feat(event_manager): collapse repeated parts in queue

Collapse repeated events in the queue and only emit the latest event but
in the position of the earlier event. Keeping the earlier position is
required to not get out of order parts

Author: cameronr

lua/opencode/event_manager.lua

@@ -1,4 +1,5 @@
 local state = require('opencode.state')
+local config = require('opencode.config')
 local ThrottlingEmitter = require('opencode.throttling_emitter')
 
 --- @class EventInstallationUpdated
@@ -136,7 +137,6 @@ function EventManager.new()
     captured_events = {},
   }, EventManager)
 
-  local config = require('opencode.config')
   local throttle_ms = config.ui.output.rendering.event_throttle_ms
   self.throttling_emitter = ThrottlingEmitter.new(function(events)
     self:_on_drained_events(events)
@@ -218,16 +218,49 @@ function EventManager:unsubscribe(event_name, callback)
   end
 end
 
----Callaback from ThrottlingEmitter when the events are now
----ready to be processed
+---Callback from ThrottlingEmitter when the events are now ready to be processed.
+---Collapses parts that are duplicated, making sure to replace earlier parts with later
+---ones (but keeping the earlier position)
 ---@param events any
 function EventManager:_on_drained_events(events)
   self:emit('custom.emit_events.started', {})
 
-  -- TODO: try collapsing events here
+  local collapsed_events = {}
+  local part_update_indices = {}
 
-  for _, event in ipairs(events) do
-    self:emit(event.type, event.properties)
+  for i, event in ipairs(events) do
+    if event.type == 'message.part.updated' and event.properties.part then
+      local part_id = event.properties.part.id
+      if part_update_indices[part_id] then
+        -- vim.notify('collapsing: ' .. part_id .. ' text: ' .. vim.inspect(event.properties.part.text))
+        -- put this event in the earlier slot
+
+        -- move this newer part to the position of the original part
+        collapsed_events[part_update_indices[part_id]] = event
+
+        -- clear out this parts now unneeded position
+        collapsed_events[i] = nil
+      else
+        part_update_indices[part_id] = i
+        collapsed_events[i] = event
+      end
+    else
+      collapsed_events[i] = event
+    end
+  end
+
+  local actually_emitted = 0
+
+  for i = 1, #events do
+    local event = collapsed_events[i]
+    if event then
+      actually_emitted = actually_emitted + 1
+      self:emit(event.type, event.properties)
+    end
+  end
+
+  if config.debug.enabled then
+    vim.notify('Drained ' .. #events .. ', actually emitted: ' .. actually_emitted)
   end
 
   self:emit('custom.emit_events.finished', {})