fix(chat): restore Facebook keyboard avoidance

src/app/chat/hooks/chat-keyboard-geometry.ts

@@ -0,0 +1,88 @@
+export const CHAT_KEYBOARD_VISIBLE_THRESHOLD_PX = 80;
+export const CHAT_KEYBOARD_ZOOM_THRESHOLD = 1.05;
+export const CHAT_KEYBOARD_FALLBACK_RATIO = 0.42;
+export const CHAT_KEYBOARD_FALLBACK_MIN_PX = 260;
+export const CHAT_KEYBOARD_FALLBACK_MAX_PX = 380;
+
+const CHAT_KEYBOARD_MAX_INSET_RATIO = 0.55;
+
+export interface ChatKeyboardViewportBaseline {
+  layoutHeight: number;
+  visualHeight: number;
+}
+
+export interface ChatKeyboardViewportSnapshot {
+  layoutHeight: number;
+  visualHeight: number;
+  visualScale: number;
+  virtualKeyboardHeight: number;
+}
+
+export type ChatKeyboardInsetSource =
+  | "content-resize"
+  | "visual-viewport"
+  | "virtual-keyboard"
+  | "none";
+
+export interface ChatKeyboardInsetResolution {
+  keyboardVisible: boolean;
+  bottomInset: number;
+  source: ChatKeyboardInsetSource;
+}
+
+export function resolveChatKeyboardInset(
+  baseline: ChatKeyboardViewportBaseline,
+  snapshot: ChatKeyboardViewportSnapshot,
+): ChatKeyboardInsetResolution {
+  const contentResize = baseline.layoutHeight - snapshot.layoutHeight;
+  if (contentResize > CHAT_KEYBOARD_VISIBLE_THRESHOLD_PX) {
+    return {
+      keyboardVisible: true,
+      bottomInset: 0,
+      source: "content-resize",
+    };
+  }
+
+  const virtualKeyboardHeight = Math.max(0, snapshot.virtualKeyboardHeight);
+  const visualViewportHeight =
+    snapshot.visualScale <= CHAT_KEYBOARD_ZOOM_THRESHOLD
+      ? Math.max(0, baseline.visualHeight - snapshot.visualHeight)
+      : 0;
+  const occludedHeight = Math.max(
+    virtualKeyboardHeight,
+    visualViewportHeight,
+  );
+
+  if (occludedHeight <= CHAT_KEYBOARD_VISIBLE_THRESHOLD_PX) {
+    return {
+      keyboardVisible: false,
+      bottomInset: 0,
+      source: "none",
+    };
+  }
+
+  const maxInset = Math.round(
+    baseline.layoutHeight * CHAT_KEYBOARD_MAX_INSET_RATIO,
+  );
+
+  return {
+    keyboardVisible: true,
+    bottomInset: Math.min(maxInset, Math.round(occludedHeight)),
+    source:
+      virtualKeyboardHeight >= visualViewportHeight
+        ? "virtual-keyboard"
+        : "visual-viewport",
+  };
+}
+
+export function resolveChatKeyboardFallbackInset(
+  layoutHeight: number,
+): number {
+  return Math.min(
+    CHAT_KEYBOARD_FALLBACK_MAX_PX,
+    Math.max(
+      CHAT_KEYBOARD_FALLBACK_MIN_PX,
+      Math.round(layoutHeight * CHAT_KEYBOARD_FALLBACK_RATIO),
+    ),
+  );
+}