var Persistence = function(table){
	this.table = table; //hold Tabulator object
	this.mode = "";
	this.id = "";
	this.persistProps = ["field", "width", "visible"];
};

// Test for whether localStorage is available for use.
Persistence.prototype.localStorageTest = function() {
	var  testKey =  "_tabulator_test";

	try {
		window.localStorage.setItem( testKey, testKey);
		window.localStorage.removeItem( testKey );
		return true;
	} catch(e) {
		return false;
	}
};

//setup parameters
Persistence.prototype.initialize = function(mode, id){
	//determine persistent layout storage type

	this.mode = mode !== true ?  mode : (this.localStorageTest() ? "local" : "cookie");

	//set storage tag
	this.id = "tabulator-" + (id || (this.table.element.getAttribute("id") || ""));
};

//load saved definitions
Persistence.prototype.load = function(type, current){

	var data = this.retreiveData(type);

	if(current){
		data = data ? this.mergeDefinition(current, data) : current;
	}

	return data;
};

//retreive data from memory
Persistence.prototype.retreiveData = function(type){
	var data = "",
	id = this.id + (type === "columns" ? "" : "-" + type);

	switch(this.mode){
		case "local":
		data = localStorage.getItem(id);
		break;

		case "cookie":

		//find cookie
		let cookie = document.cookie,
		cookiePos = cookie.indexOf(id + "="),
		end;

		//if cookie exists, decode and load column data into tabulator
		if(cookiePos > -1){
			cookie = cookie.substr(cookiePos);

			end = cookie.indexOf(";");

			if(end > -1){
				cookie = cookie.substr(0, end);
			}

			data = cookie.replace(id + "=", "");
		}
		break;

		default:
		console.warn("Persistence Load Error - invalid mode selected", this.mode);
	}

	return data ? JSON.parse(data) : false;
};

//merge old and new column definitions
Persistence.prototype.mergeDefinition = function(oldCols, newCols){
	var self = this,
	output = [];

	// oldCols = oldCols || [];
	newCols = newCols || [];

	newCols.forEach(function(column, to){

		var from = self._findColumn(oldCols, column);

		if(from){

			from.width = column.width;
			from.visible = column.visible;

			if(from.columns){
				from.columns = self.mergeDefinition(from.columns, column.columns);
			}

			output.push(from);
		}

	});
	oldCols.forEach(function (column, i) {
		var from = self._findColumn(newCols, column);
		if (!from) {
			if(output.length>i){
				output.splice(i, 0, column);
			}else{
				output.push(column);
			}
		}
	});

	return output;
};

//find matching columns
Persistence.prototype._findColumn = function(columns, subject){
	var type = subject.columns ? "group" : (subject.field ? "field" : "object");

	return columns.find(function(col){
		switch(type){
			case "group":
			return col.title === subject.title && col.columns.length === subject.columns.length;
			break;

			case "field":
			return col.field === subject.field;
			break;

			case "object":
			return col === subject;
			break;
		}
	});
};

//save data
Persistence.prototype.save = function(type){
	var data = {};


	switch(type){
		case "columns":
		data = this.parseColumns(this.table.columnManager.getColumns())
		break;

		case "filter":
		data = this.table.modules.filter.getFilters();
		break;

		case "sort":
		data = this.validateSorters(this.table.modules.sort.getSort());
		break;
	}

	var id = this.id + (type === "columns" ? "" : "-" + type);

	this.saveData(id, data);
};

//ensure sorters contain no function data
Persistence.prototype.validateSorters = function(data){
	data.forEach(function(item){
		item.column = item.field;
		delete item.field;
	});

	return data;
};

//save data to chosed medium
Persistence.prototype.saveData = function(id, data){

	data = JSON.stringify(data);

	switch(this.mode){
		case "local":
		localStorage.setItem(id, data);
		break;

		case "cookie":
		let expireDate = new Date();
		expireDate.setDate(expireDate.getDate() + 10000);

		//save cookie
		document.cookie = id + "=" + data + "; expires=" + expireDate.toUTCString();
		break;

		default:
		console.warn("Persistence Save Error - invalid mode selected", this.mode);
	}
};

//build permission list
Persistence.prototype.parseColumns = function(columns){
	var self = this,
	definitions = [];

	columns.forEach(function(column){
		var def = {};

		if(column.isGroup){
			def.title = column.getDefinition().title;
			def.columns = self.parseColumns(column.getColumns());
		}else{
			def.title = column.getDefinition().title;
			def.field = column.getField();
			def.width = column.getWidth();
			def.visible = column.visible;
		}

		definitions.push(def);
	});

	return definitions;
};

Tabulator.prototype.registerModule("persistence", Persistence);
