"use strict";

/**
 * Constructor for field paths.
 *
 * The constructed object will have getPathLength() > 0.
 * Uassert if any component field names do not pass validation.
 *
 * @class FieldPath
 * @namespace mungedb-aggregate.pipeline
 * @module mungedb-aggregate
 * @constructor
 * @param fieldPath the dotted field path string or non empty pre-split vector.
 **/
var FieldPath = module.exports = function FieldPath(path) {
	var fields = typeof path === "object" && typeof path.length === "number" ? path : path.split(".");
	if(fields.length === 0) throw new Error("FieldPath cannot be constructed from an empty vector (String or Array).; code 16409");
	for(var i = 0, n = fields.length; i < n; ++i){
		var field = fields[i];
		if(field.length === 0) throw new Error("FieldPath field names may not be empty strings; code 15998");
		if(field[0] == "$") throw new Error("FieldPath field names may not start with '$'; code 16410");
		if(field.indexOf("\0") != -1) throw new Error("FieldPath field names may not contain '\\0'; code 16411");
		if(field.indexOf(".") != -1) throw new Error("FieldPath field names may not contain '.'; code 16412");
	}
	this.path = path;
	this.fields = fields;
}, klass = FieldPath, base = Object, proto = klass.prototype = Object.create(base.prototype, {constructor:{value:klass}});

// STATIC MEMBERS
klass.PREFIX = "$";

// PROTOTYPE MEMBERS
/**
 * Get the full path.
 *
 * @method getPath
 * @param fieldPrefix whether or not to include the field prefix
 * @returns the complete field path
 **/
proto.getPath = function getPath(withPrefix) {
	return ( !! withPrefix ? FieldPath.PREFIX : "") + this.fields.join(".");
};

/**
 * A FieldPath like this but missing the first element (useful for recursion). Precondition getPathLength() > 1.
 *
 * @method tail
 **/
proto.tail = function tail() {
	return new FieldPath(this.fields.slice(1));
};

/**
 * Get a particular path element from the path.
 *
 * @method getFieldName
 * @param i the zero based index of the path element.
 * @returns the path element
 **/
proto.getFieldName = function getFieldName(i){	//TODO: eventually replace this with just using .fields[i] directly
	return this.fields[i];
};

/**
 * Get the number of path elements in the field path.
 *
 * @method getPathLength
 * @returns the number of path elements
 **/
proto.getPathLength = function getPathLength() {
	return this.fields.length;
};