# All files / src/clients/ep baseClient.ts

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     /**
     * @fileoverview Base European Parliament API Client
     *
     * Shared HTTP infrastructure for all EP API sub-clients:
     * LRU caching, token-bucket rate limiting, timeout/retry logic,
     * and structured audit/performance instrumentation.
     *
     * **ISMS Policies:**
     * - SC-002 (Secure Coding Standards)
     * - PE-001 (Performance Standards)
     * - AU-002 (Audit Logging and Monitoring)
     * - DP-001 (Data Protection and GDPR Compliance)
     *
     * @module clients/ep/baseClient
     * @see https://github.com/Hack23/ISMS-PUBLIC/blob/main/Secure_Development_Policy.md
     */

    import { fetch } from 'undici';
    import { LRUCache } from 'lru-cache';
    import { RateLimiter } from '../../utils/rateLimiter.js';
    import { withRetry, withTimeoutAndAbort, TimeoutError, DEFAULT_TIMEOUTS } from '../../utils/timeout.js';
    import { performanceMonitor } from '../../utils/performance.js';
    import { DEFAULT_RATE_LIMIT_PER_MINUTE, DEFAULT_API_URL, USER_AGENT } from '../../config.js';

    /** Exact hostnames that must never be used as API endpoints. */
    const BLOCKED_HOSTS_EXACT = new Set(['localhost', '0.0.0.0', '::1']);

    /**
     * Patterns matching private / link-local / loopback / IPv6-mapped-IPv4 address
     * prefixes. All patterns are tested against the bracket-stripped hostname.
     *
     * IPv6-mapped IPv4 patterns use the normalised hex form that the WHATWG URL
     * parser emits (e.g. `::ffff:127.0.0.1` → `::ffff:7f00:1`).
     */
    const BLOCKED_HOST_PATTERNS = [
      /^fe[89ab][0-9a-f]:/i,
      /^f[cd][0-9a-f]{2}:/i,
      /^::ffff:7f/i,
      /^::ffff:a[0-9a-f]{2}:/i,
      /^::ffff:ac1[0-9a-f]:/i,
      /^::ffff:c0a8:/i,
      /^::ffff:a9fe:/i,
      /^127\./,
      /^169\.254\./,
      /^10\./,
      /^172\.(1[6-9]|2\d|3[01])\./,
      /^192\.168\./,
    ];

    /**
     * Returns true when `host` is a loopback, link-local, or RFC-1918 address that
     * MUST NOT be used as an API endpoint (SSRF prevention).
     * @private
     */
    function isBlockedHost(host: string): boolean {
      return BLOCKED_HOSTS_EXACT.has(host) || BLOCKED_HOST_PATTERNS.some(p => p.test(host));
    }

    /**
     * Validates an EP API base URL to prevent SSRF via environment variable or
     * constructor argument poisoning.
     *
     * Enforces HTTPS-only and blocks requests to localhost, loopback addresses
     * (127.0.0.0/8), and known internal IP ranges (link-local 169.254.x.x,
     * RFC-1918 10.x.x.x / 172.16-31.x.x / 192.168.x.x, and their IPv6-mapped
     * IPv4 equivalents), as well as IPv6 loopback/link-local/unique-local ranges.
     *
     * @param url   - The URL string to validate
     * @param label - Label used in error messages (defaults to `'EP_API_URL'`)
     * @returns The validated URL string (unchanged)
     * @throws {Error} If the URL uses a non-HTTPS scheme or targets an internal host
     *
     * @security SSRF Prevention – ISMS Policy: SC-002, NE-001
     */
    export function validateApiUrl(url: string, label = 'EP_API_URL'): string {
      let parsed: URL;
      try {
        parsed = new URL(url);
      } catch {
        throw new Error(`${label} is not a valid URL`);
      }
      if (parsed.protocol !== 'https:') {
        throw new Error(`${label} must use HTTPS protocol`);
      }
      const rawHost = parsed.hostname.replace(/\.$/, '');
      const host = rawHost.startsWith('[') && rawHost.endsWith(']')
        ? rawHost.slice(1, -1)
        : rawHost;
      if (isBlockedHost(host)) {
        throw new Error(`${label} must not point to internal or loopback addresses`);
      }
      return url;
    }

    /** Default base URL for European Parliament Open Data Portal API v2 — derived from centralized config */
    export const DEFAULT_EP_API_BASE_URL = DEFAULT_API_URL;
    /**
     * Default HTTP request timeout in milliseconds — derived from the centralized
     * {@link DEFAULT_TIMEOUTS.EP_API_REQUEST_MS} constant in `timeout.ts` so there
     * is a single source of truth for the EP API request timeout value.
     */
    export const DEFAULT_REQUEST_TIMEOUT_MS = DEFAULT_TIMEOUTS.EP_API_REQUEST_MS;
    /** Whether automatic retry on transient failures is enabled by default */
    export const DEFAULT_RETRY_ENABLED = true;
    /** Default maximum number of retry attempts for failed requests */
    export const DEFAULT_MAX_RETRIES = 2;
    /** Default base retry delay in milliseconds (exponential backoff starting point) */
    export const DEFAULT_RETRY_BASE_DELAY_MS = 1_000;
    /** Default maximum retry delay in milliseconds (caps exponential backoff growth) */
    export const DEFAULT_RETRY_MAX_DELAY_MS = 30_000;
    /** Default cache time-to-live in milliseconds (15 minutes) */
    export const DEFAULT_CACHE_TTL_MS = 900_000;
    /** Default maximum number of entries in the LRU response cache */
    export const DEFAULT_MAX_CACHE_SIZE = 500;
    /** Default rate limit token bucket size (requests per interval) — derived from centralized config */
    export const DEFAULT_RATE_LIMIT_TOKENS = DEFAULT_RATE_LIMIT_PER_MINUTE;
    /** Default rate limit interval unit */
    export const DEFAULT_RATE_LIMIT_INTERVAL = 'minute' as const;
    /** Maximum allowed response body size in bytes (10 MiB, 10×1024×1024) to prevent memory exhaustion */
    export const DEFAULT_MAX_RESPONSE_BYTES = 10_485_760;

    /**
     * API Error thrown when European Parliament API requests fail.
     *
     * When thrown from {@link BaseEPClient}'s HTTP layer, the message always
     * includes the numeric HTTP status code and, when present, the HTTP reason
     * phrase (`statusText`). Some HTTP/2 responses omit `statusText`, in which
     * case the message contains only the status code — the status code is
     * therefore always surfaced in the message, never empty.
     *
     * Message format: `EP API request failed: <status>[ <statusText>]`
     *
     * @example
     * ```typescript
     * // HTTP/1.1 with a reason phrase
     * throw new APIError('EP API request failed: 404 Not Found', 404, { endpoint: '/meps/999999' });
     *
     * // HTTP/2 where statusText is empty
     * throw new APIError('EP API request failed: 404', 404, { endpoint: '/meps/999999' });
     * ```
     * @public
     */
    export class APIError extends Error {
      constructor(
        message: string,
        public statusCode?: number,
        public details?: unknown
      ) {
        super(message);
        this.name = 'APIError';
      }
    }

    /**
     * JSON-LD response format from EP API.
     * @internal
     */
    export interface JSONLDResponse<T = Record<string, unknown>>
      extends Record<string, unknown> {
      data: T[];
      '@context': unknown[];
    }

    /**
     * Configuration options for EP API clients.
     * @internal
     */
    export interface EPClientConfig {
      /** Base URL for European Parliament API. @default DEFAULT_EP_API_BASE_URL */
      baseURL?: string;
      /** Cache time-to-live in milliseconds. @default 900000 */
      cacheTTL?: number;
      /** Maximum number of entries in LRU cache. @default 500 */
      maxCacheSize?: number;
      /** Custom rate limiter instance. */
      rateLimiter?: RateLimiter;
      /** Request timeout in milliseconds. @default DEFAULT_TIMEOUTS.EP_API_REQUEST_MS */
      timeoutMs?: number;
      /** Enable automatic retry on transient failures. @default true */
      enableRetry?: boolean;
      /** Maximum number of retry attempts. @default 2 */
      maxRetries?: number;
      /** Maximum allowed response body size in bytes. @default 10485760 (10 MiB) */
      maxResponseBytes?: number;
    }

    /**
     * Pre-built shared resources passed from a facade to its sub-clients
     * so they all operate on the same cache and rate-limiter bucket.
     * @internal
     */
    export interface EPSharedResources {
      cache: LRUCache<string, Record<string, unknown>>;
      rateLimiter: RateLimiter;
      baseURL: string;
      timeoutMs: number;
      enableRetry: boolean;
      maxRetries: number;
      maxResponseBytes: number;
      /** Shared cache hit/miss counters so all sub-clients contribute to aggregate stats. */
      cacheCounters: { hits: number; misses: number };
    }

    /**
     * Base class for European Parliament API sub-clients.
     *
     * Holds the shared HTTP machinery: LRU cache, token-bucket rate limiter,
     * timeout/abort controller, and retry logic.  Sub-clients extend this class
     * and call the protected `get()` helper for all HTTP requests.
     *
     * @class BaseEPClient
     */
    export class BaseEPClient {
      /** LRU cache for API responses. */
      protected readonly cache: LRUCache<string, Record<string, unknown>>;
      /** European Parliament API base URL. */
      protected readonly baseURL: string;
      /** Token bucket rate limiter. */
      protected readonly rateLimiter: RateLimiter;
      /** Request timeout in milliseconds. */
      protected readonly timeoutMs: number;
      /** Enable automatic retry on transient failures. */
      protected readonly enableRetry: boolean;
      /** Maximum number of retry attempts. */
      protected readonly maxRetries: number;
      /** Maximum allowed response body size in bytes. */
      protected readonly maxResponseBytes: number;
      /** Shared cache hit/miss counters (shared via EPSharedResources when used as sub-client). */
      private readonly cacheCounters: { hits: number; misses: number };

      /**
       * Resolves all EPClientConfig options to their final values with defaults applied.
       * Extracted to keep constructor complexity within limits.
       * @private
       */
      private static resolveConfig(config: EPClientConfig): {
        baseURL: string;
        cacheTTL: number;
        maxCacheSize: number;
        rateLimiter: RateLimiter;
        timeoutMs: number;
        enableRetry: boolean;
        maxRetries: number;
        maxResponseBytes: number;
      } {
        const rawBaseURL = config.baseURL ?? DEFAULT_EP_API_BASE_URL;
        validateApiUrl(rawBaseURL, 'config.baseURL');
        const baseURL = rawBaseURL.endsWith('/') ? rawBaseURL : `${rawBaseURL}/`;
        return {
          baseURL,
          cacheTTL: config.cacheTTL ?? DEFAULT_CACHE_TTL_MS,
          maxCacheSize: config.maxCacheSize ?? DEFAULT_MAX_CACHE_SIZE,
          rateLimiter:
            config.rateLimiter ??
            new RateLimiter({
              tokensPerInterval: DEFAULT_RATE_LIMIT_TOKENS,
              interval: DEFAULT_RATE_LIMIT_INTERVAL,
            }),
          timeoutMs: config.timeoutMs ?? DEFAULT_REQUEST_TIMEOUT_MS,
          enableRetry: config.enableRetry ?? DEFAULT_RETRY_ENABLED,
          maxRetries: config.maxRetries ?? DEFAULT_MAX_RETRIES,
          maxResponseBytes: config.maxResponseBytes ?? DEFAULT_MAX_RESPONSE_BYTES,
        };
      }

      /**
       * Creates a BaseEPClient.
       *
       * When `shared` is provided the constructor reuses those pre-built resources
       * instead of allocating new ones; this is the mechanism used by the facade to
       * ensure all sub-clients share one cache and one rate-limiter.
       *
       * @param config - Client configuration (used when `shared` is absent)
       * @param shared - Pre-built shared resources (passed by facade to sub-clients)
       */
      constructor(config: EPClientConfig = {}, shared?: EPSharedResources) {
        if (shared !== undefined) {
          this.cache = shared.cache;
          this.rateLimiter = shared.rateLimiter;
          this.baseURL = shared.baseURL;
          this.timeoutMs = shared.timeoutMs;
          this.enableRetry = shared.enableRetry;
          this.maxRetries = shared.maxRetries;
          this.maxResponseBytes = shared.maxResponseBytes;
          this.cacheCounters = shared.cacheCounters;
        } else {
          const cfg = BaseEPClient.resolveConfig(config);
          this.baseURL = cfg.baseURL;
          this.cache = new LRUCache<string, Record<string, unknown>>({
            max: cfg.maxCacheSize,
            ttl: cfg.cacheTTL,
            allowStale: false,
            updateAgeOnGet: true,
          });
          this.rateLimiter = cfg.rateLimiter;
          this.timeoutMs = cfg.timeoutMs;
          this.enableRetry = cfg.enableRetry;
          this.maxRetries = cfg.maxRetries;
          this.maxResponseBytes = cfg.maxResponseBytes;
          this.cacheCounters = { hits: 0, misses: 0 };
        }
      }

      /**
       * Builds the full request URL from endpoint + optional params.
       * @private
       */
      private buildRequestUrl(
        endpoint: string,
        params?: Record<string, unknown>
      ): URL {
        const url = new URL(endpoint, this.baseURL);
        if (params === undefined) return url;

        for (const [key, value] of Object.entries(params)) {
          if (value === undefined || value === null) continue;
          let str: string;
          if (typeof value === 'string') {
            str = value;
          } else if (typeof value === 'number' || typeof value === 'boolean') {
            str = String(value);
          } else {
            str = JSON.stringify(value);
          }
          url.searchParams.append(key, str);
        }

        return url;
      }

      /**
       * Returns true when an error should trigger a retry.
       *
       * Retries on:
       * - 429 Too Many Requests (rate-limited by EP API; exponential backoff applied)
       * - 5xx Server Errors (transient server failures)
       * - Network / unknown errors
       *
       * Does NOT retry on 4xx client errors (except 429).
       * @private
       */
      private shouldRetryRequest(error: unknown): boolean {
        Iif (error instanceof TimeoutError) return false;
        if (error instanceof APIError) {
          const code = error.statusCode ?? 500;
          return code === 429 || code >= 500;
        }
        if (error instanceof SyntaxError) {
          return error.message.includes('Unexpected end of JSON input');
        }
        return true;
      }

      /**
       * Parses a byte buffer as JSON-LD.  Returns an empty JSON-LD shape for
       * zero-byte bodies (the EP API sends these for out-of-range offsets).
       * Non-empty bodies must contain valid JSON; any `SyntaxError` is allowed
       * to propagate so callers (including single-entity endpoints) fail fast
       * instead of receiving a misleading empty-list shape.
       * @private
       */
      private static parseJsonLdBytes(bytes: Uint8Array): JSONLDResponse {
        if (bytes.byteLength === 0) {
          return { data: [], '@context': [] };
        }
        return JSON.parse(new TextDecoder().decode(bytes)) as JSONLDResponse;
      }

      /**
       * Reads the response body as a stream, enforcing the response size cap.
       * Used as a fallback when the `content-length` header is absent (e.g. chunked
       * transfer encoding). Accumulates all chunks and parses the result as JSON.
       * @private
       */
      private async readStreamedBody<T>(response: Response): Promise<T> {
        const reader = (response.body as ReadableStream<Uint8Array> | null)?.getReader();
        if (!reader) {
          return response.json() as Promise<T>;
        }

        const chunks: Uint8Array[] = [];
        let totalBytes = 0;
        let readerReleased = false;
        try {
          for (;;) {
            const result = await reader.read();
            if (result.done) break;
            const { value } = result;
            totalBytes += value.byteLength;
            if (totalBytes > this.maxResponseBytes) {
              reader.releaseLock();
              readerReleased = true;
              await (response.body as ReadableStream<Uint8Array> | null)?.cancel();
              throw new APIError(
                `EP API response too large: exceeds limit of ${String(this.maxResponseBytes)} bytes`,
                413
              );
            }
            chunks.push(value);
          }
        } finally {
          if (!readerReleased) {
            reader.releaseLock();
          }
        }

        const combined = new Uint8Array(totalBytes);
        let offset = 0;
        for (const chunk of chunks) {
          combined.set(chunk, offset);
          offset += chunk.byteLength;
        }
        return BaseEPClient.parseJsonLdBytes(combined) as T;
      }

      /**
       * Treats a truly empty body as an empty JSON-LD shape; invalid JSON for
       * non-empty bodies is surfaced as an error.
       * @private
       */
      private static async parseResponseJson<T>(response: Response): Promise<T> {
        const raw = await response.text();

        if (raw.length === 0 || /^\s*$/.test(raw)) {
          return { data: [], '@context': [] } as unknown as T;
        }

        return JSON.parse(raw) as T;
      }

      /**
       * Validates the Content-Type header of an API response.
       * Throws if the response is not JSON (e.g. HTML error pages from reverse proxies).
       * Cancels the response body before throwing to allow connection reuse.
       *
       * A missing or empty Content-Type header is treated as acceptable because
       * the EP API occasionally omits it on valid JSON responses, and rejecting
       * those would cause false-negative failures.
       * @private
       */
      private static validateContentType(response: Response): void {
        const contentType = response.headers.get('content-type') ?? '';
        const mediaType = contentType.split(';', 1)[0]?.trim().toLowerCase() ?? '';
        const isJsonContentType =
          mediaType === '' ||
          mediaType === 'application/json' ||
          mediaType.endsWith('+json');

        if (!isJsonContentType) {
          void response.body?.cancel().catch(() => undefined);
          throw new APIError(
            `EP API returned unexpected content-type: ${contentType}`,
            502
          );
        }
      }

      /**
       * Empty JSON-LD shape returned for bodyless responses (HTTP 204, content-length: 0).
       * @private
       */
      private static readonly EMPTY_JSONLD = Object.freeze({ data: [], '@context': [] });

      /**
       * Parses the response body based on content-length header.
       * Returns `undefined` when content-length is absent or non-finite (caller
       * should fall through to streamed-body parsing).
       * @private
       */
      private async parseByContentLength<T>(response: Response): Promise<T | undefined> {
        const contentLength = response.headers.get('content-length');
        if (contentLength === null) return undefined;

        const bytes = Number.parseInt(contentLength, 10);
        if (!Number.isFinite(bytes) || bytes < 0) return undefined;

        Iif (bytes === 0) {
          await response.body?.cancel();
          return BaseEPClient.EMPTY_JSONLD as unknown as T;
        }
        if (bytes > this.maxResponseBytes) {
          await response.body?.cancel();
          throw new APIError(
            `EP API response too large: ${String(bytes)} bytes exceeds limit of ${String(this.maxResponseBytes)} bytes`,
            413
          );
        }
        return BaseEPClient.parseResponseJson<T>(response);
      }

      /**
       * Executes the HTTP fetch with timeout/abort support and response size guard.
       * @param url - Fully resolved request URL
       * @param endpoint - Relative endpoint path (for error messages)
       * @param minimumTimeoutMs - Optional per-request minimum timeout (ms).
       *   When provided, the effective timeout is `Math.max(minimumTimeoutMs, this.timeoutMs)`,
       *   so it acts as a floor that the global timeout can still extend.
       *   Use for known slow EP API endpoints (e.g. `procedures/feed`).
       * @private
       */
      private async fetchWithTimeout<T>(url: URL, endpoint: string, minimumTimeoutMs?: number): Promise<T> {
        const validMinimum =
          minimumTimeoutMs !== undefined &&
          Number.isFinite(minimumTimeoutMs) &&
          minimumTimeoutMs > 0
            ? minimumTimeoutMs
            : undefined;
        const effectiveTimeout = validMinimum !== undefined
          ? Math.max(validMinimum, this.timeoutMs)
          : this.timeoutMs;
        return withTimeoutAndAbort(
          async (signal) => {
            const response = await fetch(url.toString(), {
              headers: {
                Accept: 'application/ld+json',
                'User-Agent': USER_AGENT,
              },
              signal,
            });

            if (!response.ok) {
              throw new APIError(
                `EP API request failed: ${String(response.status)}${response.statusText ? ` ${response.statusText}` : ''}`,
                response.status
              );
            }

            if (response.status === 204) {
              await response.body?.cancel();
              return BaseEPClient.EMPTY_JSONLD as unknown as T;
            }

            BaseEPClient.validateContentType(response);

            const clResult = await this.parseByContentLength<T>(response);
            if (clResult !== undefined) return clResult;

            return this.readStreamedBody<T>(response);
          },
          effectiveTimeout,
          `EP API request to ${endpoint} timed out after ${String(effectiveTimeout)}ms`
        );
      }

      /**
       * Wraps a fetch call with the configured retry policy.
       * @param url - Fully resolved request URL
       * @param endpoint - Relative endpoint path (for error messages)
       * @param minimumTimeoutMs - Optional per-request minimum timeout (ms)
       * @private
       */
      private async fetchWithRetry<T>(url: URL, endpoint: string, minimumTimeoutMs?: number): Promise<T> {
        return withRetry(
          () => this.fetchWithTimeout<T>(url, endpoint, minimumTimeoutMs),
          {
            maxRetries: this.enableRetry ? this.maxRetries : 0,
            retryDelayMs: DEFAULT_RETRY_BASE_DELAY_MS,
            maxDelayMs: DEFAULT_RETRY_MAX_DELAY_MS,
            shouldRetry: (error) => this.shouldRetryRequest(error),
          }
        );
      }

      /**
       * Converts a caught error to a typed {@link APIError}.
       * For timeout errors, the actual timeout value is read from the
       * {@link TimeoutError} instance (which carries the effective value used
       * by `withTimeoutAndAbort`), avoiding the need to re-validate or
       * recompute the per-endpoint minimum here.
       * @param error - The caught error
       * @param endpoint - Relative endpoint path (for error messages)
       * @private
       */
      private toAPIError(error: unknown, endpoint: string): APIError {
        if (error instanceof TimeoutError) {
          const actualTimeout = error.timeoutMs ?? this.timeoutMs;
          return new APIError(
            `EP API request to ${endpoint} timed out after ${String(actualTimeout)}ms`,
            408,
            { timeoutMs: actualTimeout }
          );
        }
        if (error instanceof APIError) return error;
        return new APIError(
          `EP API request error: ${error instanceof Error ? error.message : 'Unknown error'}`,
          undefined,
          error
        );
      }

      /**
       * Executes a cached, rate-limited GET request to the EP API.
       *
       * @template T - Expected response type (extends `Record<string, unknown>`)
       * @param endpoint - API endpoint path (relative to `baseURL`)
       * @param params - Optional query parameters
       * @param minimumTimeoutMs - Optional per-request minimum timeout in milliseconds.
       *   When provided, the effective timeout is `Math.max(minimumTimeoutMs, this.timeoutMs)`,
       *   so the global timeout (set via `--timeout` or `EP_REQUEST_TIMEOUT_MS`) can still
       *   extend it beyond the per-endpoint minimum.
       *   Use for known slow EP API endpoints such as `procedures/feed`.
       * @returns Promise resolving to the typed API response
       * @throws {APIError} On HTTP errors, network failures, or parse failures
       * @protected
       */
      protected async get<T extends Record<string, unknown>>(
        endpoint: string,
        params?: Record<string, unknown>,
        minimumTimeoutMs?: number
      ): Promise<T> {
        const rlResult = await this.rateLimiter.removeTokens(1);
        Iif (!rlResult.allowed) {
          throw new APIError(
            `Rate limit exceeded. Retry after ${String(rlResult.retryAfterMs)}ms`,
            429,
            { retryAfterMs: rlResult.retryAfterMs, remainingTokens: rlResult.remainingTokens }
          );
        }

        const cacheKey = this.getCacheKey(endpoint, params);

        const cacheStart = performance.now();
        const cached = this.cache.get(cacheKey);
        if (cached !== undefined) {
          this.cacheCounters.hits++;
          performanceMonitor.recordDuration('ep_api_cache_hit', performance.now() - cacheStart);
          return cached as T;
        }
        this.cacheCounters.misses++;

        const url = this.buildRequestUrl(endpoint, params);
        const requestStart = performance.now();

        try {
          const data = await this.fetchWithRetry<T>(url, endpoint, minimumTimeoutMs);
          performanceMonitor.recordDuration('ep_api_request', performance.now() - requestStart);
          this.cache.set(cacheKey, data);
          return data;
        } catch (error: unknown) {
          performanceMonitor.recordDuration('ep_api_request_failed', performance.now() - requestStart);
          throw this.toAPIError(error, endpoint);
        }
      }

      /**
       * Generates a deterministic cache key.
       * @param endpoint - API endpoint path
       * @param params - Optional query parameters
       * @returns JSON string used as cache key
       * @private
       */
      private getCacheKey(
        endpoint: string,
        params?: Record<string, unknown>
      ): string {
        const sortedParams = params !== undefined
          ? Object.fromEntries(Object.entries(params).sort(([a], [b]) => a.localeCompare(b)))
          : undefined;
        return JSON.stringify({ endpoint, params: sortedParams });
      }

      /**
       * Clears all entries from the LRU cache.
       * @public
       */
      clearCache(): void {
        this.cache.clear();
      }

      /**
       * Evicts a single cache entry matching the given endpoint and params.
       * Sub-clients use this when they detect that a successfully-fetched payload
       * is a content-pending sentinel that must not be served from cache for the
       * remainder of the TTL — eviction lets availability recover as soon as the
       * upstream document is enriched.
       *
       * @param endpoint - API endpoint path (same value passed to {@link get})
       * @param params - Optional query parameters (same value passed to {@link get})
       * @protected
       */
      protected evictFromCache(endpoint: string, params?: Record<string, unknown>): void {
        this.cache.delete(this.getCacheKey(endpoint, params));
      }

      /**
       * Returns cache statistics for monitoring and debugging.
       * @returns `{ size, maxSize, hitRate, hits, misses }`
       * @public
       */
      getCacheStats(): { size: number; maxSize: number; hitRate: number; hits: number; misses: number } {
        const { hits, misses } = this.cacheCounters;
        const total = hits + misses;
        return {
          size: this.cache.size,
          maxSize: this.cache.max,
          hitRate: total > 0 ? hits / total : 0,
          hits,
          misses,
        };
      }
    }