/**
 * Gathers what the whole site did over a period, for the `/community` page
 * and the digests' shared sections. The digests ask {@link communityStatsOf}
 * for each reader's own period. The page reads the figures of the week and
 * the month ending at the last refresh, which {@link communityJob} redoes
 * every {@link COMMUNITY_REFRESH_MINUTES}, so a visit runs no query.
 *
 * @module
 */

import { db } from "../db/connection.ts";
import { COMMUNITY_REFRESH_MINUTES } from "../config.ts";
import type { CommunityStats } from "../../shared/community.ts";
import {
  DIGEST_CADENCES,
  type DigestCadence,
  PERIOD_MS,
} from "../../shared/settings.ts";
import type { Job } from "../lib/scheduler.ts";
import { listTopDumps } from "./dump-service.ts";
import { listNewPublicPlaylists } from "./playlist-service.ts";
import { listNewUsers } from "./user-service.ts";

/** How many top dumps a period keeps, as many as the monthly recap shows. */
const TOP_MAX = 10;

/** Returns how many rows of `table` were created from `from` to `to`. */
function countOf(
  table: string,
  from: string,
  to: string,
  where = "1",
): number {
  return (db.prepare(
    `SELECT COUNT(*) AS n FROM ${table}
      WHERE ${where} AND created_at >= ? AND created_at < ?;`,
  ).get(from, to) as { n: number }).n;
}

/**
 * Returns what the site did from `from` to `to`: its most upvoted public
 * dumps, who joined, the new public playlists, the chat's messages and the
 * totals.
 */
export function communityStatsOf(from: Date, to: Date): CommunityStats {
  const [f, t] = [from.toISOString(), to.toISOString()];
  return {
    from,
    to,
    top: listTopDumps(from, to, TOP_MAX),
    members: listNewUsers(from, to),
    playlists: listNewPublicPlaylists(from, to),
    chatMessages: countOf("chat_messages", f, t),
    totals: {
      dumps: countOf("dumps", f, t, "is_private = 0"),
      upvotes: countOf("votes", f, t),
      comments: countOf("comments", f, t, "deleted = 0"),
    },
  };
}

/** The figures {@link getCommunityStats} serves, by period. */
const latest = new Map<DigestCadence, CommunityStats>();

/** Recomputes the figures of each period, ending at `now`. */
export function refreshCommunityStats(now: Date = new Date()): void {
  for (const period of DIGEST_CADENCES) {
    latest.set(
      period,
      communityStatsOf(new Date(now.getTime() - PERIOD_MS[period]), now),
    );
  }
}

/**
 * Returns the figures of `period` as of the last refresh, for
 * `GET /api/community`, refreshing them first if there are none yet.
 */
export function getCommunityStats(period: DigestCadence): CommunityStats {
  if (!latest.has(period)) refreshCommunityStats();
  return latest.get(period)!;
}

/**
 * Refreshes the figures at startup, then every
 * {@link COMMUNITY_REFRESH_MINUTES}. `main.ts` starts it.
 */
export const communityJob: Job = {
  name: "community",
  everyMs: COMMUNITY_REFRESH_MINUTES * 60_000,
  firstAfterMs: 0,
  run: () => refreshCommunityStats(),
};