package storage

import (
	"sync"
)

// Storage is an interface for storing objects.
type Storage[T any] interface {
	// List returns all objects from the storage.
	List() []T

	// Add adds an object to the storage.
	// It overwrites the old object if one with the same id was already stored.
	Add(id string, o T)

	// Get returns an object from the storage.
	// Iff the object does not exist in the storage, ok will be false.
	Get(id string) (o T, ok bool)

	// Delete deletes the object with the passed id from the storage.
	// It does nothing if no object with the id is present in the store.
	Delete(id string)

	// Pop deletes the object with the given id from the storage and returns it.
	// Iff no such execution exists, ok is false and true otherwise.
	Pop(id string) (o T, ok bool)

	// Purge removes all objects from the storage.
	Purge()

	// Length returns the number of currently stored objects in the storage.
	Length() uint

	// Sample returns and removes an arbitrary object from the storage.
	// ok is true iff an object was returned.
	Sample() (o T, ok bool)
}

// localStorage stores objects in the local application memory.
type localStorage[T any] struct {
	sync.RWMutex
	objects map[string]T
}

// NewLocalStorage responds with a Storage implementation.
// This implementation stores the data thread-safe in the local application memory.
func NewLocalStorage[T any]() *localStorage[T] {
	return &localStorage[T]{
		objects: make(map[string]T),
	}
}

func (s *localStorage[T]) List() (o []T) {
	s.RLock()
	defer s.RUnlock()
	for _, value := range s.objects {
		o = append(o, value)
	}
	return o
}

func (s *localStorage[T]) Add(id string, o T) {
	s.Lock()
	defer s.Unlock()
	s.objects[id] = o
}

func (s *localStorage[T]) Get(id string) (o T, ok bool) {
	s.RLock()
	defer s.RUnlock()
	o, ok = s.objects[id]
	return
}

func (s *localStorage[T]) Delete(id string) {
	s.Lock()
	defer s.Unlock()
	delete(s.objects, id)
}

func (s *localStorage[T]) Pop(id string) (T, bool) {
	o, ok := s.Get(id)
	s.Delete(id)
	return o, ok
}

func (s *localStorage[T]) Purge() {
	s.Lock()
	defer s.Unlock()
	s.objects = make(map[string]T)
}

func (s *localStorage[T]) Sample() (o T, ok bool) {
	s.Lock()
	defer s.Unlock()
	for key, object := range s.objects {
		delete(s.objects, key)
		return object, true
	}
	return
}

func (s *localStorage[T]) Length() uint {
	s.RLock()
	defer s.RUnlock()
	return uint(len(s.objects))
}