'use strict';

const PUBLIC_MODES = new Set(['missing', 'latest', 'last', 'first', 'chapter', 'after', 'volume']);

function chapterNumber(value, field = 'chapter') {
  const raw = String(value ?? '').trim();
  if (!/^\d+(?:\.\d+)?$/.test(raw)) throw new Error(`${field} must be a numeric chapter`);
  const [whole, decimal = ''] = raw.split('.');
  const normalizedWhole = whole.replace(/^0+(?=\d)/, '') || '0';
  const normalizedDecimal = decimal.replace(/0+$/, '');
  return normalizedDecimal ? `${normalizedWhole}.${normalizedDecimal}` : normalizedWhole;
}

function positiveCount(value) {
  const count = Number(value);
  if (!Number.isInteger(count) || count < 1 || count > 10000) throw new Error('count must be an integer from 1 to 10000');
  return count;
}

function normalizeScope(input = {}) {
  const raw = input && typeof input === 'object' ? input : {};
  const mode = String(raw.mode || 'missing').toLowerCase();
  if (mode === 'ids') {
    if (!Array.isArray(raw.ids) || !raw.ids.length || raw.ids.length > 10000) throw new Error('ids scope requires 1 to 10000 source chapter ids');
    return { mode, ids: [...new Set(raw.ids.map(value => String(value).trim()).filter(Boolean))] };
  }
  if (!PUBLIC_MODES.has(mode)) throw new Error(`Unsupported queue scope: ${mode}`);
  if (mode === 'last' || mode === 'first') return { mode, count: positiveCount(raw.count) };
  if (mode === 'chapter' || mode === 'after') return { mode, chapter: chapterNumber(raw.chapter) };
  if (mode === 'volume') {
    const volume = String(raw.volume ?? '').trim();
    if (!/^\d+(?:\.\d+)?$/.test(volume)) throw new Error('volume must be numeric');
    return { mode, volume: chapterNumber(volume, 'volume') };
  }
  return { mode };
}

function volumeOf(ref) {
  const value = ref.volume ?? ref.book?.number;
  if (value === undefined || value === null || value === '') return null;
  try { return chapterNumber(value, 'volume'); } catch { return null; }
}

function selectByScope(chapters, input) {
  const scope = normalizeScope(input);
  const list = [...chapters];
  if (scope.mode === 'missing') return list;
  if (scope.mode === 'latest') return list.length ? [list[list.length - 1]] : [];
  if (scope.mode === 'last') return list.slice(-scope.count);
  if (scope.mode === 'first') return list.slice(0, scope.count);
  const numbered = list.filter(ref => /^\d+(?:\.\d+)?$/.test(String(ref.number)));
  if (scope.mode === 'chapter') return numbered.filter(ref => chapterNumber(ref.number) === scope.chapter);
  if (scope.mode === 'after') return numbered.filter(ref => Number(chapterNumber(ref.number)) > Number(scope.chapter));
  if (scope.mode === 'volume') return list.filter(ref => volumeOf(ref) === scope.volume);
  if (scope.mode === 'ids') {
    const ids = new Set(scope.ids);
    return list.filter(ref => ids.has(String(ref.id)));
  }
  return [];
}

function scopeLabel(input) {
  const scope = normalizeScope(input);
  if (scope.mode === 'missing') return 'all missing chapters';
  if (scope.mode === 'latest') return 'newest chapter';
  if (scope.mode === 'last') return `last ${scope.count} chapters`;
  if (scope.mode === 'first') return `first ${scope.count} chapters`;
  if (scope.mode === 'chapter') return `chapter ${scope.chapter}`;
  if (scope.mode === 'after') return `chapters after ${scope.chapter}`;
  if (scope.mode === 'volume') return `volume ${scope.volume}`;
  return `${scope.ids.length} discovered chapters`;
}

module.exports = { normalizeScope, selectByScope, scopeLabel, chapterNumber, volumeOf };