// Returns true if path is a valid field name (path),
// i.e. a sequence of identifiers, separated by "."
TiddlyWiki.isValidFieldName = function(name)
{
	var match = /[a-zA-Z_]\w*(\.[a-zA-Z_]\w*)*/.exec(name);
	return match && (match[0] == name);
};

// Throws an exception when name is not a valid field name.
TiddlyWiki.checkFieldName = function(name)
{
	if(!TiddlyWiki.isValidFieldName(name))
		throw config.messages.invalidFieldName.format([name]);
};

function StringFieldAccess(n,readOnly)
{
	this.set = readOnly ?
			function(t,v) {if(v != t[n]) throw config.messages.fieldCannotBeChanged.format([n]);} :
			function(t,v) {if(v != t[n]) {t[n] = v; return true;}};
	this.get = function(t) {return t[n];};
}

function DateFieldAccess(n)
{
	this.set = function(t,v) {
		var d = v instanceof Date ? v : Date.convertFromYYYYMMDDHHMM(v);
		if(d != t[n]) {
			t[n] = d; return true;
		}
	};
	this.get = function(t) {return t[n].convertToYYYYMMDDHHMM();};
}

function LinksFieldAccess(n)
{
	this.set = function(t,v) {
		var s = (typeof v == "string") ? v.readBracketedList() : v;
		if(s.toString() != t[n].toString()) {
			t[n] = s; return true;
		}
	};
	this.get = function(t) {return String.encodeTiddlyLinkList(t[n]);};
}

TiddlyWiki.standardFieldAccess = {
	// The set functions return true when setting the data has changed the value.
	"title":    new StringFieldAccess("title",true),
	// Handle the "tiddler" field name as the title
	"tiddler":  new StringFieldAccess("title",true),
	"text":     new StringFieldAccess("text"),
	"modifier": new StringFieldAccess("modifier"),
	"modified": new DateFieldAccess("modified"),
	"creator":  new StringFieldAccess("creator"),
	"created":  new DateFieldAccess("created"),
	"tags":     new LinksFieldAccess("tags")
};

TiddlyWiki.isStandardField = function(name)
{
	return TiddlyWiki.standardFieldAccess[name] != undefined;
};

// Sets the value of the given field of the tiddler to the value.
// Setting an ExtendedField's value to null or undefined removes the field.
// Setting a namespace to undefined removes all fields of that namespace.
// The fieldName is case-insensitive.
// All values will be converted to a string value.
TiddlyWiki.prototype.setValue = function(tiddler,fieldName,value)
{
	TiddlyWiki.checkFieldName(fieldName);
	var t = this.resolveTiddler(tiddler);
	if(!t)
		return;
	fieldName = fieldName.toLowerCase();
	var isRemove = (value === undefined) || (value === null);
	var accessor = TiddlyWiki.standardFieldAccess[fieldName];
	if(accessor) {
		if(isRemove)
			// don't remove StandardFields
			return;
		var h = TiddlyWiki.standardFieldAccess[fieldName];
		if(!h.set(t,value))
			return;
	} else {
		var oldValue = t.fields[fieldName];
		if(isRemove) {
			if(oldValue !== undefined) {
				// deletes a single field
				delete t.fields[fieldName];
			} else {
				// no concrete value is defined for the fieldName
				// so we guess this is a namespace path.
				// delete all fields in a namespace
				var re = new RegExp("^"+fieldName+"\\.");
				var dirty = false;
				var n;
				for(n in t.fields) {
					if(n.match(re)) {
						delete t.fields[n];
						dirty = true;
					}
				}
				if(!dirty)
					return;
			}
		} else {
			// the "normal" set case. value is defined (not null/undefined)
			// For convenience provide a nicer conversion Date->String
			value = value instanceof Date ? value.convertToYYYYMMDDHHMMSSMMM() : String(value);
			if(oldValue == value)
				return;
			t.fields[fieldName] = value;
		}
	}
	// When we are here the tiddler/store really was changed.
	this.notify(t.title,true);
	if(!fieldName.match(/^temp\./))
		this.setDirty(true);
};

// Returns the value of the given field of the tiddler.
// The fieldName is case-insensitive.
// Will only return String values (or undefined).
TiddlyWiki.prototype.getValue = function(tiddler,fieldName)
{
	var t = this.resolveTiddler(tiddler);
	if(!t)
		return undefined;
	if(fieldName.indexOf(config.textPrimitives.sectionSeparator) === 0 || fieldName.indexOf(config.textPrimitives.sliceSeparator) === 0) {
		var sliceType = fieldName.substr(0, 2);
		var sliceName = fieldName.substring(2);
		return store.getTiddlerText("%0%1%2".format(t.title,sliceType,sliceName));
	} else {
		fieldName = fieldName.toLowerCase();
		var accessor = TiddlyWiki.standardFieldAccess[fieldName];
		if(accessor) {
			return accessor.get(t);
		}
	}
	return t.fields[fieldName];
};

// Calls the callback function for every field in the tiddler.
// When callback function returns a non-false value the iteration stops
// and that value is returned.
// The order of the fields is not defined.
// @param callback a function(tiddler,fieldName,value).
TiddlyWiki.prototype.forEachField = function(tiddler,callback,onlyExtendedFields)
{
	var t = this.resolveTiddler(tiddler);
	if(!t)
		return undefined;
	var n,result;
	for(n in t.fields) {
		result = callback(t,n,t.fields[n]);
		if(result)
			return result;
		}
	if(onlyExtendedFields)
		return undefined;
	for(n in TiddlyWiki.standardFieldAccess) {
		if(n != "tiddler") {
			// even though the "title" field can also be referenced through the name "tiddler"
			// we only visit this field once.
			result = callback(t,n,TiddlyWiki.standardFieldAccess[n].get(t));
			if(result)
				return result;
		}
	}
	return undefined;
};