//Javascript Connect 4 Game

function start_game() {
    "use strict";

    document.body.innerHTML = '';

    const DELAY_COMP = 0.5;
    const GRID_CIRCLE = 0.7;
    const GRID_COLS = 7;
    const GRID_ROWS = 6;
    const MARGIN = 0.02;
    const COLOR_BACKGROUND = "mintcream";
    const COLOR_COMP = "yellow";
    const COLOR_COMP_DRK = "olive";
    const COLOR_FRAME = "dodgerblue";
    const COLOR_FRAME_BUTT = "royalblue";
    const COLOR_PLAY = "red";
    const COLOR_PLAY_DRK = "darkred";
    const COLOR_TIE = "darkgrey";
    const COLOR_TIE_DRK = "black";
    const COLOR_WIN = "black";
    const TEXT_COMP = "Computer";
    const TEXT_PLAY = "YOU";
    const TEXT_TIE = "DRAW";
    const TEXT_WIN = "WON!";
    class Cell {
        constructor(left, top, w, h, row, col) {
            this.bot = top + h;
            this.left = left;
            this.right = left + w;
            this.top = top;
            this.w = w;
            this.h = h;
            this.row = row;
            this.col = col;
            this.cx = left + w / 2;
            this.cy = top + h / 2;
            this.r = w * GRID_CIRCLE / 2;
            this.highlight = null;
            this.owner = null;
            this.winner = false;
        }

        contains(x, y) {
            return x > this.left && x < this.right && y > this.top && y < this.bot;
        }
        draw(/** @type {CanvasRenderingContext2D} */ ctx) {
            let color = this.owner == null ? COLOR_BACKGROUND : this.owner ? COLOR_PLAY : COLOR_COMP;
            ctx.fillStyle = color;
            ctx.beginPath();
            ctx.arc(this.cx, this.cy, this.r, 0, Math.PI * 2);
            ctx.fill();
            if (this.winner || this.highlight != null) {
                color = this.winner ? COLOR_WIN : this.highlight ? COLOR_PLAY : COLOR_COMP;
                ctx.lineWidth = this.r / 4;
                ctx.strokeStyle = color;
                ctx.beginPath();
                ctx.arc(this.cx, this.cy, this.r, 0, Math.PI * 2);
                ctx.stroke();
            }
        }
    }
    var canv = document.createElement("canvas");
    document.body.appendChild(canv);
    var ctx = canv.getContext("2d");
    var gameOver, gameTied, grid = [], playersTurn, timeComp;
    var height, width, margin;
    setDimensions();
    canv.addEventListener("click", click);
    canv.addEventListener("mousemove", highlightGrid);
    window.addEventListener("resize", setDimensions);
    var timeDelta, timeLast;
    requestAnimationFrame(loop);

    function loop(timeNow) {
        if (!timeLast) {
            timeLast = timeNow;
        }
        timeDelta = (timeNow - timeLast) / 1000; // seconds
        timeLast = timeNow;

        goComputer(timeDelta);

        drawBackground();
        drawGrid();
        drawText();

        requestAnimationFrame(loop);
    }

    function checkWin(row, col) {

        let diagL = [], diagR = [], horiz = [], vert = [];
        for (let i = 0; i < GRID_ROWS; i++) {
            for (let j = 0; j < GRID_COLS; j++) {

                if (i == row) {
                    horiz.push(grid[i][j]);
                }

                if (j == col) {
                    vert.push(grid[i][j]);
                }

                if (i - j == row - col) {
                    diagL.push(grid[i][j]);
                }

                if (i + j == row + col) {
                    diagR.push(grid[i][j]);
                }
            }
        }

        return connect4(diagL) || connect4(diagR) || connect4(horiz) || connect4(vert);
    }

    function connect4(cells = []) {
        let count = 0, lastOwner = null;
        let winningCells = [];
        for (let i = 0; i < cells.length; i++) {

            if (cells[i].owner == null) {
                count = 0;
                winningCells = [];
            }

            else if (cells[i].owner == lastOwner) {
                count++;
                winningCells.push(cells[i]);
            }

            else {
                count = 1;
                winningCells = [];
                winningCells.push(cells[i]);
            }

            lastOwner = cells[i].owner;

            if (count == 4) {
                for (let cell of winningCells) {
                    cell.winner = true;
                }
                return true;
            }
        }
        return false;
    }

    function click(ev) {

        if (gameOver) {
            newGame();
            return;
        }

        if (!playersTurn) {
            return;
        }

        selectCell();
    }

    function createGrid() {
        grid = [];

        let cell, marginX, marginY;

        if ((width - margin * 2) * GRID_ROWS / GRID_COLS < height - margin * 2) {
            cell = (width - margin * 2) / GRID_COLS;
            marginX = margin;
            marginY = (height - cell * GRID_ROWS) / 2;
        }

        else {
            cell = (height - margin * 2) / GRID_ROWS;
            marginX = (width - cell * GRID_COLS) / 2;
            marginY = margin;
        }

        for (let i = 0; i < GRID_ROWS; i++) {
            grid[i] = [];
            for (let j = 0; j < GRID_COLS; j++) {
                let left = marginX + j * cell;
                let top = marginY + i * cell;
                grid[i][j] = new Cell(left, top, cell, cell, i, j);
            }
        }
    }

    function drawBackground() {
        ctx.fillStyle = COLOR_BACKGROUND;
        ctx.fillRect(0, 0, width, height);
    }

    function drawGrid() {

        let cell = grid[0][0];
        let fh = cell.h * GRID_ROWS;
        let fw = cell.w * GRID_COLS;
        ctx.fillStyle = COLOR_FRAME;
        ctx.fillRect(cell.left, cell.top, fw, fh);
        ctx.fillStyle = COLOR_FRAME_BUTT;
        ctx.fillRect(cell.left - margin / 2, cell.top + fh - margin / 2, fw + margin, margin);

        for (let row of grid) {
            for (let cell of row) {
                cell.draw(ctx);
            }
        }
    }

    function drawText() {
        if (!gameOver) {
            return;
        }

        let size = grid[0][0].h;
        ctx.fillStyle = gameTied ? COLOR_TIE : playersTurn ? COLOR_PLAY : COLOR_COMP;
        ctx.font = size + "px dejavu sans mono";
        ctx.lineJoin = "round";
        ctx.lineWidth = size / 10;
        ctx.strokeStyle = gameTied ? COLOR_TIE_DRK : playersTurn ? COLOR_PLAY_DRK : COLOR_COMP_DRK;
        ctx.textAlign = "center";
        ctx.textBaseline = "middle";

        let offset = size * 0.55;
        let text = gameTied ? TEXT_TIE : playersTurn ? TEXT_PLAY : TEXT_COMP;
        if (gameTied) {
            ctx.strokeText(text, width / 2, height / 2);
            ctx.fillText(text, width / 2, height / 2);
        } else {
            ctx.strokeText(text, width / 2, height / 2 - offset);
            ctx.fillText(text, width / 2, height / 2 - offset);
            ctx.strokeText(TEXT_WIN, width / 2, height / 2 + offset);
            ctx.fillText(TEXT_WIN, width / 2, height / 2 + offset);
        }
    }

    function goComputer(delta) {
        if (playersTurn || gameOver) {
            return;
        }

        if (timeComp > 0) {
            timeComp -= delta;
            if (timeComp <= 0) {
                selectCell();
            }
            return;
        }

        let options = [];
        options[0] = [];
        options[1] = [];
        options[2] = [];
        options[3] = [];

        let cell;
        for (let i = 0; i < GRID_COLS; i++) {
            cell = highlightCell(grid[0][i].cx, grid[0][i].cy);

            if (cell == null) {
                continue;
            }

            cell.owner = playersTurn;
            if (checkWin(cell.row, cell.col)) {
                options[0].push(i);
            } else {

                cell.owner = !playersTurn;
                if (checkWin(cell.row, cell.col)) {
                    options[1].push(i);
                } else {
                    cell.owner = playersTurn;

                    if (cell.row > 0) {
                        grid[cell.row - 1][cell.col].owner = !playersTurn;

                        if (checkWin(cell.row - 1, cell.col)) {
                            options[3].push(i);
                        }

                        else {
                            options[2].push(i);
                        }

                        grid[cell.row - 1][cell.col].owner = null;
                    }

                    else {
                        options[2].push(i);
                    }
                }
            }

            cell.highlight = null;
            cell.owner = null;
        }

        for (let row of grid) {
            for (let cell of row) {
                cell.winner = false;
            }
        }

        let col;
        if (options[0].length > 0) {
            col = options[0][Math.floor(Math.random() * options[0].length)];
        } else if (options[1].length > 0) {
            col = options[1][Math.floor(Math.random() * options[1].length)];
        } else if (options[2].length > 0) {
            col = options[2][Math.floor(Math.random() * options[2].length)];
        } else if (options[3].length > 0) {
            col = options[3][Math.floor(Math.random() * options[3].length)];
        }

        highlightCell(grid[0][col].cx, grid[0][col].cy);

        timeComp = DELAY_COMP;
    }

    function highlightCell(x, y) {
        let col = null;
        for (let row of grid) {
            for (let cell of row) {

                cell.highlight = null;

                if (cell.contains(x, y)) {
                    col = cell.col;
                }
            }
        }

        if (col == null) {
            return;
        }

        for (let i = GRID_ROWS - 1; i >= 0; i--) {
            if (grid[i][col].owner == null) {
                grid[i][col].highlight = playersTurn;
                return grid[i][col];
            }
        }
        return null;
    }

    function highlightGrid(/** @type {MouseEvent} */ ev) {
        if (!playersTurn || gameOver) {
            return;
        }
        highlightCell(ev.clientX, ev.clientY);
    }

    function newGame() {
        playersTurn = Math.random() < 0.5;
        gameOver = false;
        gameTied = false;
        createGrid();
    }

    function selectCell() {
        let highlighting = false;
        OUTER: for (let row of grid) {
            for (let cell of row) {
                if (cell.highlight != null) {
                    highlighting = true;
                    cell.highlight = null;
                    cell.owner = playersTurn;
                    if (checkWin(cell.row, cell.col)) {
                        gameOver = true;
                    }
                    break OUTER;
                }
            }
        }

    if (!highlighting) {
        return;
    }

        if (!gameOver) {
            gameTied = true;
            OUTER: for (let row of grid) {
                for (let cell of row) {
                    if (cell.owner == null) {
                        gameTied = false;
                        break OUTER;
                    }
                }
            }

            if (gameTied) {
                gameOver = true;
            }
        }

        if (!gameOver) {
            playersTurn = !playersTurn;
        }
    }

    function setDimensions() {
        height = window.innerHeight;
        width = window.innerWidth;
        canv.height = height;
        canv.width = width;
        margin = MARGIN * Math.min(height, width);
        newGame();
    }
}