Move internal packages to an internal folder

For reference: https://go.dev/doc/go1.4#internalpackages

internal/ui/static/js/keyboard_handler.js

@@ -0,0 +1,72 @@
+class KeyboardHandler {
+    constructor() {
+        this.queue = [];
+        this.shortcuts = {};
+        this.triggers = [];
+    }
+
+    on(combination, callback) {
+        this.shortcuts[combination] = callback;
+        this.triggers.push(combination.split(" ")[0]);
+    }
+
+    listen() {
+        document.onkeydown = (event) => {
+            let key = this.getKey(event);
+            if (this.isEventIgnored(event, key) || this.isModifierKeyDown(event)) {
+                return;
+            }
+
+            event.preventDefault();
+            this.queue.push(key);
+
+            for (let combination in this.shortcuts) {
+                let keys = combination.split(" ");
+
+                if (keys.every((value, index) => value === this.queue[index])) {
+                    this.queue = [];
+                    this.shortcuts[combination](event);
+                    return;
+                }
+
+                if (keys.length === 1 && key === keys[0]) {
+                    this.queue = [];
+                    this.shortcuts[combination](event);
+                    return;
+                }
+            }
+
+            if (this.queue.length >= 2) {
+                this.queue = [];
+            }
+        };
+    }
+
+    isEventIgnored(event, key) {
+        return event.target.tagName === "INPUT" ||
+            event.target.tagName === "TEXTAREA" ||
+            (this.queue.length < 1 && !this.triggers.includes(key));
+    }
+
+    isModifierKeyDown(event) {
+        return event.getModifierState("Control") || event.getModifierState("Alt") || event.getModifierState("Meta");
+    }
+
+    getKey(event) {
+        const mapping = {
+            'Esc': 'Escape',
+            'Up': 'ArrowUp',
+            'Down': 'ArrowDown',
+            'Left': 'ArrowLeft',
+            'Right': 'ArrowRight'
+        };
+
+        for (let key in mapping) {
+            if (mapping.hasOwnProperty(key) && key === event.key) {
+                return mapping[key];
+            }
+        }
+
+        return event.key;
+    }
+}