package collections

import "pkg.icikowski.pl/collections/functions"

// Optional represents an optional value of type T.
type Optional[T any] struct {
	e       T
	present bool
}

// IsPresent determines whether the underlying value is present.
func (o *Optional[T]) IsPresent() bool {
	return o.present
}

// Get returns the underlying value.
func (o *Optional[T]) Get() T {
	return o.e
}

// OrElse returns the underlying value or given value if underlying value is not present.
func (o *Optional[T]) OrElse(e T) T {
	if !o.present {
		return e
	}
	return o.e
}

// OrElseGet returns the underlying value or value from given supplier if underlying value is not present.
func (o *Optional[T]) OrElseGet(s functions.Supplier[T]) T {
	if !o.present {
		return s()
	}
	return o.e
}

// Transform transforms the underlying value with given [functions.UnaryOperator] if the vale is present.
func (o *Optional[T]) Transform(u functions.UnaryOperator[T]) *Optional[T] {
	if o.present {
		o.e = u(o.e)
	}
	return o
}

// MapOptional maps optional of type T to optional of type U using given [functions.Function].
func MapOptional[T, U any](src *Optional[T], mapper functions.Function[T, U]) *Optional[U] {
	return &Optional[U]{mapper(src.e), src.present}
}