measurement/src/compound-units.js

A flexible library for handling unit conversions

'use strict';

var Unit = require('./units'),
    UnitTypes = require('./unit-types');

/**
 * public constructor CompoundUnit([Unit,Array] ...)
 *
 * Create a new instance of a compound unit, possibly with
 * included sub-units.
 *
 * @constructor
 */
var CompoundUnit = function compoundUnit() {
    this.subUnits = arguments.length ? Array.prototype.slice.call(arguments) : [];

    // If the first argument is an array assume that it is the
    // intended value and base subUnits off of it.
    if (Object.prototype.toString.call(this.subUnits[0]) === '[object Array]')
        this.subUnits = this.subUnits[0];

    this.type = UnitTypes.COMPOUND;
};

/**
 * private numeric combineUnitMultipliers(Array<Unit> units)
 *
 * Returns a multiplier representative of multipliers of all the
 * combined units
 */
function combineUnitMultipliers(units) {
    var result = 1;

    if (units.length) {
        result = units[0].getMultiplier();

        for(var i=1; i < units.length; ++i)
        {
            result /= units[i].getMultiplier();
        }
    }

    return result;
}

/**
 * public void addUnit(Unit unit)
 *
 * Adds a unit to the list of units that are compounded together
 */
CompoundUnit.prototype.addUnit = function(unit) {
    this.subUnits.push(unit);
    return this;
};

/**
 * public numeric getMultiplier()
 *
 * Returns a multiplier that is representative of all units in 
 * the combined unit system.
 */
CompoundUnit.prototype.getMultiplier = function() {
    return combineUnitMultipliers(this.subUnits);
};

/**
 * public string toString()
 *
 * Does what you think it would do,
 * ex) 'km/h'
 */
CompoundUnit.prototype.toString = function() {
    var result = '';
    result += this.subUnits.join('/');
    return result;
};

// Copy functionality so new units can be based off coupound units
CompoundUnit.prototype.makeBase = Unit.prototype.makeBase;


module.exports = CompoundUnit;