package helpers

import (
	"context"
	"fmt"

	"github.com/matrix-org/dendrite/roomserver/api"
	"github.com/matrix-org/dendrite/roomserver/auth"
	"github.com/matrix-org/dendrite/roomserver/state"
	"github.com/matrix-org/dendrite/roomserver/storage"
	"github.com/matrix-org/dendrite/roomserver/storage/shared"
	"github.com/matrix-org/dendrite/roomserver/types"
	"github.com/matrix-org/gomatrixserverlib"
	"github.com/matrix-org/util"
)

// TODO: temporary package which has helper functions used by both internal/perform packages.
// Move these to a more sensible place.

func UpdateToInviteMembership(
	mu *shared.MembershipUpdater, add *gomatrixserverlib.Event, updates []api.OutputEvent,
	roomVersion gomatrixserverlib.RoomVersion,
) ([]api.OutputEvent, error) {
	// We may have already sent the invite to the user, either because we are
	// reprocessing this event, or because the we received this invite from a
	// remote server via the federation invite API. In those cases we don't need
	// to send the event.
	needsSending, err := mu.SetToInvite(*add)
	if err != nil {
		return nil, err
	}
	if needsSending {
		// We notify the consumers using a special event even though we will
		// notify them about the change in current state as part of the normal
		// room event stream. This ensures that the consumers only have to
		// consider a single stream of events when determining whether a user
		// is invited, rather than having to combine multiple streams themselves.
		onie := api.OutputNewInviteEvent{
			Event:       add.Headered(roomVersion),
			RoomVersion: roomVersion,
		}
		updates = append(updates, api.OutputEvent{
			Type:           api.OutputTypeNewInviteEvent,
			NewInviteEvent: &onie,
		})
	}
	return updates, nil
}

func IsServerCurrentlyInRoom(ctx context.Context, db storage.Database, serverName gomatrixserverlib.ServerName, roomID string) (bool, error) {
	info, err := db.RoomInfo(ctx, roomID)
	if err != nil {
		return false, err
	}
	if info == nil {
		return false, fmt.Errorf("unknown room %s", roomID)
	}

	eventNIDs, err := db.GetMembershipEventNIDsForRoom(ctx, info.RoomNID, true, false)
	if err != nil {
		return false, err
	}

	events, err := db.Events(ctx, eventNIDs)
	if err != nil {
		return false, err
	}
	gmslEvents := make([]gomatrixserverlib.Event, len(events))
	for i := range events {
		gmslEvents[i] = events[i].Event
	}
	return auth.IsAnyUserOnServerWithMembership(serverName, gmslEvents, gomatrixserverlib.Join), nil
}

func IsInvitePending(
	ctx context.Context, db storage.Database,
	roomID, userID string,
) (bool, string, string, error) {
	// Look up the room NID for the supplied room ID.
	info, err := db.RoomInfo(ctx, roomID)
	if err != nil {
		return false, "", "", fmt.Errorf("r.DB.RoomInfo: %w", err)
	}
	if info == nil {
		return false, "", "", fmt.Errorf("cannot get RoomInfo: unknown room ID %s", roomID)
	}

	// Look up the state key NID for the supplied user ID.
	targetUserNIDs, err := db.EventStateKeyNIDs(ctx, []string{userID})
	if err != nil {
		return false, "", "", fmt.Errorf("r.DB.EventStateKeyNIDs: %w", err)
	}
	targetUserNID, targetUserFound := targetUserNIDs[userID]
	if !targetUserFound {
		return false, "", "", fmt.Errorf("missing NID for user %q (%+v)", userID, targetUserNIDs)
	}

	// Let's see if we have an event active for the user in the room. If
	// we do then it will contain a server name that we can direct the
	// send_leave to.
	senderUserNIDs, eventIDs, err := db.GetInvitesForUser(ctx, info.RoomNID, targetUserNID)
	if err != nil {
		return false, "", "", fmt.Errorf("r.DB.GetInvitesForUser: %w", err)
	}
	if len(senderUserNIDs) == 0 {
		return false, "", "", nil
	}
	userNIDToEventID := make(map[types.EventStateKeyNID]string)
	for i, nid := range senderUserNIDs {
		userNIDToEventID[nid] = eventIDs[i]
	}

	// Look up the user ID from the NID.
	senderUsers, err := db.EventStateKeys(ctx, senderUserNIDs)
	if err != nil {
		return false, "", "", fmt.Errorf("r.DB.EventStateKeys: %w", err)
	}
	if len(senderUsers) == 0 {
		return false, "", "", fmt.Errorf("no senderUsers")
	}

	senderUser, senderUserFound := senderUsers[senderUserNIDs[0]]
	if !senderUserFound {
		return false, "", "", fmt.Errorf("missing user for NID %d (%+v)", senderUserNIDs[0], senderUsers)
	}

	return true, senderUser, userNIDToEventID[senderUserNIDs[0]], nil
}

// GetMembershipsAtState filters the state events to
// only keep the "m.room.member" events with a "join" membership. These events are returned.
// Returns an error if there was an issue fetching the events.
func GetMembershipsAtState(
	ctx context.Context, db storage.Database, stateEntries []types.StateEntry, joinedOnly bool,
) ([]types.Event, error) {

	var eventNIDs []types.EventNID
	for _, entry := range stateEntries {
		// Filter the events to retrieve to only keep the membership events
		if entry.EventTypeNID == types.MRoomMemberNID {
			eventNIDs = append(eventNIDs, entry.EventNID)
		}
	}

	// Get all of the events in this state
	stateEvents, err := db.Events(ctx, eventNIDs)
	if err != nil {
		return nil, err
	}

	if !joinedOnly {
		return stateEvents, nil
	}

	// Filter the events to only keep the "join" membership events
	var events []types.Event
	for _, event := range stateEvents {
		membership, err := event.Membership()
		if err != nil {
			return nil, err
		}

		if membership == gomatrixserverlib.Join {
			events = append(events, event)
		}
	}

	return events, nil
}

func StateBeforeEvent(ctx context.Context, db storage.Database, info types.RoomInfo, eventNID types.EventNID) ([]types.StateEntry, error) {
	roomState := state.NewStateResolution(db, info)
	// Lookup the event NID
	eIDs, err := db.EventIDs(ctx, []types.EventNID{eventNID})
	if err != nil {
		return nil, err
	}
	eventIDs := []string{eIDs[eventNID]}

	prevState, err := db.StateAtEventIDs(ctx, eventIDs)
	if err != nil {
		return nil, err
	}

	// Fetch the state as it was when this event was fired
	return roomState.LoadCombinedStateAfterEvents(ctx, prevState)
}

func LoadEvents(
	ctx context.Context, db storage.Database, eventNIDs []types.EventNID,
) ([]gomatrixserverlib.Event, error) {
	stateEvents, err := db.Events(ctx, eventNIDs)
	if err != nil {
		return nil, err
	}

	result := make([]gomatrixserverlib.Event, len(stateEvents))
	for i := range stateEvents {
		result[i] = stateEvents[i].Event
	}
	return result, nil
}

func LoadStateEvents(
	ctx context.Context, db storage.Database, stateEntries []types.StateEntry,
) ([]gomatrixserverlib.Event, error) {
	eventNIDs := make([]types.EventNID, len(stateEntries))
	for i := range stateEntries {
		eventNIDs[i] = stateEntries[i].EventNID
	}
	return LoadEvents(ctx, db, eventNIDs)
}

func CheckServerAllowedToSeeEvent(
	ctx context.Context, db storage.Database, info types.RoomInfo, eventID string, serverName gomatrixserverlib.ServerName, isServerInRoom bool,
) (bool, error) {
	roomState := state.NewStateResolution(db, info)
	stateEntries, err := roomState.LoadStateAtEvent(ctx, eventID)
	if err != nil {
		return false, err
	}

	// TODO: We probably want to make it so that we don't have to pull
	// out all the state if possible.
	stateAtEvent, err := LoadStateEvents(ctx, db, stateEntries)
	if err != nil {
		return false, err
	}

	return auth.IsServerAllowed(serverName, isServerInRoom, stateAtEvent), nil
}

// TODO: Remove this when we have tests to assert correctness of this function
// nolint:gocyclo
func ScanEventTree(
	ctx context.Context, db storage.Database, info types.RoomInfo, front []string, visited map[string]bool, limit int,
	serverName gomatrixserverlib.ServerName,
) ([]types.EventNID, error) {
	var resultNIDs []types.EventNID
	var err error
	var allowed bool
	var events []types.Event
	var next []string
	var pre string

	// TODO: add tests for this function to ensure it meets the contract that callers expect (and doc what that is supposed to be)
	// Currently, callers like PerformBackfill will call scanEventTree with a pre-populated `visited` map, assuming that by doing
	// so means that the events in that map will NOT be returned from this function. That is not currently true, resulting in
	// duplicate events being sent in response to /backfill requests.
	initialIgnoreList := make(map[string]bool, len(visited))
	for k, v := range visited {
		initialIgnoreList[k] = v
	}

	resultNIDs = make([]types.EventNID, 0, limit)

	var checkedServerInRoom bool
	var isServerInRoom bool

	// Loop through the event IDs to retrieve the requested events and go
	// through the whole tree (up to the provided limit) using the events'
	// "prev_event" key.
BFSLoop:
	for len(front) > 0 {
		// Prevent unnecessary allocations: reset the slice only when not empty.
		if len(next) > 0 {
			next = make([]string, 0)
		}
		// Retrieve the events to process from the database.
		events, err = db.EventsFromIDs(ctx, front)
		if err != nil {
			return resultNIDs, err
		}

		if !checkedServerInRoom && len(events) > 0 {
			// It's nasty that we have to extract the room ID from an event, but many federation requests
			// only talk in event IDs, no room IDs at all (!!!)
			ev := events[0]
			isServerInRoom, err = IsServerCurrentlyInRoom(ctx, db, serverName, ev.RoomID())
			if err != nil {
				util.GetLogger(ctx).WithError(err).Error("Failed to check if server is currently in room, assuming not.")
			}
			checkedServerInRoom = true
		}

		for _, ev := range events {
			// Break out of the loop if the provided limit is reached.
			if len(resultNIDs) == limit {
				break BFSLoop
			}

			if !initialIgnoreList[ev.EventID()] {
				// Update the list of events to retrieve.
				resultNIDs = append(resultNIDs, ev.EventNID)
			}
			// Loop through the event's parents.
			for _, pre = range ev.PrevEventIDs() {
				// Only add an event to the list of next events to process if it
				// hasn't been seen before.
				if !visited[pre] {
					visited[pre] = true
					allowed, err = CheckServerAllowedToSeeEvent(ctx, db, info, pre, serverName, isServerInRoom)
					if err != nil {
						util.GetLogger(ctx).WithField("server", serverName).WithField("event_id", pre).WithError(err).Error(
							"Error checking if allowed to see event",
						)
						return resultNIDs, err
					}

					// If the event hasn't been seen before and the HS
					// requesting to retrieve it is allowed to do so, add it to
					// the list of events to retrieve.
					if allowed {
						next = append(next, pre)
					} else {
						util.GetLogger(ctx).WithField("server", serverName).WithField("event_id", pre).Info("Not allowed to see event")
					}
				}
			}
		}
		// Repeat the same process with the parent events we just processed.
		front = next
	}

	return resultNIDs, err
}