// The homepage summary's inputs, gathered ONCE for both consumers: the homepage
// (compose-homepage writes the whole summary) and the hub (compose-hub writes
// the `official` + per-site projection, lib/hubSummary.ts). Both call
// buildPoolSummary, so the two sites cannot disagree about a number.
//
// NOT read-only: buildStats keeps its incremental per-video state in the index
// LMDB (`statsByPath`), and writes the whole-pool stats pages into `statsDir`.
// Requires build:index to have populated the cues sub-DB first.

import path from "node:path";
import { mkdir, readFile } from "node:fs/promises";
import type { Paths } from "../lib/paths";
import { buildStats } from "./buildStats";
import { isListedSite, listSites, type Site } from "../lib/site";
import { getSettings } from "../lib/settings";
import { publishedMemberSlugs } from "../lib/postsVisibility";
import { readChannelConfig } from "./channels";
import {
  statsPageFileName,
  type StatsManifest,
  type VideoStat,
} from "../lib/stats";
import {
  buildHomepageSummary,
  type ChannelSitesMap,
  type HomepageSummary,
} from "../lib/homepageSummary";

// Read the whole-pool stats dataset back from the pages buildStats just wrote, so
// the lightweight summary can be derived from the same records without
// re-extracting. Pages are local files (fast) capped well under memory limits.
export async function readStatsPages(statsDir: string): Promise<VideoStat[]> {
  let manifest: StatsManifest;
  try {
    manifest = JSON.parse(
      await readFile(path.join(statsDir, "manifest.json"), "utf8"),
    ) as StatsManifest;
  } catch {
    return [];
  }
  const out: VideoStat[] = [];
  for (let i = 0; i < manifest.pageCount; i++) {
    const page = JSON.parse(
      await readFile(path.join(statsDir, statsPageFileName(i)), "utf8"),
    ) as VideoStat[];
    out.push(...page);
  }
  return out;
}

// channel slug -> the ids of the LISTED content sites that expose it: the
// published `channel-sites.json`. A channel on multiple sites maps to all of
// them; a pool-only channel is simply absent, and so is an unlisted site
// (site.json `listed: false`) and a channel only unlisted sites expose.
//
// `membersOf` answers the members a site's build publishes; absent, every
// member. buildPoolSummary passes lib/postsVisibility.ts's narrowing, so an X
// channel a public site leaves out while X posts are private is not mapped to
// that site here either.
export function channelSitesOf(
  sites: readonly Site[],
  membersOf: (site: Site) => readonly string[] = (site) =>
    site.channels.map((c) => c.slug),
): ChannelSitesMap {
  const channelSites: ChannelSitesMap = {};
  for (const site of sites) {
    if (!isListedSite(site)) continue;
    for (const slug of membersOf(site)) {
      (channelSites[slug] ??= []).push(site.siteId);
    }
  }
  return channelSites;
}

export type PoolSummary = {
  summary: HomepageSummary;
  channelSites: ChannelSitesMap;
  sites: Site[];
};

// Refresh the whole-pool stats into `statsDir`, then summarise them.
export async function buildPoolSummary(opts: {
  paths: Paths;
  statsDir: string;
  now?: Date;
}): Promise<PoolSummary> {
  const { paths, statsDir } = opts;
  await mkdir(statsDir, { recursive: true });
  // Whole-pool stats dataset (every non-excluded channel but those only
  // unlisted sites expose). buildStats also refreshes the per-site bundles as a
  // side effect, which is harmless.
  await buildStats({ paths, wholePoolStatsDir: statsDir });
  const sites = listSites(paths);
  // The members each site's build publishes (lib/postsVisibility.ts).
  const configs = new Map<string, Awaited<ReturnType<typeof readChannelConfig>>>();
  for (const slug of new Set(sites.flatMap((s) => s.channels.map((c) => c.slug)))) {
    configs.set(slug, await readChannelConfig(paths, slug).catch(() => null));
  }
  const settings = getSettings();
  const channelSites = channelSitesOf(sites, (site) =>
    publishedMemberSlugs(site, (slug) => configs.get(slug), settings),
  );
  const stats = await readStatsPages(statsDir);
  const summary = buildHomepageSummary(
    stats,
    channelSites,
    sites,
    opts.now ?? new Date(),
  );
  return { summary, channelSites, sites };
}