package activitypub

import (
	"fmt"
)

type withLinkFn func (*Link) error
type withObjectFn func (*Object) error
type withActivityFn func (*Activity) error
type withIntransitiveActivityFn func (*IntransitiveActivity) error
type withQuestionFn func (*Question) error
type withActorFn func (*Actor) error
type withCollectionInterfaceFn func (collection CollectionInterface) error
type withCollectionFn func (collection *Collection) error
type withCollectionPageFn func (*CollectionPage) error
type withOrderedCollectionFn func (*OrderedCollection) error
type withOrderedCollectionPageFn func (*OrderedCollectionPage) error
type withItemCollectionFn func (collection *ItemCollection) error

// OnLink
func OnLink(it Item, fn withLinkFn) error {
	ob, err := ToLink(it)
	if err != nil {
		return err
	}
	return fn(ob)
}

// OnObject
func OnObject(it Item, fn withObjectFn) error {
	ob, err := ToObject(it)
	if err != nil {
		return err
	}
	return fn(ob)
}

// OnActivity
func OnActivity(it Item, fn withActivityFn) error {
	if !(ActivityTypes.Contains(it.GetType()) || IntransitiveActivityTypes.Contains(it.GetType())) {
		return fmt.Errorf("%T[%s] can't be converted to Activity", it, it.GetType())
	}
	act, err  := ToActivity(it)
	if err != nil {
		return err
	}
	return fn(act)
}

// OnIntransitiveActivity
func OnIntransitiveActivity(it Item, fn withIntransitiveActivityFn) error {
	if it.GetType() == QuestionType {
		fmt.Errorf("for %T[%s] you need to use OnQuestion function", it, it.GetType())
	}
	act, err  := ToIntransitiveActivity(it)
	if err != nil {
		return err
	}
	return fn(act)
}

// OnQuestion
func OnQuestion(it Item, fn withQuestionFn) error {
	if it.GetType() != QuestionType {
		fmt.Errorf("for %T[%s] can't be converted to Question", it, it.GetType())
	}
	act, err  := ToQuestion(it)
	if err != nil {
		return err
	}
	return fn(act)
}

// OnActor
func OnActor(it Item, fn withActorFn) error {
	if !ActorTypes.Contains(it.GetType()) {
		return fmt.Errorf("%T[%s] can't be converted to Person", it, it.GetType())
	}
	act, err  := ToActor(it)
	if err != nil {
		return err
	}
	return fn(act)
}
// OnCollection
func OnCollection (it Item, fn withCollectionFn) error {
	if !(ActivityVocabularyTypes{CollectionPageType, CollectionType,}).Contains(it.GetType()) {
		return fmt.Errorf("%T[%s] can't be converted to Collection", it, it.GetType())
	}
	col, err := ToCollection(it)
	if err != nil {
		return err
	}
	return fn(col)
}

// OnCollectionIntf
func OnCollectionIntf(it Item, fn withCollectionInterfaceFn) error {
	switch it.GetType() {
	case CollectionOfItems:
		col, err := ToItemCollection(it)
		if err != nil {
			return err
		}
		return fn(col)
	case CollectionType:
		col, err := ToCollection(it)
		if err != nil {
			return err
		}
		return fn(col)
	case CollectionPageType:
		return OnCollectionPage(it, func(p *CollectionPage) error {
			col, err := ToCollectionPage(p)
			if err != nil {
				return err
			}
			return fn(col)
		})
	case OrderedCollectionType:
		col, err := ToOrderedCollection(it)
		if err != nil {
			return err
		}
		return fn(col)
	case OrderedCollectionPageType:
		return OnOrderedCollectionPage(it, func(p *OrderedCollectionPage) error {
			col, err := ToOrderedCollectionPage(p)
			if err != nil {
				return err
			}
			return fn(col)
		})
	default:
		return fmt.Errorf("%T[%s] can't be converted to Collection", it, it.GetType())
	}
}

// OnCollectionPage
func OnCollectionPage(it Item, fn withCollectionPageFn) error {
	if it.GetType() != CollectionPageType {
		return fmt.Errorf("%T[%s] can't be converted to Collection Page", it, it.GetType())
	}
	col, err  := ToCollectionPage(it)
	if err != nil {
		return err
	}
	return fn(col)
}

// OnOrderedCollection
func OnOrderedCollection(it Item, fn withOrderedCollectionFn) error {
	if !(ActivityVocabularyTypes{OrderedCollectionPageType, OrderedCollectionType,}).Contains(it.GetType()) {
		return fmt.Errorf("%T[%s] can't be converted to Ordered Collection", it, it.GetType())
	}
	col, err := ToOrderedCollection(it)
	if err != nil {
		return err
	}
	return fn(col)
}

// OnOrderedCollectionPage executes a function on an ordered collection page type item
func OnOrderedCollectionPage(it Item, fn withOrderedCollectionPageFn) error {
	if it.GetType() != OrderedCollectionPageType {
		return fmt.Errorf("%T[%s] can't be converted to OrderedCollection Page", it, it.GetType())
	}
	col, err  := ToOrderedCollectionPage(it)
	if err != nil {
		return err
	}
	return fn(col)
}

// OnItemCollection executes a function on a collection type item
func OnItemCollection(it Item, fn withItemCollectionFn) error {
	col, err  := ToItemCollection(it)
	if err != nil {
		return err
	}
	return fn(col)
}

// ItemOrderTimestamp is used for ordering a ItemCollection slice using the slice.Sort function
// It orders i1 and i2 based on their Published and Updated timestamps.
func ItemOrderTimestamp(i1, i2 Item) bool {
	o1, e1 := ToObject(i1)
	o2, e2 := ToObject(i2)
	if e1 != nil || e2 != nil {
		return false
	}
	t1 := o1.Published
	if !o1.Updated.IsZero() {
		t1 = o1.Updated
	}
	t2 := o2.Published
	if !o2.Updated.IsZero() {
		t2 = o2.Updated
	}
	return t1.Sub(t2) > 0
}