Add conversations API (#8832)

* Add conversations API

* Add web UI for conversations

* Add test for conversations API

* Add tests for ConversationAccount

* Improve web UI

* Rename ConversationAccount to AccountConversation

* Remove conversations on block and mute

* Change last_status_id to be a denormalization of status_ids

* Add optimistic locking

app/javascript/mastodon/actions/conversations.js

@@ -0,0 +1,59 @@
+import api, { getLinks } from '../api';
+import {
+  importFetchedAccounts,
+  importFetchedStatuses,
+  importFetchedStatus,
+} from './importer';
+
+export const CONVERSATIONS_FETCH_REQUEST = 'CONVERSATIONS_FETCH_REQUEST';
+export const CONVERSATIONS_FETCH_SUCCESS = 'CONVERSATIONS_FETCH_SUCCESS';
+export const CONVERSATIONS_FETCH_FAIL    = 'CONVERSATIONS_FETCH_FAIL';
+export const CONVERSATIONS_UPDATE        = 'CONVERSATIONS_UPDATE';
+
+export const expandConversations = ({ maxId } = {}) => (dispatch, getState) => {
+  dispatch(expandConversationsRequest());
+
+  const params = { max_id: maxId };
+
+  if (!maxId) {
+    params.since_id = getState().getIn(['conversations', 0, 'last_status']);
+  }
+
+  api(getState).get('/api/v1/conversations', { params })
+    .then(response => {
+      const next = getLinks(response).refs.find(link => link.rel === 'next');
+
+      dispatch(importFetchedAccounts(response.data.reduce((aggr, item) => aggr.concat(item.accounts), [])));
+      dispatch(importFetchedStatuses(response.data.map(item => item.last_status).filter(x => !!x)));
+      dispatch(expandConversationsSuccess(response.data, next ? next.uri : null));
+    })
+    .catch(err => dispatch(expandConversationsFail(err)));
+};
+
+export const expandConversationsRequest = () => ({
+  type: CONVERSATIONS_FETCH_REQUEST,
+});
+
+export const expandConversationsSuccess = (conversations, next) => ({
+  type: CONVERSATIONS_FETCH_SUCCESS,
+  conversations,
+  next,
+});
+
+export const expandConversationsFail = error => ({
+  type: CONVERSATIONS_FETCH_FAIL,
+  error,
+});
+
+export const updateConversations = conversation => dispatch => {
+  dispatch(importFetchedAccounts(conversation.accounts));
+
+  if (conversation.last_status) {
+    dispatch(importFetchedStatus(conversation.last_status));
+  }
+
+  dispatch({
+    type: CONVERSATIONS_UPDATE,
+    conversation,
+  });
+};