From bd8fc6ad7b7258c66a8abcfd5cc58d22f6391d26 Mon Sep 17 00:00:00 2001
From: vitaliy <viprogramm@gmail.com>
Date: Thu, 12 Jul 2018 01:53:42 +0300
Subject: [PATCH] ht3_2: add lazy loading

---
 .../events/events-table-virtualized.js        | 59 ++++++++++------
 admin/src/ducks/events.js                     | 67 ++++++++++++++++++-
 2 files changed, 106 insertions(+), 20 deletions(-)

diff --git a/admin/src/components/events/events-table-virtualized.js b/admin/src/components/events/events-table-virtualized.js
index 272ce38..0f2ee5e 100644
--- a/admin/src/components/events/events-table-virtualized.js
+++ b/admin/src/components/events/events-table-virtualized.js
@@ -1,9 +1,10 @@
 import React, { Component } from 'react'
 import { connect } from 'react-redux'
-import { Table, Column } from 'react-virtualized'
+import { InfiniteLoader, Table, Column } from 'react-virtualized'
 import {
-  fetchAllEvents,
+  fetchLazyEvents,
   selectEvent,
+  loadMoreEvents,
   eventListSelector,
   loadedSelector,
   loadingSelector
@@ -15,34 +16,54 @@ export class EventsTableVirtualized extends Component {
   static propTypes = {}
 
   componentDidMount() {
-    this.props.fetchAllEvents()
+    this.props.fetchLazyEvents()
   }
 
-  render() {
+  get isFirstLoading() {
     const { events, loading } = this.props
-    if (loading) return <Loader />
+    return loading && events.length === 0
+  }
 
+  render() {
+    const { events } = this.props
+    if (this.isFirstLoading) return <Loader />
     return (
-      <Table
-        rowCount={events.length}
-        width={500}
-        height={300}
-        rowHeight={40}
-        rowGetter={this.rowGetter}
-        headerHeight={50}
-        onRowClick={this.handleSelect}
-        overscanRowCount={1}
+      <InfiniteLoader
+        isRowLoaded={this.isRowLoaded}
+        loadMoreRows={this.loadMoreRows}
+        rowCount={Number.MAX_SAFE_INTEGER}
       >
-        <Column dataKey="title" width={200} label="name" />
-        <Column dataKey="where" width={300} label="place" />
-        <Column dataKey="url" width={300} label="url" />
-      </Table>
+        {({ onRowsRendered, registerChild }) => (
+          <Table
+            rowCount={events.length}
+            width={500}
+            height={300}
+            rowHeight={40}
+            rowGetter={this.rowGetter}
+            headerHeight={50}
+            onRowClick={this.handleSelect}
+            overscanRowCount={1}
+            onRowsRendered={onRowsRendered}
+            ref={registerChild}
+          >
+            <Column dataKey="title" width={200} label="name" />
+            <Column dataKey="where" width={300} label="place" />
+            <Column dataKey="url" width={300} label="url" />
+          </Table>
+        )}
+      </InfiniteLoader>
     )
   }
 
   rowGetter = ({ index }) => this.props.events[index]
 
   handleSelect = ({ rowData }) => this.props.selectEvent(rowData.uid)
+
+  isRowLoaded = ({ index }) => !!this.props.events[index]
+
+  loadMoreRows = () => {
+    this.props.fetchLazyEvents()
+  }
 }
 
 export default connect(
@@ -51,5 +72,5 @@ export default connect(
     loading: loadingSelector(state),
     loaded: loadedSelector(state)
   }),
-  { fetchAllEvents, selectEvent }
+  { fetchLazyEvents, selectEvent }
 )(EventsTableVirtualized)
diff --git a/admin/src/ducks/events.js b/admin/src/ducks/events.js
index 2718eed..b20fe72 100644
--- a/admin/src/ducks/events.js
+++ b/admin/src/ducks/events.js
@@ -14,8 +14,15 @@ const prefix = `${appName}/${moduleName}`
 export const FETCH_ALL_REQUEST = `${prefix}/FETCH_ALL_REQUEST`
 export const FETCH_ALL_START = `${prefix}/FETCH_ALL_START`
 export const FETCH_ALL_SUCCESS = `${prefix}/FETCH_ALL_SUCCESS`
+
+export const FETCH_LAZY_REQUEST = `${prefix}/FETCH_REQUEST`
+export const FETCH_LAZY_START = `${prefix}/FETCH_START`
+export const FETCH_LAZY_SUCCESS = `${prefix}/FETCH_SUCCESS`
+
 export const TOGGLE_SELECT = `${prefix}/TOGGLE_SELECT`
 
+export const REQUEST_LIMIT = 10
+
 /**
  * Reducer
  * */
@@ -41,6 +48,7 @@ export default function reducer(state = new ReducerRecord(), action) {
 
   switch (type) {
     case FETCH_ALL_START:
+    case FETCH_LAZY_START:
       return state.set('loading', true)
 
     case FETCH_ALL_SUCCESS:
@@ -49,6 +57,15 @@ export default function reducer(state = new ReducerRecord(), action) {
         .set('loaded', true)
         .set('entities', fbToEntities(payload, EventRecord))
 
+    case FETCH_LAZY_SUCCESS:
+      const { loaded, events } = payload
+      return state
+        .set('loading', false)
+        .set('loaded', loaded)
+        .update('entities', (entities) =>
+          entities.push(...fbToEntities(events, EventRecord))
+        )
+
     case TOGGLE_SELECT:
       return state.update(
         'selected',
@@ -111,6 +128,10 @@ export const selectEvent = (uid) => ({
   payload: { uid }
 })
 
+export const fetchLazyEvents = () => ({
+  type: FETCH_LAZY_REQUEST
+})
+
 /**
  * Sagas
  * */
@@ -132,6 +153,50 @@ export function* fetchAllSaga() {
   })
 }
 
+export function* fetchLazySaga(action) {
+  const eventsState = yield select(stateSelector)
+  if (eventsState.loading || eventsState.loaded) return
+
+  yield put({
+    type: FETCH_LAZY_START
+  })
+
+  const eventList = yield select(entitiesSelector)
+  const lastLoadedEvent = eventList.last()
+  const lastUId = lastLoadedEvent ? lastLoadedEvent.get('uid') : ''
+
+  const ref = firebase
+    .database()
+    .ref('events')
+    .orderByKey()
+    .limitToFirst(REQUEST_LIMIT)
+    .startAt(lastUId)
+  const snapshot = yield call([ref, ref.once], 'value')
+
+  const events = snapshot.val()
+
+  //remove repeated previous last event
+  const filteredEvents = Object.keys(events)
+    .filter((key) => key !== lastUId)
+    .reduce((obj, key) => {
+      obj[key] = events[key]
+      return obj
+    }, {})
+
+  const loaded = Object.keys(events).length < REQUEST_LIMIT
+
+  yield put({
+    type: FETCH_LAZY_SUCCESS,
+    payload: {
+      events: filteredEvents,
+      loaded
+    }
+  })
+}
+
 export function* saga() {
-  yield all([takeEvery(FETCH_ALL_REQUEST, fetchAllSaga)])
+  yield all([
+    takeEvery(FETCH_ALL_REQUEST, fetchAllSaga),
+    takeEvery(FETCH_LAZY_REQUEST, fetchLazySaga)
+  ])
 }