chore: initialize from frontend template 4dc033c

src/application/view-models/async-state.ts

@@ -0,0 +1,187 @@
+import type { AppFailure } from "../../contracts/errors.ts";
+
+export const ASYNC_BASE_STATES = Object.freeze([
+  "initial-loading",
+  "success",
+  "empty",
+  "terminal-error",
+] as const);
+
+export const ASYNC_OVERLAYS = Object.freeze([
+  "refreshing",
+  "stale-degraded",
+  "mutation-pending",
+  "mutation-effect-unknown",
+  "mutation-conflict",
+] as const);
+
+export type AsyncOverlay =
+  | Readonly<{
+      refreshing: false;
+      staleDegraded: false;
+      mutationPending: false;
+      mutationEffectUnknown: false;
+      mutationConflict: false;
+    }>
+  | Readonly<{
+      refreshing: true;
+      staleDegraded: false;
+      mutationPending: false;
+      mutationEffectUnknown: false;
+      mutationConflict: false;
+    }>
+  | Readonly<{
+      refreshing: false;
+      staleDegraded: true;
+      mutationPending: false;
+      mutationEffectUnknown: false;
+      mutationConflict: false;
+    }>
+  | Readonly<{
+      refreshing: false;
+      staleDegraded: false;
+      mutationPending: true;
+      mutationEffectUnknown: false;
+      mutationConflict: false;
+    }>
+  | Readonly<{
+      refreshing: false;
+      staleDegraded: false;
+      mutationPending: false;
+      mutationEffectUnknown: true;
+      mutationConflict: false;
+    }>
+  | Readonly<{
+      refreshing: false;
+      staleDegraded: false;
+      mutationPending: false;
+      mutationEffectUnknown: false;
+      mutationConflict: true;
+    }>;
+
+export type AsyncSignals = Readonly<{
+  data?: unknown;
+  isInitialLoading?: boolean;
+  failure?: AppFailure;
+  isFetching?: boolean;
+  isStale?: boolean;
+  isDegraded?: boolean;
+  isMutationPending?: boolean;
+  hasMutationEffectUnknown?: boolean;
+  hasMutationConflict?: boolean;
+}>;
+
+export type AsyncState = Readonly<{
+  base: (typeof ASYNC_BASE_STATES)[number];
+  data?: unknown;
+  failure?: AppFailure;
+  overlay: AsyncOverlay;
+  indicator: (typeof ASYNC_OVERLAYS)[number] | null;
+}>;
+
+export function deriveAsyncState(signals: AsyncSignals): AsyncState {
+  const hasData = signals.data !== undefined && signals.data !== null;
+  const empty =
+    hasData &&
+    ((Array.isArray(signals.data) && signals.data.length === 0) ||
+      signals.data === "");
+
+  const base =
+    signals.isInitialLoading && !hasData
+      ? "initial-loading"
+      : signals.failure && !hasData
+        ? "terminal-error"
+        : empty
+          ? "empty"
+          : hasData
+            ? "success"
+            : "initial-loading";
+
+  const indicator =
+    signals.hasMutationEffectUnknown && hasData
+      ? "mutation-effect-unknown"
+      : signals.hasMutationConflict && hasData
+        ? "mutation-conflict"
+        : signals.isMutationPending && hasData
+          ? "mutation-pending"
+          : signals.isStale && signals.isDegraded && hasData
+            ? "stale-degraded"
+            : signals.isFetching && hasData
+              ? "refreshing"
+              : null;
+  const overlay = overlayFor(indicator);
+
+  return Object.freeze({
+    base,
+    data: base === "success" || base === "empty" ? signals.data : undefined,
+    failure: base === "terminal-error" ? signals.failure : undefined,
+    overlay,
+    indicator,
+  });
+}
+
+export function selectOverlayIndicator(
+  overlay: AsyncOverlay,
+): AsyncState["indicator"] {
+  if (overlay.mutationEffectUnknown) return "mutation-effect-unknown";
+  if (overlay.mutationConflict) return "mutation-conflict";
+  if (overlay.mutationPending) return "mutation-pending";
+  if (overlay.staleDegraded) return "stale-degraded";
+  if (overlay.refreshing) return "refreshing";
+  return null;
+}
+
+function overlayFor(indicator: AsyncState["indicator"]): AsyncOverlay {
+  if (indicator === "refreshing") {
+    return Object.freeze({
+      refreshing: true,
+      staleDegraded: false,
+      mutationPending: false,
+      mutationEffectUnknown: false,
+      mutationConflict: false,
+    });
+  }
+  if (indicator === "stale-degraded") {
+    return Object.freeze({
+      refreshing: false,
+      staleDegraded: true,
+      mutationPending: false,
+      mutationEffectUnknown: false,
+      mutationConflict: false,
+    });
+  }
+  if (indicator === "mutation-pending") {
+    return Object.freeze({
+      refreshing: false,
+      staleDegraded: false,
+      mutationPending: true,
+      mutationEffectUnknown: false,
+      mutationConflict: false,
+    });
+  }
+  if (indicator === "mutation-effect-unknown") {
+    return Object.freeze({
+      refreshing: false,
+      staleDegraded: false,
+      mutationPending: false,
+      mutationEffectUnknown: true,
+      mutationConflict: false,
+    });
+  }
+  if (indicator === "mutation-conflict") {
+    return Object.freeze({
+      refreshing: false,
+      staleDegraded: false,
+      mutationPending: false,
+      mutationEffectUnknown: false,
+      mutationConflict: true,
+    });
+  }
+  return Object.freeze({
+    refreshing: false,
+    staleDegraded: false,
+    mutationPending: false,
+    mutationEffectUnknown: false,
+    mutationConflict: false,
+  });
+}