SimpleChat: Take care of system prompt

Helper to get the latest system prompt and inturn use same to
set the system prompt ui, when switching.

Ensure that system prompt is set if and when enter key is pressed.

examples/server/public_simplechat/simplechat.js

@@ -141,6 +141,17 @@ class SimpleChat {
         return false;
     }
 
+    /**
+     * Retrieve the latest system prompt.
+     */
+    get_system() {
+        let sysPrompt = this.xchat[this.iLastSys].content;
+        if (!sysPrompt) {
+            sysPrompt = "";
+        }
+        return sysPrompt;
+    }
+
 }
 
 
@@ -194,6 +205,7 @@ class MultiChatUI {
      * @param {boolean} [bSwitchSession=false]
      */
     setup_ui(defaultChatId, bSwitchSession=false) {
+
         this.curChatId = defaultChatId;
         if (bSwitchSession) {
             this.handle_session_switch(this.curChatId);
@@ -214,6 +226,17 @@ class MultiChatUI {
                 ev.preventDefault();
             }
         });
+
+        this.elInSystem.addEventListener("keyup", (ev)=> {
+            // allow user to insert enter into the system prompt using shift+enter.
+            // while just pressing enter key will lead to setting the system prompt.
+            if ((ev.key === "Enter") && (!ev.shiftKey)) {
+                let chat = this.simpleChats[this.curChatId];
+                chat.add_system_anytime(this.elInSystem.value, this.curChatId);
+                ev.preventDefault();
+            }
+        });
+
     }
 
     /**
@@ -330,6 +353,7 @@ class MultiChatUI {
             console.error(`ERRR:MCUI:Session:${chatId} missing...`);
             return;
         }
+        this.elInSystem.value = chat.get_system();
         this.elInUser.value = "";
         chat.show(this.elDivChat);
         this.elInUser.focus();