add chat members to the backup

lazily fetch the chat members and add them to the chat
during backup item downloads.

src/internal/m365/collection/teamsChats/chat_handler.go

@@ -99,6 +99,13 @@ func (bh usersChatsBackupHandler) getItem(
 
 	chat.SetMessages(msgs)
 
+	members, err := bh.ac.GetChatMembers(ctx, chatID, api.CallConfig{})
+	if err != nil {
+		return nil, nil, clues.Stack(err)
+	}
+
+	chat.SetMembers(members)
+
 	return chat, api.TeamsChatInfo(chat), nil
 }
 

src/pkg/services/m365/api/teamsChats_pager.go

@@ -12,6 +12,79 @@ import (
 	"github.com/alcionai/corso/src/pkg/services/m365/api/pagers"
 )
 
+// ---------------------------------------------------------------------------
+// chat members pager
+// ---------------------------------------------------------------------------
+
+// delta queries are not supported
+var _ pagers.NonDeltaHandler[models.ConversationMemberable] = &chatMembersPageCtrl{}
+
+type chatMembersPageCtrl struct {
+	chatID  string
+	gs      graph.Servicer
+	builder *chats.ItemMembersRequestBuilder
+	options *chats.ItemMembersRequestBuilderGetRequestConfiguration
+}
+
+func (p *chatMembersPageCtrl) SetNextLink(nextLink string) {
+	p.builder = chats.NewItemMembersRequestBuilder(nextLink, p.gs.Adapter())
+}
+
+func (p *chatMembersPageCtrl) GetPage(
+	ctx context.Context,
+) (pagers.NextLinkValuer[models.ConversationMemberable], error) {
+	resp, err := p.builder.Get(ctx, p.options)
+	return resp, graph.Stack(ctx, err).OrNil()
+}
+
+func (p *chatMembersPageCtrl) ValidModTimes() bool {
+	return true
+}
+
+func (c Chats) NewChatMembersPager(
+	chatID string,
+	cc CallConfig,
+) *chatMembersPageCtrl {
+	builder := c.Stable.
+		Client().
+		Chats().
+		ByChatId(chatID).
+		Members()
+
+	options := &chats.ItemMembersRequestBuilderGetRequestConfiguration{
+		QueryParameters: &chats.ItemMembersRequestBuilderGetQueryParameters{},
+		Headers:         newPreferHeaders(preferPageSize(maxNonDeltaPageSize)),
+	}
+
+	if len(cc.Select) > 0 {
+		options.QueryParameters.Select = cc.Select
+	}
+
+	if len(cc.Expand) > 0 {
+		options.QueryParameters.Expand = cc.Expand
+	}
+
+	return &chatMembersPageCtrl{
+		chatID:  chatID,
+		builder: builder,
+		gs:      c.Stable,
+		options: options,
+	}
+}
+
+// GetChatMembers fetches a delta of all members in the chat.
+func (c Chats) GetChatMembers(
+	ctx context.Context,
+	chatID string,
+	cc CallConfig,
+) ([]models.ConversationMemberable, error) {
+	ctx = clues.Add(ctx, "chat_id", chatID)
+	pager := c.NewChatMembersPager(chatID, cc)
+	items, err := pagers.BatchEnumerateItems[models.ConversationMemberable](ctx, pager)
+
+	return items, graph.Stack(ctx, err).OrNil()
+}
+
 // ---------------------------------------------------------------------------
 // chat message pager
 // ---------------------------------------------------------------------------

src/pkg/services/m365/api/teamsChats_pager_test.go

@@ -61,6 +61,11 @@ func (suite *ChatsPagerIntgSuite) TestEnumerateChats() {
 				ac,
 				chatID,
 				chat.GetLastMessagePreview())
+
+			testEnumerateChatMembers(
+				suite.T(),
+				ac,
+				chatID)
 		})
 	}
 }
@@ -123,3 +128,22 @@ func testEnumerateChatMessages(
 		}
 	}
 }
+
+func testEnumerateChatMembers(
+	t *testing.T,
+	ac Chats,
+	chatID string,
+) {
+	ctx, flush := tester.NewContext(t)
+	defer flush()
+
+	cc := CallConfig{}
+
+	members, err := ac.GetChatMembers(ctx, chatID, cc)
+	require.NoError(t, err, clues.ToCore(err))
+
+	// no good way to test members right now.  Even though
+	// the graph api response contains the `userID` and `email`
+	// properties, we can't access them in the sdk model
+	assert.NotEmpty(t, members)
+}