# All files / src/services FeedHealthTracker.ts

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100% Branches 20/20
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     /**
     * Feed Health Tracker Service
     *
     * Tracks the outcome of feed tool invocations to provide
     * cached health status without making upstream API calls.
     *
     * The tracker is a module-level singleton that records success/error
     * outcomes for each feed tool call. The `get_server_health` tool
     * reads from this tracker to report feed availability.
     *
     * ISMS Policy: MO-001 (Monitoring and Alerting), PE-001 (Performance Standards)
     *
     * @module services/FeedHealthTracker
     */

    /**
     * Per-feed health status.
     *
     * | Value     | Meaning |
     * |-----------|---------|
     * | `ok`      | Last invocation succeeded |
     * | `error`   | Last invocation failed |
     * | `unknown` | Feed has not been invoked yet |
     */
    export interface FeedStatus {
      /** Current feed health verdict */
      status: 'ok' | 'error' | 'unknown';
      /** ISO-8601 timestamp of the last successful invocation */
      lastSuccess?: string;
      /** Error message from the last failed invocation */
      lastError?: string;
      /** ISO-8601 timestamp of the last invocation attempt */
      lastAttempt?: string;
    }

    /**
     * Overall feed availability level.
     *
     * | Level        | Condition                                | Description |
     * |--------------|------------------------------------------|-------------|
     * | Full         | ≥10/13 ok                                | Normal operation |
     * | Degraded     | 5–9/13 ok                                | Reduced data quality expected |
     * | Sparse       | 1–4/13 ok                                | Minimal data, analysis-only mode likely |
     * | Unavailable  | 0/13 ok AND ≥1 probed feed errored       | All probed feeds failing |
     * | Unknown      | 0/13 ok AND 0 errors (no probes yet)     | Cache is empty — status cannot be determined without a live probe |
     *
     * `Unknown` is distinct from `Unavailable` to prevent consumers from
     * interpreting "no cached data" as "feeds are down". See issue #1.
     */
    export type AvailabilityLevel = 'Full' | 'Degraded' | 'Sparse' | 'Unavailable' | 'Unknown';

    /** Summary of feed availability. */
    export interface FeedAvailability {
      /** Feeds with `status === 'ok'` in the cache. */
      operationalFeeds: number;
      /** Feeds with `status === 'error'` in the cache. */
      errorFeeds: number;
      /** Feeds that have never been probed (`status === 'unknown'`). */
      unknownFeeds: number;
      totalFeeds: number;
      level: AvailabilityLevel;
    }

    /** All tracked feed tool names. */
    export const FEED_TOOL_NAMES = [
      'get_meps_feed',
      'get_events_feed',
      'get_procedures_feed',
      'get_adopted_texts_feed',
      'get_mep_declarations_feed',
      'get_documents_feed',
      'get_plenary_documents_feed',
      'get_committee_documents_feed',
      'get_plenary_session_documents_feed',
      'get_external_documents_feed',
      'get_parliamentary_questions_feed',
      'get_corporate_bodies_feed',
      'get_controlled_vocabularies_feed',
    ] as const;

    /** Threshold boundaries for availability levels. */
    const FULL_THRESHOLD = 10;
    const DEGRADED_THRESHOLD = 5;

    /**
     * Singleton service that records feed tool invocation outcomes
     * and derives per-feed and overall availability health.
     *
     * Does not make network calls — all data comes from tool dispatch hooks.
     */
    export class FeedHealthTracker {
      private readonly statuses = new Map<string, FeedStatus>();
      private readonly startTime: number;
      private readonly feedToolSet: ReadonlySet<string>;

      constructor() {
        this.startTime = Date.now();
        this.feedToolSet = new Set<string>(FEED_TOOL_NAMES);
      }

      /** Returns `true` when the tool name identifies a tracked feed tool. */
      isFeedTool(name: string): boolean {
        return this.feedToolSet.has(name);
      }

      /** Record a successful feed invocation. Silently ignores unknown feed names. */
      recordSuccess(feedName: string): void {
        if (!this.feedToolSet.has(feedName)) return;
        const now = new Date().toISOString();
        this.statuses.set(feedName, {
          status: 'ok',
          lastSuccess: now,
          lastAttempt: now,
        });
      }

      /** Record a failed feed invocation, preserving the last success timestamp. Silently ignores unknown feed names. */
      recordError(feedName: string, errorMessage: string): void {
        if (!this.feedToolSet.has(feedName)) return;
        const now = new Date().toISOString();
        const existing = this.statuses.get(feedName);
        const entry: FeedStatus = {
          status: 'error',
          lastError: errorMessage,
          lastAttempt: now,
        };
        if (existing?.lastSuccess !== undefined) {
          entry.lastSuccess = existing.lastSuccess;
        }
        this.statuses.set(feedName, entry);
      }

      /** Get the current status of a single feed (defaults to `unknown`). */
      getStatus(feedName: string): FeedStatus {
        return this.statuses.get(feedName) ?? { status: 'unknown' };
      }

      /** Get the statuses of all tracked feeds keyed by tool name. */
      getAllStatuses(): Record<string, FeedStatus> {
        const result: Record<string, FeedStatus> = {};
        for (const name of FEED_TOOL_NAMES) {
          result[name] = this.getStatus(name);
        }
        return result;
      }

      /** Server uptime in whole seconds since tracker creation. */
      getUptimeSeconds(): number {
        return Math.floor((Date.now() - this.startTime) / 1000);
      }

      /** Derive the overall availability level from current feed statuses. */
      getAvailability(): FeedAvailability {
        let operational = 0;
        let errored = 0;
        let unknown = 0;
        for (const name of FEED_TOOL_NAMES) {
          const { status } = this.getStatus(name);
          if (status === 'ok') operational++;
          else if (status === 'error') errored++;
          else unknown++;
        }

        const total = FEED_TOOL_NAMES.length;
        return {
          operationalFeeds: operational,
          errorFeeds: errored,
          unknownFeeds: unknown,
          totalFeeds: total,
          level: deriveLevel(operational, errored),
        };
      }

      /**
       * Reset all tracked statuses.
       * Intended for testing only.
       * @internal
       */
      reset(): void {
        this.statuses.clear();
      }
    }

    /**
     * Map operational feed count to an availability level.
     *
     * When `operational === 0`, we distinguish two cases:
     * - If at least one probed feed has errored, report `Unavailable` (feeds are down).
     * - Otherwise (cache is empty, no probes yet) report `Unknown` — consumers
     *   must not treat "no data" as "feeds are down". See issue #1.
     */
    function deriveLevel(operational: number, errored: number): AvailabilityLevel {
      if (operational >= FULL_THRESHOLD) return 'Full';
      if (operational >= DEGRADED_THRESHOLD) return 'Degraded';
      if (operational >= 1) return 'Sparse';
      if (errored >= 1) return 'Unavailable';
      return 'Unknown';
    }

    /** Global feed health tracker instance used by tool dispatch and the health tool. */
    export const feedHealthTracker = new FeedHealthTracker();