module.exports = function (ns) {

    // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    var HeaderProperty = function(name, type, size, defaultValue)
    {
        this.name   = name;
        this.type   = type;
        this.size   = size;
        this.length = type == 'N' ? size*4 : (type == 'n' ? size*2 : size );
        this.value  = defaultValue;
    };
    // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    var HeaderDef = function(mapData)
    {
        var map = [];
        mapData.forEach(function (def) {
            map.push(new HeaderProperty(def[0], def[1], def[2], def[3]));
        });
        this.map    = map; 
        var keys    = [];
        var indexes = {};
        var offset  = 0;
        var index   = 0;
        this.map.forEach(function(prop) {
            prop.offset = offset;
            keys[keys.length] = prop.name;
            offset += prop.length;
            indexes[prop.name] = index++;
        });
        this.indexes     = indexes;
        this.keys        = keys;
        this.length      = offset;
        this.getProperty = function(key) {
            return this.map[this.indexes[key]];
        }
    };
    // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    ns.Header = function(def) {
        this.def   = new HeaderDef(def);
        this.value = function(key) {
            return this.def.getProperty(key).value;
        };
        this.buildProperties = function(properties) {
            this.def.map.forEach(function(prop) {
                if (prop.name != 'signature') {
                    if (typeof properties[prop.name] != 'undefined') {
                        prop.value = properties[prop.name];
                    }
                }
            });
        };
    }
}