const Direction = Object.freeze({
    Up: { name: "up" },
    Right: { name: "right" },
    Down: { name: "down" },
    Left: { name: "left" },
    get values() { return Object.values(Direction); },
    fromName(name) { return this.values.filter(i=>i.name == name)[0] || null; },
});
const globals = {
    grid: null,
};

const btnStart_onClick = () => {
    globals.grid = new Grid(4, 4, new Tile(0, false));
    addRandomTile();
    // globals.grid = makeDevGrid([ // can't slide down or left
    //     [2,1,3,4],
    //     [3,5,7,9],
    //     [1,2,1,2],
    //     [3,4,5,0],
    // ]);
    redraw(globals.grid);
}

const btnRedraw_onClick = () => {
    redraw(globals.grid);
}

const getSettingsForDirection = (direction) => {    
    let settings = { 
        merge: (from, to) => {
            to.value++;
            from.value = 0;
            from.isVisible = false;
        }
    };

    if (direction === Direction.Up || direction === Direction.Left) {
        settings = {
            ...settings,
            advance: i => i + 1,
            testForDone: (fromIndex, length) => fromIndex >= length,
            getInitialFromIndex: () => 1,
            getInitialToIndex: () => 0
        };
    } else if (direction === Direction.Down || direction === Direction.Right) {
        settings = {
            ...settings,
            advance: i => i - 1,
            testForDone: fromIndex => fromIndex < 0,
            getInitialFromIndex: (length) => length - 2,
            getInitialToIndex: (length) => length - 1
        };
    }

    if (direction === Direction.Up || direction === Direction.Down) {
        settings = {
            ...settings,
            getVector: (grid, index) =>  grid.getColumn(index),
            swap: (grid, vector, columnIndex, from, to) => {
                grid.swapTiles(from, columnIndex, to, columnIndex);
                const tempTile = vector[to];
                vector[to] = vector[from];
                vector[from] = tempTile;        
            },
            getLength: (grid) => grid.numColumns
        }
    } else if (direction === Direction.Left || direction === Direction.Right) {
        settings = {
            ...settings,
            getVector: (grid, index) => grid.getRow(index),
            swap: (grid, vector, rowIndex, from, to) => {
                grid.swapTiles(rowIndex, from, rowIndex, to);
                const tempTile = vector[to];
                vector[to] = vector[from];
                vector[from] = tempTile;
            },
            getLength: (grid) => grid.numRows
        }
    }

    return settings;
}

const slideInDirection = (grid, direction) => {
    const settings = getSettingsForDirection(direction);
    const length = settings.getLength(grid);
    let didChange = false;
    
    for (let index = 0; index < length; index++) {
        const vector = settings.getVector(grid, index);
        const swap = settings.swap.bind(this, grid, vector, index);
        const initialFromIndex = settings.getInitialFromIndex(vector.length);
        const initialToIndex = settings.getInitialToIndex(vector.length);
        const didChangeThisPass = slide(
            initialFromIndex,
            initialToIndex,
            vector,
            settings.advance,
            swap,
            settings.merge,
            settings.testForDone
        );
        didChange = didChange || didChangeThisPass;
    }
    return didChange;
}

const playMove = (grid, direction) => {
    if (slideInDirection(grid, direction)) {
        addRandomTile();
        redraw(grid)
    } else {
        alert(`Unable to slide ${direction.name}.`);
    }
    checkForEnd(grid);
}

const btnUp_onClick = () => {
    playMove(globals.grid, Direction.Up);
}

const btnDown_onClick = () => {
    playMove(globals.grid, Direction.Down);
}

const btnLeft_onClick = () => {
    playMove(globals.grid, Direction.Left);
}

const btnRight_onClick = () => {
    playMove(globals.grid, Direction.Right);
}

const drawGrid = (grid, element) => {
    // grid is our grid
    // element is our div
    let text = "<table cellspacing=\"0\">\n";
    for (let rowIndex = 0; rowIndex < grid.numRows; rowIndex++) {
        text += "  <tr>\n";
        for (let columnIndex = 0; columnIndex < grid.numColumns; columnIndex++) {
            const tile = grid.getTile(rowIndex, columnIndex);
            text += "    <td title=\"(" + tile.originalPosition.row + ", " + tile.originalPosition.column + ")\"class=\"" + (tile.isVisible ? "visible " : "hidden ") + "\">" + tile.value + "</td>\n";
        }
        text += "  </tr>\n";
    }
    text += "</table>";
    element.innerHTML = text;
}

const addRandomTile = () => {
    const hiddenTiles = globals.grid.tiles.filter(tile => !tile.isVisible);
    if (hiddenTiles.length <=0) return;
    const index = Math.floor(Math.random() * hiddenTiles.length);
    const tile = hiddenTiles[index];
    tile.value = 1;
    tile.isVisible = true;
}

const redraw = (grid) => {
    const element = document.getElementById('output');
    drawGrid(grid, element);
}

const slide = (fromIndex, toIndex, vector, advance, swap, merge, testForDone) => {
    let didIDoIt = false;
    let hasMergedPrevious = false;
    while(!testForDone(fromIndex, vector.length)) {
        const fromTile = vector[fromIndex];
        const toTile = toIndex < vector.length && toIndex >= 0 ? vector[toIndex] : null;
        if (toTile == null) {
            // Advance toIndex
            toIndex = advance(toIndex);
            hasMergedPrevious = false;
            continue;
        }
        if (fromIndex == toIndex) {
            // Advance fromIndex
            fromIndex = advance(fromIndex);
            hasMergedPrevious = false;
            continue;
        }
        if (!toTile.isVisible) {
            if (fromTile.isVisible) {
                swap(fromIndex, toIndex);
                // Advance fromIndex
                fromIndex = advance(fromIndex);
                hasMergedPrevious = false;
                didIDoIt = true;
            } else {
                // Advance fromIndex
                fromIndex = advance(fromIndex);
            }
        } else {
            if (fromTile.isVisible) {
                if (fromTile.value == toTile.value) {
                    if (hasMergedPrevious) {
                        // Advance toIndex
                        toIndex = advance(toIndex);
                        hasMergedPrevious = false;
                        didIDoIt = true;
                    } else {
                        // Merge tiles
                        merge(fromTile, toTile);
                        // Advance fromIndex
                        fromIndex = advance(fromIndex);
                        hasMergedPrevious = true;
                        didIDoIt = true;
                    }
                } else {
                    // Advance toIndex
                    toIndex = advance(toIndex);
                    hasMergedPrevious = false;
                }
            } else {
                fromIndex = advance(fromIndex);
            }
        }
    }
    return didIDoIt;
}

const canSlideInDirection = (grid, direction) => {
    const clonedGrid = grid.clone();
    return slideInDirection(clonedGrid, direction);
}

const gameIsLost = (grid) => {
    return !canSlideInDirection(grid, Direction.Up)
        && !canSlideInDirection(grid, Direction.Right)
        && !canSlideInDirection(grid, Direction.Down)
        && !canSlideInDirection(grid, Direction.Left);
}

const checkForEnd = (grid) => {
    if (gameIsLost(grid)) {
        alert('A loser is you!');
    }
}

const makeDevGrid = (matrix) => {
    const numRows = matrix.length;
    const numColumns = matrix[0].length;
    const initialValue = new Tile(0, false, new GridPosition(0, 0));
    const grid = new Grid(numRows, numColumns, initialValue);
    for (let rowIndex = 0; rowIndex < numRows; rowIndex++) {
        const row = matrix[rowIndex];
        for (let colIndex = 0; colIndex < numColumns; colIndex++) {
            const value = row[colIndex];
            const tile = grid.getTile(rowIndex, colIndex);
            tile.value = value;
            tile.isVisible = value > 0;
        }
    }
    return grid;
}
/*
[0,0,0,0],
[0,0,1,0],
[0,0,0,0],
[2,1,2,2],
can't slide down.
[0,0,1,0],
[0,0,0,0],
[0,0,0,0],
[3,2,3,0],
can't slide down.
can't slide left.
up()
[1,0,1,0],
[0,0,3,0],
[0,0,0,0],
[3,2,0,0], either the 3 doesn't go up or the 1 bounces it back?
// fixed
*/

class GameBoard {
    #grid_;

    constructor() {
        
    }

};

class Grid {
    #tiles_ = [];
    #rows_ = [];
    #numRows_;
    #numColumns_;
    get tiles() { return [...this.#tiles_]; }
    get numRows() { return this.#numRows_; }
    get numColumns() { return this.#numColumns_; }

    constructor(numRows, numColumns, initialValue) {
        this.#numRows_ = numRows;
        this.#numColumns_ = numColumns;
        for (let rowIndex = 0; rowIndex < numRows; rowIndex++) {
            const row = [];
            for (let columnIndex = 0; columnIndex < this.numColumns; columnIndex++) {
                const position = new GridPosition(rowIndex, columnIndex);
                const tile = new Tile(initialValue.value, initialValue.isVisible, position);
                this.#tiles_.push(tile);
                row.push(tile);
            }
            this.#rows_.push(row);
        }
    }

    clone() {
        const newGrid = new Grid(this.numRows, this.numColumns, new Tile(0, false, new GridPosition(0, 0)));
        for (let rowIndex = 0; rowIndex < this.numRows; rowIndex++) {
            for (let columnIndex = 0; columnIndex < this.numColumns; columnIndex++) {
                const newTile = newGrid.getTile(rowIndex, columnIndex);
                const oldTile = this.getTile(rowIndex, columnIndex);
                // TODO(tom): Set the originalPosition of newTile to be the same as oldTile.
                newTile.value = oldTile.value;
                newTile.isVisible = oldTile.isVisible;
            }
        }
        return newGrid;
    }

    getColumn (columnIndex) {
        let vector = [];
        for (let rowIndex = 0; rowIndex < this.numRows; rowIndex++) {
            vector.push(this.getTile(rowIndex, columnIndex));
        }
        return vector;
    }

    getRow (rowIndex) {
        let vector = [];
        for (let columnIndex = 0; columnIndex < this.numColumns; columnIndex++) {
            vector.push(this.getTile(rowIndex, columnIndex));
        }
        return vector;
    }

    getTile (row, column) {
        if (row >= 0 && row < this.numRows && column >= 0 && column < this.numColumns) {
            // TODO(tom): Check that this is the right order.
            return this.#rows_[column][row]
        }
        return null;
    }

    setTile (row, column, tile) {
        if (row >= 0 && row < this.numRows && column >= 0 && column < this.numColumns) {
            // TODO(tom): Check that this is the right order.
            this.#rows_[column][row] = tile;
        }
    }

    swapTiles (fromRow, fromColumn, toRow, toColumn) {
        if (
                fromRow >= 0 && fromRow < this.numRows
                && fromColumn >= 0 && fromColumn < this.numColumns
                && toRow >= 0 && toRow < this.numRows
                && toColumn >= 0 && toColumn < this.numColumns) {
            const fromTile = this.getTile(fromRow, fromColumn);
            const toTile = this.getTile(toRow, toColumn);
            this.setTile(fromRow, fromColumn, toTile);
            this.setTile(toRow, toColumn, fromTile);
        }
    }

    toString (format = t => t.value) {
        return `[[${t(this.getTile(0, 0))},${t(this.getTile(0, 1))},${t(this.getTile(0, 2))},${t(this.getTile(0, 3))}],
 [${t(this.getTile(1, 0))},${t(this.getTile(1, 1))},${t(this.getTile(1, 2))},${t(this.getTile(1, 3))}],
 [${t(this.getTile(2, 0))},${t(this.getTile(2, 1))},${t(this.getTile(2, 2))},${t(this.getTile(2, 3))}],
 [${t(this.getTile(3, 0))},${t(this.getTile(3, 1))},${t(this.getTile(3, 2))},${t(this.getTile(3, 3))}]]`;
    }
};

class GridPosition {
    #row_;
    #column_;
    constructor (row, column) {
        this.#row_ = row || 0;
        this.#column_ = column || 0;
    }
    get row() { return this.#row_; }
    get column() { return this.#column_; }
    equals (other) {
        return other !== null && other !== undefined
            && this.#row_ === other.#row_
            && this.#column_ === other.#column_;
    }
    toString() {
        return `{ row: ${this.#row_}, column: ${this.#column_} }`;
    }
}

class Tile {
    #originalPosition_;
    value;
    isVisible;
    get originalPosition() {
        return {...this.#originalPosition_};
    }
    constructor (value, isVisible, originalPosition = new GridPosition(0, 0)) {
        this.value = value;
        this.isVisible = isVisible;
        this.originalPosition_ = {...originalPosition};
    }
    equals (other) {
        return other !== null && other !== undefined
            && this.value === other.value
            && this.isVisible === other.isVisible
            && this.#originalPosition_.row === other.#originalPosition_.row
            && this.#originalPosition_.column === other.#originalPosition_.column;
    }
    toString() {
        return `{ value: ${this.value}, originalPosition: { row: ${this.#originalPosition_.row}, column: ${this.#originalPosition_.column} }, isVisible: ${this.isVisible ? "true" : "false"} }`;
    }
};