var EventEmitter = require('events');
var util = require('util');

var Blocks = require('./blocks');
var Variable = require('../engine/variable');
var List = require('../engine/list');
var uid = require('../util/uid');

/**
 * @fileoverview
 * A Target is an abstract "code-running" object for the Scratch VM.
 * Examples include sprites/clones or potentially physical-world devices.
 */

/**
 * @param {?Blocks} blocks Blocks instance for the blocks owned by this target.
 * @constructor
 */
var Target = function (blocks) {
    EventEmitter.call(this);

    if (!blocks) {
        blocks = new Blocks(this);
    }
    /**
     * A unique ID for this target.
     * @type {string}
     */
    this.id = uid();
    /**
     * Blocks run as code for this target.
     * @type {!Blocks}
     */
    this.blocks = blocks;
    /**
     * Dictionary of variables and their values for this target.
     * Key is the variable name.
     * @type {Object.<string,*>}
     */
    this.variables = {};
    /**
     * Dictionary of lists and their contents for this target.
     * Key is the list name.
     * @type {Object.<string,*>}
     */
    this.lists = {};
    /**
     * Dictionary of custom state for this target.
     * This can be used to store target-specific custom state for blocks which need it.
     * TODO: do we want to persist this in SB3 files?
     * @type {Object.<string,*>}
     */
    this._customState = {};
};

/**
 * Inherit from EventEmitter
 */
util.inherits(Target, EventEmitter);

/**
 * Called when the project receives a "green flag."
 * @abstract
 */
Target.prototype.onGreenFlag = function () {};

/**
 * Return a human-readable name for this target.
 * Target implementations should override this.
 * @abstract
 * @returns {string} Human-readable name for the target.
 */
Target.prototype.getName = function () {
    return this.id;
};

/**
 * Look up a variable object, and create it if one doesn't exist.
 * Search begins for local variables; then look for globals.
 * @param {!string} name Name of the variable.
 * @return {!Variable} Variable object.
 */
Target.prototype.lookupOrCreateVariable = function (name) {
    // If we have a local copy, return it.
    if (this.variables.hasOwnProperty(name)) {
        return this.variables[name];
    }
    // If the stage has a global copy, return it.
    if (this.runtime && !this.isStage) {
        var stage = this.runtime.getTargetForStage();
        if (stage.variables.hasOwnProperty(name)) {
            return stage.variables[name];
        }
    }
    // No variable with this name exists - create it locally.
    var newVariable = new Variable(name, 0, false);
    this.variables[name] = newVariable;
    return newVariable;
};

/**
* Look up a list object for this target, and create it if one doesn't exist.
* Search begins for local lists; then look for globals.
* @param {!string} name Name of the list.
* @return {!List} List object.
 */
Target.prototype.lookupOrCreateList = function (name) {
    // If we have a local copy, return it.
    if (this.lists.hasOwnProperty(name)) {
        return this.lists[name];
    }
    // If the stage has a global copy, return it.
    if (this.runtime && !this.isStage) {
        var stage = this.runtime.getTargetForStage();
        if (stage.lists.hasOwnProperty(name)) {
            return stage.lists[name];
        }
    }
    // No list with this name exists - create it locally.
    var newList = new List(name, []);
    this.lists[name] = newList;
    return newList;
};

/**
 * Post/edit sprite info.
 * @param {object} data An object with sprite info data to set.
 * @abstract
 */
Target.prototype.postSpriteInfo = function () {};

/**
 * Retrieve custom state associated with this target and the provided state ID.
 * @param {string} stateId - specify which piece of state to retrieve.
 * @returns {*} the associated state, if any was found.
 */
Target.prototype.getCustomState = function (stateId) {
    return this._customState[stateId];
};

/**
 * Store custom state associated with this target and the provided state ID.
 * @param {string} stateId - specify which piece of state to store on this target.
 * @param {*} newValue - the state value to store.
 */
Target.prototype.setCustomState = function (stateId, newValue) {
    this._customState[stateId] = newValue;
};

/**
 * Call to destroy a target.
 * @abstract
 */
Target.prototype.dispose = function () {
    this._customState = {};
};

module.exports = Target;