// 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 auth

import (
	"encoding/json"
	"fmt"

	"github.com/matrix-org/gomatrixserverlib"
)

const (
	shared = "shared"
)

// TODO: This logic should live in gomatrixserverlib

// IsServerAllowed returns true if the server is allowed to see events in the room
// at this particular state. This function implements https://matrix.org/docs/spec/client_server/r0.6.0#id87
func IsServerAllowed(
	serverName gomatrixserverlib.ServerName,
	serverCurrentlyInRoom bool,
	authEvents []gomatrixserverlib.Event,
) bool {
	var hisVisEvent *gomatrixserverlib.Event
	for i, ae := range authEvents {
		if ae.Type() == gomatrixserverlib.MRoomHistoryVisibility && ae.StateKeyEquals("") {
			hisVisEvent = &authEvents[i]
			break
		}
	}
	historyVisibility, err := HistoryVisibilityForRoom(hisVisEvent)
	if err != nil {
		return false
	}

	// 1. If the history_visibility was set to world_readable, allow.
	if historyVisibility == "world_readable" {
		return true
	}
	// 2. If the user's membership was join, allow.
	joinedUserExists := IsAnyUserOnServerWithMembership(serverName, authEvents, gomatrixserverlib.Join)
	if joinedUserExists {
		return true
	}
	// 3. If history_visibility was set to shared, and the user joined the room at any point after the event was sent, allow.
	if historyVisibility == shared && serverCurrentlyInRoom {
		return true
	}
	// 4. If the user's membership was invite, and the history_visibility was set to invited, allow.
	invitedUserExists := IsAnyUserOnServerWithMembership(serverName, authEvents, gomatrixserverlib.Invite)
	if invitedUserExists && historyVisibility == "invited" {
		return true
	}

	// 5. Otherwise, deny.
	return false
}

func HistoryVisibilityForRoom(hisVisEvent *gomatrixserverlib.Event) (string, error) {
	// https://matrix.org/docs/spec/client_server/r0.6.0#id87
	// By default if no history_visibility is set, or if the value is not understood, the visibility is assumed to be shared.
	if hisVisEvent == nil {
		return shared, nil
	}
	visibility := shared
	knownStates := []string{"invited", "joined", shared, "world_readable"}
	if hisVisEvent.Type() != gomatrixserverlib.MRoomHistoryVisibility {
		return "", fmt.Errorf("HistoryVisibilityForRoom: passed a non history visibility event: %s", hisVisEvent.Type())
	}
	// TODO: This should be HistoryVisibilityContent to match things like 'MemberContent'. Do this when moving to GMSL
	content := struct {
		HistoryVisibility string `json:"history_visibility"`
	}{}
	if err := json.Unmarshal(hisVisEvent.Content(), &content); err != nil {
		return visibility, nil // value is not understood
	}
	for _, s := range knownStates {
		if s == content.HistoryVisibility {
			visibility = s
			break
		}
	}
	return visibility, nil
}

func IsAnyUserOnServerWithMembership(serverName gomatrixserverlib.ServerName, authEvents []gomatrixserverlib.Event, wantMembership string) bool {
	for _, ev := range authEvents {
		membership, err := ev.Membership()
		if err != nil || membership != wantMembership {
			continue
		}

		stateKey := ev.StateKey()
		if stateKey == nil {
			continue
		}

		_, domain, err := gomatrixserverlib.SplitID('@', *stateKey)
		if err != nil {
			continue
		}

		if domain == serverName {
			return true
		}
	}
	return false
}