Rework rounding and building lua script

To allow user script to specify what was modified where

processor/processor.go

@@ -129,7 +129,10 @@ func InitLuaHelpers(L *lua.LState) error {
 -- Custom Lua helpers for math operations
 function min(a, b) return math.min(a, b) end
 function max(a, b) return math.max(a, b) end
-function round(x) return math.floor(x + 0.5) end
+function round(x, n) 
+	if n == nil then n = 0 end
+	return math.floor(x * 10^n + 0.5) / 10^n 
+end
 function floor(x) return math.floor(x) end
 function ceil(x) return math.ceil(x) end
 function upper(s) return string.upper(s) end
@@ -149,6 +152,8 @@ end
 function is_number(str)
     return tonumber(str) ~= nil
 end
+
+modified = false
 `
 	if err := L.DoString(helperScript); err != nil {
 		return fmt.Errorf("error loading helper functions: %v", err)
@@ -187,7 +192,21 @@ func BuildLuaScript(luaExpr string) string {
 		luaExpr = "v1 = " + luaExpr
 	}
 
-	return luaExpr
+	// This allows the user to specify whether or not they modified a value
+	// If they do nothing we assume they did modify (no return at all)
+	// If they return before our return then they themselves specify what they did
+	// If nothing is returned lua assumes nil
+	// So we can say our value was modified if the return value is either nil or true
+	// If the return value is false then the user wants to keep the original
+	fullScript := fmt.Sprintf(`
+		function run()
+			%s
+		end
+		local res = run()
+		modified = res == nil or res
+	`, luaExpr)
+
+	return fullScript
 }
 
 // Max returns the maximum of two integers