[SPARK-31440][SQL] Improve SQL Rest API

### What changes were proposed in this pull request?
SQL Rest API exposes query execution metrics as Public API. This PR aims to apply following improvements on SQL Rest API by aligning Spark-UI.

**Proposed Improvements:**
1- Support Physical Operations and group metrics per physical operation by aligning Spark UI.
2- Support `wholeStageCodegenId` for Physical Operations
3- `nodeId` can be useful for grouping metrics and sorting physical operations (according to execution order) to differentiate same operators (if used multiple times during the same query execution) and their metrics.
4- Filter `empty` metrics by aligning with Spark UI - SQL Tab. Currently, Spark UI does not show empty metrics.
5- Remove line breakers(`\n`) from `metricValue`.
6- `planDescription` can be `optional` Http parameter to avoid network cost where there is specially complex jobs creating big-plans.
7- `metrics` attribute needs to be exposed at the bottom order as `nodes`. Specially, this can be useful for the user where `nodes` array size is high.
8- `edges` attribute is being exposed to show relationship between `nodes`.
9- Reverse order on `metricDetails` aims to match with Spark UI by supporting Physical Operators' execution order.

### Why are the changes needed?
Proposed improvements provides more useful (e.g: physical operations and metrics correlation, grouping) and clear (e.g: filtering blank metrics, removing line breakers) result for the end-user.

### Does this PR introduce any user-facing change?
Yes. Please find both current and improved versions of the results as attached for following SQL Rest Endpoint:
```
curl -X GET http://localhost:4040/api/v1/applications/$appId/sql/$executionId?details=true
```
**Current version:**
https://issues.apache.org/jira/secure/attachment/12999821/current_version.json

**Improved version:**
https://issues.apache.org/jira/secure/attachment/13000621/improved_version.json

### Backward Compatibility
SQL Rest API will be started to expose with `Spark 3.0` and `3.0.0-preview2` (released on 12/23/19) does not cover this API so if PR can catch 3.0 release, this will not have any backward compatibility issue.

### How was this patch tested?
1. New Unit tests are added.
2. Also, patch has been tested manually through both **Spark Core** and **History Server** Rest APIs.

Closes #28208 from erenavsarogullari/SPARK-31440.

Authored-by: Eren Avsarogullari <eren.avsarogullari@gmail.com>
Signed-off-by: Gengliang Wang <gengliang.wang@databricks.com>
(cherry picked from commit ab4cf49)
Signed-off-by: Gengliang Wang <gengliang.wang@databricks.com>

sql/core/src/main/scala/org/apache/spark/sql/execution/ui/SparkPlanGraph.scala

@@ -153,7 +153,7 @@ object SparkPlanGraph {
  * @param name the name of this SparkPlan node
  * @param metrics metrics that this SparkPlan node will track
  */
-private[ui] class SparkPlanGraphNode(
+class SparkPlanGraphNode(
     val id: Long,
     val name: String,
     val desc: String,
@@ -193,7 +193,7 @@ private[ui] class SparkPlanGraphNode(
 /**
  * Represent a tree of SparkPlan for WholeStageCodegen.
  */
-private[ui] class SparkPlanGraphCluster(
+class SparkPlanGraphCluster(
     id: Long,
     name: String,
     desc: String,
@@ -229,7 +229,7 @@ private[ui] class SparkPlanGraphCluster(
  * Represent an edge in the SparkPlan tree. `fromId` is the child node id, and `toId` is the parent
  * node id.
  */
-private[ui] case class SparkPlanGraphEdge(fromId: Long, toId: Long) {
+case class SparkPlanGraphEdge(fromId: Long, toId: Long) {
 
   def makeDotEdge: String = s"""  $fromId->$toId;\n"""
 }

sql/core/src/main/scala/org/apache/spark/status/api/v1/sql/SqlResource.scala

@@ -21,46 +21,55 @@ import java.util.Date
 import javax.ws.rs._
 import javax.ws.rs.core.MediaType
 
+import scala.util.{Failure, Success, Try}
+
 import org.apache.spark.JobExecutionStatus
-import org.apache.spark.sql.execution.ui.{SQLAppStatusStore, SQLExecutionUIData, SQLPlanMetric}
+import org.apache.spark.sql.execution.ui.{SparkPlanGraph, SparkPlanGraphCluster, SparkPlanGraphNode, SQLAppStatusStore, SQLExecutionUIData}
 import org.apache.spark.status.api.v1.{BaseAppResource, NotFoundException}
 
 @Produces(Array(MediaType.APPLICATION_JSON))
 private[v1] class SqlResource extends BaseAppResource {
 
+  val WHOLE_STAGE_CODEGEN = "WholeStageCodegen"
+
   @GET
   def sqlList(
-      @DefaultValue("false") @QueryParam("details") details: Boolean,
+      @DefaultValue("true") @QueryParam("details") details: Boolean,
+      @DefaultValue("true") @QueryParam("planDescription") planDescription: Boolean,
       @DefaultValue("0") @QueryParam("offset") offset: Int,
       @DefaultValue("20") @QueryParam("length") length: Int): Seq[ExecutionData] = {
     withUI { ui =>
       val sqlStore = new SQLAppStatusStore(ui.store.store)
-      sqlStore.executionsList(offset, length).map(prepareExecutionData(_, details))
+      sqlStore.executionsList(offset, length).map { exec =>
+        val graph = sqlStore.planGraph(exec.executionId)
+        prepareExecutionData(exec, graph, details, planDescription)
+      }
     }
   }
 
   @GET
   @Path("{executionId:\\d+}")
   def sql(
       @PathParam("executionId") execId: Long,
-      @DefaultValue("false") @QueryParam("details") details: Boolean): ExecutionData = {
+      @DefaultValue("true") @QueryParam("details") details: Boolean,
+      @DefaultValue("true") @QueryParam("planDescription")
+      planDescription: Boolean): ExecutionData = {
     withUI { ui =>
       val sqlStore = new SQLAppStatusStore(ui.store.store)
+      val graph = sqlStore.planGraph(execId)
       sqlStore
         .execution(execId)
-        .map(prepareExecutionData(_, details))
-        .getOrElse(throw new NotFoundException("unknown id: " + execId))
+        .map(prepareExecutionData(_, graph, details, planDescription))
+        .getOrElse(throw new NotFoundException("unknown query execution id: " + execId))
     }
   }
 
-  private def printableMetrics(
-      metrics: Seq[SQLPlanMetric],
-      metricValues: Map[Long, String]): Seq[Metrics] = {
-    metrics.map(metric =>
-      Metrics(metric.name, metricValues.get(metric.accumulatorId).getOrElse("")))
-  }
+  private def prepareExecutionData(
+    exec: SQLExecutionUIData,
+    graph: SparkPlanGraph,
+    details: Boolean,
+    planDescription: Boolean): ExecutionData = {
 
-  private def prepareExecutionData(exec: SQLExecutionUIData, details: Boolean): ExecutionData = {
     var running = Seq[Int]()
     var completed = Seq[Int]()
     var failed = Seq[Int]()
@@ -84,18 +93,65 @@ private[v1] class SqlResource extends BaseAppResource {
     }
 
     val duration = exec.completionTime.getOrElse(new Date()).getTime - exec.submissionTime
-    val planDetails = if (details) exec.physicalPlanDescription else ""
-    val metrics = if (details) printableMetrics(exec.metrics, exec.metricValues) else Seq.empty
+    val planDetails = if (planDescription) exec.physicalPlanDescription else ""
+    val nodes = if (details) printableMetrics(graph.allNodes, exec.metricValues) else Seq.empty
+    val edges = if (details) graph.edges else Seq.empty
+
     new ExecutionData(
       exec.executionId,
       status,
       exec.description,
       planDetails,
-      metrics,
       new Date(exec.submissionTime),
       duration,
       running,
       completed,
-      failed)
+      failed,
+      nodes,
+      edges)
   }
+
+  private def printableMetrics(allNodes: Seq[SparkPlanGraphNode],
+    metricValues: Map[Long, String]): Seq[Node] = {
+
+    def getMetric(metricValues: Map[Long, String], accumulatorId: Long,
+      metricName: String): Option[Metric] = {
+
+      metricValues.get(accumulatorId).map( mv => {
+        val metricValue = if (mv.startsWith("\n")) mv.substring(1, mv.length) else mv
+        Metric(metricName, metricValue)
+      })
+    }
+
+    val nodeIdAndWSCGIdMap = getNodeIdAndWSCGIdMap(allNodes)
+    val nodes = allNodes.map { node =>
+      val wholeStageCodegenId = nodeIdAndWSCGIdMap.get(node.id).flatten
+      val metrics =
+        node.metrics.flatMap(m => getMetric(metricValues, m.accumulatorId, m.name.trim))
+      Node(nodeId = node.id, nodeName = node.name.trim, wholeStageCodegenId, metrics)
+    }
+
+    nodes.sortBy(_.nodeId).reverse
+  }
+
+  private def getNodeIdAndWSCGIdMap(allNodes: Seq[SparkPlanGraphNode]): Map[Long, Option[Long]] = {
+    val wscgNodes = allNodes.filter(_.name.trim.startsWith(WHOLE_STAGE_CODEGEN))
+    val nodeIdAndWSCGIdMap: Map[Long, Option[Long]] = wscgNodes.flatMap {
+      _ match {
+        case x: SparkPlanGraphCluster => x.nodes.map(_.id -> getWholeStageCodegenId(x.name.trim))
+        case _ => Seq.empty
+      }
+    }.toMap
+
+    nodeIdAndWSCGIdMap
+  }
+
+  private def getWholeStageCodegenId(wscgNodeName: String): Option[Long] = {
+    Try(wscgNodeName.substring(
+      s"$WHOLE_STAGE_CODEGEN (".length, wscgNodeName.length - 1).toLong) match {
+      case Success(wscgId) => Some(wscgId)
+      case Failure(t) => None
+    }
+  }
+
 }

sql/core/src/main/scala/org/apache/spark/status/api/v1/sql/api.scala

@@ -18,16 +18,25 @@ package org.apache.spark.status.api.v1.sql
 
 import java.util.Date
 
+import org.apache.spark.sql.execution.ui.SparkPlanGraphEdge
+
 class ExecutionData private[spark] (
     val id: Long,
     val status: String,
     val description: String,
     val planDescription: String,
-    val metrics: Seq[Metrics],
     val submissionTime: Date,
     val duration: Long,
     val runningJobIds: Seq[Int],
     val successJobIds: Seq[Int],
-    val failedJobIds: Seq[Int])
+    val failedJobIds: Seq[Int],
+    val nodes: Seq[Node],
+    val edges: Seq[SparkPlanGraphEdge])
+
+case class Node private[spark](
+    nodeId: Long,
+    nodeName: String,
+    wholeStageCodegenId: Option[Long] = None,
+    metrics: Seq[Metric])
 
-case class Metrics private[spark] (metricName: String, metricValue: String)
+case class Metric private[spark] (name: String, value: String)