feat: add RandomWriter C# example

csharp/random-writer/.gitignore

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+src/*/bin/
+src/*/obj/

csharp/random-writer/README.md

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+# RandomWriter
+
+## Overview
+This sample application demonstrates some essential mechanisms of the *AWS Cloud
+Development Kit* (*AWS CDK*) for .NET (in this case, using **C#**):
+- Creating a user-defined *construct*
+- Having this *construct* implement a feature interface
+  (`Amazon.CDK.AWS.Events.IRuleTarget`) to bring specific capabilities to the
+  *construct*
+- Granting permissions (for a *Lambda* function to write into a *DynamoDB*
+  table) using the `.Grant*` methods.
+
+## Application Resources
+> All resources provisioned by this application are *[free-tier] eligible* or
+> generally free to provision and use.
+
+The application provisions the following elements (shown in their hierarchical
+presentation withing the *CDK construct tree*):
+
+- A *stack* named `RandomWriterStack`
+  - A user-defined *construct* named `RandomWriter`
+    - A *DynamoDB* table (the physical name of which is to be determined by
+      *AWS CloudFormation* upon creation)
+    - A *Lambda* function
+      * It writes a random hash into the *DynamoDB* table when invoked
+  - A *CloudWatch* event rule that triggers an execution of the *Lambda*
+    function *every minute*.
+
+[free-tier]: https://aws.amazon.com/free/

csharp/random-writer/cdk.json

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+{
+  "app": "dotnet run --project src/RandomWriter/RandomWriter.csproj"
+}

csharp/random-writer/src/RandomWriter.sln

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+
+Microsoft Visual Studio Solution File, Format Version 12.00
+# Visual Studio 15
+VisualStudioVersion = 15.0.26124.0
+MinimumVisualStudioVersion = 15.0.26124.0
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "RandomWriter", "RandomWriter\RandomWriter.csproj", "{0B87A53B-C322-4A64-9C52-7A047E296339}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Debug|x64 = Debug|x64
+		Debug|x86 = Debug|x86
+		Release|Any CPU = Release|Any CPU
+		Release|x64 = Release|x64
+		Release|x86 = Release|x86
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{0B87A53B-C322-4A64-9C52-7A047E296339}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{0B87A53B-C322-4A64-9C52-7A047E296339}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{0B87A53B-C322-4A64-9C52-7A047E296339}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{0B87A53B-C322-4A64-9C52-7A047E296339}.Debug|x64.Build.0 = Debug|Any CPU
+		{0B87A53B-C322-4A64-9C52-7A047E296339}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{0B87A53B-C322-4A64-9C52-7A047E296339}.Debug|x86.Build.0 = Debug|Any CPU
+		{0B87A53B-C322-4A64-9C52-7A047E296339}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{0B87A53B-C322-4A64-9C52-7A047E296339}.Release|Any CPU.Build.0 = Release|Any CPU
+		{0B87A53B-C322-4A64-9C52-7A047E296339}.Release|x64.ActiveCfg = Release|Any CPU
+		{0B87A53B-C322-4A64-9C52-7A047E296339}.Release|x64.Build.0 = Release|Any CPU
+		{0B87A53B-C322-4A64-9C52-7A047E296339}.Release|x86.ActiveCfg = Release|Any CPU
+		{0B87A53B-C322-4A64-9C52-7A047E296339}.Release|x86.Build.0 = Release|Any CPU
+	EndGlobalSection
+EndGlobal

csharp/random-writer/src/RandomWriter/Program.cs

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+using Amazon.CDK;
+
+namespace RandomWriter
+{
+    public sealed class Program
+    {
+        public static void Main(string[] args)
+        {
+            var app = new App();
+            new RandomWriterStack(app, "RandomWriterStack");
+            app.Synth();
+        }
+    }
+}

csharp/random-writer/src/RandomWriter/RandomWriter.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>netcoreapp3.0</TargetFramework>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Amazon.CDK" Version="1.15.0-devpreview" />
+    <PackageReference Include="Amazon.CDK.AWS.DynamoDb" Version="1.15.0-devpreview" />
+    <PackageReference Include="Amazon.CDK.AWS.Events" Version="1.15.0-devpreview" />
+    <PackageReference Include="Amazon.CDK.AWS.Events.Targets" Version="1.15.0-devpreview" />
+    <PackageReference Include="Amazon.CDK.AWS.Lambda" Version="1.15.0-devpreview" />
+
+    <PackageReference Include="Amazon.JSII.Analyzers" Version="0.20.1" />
+  </ItemGroup>
+</Project>

csharp/random-writer/src/RandomWriter/RandomWriterStack.cs

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+using System.Collections.Generic;
+using Amazon.CDK;
+using Amazon.CDK.AWS.DynamoDB;
+using Amazon.CDK.AWS.Events;
+using Amazon.CDK.AWS.Events.Targets;
+using Amazon.CDK.AWS.Lambda;
+
+namespace RandomWriter
+{
+    internal sealed class RandomWriterStack : Stack
+    {
+        public RandomWriterStack(Construct parent, string id, IStackProps props = null) : base(parent, id, props)
+        {
+            // The code that defines your stack goes here
+            var randomWriter = new RandomWriter(this, "RandomWriter");
+            new Rule(this, "Trigger", new RuleProps()
+            {
+                Description = "Triggers a RandomWrite every minute",
+                Schedule = Schedule.Rate(Duration.Minutes(1)),
+                Targets = new [] { randomWriter }
+            });
+        }
+    }
+
+    internal sealed class RandomWriter : Construct, IRuleTarget
+    {
+        private IFunction Function { get; }
+
+        public RandomWriter(Construct scope, string id): base(scope, id)
+        {
+            var table = new Table(this, "Table", new TableProps
+            {
+                PartitionKey = new Attribute
+                {
+                    Name = "ID",
+                    Type = AttributeType.STRING
+                }
+            });
+
+            Function = new Function(this, "Lambda", new FunctionProps
+            {
+                Runtime = Runtime.NODEJS_10_X,
+                Handler = "index.handler",
+                Code = Code.FromAsset("src/RandomWriter/resources"),
+                Environment = new Dictionary<string, string>
+                {
+                    { "TABLE_NAME", table.TableName }
+                }
+            });
+
+            table.GrantReadWriteData(Function);
+        }
+
+        public IRuleTargetConfig Bind(IRule rule, string id = null)
+        {
+            return new LambdaFunction(Function).Bind(rule, id);
+        }
+    }
+}

csharp/random-writer/src/RandomWriter/resources/index.js

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+const { DynamoDB } = require('aws-sdk');
+const crypto = require('crypto');
+
+/**
+ * This Lambda event handler expects the name of a DynamoDB table to be passed
+ * in the `TABLE_NAME` environment variable. The Lambda function must be granted
+ * WRITE permissions on the DynamoDB table (for it will add new items in the
+ * table).
+ *
+ * The DynamoDB table must have a hash-only primary key, where the hash key is
+ * named `ID` and is of type STRING.
+ */
+exports.handler = async function handler(event, context) {
+  console.log(JSON.stringify(event, undefined, 2));
+
+  var seed = `${Date.now}${Math.random()}`;
+  const id = crypto.createHash('sha1').update(seed).digest('hex');
+
+  const ddb = new DynamoDB();
+  await ddb.putItem({
+    TableName: process.env.TABLE_NAME,
+    Item: {
+      ID: { S: id }
+    }
+  }).promise();
+};