package roomserver

import (
	"context"
	"crypto/rand"
	"encoding/base64"
	"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/id"
	"github.com/dariuszjaniak/warp/server/internal/matrix/roomversion"
	"github.com/dariuszjaniak/warp/server/internal/storage"
)

// The createRoom presets, which are shorthand for a join rule, a history
// visibility and a guest access policy together.
const (
	PresetPrivateChat        = "private_chat"
	PresetTrustedPrivateChat = "trusted_private_chat"
	PresetPublicChat         = "public_chat"
)

// Directory visibility values for createRoom and
// /directory/list/room/{roomID}.
const (
	VisibilityPublic  = "public"
	VisibilityPrivate = "private"
)

// CreateRoomRequest is the createRoom body, already parsed.
type CreateRoomRequest struct {
	// Creator is the full user ID creating the room.
	Creator string

	// Version is the room version to create at; empty uses this server's
	// default.
	Version string

	// Preset is one of the three presets; empty derives it from Visibility
	// the way the spec does.
	Preset string

	// Visibility is "public" to publish the room in this server's directory.
	Visibility string

	// RoomAliasName is the localpart of an alias to create and set as the
	// canonical alias.
	RoomAliasName string

	Name  string
	Topic string

	// Invite lists user IDs to invite once the room exists.
	Invite []string

	// CreationContent is merged into the m.room.create content. It is how a
	// client sets m.federate and creates a space.
	CreationContent json.RawMessage

	// InitialState are state events to send after the room's own setup
	// events and before the invites.
	InitialState []StateEvent

	// PowerLevelContentOverride is merged over the m.room.power_levels
	// content this server would otherwise send.
	PowerLevelContentOverride json.RawMessage

	// IsDirect marks the creator's and the invitees' membership events as a
	// direct chat.
	IsDirect bool
}

// StateEvent is one state event in createRoom's initial_state.
type StateEvent struct {
	Type     string          `json:"type"`
	StateKey string          `json:"state_key"`
	Content  json.RawMessage `json:"content"`
}

// CreateRoomResponse is what the client is told.
type CreateRoomResponse struct {
	RoomID string

	// Alias is the full alias created from RoomAliasName, or empty.
	Alias string
}

// CreateRoom builds a room from nothing.
//
// The order of the events is the spec's order, and it is not arbitrary: each
// one is authorised against the state the ones before it produced. The
// create event comes first because nothing can be authorised without it; the
// creator's join comes next because every later event needs a sender who is
// in the room; the power levels come before the join rules so that the
// creator still has the power to set them.
//
// A failure part-way through leaves a room that exists and is incomplete.
// That is the lesser evil: the alternative is holding every event of a new
// room in memory and writing them in one transaction, which would make the
// pipeline that authorises them a special case, and the pipeline is the one
// thing in here that must not have special cases. A half-built room is
// visible only to its creator and can be purged.
func (r *API) CreateRoom(ctx context.Context, req CreateRoomRequest) (CreateRoomResponse, error) {
	if !r.isLocal(req.Creator) {
		return CreateRoomResponse{}, fmt.Errorf("%w: %s is not a user of this server", ErrForbidden, req.Creator)
	}

	version := r.defaultRoomVersion
	if req.Version != "" {
		if err := roomversion.Validate(req.Version); err != nil {
			return CreateRoomResponse{}, fmt.Errorf("%w: %s", ErrUnknownRoomVersion, err)
		}
		version = roomversion.Version(req.Version)
	}
	rules, err := roomversion.Get(version)
	if err != nil {
		return CreateRoomResponse{}, err
	}

	preset, err := presetFor(req)
	if err != nil {
		return CreateRoomResponse{}, err
	}

	var alias string
	if req.RoomAliasName != "" {
		if alias, err = r.aliasFor(req.RoomAliasName); err != nil {
			return CreateRoomResponse{}, err
		}
	}

	roomID, createEvent, err := r.buildCreateEvent(ctx, req, rules)
	if err != nil {
		return CreateRoomResponse{}, err
	}

	if err := r.store.CreateRoom(ctx, storage.NewRoom{
		ID:          roomID,
		Version:     string(version),
		Creator:     req.Creator,
		Published:   req.Visibility == VisibilityPublic,
		CreatedAtMS: r.nowMS(),
	}); err != nil {
		return CreateRoomResponse{}, err
	}

	// The alias is claimed before any event is signed, so that a name
	// already taken does not leave a room behind. It cannot be claimed
	// before the room row, because an alias points at a room; so a clash
	// takes the room row back out, which is safe precisely because nothing
	// has been written into the room yet.
	if alias != "" {
		if err := r.store.CreateAlias(ctx, storage.RoomAlias{
			Alias:       alias,
			RoomID:      roomID,
			Creator:     req.Creator,
			CreatedAtMS: r.nowMS(),
		}); err != nil {
			if purgeErr := r.store.PurgeRoom(ctx, roomID); purgeErr != nil {
				r.log.Error("could not remove the room an alias clash abandoned",
					"room_id", roomID, "error", purgeErr)
			}
			return CreateRoomResponse{}, err
		}
	}

	// The create event is the one event that cannot go through send: there
	// is no room state to read and no extremity to descend from, and in
	// room version 12 the room ID is its own event ID, so it has to exist
	// before the room does.
	if err := r.persistCreateEvent(ctx, roomID, string(version), rules, createEvent); err != nil {
		return CreateRoomResponse{}, err
	}

	for _, step := range r.creationEvents(ctx, req, preset, rules, roomID) {
		if _, err := r.send(ctx, step); err != nil {
			return CreateRoomResponse{}, fmt.Errorf("creating %s: setting up %s: %w", roomID, step.Type, err)
		}
	}

	if alias != "" {
		if _, err := r.send(ctx, sendRequest{
			RoomID:   roomID,
			Type:     TypeCanonicalAlias,
			StateKey: statePtr(""),
			Sender:   req.Creator,
			Content:  mustMarshal(map[string]any{"alias": alias}),
		}); err != nil {
			return CreateRoomResponse{}, fmt.Errorf("creating %s: setting the canonical alias: %w", roomID, err)
		}
	}

	// Invites come last, so that an invited user who looks immediately
	// finds a room that is fully set up.
	for _, invitee := range req.Invite {
		if err := r.InviteUser(ctx, InviteRequest{
			RoomID:   roomID,
			Sender:   req.Creator,
			Target:   invitee,
			IsDirect: req.IsDirect,
		}); err != nil {
			return CreateRoomResponse{}, fmt.Errorf("creating %s: inviting %s: %w", roomID, invitee, err)
		}
	}

	r.log.Info("created room",
		"room_id", roomID, "version", version, "creator", req.Creator, "preset", preset)
	return CreateRoomResponse{RoomID: roomID, Alias: alias}, nil
}

// buildCreateEvent builds the m.room.create event and works out the room ID.
//
// From room version 12 the room ID *is* the create event's ID, so the event
// has to be built before the room can be named; in earlier versions the ID
// is minted here and written into the event. The event is checked against
// the authorisation rules with an empty state, which is the one case rule 1
// covers.
func (r *API) buildCreateEvent(ctx context.Context, req CreateRoomRequest, rules roomversion.Rules) (string, *event.Event, error) {
	content, err := r.createContent(req, rules)
	if err != nil {
		return "", nil, err
	}

	roomID := ""
	if !rules.RoomIDIsCreateEventID {
		if roomID, err = r.generateRoomID(); err != nil {
			return "", nil, err
		}
	}

	builder := event.Builder{
		RoomID:   roomID,
		Type:     event.TypeCreate,
		StateKey: statePtr(""),
		Sender:   req.Creator,
		Content:  content,
		Depth:    1,
	}
	created, err := builder.Build(r.now(), r.signingKey, rules)
	if err != nil {
		return "", nil, fmt.Errorf("building the create event: %w", err)
	}

	if rules.RoomIDIsCreateEventID {
		if roomID, err = event.RoomIDOfCreateEvent(created); err != nil {
			return "", nil, err
		}
	}

	// Rule 1 against an empty state: the version is one we support, the
	// creator is well-formed, and in version 12 the room ID matches.
	if err := auth.Check(ctx, created, auth.State{}, nil); err != nil {
		return "", nil, err
	}
	return roomID, created, nil
}

// createContent assembles the m.room.create content.
//
// creation_content from the client is merged in underneath, so a client can
// set m.federate or make a space without being able to overwrite the
// properties the room version defines — room_version and creator are put on
// last for that reason.
func (r *API) createContent(req CreateRoomRequest, rules roomversion.Rules) (json.RawMessage, error) {
	content := map[string]json.RawMessage{}
	if len(req.CreationContent) > 0 {
		if err := json.Unmarshal(req.CreationContent, &content); err != nil {
			return nil, fmt.Errorf("%w: creation_content must be a JSON object", ErrInvalidContent)
		}
		// These are the server's to decide, whatever the client sent.
		delete(content, "room_version")
		delete(content, "creator")
		delete(content, "additional_creators")
	}
	content["room_version"] = mustMarshal(string(rules.Version))
	if rules.CreateEventRequiresCreator {
		content["creator"] = mustMarshal(req.Creator)
	}

	raw, err := json.Marshal(content)
	if err != nil {
		return nil, fmt.Errorf("%w: creation_content cannot be encoded: %v", ErrInvalidContent, err)
	}
	return raw, nil
}

// persistCreateEvent writes the create event, which is the room's entire
// state and its only extremity.
//
// The state it is authorised against is empty, which is what an empty
// snapshot records; the state *after* it — the create event alone — persist
// derives from the event itself, as it does for any other state event.
func (r *API) persistCreateEvent(ctx context.Context, roomID, version string, rules roomversion.Rules, created *event.Event) error {
	return r.persist(ctx, persistRequest{
		Room:        storage.Room{ID: roomID, Version: version},
		Rules:       rules,
		Event:       created,
		StateBefore: auth.State{},
	})
}

// creationEvents are the events that turn a bare create event into a usable
// room, in the order they have to be sent.
func (r *API) creationEvents(ctx context.Context, req CreateRoomRequest, preset string, rules roomversion.Rules, roomID string) []sendRequest {
	steps := []sendRequest{
		// The creator joins before anything else: every event after this
		// one has to be sent by a member of the room.
		{
			RoomID:   roomID,
			Type:     event.TypeMember,
			StateKey: statePtr(req.Creator),
			Sender:   req.Creator,
			Content:  r.membershipContent(ctx, event.MembershipJoin, req.Creator, "", req.IsDirect),
		},
		// Power levels before the join rules, so that the creator is still
		// the only one who can set them.
		{
			RoomID:   roomID,
			Type:     event.TypePowerLevels,
			StateKey: statePtr(""),
			Sender:   req.Creator,
			Content:  r.powerLevelsContent(req, preset, rules),
		},
		{
			RoomID:   roomID,
			Type:     event.TypeJoinRules,
			StateKey: statePtr(""),
			Sender:   req.Creator,
			Content:  mustMarshal(map[string]any{"join_rule": presetJoinRule(preset)}),
		},
		{
			RoomID:   roomID,
			Type:     TypeHistoryVisibility,
			StateKey: statePtr(""),
			Sender:   req.Creator,
			Content: mustMarshal(map[string]any{
				"history_visibility": HistoryVisibilityShared,
			}),
		},
		{
			RoomID:   roomID,
			Type:     TypeGuestAccess,
			StateKey: statePtr(""),
			Sender:   req.Creator,
			Content: mustMarshal(map[string]any{
				"guest_access": presetGuestAccess(preset),
			}),
		},
	}

	// initial_state comes after the server's own setup events and may
	// overwrite any of them, which is what lets a client create an
	// encrypted or world-readable room in one call.
	for _, s := range req.InitialState {
		steps = append(steps, sendRequest{
			RoomID:   roomID,
			Type:     s.Type,
			StateKey: statePtr(s.StateKey),
			Sender:   req.Creator,
			Content:  s.Content,
		})
	}

	// name and topic come after initial_state, because the spec gives the
	// dedicated parameters precedence over an initial_state event of the
	// same type.
	if req.Name != "" {
		steps = append(steps, sendRequest{
			RoomID:   roomID,
			Type:     TypeName,
			StateKey: statePtr(""),
			Sender:   req.Creator,
			Content:  mustMarshal(map[string]any{"name": req.Name}),
		})
	}
	if req.Topic != "" {
		steps = append(steps, sendRequest{
			RoomID:   roomID,
			Type:     TypeTopic,
			StateKey: statePtr(""),
			Sender:   req.Creator,
			Content:  mustMarshal(map[string]any{"topic": req.Topic}),
		})
	}
	return steps
}

// powerLevelsContent is the m.room.power_levels event a new room gets.
//
// The levels are the spec's defaults written out rather than left implicit,
// because a client reading the event is entitled to see what the room
// actually does, and because power_level_content_override has to have
// something to override.
func (r *API) powerLevelsContent(req CreateRoomRequest, preset string, rules roomversion.Rules) json.RawMessage {
	users := map[string]any{}
	if !rules.CreatorsHaveInfinitePower {
		// Up to room version 11 the creator's power has to be written down.
		// From version 12 it cannot be: naming a creator in this event is
		// itself a rejection.
		users[req.Creator] = auth.CreatorPowerLevel
	}
	// trusted_private_chat makes everyone invited an equal, which is the
	// whole point of the preset.
	if preset == PresetTrustedPrivateChat {
		for _, invitee := range req.Invite {
			if rules.CreatorsHaveInfinitePower && invitee == req.Creator {
				continue
			}
			users[invitee] = auth.CreatorPowerLevel
		}
	}

	content := map[string]any{
		"ban":            auth.DefaultBan,
		"kick":           auth.DefaultKick,
		"redact":         auth.DefaultRedact,
		"invite":         auth.DefaultInvite,
		"events_default": auth.DefaultEventsDefault,
		"state_default":  auth.DefaultStateDefault,
		"users_default":  auth.DefaultUsersDefault,
		"users":          users,
		"events": map[string]any{
			// Tombstoning a room replaces it, so it is kept at the level
			// the spec reserves for the room's owner even once others have
			// been promoted to moderator.
			"m.room.tombstone":          100,
			"m.room.power_levels":       100,
			"m.room.history_visibility": 100,
			"m.room.canonical_alias":    auth.DefaultStateDefault,
			"m.room.avatar":             auth.DefaultStateDefault,
			TypeEncryption:              100,
			"m.room.server_acl":         100,
			// Joining a group call is a state event of the member's own
			// (MatrixRTC, MSC3401), so anyone who may talk in the room
			// may also join its call. Starting one is not a separate act.
			TypeCallMember: 0,
		},
		"notifications": map[string]any{"room": auth.DefaultNotification},
	}

	raw := mustMarshal(content)
	if len(req.PowerLevelContentOverride) == 0 {
		return raw
	}
	// A malformed override is left out rather than failing the room: the
	// client is told nothing either way, and a room with the default levels
	// is recoverable where a room that does not exist is not. The override
	// is still authorised like any other power levels event, so it cannot
	// be used to give anybody more power than the creator has.
	merged, err := mergeJSON(raw, req.PowerLevelContentOverride)
	if err != nil {
		r.log.Warn("ignoring an unusable power_level_content_override", "error", err)
		return raw
	}
	return merged
}

// presetFor resolves the preset, defaulting the way the spec does: from the
// directory visibility when the client named no preset.
func presetFor(req CreateRoomRequest) (string, error) {
	switch req.Preset {
	case PresetPrivateChat, PresetTrustedPrivateChat, PresetPublicChat:
		return req.Preset, nil
	case "":
		if req.Visibility == VisibilityPublic {
			return PresetPublicChat, nil
		}
		return PresetPrivateChat, nil
	default:
		return "", fmt.Errorf("%w: %q is not a known preset", ErrInvalidContent, req.Preset)
	}
}

func presetJoinRule(preset string) string {
	if preset == PresetPublicChat {
		return auth.JoinRulePublic
	}
	return auth.JoinRuleInvite
}

func presetGuestAccess(preset string) string {
	if preset == PresetPublicChat {
		return GuestAccessForbidden
	}
	return GuestAccessCanJoin
}

// roomIDRandomBytes is how much randomness a room ID of a version that
// still needs one carries. 16 bytes is the same 128 bits as a UUID, encoded
// without padding.
const roomIDRandomBytes = 16

// generateRoomID mints a "!opaque:server" room ID, for the room versions
// before 12 where the ID is not derived from the create event.
func (r *API) generateRoomID() (string, error) {
	buf := make([]byte, roomIDRandomBytes)
	if _, err := rand.Read(buf); err != nil {
		return "", fmt.Errorf("generating a room ID: %w", err)
	}
	roomID := "!" + base64.RawURLEncoding.EncodeToString(buf) + ":" + r.serverName
	if err := id.ValidateRoomID(roomID); err != nil {
		return "", err
	}
	return roomID, nil
}

// statePtr makes a state key addressable, since the empty string is a
// perfectly good one and nil means "not a state event".
func statePtr(s string) *string { return &s }

// mustMarshal encodes a value this package built itself.
//
// Every caller passes a map or a string, which cannot fail to encode; a
// failure here would be a bug in this file rather than anything a client
// could cause.
func mustMarshal(v any) json.RawMessage {
	raw, err := json.Marshal(v)
	if err != nil {
		panic("roomserver: encoding a value this package built: " + err.Error())
	}
	return raw
}

// mergeJSON overlays the properties of override onto base, at the top level
// only.
//
// A shallow merge is what the spec asks for: power_level_content_override
// replacing the whole "users" map rather than merging into it is the
// documented behaviour, and the one a client setting up a room relies on.
func mergeJSON(base, override json.RawMessage) (json.RawMessage, error) {
	var merged, extra map[string]json.RawMessage
	if err := json.Unmarshal(base, &merged); err != nil {
		return nil, err
	}
	if err := json.Unmarshal(override, &extra); err != nil {
		return nil, fmt.Errorf("%w: the override must be a JSON object", ErrInvalidContent)
	}
	for key, value := range extra {
		merged[key] = value
	}
	return json.Marshal(merged)
}

// TypeCallMember is a member's state in a room's group call (MatrixRTC).
// It is still under its MSC3401 name, which is what clients send.
const TypeCallMember = "org.matrix.msc3401.call.member"