policy-node: handle nodes-follow-default in handleLinkable

Since nodes may have a target specified in their props, the logic in
cleanupTargetNodeMetadata does not work correctly.

Instead, set target via metadata in handleLinkable, if we see a
reconnectable node with a defined target that is the same as the
configured default target.

src/scripts/policy-node.lua

@@ -590,6 +590,35 @@ function checkPending ()
   return false
 end
 
+function checkFollowDefault (si, si_target)
+  local si_props = si.properties
+  local target_props = si_target.properties
+  local reconnect = not parseBool(si_props["node.dont-reconnect"])
+
+  if config.follow and default_nodes ~= nil and reconnect then
+    -- If it got linked to the configured default target, it should
+    -- follow it from now on. We don't consider linkings to non-configured
+    -- defaults, because this can move streams the user doesn't want to move.
+    local def_id = getDefaultNode(si_props, getTargetDirection(si_props))
+    local configured_name =
+        default_nodes:call("get-default-configured-node-name", target_props['media.class'])
+
+    if target_props["node.id"] == tostring(def_id) and
+          target_props["node.name"] == configured_name then
+      local metadata = metadata_om:lookup()
+      -- Until pipewire-pulse starts setting target.object to metadata,
+      -- set it only if it was already present.
+      if metadata:find(si_props["node.id"], "target.object") ~= nil then
+        metadata:set(tonumber(si_props["node.id"]), "target.object", "Spa:Id", "-1")
+        metadata:set(tonumber(si_props["node.id"]), "target.node", nil, nil)
+      else
+        metadata:set(tonumber(si_props["node.id"]), "target.node", "Spa:Id", "-1")
+      end
+      Log.info (si, "... set metadata to follow default")
+    end
+  end
+end
+
 function handleLinkable (si)
   if checkPending () then
     return
@@ -650,6 +679,10 @@ function handleLinkable (si)
   if si_flags[si_id].peer_id then
     if si_target and si_flags[si_id].peer_id == si_target.id then
       Log.debug (si, "... already linked to proper target")
+      if has_defined_target then
+        -- Check this also here, in case in default targets changed
+        checkFollowDefault (si, si_target)
+      end
       return
     end
     local link = lookupLink (si_id, si_flags[si_id].peer_id)
@@ -723,6 +756,10 @@ function handleLinkable (si)
   else
     createLink (si, si_target, can_passthrough, exclusive)
     si_flags[si.id].was_handled = true
+
+    if has_defined_target then
+      checkFollowDefault (si, si_target)
+    end
   end
 end
 
@@ -796,38 +833,9 @@ links_om = ObjectManager {
   }
 }
 
-function cleanupTargetNodeMetadata()
-  local metadata = metadata_om:lookup()
-  if metadata and default_nodes ~= nil then
-    local to_remove = {}
-    for s, k, t, v in metadata:iterate(Id.ANY) do
-      if k == "target.node" then
-        if v == "-1" then
-          -- target.node == -1 is useless, it means the default node
-          table.insert(to_remove, s)
-        else
-          -- if the target.node value is the same as the default node
-          -- that would be selected for this stream, remove it
-          local si = linkables_om:lookup { Constraint { "node.id", "=", s } }
-          local properties = si.properties
-          local def_id = getDefaultNode(properties, getTargetDirection(properties))
-          if tostring(def_id) == v then
-            table.insert(to_remove, s)
-          end
-        end
-      end
-    end
-
-    for _, s in ipairs(to_remove) do
-      metadata:set(s, "target.node", nil, nil)
-    end
-  end
-end
-
 -- listen for default node changes if config.follow is enabled
 if config.follow and default_nodes ~= nil then
   default_nodes:connect("changed", function ()
-    cleanupTargetNodeMetadata()
     scheduleRescan ()
   end)
 end