interface LessonLike {
  day: number;
  date: string | null;
  start: string;
  end: string | null;
  subject: string;
  teacher: string;
  room: string;
  place?: string;
  type: string;
  condition: string;
  variant: "all" | "upper" | "lower";
  groups: string[];
  subgroups: { group: string; label: string }[];
}
export interface FieldChange {
  field: string;
  label: string;
  from: string | number;
  to: string | number;
}
export interface ScheduleDiff<L> {
  added: L[];
  removed: L[];
  changed: { before: L; after: L; fields: FieldChange[] }[];
}
export interface PersonalPrefs {
  subgroup?: string | null;
  hidden?: string[];
}
export function lessonKey(lesson: LessonLike, group: string): string;
export function diffSchedules<L extends LessonLike>(
  before: { lessons: L[] } | null | undefined,
  after: { lessons: L[] } | null | undefined,
  group: string,
): ScheduleDiff<L>;
export function changeCount(diff: ScheduleDiff<unknown> | null | undefined): number;
export function personalFilter(
  lesson: LessonLike,
  group: string,
  prefs: PersonalPrefs | null | undefined,
): "shown" | "hidden" | "other-subgroup";
export function subgroupsOf(
  schedule: { lessons: LessonLike[] } | null | undefined,
  group: string,
): string[];