Add state backed by storage bucket

[changelog:added]

index.ts

@@ -84,6 +84,7 @@ export {
     SlackFileMessage,
 } from "./lib/message";
 export {} from "./lib/payload";
+export * as state from "./lib/state";
 export * as status from "./lib/status";
 export { runSteps, Step, StepListener } from "./lib/steps";
 export { StorageProvider } from "./lib/storage";

lib/state.ts

@@ -0,0 +1,48 @@
+/*
+ * Copyright © 2020 Atomist, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import * as fs from "fs-extra";
+import * as os from "os";
+import * as path from "path";
+import { Contextual } from "./handler";
+import { warn } from "./log/console";
+import { guid } from "./util";
+
+export async function hydrate<T>(ctx: Contextual<any, any>): Promise<T> {
+    const key = stateKey(ctx);
+    try {
+        const stateFile = await ctx.storage.retrieve(key);
+        return fs.readJson(stateFile);
+    } catch (e) {
+        return {} as T;
+    }
+}
+
+export async function save(state: any, ctx: Contextual<any, any>): Promise<void> {
+    const key = stateKey(ctx);
+    try {
+        const targetFilePath = path.join(os.tmpdir() || "/tmp", guid());
+        await fs.ensureDir(path.dirname(targetFilePath));
+        await fs.writeJson(targetFilePath, state);
+        await ctx.storage.store(key, targetFilePath);
+    } catch (e) {
+        warn(`Failed to save state: ${e.message}`);
+    }
+}
+
+function stateKey(ctx: Contextual<any, any>): string {
+    return `state/${ctx.workspaceId}/${ctx.skill.namespace}/${ctx.skill.name}/${ctx.skill.id}.json`;
+}