package noiseutil

import (
	"fmt"

	"github.com/flynn/noise"
)

// CipherState is the post-handshake AEAD cipher used for the data plane.
// Each supported cipher has its own concrete implementation in this package with the nonce endianness hardcoded,
// so the encrypt/decrypt fast path avoids interface dispatch on the byte order.
type CipherState interface {
	// EncryptDanger encrypts and authenticates a given payload.
	//
	// out is a destination slice to hold the output of the EncryptDanger operation.
	//   - ad is additional data, which will be authenticated and appended to out, but not encrypted.
	//   - plaintext is encrypted, authenticated and appended to out.
	//   - n is a nonce value which must never be re-used with this key.
	//   - nb is a scratch buffer used to assemble the nonce.
	EncryptDanger(out, ad, plaintext []byte, n uint64, nb []byte) ([]byte, error)

	// DecryptDanger authenticates and decrypts a given payload, with the same argument shape as EncryptDanger.
	DecryptDanger(out, ad, ciphertext []byte, n uint64, nb []byte) ([]byte, error)

	// Overhead returns the AEAD tag size, or 0 if the receiver is nil.
	Overhead() int
}

// NewCipherState wraps the post-handshake noise.CipherState in the per-cipher type that matches cipherFunc.
// cipherFunc must be the same cipher used to build the noise CipherSuite that produced s.
func NewCipherState(s *noise.CipherState, cipherFunc noise.CipherFunc) CipherState {
	switch cipherFunc.CipherName() {
	case CipherAESGCM.CipherName():
		return NewCipherStateAESGCM(s)
	case noise.CipherChaChaPoly.CipherName():
		return NewCipherStateChaChaPoly(s)
	default:
		panic(fmt.Sprintf("noiseutil: unsupported cipher %q", cipherFunc.CipherName()))
	}
}