const REMINDER_EXPIRY_MS = 72 * 60 * 60 * 1000;
const DISMISSALS_STORAGE_KEY = "ptf:mission-reminder:dismissals";

export type ReminderLeader = {
  readonly id: number;
  readonly username: string;
  readonly displayName: string;
};

export type MissionReminder = {
  readonly missionId: number;
  readonly missionName: string;
  readonly missionCodeName: string | null;
  readonly completedAt: string;
  readonly leaders: readonly ReminderLeader[];
};

export type ReminderEntry = MissionReminder & {
  readonly key: string;
  readonly leader: ReminderLeader;
  readonly expiresAt: number;
};

export type Dismissals = Record<string, number>;

function isRecord(value: unknown): value is Record<string, unknown> {
  return typeof value === "object" && value !== null;
}

function isReminderLeader(value: unknown): value is ReminderLeader {
  return (
    isRecord(value) &&
    typeof value.id === "number" &&
    typeof value.username === "string" &&
    typeof value.displayName === "string"
  );
}

function isMissionReminder(value: unknown): value is MissionReminder {
  return (
    isRecord(value) &&
    typeof value.missionId === "number" &&
    typeof value.missionName === "string" &&
    (value.missionCodeName === null || typeof value.missionCodeName === "string") &&
    typeof value.completedAt === "string" &&
    Array.isArray(value.leaders) &&
    value.leaders.every(isReminderLeader)
  );
}

export function parseMissionReminders(value: unknown): readonly MissionReminder[] {
  if (!isRecord(value) || !Array.isArray(value.reminders)) return [];
  return value.reminders.filter(isMissionReminder);
}

export function missionReminderKey(missionId: number, leaderId: number): string {
  return `${missionId}:${leaderId}`;
}

export function buildReminderEntries(
  reminders: readonly MissionReminder[],
  now: number,
): readonly ReminderEntry[] {
  const entries: ReminderEntry[] = [];
  const seen = new Set<string>();

  for (const reminder of reminders) {
    const completedAt = Date.parse(reminder.completedAt);
    if (!Number.isFinite(completedAt)) continue;
    const expiresAt = completedAt + REMINDER_EXPIRY_MS;
    if (expiresAt <= now) continue;

    for (const leader of reminder.leaders) {
      const key = missionReminderKey(reminder.missionId, leader.id);
      if (seen.has(key)) continue;
      seen.add(key);
      entries.push({ ...reminder, key, leader, expiresAt });
    }
  }

  return entries;
}

// Browser storage is read during mount and written during mount or the
// explicit dismissal handler; it is never accessed during render.
export function readReminderDismissals(now: number): Dismissals {
  if (typeof window === "undefined") return {};

  try {
    const raw = window.localStorage.getItem(DISMISSALS_STORAGE_KEY);
    if (!raw) return {};
    const parsed: unknown = JSON.parse(raw);
    if (!isRecord(parsed)) return {};

    const dismissals: Dismissals = {};
    for (const [key, value] of Object.entries(parsed)) {
      if (typeof value === "number" && Number.isFinite(value) && value > now) {
        dismissals[key] = value;
      }
    }
    return dismissals;
  } catch (error) {
    if (error instanceof Error) return {};
    throw error;
  }
}

export function writeReminderDismissals(dismissals: Dismissals, now: number): void {
  if (typeof window === "undefined") return;

  const activeDismissals: Dismissals = {};
  for (const [key, expiresAt] of Object.entries(dismissals)) {
    if (expiresAt > now) activeDismissals[key] = expiresAt;
  }

  try {
    window.localStorage.setItem(DISMISSALS_STORAGE_KEY, JSON.stringify(activeDismissals));
  } catch (error) {
    if (error instanceof Error) return;
    throw error;
  }
}