import "server-only";

import { prisma } from "@/lib/db";
import { addUTCDays, getWeekStart, startOfUTCDate, toDateKey } from "@/lib/dates";
import { expandOccurrences } from "@/lib/rrule-utils";
import type { ScheduledBoardDTO, ScheduledDayDTO, ScheduledOccurrenceDTO } from "@/types/scheduled-todo";

// A recurring to-do that's never checked off would otherwise surface a
// missed occurrence for every day since it was created, forever -- cap how
// far back "overdue" looks so the column stays meaningful instead of
// endless.
const OVERDUE_LOOKBACK_DAYS = 30;

/**
 * Fetches one Scheduled board's worth of occurrences, bucketed the way the
 * panel renders them -- shared by the Home board and every Project board,
 * which differ only in which ScheduledTodos they scope to (mirrors
 * lib/board.ts's getBoard).
 */
export async function getScheduledTodoBoard(
  where: { userId: string; projectId: null } | { projectId: string }
): Promise<ScheduledBoardDTO> {
  const today = startOfUTCDate(new Date());
  const todayKey = toDateKey(today);
  const weekStart = getWeekStart(today);
  const weekEnd = addUTCDays(weekStart, 6);
  const windowStart = addUTCDays(today, -OVERDUE_LOOKBACK_DAYS);

  const scheduledTodos = await prisma.scheduledTodo.findMany({
    where,
    include: { completions: true },
    orderBy: { createdAt: "asc" },
  });

  const overdue: ScheduledOccurrenceDTO[] = [];
  const todayOccurrences: ScheduledOccurrenceDTO[] = [];
  // Seeded up front so every remaining weekday gets a header even with
  // nothing scheduled that day.
  const upcomingByDate = new Map<string, ScheduledOccurrenceDTO[]>();
  for (let d = addUTCDays(today, 1); d <= weekEnd; d = addUTCDays(d, 1)) {
    upcomingByDate.set(toDateKey(d), []);
  }

  for (const todo of scheduledTodos) {
    const completedDates = new Set(todo.completions.map((c) => toDateKey(c.occurrenceDate)));
    const occurrences = expandOccurrences(todo.startDate, todo.rrule, windowStart, weekEnd);

    for (const occurrenceDate of occurrences) {
      const key = toDateKey(occurrenceDate);
      const dto: ScheduledOccurrenceDTO = {
        scheduledTodoId: todo.id,
        title: todo.title,
        details: todo.details,
        occurrenceDate: key,
        completed: completedDates.has(key),
        isRecurring: !!todo.rrule,
        timeDue: todo.timeDue,
        remindMinutesBefore: todo.remindMinutesBefore,
      };

      if (key < todayKey) {
        if (!dto.completed) overdue.push(dto);
      } else if (key === todayKey) {
        todayOccurrences.push(dto);
      } else {
        upcomingByDate.get(key)?.push(dto);
      }
    }
  }

  overdue.sort((a, b) => a.occurrenceDate.localeCompare(b.occurrenceDate));

  const upcoming: ScheduledDayDTO[] = Array.from(upcomingByDate, ([date, occurrences]) => ({
    date,
    occurrences,
  })).sort((a, b) => a.date.localeCompare(b.date));

  return {
    overdue,
    today: { date: todayKey, occurrences: todayOccurrences },
    upcoming,
  };
}