1 files changed, 91 insertions, 0 deletions
diff --git a/src/adapters/ws/logic.ts b/src/adapters/ws/logic.ts
new file mode 100644
index 0000000..83a5802
--- /dev/null
+++ b/src/adapters/ws/logic.ts
@@ -0,0 +1,91 @@
+import type {
+	CatalogMessage,
+	SurfaceClientMessage,
+	SurfaceErrorMessage,
+	SurfaceMessage,
+	SurfaceServerMessage,
+	SurfaceUpdateMessage,
+} from "@dispatch/ui-contract";
+
+const VALID_SERVER_TYPES = new Set(["catalog", "surface", "update", "error"]);
+
+/** Serialize a client message to a JSON string for the wire. */
+export function serialize(msg: SurfaceClientMessage): string {
+	return JSON.stringify(msg);
+}
+
+function isRecord(v: unknown): v is Record<string, unknown> {
+	return v !== null && typeof v === "object" && !Array.isArray(v);
+}
+
+/**
+ * Parse a raw server message string into a typed SurfaceServerMessage.
+ * Returns null for malformed JSON or shapes that don't match the protocol.
+ */
+export function parseServerMessage(data: string): SurfaceServerMessage | null {
+	let parsed: unknown;
+	try {
+		parsed = JSON.parse(data);
+	} catch {
+		return null;
+	}
+	if (!isRecord(parsed)) {
+		return null;
+	}
+	const t = parsed.type;
+	if (typeof t !== "string" || !VALID_SERVER_TYPES.has(t)) {
+		return null;
+	}
+	switch (t) {
+		case "catalog": {
+			if (!Array.isArray(parsed.catalog)) return null;
+			return { type: "catalog", catalog: parsed.catalog as CatalogMessage["catalog"] };
+		}
+		case "surface": {
+			const spec = parsed.spec;
+			if (!isRecord(spec)) return null;
+			if (typeof spec.id !== "string") return null;
+			if (typeof spec.region !== "string") return null;
+			if (typeof spec.title !== "string") return null;
+			if (!Array.isArray(spec.fields)) return null;
+			return { type: "surface", spec: spec as unknown as SurfaceMessage["spec"] };
+		}
+		case "update": {
+			const update = parsed.update;
+			if (!isRecord(update)) return null;
+			if (typeof update.surfaceId !== "string") return null;
+			const spec = update.spec;
+			if (!isRecord(spec)) return null;
+			if (typeof spec.id !== "string") return null;
+			if (typeof spec.region !== "string") return null;
+			if (typeof spec.title !== "string") return null;
+			if (!Array.isArray(spec.fields)) return null;
+			return { type: "update", update: update as unknown as SurfaceUpdateMessage["update"] };
+		}
+		case "error": {
+			if (typeof parsed.message !== "string") return null;
+			const surfaceId = parsed.surfaceId;
+			if (surfaceId !== undefined && typeof surfaceId !== "string") return null;
+			const msg: SurfaceErrorMessage =
+				surfaceId !== undefined
+					? { type: "error", surfaceId, message: parsed.message }
+					: { type: "error", message: parsed.message };
+			return msg;
+		}
+		default:
+			return null;
+	}
+}
+
+/**
+ * Bounded exponential backoff with jitter.
+ * Base: 500ms, doubles each attempt, caps at 30s, adds ±20% jitter.
+ */
+export function nextBackoffMs(attempt: number): number {
+	const base = 500;
+	const max = 30_000;
+	const exponential = base * 2 ** Math.max(0, attempt);
+	const capped = Math.min(exponential, max);
+	const jitter = 0.8 + Math.random() * 0.4;
+	return Math.round(capped * jitter);
+}