//go:build darwin
// +build darwin

// Package macse provides Go bindings for macOS Secure Enclave operations
// using CryptoTokenKit identities created via sc_auth.
// Key creation and deletion shell out to sc_auth (which has SE entitlements).
// Encrypt/decrypt use Security.framework ECIES directly (works unsigned).
package macse

/*
#cgo CFLAGS: -x objective-c -fobjc-arc
#cgo LDFLAGS: -framework Security -framework Foundation -framework CoreFoundation
#include <stdlib.h>
#include "secure_enclave.h"
*/
import "C"

import (
	"fmt"
	"unsafe"
)

const (
	// p256UncompressedKeySize is the size of an uncompressed P-256 public key.
	p256UncompressedKeySize = 65

	// errorBufferSize is the size of the C error message buffer.
	errorBufferSize = 512

	// hashBufferSize is the size of the hash output buffer.
	hashBufferSize = 128

	// maxCiphertextSize is the max buffer for ECIES ciphertext.
	// ECIES overhead for P-256: 65 (ephemeral pub) + 16 (GCM tag) + 16 (IV) + plaintext.
	maxCiphertextSize = 8192

	// maxPlaintextSize is the max buffer for decrypted plaintext.
	maxPlaintextSize = 8192
)

// CreateKey creates a new P-256 non-exportable key in the Secure Enclave via sc_auth.
// Returns the uncompressed public key bytes (65 bytes) and the identity hash (for deletion).
func CreateKey(label string) (publicKey []byte, hash string, err error) {
	cLabel := C.CString(label)

	defer C.free(unsafe.Pointer(cLabel))

	pubKeyBuf := make([]C.uint8_t, p256UncompressedKeySize)
	pubKeyLen := C.int(p256UncompressedKeySize)

	var hashBuf [hashBufferSize]C.char
	var errBuf [errorBufferSize]C.char

	result := C.se_create_key(cLabel,
		&pubKeyBuf[0], &pubKeyLen,
		&hashBuf[0], C.int(hashBufferSize),
		&errBuf[0], C.int(errorBufferSize))

	if result != 0 {
		return nil, "", fmt.Errorf("secure enclave: %s", C.GoString(&errBuf[0]))
	}

	pk := C.GoBytes(unsafe.Pointer(&pubKeyBuf[0]), pubKeyLen)
	h := C.GoString(&hashBuf[0])

	return pk, h, nil
}

// Encrypt encrypts plaintext using the SE-backed public key via ECIES
// (eciesEncryptionStandardVariableIVX963SHA256AESGCM).
// Encryption uses only the public key; no SE interaction required.
func Encrypt(label string, plaintext []byte) ([]byte, error) {
	cLabel := C.CString(label)

	defer C.free(unsafe.Pointer(cLabel))

	ciphertextBuf := make([]C.uint8_t, maxCiphertextSize)
	ciphertextLen := C.int(maxCiphertextSize)

	var errBuf [errorBufferSize]C.char

	result := C.se_encrypt(cLabel,
		(*C.uint8_t)(unsafe.Pointer(&plaintext[0])), C.int(len(plaintext)),
		&ciphertextBuf[0], &ciphertextLen,
		&errBuf[0], C.int(errorBufferSize))

	if result != 0 {
		return nil, fmt.Errorf("secure enclave: %s", C.GoString(&errBuf[0]))
	}

	return C.GoBytes(unsafe.Pointer(&ciphertextBuf[0]), ciphertextLen), nil
}

// Decrypt decrypts ECIES ciphertext using the SE-backed private key.
// The ECDH portion of decryption is performed inside the Secure Enclave.
func Decrypt(label string, ciphertext []byte) ([]byte, error) {
	cLabel := C.CString(label)

	defer C.free(unsafe.Pointer(cLabel))

	plaintextBuf := make([]C.uint8_t, maxPlaintextSize)
	plaintextLen := C.int(maxPlaintextSize)

	var errBuf [errorBufferSize]C.char

	result := C.se_decrypt(cLabel,
		(*C.uint8_t)(unsafe.Pointer(&ciphertext[0])), C.int(len(ciphertext)),
		&plaintextBuf[0], &plaintextLen,
		&errBuf[0], C.int(errorBufferSize))

	if result != 0 {
		return nil, fmt.Errorf("secure enclave: %s", C.GoString(&errBuf[0]))
	}

	return C.GoBytes(unsafe.Pointer(&plaintextBuf[0]), plaintextLen), nil
}

// DeleteKey removes a CTK identity from the Secure Enclave via sc_auth.
func DeleteKey(hash string) error {
	cHash := C.CString(hash)

	defer C.free(unsafe.Pointer(cHash))

	var errBuf [errorBufferSize]C.char

	result := C.se_delete_key(cHash, &errBuf[0], C.int(errorBufferSize))

	if result != 0 {
		return fmt.Errorf("secure enclave: %s", C.GoString(&errBuf[0]))
	}

	return nil
}