package clientdb

import (
	"bytes"
	"errors"
	"io"

	"github.com/btcsuite/btcd/btcec/v2"
	"github.com/lightninglabs/pool/account"
	"github.com/lightningnetwork/lnd/tlv"
	"go.etcd.io/bbolt"
)

const (
	// accountStateVersionedMask is a bit mask for detecting from the state
	// of an account whether that account has a version field encoded with
	// it or not. We use the first bit of the uint8 state field because we
	// are unlikely to ever have more than 127 different states.
	accountStateVersionedMask account.State = 0b1000_0000

	// accountVersionType is the first additional field we added to the
	// account as a TLV field and it encodes the account's version.
	accountVersionType tlv.Type = 0
)

var (
	// accountBucketKey is the top level bucket where we can find all
	// information about complete accounts. These accounts are indexed by
	// their trader key locator.
	accountBucketKey = []byte("account")

	// ErrAccountNotFound is an error returned when we attempt to retrieve
	// information about an account but it is not found.
	ErrAccountNotFound = errors.New("account not found")
)

// isVersioned returns true if the version bit is set in the given account
// state.
func isVersioned(state account.State) bool {
	return state&accountStateVersionedMask == accountStateVersionedMask
}

// setVersionBit sets the version bit in the given account state.
func setVersionBit(state account.State) account.State {
	return state | accountStateVersionedMask
}

// clearVersionBit clears the version bit in the given account state.
func clearVersionBit(state account.State) account.State {
	// The &^ operator means AND NOT, also known as the Bitclear operator.
	return state &^ accountStateVersionedMask
}

// getAccountKey returns the key for an account which is not partial.
func getAccountKey(account *account.Account) []byte {
	return account.TraderKey.PubKey.SerializeCompressed()
}

// AddAccount adds a record for the account to the database.
func (db *DB) AddAccount(account *account.Account) error {
	return db.Update(func(tx *bbolt.Tx) error {
		accounts, err := getBucket(tx, accountBucketKey)
		if err != nil {
			return err
		}

		return storeAccount(accounts, account)
	})
}

// UpdateAccount updates an account in the database according to the given
// modifiers.
func (db *DB) UpdateAccount(acct *account.Account,
	modifiers ...account.Modifier) error {

	err := db.Update(func(tx *bbolt.Tx) error {
		accounts, err := getBucket(tx, accountBucketKey)
		if err != nil {
			return err
		}
		accountKey := getAccountKey(acct)
		_, err = updateAccount(accounts, accounts, accountKey, modifiers)
		return err
	})
	if err != nil {
		return err
	}

	for _, modifier := range modifiers {
		modifier(acct)
	}

	return nil
}

// updateAccount reads an account from the src bucket, applies the given
// modifiers to it, and store it back into dst bucket.
func updateAccount(src, dst *bbolt.Bucket, accountKey []byte,
	modifiers []account.Modifier) (*account.Account, error) {

	dbAccount, err := readAccount(src, accountKey)
	if err != nil {
		return nil, err
	}

	for _, modifier := range modifiers {
		modifier(dbAccount)
	}

	return dbAccount, storeAccount(dst, dbAccount)
}

// Account retrieves a specific account by trader key or returns
// ErrAccountNotFound if it's not found.
func (db *DB) Account(traderKey *btcec.PublicKey) (*account.Account, error) {
	var acct *account.Account
	err := db.View(func(tx *bbolt.Tx) error {
		accounts, err := getBucket(tx, accountBucketKey)
		if err != nil {
			return err
		}

		acct, err = readAccount(
			accounts, traderKey.SerializeCompressed(),
		)
		return err
	})
	if err != nil {
		return nil, err
	}

	return acct, nil
}

// Accounts retrieves all known accounts from the database.
func (db *DB) Accounts() ([]*account.Account, error) {
	var res []*account.Account
	err := db.View(func(tx *bbolt.Tx) error {
		accounts, err := getBucket(tx, accountBucketKey)
		if err != nil {
			return err
		}

		return accounts.ForEach(func(k, v []byte) error {
			// We'll also get buckets here, skip those (identified
			// by nil value).
			if v == nil {
				return nil
			}

			acct, err := readAccount(accounts, k)
			if err != nil {
				return err
			}
			res = append(res, acct)
			return nil
		})
	})
	if err != nil {
		return nil, err
	}

	return res, nil
}

func storeAccount(targetBucket *bbolt.Bucket, a *account.Account) error {
	accountKey := getAccountKey(a)

	var accountBuf bytes.Buffer
	if err := serializeAccount(&accountBuf, a); err != nil {
		return err
	}

	return targetBucket.Put(accountKey, accountBuf.Bytes())
}

func readAccount(sourceBucket *bbolt.Bucket,
	accountKey []byte) (*account.Account, error) {

	accountBytes := sourceBucket.Get(accountKey)
	if accountBytes == nil {
		return nil, ErrAccountNotFound
	}

	return deserializeAccount(bytes.NewReader(accountBytes))
}

func serializeAccount(w *bytes.Buffer, a *account.Account) error {
	rawState := a.State
	accountIsVersioned := a.Version > account.VersionInitialNoVersion
	if accountIsVersioned {
		rawState = setVersionBit(rawState)
	}

	err := WriteElements(
		w, a.Value, a.Expiry, a.TraderKey, a.AuctioneerKey, a.BatchKey,
		a.Secret, rawState, a.HeightHint, a.OutPoint,
	)
	if err != nil {
		return err
	}

	// The latest transaction is not found within StateInitiated and
	// StateCanceledAfterRecovery.
	switch a.State {
	case account.StateInitiated, account.StateCanceledAfterRecovery:

	default:
		if err := WriteElement(w, a.LatestTx); err != nil {
			return err
		}
	}

	// The version flag encoded within the state will inform the
	// de-serialize method that it should read another field. Therefore, we
	// can safely write it here.
	if accountIsVersioned {
		if err := serializeAccountTlvData(w, a); err != nil {
			return err
		}
	}

	return nil
}

// serializeAccountTlvData writes all additional TLV fields of an account to the
// given writer. This should only be called for accounts with a version > 0 as
// otherwise this will mess up the assumptions used for encoding/decoding
// accounts within a batch snapshot blob.
func serializeAccountTlvData(w *bytes.Buffer, a *account.Account) error {
	version := uint8(a.Version)
	tlvRecords := []tlv.Record{
		tlv.MakePrimitiveRecord(accountVersionType, &version),
	}

	tlvStream, err := tlv.NewStream(tlvRecords...)
	if err != nil {
		return err
	}

	// We can't just encode the stream to the writer directly, because there
	// might be multiple accounts lined up after each other. And since a TLV
	// reader will always try to read until the end of a stream, we need to
	// be able to cap it somehow. So we write the number of bytes and then
	// the stream bytes itself.
	var buf bytes.Buffer
	err = tlvStream.Encode(&buf)
	if err != nil {
		return err
	}

	return WriteElements(w, uint32(buf.Len()), buf.Bytes())
}

// deserializeAccountTlvData reads all additional TLV fields of an account from
// the given reader. This should only be called for accounts with a version > 0
// as otherwise this will mess up the assumptions used for encoding/decoding
// accounts within a batch snapshot blob.
func deserializeAccountTlvData(r io.Reader, a *account.Account) error {
	// We first need to find out how many bytes there are for this TLV
	// stream and only read those bytes. Otherwise, the TLV reader will try
	// to read as many bytes as it can.
	var streamLen uint32
	if err := ReadElement(r, &streamLen); err != nil {
		return err
	}

	streamBytes := make([]byte, streamLen)
	if err := ReadElement(r, streamBytes); err != nil {
		return err
	}

	var (
		version uint8
	)
	tlvStream, err := tlv.NewStream(
		tlv.MakePrimitiveRecord(accountVersionType, &version),
	)
	if err != nil {
		return err
	}

	parsedTypes, err := tlvStream.DecodeWithParsedTypes(
		bytes.NewReader(streamBytes),
	)
	if err != nil {
		return err
	}

	if t, ok := parsedTypes[accountVersionType]; ok && t == nil {
		a.Version = account.Version(version)
	}

	return nil
}

func deserializeAccount(r io.Reader) (*account.Account, error) {
	var (
		a        account.Account
		rawState account.State
	)
	err := ReadElements(
		r, &a.Value, &a.Expiry, &a.TraderKey, &a.AuctioneerKey,
		&a.BatchKey, &a.Secret, &rawState, &a.HeightHint, &a.OutPoint,
	)
	if err != nil {
		return nil, err
	}

	// We might have a version flag encoded within the state. We want to
	// hide that internal mechanism from the caller, so we need to remove
	// the flag again.
	a.State = clearVersionBit(rawState)

	// The latest transaction is not found within StateInitiated and
	// StateCanceledAfterRecovery.
	switch a.State {
	case account.StateInitiated, account.StateCanceledAfterRecovery:

	default:
		if err := ReadElement(r, &a.LatestTx); err != nil {
			return nil, err
		}
	}

	// If there was a version flag, we know we're supposed to read another
	// field here.
	if isVersioned(rawState) {
		if err := deserializeAccountTlvData(r, &a); err != nil {
			return nil, err
		}
	}

	return &a, nil
}