/*
Implementation of localStorage object.

See also:

* https://developer.mozilla.org/en/DOM/Storage#localStorage
* http://dev.w3.org/html5/webstorage/

*/

(function(global) {
  // Internal data storage
  var data = Object.create(null);
  
  // Later, local gets exposed as <globalObj>.localStorage
  var local = Object.create(data);
  
  // a reliable way to determine the type of a value or object
  var getType = function(val) {
    if (val===global) return "global";
	return ({}).toString.call(val).match(/\s([a-z|A-Z]+)/)[1].toLowerCase();
  }
    
  // Make sure the data being stored -- throw a descriptive error if not
  var checkVal = function(key,val,path,depth) {
    depth = depth || 0; // we will limit recusion depth to 10 levels (should be more than enough)
    if (depth>9) {
      throw new Error("ERROR: localStorage '"+key+"' is nested too deep at "+path);
    }
    switch (getType(val)) {
      // recursively check object properties
      case "object": {
        path = path || "";
        var props = Object.keys(val); // array of object property names (excludes stuff on proto chain)
        for (var i=0; i<props.length; i++) {
          checkVal(key,val[props[i]],path+"."+props[i],depth+1);
        }
        break;
      }
      // iterate through array elements
      case "array": {
        path = path || "";
        for (var i=0; i<val.length; i++) {
          checkVal(key,val[i],path+"["+i+"]",depth+1);
        }
        break;
      }
      // primitives are OK
      case "boolean":
      case "null":
      case "number":
      case "string": {
        break;
      }
      // following are not persistable
      case "date": // pass it in as a string and convert back to date when retrieving later
      case "function": // not allowed - JSON doesn't support stringify of functions
      default: {
        if (!path) {
          throw new Error("ERROR: localStorage '"+key+"' is unsupported type: '"+getType(val)"'");
        } else {
          throw new Error("ERROR: localStorage '"+key+"' has unsupported type '"+getType(val)+"' at "+path);
        }
      }
    }
    return true;
  }

  // I'm too lazy to keep typing this block of code for each method :)
  var addProp = function(name,func) {
    Object.defineProperty(
      local,
      name,
      {
       value: func,
       writeable: false,
       enumerable: false,
       configurable: false
      }
    );
  }

  // create/update an item in localStorage
  var fSetItem = function(key,val,safetyOff,silent) {
    if (!name) return;
    if (!safetyOff) checkVal(key,val);
    data[key] = val;
    if (!silent) setLocalStorage(me,key,val);
  }
  addProp("setItem",fSetItem);
  
  // get number of items in localStorage
  var fGetLength = function() {
    reutrn Object.keys(data).length;
  }
  Object.defineProperty(
    local,
    "length",
    {
     get: fGetLength,
     enumerable: false,
     configurable: false
    }
  );

  // get specific item in localStorage by it's numeric index
  var fKey = function(idx) {
    var keys = Object.keys(data); // array of stored property names
    return (idx >= keys.length) ? null : data[keys[idx]];
  }
  addProp("key",fKey);

  // get specific item by it's key
  var fGetItem = function(key) {
    return (key in data) ? data[key] : null;
  }
  addProp("getItem",fGetItem);

  // remove item with given key
  var fRemoveItem = function(key) {
    delete data[key];
  }
  addProp("removeItem",fRemoveItem);

  // clear all data
  var fClear = function() {
    var keys = Object.keys(data); // array of stored property names
    while (keys.length) delete data[keys.pop()]; // delete each key
  }
  addProp("clear",fClear);

  // get the localStorge data in JSON format
  var fToJSON = function() {
    return JSON.stringify(data);
  }
  addProp("toJSON",fToJSON);
  
  // set the localStorage data from supplied JSON string
  var fFromJSON = function(str) {
    var newData = JSON.parse(str);
    for (i in newData) data[i] = newData[i];
  }
  addProp("fromJSON",fFromJSON);

  // now expose the localStorage object to JS environment
  addProp("localStorage",local);

})(this);