backporting cli command history scrolling into dos

assets/tvdos/command.js

@@ -22,9 +22,74 @@ println("Starting TVDOS...");
 
 greet();
 
+let cmdHistory = []; // zeroth element is the oldest
+let cmdHistoryScroll = 0; // 0 for outside-of-buffer, 1 for most recent
 while (true) {
     print(get_prompt_text());
-    var s = read();
-    println();
-    println("String read: " + s + "@");
+
+    let cmdbuf = "";
+
+    while (true) {
+        let key = con.getch();
+
+        // printable chars
+        if (key >= 32 && key <= 126) {
+            let s = String.fromCharCode(key);
+            cmdbuf += s;
+            print(s);
+        }
+        // backspace
+        else if (key === 8 && cmdbuf.length > 0) {
+            cmdbuf = cmdbuf.substring(0, cmdbuf.length - 1);
+            print(String.fromCharCode(key));
+        }
+        // enter
+        else if (key === 10 || key === 13) {
+            println();
+            try {
+                println("You entered: " + cmdbuf);
+            }
+            catch (e) {
+                println(e);
+            }
+            finally {
+                if (cmdbuf.trim().length > 0)
+                    cmdHistory.push(cmdbuf);
+
+                cmdHistoryScroll = 0;
+                break;
+            }
+        }
+        // up arrow
+        else if (key === 19 && cmdHistory.length > 0 && cmdHistoryScroll < cmdHistory.length) {
+            cmdHistoryScroll += 1;
+
+            // back the cursor in order to type new cmd
+            let x = 0;
+            for (x = 0; x < cmdbuf.length; x++) print(String.fromCharCode(8));
+            cmdbuf = cmdHistory[cmdHistory.length - cmdHistoryScroll];
+            // re-type the new command
+            print(cmdbuf);
+
+        }
+        // down arrow
+        else if (key === 20) {
+            if (cmdHistoryScroll > 0) {
+                // back the cursor in order to type new cmd
+                let x = 0;
+                for (x = 0; x < cmdbuf.length; x++) print(String.fromCharCode(8));
+                cmdbuf = cmdHistory[cmdHistory.length - cmdHistoryScroll];
+                // re-type the new command
+                print(cmdbuf);
+
+                cmdHistoryScroll -= 1;
+            }
+            else {
+                // back the cursor in order to type new cmd
+                let x = 0;
+                for (x = 0; x < cmdbuf.length; x++) print(String.fromCharCode(8));
+                cmdbuf = "";
+            }
+        }
+    }
 }