feat(iotevents): support SetVariable action (aws#19305)

This PR implememts `SetVariable` actions.
This action allow to set variable to detector instanse.

If use this action as following and deploy it:
```ts
actions: [
  new actions.IoteventsSetVariableAction(
    'MyVariable',
    iotevents.Expression.inputAttribute(input, 'payload.temperature'),
  ),
],
```

And send message via cli as following:
```
aws iotevents-data batch-put-message --messages=messageId=(date | md5),inputName=test_input,payload=(echo '{"payload":{"deviceId":"000","temperature":18.5}}' | base64)
```

You can see the created detector instanse on web console:
![image](https://user-images.githubusercontent.com/11013683/157444640-c93e4229-ba75-46dd-8d35-cd171fed6145.png)


----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/@aws-cdk/aws-iotevents-actions/README.md

@@ -24,8 +24,37 @@ AWS IoT Events can trigger actions when it detects a specified event or transiti
 
 Currently supported are:
 
+- Set variable to detector instanse
 - Invoke a Lambda function
 
+## Set variable to detector instanse
+
+The code snippet below creates an Action that set variable to detector instanse
+when it is triggered.
+
+```ts
+import * as iotevents from '@aws-cdk/aws-iotevents';
+import * as actions from '@aws-cdk/aws-iotevents-actions';
+
+declare const input: iotevents.IInput;
+
+const state = new iotevents.State({
+  stateName: 'MyState',
+  onEnter: [{
+    eventName: 'test-event',
+    condition: iotevents.Expression.currentInput(input),
+    actions: [
+      actions: [
+        new actions.SetVariableAction(
+          'MyVariable',
+          iotevents.Expression.inputAttribute(input, 'payload.temperature'),
+        ),
+      ],
+    ],
+  }],
+});
+```
+
 ## Invoke a Lambda function
 
 The code snippet below creates an Action that invoke a Lambda function

packages/@aws-cdk/aws-iotevents-actions/lib/index.ts

@@ -1 +1,2 @@
+export * from './set-variable-action';
 export * from './lambda-invoke-action';

packages/@aws-cdk/aws-iotevents-actions/lib/set-variable-action.ts

@@ -0,0 +1,25 @@
+import * as iotevents from '@aws-cdk/aws-iotevents';
+import { Construct } from 'constructs';
+
+/**
+ * The action to create a variable with a specified value.
+ */
+export class SetVariableAction implements iotevents.IAction {
+  /**
+   * @param variableName the name of the variable
+   * @param value the new value of the variable
+   */
+  constructor(private readonly variableName: string, private readonly value: iotevents.Expression) {
+  }
+
+  bind(_scope: Construct, _options: iotevents.ActionBindOptions): iotevents.ActionConfig {
+    return {
+      configuration: {
+        setVariable: {
+          variableName: this.variableName,
+          value: this.value.evaluate(),
+        },
+      },
+    };
+  }
+}

packages/@aws-cdk/aws-iotevents-actions/test/iot/integ.set-variable-action.expected.json

@@ -0,0 +1,95 @@
+{
+  "Resources": {
+    "MyInput08947B23": {
+      "Type": "AWS::IoTEvents::Input",
+      "Properties": {
+        "InputDefinition": {
+          "Attributes": [
+            {
+              "JsonPath": "payload.deviceId"
+            },
+            {
+              "JsonPath": "payload.temperature"
+            }
+          ]
+        },
+        "InputName": "test_input"
+      }
+    },
+    "MyDetectorModelDetectorModelRoleF2FB4D88": {
+      "Type": "AWS::IAM::Role",
+      "Properties": {
+        "AssumeRolePolicyDocument": {
+          "Statement": [
+            {
+              "Action": "sts:AssumeRole",
+              "Effect": "Allow",
+              "Principal": {
+                "Service": "iotevents.amazonaws.com"
+              }
+            }
+          ],
+          "Version": "2012-10-17"
+        }
+      }
+    },
+    "MyDetectorModel559C0B0E": {
+      "Type": "AWS::IoTEvents::DetectorModel",
+      "Properties": {
+        "DetectorModelDefinition": {
+          "InitialStateName": "MyState",
+          "States": [
+            {
+              "OnEnter": {
+                "Events": [
+                  {
+                    "Actions": [
+                      {
+                        "SetVariable": {
+                          "Value": {
+                            "Fn::Join": [
+                              "",
+                              [
+                                "$input.",
+                                {
+                                  "Ref": "MyInput08947B23"
+                                },
+                                ".payload.temperature"
+                              ]
+                            ]
+                          },
+                          "VariableName": "MyVariable"
+                        }
+                      }
+                    ],
+                    "Condition": {
+                      "Fn::Join": [
+                        "",
+                        [
+                          "currentInput(\"",
+                          {
+                            "Ref": "MyInput08947B23"
+                          },
+                          "\")"
+                        ]
+                      ]
+                    },
+                    "EventName": "enter-event"
+                  }
+                ]
+              },
+              "StateName": "MyState"
+            }
+          ]
+        },
+        "RoleArn": {
+          "Fn::GetAtt": [
+            "MyDetectorModelDetectorModelRoleF2FB4D88",
+            "Arn"
+          ]
+        },
+        "Key": "payload.deviceId"
+      }
+    }
+  }
+}

packages/@aws-cdk/aws-iotevents-actions/test/iot/integ.set-variable-action.ts

@@ -0,0 +1,42 @@
+/**
+ * Stack verification steps:
+ * * put a message
+ *   * aws iotevents-data batch-put-message --messages=messageId=(date | md5),inputName=test_input,payload=(echo '{"payload":{"temperature":31.9,"deviceId":"000"}}' | base64)
+ */
+import * as iotevents from '@aws-cdk/aws-iotevents';
+import * as cdk from '@aws-cdk/core';
+import * as actions from '../../lib';
+
+class TestStack extends cdk.Stack {
+  constructor(scope: cdk.App, id: string, props?: cdk.StackProps) {
+    super(scope, id, props);
+
+    const input = new iotevents.Input(this, 'MyInput', {
+      inputName: 'test_input',
+      attributeJsonPaths: ['payload.deviceId', 'payload.temperature'],
+    });
+
+    const state = new iotevents.State({
+      stateName: 'MyState',
+      onEnter: [{
+        eventName: 'enter-event',
+        condition: iotevents.Expression.currentInput(input),
+        actions: [
+          new actions.SetVariableAction(
+            'MyVariable',
+            iotevents.Expression.inputAttribute(input, 'payload.temperature'),
+          ),
+        ],
+      }],
+    });
+
+    new iotevents.DetectorModel(this, 'MyDetectorModel', {
+      detectorKey: 'payload.deviceId',
+      initialState: state,
+    });
+  }
+}
+
+const app = new cdk.App();
+new TestStack(app, 'iotevents-set-variable-action-test-stack');
+app.synth();

packages/@aws-cdk/aws-iotevents-actions/test/iot/set-variable-action.test.ts

@@ -0,0 +1,43 @@
+import { Template } from '@aws-cdk/assertions';
+import * as iotevents from '@aws-cdk/aws-iotevents';
+import * as cdk from '@aws-cdk/core';
+import * as actions from '../../lib';
+
+let stack: cdk.Stack;
+let input: iotevents.IInput;
+beforeEach(() => {
+  stack = new cdk.Stack();
+  input = iotevents.Input.fromInputName(stack, 'MyInput', 'test-input');
+});
+
+test('Default property', () => {
+  // WHEN
+  new iotevents.DetectorModel(stack, 'MyDetectorModel', {
+    initialState: new iotevents.State({
+      stateName: 'test-state',
+      onEnter: [{
+        eventName: 'test-eventName',
+        condition: iotevents.Expression.currentInput(input),
+        actions: [new actions.SetVariableAction('MyVariable', iotevents.Expression.fromString('foo'))],
+      }],
+    }),
+  });
+
+  // THEN
+  Template.fromStack(stack).hasResourceProperties('AWS::IoTEvents::DetectorModel', {
+    DetectorModelDefinition: {
+      States: [{
+        OnEnter: {
+          Events: [{
+            Actions: [{
+              SetVariable: {
+                VariableName: 'MyVariable',
+                Value: 'foo',
+              },
+            }],
+          }],
+        },
+      }],
+    },
+  });
+});