MM-64330 - filter abac users in channel invite (#31219)

* MM-64330 - filter abac users in channel invite

* implement cursor functionality for abac user filtering

* remove unnecessary comments

* refactor the backend implementation simplifying the functions

* refactor api to use opts as parameters, rename function

* add missing translation

* remove unnecesary test code

---------

Co-authored-by: Mattermost Build <build@mattermost.com>

server/public/model/client4.go

@@ -1396,8 +1396,23 @@ func (c *Client4) GetUsersInChannelByStatus(ctx context.Context, channelId strin
 
 // GetUsersNotInChannel returns a page of users not in a channel. Page counting starts at 0.
 func (c *Client4) GetUsersNotInChannel(ctx context.Context, teamId, channelId string, page int, perPage int, etag string) ([]*User, *Response, error) {
-	query := fmt.Sprintf("?in_team=%v&not_in_channel=%v&page=%v&per_page=%v", teamId, channelId, page, perPage)
-	r, err := c.DoAPIGet(ctx, c.usersRoute()+query, etag)
+	options := &GetUsersNotInChannelOptions{
+		TeamID:   teamId,
+		Page:     page,
+		Limit:    perPage,
+		Etag:     etag,
+		CursorID: "",
+	}
+	return c.GetUsersNotInChannelWithOptions(ctx, channelId, options)
+}
+
+// GetUsersNotInChannelWithOptionsStruct returns a page of users not in a channel using the options struct.
+func (c *Client4) GetUsersNotInChannelWithOptions(ctx context.Context, channelId string, options *GetUsersNotInChannelOptions) ([]*User, *Response, error) {
+	query := fmt.Sprintf("?in_team=%v&not_in_channel=%v&page=%v&per_page=%v", options.TeamID, channelId, options.Page, options.Limit)
+	if options.CursorID != "" {
+		query += fmt.Sprintf("&cursor_id=%v", options.CursorID)
+	}
+	r, err := c.DoAPIGet(ctx, c.usersRoute()+query, options.Etag)
 	if err != nil {
 		return nil, BuildResponse(r), err
 	}
@@ -1407,7 +1422,7 @@ func (c *Client4) GetUsersNotInChannel(ctx context.Context, teamId, channelId st
 		return list, BuildResponse(r), nil
 	}
 	if err := json.NewDecoder(r.Body).Decode(&list); err != nil {
-		return nil, nil, NewAppError("GetUsersNotInChannel", "api.unmarshal_error", nil, "", http.StatusInternalServerError).Wrap(err)
+		return nil, nil, NewAppError("GetUsersNotInChannelWithOptionsStruct", "api.unmarshal_error", nil, "", http.StatusInternalServerError).Wrap(err)
 	}
 	return list, BuildResponse(r), nil
 }

server/public/model/user.go

@@ -243,6 +243,19 @@ type ViewUsersRestrictions struct {
 	Channels []string
 }
 
+//msgp:ignore GetUsersNotInChannelOptions
+type GetUsersNotInChannelOptions struct {
+	TeamID string `json:"team_id"`
+	// Page-based pagination (used for non-ABAC channels)
+	// This will be discarded if the channel has an ABAC policy and CursorID will be used.
+	Page  int `json:"page"`
+	Limit int `json:"limit"`
+	// Cursor-based pagination (used for ABAC channels)
+	// If CursorID is empty for ABAC channels, it will start from the beginning
+	CursorID string `json:"cursor_id"`
+	Etag     string `json:"etag"`
+}
+
 func (r *ViewUsersRestrictions) Hash() string {
 	if r == nil {
 		return ""