[bugfix] support both CollectionPage AND OrderedCollectionPage in status replies (#2220)

3 files changed, 406 insertions, 225 deletions

diff --git a/internal/ap/activitystreams.go b/internal/ap/activitystreams.go
index 34a3013a4..f6c412e51 100644
--- a/internal/ap/activitystreams.go
+++ b/internal/ap/activitystreams.go
@@ -17,15 +17,6 @@
 
 package ap
 
-import (
-	"net/url"
-	"strconv"
-
-	"github.com/superseriousbusiness/activity/streams"
-	"github.com/superseriousbusiness/activity/streams/vocab"
-	"github.com/superseriousbusiness/gotosocial/internal/paging"
-)
-
 // https://www.w3.org/TR/activitystreams-vocabulary
 const (
 	ActivityAccept          = "Accept"          // ActivityStreamsAccept https://www.w3.org/TR/activitystreams-vocabulary/#dfn-accept
@@ -63,21 +54,22 @@ const (
 	ActorPerson       = "Person"       // ActivityStreamsPerson https://www.w3.org/TR/activitystreams-vocabulary/#dfn-person
 	ActorService      = "Service"      // ActivityStreamsService https://www.w3.org/TR/activitystreams-vocabulary/#dfn-service
 
-	ObjectArticle           = "Article"           // ActivityStreamsArticle https://www.w3.org/TR/activitystreams-vocabulary/#dfn-article
-	ObjectAudio             = "Audio"             // ActivityStreamsAudio https://www.w3.org/TR/activitystreams-vocabulary/#dfn-audio
-	ObjectDocument          = "Document"          // ActivityStreamsDocument https://www.w3.org/TR/activitystreams-vocabulary/#dfn-document
-	ObjectEvent             = "Event"             // ActivityStreamsEvent https://www.w3.org/TR/activitystreams-vocabulary/#dfn-event
-	ObjectImage             = "Image"             // ActivityStreamsImage https://www.w3.org/TR/activitystreams-vocabulary/#dfn-image
-	ObjectNote              = "Note"              // ActivityStreamsNote https://www.w3.org/TR/activitystreams-vocabulary/#dfn-note
-	ObjectPage              = "Page"              // ActivityStreamsPage https://www.w3.org/TR/activitystreams-vocabulary/#dfn-page
-	ObjectPlace             = "Place"             // ActivityStreamsPlace https://www.w3.org/TR/activitystreams-vocabulary/#dfn-place
-	ObjectProfile           = "Profile"           // ActivityStreamsProfile https://www.w3.org/TR/activitystreams-vocabulary/#dfn-profile
-	ObjectRelationship      = "Relationship"      // ActivityStreamsRelationship https://www.w3.org/TR/activitystreams-vocabulary/#dfn-relationship
-	ObjectTombstone         = "Tombstone"         // ActivityStreamsTombstone https://www.w3.org/TR/activitystreams-vocabulary/#dfn-tombstone
-	ObjectVideo             = "Video"             // ActivityStreamsVideo https://www.w3.org/TR/activitystreams-vocabulary/#dfn-video
-	ObjectCollection        = "Collection"        // ActivityStreamsCollection https://www.w3.org/TR/activitystreams-vocabulary/#dfn-collection
-	ObjectCollectionPage    = "CollectionPage"    // ActivityStreamsCollectionPage https://www.w3.org/TR/activitystreams-vocabulary/#dfn-collectionpage
-	ObjectOrderedCollection = "OrderedCollection" // ActivityStreamsOrderedCollection https://www.w3.org/TR/activitystreams-vocabulary/#dfn-orderedcollection
+	ObjectArticle               = "Article"               // ActivityStreamsArticle https://www.w3.org/TR/activitystreams-vocabulary/#dfn-article
+	ObjectAudio                 = "Audio"                 // ActivityStreamsAudio https://www.w3.org/TR/activitystreams-vocabulary/#dfn-audio
+	ObjectDocument              = "Document"              // ActivityStreamsDocument https://www.w3.org/TR/activitystreams-vocabulary/#dfn-document
+	ObjectEvent                 = "Event"                 // ActivityStreamsEvent https://www.w3.org/TR/activitystreams-vocabulary/#dfn-event
+	ObjectImage                 = "Image"                 // ActivityStreamsImage https://www.w3.org/TR/activitystreams-vocabulary/#dfn-image
+	ObjectNote                  = "Note"                  // ActivityStreamsNote https://www.w3.org/TR/activitystreams-vocabulary/#dfn-note
+	ObjectPage                  = "Page"                  // ActivityStreamsPage https://www.w3.org/TR/activitystreams-vocabulary/#dfn-page
+	ObjectPlace                 = "Place"                 // ActivityStreamsPlace https://www.w3.org/TR/activitystreams-vocabulary/#dfn-place
+	ObjectProfile               = "Profile"               // ActivityStreamsProfile https://www.w3.org/TR/activitystreams-vocabulary/#dfn-profile
+	ObjectRelationship          = "Relationship"          // ActivityStreamsRelationship https://www.w3.org/TR/activitystreams-vocabulary/#dfn-relationship
+	ObjectTombstone             = "Tombstone"             // ActivityStreamsTombstone https://www.w3.org/TR/activitystreams-vocabulary/#dfn-tombstone
+	ObjectVideo                 = "Video"                 // ActivityStreamsVideo https://www.w3.org/TR/activitystreams-vocabulary/#dfn-video
+	ObjectCollection            = "Collection"            // ActivityStreamsCollection https://www.w3.org/TR/activitystreams-vocabulary/#dfn-collection
+	ObjectCollectionPage        = "CollectionPage"        // ActivityStreamsCollectionPage https://www.w3.org/TR/activitystreams-vocabulary/#dfn-collectionpage
+	ObjectOrderedCollection     = "OrderedCollection"     // ActivityStreamsOrderedCollection https://www.w3.org/TR/activitystreams-vocabulary/#dfn-orderedcollection
+	ObjectOrderedCollectionPage = "OrderedCollectionPage" // ActivityStreamsOrderedCollectionPage https://www.w3.org/TR/activitystreams-vocabulary/#dfn-orderedcollectionPage
 
 	// Hashtag is not in the AS spec per se, but it tends to get used
 	// as though 'Hashtag' is a named type under the Tag property.
@@ -86,197 +78,3 @@ const (
 	// and https://www.w3.org/TR/activitystreams-vocabulary/#dfn-tag
 	TagHashtag = "Hashtag"
 )
-
-type CollectionParams struct {
-	// Containing collection
-	// ID (i.e. NOT the page).
-	ID *url.URL
-
-	// Total no. items.
-	Total int
-}
-
-type CollectionPageParams struct {
-	// containing collection.
-	CollectionParams
-
-	// Paging details.
-	Current *paging.Page
-	Next    *paging.Page
-	Prev    *paging.Page
-	Query   url.Values
-
-	// Item appender for each item at index.
-	Append func(int, ItemsPropertyBuilder)
-	Count  int
-}
-
-// CollectionPage is a simplified interface type
-// that can be fulfilled by either of (where required):
-// vocab.ActivityStreamsCollection
-// vocab.ActivityStreamsOrderedCollection
-type CollectionBuilder interface {
-	SetJSONLDId(vocab.JSONLDIdProperty)
-	SetActivityStreamsFirst(vocab.ActivityStreamsFirstProperty)
-	SetActivityStreamsTotalItems(i vocab.ActivityStreamsTotalItemsProperty)
-}
-
-// CollectionPageBuilder is a simplified interface type
-// that can be fulfilled by either of (where required):
-// vocab.ActivityStreamsCollectionPage
-// vocab.ActivityStreamsOrderedCollectionPage
-type CollectionPageBuilder interface {
-	SetJSONLDId(vocab.JSONLDIdProperty)
-	SetActivityStreamsPartOf(vocab.ActivityStreamsPartOfProperty)
-	SetActivityStreamsNext(vocab.ActivityStreamsNextProperty)
-	SetActivityStreamsPrev(vocab.ActivityStreamsPrevProperty)
-	SetActivityStreamsTotalItems(i vocab.ActivityStreamsTotalItemsProperty)
-}
-
-// ItemsPropertyBuilder is a simplified interface type
-// that can be fulfilled by either of (where required):
-// vocab.ActivityStreamsItemsProperty
-// vocab.ActivityStreamsOrderedItemsProperty
-type ItemsPropertyBuilder interface {
-	AppendIRI(*url.URL)
-
-	// NOTE: add more of the items-property-like interface
-	// functions here as you require them for building pages.
-}
-
-// NewASCollection builds and returns a new ActivityStreams Collection from given parameters.
-func NewASCollection(params CollectionParams) vocab.ActivityStreamsCollection {
-	collection := streams.NewActivityStreamsCollection()
-	buildCollection(collection, params, 40)
-	return collection
-}
-
-// NewASCollectionPage builds and returns a new ActivityStreams CollectionPage from given parameters (including item property appending function).
-func NewASCollectionPage(params CollectionPageParams) vocab.ActivityStreamsCollectionPage {
-	collectionPage := streams.NewActivityStreamsCollectionPage()
-	itemsProp := streams.NewActivityStreamsItemsProperty()
-	buildCollectionPage(collectionPage, itemsProp, collectionPage.SetActivityStreamsItems, params)
-	return collectionPage
-}
-
-// NewASOrderedCollection builds and returns a new ActivityStreams OrderedCollection from given parameters.
-func NewASOrderedCollection(params CollectionParams) vocab.ActivityStreamsOrderedCollection {
-	collection := streams.NewActivityStreamsOrderedCollection()
-	buildCollection(collection, params, 40)
-	return collection
-}
-
-// NewASOrderedCollectionPage builds and returns a new ActivityStreams OrderedCollectionPage from given parameters (including item property appending function).
-func NewASOrderedCollectionPage(params CollectionPageParams) vocab.ActivityStreamsOrderedCollectionPage {
-	collectionPage := streams.NewActivityStreamsOrderedCollectionPage()
-	itemsProp := streams.NewActivityStreamsOrderedItemsProperty()
-	buildCollectionPage(collectionPage, itemsProp, collectionPage.SetActivityStreamsOrderedItems, params)
-	return collectionPage
-}
-
-func buildCollection[C CollectionBuilder](collection C, params CollectionParams, pageLimit int) {
-	// Add the collection ID property.
-	idProp := streams.NewJSONLDIdProperty()
-	idProp.SetIRI(params.ID)
-	collection.SetJSONLDId(idProp)
-
-	// Add the collection totalItems count property.
-	totalItems := streams.NewActivityStreamsTotalItemsProperty()
-	totalItems.Set(params.Total)
-	collection.SetActivityStreamsTotalItems(totalItems)
-
-	// Clone the collection ID page
-	// to add first page query data.
-	firstIRI := new(url.URL)
-	*firstIRI = *params.ID
-
-	// Note that simply adding a limit signals to our
-	// endpoint to use paging (which will start at beginning).
-	limit := "limit=" + strconv.Itoa(pageLimit)
-	firstIRI.RawQuery = appendQuery(firstIRI.RawQuery, limit)
-
-	// Add the collection first IRI property.
-	first := streams.NewActivityStreamsFirstProperty()
-	first.SetIRI(firstIRI)
-	collection.SetActivityStreamsFirst(first)
-}
-
-func buildCollectionPage[C CollectionPageBuilder, I ItemsPropertyBuilder](collectionPage C, itemsProp I, setItems func(I), params CollectionPageParams) {
-	// Add the partOf property for its containing collection ID.
-	partOfProp := streams.NewActivityStreamsPartOfProperty()
-	partOfProp.SetIRI(params.ID)
-	collectionPage.SetActivityStreamsPartOf(partOfProp)
-
-	// Build the current page link IRI.
-	currentIRI := params.Current.ToLinkURL(
-		params.ID.Scheme,
-		params.ID.Host,
-		params.ID.Path,
-		params.Query,
-	)
-
-	// Add the collection ID property for
-	// the *current* collection page params.
-	idProp := streams.NewJSONLDIdProperty()
-	idProp.SetIRI(currentIRI)
-	collectionPage.SetJSONLDId(idProp)
-
-	// Build the next page link IRI.
-	nextIRI := params.Next.ToLinkURL(
-		params.ID.Scheme,
-		params.ID.Host,
-		params.ID.Path,
-		params.Query,
-	)
-
-	if nextIRI != nil {
-		// Add the collection next property for the next page.
-		nextProp := streams.NewActivityStreamsNextProperty()
-		nextProp.SetIRI(nextIRI)
-		collectionPage.SetActivityStreamsNext(nextProp)
-	}
-
-	// Build the prev page link IRI.
-	prevIRI := params.Prev.ToLinkURL(
-		params.ID.Scheme,
-		params.ID.Host,
-		params.ID.Path,
-		params.Query,
-	)
-
-	if prevIRI != nil {
-		// Add the collection prev property for the prev page.
-		prevProp := streams.NewActivityStreamsPrevProperty()
-		prevProp.SetIRI(prevIRI)
-		collectionPage.SetActivityStreamsPrev(prevProp)
-	}
-
-	// Add the collection totalItems count property.
-	totalItems := streams.NewActivityStreamsTotalItemsProperty()
-	totalItems.Set(params.Total)
-	collectionPage.SetActivityStreamsTotalItems(totalItems)
-
-	if params.Append == nil {
-		// nil check outside the for loop.
-		panic("nil params.Append function")
-	}
-
-	// Append each of the items to the provided
-	// pre-allocated items property builder type.
-	for i := 0; i < params.Count; i++ {
-		params.Append(i, itemsProp)
-	}
-
-	// Set the collection
-	// page items property.
-	setItems(itemsProp)
-}
-
-// appendQuery appends part to an existing raw
-// query with ampersand, else just returning part.
-func appendQuery(raw, part string) string {
-	if raw != "" {
-		return raw + "&" + part
-	}
-	return part
-}
diff --git a/internal/ap/collections.go b/internal/ap/collections.go
new file mode 100644
index 000000000..471dae0a1
--- /dev/null
+++ b/internal/ap/collections.go
@@ -0,0 +1,359 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package ap
+
+import (
+	"fmt"
+	"net/url"
+	"strconv"
+
+	"github.com/superseriousbusiness/activity/streams"
+	"github.com/superseriousbusiness/activity/streams/vocab"
+	"github.com/superseriousbusiness/gotosocial/internal/paging"
+)
+
+// ToCollectionPageIterator attempts to resolve the given vocab type as a CollectionPage
+// like object and wrap in a standardised interface in order to iterate its contents.
+func ToCollectionPageIterator(t vocab.Type) (CollectionPageIterator, error) {
+	switch name := t.GetTypeName(); name {
+	case ObjectCollectionPage:
+		t := t.(vocab.ActivityStreamsCollectionPage) //nolint:forcetypeassert
+		return WrapCollectionPage(t), nil
+	case ObjectOrderedCollectionPage:
+		t := t.(vocab.ActivityStreamsOrderedCollectionPage) //nolint:forcetypeassert
+		return WrapOrderedCollectionPage(t), nil
+	default:
+		return nil, fmt.Errorf("%T(%s) was not CollectionPage-like", t, name)
+	}
+}
+
+// WrapCollectionPage wraps an ActivityStreamsCollectionPage in a standardised collection page interface.
+func WrapCollectionPage(page vocab.ActivityStreamsCollectionPage) CollectionPageIterator {
+	return &regularCollectionPageIterator{ActivityStreamsCollectionPage: page}
+}
+
+// WrapOrderedCollectionPage wraps an ActivityStreamsOrderedCollectionPage in a standardised collection page interface.
+func WrapOrderedCollectionPage(page vocab.ActivityStreamsOrderedCollectionPage) CollectionPageIterator {
+	return &orderedCollectionPageIterator{ActivityStreamsOrderedCollectionPage: page}
+}
+
+// regularCollectionPageIterator implements CollectionPageIterator
+// for the vocab.ActivitiyStreamsCollectionPage type.
+type regularCollectionPageIterator struct {
+	vocab.ActivityStreamsCollectionPage
+	items vocab.ActivityStreamsItemsPropertyIterator
+	once  bool // only init items once
+}
+
+func (iter *regularCollectionPageIterator) NextPage() WithIRI {
+	if iter.ActivityStreamsCollectionPage == nil {
+		return nil
+	}
+	return iter.GetActivityStreamsNext()
+}
+
+func (iter *regularCollectionPageIterator) PrevPage() WithIRI {
+	if iter.ActivityStreamsCollectionPage == nil {
+		return nil
+	}
+	return iter.GetActivityStreamsPrev()
+}
+
+func (iter *regularCollectionPageIterator) NextItem() IteratorItemable {
+	if !iter.initItems() {
+		return nil
+	}
+	cur := iter.items
+	iter.items = iter.items.Next()
+	return cur
+}
+
+func (iter *regularCollectionPageIterator) PrevItem() IteratorItemable {
+	if !iter.initItems() {
+		return nil
+	}
+	cur := iter.items
+	iter.items = iter.items.Prev()
+	return cur
+}
+
+func (iter *regularCollectionPageIterator) initItems() bool {
+	if iter.once {
+		return (iter.items != nil)
+	}
+	iter.once = true
+	if iter.ActivityStreamsCollectionPage == nil {
+		return false // no page set
+	}
+	items := iter.GetActivityStreamsItems()
+	if items == nil {
+		return false // no items found
+	}
+	iter.items = items.Begin()
+	return (iter.items != nil)
+}
+
+// orderedCollectionPageIterator implements CollectionPageIterator
+// for the vocab.ActivitiyStreamsOrderedCollectionPage type.
+type orderedCollectionPageIterator struct {
+	vocab.ActivityStreamsOrderedCollectionPage
+	items vocab.ActivityStreamsOrderedItemsPropertyIterator
+	once  bool // only init items once
+}
+
+func (iter *orderedCollectionPageIterator) NextPage() WithIRI {
+	if iter.ActivityStreamsOrderedCollectionPage == nil {
+		return nil
+	}
+	return iter.GetActivityStreamsNext()
+}
+
+func (iter *orderedCollectionPageIterator) PrevPage() WithIRI {
+	if iter.ActivityStreamsOrderedCollectionPage == nil {
+		return nil
+	}
+	return iter.GetActivityStreamsPrev()
+}
+
+func (iter *orderedCollectionPageIterator) NextItem() IteratorItemable {
+	if !iter.initItems() {
+		return nil
+	}
+	cur := iter.items
+	iter.items = iter.items.Next()
+	return cur
+}
+
+func (iter *orderedCollectionPageIterator) PrevItem() IteratorItemable {
+	if !iter.initItems() {
+		return nil
+	}
+	cur := iter.items
+	iter.items = iter.items.Prev()
+	return cur
+}
+
+func (iter *orderedCollectionPageIterator) initItems() bool {
+	if iter.once {
+		return (iter.items != nil)
+	}
+	iter.once = true
+	if iter.ActivityStreamsOrderedCollectionPage == nil {
+		return false // no page set
+	}
+	items := iter.GetActivityStreamsOrderedItems()
+	if items == nil {
+		return false // no items found
+	}
+	iter.items = items.Begin()
+	return (iter.items != nil)
+}
+
+type CollectionParams struct {
+	// Containing collection
+	// ID (i.e. NOT the page).
+	ID *url.URL
+
+	// Total no. items.
+	Total int
+}
+
+type CollectionPageParams struct {
+	// containing collection.
+	CollectionParams
+
+	// Paging details.
+	Current *paging.Page
+	Next    *paging.Page
+	Prev    *paging.Page
+	Query   url.Values
+
+	// Item appender for each item at index.
+	Append func(int, ItemsPropertyBuilder)
+	Count  int
+}
+
+// CollectionPage is a simplified interface type
+// that can be fulfilled by either of (where required):
+// vocab.ActivityStreamsCollection
+// vocab.ActivityStreamsOrderedCollection
+type CollectionBuilder interface {
+	SetJSONLDId(vocab.JSONLDIdProperty)
+	SetActivityStreamsFirst(vocab.ActivityStreamsFirstProperty)
+	SetActivityStreamsTotalItems(i vocab.ActivityStreamsTotalItemsProperty)
+}
+
+// CollectionPageBuilder is a simplified interface type
+// that can be fulfilled by either of (where required):
+// vocab.ActivityStreamsCollectionPage
+// vocab.ActivityStreamsOrderedCollectionPage
+type CollectionPageBuilder interface {
+	SetJSONLDId(vocab.JSONLDIdProperty)
+	SetActivityStreamsPartOf(vocab.ActivityStreamsPartOfProperty)
+	SetActivityStreamsNext(vocab.ActivityStreamsNextProperty)
+	SetActivityStreamsPrev(vocab.ActivityStreamsPrevProperty)
+	SetActivityStreamsTotalItems(i vocab.ActivityStreamsTotalItemsProperty)
+}
+
+// ItemsPropertyBuilder is a simplified interface type
+// that can be fulfilled by either of (where required):
+// vocab.ActivityStreamsItemsProperty
+// vocab.ActivityStreamsOrderedItemsProperty
+type ItemsPropertyBuilder interface {
+	AppendIRI(*url.URL)
+
+	// NOTE: add more of the items-property-like interface
+	// functions here as you require them for building pages.
+}
+
+// NewASCollection builds and returns a new ActivityStreams Collection from given parameters.
+func NewASCollection(params CollectionParams) vocab.ActivityStreamsCollection {
+	collection := streams.NewActivityStreamsCollection()
+	buildCollection(collection, params, 40)
+	return collection
+}
+
+// NewASCollectionPage builds and returns a new ActivityStreams CollectionPage from given parameters (including item property appending function).
+func NewASCollectionPage(params CollectionPageParams) vocab.ActivityStreamsCollectionPage {
+	collectionPage := streams.NewActivityStreamsCollectionPage()
+	itemsProp := streams.NewActivityStreamsItemsProperty()
+	buildCollectionPage(collectionPage, itemsProp, collectionPage.SetActivityStreamsItems, params)
+	return collectionPage
+}
+
+// NewASOrderedCollection builds and returns a new ActivityStreams OrderedCollection from given parameters.
+func NewASOrderedCollection(params CollectionParams) vocab.ActivityStreamsOrderedCollection {
+	collection := streams.NewActivityStreamsOrderedCollection()
+	buildCollection(collection, params, 40)
+	return collection
+}
+
+// NewASOrderedCollectionPage builds and returns a new ActivityStreams OrderedCollectionPage from given parameters (including item property appending function).
+func NewASOrderedCollectionPage(params CollectionPageParams) vocab.ActivityStreamsOrderedCollectionPage {
+	collectionPage := streams.NewActivityStreamsOrderedCollectionPage()
+	itemsProp := streams.NewActivityStreamsOrderedItemsProperty()
+	buildCollectionPage(collectionPage, itemsProp, collectionPage.SetActivityStreamsOrderedItems, params)
+	return collectionPage
+}
+
+func buildCollection[C CollectionBuilder](collection C, params CollectionParams, pageLimit int) {
+	// Add the collection ID property.
+	idProp := streams.NewJSONLDIdProperty()
+	idProp.SetIRI(params.ID)
+	collection.SetJSONLDId(idProp)
+
+	// Add the collection totalItems count property.
+	totalItems := streams.NewActivityStreamsTotalItemsProperty()
+	totalItems.Set(params.Total)
+	collection.SetActivityStreamsTotalItems(totalItems)
+
+	// Clone the collection ID page
+	// to add first page query data.
+	firstIRI := new(url.URL)
+	*firstIRI = *params.ID
+
+	// Note that simply adding a limit signals to our
+	// endpoint to use paging (which will start at beginning).
+	limit := "limit=" + strconv.Itoa(pageLimit)
+	firstIRI.RawQuery = appendQuery(firstIRI.RawQuery, limit)
+
+	// Add the collection first IRI property.
+	first := streams.NewActivityStreamsFirstProperty()
+	first.SetIRI(firstIRI)
+	collection.SetActivityStreamsFirst(first)
+}
+
+func buildCollectionPage[C CollectionPageBuilder, I ItemsPropertyBuilder](collectionPage C, itemsProp I, setItems func(I), params CollectionPageParams) {
+	// Add the partOf property for its containing collection ID.
+	partOfProp := streams.NewActivityStreamsPartOfProperty()
+	partOfProp.SetIRI(params.ID)
+	collectionPage.SetActivityStreamsPartOf(partOfProp)
+
+	// Build the current page link IRI.
+	currentIRI := params.Current.ToLinkURL(
+		params.ID.Scheme,
+		params.ID.Host,
+		params.ID.Path,
+		params.Query,
+	)
+
+	// Add the collection ID property for
+	// the *current* collection page params.
+	idProp := streams.NewJSONLDIdProperty()
+	idProp.SetIRI(currentIRI)
+	collectionPage.SetJSONLDId(idProp)
+
+	// Build the next page link IRI.
+	nextIRI := params.Next.ToLinkURL(
+		params.ID.Scheme,
+		params.ID.Host,
+		params.ID.Path,
+		params.Query,
+	)
+
+	if nextIRI != nil {
+		// Add the collection next property for the next page.
+		nextProp := streams.NewActivityStreamsNextProperty()
+		nextProp.SetIRI(nextIRI)
+		collectionPage.SetActivityStreamsNext(nextProp)
+	}
+
+	// Build the prev page link IRI.
+	prevIRI := params.Prev.ToLinkURL(
+		params.ID.Scheme,
+		params.ID.Host,
+		params.ID.Path,
+		params.Query,
+	)
+
+	if prevIRI != nil {
+		// Add the collection prev property for the prev page.
+		prevProp := streams.NewActivityStreamsPrevProperty()
+		prevProp.SetIRI(prevIRI)
+		collectionPage.SetActivityStreamsPrev(prevProp)
+	}
+
+	// Add the collection totalItems count property.
+	totalItems := streams.NewActivityStreamsTotalItemsProperty()
+	totalItems.Set(params.Total)
+	collectionPage.SetActivityStreamsTotalItems(totalItems)
+
+	if params.Append == nil {
+		// nil check outside the for loop.
+		panic("nil params.Append function")
+	}
+
+	// Append each of the items to the provided
+	// pre-allocated items property builder type.
+	for i := 0; i < params.Count; i++ {
+		params.Append(i, itemsProp)
+	}
+
+	// Set the collection
+	// page items property.
+	setItems(itemsProp)
+}
+
+// appendQuery appends part to an existing raw
+// query with ampersand, else just returning part.
+func appendQuery(raw, part string) string {
+	if raw != "" {
+		return raw + "&" + part
+	}
+	return part
+}
diff --git a/internal/ap/interfaces.go b/internal/ap/interfaces.go
index 611f4bde0..5372eb01e 100644
--- a/internal/ap/interfaces.go
+++ b/internal/ap/interfaces.go
@@ -17,7 +17,11 @@
 
 package ap
 
-import "github.com/superseriousbusiness/activity/streams/vocab"
+import (
+	"net/url"
+
+	"github.com/superseriousbusiness/activity/streams/vocab"
+)
 
 // Accountable represents the minimum activitypub interface for representing an 'account'.
 // This interface is fulfilled by: Person, Application, Organization, Service, and Group
@@ -153,14 +157,23 @@ type ReplyToable interface {
 	WithInReplyTo
 }
 
-// CollectionPageable represents the minimum interface for an activitystreams 'CollectionPage' object.
-type CollectionPageable interface {
+// CollectionPageIterator represents the minimum interface for interacting with a wrapped
+// CollectionPage or OrderedCollectionPage in order to access both next / prev pages and items.
+type CollectionPageIterator interface {
 	WithJSONLDId
 	WithTypeName
 
-	WithNext
-	WithPartOf
-	WithItems
+	NextPage() WithIRI
+	PrevPage() WithIRI
+
+	NextItem() IteratorItemable
+	PrevItem() IteratorItemable
+}
+
+// IteratorItemable represents the minimum interface for an item in an iterator.
+type IteratorItemable interface {
+	WithIRI
+	WithType
 }
 
 // Flaggable represents the minimum interface for an activitystreams 'Flag' activity.
@@ -173,11 +186,22 @@ type Flaggable interface {
 	WithObject
 }
 
-// WithJSONLDId represents an activity with JSONLDIdProperty
+// WithJSONLDId represents an activity with JSONLDIdProperty.
 type WithJSONLDId interface {
 	GetJSONLDId() vocab.JSONLDIdProperty
 }
 
+// WithIRI represents an object (possibly) representable as an IRI.
+type WithIRI interface {
+	GetIRI() *url.URL
+	IsIRI() bool
+}
+
+// WithType ...
+type WithType interface {
+	GetType() vocab.Type
+}
+
 // WithTypeName represents an activity with a type name
 type WithTypeName interface {
 	GetTypeName() string