[chore] much improved paging package (#2182)

internal/paging/response.go

@@ -0,0 +1,91 @@
+// 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 paging
+
+import (
+	"strings"
+
+	apimodel "github.com/superseriousbusiness/gotosocial/internal/api/model"
+	"github.com/superseriousbusiness/gotosocial/internal/config"
+)
+
+// ResponseParams models the parameters to pass to PageableResponse.
+//
+// The given items will be provided in the paged response.
+//
+// The other values are all used to create the Link header so that callers know
+// which endpoint to query next and previously in order to do paging.
+type ResponseParams struct {
+	Items []interface{} // Sorted slice of items (statuses, notifications, etc)
+	Path  string        // path to use for next/prev queries in the link header
+	Next  *Page         // page details for the next page
+	Prev  *Page         // page details for the previous page
+	Query []string      // any extra query parameters to provide in the link header, should be in the format 'example=value'
+}
+
+// PackageResponse is a convenience function for returning
+// a bunch of pageable items (notifications, statuses, etc), as well
+// as a Link header to inform callers of where to find next/prev items.
+func PackageResponse(params ResponseParams) *apimodel.PageableResponse {
+	if len(params.Items) == 0 {
+		// No items to page through.
+		return EmptyResponse()
+	}
+
+	var (
+		// Extract paging params.
+		nextPg = params.Next
+		prevPg = params.Prev
+
+		// Host app configuration.
+		proto = config.GetProtocol()
+		host  = config.GetHost()
+
+		// Combined next/prev page link header parts.
+		linkHeaderParts = make([]string, 0, 2)
+	)
+
+	// Build the next / previous page links from page and host config.
+	nextLink := nextPg.ToLink(proto, host, params.Path, params.Query)
+	prevLink := prevPg.ToLink(proto, host, params.Path, params.Query)
+
+	if nextLink != "" {
+		// Append page "next" link to header parts.
+		linkHeaderParts = append(linkHeaderParts, `<`+nextLink+`>; rel="next"`)
+	}
+
+	if prevLink != "" {
+		// Append page "prev" link to header parts.
+		linkHeaderParts = append(linkHeaderParts, `<`+prevLink+`>; rel="prev"`)
+	}
+
+	return &apimodel.PageableResponse{
+		Items:      params.Items,
+		NextLink:   nextLink,
+		PrevLink:   prevLink,
+		LinkHeader: strings.Join(linkHeaderParts, ", "),
+	}
+}
+
+// EmptyResponse just returns an empty
+// PageableResponse with no link header or items.
+func EmptyResponse() *apimodel.PageableResponse {
+	return &apimodel.PageableResponse{
+		Items: []interface{}{},
+	}
+}