feat(image-pipeline): add backend rollout flags

lib/image-pipeline/backend/feature-flags.ts

@@ -0,0 +1,100 @@
+export const IMAGE_PIPELINE_BACKEND_FLAG_KEYS = {
+  forceCpu: "imagePipeline.backend.forceCpu",
+  webglEnabled: "imagePipeline.backend.webgl.enabled",
+  wasmEnabled: "imagePipeline.backend.wasm.enabled",
+} as const;
+
+export type BackendFeatureFlags = {
+  forceCpu: boolean;
+  webglEnabled: boolean;
+  wasmEnabled: boolean;
+};
+
+export type BackendFeatureFlagReader = (
+  key: (typeof IMAGE_PIPELINE_BACKEND_FLAG_KEYS)[keyof typeof IMAGE_PIPELINE_BACKEND_FLAG_KEYS],
+) => unknown;
+
+const DEFAULT_BACKEND_FEATURE_FLAGS: BackendFeatureFlags = {
+  forceCpu: false,
+  webglEnabled: false,
+  wasmEnabled: false,
+};
+
+type RuntimeFeatureFlagStore = {
+  [IMAGE_PIPELINE_BACKEND_FLAG_KEYS.forceCpu]?: unknown;
+  [IMAGE_PIPELINE_BACKEND_FLAG_KEYS.webglEnabled]?: unknown;
+  [IMAGE_PIPELINE_BACKEND_FLAG_KEYS.wasmEnabled]?: unknown;
+};
+
+declare global {
+  interface Window {
+    __LEMONSPACE_FEATURE_FLAGS__?: RuntimeFeatureFlagStore;
+  }
+
+  var __LEMONSPACE_FEATURE_FLAGS__: RuntimeFeatureFlagStore | undefined;
+}
+
+function parseBooleanFlag(value: unknown): boolean | undefined {
+  if (typeof value === "boolean") {
+    return value;
+  }
+
+  if (typeof value === "number") {
+    if (value === 1) {
+      return true;
+    }
+    if (value === 0) {
+      return false;
+    }
+    return undefined;
+  }
+
+  if (typeof value === "string") {
+    const normalized = value.trim().toLowerCase();
+    if (normalized === "true" || normalized === "1" || normalized === "on") {
+      return true;
+    }
+    if (normalized === "false" || normalized === "0" || normalized === "off") {
+      return false;
+    }
+  }
+
+  return undefined;
+}
+
+function readFlagFromRuntimeStore(
+  key: (typeof IMAGE_PIPELINE_BACKEND_FLAG_KEYS)[keyof typeof IMAGE_PIPELINE_BACKEND_FLAG_KEYS],
+): unknown {
+  const runtimeStore =
+    globalThis.__LEMONSPACE_FEATURE_FLAGS__ ??
+    (typeof window !== "undefined" ? window.__LEMONSPACE_FEATURE_FLAGS__ : undefined);
+  if (runtimeStore && key in runtimeStore) {
+    return runtimeStore[key];
+  }
+
+  try {
+    if (typeof localStorage !== "undefined") {
+      return localStorage.getItem(key);
+    }
+  } catch {
+    return undefined;
+  }
+
+  return undefined;
+}
+
+export function getBackendFeatureFlags(readFlag?: BackendFeatureFlagReader): BackendFeatureFlags {
+  const reader = readFlag ?? readFlagFromRuntimeStore;
+
+  return {
+    forceCpu:
+      parseBooleanFlag(reader(IMAGE_PIPELINE_BACKEND_FLAG_KEYS.forceCpu)) ??
+      DEFAULT_BACKEND_FEATURE_FLAGS.forceCpu,
+    webglEnabled:
+      parseBooleanFlag(reader(IMAGE_PIPELINE_BACKEND_FLAG_KEYS.webglEnabled)) ??
+      DEFAULT_BACKEND_FEATURE_FLAGS.webglEnabled,
+    wasmEnabled:
+      parseBooleanFlag(reader(IMAGE_PIPELINE_BACKEND_FLAG_KEYS.wasmEnabled)) ??
+      DEFAULT_BACKEND_FEATURE_FLAGS.wasmEnabled,
+  };
+}