MangaCircus/chapter-dates.js

'use strict';
// Chapter dates (BL-0047). chapter.json keeps three independent dates:
//   added           when the chapter entered this library (kept on replace)
//   x-dates.source  when the source site uploaded it; batch=true marks a bulk import, not a release
//   x-dates.release the official public release (filled by a metadata job; precision "day")
//   x-dates.ecosystem  when it first entered any Manga Circus library; travels over peering, earliest wins
// The reader shows one release date per chapter by tier: official > source (not batch) > ecosystem > library.

const BATCH_SIZE = 3;          // this many uploads ...
const BATCH_GAP_MS = 10 * 60e3; // ... each within 10 minutes of the next form a bulk import

const iso = value => {
  const time = typeof value === 'number' ? value : Date.parse(value);
  return Number.isFinite(time) && time > 0 ? new Date(time).toISOString() : null;
};
const text = (value, max = 120) => (typeof value === 'string' ? value.trim().slice(0, max) : '');

// Returns one flag per item: true when its upload time belongs to a bulk import, null without a time.
function batchFlags(times) {
  const order = times.map((value, index) => ({ index, time: Date.parse(value) }))
    .filter(item => Number.isFinite(item.time)).sort((a, b) => a.time - b.time);
  const flags = times.map(() => null);
  for (let start = 0; start < order.length;) {
    let end = start + 1;
    while (end < order.length && order[end].time - order[end - 1].time <= BATCH_GAP_MS) end++;
    for (let i = start; i < end; i++) flags[order[i].index] = end - start >= BATCH_SIZE;
    start = end;
  }
  return flags;
}

function sourceDate(at, name, batch) {
  const value = iso(at);
  return value ? { at: value, name: text(name), batch: !!batch } : null;
}

function cleanSource(value) {
  return value && typeof value === 'object' ? sourceDate(value.at, value.name, value.batch) : null;
}
function cleanRelease(value) {
  if (!value || typeof value !== 'object' || !iso(value.at)) return null;
  const precision = ['day', 'month', 'year'].includes(value.precision) ? value.precision : 'day';
  return { at: String(value.at).slice(0, 30), precision, source: text(value.source) };
}
function cleanEcosystem(value) {
  if (!value || typeof value !== 'object' || !iso(value.at)) return null;
  return { at: iso(value.at), via: text(value.via) || 'this server' };
}

// chapter.json fields for a (re)published chapter. A prior "added" and an earlier ecosystem
// date always survive; a peer's ecosystem claim may lower the date but never raise it.
function publishedDates(priorMeta = {}, incoming = {}, now = Date.now()) {
  const prior = priorMeta['x-dates'] && typeof priorMeta['x-dates'] === 'object' ? priorMeta['x-dates'] : {};
  const added = iso(priorMeta.added) || iso(incoming.added) || iso(now);
  const source = cleanSource(incoming.source) || cleanSource(prior.source);
  const release = cleanRelease(incoming.release) || cleanRelease(prior.release);
  let claim = cleanEcosystem(incoming.ecosystem);
  if (claim) {
    // Nobody can have had the chapter before the source uploaded it, or in the future.
    const floor = source ? Date.parse(source.at) : 0, time = Math.min(Date.parse(claim.at), now);
    claim = { ...claim, at: iso(Math.max(time, floor)) };
  }
  const candidates = [cleanEcosystem(prior.ecosystem), claim, { at: added, via: 'this server' }].filter(Boolean);
  const ecosystem = candidates.reduce((best, item) => (Date.parse(item.at) < Date.parse(best.at) ? item : best));
  return { added, 'x-dates': { version: 1, ...(source ? { source } : {}), ...(release ? { release } : {}), ecosystem } };
}

// Dates of one library chapter from its versions ({ added: ms, meta: chapter.json }).
function chapterDates(versions) {
  const known = {};
  const keep = (slot, time, value) => {
    if (Number.isFinite(time) && (!known[slot] || time < known[slot].time)) known[slot] = { time, ...value };
  };
  for (const version of versions) {
    const dates = (version.meta && version.meta['x-dates']) || {};
    const release = cleanRelease(dates.release), source = cleanSource(dates.source), ecosystem = cleanEcosystem(dates.ecosystem);
    if (release) keep('official', Date.parse(release.at), { at: release.at, precision: release.precision, name: release.source });
    if (source) keep(source.batch ? 'batch' : 'source', Date.parse(source.at), { at: source.at, name: source.name });
    if (ecosystem) keep('ecosystem', Date.parse(ecosystem.at), { at: ecosystem.at, name: ecosystem.via });
    if (Number.isFinite(version.added)) keep('library', version.added, { at: iso(version.added) });
  }
  const tier = ['official', 'source', 'ecosystem', 'library'].find(slot => known[slot]) || null;
  const out = {};
  for (const [slot, { time, ...value }] of Object.entries(known)) out[slot] = value;
  return { tier, release: tier ? out[tier] : null, known: out };
}

// Ecosystem dates offered to peers: the earliest per chapter number, falling back to "added"
// for chapters published before x-dates existed (this server was then the one that had it).
function ecosystemOf(meta, fallbackMs) {
  const dates = (meta && meta['x-dates']) || {};
  return cleanEcosystem(dates.ecosystem)?.at || iso(meta && meta.added) || iso(fallbackMs);
}
// What a gateway sends with a chapter: only cleaned, non-identifying date fields.
function peerDates(meta, fallbackMs) {
  const dates = (meta && meta['x-dates']) || {};
  const source = cleanSource(dates.source), release = cleanRelease(dates.release), ecosystem = ecosystemOf(meta, fallbackMs);
  return { ...(ecosystem ? { ecosystem } : {}), ...(source ? { source } : {}), ...(release ? { release } : {}) };
}
// Incoming peer dates in publishedDates() shape.
function fromPeer(value, alias) {
  if (!value || typeof value !== 'object') return {};
  const ecosystem = iso(value.ecosystem);
  return { ...(ecosystem ? { ecosystem: { at: ecosystem, via: `peer ${text(alias, 40)}`.trim() } } : {}),
    ...(cleanSource(value.source) ? { source: cleanSource(value.source) } : {}),
    ...(cleanRelease(value.release) ? { release: cleanRelease(value.release) } : {}) };
}

module.exports = { BATCH_SIZE, BATCH_GAP_MS, batchFlags, sourceDate, publishedDates, chapterDates, ecosystemOf, peerDates, fromPeer };