+function rrdargs( graph, plugin, plugin_instance )
+
+ local lu = require("luci.util")
+ local rv = { }
+
+ -- Types and instances supported by APC UPS
+ -- e.g. ups_types -> { 'timeleft', 'charge', 'percent', 'voltage' }
+ -- e.g. ups_inst['voltage'] -> { 'input', 'battery' }
+
+ local ups_types = graph.tree:data_types( plugin, plugin_instance )
+
+ local ups_inst = {}
+ for _, t in ipairs(ups_types) do
+ ups_inst[t] = graph.tree:data_instances( plugin, plugin_instance, t )
+ end
+
+
+ -- Check if hash table or array is empty or nil-filled
+
+ local function empty( t )
+ for _, v in pairs(t) do
+ if type(v) then return false end
+ end
+ return true
+ end
+
+
+ -- Append graph definition but only types/instances which are
+ -- supported and available to the plugin and UPS.
+
+ local function add_supported( t, defs )
+ local def_inst = defs['data']['instances']
+
+ if type(def_inst) == "table" then
+ for k, v in pairs( def_inst ) do
+ if lu.contains( ups_types, k) then
+ for j = #v, 1, -1 do
+ if not lu.contains( ups_inst[k], v[j] ) then
+ table.remove( v, j )
+ end
+ end
+ if #v == 0 then
+ def_inst[k] = nil -- can't assign v: immutable
+ end
+ else
+ def_inst[k] = nil -- can't assign v: immutable
+ end
+ end
+ if empty(def_inst) then return end
+ end
+ table.insert( t, defs )
+ end
+
+
+ -- Graph definitions for APC UPS measurements MUST use only 'instances':
+ -- e.g. instances = { voltage = { "input", "output" } }