var events = require("events"),
  util = require("util");

var priv = new Map();

/**
 * Ping
 * @param {Object} opts Options: addr freq
 */

function Ping(opts) {

  if (!(this instanceof Ping)) {
    return new Ping(opts);
  }

  var last = null;

  this.addr = opts && opts.addr || 0x27;
  this.freq = opts.freq || 100;
  this.board = opts.board || null;

  var state = {
    value: 0
  };

  // Private settings object
  var settings = {
    addr: this.addr,
    value: this.board.io.HIGH,
    readBytes: 2, // the duration that comes off the ping is a 16 bit int
    pingFreq: 110, // an optimium period to poll the sensor on i2c.
  };

  this.board.io.setMaxListeners(100);

    this.board.io.i2cConfig();
  // Interval for polling pulse duration as reported in microseconds
  setInterval(function() {
    this.board.io.i2cReadOnce(settings.addr, settings.readBytes, function(data) {
      state.value = (data[0] << 8) + data[1];
    });
  }.bind(this), settings.pingFreq);

  // Interval for throttled event
  setInterval(function() {
    var err = null;

    if (!state.value) {
      return;
    }

    // The "read" event has been deprecated in
    // favor of a "data" event.
    this.emit("data", err, state.value);

    // If the state.value for this interval is not the same as the
    // state.value in the last interval, fire a "change" event.
    if (state.value !== last) {
      this.emit("change", err, state.value);
    }

    // Store state.value for comparison in next interval
    last = state.value;

    // Reset samples;
    // samples.length = 0;
  }.bind(this), this.freq);

  Object.defineProperties(this, {
    value: {
      get: function() {
        return state.value;
      }
    },
    // Based on the round trip travel time in microseconds,
    // Calculate the distance in inches and centimeters
    inches: {
      get: function() {
        return +(state.value / 74 / 2).toFixed(2);
      }
    },
    in: {
      get: function() {
        return this.inches;
      }
    },
    cm: {
      get: function() {
        return +(state.value / 29 / 2).toFixed(3);
      }
    }
  });

  priv.set(this, state);
}

util.inherits(Ping, events.EventEmitter);

module.exports = Ping;

//http://protolab.pbworks.com/w/page/19403657/TutorialPings