; i++) {
    if (/\d/.test(inputString[i])) {
      digitPositions.push(i);
    }
  }

  // Select `numToHide` random digit positions to hide
  const digitsToHide = [];
  for (let i = 0; i < Math.min(numToHide, digitPositions.length); i++) {
    const randomIndex = Math.floor(Math.random() * digitPositions.length);
    digitsToHide.push(digitPositions.splice(randomIndex, 1)[0]);
  }

  // Replace the selected digit positions with '-' character
  let outputString = '';
  for (let i = 0; i < inputString.length; i++) {
    if (digitsToHide.includes(i)) {
      outputString += '-';
    } else {
      outputString += inputString[i];
    }
  }

  return outputString;
}

const EASY_LABEL = '30';
const MEDIUM_LABEL = '40';
const HARD_LABEL = '50';

// Load board from files or manually
const GENERATED_SODOKU = generateSudoku();
const easyProbSol = {
  solution: GENERATED_SODOKU,
  problem: hideRandomDigits(GENERATED_SODOKU, EASY_LABEL)
};

const mediumProbSol = {
  solution: GENERATED_SODOKU,
  problem: hideRandomDigits(GENERATED_SODOKU, MEDIUM_LABEL)
};

const hardProbSol = {
  solution: GENERATED_SODOKU,
  problem: hideRandomDigits(GENERATED_SODOKU, HARD_LABEL)
};

const easy = [
  easyProbSol.problem,
  easyProbSol.solution
];
const medium = [
  mediumProbSol.problem,
  mediumProbSol.solution
];
const hard = [
  hardProbSol.problem,
  hardProbSol.solution
];

//create variable
var timer;
var timeRemaining;
var lives;
var selectedTile;
var disableSelect;
var selectedNum;

window.onload = function () {
  // start the game when new game button is clicked
  id("start-btn").addEventListener("click", startGame);

  //add eventlisteners to number board and number container
  for(let i=0;i<id("number-container").children.length;i++){
    id("number-container").children[i].addEventListener("click",function(){
      //disable select 
      if(!disableSelect) {
        //if number is already select
        if(this.classList.contains("selected")){
          //remove selected
          this.classList.remove("selected");
          selectedNum=null;
        }
        else{
          //deselct all other
          for(let i=0;i<9;i++){
            id("number-container").children[i].classList.remove("selected");
          }
          //selected it and update the selectedNUm variable
          this.classList.add("selected");
          selectedNum=this;
          updateMove();
        }
      }
    });
  }
};

function startGame() {
  //console.log("Start!!");
  //choose game difficulty
  let board;
  if (id("diff-1").checked) board = easy[0];
  else if (id("diff-2").checked) board = medium[0];
  else board = hard[0];

  //lives count =3
  lives = 3;
  disableSelect = false;
  id("lives").textContent = "Lives Remaining: 3";

  //board create as per difficulty
  generateBoard(board);

  //Timer
  startTimer();

  //Sets on basis of input
  if (id("theme-1").checked) {
    qs("body").classList.remove("dark");
  } else {
    qs("body").classList.add("dark");
  }

  //show number container
  id("number-container").classList.remove("hidden");
}
function generateBoard(board) {
  // Clear the old board
  clearPrevious();

  //let is used to incrementt tiles ids
  let idCount = 0;

  //create tiles for board
  for (let i = 0; i < 81; i++) {
    //create new paragraph element
    let tile = document.createElement("p");
    //if tiles have number
    if (board.charAt(i) != "-") {
      tile.textContent = board.charAt(i);
    } else {
      //add the click event listner
      tile.addEventListener("click",function(){
        //if selecting is not disabled
        if(!disableSelect){
          //if tile is selected
          if(tile.classList.contains("selected")){
            //remove selection
            tile.classList.remove("selected");
            selectedTile=null;
          }
          else{
            //deslect all other tiles
            for(let i=0;i<81;i++){
              qsa(".tile")[i].classList.remove("selected");
            }
            //add selection and update
            tile.classList.add("selected");
            selectedTile=tile;
            updateMove();
          }
        }
      });
    }
    //tile ids
    tile.id = idCount;
    //increament for next tile
    idCount++;
    //add tiles class to all tiles
    tile.classList.add("tile");
    if ((tile.id > 17 && tile.id < 27) || (tile.id > 44 && tile.id < 54)) {
      tile.classList.add("bottomBorder");
    }
    if ((tile.id + 1) % 9 == 3 || (tile.id + 1) % 9 == 6) {
      tile.classList.add("rightBorder");
    }
    //Adding tiles
    id("board").appendChild(tile);
  }
}

// function to update the numbers on tile
function updateMove(){
  //if tile & num is selected
  if(selectedTile && selectedNum){
    //set the tile to the corect num
    selectedTile.textContent=selectedNum.textContent;
    //if the num mathces the corresponding num in the key
    if(checkCorrect(selectedTile)){
      //deselect the tile
      selectedTile.classList.remove("selected");
      selectedNum.classList.remove("selected");
      //clear variable
      selectedNum=null;
      selectedTile=null;  
      //check if board is fill
      if(checkDone()) endGame();
    }
    //if num doesnt match sol key
    else{
      //disable selecting new num for one second
      disableSelect=true;
      //make tile red
      selectedTile.classList.add("incorrect");
      //run in one sec
      setTimeout(function(){
        //subtract lives by one
        lives--;
        //if lives =0
        if(lives===0) endGame();
        else{
          //if lives>0
          //update lives text
          id("lives").textContent="Lives Remaining: "+lives;
          //renable selecting nums and tiles
          disableSelect=false;
        }
        //restore tile color and remove selected from both
        selectedTile.classList.remove("incorrect");
        selectedTile.classList.remove("selected");
        selectedNum.classList.remove("selected");
        //clear the tiles text and clear selected variables
        selectedTile.textContent="";
        selectedTile=null;
        selectedNum=null;
    },1000)
    }
  }
}

function endGame(){
  //disable mves and update the timer
  disableSelect=true;
  clearTimeout(timer);
  //dispaly win or loose
  if(lives===0 || timeRemaining===0){
    id("lives").textContent="You Lost!!";
  }
  else{
    id("lives").textContent="Yeah! You Won";
  }
}

function checkDone(){
  let tiles=qsa(".tile");
  for(let i=0;i<81;i++){
    if(tiles[i].textContent==="") return false;
  }
  return true;
}

function checkCorrect(tile){
  //set the solution based on difficulty label
  let sol;
  if (id("diff-1").checked) sol = easy[1];
  else if (id("diff-2").checked) sol = medium[1];
  else sol = hard[1];
  //if tiles num is equal to sol num
  if(sol.charAt(tile.id)===tile.textContent) return true;
  else return false;
}

function clearPrevious() {
  //access all the tiles
  let tiles = qsa(".tile");

  //remove tiles
  for (let i = 0; i < tiles.length; i++) {
    tiles[i].remove();
  }
  //if timer than clear it
  if (timer) clearTimeout(timer);

  //deselect any number
  for (let i = 0; i < id("number-container").children.length; i++) {
    id("number-container").children[i].classList.remove("selected");
  }

  //clear selected variables
  selectedTile = null;
  selectedNum = null;
}

function startTimer() {
  //set timer on basis of input
  if (id("time-1").checked) timeRemaining = 180;
  else if (id("time-2").checked) timeRemaining = 300;
  else timeRemaining = 600;

  //sets the timer for start sec
  id("timer").textContent = timeConversion(timeRemaining);

  //update timer
  timer = setInterval(function () {
    timeRemaining--;

    //end of time
    if (timeRemaining === 0) endGame(); 
    id("timer").textContent= timeConversion(timeRemaining);
  }, 1000);
}

//secs into time format
function timeConversion(time) {
  let min = Math.floor(time / 60);
  if (min < 10) min = "0" + min;
  let sec = time % 60;
  if (sec < 10) sec = "0" + sec;
  return min + ":" + sec;
}
//Helper functions

function qs(selector) {
  return document.querySelector(selector);
}

function qsa(selector) {
  return document.querySelectorAll(selector);
}

function id(id) {
  return document.getElementById(id);
}