secret/internal/secret/keychainunlocker.go

//go:build darwin
// +build darwin

package secret

import (
	"encoding/hex"
	"encoding/json"
	"fmt"
	"log/slog"
	"os"
	"path/filepath"
	"regexp"
	"runtime"
	"time"

	"filippo.io/age"
	"git.eeqj.de/sneak/secret/pkg/agehd"
	"github.com/awnumar/memguard"
	keychain "github.com/keybase/go-keychain"
	"github.com/spf13/afero"
)

const (
	agePrivKeyPassphraseLength = 64
	// KEYCHAIN_APP_IDENTIFIER is the service name used for keychain items
	KEYCHAIN_APP_IDENTIFIER = "berlin.sneak.app.secret" //nolint:revive // ALL_CAPS is intentional for this constant
)

// keychainItemNameRegex validates keychain item names
// Allows alphanumeric characters, dots, hyphens, and underscores only
var keychainItemNameRegex = regexp.MustCompile(`^[A-Za-z0-9._-]+$`)

// KeychainUnlockerMetadata extends UnlockerMetadata with keychain-specific data
type KeychainUnlockerMetadata struct {
	UnlockerMetadata
	// Keychain item name
	KeychainItemName string `json:"keychainItemName"`
}

// KeychainUnlocker represents a macOS Keychain-protected unlocker
type KeychainUnlocker struct {
	Directory string
	Metadata  UnlockerMetadata
	fs        afero.Fs
}

// KeychainData represents the data stored in the macOS keychain
type KeychainData struct {
	AgePublicKey         string `json:"agePublicKey"`
	AgePrivKeyPassphrase string `json:"agePrivKeyPassphrase"`
	EncryptedLongtermKey string `json:"encryptedLongtermKey"`
}

// GetIdentity implements Unlocker interface for Keychain-based unlockers
func (k *KeychainUnlocker) GetIdentity() (*age.X25519Identity, error) {
	DebugWith("Getting keychain unlocker identity",
		slog.String("unlocker_id", k.GetID()),
		slog.String("unlocker_type", k.GetType()),
	)

	// Step 1: Get keychain item name
	keychainItemName, err := k.GetKeychainItemName()
	if err != nil {
		Debug("Failed to get keychain item name", "error", err, "unlocker_id", k.GetID())

		return nil, fmt.Errorf("failed to get keychain item name: %w", err)
	}

	// Step 2: Retrieve data from keychain
	Debug("Retrieving data from macOS keychain", "keychain_item", keychainItemName)
	keychainDataBytes, err := retrieveFromKeychain(keychainItemName)
	if err != nil {
		Debug("Failed to retrieve data from keychain", "error", err, "keychain_item", keychainItemName)

		return nil, fmt.Errorf("failed to retrieve data from keychain: %w", err)
	}

	DebugWith("Retrieved data from keychain",
		slog.String("unlocker_id", k.GetID()),
		slog.Int("data_length", len(keychainDataBytes)),
	)

	// Step 3: Parse keychain data
	var keychainData KeychainData
	if err := json.Unmarshal(keychainDataBytes, &keychainData); err != nil {
		Debug("Failed to parse keychain data", "error", err, "unlocker_id", k.GetID())

		return nil, fmt.Errorf("failed to parse keychain data: %w", err)
	}

	Debug("Parsed keychain data successfully", "unlocker_id", k.GetID())

	// Step 4: Read the encrypted age private key from filesystem
	agePrivKeyPath := filepath.Join(k.Directory, "priv.age")
	Debug("Reading encrypted age private key", "path", agePrivKeyPath)

	encryptedAgePrivKeyData, err := afero.ReadFile(k.fs, agePrivKeyPath)
	if err != nil {
		Debug("Failed to read encrypted age private key", "error", err, "path", agePrivKeyPath)

		return nil, fmt.Errorf("failed to read encrypted age private key: %w", err)
	}

	DebugWith("Read encrypted age private key",
		slog.String("unlocker_id", k.GetID()),
		slog.Int("encrypted_length", len(encryptedAgePrivKeyData)),
	)

	// Step 5: Decrypt the age private key using the passphrase from keychain
	Debug("Decrypting age private key with keychain passphrase", "unlocker_id", k.GetID())
	// Create secure buffer for the keychain passphrase
	passphraseBuffer := memguard.NewBufferFromBytes([]byte(keychainData.AgePrivKeyPassphrase))
	defer passphraseBuffer.Destroy()

	agePrivKeyBuffer, err := DecryptWithPassphrase(encryptedAgePrivKeyData, passphraseBuffer)
	if err != nil {
		Debug("Failed to decrypt age private key with keychain passphrase", "error", err, "unlocker_id", k.GetID())

		return nil, fmt.Errorf("failed to decrypt age private key with keychain passphrase: %w", err)
	}
	defer agePrivKeyBuffer.Destroy()

	DebugWith("Successfully decrypted age private key with keychain passphrase",
		slog.String("unlocker_id", k.GetID()),
		slog.Int("decrypted_length", agePrivKeyBuffer.Size()),
	)

	// Step 6: Parse the decrypted age private key
	Debug("Parsing decrypted age private key", "unlocker_id", k.GetID())

	ageIdentity, err := age.ParseX25519Identity(agePrivKeyBuffer.String())
	if err != nil {
		Debug("Failed to parse age private key", "error", err, "unlocker_id", k.GetID())

		return nil, fmt.Errorf("failed to parse age private key: %w", err)
	}

	DebugWith("Successfully parsed keychain age identity",
		slog.String("unlocker_id", k.GetID()),
		slog.String("public_key", ageIdentity.Recipient().String()),
	)

	return ageIdentity, nil
}

// GetType implements Unlocker interface
func (k *KeychainUnlocker) GetType() string {
	return "keychain"
}

// GetMetadata implements Unlocker interface
func (k *KeychainUnlocker) GetMetadata() UnlockerMetadata {
	return k.Metadata
}

// GetDirectory implements Unlocker interface
func (k *KeychainUnlocker) GetDirectory() string {
	return k.Directory
}

// GetID implements Unlocker interface - generates ID from keychain item name
func (k *KeychainUnlocker) GetID() string {
	// Generate ID using keychain item name
	keychainItemName, err := k.GetKeychainItemName()
	if err != nil {
		// The vault metadata is corrupt - this is a fatal error
		// We cannot continue with a fallback ID as that would mask data corruption
		panic(fmt.Sprintf("Keychain unlocker metadata is corrupt or missing keychain item name: %v", err))
	}

	return fmt.Sprintf("%s-keychain", keychainItemName)
}

// Remove implements Unlocker interface - removes the keychain unlocker
func (k *KeychainUnlocker) Remove() error {
	// Step 1: Get keychain item name
	keychainItemName, err := k.GetKeychainItemName()
	if err != nil {
		Debug("Failed to get keychain item name during removal", "error", err, "unlocker_id", k.GetID())

		return fmt.Errorf("failed to get keychain item name: %w", err)
	}

	// Step 2: Remove from keychain
	Debug("Removing keychain item", "keychain_item", keychainItemName)
	if err := deleteFromKeychain(keychainItemName); err != nil {
		Debug("Failed to remove keychain item", "error", err, "keychain_item", keychainItemName)

		return fmt.Errorf("failed to remove keychain item: %w", err)
	}

	// Step 3: Remove directory
	Debug("Removing keychain unlocker directory", "directory", k.Directory)
	if err := k.fs.RemoveAll(k.Directory); err != nil {
		Debug("Failed to remove keychain unlocker directory", "error", err, "directory", k.Directory)

		return fmt.Errorf("failed to remove keychain unlocker directory: %w", err)
	}

	Debug("Successfully removed keychain unlocker", "unlocker_id", k.GetID(), "keychain_item", keychainItemName)

	return nil
}

// NewKeychainUnlocker creates a new KeychainUnlocker instance
func NewKeychainUnlocker(fs afero.Fs, directory string, metadata UnlockerMetadata) *KeychainUnlocker {
	return &KeychainUnlocker{
		Directory: directory,
		Metadata:  metadata,
		fs:        fs,
	}
}

// GetKeychainItemName returns the keychain item name from metadata
func (k *KeychainUnlocker) GetKeychainItemName() (string, error) {
	// Load the metadata
	metadataPath := filepath.Join(k.Directory, "unlocker-metadata.json")
	metadataData, err := afero.ReadFile(k.fs, metadataPath)
	if err != nil {
		return "", fmt.Errorf("failed to read keychain metadata: %w", err)
	}

	var keychainMetadata KeychainUnlockerMetadata
	if err := json.Unmarshal(metadataData, &keychainMetadata); err != nil {
		return "", fmt.Errorf("failed to parse keychain metadata: %w", err)
	}

	return keychainMetadata.KeychainItemName, nil
}

// generateKeychainUnlockerName generates a unique name for the keychain unlocker
func generateKeychainUnlockerName(vaultName string) (string, error) {
	hostname, err := os.Hostname()
	if err != nil {
		return "", fmt.Errorf("failed to get hostname: %w", err)
	}

	// Format: secret-<vault>-<hostname>-<date>
	enrollmentDate := time.Now().Format("2006-01-02")

	return fmt.Sprintf("secret-%s-%s-%s", vaultName, hostname, enrollmentDate), nil
}

// getLongTermPrivateKey retrieves the long-term private key either from environment or current unlocker
// Returns a LockedBuffer to ensure the private key is protected in memory
func getLongTermPrivateKey(fs afero.Fs, vault VaultInterface) (*memguard.LockedBuffer, error) {
	// Check if mnemonic is available in environment variable
	envMnemonic := os.Getenv(EnvMnemonic)
	if envMnemonic != "" {
		// Use mnemonic directly to derive long-term key
		ltIdentity, err := agehd.DeriveIdentity(envMnemonic, 0)
		if err != nil {
			return nil, fmt.Errorf("failed to derive long-term key from mnemonic: %w", err)
		}

		// Return the private key in a secure buffer
		return memguard.NewBufferFromBytes([]byte(ltIdentity.String())), nil
	}

	// Get the vault to access current unlocker
	currentUnlocker, err := vault.GetCurrentUnlocker()
	if err != nil {
		return nil, fmt.Errorf("failed to get current unlocker: %w", err)
	}

	// Get the current unlocker identity
	currentUnlockerIdentity, err := currentUnlocker.GetIdentity()
	if err != nil {
		return nil, fmt.Errorf("failed to get current unlocker identity: %w", err)
	}

	// Get encrypted long-term key from current unlocker, handling different types
	var encryptedLtPrivKey []byte
	switch currentUnlocker := currentUnlocker.(type) {
	case *PassphraseUnlocker:
		// Read the encrypted long-term private key from passphrase unlocker
		encryptedLtPrivKey, err = afero.ReadFile(fs, filepath.Join(currentUnlocker.GetDirectory(), "longterm.age"))
		if err != nil {
			return nil, fmt.Errorf("failed to read encrypted long-term key from current passphrase unlocker: %w", err)
		}

	case *PGPUnlocker:
		// Read the encrypted long-term private key from PGP unlocker
		encryptedLtPrivKey, err = afero.ReadFile(fs, filepath.Join(currentUnlocker.GetDirectory(), "longterm.age"))
		if err != nil {
			return nil, fmt.Errorf("failed to read encrypted long-term key from current PGP unlocker: %w", err)
		}

	case *KeychainUnlocker:
		// Read the encrypted long-term private key from another keychain unlocker
		encryptedLtPrivKey, err = afero.ReadFile(fs, filepath.Join(currentUnlocker.GetDirectory(), "longterm.age"))
		if err != nil {
			return nil, fmt.Errorf("failed to read encrypted long-term key from current keychain unlocker: %w", err)
		}

	default:
		return nil, fmt.Errorf("unsupported current unlocker type for keychain unlocker creation")
	}

	// Decrypt long-term private key using current unlocker
	ltPrivKeyBuffer, err := DecryptWithIdentity(encryptedLtPrivKey, currentUnlockerIdentity)
	if err != nil {
		return nil, fmt.Errorf("failed to decrypt long-term private key: %w", err)
	}

	// Return the decrypted key buffer
	return ltPrivKeyBuffer, nil
}

// CreateKeychainUnlocker creates a new keychain unlocker and stores it in the vault
func CreateKeychainUnlocker(fs afero.Fs, stateDir string) (*KeychainUnlocker, error) {
	// Check if we're on macOS
	if err := checkMacOSAvailable(); err != nil {
		return nil, err
	}

	// Get current vault using the GetCurrentVault function from the same package
	vault, err := GetCurrentVault(fs, stateDir)
	if err != nil {
		return nil, fmt.Errorf("failed to get current vault: %w", err)
	}

	// Generate the keychain item name
	keychainItemName, err := generateKeychainUnlockerName(vault.GetName())
	if err != nil {
		return nil, fmt.Errorf("failed to generate keychain item name: %w", err)
	}

	// Create unlocker directory using the keychain item name as the directory name
	vaultDir, err := vault.GetDirectory()
	if err != nil {
		return nil, fmt.Errorf("failed to get vault directory: %w", err)
	}

	unlockerDir := filepath.Join(vaultDir, "unlockers.d", keychainItemName)
	if err := fs.MkdirAll(unlockerDir, DirPerms); err != nil {
		return nil, fmt.Errorf("failed to create unlocker directory: %w", err)
	}

	// Step 1: Generate a new age keypair for the keychain unlocker
	ageIdentity, err := age.GenerateX25519Identity()
	if err != nil {
		return nil, fmt.Errorf("failed to generate age keypair: %w", err)
	}

	// Step 2: Generate a random passphrase for encrypting the age private key
	agePrivKeyPassphrase, err := generateRandomPassphrase(agePrivKeyPassphraseLength)
	if err != nil {
		return nil, fmt.Errorf("failed to generate age private key passphrase: %w", err)
	}

	// Step 3: Store age recipient as plaintext
	ageRecipient := ageIdentity.Recipient().String()
	recipientPath := filepath.Join(unlockerDir, "pub.txt")
	if err := afero.WriteFile(fs, recipientPath, []byte(ageRecipient), FilePerms); err != nil {
		return nil, fmt.Errorf("failed to write age recipient: %w", err)
	}

	// Step 4: Encrypt age private key with the generated passphrase and store on disk
	// Create secure buffers for both the private key and passphrase
	agePrivKeyStr := ageIdentity.String()
	agePrivKeyBuffer := memguard.NewBufferFromBytes([]byte(agePrivKeyStr))
	defer agePrivKeyBuffer.Destroy()

	passphraseBuffer := memguard.NewBufferFromBytes([]byte(agePrivKeyPassphrase))
	defer passphraseBuffer.Destroy()

	encryptedAgePrivKey, err := EncryptWithPassphrase(agePrivKeyBuffer, passphraseBuffer)
	if err != nil {
		return nil, fmt.Errorf("failed to encrypt age private key with passphrase: %w", err)
	}

	agePrivKeyPath := filepath.Join(unlockerDir, "priv.age")
	if err := afero.WriteFile(fs, agePrivKeyPath, encryptedAgePrivKey, FilePerms); err != nil {
		return nil, fmt.Errorf("failed to write encrypted age private key: %w", err)
	}

	// Step 5: Get or derive the long-term private key
	ltPrivKeyData, err := getLongTermPrivateKey(fs, vault)
	if err != nil {
		return nil, err
	}
	defer ltPrivKeyData.Destroy()

	// Step 6: Encrypt long-term private key to the new age unlocker
	encryptedLtPrivKeyToAge, err := EncryptToRecipient(ltPrivKeyData, ageIdentity.Recipient())
	if err != nil {
		return nil, fmt.Errorf("failed to encrypt long-term private key to age unlocker: %w", err)
	}

	// Write encrypted long-term private key
	ltPrivKeyPath := filepath.Join(unlockerDir, "longterm.age")
	if err := afero.WriteFile(fs, ltPrivKeyPath, encryptedLtPrivKeyToAge, FilePerms); err != nil {
		return nil, fmt.Errorf("failed to write encrypted long-term private key: %w", err)
	}

	// Step 7: Prepare keychain data
	keychainData := KeychainData{
		AgePublicKey:         ageRecipient,
		AgePrivKeyPassphrase: agePrivKeyPassphrase,
		EncryptedLongtermKey: hex.EncodeToString(encryptedLtPrivKeyToAge),
	}

	keychainDataBytes, err := json.Marshal(keychainData)
	if err != nil {
		return nil, fmt.Errorf("failed to marshal keychain data: %w", err)
	}

	// Create a secure buffer for keychain data
	keychainDataBuffer := memguard.NewBufferFromBytes(keychainDataBytes)
	defer keychainDataBuffer.Destroy()

	// Step 8: Store data in keychain
	if err := storeInKeychain(keychainItemName, keychainDataBuffer); err != nil {
		return nil, fmt.Errorf("failed to store data in keychain: %w", err)
	}

	// Step 9: Create and write enhanced metadata
	keychainMetadata := KeychainUnlockerMetadata{
		UnlockerMetadata: UnlockerMetadata{
			Type:      "keychain",
			CreatedAt: time.Now(),
			Flags:     []string{"keychain", "macos"},
		},
		KeychainItemName: keychainItemName,
	}

	metadataBytes, err := json.MarshalIndent(keychainMetadata, "", "  ")
	if err != nil {
		return nil, fmt.Errorf("failed to marshal unlocker metadata: %w", err)
	}

	if err := afero.WriteFile(fs,
		filepath.Join(unlockerDir, "unlocker-metadata.json"),
		metadataBytes, FilePerms); err != nil {
		return nil, fmt.Errorf("failed to write unlocker metadata: %w", err)
	}

	return &KeychainUnlocker{
		Directory: unlockerDir,
		Metadata:  keychainMetadata.UnlockerMetadata,
		fs:        fs,
	}, nil
}

// checkMacOSAvailable verifies that we're running on macOS
func checkMacOSAvailable() error {
	if runtime.GOOS != "darwin" {
		return fmt.Errorf("keychain unlockers are only supported on macOS, current OS: %s", runtime.GOOS)
	}

	return nil
}

// validateKeychainItemName validates that a keychain item name is safe for command execution
func validateKeychainItemName(itemName string) error {
	if itemName == "" {
		return fmt.Errorf("keychain item name cannot be empty")
	}

	if !keychainItemNameRegex.MatchString(itemName) {
		return fmt.Errorf("invalid keychain item name format: %s", itemName)
	}

	return nil
}

// storeInKeychain stores data in the macOS keychain using keybase/go-keychain
func storeInKeychain(itemName string, data *memguard.LockedBuffer) error {
	if data == nil {
		return fmt.Errorf("data buffer is nil")
	}
	if err := validateKeychainItemName(itemName); err != nil {
		return fmt.Errorf("invalid keychain item name: %w", err)
	}

	item := keychain.NewItem()
	item.SetSecClass(keychain.SecClassGenericPassword)
	item.SetService(KEYCHAIN_APP_IDENTIFIER)
	item.SetAccount(itemName)
	item.SetLabel(fmt.Sprintf("%s - %s", KEYCHAIN_APP_IDENTIFIER, itemName))
	item.SetDescription("Secret vault keychain data")
	item.SetData([]byte(data.String()))
	item.SetSynchronizable(keychain.SynchronizableNo)
	// Use AccessibleWhenUnlockedThisDeviceOnly for better security and to trigger auth
	item.SetAccessible(keychain.AccessibleWhenUnlockedThisDeviceOnly)

	// First try to delete any existing item
	deleteItem := keychain.NewItem()
	deleteItem.SetSecClass(keychain.SecClassGenericPassword)
	deleteItem.SetService(KEYCHAIN_APP_IDENTIFIER)
	deleteItem.SetAccount(itemName)
	_ = keychain.DeleteItem(deleteItem) // Ignore error as item might not exist

	// Add the new item
	if err := keychain.AddItem(item); err != nil {
		return fmt.Errorf("failed to store item in keychain: %w", err)
	}

	return nil
}

// retrieveFromKeychain retrieves data from the macOS keychain using keybase/go-keychain
func retrieveFromKeychain(itemName string) ([]byte, error) {
	if err := validateKeychainItemName(itemName); err != nil {
		return nil, fmt.Errorf("invalid keychain item name: %w", err)
	}

	query := keychain.NewItem()
	query.SetSecClass(keychain.SecClassGenericPassword)
	query.SetService(KEYCHAIN_APP_IDENTIFIER)
	query.SetAccount(itemName)
	query.SetMatchLimit(keychain.MatchLimitOne)
	query.SetReturnData(true)

	results, err := keychain.QueryItem(query)
	if err != nil {
		return nil, fmt.Errorf("failed to retrieve item from keychain: %w", err)
	}

	if len(results) == 0 {
		return nil, fmt.Errorf("keychain item not found: %s", itemName)
	}

	return results[0].Data, nil
}

// deleteFromKeychain removes an item from the macOS keychain using keybase/go-keychain
func deleteFromKeychain(itemName string) error {
	if err := validateKeychainItemName(itemName); err != nil {
		return fmt.Errorf("invalid keychain item name: %w", err)
	}

	item := keychain.NewItem()
	item.SetSecClass(keychain.SecClassGenericPassword)
	item.SetService(KEYCHAIN_APP_IDENTIFIER)
	item.SetAccount(itemName)

	if err := keychain.DeleteItem(item); err != nil {
		return fmt.Errorf("failed to delete item from keychain: %w", err)
	}

	return nil
}

// generateRandomPassphrase generates a random passphrase for encrypting the age private key
func generateRandomPassphrase(length int) (string, error) {
	return generateRandomString(length, "0123456789abcdef")
}