/**
 * Aggregate `download_stats.events` into the public `stats/downloads.json`.
 *
 *   bun stats/publish.ts --out downloads.json   # write locally only
 *   bun stats/publish.ts                        # upload to the bucket and purge the CDN copy
 *
 * The output holds counts only. Distinct clients are counted from the stored
 * HMAC, which never leaves the database, and countries seen from fewer than
 * MIN_CLIENTS clients are folded into "other" so no single client can be
 * picked out by where it is.
 *
 * Every number excludes our own CI runners. Cloud and CI networks are kept but
 * reported separately, since one pipeline can outweigh every person combined.
 */
import { S3Client, type SQL } from 'bun';
import { KNOWN_MINORS, RULESET } from './classify';
import { connect, migrate } from './db';

const MIN_CLIENTS = 3;
const PUBLIC_URL = 'https://cran.rpkgs.com/stats/downloads.json';
const OBJECT_KEY = 'stats/downloads.json';

/** Split of a count by network class. */
export interface Split {
  total: number;
  cloud: number;
  other: number;
}

export interface DayStats {
  date: string;
  /** Hours of this UTC day for which logs were collected (24 = complete). */
  coveredHours: number;
  /** Tarball requests served, before any de-duplication. */
  requests: number;
  /** Distinct (client, package, version) served on the day. */
  downloads: Split;
  /** Distinct clients that fetched an index or a package. */
  clients: Split;
  /** Distinct clients sent to CRAN because we do not build for their R minor. */
  unsupportedMinorClients: number;
  bytes: number;
}

export interface WindowStats {
  days: number;
  downloads: Split;
  /** Distinct clients across the whole window. */
  clients: Split;
  /** Sum of daily distinct clients: roughly, install sessions. */
  clientDays: Split;
}

export interface Breakdown {
  key: string;
  clients: number;
  downloads: number;
}

export interface PackageStats {
  name: string;
  downloads30d: number;
  clients30d: number;
  downloadsAll: number;
}

export interface PublicStats {
  schema: 1;
  ruleset: number;
  generatedAt: string;
  firstDay: string | null;
  lastDay: string | null;
  supportedMinors: string[];
  daily: DayStats[];
  windows: { last7: WindowStats; last30: WindowStats; all: WindowStats };
  /** Distribution of distinct packages fetched per client per day (30 days). */
  packagesPerClientDay: { median: number; p90: number };
  /** Last 30 days. */
  breakdowns: {
    network: Breakdown[];
    os: Breakdown[];
    arch: Breakdown[];
    rMinor: Breakdown[];
    tool: Breakdown[];
    country: Breakdown[];
  };
  /** Last 30 days: clients we sent elsewhere, and why. */
  redirects: { reason: string; clients: number; requests: number }[];
  unsupportedMinors: Breakdown[];
  /** Last 30 days: requests that were not repository use at all. */
  excluded: { ownRunners: number; probes: number; noise: number; errors: number };
  packages: PackageStats[];
}

const split = (row: Record<string, unknown>, prefix: string): Split => ({
  total: Number(row[`${prefix}_total`] ?? 0),
  cloud: Number(row[`${prefix}_cloud`] ?? 0),
  other: Number(row[`${prefix}_other`] ?? 0),
});

async function coverage(sql: SQL): Promise<Map<string, number>> {
  const runs: { window_from: Date; window_to: Date }[] =
    await sql`select window_from, window_to from download_stats.runs order by window_from`;
  const merged: [number, number][] = [];
  for (const run of runs) {
    const from = run.window_from.getTime();
    const to = run.window_to.getTime();
    const last = merged.at(-1);
    if (last && from <= last[1]) last[1] = Math.max(last[1], to);
    else merged.push([from, to]);
  }
  const hours = new Map<string, number>();
  const DAY = 86400000;
  for (const [from, to] of merged) {
    for (let day = Math.floor(from / DAY) * DAY; day < to; day += DAY) {
      const overlap = Math.min(to, day + DAY) - Math.max(from, day);
      const key = new Date(day).toISOString().slice(0, 10);
      hours.set(key, (hours.get(key) ?? 0) + overlap / 3600000);
    }
  }
  return hours;
}

async function windowStats(sql: SQL, days: number | null): Promise<WindowStats> {
  const since = days === null ? new Date(0) : new Date(Date.now() - days * 86400000);
  const [row] = await sql`
    with ev as (
      select client, network, kind, package, version, (ts at time zone 'UTC')::date as day
      from download_stats.events
      where network <> 'own' and outcome = 'served' and kind in ('download', 'index') and ts >= ${since}
    ),
    dl as (select distinct client, network, package, version, day from ev where kind = 'download'),
    cd as (select distinct client, network, day from ev)
    select
      (select count(*) from dl) as downloads_total,
      (select count(*) from dl where network = 'cloud') as downloads_cloud,
      (select count(*) from dl where network = 'other') as downloads_other,
      (select count(distinct client) from ev) as clients_total,
      (select count(distinct client) from ev where network = 'cloud') as clients_cloud,
      (select count(distinct client) from ev where network = 'other') as clients_other,
      (select count(*) from cd) as client_days_total,
      (select count(*) from cd where network = 'cloud') as client_days_cloud,
      (select count(*) from cd where network = 'other') as client_days_other,
      (select min(day) from ev) as first_day`;
  const firstDay = row.first_day ? new Date(row.first_day) : null;
  const span = firstDay ? Math.max(1, Math.ceil((Date.now() - firstDay.getTime()) / 86400000)) : 0;
  return {
    days: days === null ? span : Math.min(days, span),
    downloads: split(row, 'downloads'),
    clients: split(row, 'clients'),
    clientDays: split(row, 'client_days'),
  };
}

async function breakdown(sql: SQL, column: string, since: Date): Promise<Breakdown[]> {
  const rows: { key: string | null; clients: number; downloads: number }[] = await sql`
    with ev as (
      select ${sql(column)}::text as key, client, kind, package, version, (ts at time zone 'UTC')::date as day
      from download_stats.events
      where network <> 'own' and outcome = 'served' and kind in ('download', 'index') and ts >= ${since}
    )
    select key, count(distinct client)::int as clients,
      (select count(*) from (select distinct client, package, version, day from ev e2
        where e2.kind = 'download' and e2.key is not distinct from ev.key) d)::int as downloads
    from ev group by key order by clients desc`;
  return rows.map((row) => ({ key: row.key ?? 'unknown', clients: row.clients, downloads: row.downloads }));
}

/** Fold rows below the client threshold into one "other" row. */
function suppress(rows: Breakdown[]): Breakdown[] {
  const kept = rows.filter((row) => row.clients >= MIN_CLIENTS);
  const folded = rows.filter((row) => row.clients < MIN_CLIENTS);
  if (folded.length === 0) return kept;
  return [
    ...kept,
    {
      key: 'other',
      clients: folded.reduce((sum, row) => sum + row.clients, 0),
      downloads: folded.reduce((sum, row) => sum + row.downloads, 0),
    },
  ];
}

export async function buildStats(sql: SQL): Promise<PublicStats> {
  const since30 = new Date(Date.now() - 30 * 86400000);
  const covered = await coverage(sql);

  const dailyRows: Record<string, unknown>[] = await sql`
    with ev as (
      select *, (ts at time zone 'UTC')::date as day from download_stats.events where network <> 'own'
    ),
    served as (select * from ev where outcome = 'served' and kind in ('download', 'index')),
    dl as (select distinct client, network, package, version, day from served where kind = 'download'),
    cl as (select distinct client, network, day from served)
    select d.day::text as date,
      (select count(*) from served s where s.day = d.day and s.kind = 'download')::int as requests,
      (select count(*) from dl where dl.day = d.day)::int as downloads_total,
      (select count(*) from dl where dl.day = d.day and network = 'cloud')::int as downloads_cloud,
      (select count(*) from dl where dl.day = d.day and network = 'other')::int as downloads_other,
      (select count(*) from cl where cl.day = d.day)::int as clients_total,
      (select count(*) from cl where cl.day = d.day and network = 'cloud')::int as clients_cloud,
      (select count(*) from cl where cl.day = d.day and network = 'other')::int as clients_other,
      (select count(distinct client) from ev e where e.day = d.day and e.redirect_reason = 'unsupported_r_minor')::int
        as unsupported,
      (select coalesce(sum(bytes), 0) from served s where s.day = d.day)::bigint as bytes
    from (select distinct day from ev) d order by d.day`;

  const daily: DayStats[] = dailyRows.map((row) => ({
    date: String(row.date),
    coveredHours: Math.round(Math.min(24, covered.get(String(row.date)) ?? 0) * 10) / 10,
    requests: Number(row.requests),
    downloads: split(row, 'downloads'),
    clients: split(row, 'clients'),
    unsupportedMinorClients: Number(row.unsupported),
    bytes: Number(row.bytes),
  }));

  const [perSession] = await sql`
    with per as (
      select client, (ts at time zone 'UTC')::date as day, count(distinct (package, version)) as n
      from download_stats.events
      where network <> 'own' and outcome = 'served' and kind = 'download' and ts >= ${since30}
      group by 1, 2
    )
    select coalesce(percentile_cont(0.5) within group (order by n), 0) as median,
      coalesce(percentile_cont(0.9) within group (order by n), 0) as p90
    from per`;

  const redirects: { reason: string; clients: number; requests: number }[] = await sql`
    select redirect_reason as reason, count(distinct client)::int as clients, count(*)::int as requests
    from download_stats.events
    where network <> 'own' and outcome = 'redirect' and ts >= ${since30}
      and redirect_reason not in ('minor_routing', 'slot_resolution', 'https')
    group by 1 order by clients desc`;

  const unsupportedMinors: Breakdown[] = await sql`
    select r_minor as key, count(distinct client)::int as clients, count(*)::int as downloads
    from download_stats.events
    where network <> 'own' and redirect_reason = 'unsupported_r_minor' and ts >= ${since30}
    group by 1 order by clients desc`;

  const [excluded] = await sql`
    select
      count(*) filter (where network = 'own')::int as own,
      count(*) filter (where network <> 'own' and kind = 'probe')::int as probes,
      count(*) filter (where network <> 'own' and kind = 'noise')::int as noise,
      count(*) filter (where network <> 'own' and kind in ('download', 'index') and outcome = 'error')::int as errors
    from download_stats.events where ts >= ${since30}`;

  const packages: PackageStats[] = (
    await sql`
      with dl as (
        select distinct client, package, version, (ts at time zone 'UTC')::date as day, ts >= ${since30} as recent
        from download_stats.events
        where network <> 'own' and outcome = 'served' and kind = 'download' and package is not null
      )
      select package as name,
        count(*) filter (where recent)::int as downloads30d,
        count(distinct client) filter (where recent)::int as clients30d,
        count(*)::int as downloadsall
      from dl group by package order by downloads30d desc, downloadsall desc, name`
  ).map((row: Record<string, unknown>) => ({
    name: String(row.name),
    downloads30d: Number(row.downloads30d),
    clients30d: Number(row.clients30d),
    downloadsAll: Number(row.downloadsall),
  }));

  return {
    schema: 1,
    ruleset: RULESET,
    generatedAt: new Date().toISOString(),
    firstDay: daily[0]?.date ?? null,
    lastDay: daily.at(-1)?.date ?? null,
    supportedMinors: [...KNOWN_MINORS],
    daily,
    windows: {
      last7: await windowStats(sql, 7),
      last30: await windowStats(sql, 30),
      all: await windowStats(sql, null),
    },
    packagesPerClientDay: { median: Number(perSession.median), p90: Number(perSession.p90) },
    breakdowns: {
      network: await breakdown(sql, 'network', since30),
      os: await breakdown(sql, 'os', since30),
      arch: await breakdown(sql, 'arch', since30),
      rMinor: await breakdown(sql, 'r_minor', since30),
      tool: await breakdown(sql, 'tool', since30),
      country: suppress(await breakdown(sql, 'country', since30)),
    },
    redirects,
    unsupportedMinors,
    excluded: {
      ownRunners: Number(excluded.own),
      probes: Number(excluded.probes),
      noise: Number(excluded.noise),
      errors: Number(excluded.errors),
    },
    packages,
  };
}

async function upload(body: string): Promise<void> {
  const s3 = new S3Client({
    accessKeyId: process.env.B2_S3_ACCESS_KEY,
    secretAccessKey: process.env.B2_S3_SECRET_KEY,
    bucket: process.env.STATS_BUCKET ?? 'devxy-rpkgs-binaries',
    endpoint: 'https://s3.eu-central-003.backblazeb2.com',
    region: 'eu-central-003',
  });
  await s3.write(OBJECT_KEY, body, { type: 'application/json' });

  // The pull zone overrides origin caching with a one-year TTL, so the edge
  // copy has to be purged for the new file to show up.
  const purge = new URL('https://api.bunny.net/purge');
  purge.searchParams.set('url', PUBLIC_URL);
  purge.searchParams.set('async', 'false');
  const response = await fetch(purge, { method: 'POST', headers: { AccessKey: process.env.BUNNYNET_API_KEY ?? '' } });
  if (!response.ok) throw new Error(`purging ${PUBLIC_URL} failed with ${response.status}: ${await response.text()}`);
}

if (import.meta.main) {
  const sql = connect();
  await migrate(sql);
  const stats = await buildStats(sql);
  await sql.close();
  const body = JSON.stringify(stats);

  const outIndex = process.argv.indexOf('--out');
  if (outIndex !== -1) {
    await Bun.write(process.argv[outIndex + 1], JSON.stringify(stats, null, 2));
    console.log(`wrote ${process.argv[outIndex + 1]} (${body.length} bytes)`);
  } else {
    await upload(body);
    console.log(
      `published ${PUBLIC_URL} (${body.length} bytes, ${stats.daily.length} days, ${stats.packages.length} packages)`,
    );
  }
}