From 2269cc653577dffc58dba4ad5534583f28f224de Mon Sep 17 00:00:00 2001
From: xengineering <mail2xengineering@protonmail.com>
Date: Mon, 14 Jun 2021 11:48:39 +0200
Subject: Implement Frontend Status Display

---
 data/html/index.html |  1 +
 data/js/birdscan.js  | 32 ++++++++++++++++++++++++++++++-
 src/state.go         | 54 +++++++++++++++++++++++++++++++++++++++++++++++++++-
 src/web.go           |  7 ++++++-
 4 files changed, 91 insertions(+), 3 deletions(-)

diff --git a/data/html/index.html b/data/html/index.html
index eddc2b3..268aad9 100644
--- a/data/html/index.html
+++ b/data/html/index.html
@@ -25,6 +25,7 @@
 		<main>
 			<h1>birdscan</h1>
 			<p>A software to take beautiful pictures of birds with a Raspberry Pi Camera.</p>
+			<p id="state"></p>
 			<button onclick="singlePicture()">Take single picture</button>
 		</main>
 
diff --git a/data/js/birdscan.js b/data/js/birdscan.js
index d1bba04..d3a46c3 100644
--- a/data/js/birdscan.js
+++ b/data/js/birdscan.js
@@ -1,7 +1,37 @@
 
+var state = "unknown";
+var updateStatePending = false;
+
 function singlePicture() {
     const xhttp = new XMLHttpRequest();
-    xhttp.open("POST", "./api/single_picture");
+    xhttp.open("POST", "./api/single_picture", true);
     xhttp.send();
 }
 
+function updateState() {
+    if (!updateStatePending) {
+        updateStatePending = true;
+        var state_request = new XMLHttpRequest();
+        state_request.onreadystatechange = updateStateCallback;
+        state_request.open("POST", "./api/state?known_state=" + state, true);
+        state_request.send();
+    }
+}
+
+function updateStateCallback() {
+    if (this.readyState == 4) {  // readyState=DONE
+        updateStatePending = false;
+        if (this.status == 200) {  // status=OK
+            state = this.responseText;
+            document.getElementById("state").innerHTML = "Current state: " + state;
+            setTimeout(updateState, 100);  // restart state poll after short time on success
+        } else {
+            state = "Verbindung abgebrochen!";
+            document.getElementById("state").innerHTML = "Current state: " + state;
+        }
+    }
+}
+
+document.getElementById("state").innerHTML = "Current state: " + state;
+updateState();
+
diff --git a/src/state.go b/src/state.go
index 9c6ab66..9a08738 100644
--- a/src/state.go
+++ b/src/state.go
@@ -13,6 +13,7 @@ type Machine struct {
 	current string
 	states StateMap
 	api chan string
+	state_listeners []*(chan string)
 }
 
 type StateMap map[string]MachineState
@@ -34,6 +35,49 @@ func (m Machine) GetState() string {
 	return m.current
 }
 
+func (m *Machine) GetStateOnChange(known string) string {
+	listener := make(chan string)
+	var current string
+	m.RegisterListener(&listener)
+	for {
+		if m.GetState() != known {
+			current = m.GetState()
+			break
+		}
+		current = <-listener
+		if current != known {
+			break
+		}
+	}
+	m.DeregisterListener(&listener)
+	return current
+}
+
+func (m *Machine) RegisterListener(listener *(chan string)) {
+	m.state_listeners = append(m.state_listeners, listener)
+}
+
+func (m *Machine) DeregisterListener(listener *(chan string)) {
+	wasRemoved := false
+	if len(m.state_listeners) == 0 {
+		log.Println("Not able to unregister listener from empty state_listener slice")
+	}
+	for index,item := range(m.state_listeners) {
+		if item == listener {
+			if index == len(m.state_listeners) - 1 {
+				m.state_listeners = m.state_listeners[: len(m.state_listeners) - 1]
+			} else {
+				m.state_listeners[index] = m.state_listeners[len(m.state_listeners) - 1]
+				m.state_listeners = m.state_listeners[: len(m.state_listeners) - 1]
+			}
+			wasRemoved = true
+		}
+	}
+	if !wasRemoved {
+		log.Println("Could not find listener in slice state_listeners")
+	}
+}
+
 func (m *Machine) processEvent(event string) string {
 	current := m.GetState()
 	next := m.states[current].on[event].to
@@ -59,7 +103,14 @@ func (m *Machine) run() {
 }
 
 func (m *Machine) runHooks(last string, next string) {
-	if next == "single_picture" {
+
+	log.Println("Send state to listeners ...")
+	for _,listener := range(m.state_listeners) {
+		*listener <- next
+	}
+	log.Println("State sent to listeners")
+
+	if last == "idle" && next == "single_picture" {
 		// TODO implement launch of python subprocess here
 		go func() {
 			time.Sleep(1 * time.Second)
@@ -89,6 +140,7 @@ func newCamStateMachine() Machine {
 			},
 		},
 		api: make(chan string),
+		state_listeners: make([]*(chan string), 0),
 	}
 }
 
diff --git a/src/web.go b/src/web.go
index 6515f47..206681d 100644
--- a/src/web.go
+++ b/src/web.go
@@ -37,6 +37,7 @@ func (server *WebServer) run() {
 	router.Get("/", indexHandler)
 	router.Get("/css/birdscan.css", cssHandler)
 	router.Get("/js/birdscan.js", jsHandler)
+	router.Post("/api/state", stateHandler)
 	router.Post("/api/single_picture", singlePictureHandler)
 
 	log.Println("Binding to 'http://" + server.config.BindAddress + ":" + server.config.BindPort + "'")
@@ -55,8 +56,12 @@ func jsHandler(w http.ResponseWriter, r *http.Request) {
 	http.ServeFile(w, r, fmt.Sprintf("%s/js/birdscan.js", APP_DATA))
 }
 
+func stateHandler(w http.ResponseWriter, r *http.Request) {
+	known_state := r.FormValue("known_state")
+	w.Write([]byte(fmt.Sprintf("%s", camera.GetStateOnChange(known_state))))
+}
+
 func singlePictureHandler(w http.ResponseWriter, r *http.Request) {
-	log.Println("Received request for a single picture")
 	camera.SendEvent("take_single_picture")
 	fmt.Fprintf(w, http.StatusText(http.StatusOK))
 }
-- 
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