gluon-web-model: add state tracking to sections

This add support for a write() method on sections, in addition to the
value and form level write(). write() is only called when the section is
valid and visible. In addition, write() is empty by default, so it can be
overridden more easily.

package/gluon-web-model/luasrc/usr/lib/lua/gluon/web/model/classes.lua

@@ -53,6 +53,7 @@ function Node:__init__(name, title, description)
 	self.name = name
 	self.index = nil
 	self.parent = nil
+	self.state = M.FORM_NODATA
 	self.package = 'gluon-web-model'
 end
 
@@ -73,17 +74,32 @@ function Node:id()
 end
 
 function Node:reset_node()
+	self.state = M.FORM_NODATA
 	for _, child in ipairs(self.children) do
 		child:reset_node()
 	end
 end
 
 function Node:parse(http)
+	self.state = M.FORM_VALID
 	for _, child in ipairs(self.children) do
 		child:parse(http)
 	end
 end
 
+function Node:propagate_state()
+	if self.state == M.FORM_NODATA then
+		return
+	end
+
+	for _, child in ipairs(self.children) do
+		child:propagate_state()
+		if child.state == M.FORM_INVALID then
+			self.state = M.FORM_INVALID
+		end
+	end
+end
+
 function Node:render(renderer, scope)
 	if self.template then
 		local env = setmetatable({
@@ -158,10 +174,17 @@ function Node:resolve_node_depends()
 	return true
 end
 
+-- will be overridden: write(value)
+function Node:write()
+end
+
 function Node:handle()
+	if self.state == M.FORM_VALID then
 		for _, node in ipairs(self.children) do
 			node:handle()
 		end
+		self:write(self.data)
+	end
 end
 
 
@@ -187,7 +210,6 @@ function AbstractValue:__init__(...)
 	self.template  = "model/valuewrapper"
 
 	self.error = false
-	self.state = M.FORM_NODATA
 end
 
 function AbstractValue:defaultvalue()
@@ -250,16 +272,6 @@ function AbstractValue:validate()
 
 end
 
-function AbstractValue:handle()
-	if self.state == M.FORM_VALID then
-		self:write(self.data)
-	end
-end
-
--- will be overridden: write(value)
-function AbstractValue:write()
-end
-
 
 local Value = class(AbstractValue)
 M.Value = Value
@@ -438,26 +450,7 @@ function Form:parse(http)
 
 	while self:resolve_depends() do end
 
-	for _, s in ipairs(self.children) do
-		for _, v in ipairs(s.children) do
-			if v.state == M.FORM_INVALID then
-				self.state = M.FORM_INVALID
-				return
-			end
-		end
-	end
-
-	self.state = M.FORM_VALID
-end
-
-function Form:handle()
-	if self.state == M.FORM_VALID then
-		Node.handle(self)
-		self:write()
-	end
-end
-
-function Form:write()
+	self:propagate_state()
 end
 
 function Form:section(t, ...)