package wtdb

import (
	"errors"
	"io"

	"github.com/btcsuite/btcd/btcec"
	"github.com/lightningnetwork/lnd/lnwire"
	"github.com/lightningnetwork/lnd/watchtower/wtpolicy"
)

var (
	// ErrClientSessionNotFound signals that the requested client session
	// was not found in the database.
	ErrClientSessionNotFound = errors.New("client session not found")

	// ErrUpdateAlreadyCommitted signals that the chosen sequence number has
	// already been committed to an update with a different breach hint.
	ErrUpdateAlreadyCommitted = errors.New("update already committed")

	// ErrCommitUnorderedUpdate signals the client tried to commit a
	// sequence number other than the next unallocated sequence number.
	ErrCommitUnorderedUpdate = errors.New("update seqnum not monotonic")

	// ErrCommittedUpdateNotFound signals that the tower tried to ACK a
	// sequence number that has not yet been allocated by the client.
	ErrCommittedUpdateNotFound = errors.New("committed update not found")

	// ErrUnallocatedLastApplied signals that the tower tried to provide a
	// LastApplied value greater than any allocated sequence number.
	ErrUnallocatedLastApplied = errors.New("tower echoed last appiled " +
		"greater than allocated seqnum")

	// ErrNoReservedKeyIndex signals that a client session could not be
	// created because no session key index was reserved.
	ErrNoReservedKeyIndex = errors.New("key index not reserved")

	// ErrIncorrectKeyIndex signals that the client session could not be
	// created because session key index differs from the reserved key
	// index.
	ErrIncorrectKeyIndex = errors.New("incorrect key index")

	// ErrClientSessionAlreadyExists signals an attempt to reinsert
	// a client session that has already been created.
	ErrClientSessionAlreadyExists = errors.New(
		"client session already exists",
	)
)

// ClientSession encapsulates a SessionInfo returned from a successful
// session negotiation, and also records the tower and ephemeral secret used for
// communicating with the tower.
type ClientSession struct {
	// ID is the client's public key used when authenticating with the
	// tower.
	//
	// NOTE: This value is not serialized with the body of the struct, it
	// should be set and recovered as the ClientSession's key.
	ID SessionID

	ClientSessionBody

	// CommittedUpdates is a sorted list of unacked updates. These updates
	// can be resent after a restart if the updates failed to send or
	// receive an acknowledgment.
	//
	// NOTE: This list is serialized in it's own bucket, separate from the
	// body of the ClientSession. The representation on disk is a key value
	// map from sequence number to CommittedUpdateBody to allow efficient
	// insertion and retrieval.
	CommittedUpdates []CommittedUpdate

	// AckedUpdates is a map from sequence number to backup id to record
	// which revoked states were uploaded via this session.
	//
	// NOTE: This map is serialized in it's own bucket, separate from the
	// body of the ClientSession.
	AckedUpdates map[uint16]BackupID

	// Tower holds the pubkey and address of the watchtower.
	//
	// NOTE: This value is not serialized. It is recovered by looking up the
	// tower with TowerID.
	Tower *Tower

	// SessionPrivKey is the ephemeral secret key used to connect to the
	// watchtower.
	//
	// NOTE: This value is not serialized. It is derived using the KeyIndex
	// on startup to avoid storing private keys on disk.
	SessionPrivKey *btcec.PrivateKey
}

// ClientSessionBody represents the primary components of a ClientSession that
// are serialized together within the database. The CommittedUpdates and
// AckedUpdates are serialized in buckets separate from the body.
type ClientSessionBody struct {
	// SeqNum is the next unallocated sequence number that can be sent to
	// the tower.
	SeqNum uint16

	// TowerLastApplied the last last-applied the tower has echoed back.
	TowerLastApplied uint16

	// TowerID is the unique, db-assigned identifier that references the
	// Tower with which the session is negotiated.
	TowerID TowerID

	// KeyIndex is the index of key locator used to derive the client's
	// session key so that it can authenticate with the tower to update its
	// session. In order to rederive the private key, the key locator should
	// use the keychain.KeyFamilyTowerSession key family.
	KeyIndex uint32

	// Policy holds the negotiated session parameters.
	Policy wtpolicy.Policy

	// RewardPkScript is the pkscript that the tower's reward will be
	// deposited to if a sweep transaction confirms and the sessions
	// specifies a reward output.
	RewardPkScript []byte
}

// Encode writes a ClientSessionBody to the passed io.Writer.
func (s *ClientSessionBody) Encode(w io.Writer) error {
	return WriteElements(w,
		s.SeqNum,
		s.TowerLastApplied,
		uint64(s.TowerID),
		s.KeyIndex,
		s.Policy,
		s.RewardPkScript,
	)
}

// Decode reads a ClientSessionBody from the passed io.Reader.
func (s *ClientSessionBody) Decode(r io.Reader) error {
	var towerID uint64
	err := ReadElements(r,
		&s.SeqNum,
		&s.TowerLastApplied,
		&towerID,
		&s.KeyIndex,
		&s.Policy,
		&s.RewardPkScript,
	)
	if err != nil {
		return err
	}

	s.TowerID = TowerID(towerID)

	return nil
}

// BackupID identifies a particular revoked, remote commitment by channel id and
// commitment height.
type BackupID struct {
	// ChanID is the channel id of the revoked commitment.
	ChanID lnwire.ChannelID

	// CommitHeight is the commitment height of the revoked commitment.
	CommitHeight uint64
}

// Encode writes the BackupID from the passed io.Writer.
func (b *BackupID) Encode(w io.Writer) error {
	return WriteElements(w,
		b.ChanID,
		b.CommitHeight,
	)
}

// Decode reads a BackupID from the passed io.Reader.
func (b *BackupID) Decode(r io.Reader) error {
	return ReadElements(r,
		&b.ChanID,
		&b.CommitHeight,
	)
}

// CommittedUpdate holds a state update sent by a client along with its
// allocated sequence number and the exact remote commitment the encrypted
// justice transaction can rectify.
type CommittedUpdate struct {
	// SeqNum is the unique sequence number allocated by the session to this
	// update.
	SeqNum uint16

	CommittedUpdateBody
}

// CommittedUpdateBody represents the primary components of a CommittedUpdate.
// On disk, this is stored under the sequence number, which acts as its key.
type CommittedUpdateBody struct {
	// BackupID identifies the breached commitment that the encrypted blob
	// can spend from.
	BackupID BackupID

	// Hint is the 16-byte prefix of the revoked commitment transaction ID.
	Hint BreachHint

	// EncryptedBlob is a ciphertext containing the sweep information for
	// exacting justice if the commitment transaction matching the breach
	// hint is broadcast.
	EncryptedBlob []byte
}

// Encode writes the CommittedUpdateBody to the passed io.Writer.
func (u *CommittedUpdateBody) Encode(w io.Writer) error {
	err := u.BackupID.Encode(w)
	if err != nil {
		return err
	}

	return WriteElements(w,
		u.Hint,
		u.EncryptedBlob,
	)
}

// Decode reads a CommittedUpdateBody from the passed io.Reader.
func (u *CommittedUpdateBody) Decode(r io.Reader) error {
	err := u.BackupID.Decode(r)
	if err != nil {
		return err
	}

	return ReadElements(r,
		&u.Hint,
		&u.EncryptedBlob,
	)
}