Pagination

rest-api-spec/src/main/resources/rest-api-spec/api/wlm_stats_list.json

@@ -0,0 +1,35 @@
+{
+  "wlm_stats_list": {
+    "stability": "experimental",
+    "url": {
+      "paths": [
+        {
+          "path": "/_list/wlm_stats",
+          "methods": ["GET"]
+        }
+      ]
+    },
+    "params": {
+      "size": {
+        "type": "int",
+        "required": false,
+        "description": "Number of results per page"
+      },
+      "next_token": {
+        "type": "string",
+        "required": false,
+        "description": "Pagination token for next page"
+      },
+      "sort": {
+        "type": "string",
+        "required": false,
+        "description": "Sort field"
+      },
+      "order": {
+        "type": "string",
+        "required": false,
+        "description": "Sort order (asc or desc)"
+      }
+    }
+  }
+}

rest-api-spec/src/main/resources/rest-api-spec/test/wlm_stats/10_basic.yml

@@ -0,0 +1,55 @@
+---
+"Basic usage returns expected table header":
+  - do:
+      wlm_stats_list: {}
+  - is_true: $body
+  - match:
+      $body: /(?s).*NODE_ID\s+\|\s+QUERY_GROUP_ID\s+\|\s+TOTAL_COMPLETIONS\s+\|\s+TOTAL_REJECTIONS\s+\|\s+TOTAL_CANCELLATIONS\s+\|\s+CPU_USAGE\s+\|\s+MEMORY_USAGE.*/
+
+---
+"Custom size param still returns headers":
+  - do:
+      wlm_stats_list:
+        size: 1
+  - is_true: $body
+  - match:
+      $body: /TOTAL_REJECTIONS/
+
+---
+"Sort by node_id asc does not error":
+  - do:
+      wlm_stats_list:
+        sort: node_id
+        order: asc
+  - is_true: $body
+  - match:
+      $body: /NODE_ID/
+
+---
+"Sort by query_group_id desc does not error":
+  - do:
+      wlm_stats_list:
+        sort: query_group_id
+        order: desc
+  - is_true: $body
+  - match:
+      $body: /QUERY_GROUP_ID/
+
+---
+"Invalid sort field returns error":
+  - do:
+      catch: bad_request
+      wlm_stats_list:
+        sort: memory_usage
+        order: desc
+  - match:
+      error.reason: "Invalid value for 'sort'. Allowed: 'node_id', 'query_group_id'."
+
+---
+"Invalid sort order returns error":
+  - do:
+      catch: bad_request
+      wlm_stats_list:
+        order: upside_down
+  - match:
+      error.reason: "Invalid value for 'order'. Allowed: 'asc', 'desc'."

server/src/main/java/org/opensearch/action/admin/cluster/wlm/WlmStatsResponse.java

@@ -33,7 +33,7 @@ public class WlmStatsResponse extends BaseNodesResponse<WlmStats> implements ToX
         super(in);
     }
 
-    WlmStatsResponse(ClusterName clusterName, List<WlmStats> nodes, List<FailedNodeException> failures) {
+    public WlmStatsResponse(ClusterName clusterName, List<WlmStats> nodes, List<FailedNodeException> failures) {
         super(clusterName, nodes, failures);
     }
 

server/src/main/java/org/opensearch/action/pagination/SortBy.java

@@ -0,0 +1,52 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+package org.opensearch.action.pagination;
+
+import org.opensearch.wlm.stats.WlmStats;
+
+import java.util.Comparator;
+
+public enum SortBy {
+    QUERY_GROUP {
+        @Override
+        public Comparator<WlmStats> getComparator() {
+            return Comparator.comparing(
+                (WlmStats wlmStats) -> wlmStats.getQueryGroupStats().getStats().isEmpty()
+                    ? ""
+                    : wlmStats.getQueryGroupStats().getStats().keySet().iterator().next()
+            ).thenComparing(wlmStats -> wlmStats.getNode().getId());
+        }
+    },
+    NODE_ID {
+        @Override
+        public Comparator<WlmStats> getComparator() {
+            return Comparator.comparing(
+                (WlmStats wlmStats) -> wlmStats.getNode().getId()
+            ).thenComparing(
+                wlmStats -> wlmStats.getQueryGroupStats().getStats().isEmpty()
+                    ? ""
+                    : wlmStats.getQueryGroupStats().getStats().keySet().iterator().next()
+            );
+        }
+    };
+
+    public abstract Comparator<WlmStats> getComparator();
+
+    public static SortBy fromString(String input) {
+        switch (input.toLowerCase()) {
+            case "query_group":
+                return QUERY_GROUP;
+            case "node_id":
+                return NODE_ID;
+            default:
+                throw new IllegalArgumentException("Invalid sort field: " + input);
+        }
+    }
+}
+

server/src/main/java/org/opensearch/action/pagination/SortOrder.java

@@ -0,0 +1,41 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+package org.opensearch.action.pagination;
+
+import org.opensearch.wlm.stats.WlmStats;
+
+import java.util.Comparator;
+
+public enum SortOrder {
+    ASC {
+        @Override
+        public Comparator<WlmStats> apply(Comparator<WlmStats> baseComparator) {
+            return baseComparator;
+        }
+    },
+    DESC {
+        @Override
+        public Comparator<WlmStats> apply(Comparator<WlmStats> baseComparator) {
+            return baseComparator.reversed();
+        }
+    };
+
+    public abstract Comparator<WlmStats> apply(Comparator<WlmStats> baseComparator);
+
+    public static SortOrder fromString(String input) {
+        switch (input.toLowerCase()) {
+            case "asc":
+                return ASC;
+            case "desc":
+                return DESC;
+            default:
+                throw new IllegalArgumentException("Invalid sort order: " + input);
+        }
+    }
+}