-- A learning path is deliberately only a curated, ordered collection of
-- existing courses. Lessons remain owned by their courses, so a course edit
-- is reflected everywhere that course appears.
create table learning_paths (
  id uuid primary key default gen_random_uuid(),
  title text not null check (char_length(trim(title)) between 1 and 160),
  description text not null default '',
  cover_image_url text,
  cover_image_zoom real not null default 1 check (cover_image_zoom between 1 and 2.5),
  cover_image_position_x real not null default 50 check (cover_image_position_x between 0 and 100),
  cover_image_position_y real not null default 50 check (cover_image_position_y between 0 and 100),
  status course_status not null default 'draft',
  published_at timestamptz,
  created_at timestamptz not null default now(),
  updated_at timestamptz not null default now(),
  constraint learning_paths_published_at_check check (
    (status = 'published' and published_at is not null) or status <> 'published'
  )
);

create table learning_path_courses (
  learning_path_id uuid not null references learning_paths(id) on delete cascade,
  course_id uuid not null references courses(id) on delete restrict,
  position integer not null check (position > 0),
  primary key (learning_path_id, course_id),
  unique (learning_path_id, position)
);

create index learning_paths_published_index on learning_paths (published_at desc) where status = 'published';
create index learning_path_courses_position_index on learning_path_courses (learning_path_id, position);

create trigger learning_paths_set_updated_at before update on learning_paths for each row execute function set_updated_at();