/**
 * VideoEventBuffer
 *
 * Handles buffering and batch processing of incoming video events
 * to prevent UI thrashing during high-volume updates (e.g. initial load).
 */

import { isDevMode } from "../config.js";
import { devLogger, userLogger } from "../utils/logger.js";
import { convertEventToVideo } from "./nip71.js";

// Default: trust relays for the public video feed (no per-event signature
// verification). Verifying every feed event off-thread proved fragile (it could
// hang/blank the feed and added load latency), so it is opt-in: pass a
// `verifyEvents` function (e.g. verifyEventsInWorker) to re-enable it.
const trustAllVerifier = (events) =>
  Promise.resolve(new Set((events || []).map((e) => e && e.id).filter(Boolean)));

export class VideoEventBuffer {
  /**
   * @param {import("./client.js").NostrClient} client - The parent client instance (for state access).
   * @param {function(object[]): void} onVideo - The UI callback to fire with batched updates.
   * @param {{ verifyEvents?: (events: object[]) => Promise<Set<string>> }} [options]
   *   Optional signature verifier (returns the set of valid event ids). Defaults
   *   to trusting relays (no verification) for the public feed.
   */
  constructor(client, onVideo, options = {}) {
    this.client = client;
    this.onVideo = onVideo;
    this.buffer = [];
    this.invalidEvents = [];
    this.flushTimerId = null;
    this.FLUSH_DEBOUNCE_MS = 75;
    this._verifyEvents =
      typeof options.verifyEvents === "function"
        ? options.verifyEvents
        : trustAllVerifier;
    // Tracks the in-flight verify+commit so callers/tests can await a flush.
    this._flushPromise = Promise.resolve();

    // Buffer updates while hidden to avoid UI thrashing
    this.pendingVideos = [];
    this.handleVisibilityChange = this.handleVisibilityChange.bind(this);
    if (typeof document !== "undefined") {
      document.addEventListener("visibilitychange", this.handleVisibilityChange);
    }
  }

  /**
   * Pushes a raw event into the buffer and schedules a debounced flush.
   * @param {import("nostr-tools").Event} event - The incoming Nostr event.
   */
  push(event) {
    this.buffer.push(event);
    this.scheduleFlush(false);
  }

  /**
   * Schedules processing of the buffer.
   * Uses a debounce timer to wait for the stream to pause (pressure valve).
   *
   * @param {boolean} [immediate=false] - If true, flushes immediately (e.g. on EOSE).
   */
  scheduleFlush(immediate = false) {
    if (this.flushTimerId) {
      if (!immediate) {
        return this._flushPromise;
      }
      clearTimeout(this.flushTimerId);
      this.flushTimerId = null;
    }

    if (immediate) {
      return this.flush();
    }

    this.flushTimerId = setTimeout(() => {
      this.flushTimerId = null;
      this.flush();
    }, this.FLUSH_DEBOUNCE_MS);
    return this._flushPromise;
  }

  /**
   * Processes all buffered events in a single batch.
   *
   * **Steps:**
   * 1. Validates and converts raw events to Video objects.
   * 2. Checks for tombstones (deleted videos).
   * 3. Updates the client's `activeMap` (Latest Wins).
   * 4. Triggers the UI callback *once*.
   * 5. Triggers background hydration of NIP-71 metadata.
   * 6. Persists state to IndexedDB.
   */
  flush() {
    if (!this.buffer.length) {
      return;
    }

    const toProcess = this.buffer;
    this.buffer = [];
    // The relay pool no longer verifies signatures on the main thread (that cost
    // ~1.2s during feed load). Verify this batch off-thread and commit only the
    // events that pass; fail closed (drop the batch) on total verification
    // failure rather than rendering unverified content. Returns the in-flight
    // promise so callers/tests can await commit completion.
    this._flushPromise = this._verifyAndCommit(toProcess);
    return this._flushPromise;
  }

  async _verifyAndCommit(toProcess) {
    let verified;
    try {
      const validIds = await this._verifyEvents(toProcess);
      verified = toProcess.filter((evt) => evt && evt.id && validIds.has(evt.id));
      const dropped = toProcess.length - verified.length;
      if (dropped > 0) {
        devLogger.warn(
          `[VideoEventBuffer] Dropped ${dropped} event(s) with invalid/unverifiable signatures.`,
        );
      }
    } catch (error) {
      devLogger.error(
        "[VideoEventBuffer] Signature verification failed; dropping batch:",
        error,
      );
      return;
    }
    if (!verified.length) {
      return;
    }
    this._commitVerifiedBatch(verified);
  }

  _commitVerifiedBatch(toProcess) {
    const updatedVideos = [];

    for (const evt of toProcess) {
      try {
        if (evt && evt.id) {
          this.client.rawEvents.set(evt.id, evt);
        }
        const video = convertEventToVideo(evt);

        if (video.invalid) {
          this.invalidEvents.push({ id: video.id, reason: video.reason });
          continue;
        }

        // Merge any NIP-71 metadata we might already have cached for this video
        this.client.mergeNip71MetadataIntoVideo(video);
        // Determine the "true" creation time of the root video
        this.client.applyRootCreatedAt(video);

        const activeKey = this.client.getActiveKey(video);
        const wasDeletedEvent = video.deleted === true;

        // If this is a deletion event (Kind 5 or deletion marker), record a tombstone
        // to prevent older versions from resurrecting.
        if (wasDeletedEvent) {
          this.client.recordTombstone(activeKey, video.created_at);
        } else {
          // Otherwise, check if this video is already known to be deleted
          this.client.applyTombstoneGuard(video);
        }

        // Store in allEvents (history preservation)
        this.client.allEvents.set(evt.id, video);
        this.client.dirtyEventIds.add(evt.id);

        // If it's a "deleted" note, remove from activeMap
        if (video.deleted) {
          if (activeKey) {
            if (wasDeletedEvent) {
              this.client.activeMap.delete(activeKey);
            } else {
              const currentActive = this.client.activeMap.get(activeKey);
              if (currentActive?.id === video.id) {
                this.client.activeMap.delete(activeKey);
              }
            }
          }
          updatedVideos.push(video);
          continue;
        }

        // LATEST-WINS LOGIC
        // We only update the UI if the incoming video is newer than what we have.
        // This handles the "Edit" case where multiple versions exist on relays.
        const prevActive = this.client.activeMap.get(activeKey);
        if (!prevActive || video.created_at > prevActive.created_at) {
          this.client.activeMap.set(activeKey, video);
          updatedVideos.push(video);
        }
      } catch (err) {
        devLogger.error("[VideoEventBuffer] Error processing event:", err);
      }
    }

    if (updatedVideos.length > 0) {
      if (typeof document !== "undefined" && document.hidden) {
        this.pendingVideos.push(...updatedVideos);
      } else {
        // Trigger the callback once per batch to avoid UI thrashing
        this.onVideo(updatedVideos);
      }

      // Fetch NIP-71 metadata (categorization tags) in the background for the whole batch
      this.client.populateNip71MetadataForVideos(updatedVideos)
        .then(() => {
          for (const video of updatedVideos) {
            this.client.applyRootCreatedAt(video);
          }
        })
        .catch((error) => {
          devLogger.warn(
            "[nostr] Failed to hydrate NIP-71 metadata for live video batch:",
            error
          );
        });
    }

    // Persist processed events after each flush so reloads warm quickly.
    this.client.saveLocalData("subscribeVideos:flush");
  }

  handleVisibilityChange() {
    if (typeof document !== "undefined" && !document.hidden) {
      if (this.pendingVideos.length > 0) {
        const batch = this.pendingVideos;
        this.pendingVideos = [];
        this.onVideo(batch);
      }
    }
  }

  /**
   * Called when the subscription reaches End-of-Stored-Events (EOSE).
   * Triggers an immediate flush to ensure the UI is fully up-to-date.
   */
  handleEose() {
    if (isDevMode && this.invalidEvents.length > 0) {
      userLogger.warn(
        `[subscribeVideos] found ${this.invalidEvents.length} invalid video notes (with reasons):`,
        this.invalidEvents
      );
    }
    devLogger.log(
      "[subscribeVideos] Reached EOSE for all relays (historical load done)"
    );
    return this.scheduleFlush(true);
  }

  /**
   * Cleans up timers and flushes any remaining events.
   * Call when unsubscribing.
   */
  cleanup() {
    if (this.flushTimerId) {
      clearTimeout(this.flushTimerId);
      this.flushTimerId = null;
    }
    if (typeof document !== "undefined") {
      document.removeEventListener("visibilitychange", this.handleVisibilityChange);
    }
    // Ensure any straggling events are flushed before tearing down.
    return this.flush();
  }
}