golang_option

type User struct {
	Name string
	Age  int
}

type UserOption func(*User)

func NewUser(options ...UserOption) *User {
	u := &User{}
	for _, option := range options {
		option(u)
	}
	return u
}

func WithName(name string) UserOption {
	return func(u *User) {
		u.Name = name
	}
}

func WithAge(age int) UserOption {
	return func(u *User) {
		u.Age = age
	}
}

type QueryOption interface {
	ApplyTo(users []*User) []*User
}

func FindUser(users []*User, options ...QueryOption) []*User {
	for _, option := range options {
		users = option.ApplyTo(users)
	}
	return users
}

type Where struct {
	Name string
	Age  int
}

func (w *Where) ApplyTo(users []*User) []*User {
	res := make([]*User, 0, len(users))
	for _, u := range users {
		if u.Name == w.Name && u.Age == w.Age {
			res = append(res, u)
		}
	}
	return res
}

type Range struct {
	Offset int
	Limit  int
}

func (r *Range) ApplyTo(users []*User) []*User {
	res := make([]*User, 0, len(users))
	for i := r.Offset; i < len(users) && i < r.Offset+r.Limit; i++ {
		res = append(res, users[i])
	}
	return res
}

func TestFindUser(t *testing.T) {
	u1 := NewUser(WithName("a"), WithAge(18))
	u2 := NewUser(WithName("b"), WithAge(28))
	u3 := NewUser(WithName("c"), WithAge(18))
	u4 := NewUser(WithName("d"), WithAge(38))

	users := FindUser([]*User{u1, u2, u3, u4}, &Where{Name: "a", Age: 38}, &Range{Offset: 0, Limit: 2})
	fmt.Printf("%#v", users)
}