refactor(image-pipeline): add backend router seam

lib/image-pipeline/backend/backend-router.ts

@@ -0,0 +1,83 @@
+import { applyPipelineStep, applyPipelineSteps } from "@/lib/image-pipeline/render-core";
+
+import {
+  CPU_BACKEND_ID,
+  type BackendHint,
+  type BackendRouter,
+  type FullBackendRequest,
+  type ImagePipelineBackend,
+  type PreviewBackendRequest,
+} from "@/lib/image-pipeline/backend/backend-types";
+
+const cpuBackend: ImagePipelineBackend = {
+  id: CPU_BACKEND_ID,
+  runPreviewStep(request) {
+    applyPipelineStep(
+      request.pixels,
+      request.step,
+      request.width,
+      request.height,
+      request.executionOptions,
+    );
+  },
+  runFullPipeline(request) {
+    applyPipelineSteps(
+      request.pixels,
+      request.steps,
+      request.width,
+      request.height,
+      request.executionOptions,
+    );
+  },
+};
+
+function normalizeBackendHint(value: BackendHint): string | null {
+  if (!value) {
+    return null;
+  }
+
+  const normalized = value.trim().toLowerCase();
+  return normalized.length > 0 ? normalized : null;
+}
+
+export function createBackendRouter(options?: {
+  backends?: readonly ImagePipelineBackend[];
+  defaultBackendId?: string;
+}): BackendRouter {
+  const configuredBackends = options?.backends?.length ? [...options.backends] : [cpuBackend];
+  const byId = new Map(configuredBackends.map((backend) => [backend.id.toLowerCase(), backend]));
+  const defaultBackend =
+    byId.get(options?.defaultBackendId?.toLowerCase() ?? "") ??
+    byId.get(CPU_BACKEND_ID) ??
+    configuredBackends[0] ??
+    cpuBackend;
+
+  return {
+    resolveBackend(backendHint) {
+      const normalizedHint = normalizeBackendHint(backendHint);
+      if (!normalizedHint) {
+        return defaultBackend;
+      }
+
+      return byId.get(normalizedHint) ?? defaultBackend;
+    },
+    runPreviewStep(request) {
+      const backend = this.resolveBackend(request.backendHint);
+      backend.runPreviewStep(request);
+    },
+    runFullPipeline(request) {
+      const backend = this.resolveBackend(request.backendHint);
+      backend.runFullPipeline(request);
+    },
+  };
+}
+
+const defaultRouter = createBackendRouter();
+
+export function runPreviewStepWithBackendRouter(request: PreviewBackendRequest): void {
+  defaultRouter.runPreviewStep(request);
+}
+
+export function runFullPipelineWithBackendRouter(request: FullBackendRequest): void {
+  defaultRouter.runFullPipeline(request);
+}

lib/image-pipeline/backend/backend-types.ts

@@ -0,0 +1,42 @@
+import type { PipelineStep } from "@/lib/image-pipeline/contracts";
+
+export const CPU_BACKEND_ID = "cpu" as const;
+
+export type BackendHint = string | undefined;
+
+export type BackendExecutionOptions = {
+  shouldAbort?: () => boolean;
+};
+
+export type PreviewBackendRequest = {
+  pixels: Uint8ClampedArray;
+  step: PipelineStep<string, unknown>;
+  width: number;
+  height: number;
+  backendHint?: BackendHint;
+  executionOptions?: BackendExecutionOptions;
+};
+
+export type FullBackendRequest = {
+  pixels: Uint8ClampedArray;
+  steps: readonly PipelineStep[];
+  width: number;
+  height: number;
+  backendHint?: BackendHint;
+  executionOptions?: BackendExecutionOptions;
+};
+
+export type BackendStepRequest = Omit<PreviewBackendRequest, "backendHint">;
+export type BackendPipelineRequest = Omit<FullBackendRequest, "backendHint">;
+
+export type ImagePipelineBackend = {
+  id: string;
+  runPreviewStep: (request: BackendStepRequest) => void;
+  runFullPipeline: (request: BackendPipelineRequest) => void;
+};
+
+export type BackendRouter = {
+  resolveBackend: (backendHint?: BackendHint) => ImagePipelineBackend;
+  runPreviewStep: (request: PreviewBackendRequest) => void;
+  runFullPipeline: (request: FullBackendRequest) => void;
+};