package stl

// ImplicitSortable are types that can be compared with
// the less operator <, among others.
//
// As with C++, two keys are considered equal if neither
// x < y nor y < x, so these interfaces have nothing to
// do with Go's 'comparable' whatsoever.
//
// This behavior can be overridden by defining another
// type and then add a Compare method to the original key.
type ImplicitSortable interface {
	~int | ~int8 | ~int16 | ~int32 | ~int64 | ~uint | ~uint8 | ~uint16 | ~uint32 | ~uint64 | ~uintptr | ~string | ~float32 | ~float64
}

// Sorter is a interface used in the construction of
// many collection types, to compare two keys with
// the '<' operator by default.
type Sorter[T any] interface {
	Compare(x, y T) bool
}

// Less implements Sorter for ImplicitSortables using the '<' operator.
type Less[T ImplicitSortable] struct{}

func (Less[T]) Compare(x, y T) bool {
	return x < y
}

// Greater implements Sorter for ImplicitSortables using the '>' operator.
type Greater[T ImplicitSortable] struct{}

func (Greater[T]) Compare(x, y T) bool {
	return x > y
}

// Equal determines if the two keys are considered equal,
// i.e., neither x < y nor y < x, per C++ traditions.
func Equal[C Sorter[T], T any](x, y T) bool {
	var c C
	return !c.Compare(x, y) && !c.Compare(y, x)
}