GoToSocial/internal/util/paging.go

// 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 util

import (
	"fmt"
	"net/url"
	"strings"

	apimodel "github.com/superseriousbusiness/gotosocial/internal/api/model"
	"github.com/superseriousbusiness/gotosocial/internal/config"
	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
)

// PageableResponseParams models the parameters to pass to PackagePageableResponse.
//
// 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 PageableResponseParams struct {
	Items            []interface{} // Sorted slice of items (statuses, notifications, etc)
	Path             string        // path to use for next/prev queries in the link header
	NextMaxIDKey     string        // key to use for the next max id query param in the link header, defaults to 'max_id'
	NextMaxIDValue   string        // value to use for next max id
	PrevMinIDKey     string        // key to use for the prev min id query param in the link header, defaults to 'min_id'
	PrevMinIDValue   string        // value to use for prev min id
	Limit            int           // limit number of entries to return
	ExtraQueryParams []string      // any extra query parameters to provide in the link header, should be in the format 'example=value'
}

// PackagePageableResponse 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 PackagePageableResponse(params PageableResponseParams) (*apimodel.PageableResponse, gtserror.WithCode) {
	if len(params.Items) == 0 {
		// No items to page through.
		return EmptyPageableResponse(), nil
	}

	// Set default paging values, if
	// they weren't set by the caller.
	if params.NextMaxIDKey == "" {
		params.NextMaxIDKey = "max_id"
	}

	if params.PrevMinIDKey == "" {
		params.PrevMinIDKey = "min_id"
	}

	var (
		protocol        = config.GetProtocol()
		host            = config.GetHost()
		nextLink        string
		prevLink        string
		linkHeaderParts = make([]string, 0, 2)
	)

	// Parse next link.
	if params.NextMaxIDValue != "" {
		nextRaw := params.NextMaxIDKey + "=" + params.NextMaxIDValue

		if params.Limit != 0 {
			nextRaw = fmt.Sprintf("limit=%d&", params.Limit) + nextRaw
		}

		for _, p := range params.ExtraQueryParams {
			nextRaw += "&" + p
		}

		nextLink = func() string {
			u := &url.URL{
				Scheme:   protocol,
				Host:     host,
				Path:     params.Path,
				RawQuery: nextRaw,
			}
			return u.String()
		}()

		linkHeaderParts = append(linkHeaderParts, `<`+nextLink+`>; rel="next"`)
	}

	// Parse prev link.
	if params.PrevMinIDValue != "" {
		prevRaw := params.PrevMinIDKey + "=" + params.PrevMinIDValue

		if params.Limit != 0 {
			prevRaw = fmt.Sprintf("limit=%d&", params.Limit) + prevRaw
		}

		for _, p := range params.ExtraQueryParams {
			prevRaw = prevRaw + "&" + p
		}

		prevLink = func() string {
			u := &url.URL{
				Scheme:   protocol,
				Host:     host,
				Path:     params.Path,
				RawQuery: prevRaw,
			}
			return u.String()
		}()

		linkHeaderParts = append(linkHeaderParts, `<`+prevLink+`>; rel="prev"`)
	}

	return &apimodel.PageableResponse{
		Items:      params.Items,
		LinkHeader: strings.Join(linkHeaderParts, ", "),
		NextLink:   nextLink,
		PrevLink:   prevLink,
	}, nil
}

// EmptyPageableResponse just returns an empty
// PageableResponse with no link header or items.
func EmptyPageableResponse() *apimodel.PageableResponse {
	return &apimodel.PageableResponse{
		Items: []interface{}{},
	}
}