package sets

// Union returns a union of the given sets (left ∪ right).
func Union[T comparable](left, right *Set[T]) *Set[T] {
	left.mux.RLock()
	right.mux.RLock()
	defer left.mux.RUnlock()
	defer right.mux.RUnlock()

	store := map[T]struct{}{}

	for k := range left.store {
		store[k] = struct{}{}
	}
	for k := range right.store {
		if _, ok := store[k]; !ok {
			store[k] = struct{}{}
		}
	}

	return &Set[T]{
		store: store,
	}
}

// Intersection returns an intersection of the given sets (left ∩ right).
func Intersection[T comparable](left, right *Set[T]) *Set[T] {
	left.mux.RLock()
	right.mux.RLock()
	defer left.mux.RUnlock()
	defer right.mux.RUnlock()

	store := map[T]struct{}{}

	for lk := range left.store {
		if _, ok := right.store[lk]; ok {
			store[lk] = struct{}{}
		}
	}

	return &Set[T]{
		store: store,
	}
}

// Diff returns the relative complement of sets (left ∖ right).
func Diff[T comparable](left, right *Set[T]) *Set[T] {
	left.mux.RLock()
	right.mux.RLock()
	defer left.mux.RUnlock()
	defer right.mux.RUnlock()

	store := map[T]struct{}{}

	for lk := range left.store {
		if _, ok := right.store[lk]; !ok {
			store[lk] = struct{}{}
		}
	}

	return &Set[T]{
		store: store,
	}
}

// SymmetricDiff returns the symmetric difference between sets (left ⊖ right).
func SymmetricDiff[T comparable](left, right *Set[T]) *Set[T] {
	left.mux.RLock()
	right.mux.RLock()
	defer left.mux.RUnlock()
	defer right.mux.RUnlock()

	store := map[T]struct{}{}

	for lk := range left.store {
		if _, ok := right.store[lk]; !ok {
			store[lk] = struct{}{}
		}
	}
	for rk := range right.store {
		if _, ok := left.store[rk]; !ok {
			store[rk] = struct{}{}
		}
	}

	return &Set[T]{
		store: store,
	}
}

// Equal checks whether the sets are equal (left = right).
func Equal[T comparable](left, right *Set[T]) bool {
	left.mux.RLock()
	right.mux.RLock()
	defer left.mux.RUnlock()
	defer right.mux.RUnlock()

	if len(left.store) != len(right.store) {
		return false
	}

	for lk := range left.store {
		if _, ok := right.store[lk]; !ok {
			return false
		}
	}
	return true
}