From 2cb2a300fb081ed348153e00322ef2e0c770d2e8 Mon Sep 17 00:00:00 2001
From: UnicodingUnicorn <7555ic@gmail.com>
Date: Sun, 17 Feb 2019 07:47:32 +0800
Subject: [PATCH] Initial commit

---
 README.md | 52 ++++++++++++++++++++++++++++++-
 main.go   | 91 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 142 insertions(+), 1 deletion(-)
 create mode 100644 main.go

diff --git a/README.md b/README.md
index 77a8fbd..d23d648 100644
--- a/README.md
+++ b/README.md
@@ -1,3 +1,53 @@
 # backend-heartbeat
 
-Beep backend records and makes available the last seen times of users.
\ No newline at end of file
+Beep backend records and makes available the last seen times of users.
+
+## API
+
+### Subscribe User
+
+```
+GET /subscribe/:userid/client/:clientid
+```
+
+Subscribe to a user. Every time a user pings this service, the time will be sent to all subscribed users.
+
+```js
+const es = new EventSource(`${host}/subscribe/${user}/client/${device}`);
+es.onmessage = (e) => {
+  const timestamp = e.data;
+  // Do whatever with the timestamp
+};
+```
+
+#### URL Params
+
+| Name | Type | Description | Required |
+| ---- | ---- | ----------- | -------- |
+| userid | String | Target user's ID. | ✓ |
+| clientid | String | Target user's device's ID. | ✓ |
+
+#### Success Response (200 OK)
+
+An [EventSource](https://developer.mozilla.org/en-US/docs/Web/API/EventSource) stream.
+
+---
+
+### Ping Server
+
+```
+POST /ping/:userid/client/:clientid
+```
+
+Ping the server.
+
+#### URL Params
+
+| Name | Type | Description | Required |
+| ---- | ---- | ----------- | -------- |
+| userid | String | User's ID. | ✓ |
+| clientid | String | User's device's ID. | ✓ |
+
+#### Success Response (200 OK)
+
+Empty body.
diff --git a/main.go b/main.go
new file mode 100644
index 0000000..3f5e455
--- /dev/null
+++ b/main.go
@@ -0,0 +1,91 @@
+package main
+
+import (
+  "flag"
+  "fmt"
+  "log"
+  "net/http"
+  "strconv"
+  "time"
+
+  "github.com/julienschmidt/httprouter"
+)
+
+var listen string
+
+type RawClient struct {
+  UserId string
+  ClientId string
+}
+
+var connections map[RawClient][]chan []byte
+
+func main() {
+  // Parse flags
+  flag.StringVar(&listen, "listen", ":8080", "host and port to listen on")
+  flag.Parse()
+
+  connections = make(map[RawClient][]chan []byte)
+
+  // Routes
+	router := httprouter.New()
+  router.GET("/subscribe/:userid/client/:clientid", Subscribe)
+  router.POST("/ping/:userid/client/:clientid", PostTime)
+
+  // Start server
+  log.Printf("starting server on %s", listen)
+	log.Fatal(http.ListenAndServe(listen, router))
+}
+
+func Subscribe(w http.ResponseWriter, r *http.Request, p httprouter.Params) {
+  flusher, ok := w.(http.Flusher)
+  if !ok {
+    http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
+    return
+  }
+
+  w.Header().Set("Content-Type", "text/event-stream")
+  w.Header().Set("Cache-Control", "no-cache")
+  w.Header().Set("Connection", "keep-alive")
+
+  client := RawClient {
+    UserId: p.ByName("userid"),
+    ClientId: p.ByName("clintid"),
+  }
+  recv := make(chan []byte)
+  connections[client] = append(connections[client], recv);
+
+  // Refresh connection periodically
+  resClosed := w.(http.CloseNotifier).CloseNotify()
+  ticker := time.NewTicker(25 * time.Second)
+
+  for {
+    select {
+      case msg := <- recv:
+        fmt.Fprintf(w, "data: %s\n\n", msg)
+        flusher.Flush()
+      case <- ticker.C:
+        w.Write([]byte(":\n\n"))
+      case <- resClosed:
+        ticker.Stop()
+        delete(connections, client)
+        return
+    }
+  }
+}
+
+// TODO: Take client data from token
+func PostTime(w http.ResponseWriter, r *http.Request, p httprouter.Params) {
+  client := RawClient {
+    UserId: p.ByName("userid"),
+    ClientId: p.ByName("clientid"),
+  }
+
+  time := time.Now().UTC().Unix()
+
+  for _, connection := range connections[client] {
+    connection <- []byte(strconv.FormatInt(time, 10))
+  }
+
+  w.WriteHeader(http.StatusOK)
+}