// A group's timetable by date, with week numbers already applied. Native and
// third-party clients use it instead of re-implementing the white/green week rules.
import { semesterView, addDays, weekday, weekIndexOf } from "../shared/weeks.js";
import { lessonKey, subgroupsOf } from "../shared/lessons.js";
import { occurrence, peopleAndRooms, roomsOn } from "./directory.js";
import { apiError } from "./errors.js";

const MAX_DAYS = 62;
// A whole semester with its session fits easily; the cap only guards against abuse.
const MAX_SEMESTER_DAYS = 200;
const DAY_MS = 86_400_000;

function lessonOut(lesson, group, people, date, status, calendar) {
  const bell = calendar?.bells.find((b) => b.start === lesson.start);
  const rooms = date ? roomsOn(people, date) : people.rooms;
  return {
    key: lessonKey(lesson, group),
    start: lesson.start,
    end: lesson.end || bell?.end || null,
    pair: bell?.pair ?? null,
    subject: lesson.subject,
    type: lesson.type,
    teachers: people.teachers,
    rooms,
    roomMoved: Boolean(date && rooms !== people.rooms),
    distance: people.distance,
    condition: lesson.condition,
    variant: lesson.variant,
    subgroup: lesson.subgroups.find((s) => s.group === group)?.label || null,
    groups: lesson.groups,
    uncertain: status === "maybe",
    raw: lesson.raw,
  };
}

/**
 * days: one entry per date from `from`, with the lessons that take place that day.
 * weekly: the Word rows by weekday, for when dates cannot be calculated.
 */
export function timetable({ file, schedule, calendar, group, from, days, range, today, session: extra = [] }) {
  if (!schedule.groups.includes(group)) {
    throw apiError(404, "group_not_found", `В документе нет группы ${group}.`);
  }
  let count = Math.min(Math.max(Number(days) || 7, 1), MAX_DAYS);
  const lessons = schedule.lessons.filter((l) => l.groups.includes(group));
  // A session schedule printed with a date on every day needs no week table: its own dates
  // say when each lesson takes place, even in a year the table no longer covers.
  const sessionDates = lessons.every((l) => l.date || l.dates?.length)
    ? lessons.flatMap((l) => (l.date ? [l.date] : l.dates)).sort()
    : [];
  const session = sessionDates.length
    ? {
        id: `session-${sessionDates[0]}`,
        label: schedule.period || "Сессия",
        start: sessionDates[0],
        end: sessionDates.at(-1),
      }
    : null;
  // range=semester: every day of the semester `today` falls in, so a client can keep
  // the whole term offline; a session schedule keeps its own span. Without either it
  // keeps the plain from/days window. Exams and credits from other documents may follow
  // the last week of the semester: the span then runs on to the last of them (up to 60 days).
  if (range === "semester") {
    const current = semesterView(calendar, schedule, today || from);
    const span = current?.semester || session;
    if (span) {
      from = span.start;
      const limit = addDays(span.end, 60);
      const end = [span.end, ...extra.flatMap((e) => (e.lesson.date ? [e.lesson.date] : e.lesson.dates))]
        .filter((d) => d >= from && d <= limit)
        .sort()
        .at(-1);
      const length = Math.round((Date.parse(end) - Date.parse(from)) / DAY_MS) + 1;
      count = Math.min(Math.max(length, 1), MAX_SEMESTER_DAYS);
    }
  }
  const entries = lessons.map((lesson) => ({
    doc: { id: file.id, schedule },
    lesson,
    ...peopleAndRooms(lesson, schedule.academicYear),
  }));
  const view = semesterView(calendar, schedule, from);
  const views = new Map();
  const out = [];
  for (let i = 0; i < count; i++) {
    const date = addDays(from, i);
    const week = view ? view.weeks[weekIndexOf(view, date)] || null : null;
    const dayLessons = [];
    if (view || session)
      for (const entry of entries) {
        const status = occurrence(entry, date, calendar, views);
        if (status === "yes" || status === "maybe")
          dayLessons.push(lessonOut(entry.lesson, group, entry, date, status, calendar));
      }
    // Session events printed with their own date need no week table.
    for (const entry of extra)
      if (entry.lesson.date === date || entry.lesson.dates?.includes(date))
        dayLessons.push(lessonOut(entry.lesson, group, entry, date, "yes", calendar));
    dayLessons.sort((a, b) => a.start.localeCompare(b.start));
    out.push({
      date,
      weekday: weekday(date),
      week: week ? { n: week.n, color: week.color } : null,
      lessons: dayLessons,
    });
  }
  const weekly = [1, 2, 3, 4, 5, 6, 7]
    .map((day) => ({
      day,
      lessons: entries
        .filter((e) => e.lesson.day === day && !e.lesson.date)
        .map((e) => lessonOut(e.lesson, group, e, null, "yes", calendar))
        .sort((a, b) => a.start.localeCompare(b.start)),
    }))
    .filter((d) => d.lessons.length);
  return {
    group,
    document: {
      id: file.id,
      name: file.name,
      faculty: file.faculty || schedule.source.faculty || "",
      course: file.course || schedule.source.course || "",
      modified: file.modified || schedule.source.modified || null,
    },
    period: schedule.period,
    semester: view?.semester || session,
    note: view || session
      ? null
      : "Семестр этого расписания не найден в таблице недель: даты не рассчитаны, смотрите строки Word (weekly).",
    subgroups: [
      ...new Set([
        ...subgroupsOf(schedule, group),
        ...extra.map((e) => e.lesson.subgroups?.find((s) => s.group === group)?.label).filter(Boolean),
      ]),
    ].sort((a, b) => a.localeCompare(b, "ru", { numeric: true })),
    bells: calendar?.bells || [],
    from,
    days: out,
    weekly,
    notes: schedule.notes,
  };
}