ev3js/device.js

LEGO Mindstorms EV3 API for Node.js

var fs = require('fs'),
    EventEmitter = require('events').EventEmitter;

var Device = function(){};

Device.prototype = new EventEmitter();

(function(){
    var cast = {
        str2num: function(n){return +n},
        strnum2bool: function(b){return !!+b;},
        bool2num: function(b){return +!!b;},
        str2onoff: function(b){return b === 'on';},
        onoff2str: function(b){return b ? 'on' : 'off';},
    };
    this.path = '/sys/bus/legoev3/devices/';
    this.polling = [];

    this.read = function(file, callback){
        if(typeof callback === 'function'){
            return fs.readFile(this.path + file, {encoding: 'utf8'}, callback);
        } else {
            return fs.readFileSync(this.path + file, {encoding: 'utf8'});
        }
    };

    this.write = function(file, value, callback){
        if(typeof callback === 'function'){
            fs.writeFile(this.path + file, value, callback);
        } else {
            fs.writeFileSync(this.path + file, value);
        }
    };

    this.search = function(name){
        var ports = fs.readdirSync(this.path);
        for(var i = 0; i < ports.length; i++){
            var port = ports[i];
            var portName = fs.readFileSync([this.path, port, 'port_name'].join('/'), {encoding: 'utf8'});
            if(portName.match(name)){
                return port;
            }
        }
    };

    this.accessor = function(name, getter, setter){
        this[name.replace(/_(\w)/g, function(a, b){return b.toUpperCase();})] = function(value, callback){
            if(getter && (arguments.length === 0 || (arguments.length === 1 && typeof value === 'function'))){
                callback = value;
                value = this.read(name, callback);
                if(typeof getter === 'string'){
                    getter = cast[getter];
                }
                if(typeof getter === 'function'){
                    value = getter(value);
                }
                return value;
            } else if(setter && arguments.length >= 1){
                if(typeof setter === 'string'){
                    setter = cast[setter];
                }
                if(typeof setter === 'function'){
                    value = setter(value);
                }
                this.write(name, value, callback);
            }
        };
    };

    this.poll = function(property, callback, interval){
        var id = this.polling.length;
        this.polling[id] = true;
        fs.open(this.path + property, 'r', function(err, fd){
            if(err){
                throw new Error(err);
            }
            (function(){
                var buf = new Buffer(64);
                var len = fs.readSync(fd, buf, 0, 64, 0);
                this.polling[id] = callback(buf.toString('utf8', 0, len - 1));
                if(this.polling[id] !== false){
                    setTimeout(arguments.callee.bind(this), interval || 1);
                } else {
                    fs.close(fd);
                }
            }.bind(this))();
        }.bind(this));
        return id;
    };

    this.abort = function(id){
        if(arguments.length){
            this.polling[id] = false;
        } else {
            this.polling = this.polling.map(function(){
                return false;
            });
        }
    };

}.bind(Device.prototype))();

module.exports = Device;