function shortestPath(board, start, end) {
    let newBoard = board.slice();
    var num = 1;
    let frontier = [start];
    newBoard[start.row][start.col] = 0;

    function addSquareToFrontier(newFrontier, coords) {
        let curRow = newBoard[coords.row];
        let curSquare = curRow ? curRow[coords.col] : undefined;
        if (curSquare === -1) {
            newBoard[coords.row][coords.col] = num;
            newFrontier.push(coords);
            return true;
        } else {
            return false;
        }
    }

    let result;

    while (!result) {
        console.log('=====================================');
        let newFrontier = [];

        frontier.forEach(square => {
            if (square.row === end.row && square.col === end.col) {
                result = end;
                return square;
            }

            // set current as visited (no longer frontier)
            // newBoard[square.row][square.col] = 'o';
            let curCol = square.col;
            let curRow = square.row;
            addSquareToFrontier(newFrontier, {col: (curCol), row: (curRow - 1)}); // top
            addSquareToFrontier(newFrontier, {col: (curCol + 1), row:(curRow)}); // right
            addSquareToFrontier(newFrontier, {col: (curCol), row: (curRow + 1)}); // bottom
            addSquareToFrontier(newFrontier, {col: (curCol - 1), row:(curRow)}); // left
        });

        if (!result) {
            frontier = newFrontier;
            printMatrix(newBoard);
            num++;
        }
    }
}

function printMatrix(b) {
    b.forEach((row, i) => console.log('  ' + row.map(x => (x === -1 ? '  ' : (x < 10 ? ' ' + x : x))).join('  ')));
}





// create empty 8x8 board
var board = Array(8).fill(-1).map((x,i) => Array(8).fill(-1));

// add walls to map
// vertical
board = board.map((row, y) => row.map((squareVal, x) => ((x === 2 && y >= 0 && y <= 5) ? '██' : squareVal)));
// horizontal
board = board.map((row, y) => row.map((squareVal, x) => ((x >= 2 && x <= 5 && y === 6) ? '██' : squareVal)));
board = board.map((row, y) => row.map((squareVal, x) => ((x >= 4 && x <= 6 && y === 2) ? '██' : squareVal)));

// set start and end coordinates
var startCoords = {col: 0, row: 0};
var endCoords = {col: 7, row: 0};

shortestPath(board, startCoords, endCoords);