// Copyright 2022 The Matrix.org Foundation C.I.C.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package routing

import (
	"net/http"
	"strconv"

	"github.com/matrix-org/gomatrixserverlib"
	"github.com/matrix-org/util"
	"github.com/sirupsen/logrus"

	"github.com/matrix-org/dendrite/clientapi/jsonerror"
	"github.com/matrix-org/dendrite/internal/sqlutil"
	"github.com/matrix-org/dendrite/roomserver/api"
	"github.com/matrix-org/dendrite/syncapi/internal"
	"github.com/matrix-org/dendrite/syncapi/storage"
	"github.com/matrix-org/dendrite/syncapi/types"
	userapi "github.com/matrix-org/dendrite/userapi/api"
)

type RelationsResponse struct {
	Chunk     []gomatrixserverlib.ClientEvent `json:"chunk"`
	NextBatch string                          `json:"next_batch,omitempty"`
	PrevBatch string                          `json:"prev_batch,omitempty"`
}

// nolint:gocyclo
func Relations(
	req *http.Request, device *userapi.Device,
	syncDB storage.Database,
	rsAPI api.SyncRoomserverAPI,
	roomID, eventID, relType, eventType string,
) util.JSONResponse {
	var err error
	var from, to types.StreamPosition
	var limit int
	dir := req.URL.Query().Get("dir")
	if f := req.URL.Query().Get("from"); f != "" {
		if from, err = types.NewStreamPositionFromString(f); err != nil {
			return util.ErrorResponse(err)
		}
	}
	if t := req.URL.Query().Get("to"); t != "" {
		if to, err = types.NewStreamPositionFromString(t); err != nil {
			return util.ErrorResponse(err)
		}
	}
	if l := req.URL.Query().Get("limit"); l != "" {
		if limit, err = strconv.Atoi(l); err != nil {
			return util.ErrorResponse(err)
		}
	}
	if limit == 0 || limit > 50 {
		limit = 50
	}
	if dir == "" {
		dir = "b"
	}
	if dir != "b" && dir != "f" {
		return util.JSONResponse{
			Code: http.StatusBadRequest,
			JSON: jsonerror.MissingArgument("Bad or missing dir query parameter (should be either 'b' or 'f')"),
		}
	}

	snapshot, err := syncDB.NewDatabaseSnapshot(req.Context())
	if err != nil {
		logrus.WithError(err).Error("Failed to get snapshot for relations")
		return jsonerror.InternalServerError()
	}
	var succeeded bool
	defer sqlutil.EndTransactionWithCheck(snapshot, &succeeded, &err)

	res := &RelationsResponse{
		Chunk: []gomatrixserverlib.ClientEvent{},
	}
	var events []types.StreamEvent
	events, res.PrevBatch, res.NextBatch, err = snapshot.RelationsFor(
		req.Context(), roomID, eventID, relType, eventType, from, to, dir == "b", limit,
	)
	if err != nil {
		return util.ErrorResponse(err)
	}

	headeredEvents := make([]*gomatrixserverlib.HeaderedEvent, 0, len(events))
	for _, event := range events {
		headeredEvents = append(headeredEvents, event.HeaderedEvent)
	}

	// Apply history visibility to the result events.
	filteredEvents, err := internal.ApplyHistoryVisibilityFilter(req.Context(), snapshot, rsAPI, headeredEvents, nil, device.UserID, "relations")
	if err != nil {
		return util.ErrorResponse(err)
	}

	// Convert the events into client events, and optionally filter based on the event
	// type if it was specified.
	res.Chunk = make([]gomatrixserverlib.ClientEvent, 0, len(filteredEvents))
	for _, event := range filteredEvents {
		res.Chunk = append(
			res.Chunk,
			gomatrixserverlib.ToClientEvent(event.Event, gomatrixserverlib.FormatAll),
		)
	}

	succeeded = true
	return util.JSONResponse{
		Code: http.StatusOK,
		JSON: res,
	}
}