package roomserver

import (
	"context"
	"encoding/json"
	"fmt"

	"github.com/dariuszjaniak/warp/server/internal/matrix/auth"
	"github.com/dariuszjaniak/warp/server/internal/matrix/event"
	"github.com/dariuszjaniak/warp/server/internal/matrix/roomversion"
	"github.com/dariuszjaniak/warp/server/internal/storage"
)

// currentState reads a room's current state as the authorisation rules see
// it.
func (r *API) currentState(ctx context.Context, room storage.Room, rules roomversion.Rules) (auth.State, error) {
	stored, err := r.store.CurrentStateEvents(ctx, room.ID)
	if err != nil {
		return nil, err
	}
	events, err := parseEvents(stored, rules)
	if err != nil {
		return nil, err
	}
	return auth.NewState(events), nil
}

// ClientEvent is an event in the shape the Client-Server API returns it.
//
// It is not the event as it was signed. A client is given the event ID
// explicitly — in every room version since 3 it is a hash, not a property —
// and is not given the hashes, signatures, auth_events or depth, which are
// a server's business. What it does get that the signed event never carried
// is `unsigned`, which is per-server annotation: the age of the event, the
// state it replaced, and the redaction that stripped it.
type ClientEvent struct {
	EventID string `json:"event_id"`

	// RoomID is omitted when empty, because a /sync response carries its
	// events without one: they are already nested under the room they
	// belong to, and repeating it on every event of a client with a
	// thousand rooms is a measurable part of every response. Every other
	// endpoint sets it, and the spec has a separate name for the shape
	// without it — ClientEventWithoutRoomID — rather than two event types.
	RoomID string `json:"room_id,omitempty"`

	Type           string          `json:"type"`
	StateKey       *string         `json:"state_key,omitempty"`
	Sender         string          `json:"sender"`
	Content        json.RawMessage `json:"content"`
	OriginServerTS int64           `json:"origin_server_ts"`
	Unsigned       json.RawMessage `json:"unsigned,omitempty"`

	// Redacts is only on an m.room.redaction event, and only in the room
	// versions that keep it at the top level. Clients still read it there.
	Redacts string `json:"redacts,omitempty"`
}

// clientEvent projects a stored event into the client shape.
func (r *API) clientEvent(stored storage.StoredEvent, e *event.Event, roomID string) ClientEvent {
	out := ClientEvent{
		EventID:        e.EventID(),
		RoomID:         roomID,
		Type:           e.Type(),
		Sender:         e.Sender(),
		Content:        e.Content(),
		OriginServerTS: e.OriginServerTS(),
		Redacts:        e.Redacts(),
	}
	if stateKey, ok := e.StateKey(); ok {
		out.StateKey = &stateKey
	}
	out.Unsigned = r.unsigned(stored, e)
	return out
}

// unsigned builds the `unsigned` block a client is given.
//
// `age` is computed on the way out rather than stored: it is how long ago
// the event happened as far as this server can tell, and a value written
// down at persist time would be wrong by however long the event sat in the
// database.
func (r *API) unsigned(stored storage.StoredEvent, e *event.Event) json.RawMessage {
	block := map[string]json.RawMessage{}
	if existing := e.Unsigned(); len(existing) > 0 {
		if err := json.Unmarshal(existing, &block); err != nil {
			// The unsigned block is this server's own annotation and is
			// written as an object everywhere; anything else is a bug here
			// rather than something a client sent, and dropping it is
			// better than failing the read.
			r.log.Warn("stored event has an unreadable unsigned block", "event_id", e.EventID())
			block = map[string]json.RawMessage{}
		}
	}
	if age := r.nowMS() - e.OriginServerTS(); age >= 0 {
		block["age"] = mustMarshal(age)
	}
	if stored.RedactedBy != "" {
		block["redacted_because"] = mustMarshal(map[string]any{"event_id": stored.RedactedBy})
	}
	if len(block) == 0 {
		return nil
	}
	return mustMarshal(block)
}

// Event returns one event of a room, if the user may see it.
func (r *API) Event(ctx context.Context, roomID, userID, eventID string) (ClientEvent, error) {
	_, rules, err := r.roomAndRules(ctx, roomID)
	if err != nil {
		return ClientEvent{}, err
	}
	visible, err := r.requireReadable(ctx, roomID, userID)
	if err != nil {
		return ClientEvent{}, err
	}

	stored, err := r.store.Event(ctx, roomID, eventID)
	if err != nil {
		return ClientEvent{}, err
	}
	// An event outside the user's window is reported as unknown rather
	// than as forbidden: whether a particular event ID exists in a room is
	// itself something they are not entitled to know.
	if !visible.Contains(stored.StreamOrdering) {
		return ClientEvent{}, fmt.Errorf("event %q: %w", eventID, ErrNoSuchEvent)
	}
	e, err := parseEvent(stored, rules)
	if err != nil {
		return ClientEvent{}, err
	}
	return r.clientEvent(stored, e, roomID), nil
}

// RoomState returns a room's state in the client shape: the current state
// for a member, and the state as it was when they left for a user who has.
func (r *API) RoomState(ctx context.Context, roomID, userID string) ([]ClientEvent, error) {
	_, rules, err := r.roomAndRules(ctx, roomID)
	if err != nil {
		return nil, err
	}
	visible, err := r.requireReadable(ctx, roomID, userID)
	if err != nil {
		return nil, err
	}
	return r.stateAt(ctx, roomID, rules, visible.To)
}

// StateEventContent returns the content of one piece of a room's current
// state, which is what GET /rooms/{roomID}/state/{type}/{key} answers.
//
// The endpoint returns the content alone, not the event: a quirk of the
// Client-Server API that predates the rest of it, and one clients depend on.
func (r *API) StateEventContent(ctx context.Context, roomID, userID, eventType, stateKey string) (json.RawMessage, error) {
	e, err := r.StateEvent(ctx, roomID, userID, eventType, stateKey)
	if err != nil {
		return nil, err
	}
	return e.Content, nil
}

// StateEvent returns one piece of a room's current state as a whole event.
//
// It is what ?format=event asks for on the state endpoint, and the only way
// a client can see who set a piece of state and when.
func (r *API) StateEvent(ctx context.Context, roomID, userID, eventType, stateKey string) (ClientEvent, error) {
	_, rules, err := r.roomAndRules(ctx, roomID)
	if err != nil {
		return ClientEvent{}, err
	}
	visible, err := r.requireReadable(ctx, roomID, userID)
	if err != nil {
		return ClientEvent{}, err
	}

	// A member reads the one row they asked for. A user who has left has to
	// be served from the state as of their departure, which means reading
	// the snapshot and picking the tuple out of it — the room has moved on
	// since, and the current row is not theirs to see.
	if visible.To != 0 {
		state, err := r.stateAt(ctx, roomID, rules, visible.To)
		if err != nil {
			return ClientEvent{}, err
		}
		for _, e := range state {
			if e.Type == eventType && e.StateKey != nil && *e.StateKey == stateKey {
				return e, nil
			}
		}
		return ClientEvent{}, fmt.Errorf("state %s/%s of %q: %w",
			eventType, stateKey, roomID, ErrNoSuchEvent)
	}

	stored, err := r.store.CurrentStateEvent(ctx, roomID, eventType, stateKey)
	if err != nil {
		return ClientEvent{}, err
	}
	e, err := parseEvent(stored, rules)
	if err != nil {
		return ClientEvent{}, err
	}
	return r.clientEvent(stored, e, roomID), nil
}

// MembersRequest filters GET /rooms/{roomID}/members.
type MembersRequest struct {
	RoomID string

	// User is the full user ID asking.
	User string

	// Membership and NotMembership filter the result; either may be empty.
	Membership    string
	NotMembership string

	// At is the stream position to report the membership as of, or 0 for
	// the current one.
	//
	// It is what ?at= asks for, and what a client that is rendering an
	// older part of a room's timeline needs: the names and avatars to show
	// against those messages are the ones their senders had then, not now.
	At int64
}

// Members returns a room's m.room.member events.
func (r *API) Members(ctx context.Context, req MembersRequest) ([]ClientEvent, error) {
	_, rules, err := r.roomAndRules(ctx, req.RoomID)
	if err != nil {
		return nil, err
	}
	visible, err := r.requireReadable(ctx, req.RoomID, req.User)
	if err != nil {
		return nil, err
	}

	// The position to report as of: the one asked for, held inside what
	// the user may see. A user who has left is pinned to their departure
	// whatever they asked for — the room has moved on since, and the
	// current membership is not theirs to read.
	at := req.At
	if visible.To != 0 && (at == 0 || at > visible.To) {
		at = visible.To
	}
	if at != 0 && at <= visible.From {
		return nil, fmt.Errorf("%w: %s may not see %s as it was at %d",
			ErrForbidden, req.User, req.RoomID, req.At)
	}

	var members []ClientEvent
	if at != 0 {
		state, err := r.stateAt(ctx, req.RoomID, rules, at)
		if err != nil {
			return nil, err
		}
		members = filterClientEvents(state, storage.TimelineFilter{Types: []string{event.TypeMember}})
	} else {
		var filter []string
		if req.Membership != "" {
			filter = append(filter, req.Membership)
		}
		stored, err := r.store.Members(ctx, req.RoomID, filter)
		if err != nil {
			return nil, err
		}
		if members, err = r.clientEvents(stored, rules, req.RoomID); err != nil {
			return nil, err
		}
	}

	out := make([]ClientEvent, 0, len(members))
	for _, e := range members {
		membership := membershipOf(e)
		if req.Membership != "" && membership != req.Membership {
			continue
		}
		if req.NotMembership != "" && membership == req.NotMembership {
			continue
		}
		out = append(out, e)
	}
	return out, nil
}

// membershipOf reads content.membership out of a projected member event.
//
// A member event that reached a room always has one — the authorisation
// rules refuse one that does not — so an empty answer means the event is
// not a member event at all.
func membershipOf(e ClientEvent) string {
	var content struct {
		Membership string `json:"membership"`
	}
	_ = json.Unmarshal(e.Content, &content)
	return content.Membership
}

// RoomMember is one joined member, as /joined_members reports them.
type RoomMember struct {
	DisplayName string `json:"display_name,omitempty"`
	AvatarURL   string `json:"avatar_url,omitempty"`
}

// JoinedMembers returns the joined members of a room with their profiles.
//
// Unlike /members this one is for members only: the spec says so, and the
// reason is that it exists to let a client that is in a room render it, not
// to let anyone enumerate who is in it.
func (r *API) JoinedMembers(ctx context.Context, roomID, userID string) (map[string]RoomMember, error) {
	if err := r.requireJoined(ctx, roomID, userID); err != nil {
		return nil, err
	}
	_, rules, err := r.roomAndRules(ctx, roomID)
	if err != nil {
		return nil, err
	}

	stored, err := r.store.Members(ctx, roomID, []string{event.MembershipJoin})
	if err != nil {
		return nil, err
	}

	out := make(map[string]RoomMember, len(stored))
	for _, s := range stored {
		e, err := parseEvent(s, rules)
		if err != nil {
			return nil, err
		}
		stateKey, ok := e.StateKey()
		if !ok {
			continue
		}
		var content struct {
			DisplayName string `json:"displayname"`
			AvatarURL   string `json:"avatar_url"`
		}
		// A member event with a malformed profile still counts as a member;
		// the profile is simply not shown.
		_ = json.Unmarshal(e.Content(), &content)
		out[stateKey] = RoomMember{DisplayName: content.DisplayName, AvatarURL: content.AvatarURL}
	}
	return out, nil
}

// JoinedRooms lists the rooms a user is joined to.
func (r *API) JoinedRooms(ctx context.Context, userID string) ([]string, error) {
	rooms, err := r.store.RoomsForUser(ctx, userID, []string{event.MembershipJoin})
	if err != nil {
		return nil, err
	}
	if rooms == nil {
		rooms = []string{}
	}
	return rooms, nil
}

// Membership returns a user's membership in a room, which is empty for a
// user who was never in it.
func (r *API) Membership(ctx context.Context, roomID, userID string) (string, error) {
	entry, err := r.store.Membership(ctx, roomID, userID)
	if err != nil {
		return "", err
	}
	return entry.Membership, nil
}

// roomAndRules reads a room and the rules its events are under.
func (r *API) roomAndRules(ctx context.Context, roomID string) (storage.Room, roomversion.Rules, error) {
	room, err := r.store.Room(ctx, roomID)
	if err != nil {
		return storage.Room{}, roomversion.Rules{}, err
	}
	rules, err := r.rules(room)
	if err != nil {
		return storage.Room{}, roomversion.Rules{}, err
	}
	return room, rules, nil
}

// requireJoined refuses a caller who is not currently in the room.
func (r *API) requireJoined(ctx context.Context, roomID, userID string) error {
	entry, err := r.store.Membership(ctx, roomID, userID)
	if err != nil {
		return err
	}
	if entry.Membership != event.MembershipJoin {
		return fmt.Errorf("%w: %s is not joined to %s", ErrForbidden, userID, roomID)
	}
	return nil
}

// CanSendStateEvent reports whether a user may send a state event of a type
// into a room.
//
// It exists for the two endpoints that are *about* a room rather than in it
// — publishing the room in the directory, and deleting one of its aliases —
// where the spec's permission is "could set the canonical alias". Nothing
// that sends an event uses it: an event's permission is decided by the
// authorisation rules when it is sent, and asking twice would be two
// answers to maintain.
func (r *API) CanSendStateEvent(ctx context.Context, roomID, userID, eventType string) (bool, error) {
	room, rules, err := r.roomAndRules(ctx, roomID)
	if err != nil {
		return false, err
	}
	st, err := r.currentState(ctx, room, rules)
	if err != nil {
		return false, err
	}
	if st.Membership(userID) != event.MembershipJoin {
		return false, nil
	}
	create := st.Create()
	if create == nil {
		return false, fmt.Errorf("%w: %s has no create event in its state", ErrRejected, roomID)
	}
	powerLevels, err := auth.ResolvePowerLevels(st.PowerLevels(), create, rules)
	if err != nil {
		return false, fmt.Errorf("%w: %v", ErrRejected, err)
	}
	return powerLevels.UserLevel(userID) >= powerLevels.SendLevel(eventType, true), nil
}

// RoomVersion returns a room's version, for the handful of callers that
// need to report it.
func (r *API) RoomVersion(ctx context.Context, roomID string) (string, error) {
	room, err := r.store.Room(ctx, roomID)
	if err != nil {
		return "", err
	}
	return room.Version, nil
}