void EnsureExecutionStartedIsFirst()

in src/DurableTask.Core/TaskOrchestrationDispatcher.cs [151:202]
35 lines of code
9 McCabe index (conditional complexity)

        void EnsureExecutionStartedIsFirst(IList<TaskMessage> batch)
        {
            // We look for *the first* instance of an ExecutionStarted event in the batch, if any.
            int index = 0;
            string previousExecutionId = "";
            int targetPosition = 0; // new position of ExecutionStarted in case of a re-ordering
            TaskMessage? executionStartedEvent = null;
            foreach (TaskMessage message in batch)
            {
                // Keep track of orchestrator generation changes, maybe update target position
                string executionId = message.OrchestrationInstance.ExecutionId;
                if (previousExecutionId != executionId)
                {
                    // We want to re-position the ExecutionStarted event after the "right-most"
                    // event with a non-null executionID that came before it.
                    // So, only update target position if the executionID changed
                    // and the previous executionId was not null.
                    if (previousExecutionId != null)
                    {
                        targetPosition = index;
                    }

                    previousExecutionId = executionId;
                }

                // Find the first ExecutionStarted event.
                if (message.Event.EventType == EventType.ExecutionStarted)
                {
                    // ParentInstance needs to be null to avoid re-ordering
                    // ContinueAsNew events
                    if ((message.Event is ExecutionStartedEvent eventData) &&
                        (eventData.ParentInstance == null))
                    {
                        executionStartedEvent = message;
                    }
                    // We only consider the first ExecutionStarted event in the
                    // list, so we always break.
                    break;
                }
                index++;
            }

            // If we found an ExecutionStartedEvent, we place it either
            // (A) in the beginning or
            // (B) after the "right-most" event with non-null executionID that came before it.
            int executionStartedIndex = index;
            if ((executionStartedEvent != null) && (executionStartedIndex != targetPosition))
            {
                batch.RemoveAt(executionStartedIndex);
                batch.Insert(targetPosition, executionStartedEvent);
            }
        }