package sliceutil

// AppendFilter takes two slice, 's' as source and 'd' as destination
// and a predicate function, then applies it to each element of 's',
// when 'p' returns true it appends the element into d, otherwise omit it.
func AppendFilter[T any](s []T, d *[]T, p func(T) bool) {
	for _, e := range s {
		if p(e) {
			*d = append(*d, e)
		}
	}
}

// AssignFilter takes two slice, 's' as source and 'd' as destination
// and a predicate function, then applies it to each element of 's'.
// 'd' slice will have the same capacity of 's' but starts with 0 length.
// When 'p' returns true it appends the element into d, otherwise omit it.
func AssignFilter[T any](s []T, d *[]T, p func(T) bool) {
	if cap(*d) == 0 {
		*d = make([]T, 0, len(s))
	}
	for _, e := range s {
		if p(e) {
			*d = append(*d, e)
		}
	}
}

// DisposeFilter takes two slice, 's' as source and 'd' as destination
// and a predicate function, then applies it to each element of 's'.
// 'd' slice will share the exact same memory address of 's'.
// When 'p' returns true it appends the element into d, otherwise omit it.
// Then disposes the 's'. IMPORTANT: 's' cannot be used again.
func DisposeFilter[T any](s []T, d *[]T, p func(T) bool) {
	*d = s[:0]
	for _, e := range s {
		if p(e) {
			*d = append(*d, e)
		}
	}
	var NIL T
	for i := len(*d); i < len(s); i++ {
		s[i] = NIL
	}
}

// InPlaceFilter takes a slice and a predicate function, then applies it to each element of 's'.
// When 'p' returns true it assign the value to the last index plus one where p was true, otherwise omit it.
func InPlaceFilter[T any](s *[]T, p func(T) bool) {
	i := 0
	for _, e := range *s {
		if p(e) {
			(*s)[i] = e
			i++
		}
	}
	*s = (*s)[:i]
}

// Filter takes a slice and a predcate function, then applies it to each element of 's'.
// When 'p' returns true it appends the value to the output slice.
func Filter[T any](s []T, p func(T) bool) []T {
	o := make([]T, 0, len(s))
	for _, e := range s {
		if p(e) {
			o = append(o, e)
		}
	}
	return o
}