var Utils = require('../utils/Utils')
,   EventEmitter = require('../events/EventEmitter');

module.exports = Solver;

/**
 * Base class for constraint solvers.
 * @class Solver
 * @constructor
 * @extends EventEmitter
 */
function Solver(options,type){
    options = options || {};

    EventEmitter.call(this);

    this.type = type;

    /**
     * Current equations in the solver.
     *
     * @property equations
     * @type {Array}
     */
    this.equations = [];

    /**
     * Function that is used to sort all equations before each solve.
     * @property equationSortFunction
     * @type {function|boolean}
     */
    this.equationSortFunction = options.equationSortFunction || false;
}
Solver.prototype = new EventEmitter();
Solver.prototype.constructor = Solver;

/**
 * Method to be implemented in each subclass
 * @method solve
 * @param  {Number} dt
 * @param  {World} world
 */
Solver.prototype.solve = function(dt,world){
    throw new Error("Solver.solve should be implemented by subclasses!");
};

var mockWorld = {bodies:[]};

/**
 * Solves all constraints in an island.
 * @method solveIsland
 * @param  {Number} dt
 * @param  {Island} island
 */
Solver.prototype.solveIsland = function(dt,island){

    this.removeAllEquations();

    if(island.equations.length){
        // Add equations to solver
        this.addEquations(island.equations);
        mockWorld.bodies.length = 0;
        island.getBodies(mockWorld.bodies);

        // Solve
        if(mockWorld.bodies.length){
            this.solve(dt,mockWorld);
        }
    }
};

/**
 * Sort all equations using the .equationSortFunction. Should be called by subclasses before solving.
 * @method sortEquations
 */
Solver.prototype.sortEquations = function(){
    if(this.equationSortFunction){
        this.equations.sort(this.equationSortFunction);
    }
};

/**
 * Add an equation to be solved.
 *
 * @method addEquation
 * @param {Equation} eq
 */
Solver.prototype.addEquation = function(eq){
    if(eq.enabled){
        this.equations.push(eq);
    }
};

/**
 * Add equations. Same as .addEquation, but this time the argument is an array of Equations
 *
 * @method addEquations
 * @param {Array} eqs
 */
Solver.prototype.addEquations = function(eqs){
    //Utils.appendArray(this.equations,eqs);
    for(var i=0, N=eqs.length; i!==N; i++){
        var eq = eqs[i];
        if(eq.enabled){
            this.equations.push(eq);
        }
    }
};

/**
 * Remove an equation.
 *
 * @method removeEquation
 * @param {Equation} eq
 */
Solver.prototype.removeEquation = function(eq){
    var i = this.equations.indexOf(eq);
    if(i !== -1){
        this.equations.splice(i,1);
    }
};

/**
 * Remove all currently added equations.
 *
 * @method removeAllEquations
 */
Solver.prototype.removeAllEquations = function(){
    this.equations.length=0;
};

Solver.GS = 1;
Solver.ISLAND = 2;