// 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 dereferencing

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"net/url"
	"strings"

	apimodel "github.com/superseriousbusiness/gotosocial/internal/api/model"
	"github.com/superseriousbusiness/gotosocial/internal/transport"
	"github.com/superseriousbusiness/gotosocial/internal/util"
)

func (d *deref) fingerRemoteAccount(ctx context.Context, transport transport.Transport, targetUsername string, targetHost string) (accountDomain string, accountURI *url.URL, err error) {
	b, err := transport.Finger(ctx, targetUsername, targetHost)
	if err != nil {
		err = fmt.Errorf("fingerRemoteAccount: error fingering @%s@%s: %s", targetUsername, targetHost, err)
		return
	}

	resp := &apimodel.WellKnownResponse{}
	if err = json.Unmarshal(b, resp); err != nil {
		err = fmt.Errorf("fingerRemoteAccount: could not unmarshal server response as WebfingerAccountResponse while dereferencing @%s@%s: %s", targetUsername, targetHost, err)
		return
	}

	if len(resp.Links) == 0 {
		err = fmt.Errorf("fingerRemoteAccount: no links found in webfinger response %s", string(b))
		return
	}

	if resp.Subject == "" {
		err = fmt.Errorf("fingerRemoteAccount: no subject found in webfinger response %s", string(b))
		return
	}

	_, accountDomain, err = util.ExtractWebfingerParts(resp.Subject)
	if err != nil {
		err = fmt.Errorf("fingerRemoteAccount: error extracting webfinger subject parts: %s", err)
	}

	// look through the links for the first one that matches what we need
	for _, l := range resp.Links {
		if l.Rel == "self" && (strings.EqualFold(l.Type, "application/activity+json") || strings.EqualFold(l.Type, "application/ld+json; profile=\"https://www.w3.org/ns/activitystreams\"")) {
			if uri, thiserr := url.Parse(l.Href); thiserr == nil && (uri.Scheme == "http" || uri.Scheme == "https") {
				// found it!
				accountURI = uri
				return
			}
		}
	}

	err = errors.New("fingerRemoteAccount: no match found in webfinger response")
	return
}