feat: resolve and validate plugin config

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/config.ts

@@ -0,0 +1,63 @@
+export type Config = {
+  baseURL: string
+  apiKey: string | undefined
+  limit: number
+  lang: string | undefined
+  tbs: string | undefined
+}
+
+const DEFAULT_BASE_URL = "http://localhost:3000"
+const DEFAULT_LIMIT = 8
+const TBS_VALUES = ["qdr:h", "qdr:d", "qdr:w", "qdr:m", "qdr:y"]
+
+// Blank strings count as unset so an empty env var does not shadow the default.
+function str(value: unknown, name: string, secret = false): string | undefined {
+  if (value === undefined || value === null) return undefined
+  if (typeof value !== "string") {
+    throw new Error(
+      `fastCRW: option ${name} must be a string${secret ? "" : `, got ${JSON.stringify(value)}`}`,
+    )
+  }
+  return value.trim() || undefined
+}
+
+function baseURL(value: string): string {
+  let url: URL
+  try {
+    url = new URL(value)
+  } catch {
+    throw new Error(`fastCRW: invalid baseURL ${JSON.stringify(value)} (expected an http(s) URL)`)
+  }
+  if (url.protocol !== "http:" && url.protocol !== "https:") {
+    throw new Error(`fastCRW: invalid baseURL ${JSON.stringify(value)} (expected an http(s) URL)`)
+  }
+  return value.replace(/\/+$/, "")
+}
+
+function limit(value: unknown): number {
+  const n = typeof value === "string" && value.trim() ? Number(value) : value
+  if (typeof n !== "number" || !Number.isFinite(n)) return DEFAULT_LIMIT
+  return Math.min(20, Math.max(1, Math.trunc(n)))
+}
+
+export function resolveConfig(
+  options: Record<string, unknown> | undefined,
+  env: Record<string, string | undefined>,
+): Config {
+  const opts = options ?? {}
+  const tbs = str(opts.tbs, "tbs")
+  if (tbs !== undefined && !TBS_VALUES.includes(tbs)) {
+    throw new Error(
+      `fastCRW: invalid tbs ${JSON.stringify(tbs)} (expected one of ${TBS_VALUES.join(", ")})`,
+    )
+  }
+  return {
+    baseURL: baseURL(
+      str(opts.baseURL, "baseURL") ?? str(env.CRW_API_URL, "CRW_API_URL") ?? DEFAULT_BASE_URL,
+    ),
+    apiKey: str(opts.apiKey, "apiKey", true) ?? str(env.CRW_API_KEY, "CRW_API_KEY", true),
+    limit: limit(opts.limit),
+    lang: str(opts.lang, "lang"),
+    tbs,
+  }
+}