snort/src/Feed/Subscription.ts

import { useEffect, useMemo, useReducer, useState } from "react";
import { System } from "Nostr/System";
import { TaggedRawEvent } from "Nostr";
import { Subscriptions } from "Nostr/Subscriptions";
import { debounce } from "Util";
import { db } from "Db";

export type NoteStore = {
  notes: Array<TaggedRawEvent>;
  end: boolean;
};

export type UseSubscriptionOptions = {
  leaveOpen: boolean;
  cache: boolean;
};

interface ReducerArg {
  type: "END" | "EVENT" | "CLEAR";
  ev?: TaggedRawEvent | Array<TaggedRawEvent>;
  end?: boolean;
}

function notesReducer(state: NoteStore, arg: ReducerArg) {
  if (arg.type === "END") {
    return {
      notes: state.notes,
      end: arg.end!,
    } as NoteStore;
  }

  if (arg.type === "CLEAR") {
    return {
      notes: [],
      end: state.end,
    } as NoteStore;
  }

  let evs = arg.ev!;
  if (!Array.isArray(evs)) {
    evs = [evs];
  }
  let existingIds = new Set(state.notes.map((a) => a.id));
  evs = evs.filter((a) => !existingIds.has(a.id));
  if (evs.length === 0) {
    return state;
  }
  return {
    notes: [...state.notes, ...evs],
  } as NoteStore;
}

const initStore: NoteStore = {
  notes: [],
  end: false,
};

export interface UseSubscriptionState {
  store: NoteStore;
  clear: () => void;
  append: (notes: TaggedRawEvent[]) => void;
}

/**
 * Wait time before returning changed state
 */
const DebounceMs = 200;

/**
 *
 * @param {Subscriptions} sub
 * @param {any} opt
 * @returns
 */
export default function useSubscription(
  sub: Subscriptions | null,
  options?: UseSubscriptionOptions
): UseSubscriptionState {
  const [state, dispatch] = useReducer(notesReducer, initStore);
  const [debounceOutput, setDebounceOutput] = useState<number>(0);
  const [subDebounce, setSubDebounced] = useState<Subscriptions>();
  const useCache = useMemo(() => options?.cache === true, [options]);

  useEffect(() => {
    if (sub) {
      return debounce(DebounceMs, () => {
        setSubDebounced(sub);
      });
    }
  }, [sub, options]);

  useEffect(() => {
    if (subDebounce) {
      dispatch({
        type: "END",
        end: false,
      });

      if (useCache) {
        // preload notes from db
        PreloadNotes(subDebounce.Id)
          .then((ev) => {
            dispatch({
              type: "EVENT",
              ev: ev,
            });
          })
          .catch(console.warn);
      }
      subDebounce.OnEvent = (e) => {
        dispatch({
          type: "EVENT",
          ev: e,
        });
        if (useCache) {
          db.events.put(e);
        }
      };

      subDebounce.OnEnd = (c) => {
        if (!(options?.leaveOpen ?? false)) {
          c.RemoveSubscription(subDebounce.Id);
          if (subDebounce.IsFinished()) {
            System.RemoveSubscription(subDebounce.Id);
          }
        }
        dispatch({
          type: "END",
          end: true,
        });
      };

      console.debug("Adding sub: ", subDebounce.ToObject());
      System.AddSubscription(subDebounce);
      return () => {
        console.debug("Removing sub: ", subDebounce.ToObject());
        System.RemoveSubscription(subDebounce.Id);
      };
    }
  }, [subDebounce, useCache]);

  useEffect(() => {
    if (subDebounce && useCache) {
      return debounce(500, () => {
        TrackNotesInFeed(subDebounce.Id, state.notes).catch(console.warn);
      });
    }
  }, [state, useCache]);

  useEffect(() => {
    return debounce(DebounceMs, () => {
      setDebounceOutput((s) => (s += 1));
    });
  }, [state]);

  const stateDebounced = useMemo(() => state, [debounceOutput]);
  return {
    store: stateDebounced,
    clear: () => {
      dispatch({ type: "CLEAR" });
    },
    append: (n: TaggedRawEvent[]) => {
      dispatch({
        type: "EVENT",
        ev: n,
      });
    },
  };
}

/**
 * Lookup cached copy of feed
 */
const PreloadNotes = async (id: string): Promise<TaggedRawEvent[]> => {
  const feed = await db.feeds.get(id);
  if (feed) {
    const events = await db.events.bulkGet(feed.ids);
    return events.filter((a) => a !== undefined).map((a) => a!);
  }
  return [];
};

const TrackNotesInFeed = async (id: string, notes: TaggedRawEvent[]) => {
  const existing = await db.feeds.get(id);
  const ids = Array.from(
    new Set([...(existing?.ids || []), ...notes.map((a) => a.id)])
  );
  const since = notes.reduce(
    (acc, v) => (acc > v.created_at ? v.created_at : acc),
    +Infinity
  );
  const until = notes.reduce(
    (acc, v) => (acc < v.created_at ? v.created_at : acc),
    -Infinity
  );
  await db.feeds.put({ id, ids, since, until });
};