// Copyright (c) 2024 mStar
//
// Licensed under the EUPL, Version 1.2
//
// You may not use this work except in compliance with the Licence.
// You should have received a copy of the Licence along with this work. If not, see:
// <https://joinup.ec.europa.eu/collection/eupl/eupl-text-eupl-12>.
// See the Licence for the specific language governing permissions and limitations under the Licence.
//

package ap

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

	"github.com/julienschmidt/httprouter"
	"gitlab.com/mstarongitlab/goutils/other"
	"gitlab.com/mstarongitlab/linstrom/server"
	"gitlab.com/mstarongitlab/linstrom/storage"
	"gitlab.com/mstarongitlab/linstrom/types"
)

var ErrInvalidResource = errors.New("invalid resource")

type webfingerLink struct {
	Rel    string  `json:"self"`
	Type   string  `json:"type"`
	Target url.URL `json:"href"`
}

type WebfingerResponse struct {
	Subject string          `json:"subject"`
	Links   []webfingerLink `json:"links"`
}

func WebfingerEndpoint(server *server.Server) func(http.ResponseWriter, *http.Request, httprouter.Params) {
	return func(w http.ResponseWriter, r *http.Request, _ httprouter.Params) {
		r.ParseForm()
		req := r.FormValue("resource")
		if req == "" {
			http.NotFound(w, r)
			return
		}
		acc, err := getAccountFromWebfingerResource(req)
		if errors.Is(err, ErrInvalidResource) {
			http.Error(w, err.Error(), http.StatusBadRequest)
			return
		}
		if acc.Host.Hostname() != server.Config.General.Domain {
			http.Error(w, fmt.Sprintf("wrong host, try %s", &acc.Host), http.StatusNotFound)
			return
		}

		person, err := server.Storage.GetPersonByName(acc.Name)
		if err != nil {
			if errors.Is(err, storage.ErrNotFound) {
				http.Error(w, fmt.Sprintf("Account %s not found", acc), http.StatusNotFound)
				return
			} else {
				http.Error(w, fmt.Sprintf("Internal error: %s, please report", err.Error()), http.StatusInternalServerError)
			}
		}

		response := WebfingerResponse{
			Links: []webfingerLink{
				{
					Rel:  "me",
					Type: "application/activity+json",
					Target: *other.Must(url.Parse(fmt.Sprintf(
						"https://%s/api/ap/user/%s",
						server.Config.General.Domain,
						person.Uid,
					))),
				},
			},
		}
		json.Marshal(response)
	}
}

// turns "acct:bugle@bugle.lol" into { Name: bugle, Host: bugle.lol }
func getAccountFromWebfingerResource(r string) (*types.AccountHandle, error) {
	acctCheck, acc, found := strings.Cut(r, ":")
	if !found || acctCheck != "acct" {
		return nil, ErrInvalidResource
	}
	name, rawHost, found := strings.Cut(acc, "@")
	if !found {
		return nil, ErrInvalidResource
	}
	host, err := url.Parse(rawHost)
	if err != nil {
		return nil, fmt.Errorf("%w: Invalid url: %w", ErrInvalidResource, err)
	}

	return &types.AccountHandle{
		Name: name,
		Host: *host,
	}, nil
}