/*

    Copyright (C) 2016 Apple Inc. All Rights Reserved.

    See LICENSE.txt for this sample’s licensing information

    Abstract:

    Handles data for a maze.

*/

import GameplayKit

import SpriteKit

class Maze {

    // MARK: Properties

    /**

        Defines the width (and height) of the maze. This is the actual number of rows (and columns) of the maze graph. Since the maze contains walls between traversable areas, these walls must be represented in the navigability graph. 

        - Note: This value must be odd.

    */

    static let dimensions = 25

    /// A grid-based graph representing the navigability space of the maze.

    var graph: GKGridGraph<GKGridGraphNode>

    /// A node in a grid-based graph representing the starting point of the maze.

    var startNode: GKGridGraphNode

    /// A node in a grid-based graph representing the ending point of the maze.

    var endNode: GKGridGraphNode

    /**

        Computes a solution to the maze by using GameplayKit's pathfinding

        on the maze's GKGridGraph.

    */

    var solutionPath: [GKGridGraphNode]? {

        // Calculate a solution path to the maze.

        let solution = graph.findPath(from: startNode, to: endNode) as! [GKGridGraphNode]

        /*

            If the solution path is not empty, return the path. Otherwise, 

            throw an error.

        */

        if solution.isEmpty {

            assertionFailure("No path exists between startNode and endNode.")

            return nil

        }

        else {

            return solution

        }

    }

    // MARK: Initialization

    init() {

        // Initialize the maze graph. At this point, the graph has no walls.

        graph = GKGridGraph(fromGridStartingAt: int2(0, 0), width: Int32(Maze.dimensions), height: Int32(Maze.dimensions), diagonalsAllowed: false)

        /* 

            Define the maze's start and end nodes.

            - Note: These nodes must have both an even x and an even y 

            coordinate, otherwise they may not remain on the maze graph after 

            the maze walls are removed.

        */

        startNode = graph.node(atGridPosition: int2(0, Int32(Maze.dimensions - 1)))!

        endNode   = graph.node(atGridPosition: int2(Int32(Maze.dimensions - 1), 0))!

        /*

            Create a MazeBuilder to generate a random set of walls, then remove 

            them from the maze graph. By removing these nodes, you prevent them 

            from being traversable, so they serve as impassible walls.

        */

        let mazeBuilder = MazeBuilder(maze: self)

        let mazeWalls = mazeBuilder.mazeWallsForRemoval()

        graph.remove(mazeWalls)

    }

}