1 files changed, 75 insertions, 0 deletions
diff --git a/lib/gitlab/kubernetes/rollout_instances.rb b/lib/gitlab/kubernetes/rollout_instances.rb
new file mode 100644
index 00000000000..c5dba71f505
--- /dev/null
+++ b/lib/gitlab/kubernetes/rollout_instances.rb
@@ -0,0 +1,75 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module Kubernetes
+    class RolloutInstances
+      include ::Gitlab::Utils::StrongMemoize
+
+      def initialize(deployments, pods)
+        @deployments = deployments
+        @pods = pods
+      end
+
+      def pod_instances
+        pods = matching_pods + extra_pending_pods
+
+        pods.sort_by(&:order).map do |pod|
+          to_hash(pod)
+        end
+      end
+
+      private
+
+      attr_reader :deployments, :pods
+
+      def matching_pods
+        strong_memoize(:matching_pods) do
+          deployment_tracks = deployments.map(&:track)
+          pods.select { |p| deployment_tracks.include?(p.track) }
+        end
+      end
+
+      def extra_pending_pods
+        wanted_instances = sum_hashes(deployments.map { |d| { d.track => d.wanted_instances } })
+        present_instances = sum_hashes(matching_pods.map { |p| { p.track => 1 } })
+        pending_instances = subtract_hashes(wanted_instances, present_instances)
+
+        pending_instances.flat_map do |track, num|
+          Array.new(num, pending_pod_for(track))
+        end
+      end
+
+      def sum_hashes(hashes)
+        hashes.reduce({}) do |memo, hash|
+          memo.merge(hash) { |_key, memo_val, hash_val| memo_val + hash_val }
+        end
+      end
+
+      def subtract_hashes(hash_a, hash_b)
+        hash_a.merge(hash_b) { |_key, val_a, val_b| [0, val_a - val_b].max }
+      end
+
+      def pending_pod_for(track)
+        ::Gitlab::Kubernetes::Pod.new({
+          'status' => { 'phase' => 'Pending' },
+          'metadata' => {
+            'name' => 'Not provided',
+            'labels' => {
+              'track' => track
+            }
+          }
+        })
+      end
+
+      def to_hash(pod)
+        {
+          status: pod.status&.downcase,
+          pod_name: pod.name,
+          tooltip: "#{pod.name} (#{pod.status})",
+          track: pod.track,
+          stable: pod.stable?
+        }
+      end
+    end
+  end
+end