Checkpoint web parity through Chromium input tasks

web/protocol/input-modal.ts

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+export const INPUT_MODAL_SCHEMA_VERSION = 1 as const;
+
+export type InputModalKind = "NONE" | "TOUCH_NAVIGATION" | "PEN_STROKE";
+
+export interface InputModalState {
+  schemaVersion: typeof INPUT_MODAL_SCHEMA_VERSION;
+  kind: InputModalKind;
+  activePointerIds: number[];
+  cancelled: boolean;
+  navigationRevision: number;
+  mainCommitCount: number;
+}
+
+export function createInputModalState(): InputModalState {
+  return { schemaVersion: 1, kind: "NONE", activePointerIds: [], cancelled: false, navigationRevision: 0, mainCommitCount: 0 };
+}
+
+export function beginTouch(state: InputModalState, pointerId: number): InputModalState {
+  if (!Number.isSafeInteger(pointerId) || pointerId < 0) throw new Error("POINTER_ID_INVALID");
+  const ids = state.activePointerIds.includes(pointerId) ? state.activePointerIds : [...state.activePointerIds, pointerId].sort((a, b) => a - b);
+  return { ...state, kind: "TOUCH_NAVIGATION", activePointerIds: ids, cancelled: false, navigationRevision: ids.length >= 2 && state.activePointerIds.length < 2 ? state.navigationRevision + 1 : state.navigationRevision };
+}
+
+export function cancelInputModal(state: InputModalState): InputModalState {
+  return { ...state, kind: "NONE", activePointerIds: [], cancelled: true };
+}
+
+export function endTouch(state: InputModalState, pointerId: number): InputModalState {
+  const ids = state.activePointerIds.filter((id) => id !== pointerId);
+  return { ...state, kind: ids.length > 0 ? "TOUCH_NAVIGATION" : "NONE", activePointerIds: ids };
+}
+
+export function beginPenStroke(state: InputModalState, pointerId: number): InputModalState {
+  if (!Number.isSafeInteger(pointerId) || pointerId < 0) throw new Error("POINTER_ID_INVALID");
+  return { ...state, kind: "PEN_STROKE", activePointerIds: [pointerId], cancelled: false };
+}
+
+export function commitPenStroke(state: InputModalState, pointerId: number): InputModalState {
+  if (state.kind !== "PEN_STROKE" || !state.activePointerIds.includes(pointerId) || state.cancelled) return state;
+  return { ...state, kind: "NONE", activePointerIds: [], mainCommitCount: state.mainCommitCount + 1 };
+}