refactor: centralize discord api errors

src/discord/api.ts

@@ -0,0 +1,61 @@
+const DISCORD_API_BASE = "https://discord.com/api/v10";
+
+type DiscordApiErrorPayload = {
+  message?: string;
+  retry_after?: number;
+  code?: number;
+  global?: boolean;
+};
+
+function parseDiscordApiErrorPayload(text: string): DiscordApiErrorPayload | null {
+  const trimmed = text.trim();
+  if (!trimmed.startsWith("{") || !trimmed.endsWith("}")) return null;
+  try {
+    const payload = JSON.parse(trimmed);
+    if (payload && typeof payload === "object") return payload as DiscordApiErrorPayload;
+  } catch {
+    return null;
+  }
+  return null;
+}
+
+function formatRetryAfterSeconds(value: number | undefined): string | undefined {
+  if (value === undefined || !Number.isFinite(value) || value < 0) return undefined;
+  const rounded = value < 10 ? value.toFixed(1) : Math.round(value).toString();
+  return `${rounded}s`;
+}
+
+function formatDiscordApiErrorText(text: string): string | undefined {
+  const trimmed = text.trim();
+  if (!trimmed) return undefined;
+  const payload = parseDiscordApiErrorPayload(trimmed);
+  if (!payload) {
+    const looksJson = trimmed.startsWith("{") && trimmed.endsWith("}");
+    return looksJson ? "unknown error" : trimmed;
+  }
+  const message =
+    typeof payload.message === "string" && payload.message.trim()
+      ? payload.message.trim()
+      : "unknown error";
+  const retryAfter = formatRetryAfterSeconds(
+    typeof payload.retry_after === "number" ? payload.retry_after : undefined,
+  );
+  return retryAfter ? `${message} (retry after ${retryAfter})` : message;
+}
+
+export async function fetchDiscord<T>(
+  path: string,
+  token: string,
+  fetcher: typeof fetch = fetch,
+): Promise<T> {
+  const res = await fetcher(`${DISCORD_API_BASE}${path}`, {
+    headers: { Authorization: `Bot ${token}` },
+  });
+  if (!res.ok) {
+    const text = await res.text().catch(() => "");
+    const detail = formatDiscordApiErrorText(text);
+    const suffix = detail ? `: ${detail}` : "";
+    throw new Error(`Discord API ${path} failed (${res.status})${suffix}`);
+  }
+  return (await res.json()) as T;
+}