feat: Implement FlagshipLink

When hosted in the Flagship app, we want the cozy-apps to be able to
forward their queries to the native code

This will allow the native code to have control on the data lifecycle
and chose between the cozy-stack or a local Pouch database as the
source for executing the query

For now we use cozy-intent in order to communicate through post
messages as it is the fastest implementation possible but this may
change in the future if we encounter performances issues (i.e. using a
local HTTP server)

packages/cozy-client/src/FlagshipLink.js

@@ -0,0 +1,38 @@
+import CozyLink from './CozyLink'
+import logger from './logger'
+
+export default class FlagshipLink extends CozyLink {
+  /**
+   * @param {object} [options] - Options
+   * @param  {object} [options.stackClient] - A StackClient
+   * @param  {object} [options.client] - A StackClient (deprecated)
+   * @param  {import('cozy-intent').WebviewService} [options.webviewIntent] - The webview's intent reference
+   */
+  constructor({ client, stackClient, webviewIntent } = {}) {
+    super()
+    if (client) {
+      logger.warn(
+        'Using options.client is deprecated, prefer options.stackClient'
+      )
+    }
+    this.stackClient = stackClient || client
+    this.webviewIntent = webviewIntent
+  }
+
+  registerClient(client) {
+    this.stackClient = client.stackClient || client.client
+  }
+
+  reset() {
+    this.stackClient = null
+  }
+
+  async request(operation, result, forward) {
+    return this.webviewIntent.call('flagshipLinkRequest', operation)
+  }
+
+  async persistData(data, forward) {
+    // Persist data should do nothing here as data is already persisted on Flagship side
+    return
+  }
+}

packages/cozy-client/src/index.js

@@ -1,6 +1,7 @@
 export { default } from './CozyClient'
 export { default as CozyLink } from './CozyLink'
 export { default as StackLink } from './StackLink'
+export { default as FlagshipLink } from './FlagshipLink'
 export { default as compose } from 'lodash/flow'
 export {
   QueryDefinition,