// Package vault provides functionality for managing encrypted vaults.
package vault

import (
	"fmt"
	"path/filepath"
	"regexp"
	"strings"
	"time"

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

// Register the GetCurrentVault function with the secret package
//
//nolint:gochecknoinits // registers the vault accessor with the secret package
func init() {
	secret.RegisterGetCurrentVaultFunc(
		func(fs afero.Fs, stateDir string) (secret.VaultInterface, error) {
			return GetCurrentVault(fs, stateDir)
		})
}

// isValidVaultName reports whether name is a valid vault name: only
// lowercase ASCII letters, digits, '.', '-' and '_', and not empty, "." or
// "..". With no path separator allowed, a vault is always one directory
// directly under vaults.d.
func isValidVaultName(name string) bool {
	if name == "" || name == "." || name == ".." {
		return false
	}

	matched, _ := regexp.MatchString(`^[a-z0-9\.\-\_]+$`, name)

	return matched
}

// ValidateVaultName returns an error wrapping ErrInvalidVaultName when name
// is not a valid vault name. Call it on the name exactly as the user gave it,
// before building any path from it.
func ValidateVaultName(name string) error {
	if !isValidVaultName(name) {
		return fmt.Errorf(
			"%w '%s': only lowercase ASCII letters, digits, '.', '-' and '_' "+
				"are allowed, and a name must not be empty, '.' or '..'",
			ErrInvalidVaultName, name,
		)
	}

	return nil
}

// ResolveVaultSymlink reads the currentvault file to get the path to the current vault
// The file contains just the vault name (e.g., "default")
func ResolveVaultSymlink(fs afero.Fs, currentVaultPath string) (string, error) {
	secret.Debug("resolveVaultSymlink starting", "path", currentVaultPath)

	fileData, err := afero.ReadFile(fs, currentVaultPath)
	if err != nil {
		secret.Debug("Failed to read currentvault file", "error", err)

		return "", fmt.Errorf("failed to read currentvault file: %w", err)
	}

	// The file contains just the vault name like "default"
	vaultName := strings.TrimSpace(string(fileData))
	secret.Debug("Read vault name from file", "vault_name", vaultName)

	// Resolve to absolute path: stateDir/vaults.d/vaultName
	stateDir := filepath.Dir(currentVaultPath)
	absolutePath := filepath.Join(stateDir, "vaults.d", vaultName)

	secret.Debug("Resolved to absolute path", "absolute_path", absolutePath)

	return absolutePath, nil
}

// GetCurrentVault gets the current vault from the file system
func GetCurrentVault(fs afero.Fs, stateDir string) (*Vault, error) {
	secret.Debug("Getting current vault", "state_dir", stateDir)

	// Check if the current vault symlink exists
	currentVaultPath := filepath.Join(stateDir, "currentvault")

	secret.Debug("Checking current vault symlink", "path", currentVaultPath)

	_, err := fs.Stat(currentVaultPath)
	if err != nil {
		secret.Debug("Failed to stat current vault symlink",
			"error", err, "path", currentVaultPath)

		return nil, fmt.Errorf("failed to read current vault symlink: %w", err)
	}

	secret.Debug("Current vault symlink exists")

	// Resolve the symlink to get the actual vault directory
	secret.Debug("Resolving vault symlink")

	targetPath, err := ResolveVaultSymlink(fs, currentVaultPath)
	if err != nil {
		return nil, err
	}

	secret.Debug("Resolved vault symlink", "target_path", targetPath)

	// Extract the vault name from the path
	// The path will be something like "/path/to/vaults.d/default"
	vaultName := filepath.Base(targetPath)
	secret.Debug("Extracted vault name", "vault_name", vaultName)

	secret.Debug("Current vault resolved",
		"vault_name", vaultName, "target_path", targetPath)

	// Create and return the vault
	return NewVault(fs, stateDir, vaultName), nil
}

// ListVaults lists all vaults in the state directory
func ListVaults(fs afero.Fs, stateDir string) ([]string, error) {
	vaultsDir := filepath.Join(stateDir, "vaults.d")

	// Check if vaults directory exists
	exists, err := afero.DirExists(fs, vaultsDir)
	if err != nil {
		return nil, fmt.Errorf("failed to check if vaults directory exists: %w", err)
	}

	if !exists {
		return []string{}, nil
	}

	// Read the vaults directory
	entries, err := afero.ReadDir(fs, vaultsDir)
	if err != nil {
		return nil, fmt.Errorf("failed to read vaults directory: %w", err)
	}

	// Extract vault names
	var vaults []string

	for _, entry := range entries {
		if entry.IsDir() {
			vaults = append(vaults, entry.Name())
		}
	}

	return vaults, nil
}

// processMnemonicForVault handles mnemonic processing for vault creation.
// It returns the long-term key, nil when there is no mnemonic, and the
// derivation index, public key hash, and family hash.
func processMnemonicForVault(
	fs afero.Fs, stateDir, vaultDir, vaultName string,
	mnemonicBuffer *memguard.LockedBuffer,
) (*age.X25519Identity, uint32, string, string, error) {
	if mnemonicBuffer == nil {
		secret.Debug("No mnemonic given, vault created without long-term key",
			"vault", vaultName)
		// Use 0 for derivation index when no mnemonic is provided
		return nil, 0, "", "", nil
	}

	mnemonic := mnemonicBuffer.String()

	secret.Debug("Mnemonic given, deriving long-term key", "vault", vaultName)

	// Get the next available derivation index for this mnemonic
	derivationIndex, err := GetNextDerivationIndex(fs, stateDir, mnemonic)
	if err != nil {
		return nil, 0, "", "",
			fmt.Errorf("failed to get next derivation index: %w", err)
	}

	// Derive the long-term key using the actual derivation index
	ltIdentity, err := agehd.DeriveIdentity(mnemonic, derivationIndex)
	if err != nil {
		return nil, 0, "", "", fmt.Errorf("failed to derive long-term key: %w", err)
	}

	// Write the public key
	ltPubKey := ltIdentity.Recipient().String()

	ltPubKeyPath := filepath.Join(vaultDir, "pub.age")

	err = secret.WriteFileAtomic(fs, ltPubKeyPath, []byte(ltPubKey))
	if err != nil {
		return nil, 0, "", "",
			fmt.Errorf("failed to write long-term public key: %w", err)
	}

	secret.Debug("Wrote long-term public key", "path", ltPubKeyPath)

	// Compute verification hash from actual derivation index
	publicKeyHash := ComputeDoubleSHA256([]byte(ltIdentity.Recipient().String()))

	// Compute family hash from index 0 (same for all vaults with this mnemonic)
	// This is used to identify which vaults belong to the same mnemonic family
	identity0, err := agehd.DeriveIdentity(mnemonic, 0)
	if err != nil {
		return nil, 0, "", "",
			fmt.Errorf("failed to derive identity for index 0: %w", err)
	}

	familyHash := ComputeDoubleSHA256([]byte(identity0.Recipient().String()))

	return ltIdentity, derivationIndex, publicKeyHash, familyHash, nil
}

// CreateVault creates a new vault and selects it as the current vault. When
// mnemonic is not nil, the vault's long-term key is derived from it, and the
// returned vault has it as its Mnemonic; when it is nil, the vault has no
// long-term key until one is imported. When passphrase is not nil, the vault
// gets a passphrase unlocker protected by it, as its current unlocker; that
// needs a mnemonic. It refuses a vault that already exists before writing
// anything: creating it again would replace its keys, and its secrets could
// no longer be decrypted. The commands that call it hold the state directory
// lock, so no other command can create the vault between the check and the
// writes.
//
// The vault is written whole into a temporary directory, which is renamed
// into vaults.d only once complete, and only then selected: a crash at any
// point leaves either no vault or a complete one. The next command that
// takes the lock deletes what the crash left under a temporary name.
func CreateVault(
	fs afero.Fs, stateDir string, name string,
	mnemonic, passphrase *memguard.LockedBuffer,
) (*Vault, error) {
	secret.Debug("Creating new vault", "name", name, "state_dir", stateDir)

	err := ValidateVaultName(name)
	if err != nil {
		secret.Debug("Invalid vault name provided", "vault_name", name)

		return nil, err
	}

	secret.Debug("Vault name validation passed", "vault_name", name)

	vaultDir := filepath.Join(stateDir, "vaults.d", name)

	exists, err := afero.DirExists(fs, vaultDir)
	if err != nil {
		return nil, fmt.Errorf("failed to check if vault exists: %w", err)
	}

	if exists {
		return nil, fmt.Errorf("vault %s %w", name, ErrVaultExists)
	}

	if passphrase != nil && mnemonic == nil {
		return nil, fmt.Errorf("vault %s %w", name, ErrUnlockerWithoutMnemonic)
	}

	secret.Debug("Creating vault directory structure", "vault_dir", vaultDir)

	err = secret.WriteDir(fs, vaultDir, func(dir string) error {
		return writeVaultFiles(fs, stateDir, dir, name, mnemonic, passphrase)
	})
	if err != nil {
		return nil, err
	}

	// Select the newly created vault as current
	secret.Debug("Selecting newly created vault as current", "name", name)

	err = SelectVault(fs, stateDir, name)
	if err != nil {
		return nil, fmt.Errorf("failed to select vault: %w", err)
	}

	// Create and return the vault
	secret.Debug("Successfully created vault", "name", name)

	vlt := NewVault(fs, stateDir, name)
	vlt.Mnemonic = mnemonic

	return vlt, nil
}

// writeVaultFiles writes the files of the new vault name into vaultDir: its
// secrets and unlockers directories, its long-term public key and metadata,
// and, when passphrase is not nil, a passphrase unlocker as its current one.
func writeVaultFiles(
	fs afero.Fs, stateDir, vaultDir, name string,
	mnemonic, passphrase *memguard.LockedBuffer,
) error {
	for _, subdir := range []string{"secrets.d", "unlockers.d"} {
		err := fs.MkdirAll(filepath.Join(vaultDir, subdir), secret.DirPerms)
		if err != nil {
			return fmt.Errorf("failed to create %s directory: %w", subdir, err)
		}
	}

	ltIdentity, derivationIndex, publicKeyHash, familyHash, err :=
		processMnemonicForVault(fs, stateDir, vaultDir, name, mnemonic)
	if err != nil {
		return err
	}

	metadata := &Metadata{
		CreatedAt:          time.Now(),
		DerivationIndex:    derivationIndex,
		PublicKeyHash:      publicKeyHash,
		MnemonicFamilyHash: familyHash,
	}

	err = SaveVaultMetadata(fs, vaultDir, metadata)
	if err != nil {
		return fmt.Errorf("failed to save vault metadata: %w", err)
	}

	if passphrase == nil {
		return nil
	}

	_, err = writePassphraseUnlocker(fs, vaultDir, ltIdentity, passphrase)

	return err
}

// SelectVault selects the given vault as the current vault
func SelectVault(fs afero.Fs, stateDir string, name string) error {
	secret.Debug("Selecting vault", "vault_name", name, "state_dir", stateDir)

	err := ValidateVaultName(name)
	if err != nil {
		secret.Debug("Invalid vault name provided", "vault_name", name)

		return err
	}

	secret.Debug("Vault name validation passed", "vault_name", name)

	// Check if vault exists
	vaultDir := filepath.Join(stateDir, "vaults.d", name)

	exists, err := afero.DirExists(fs, vaultDir)
	if err != nil {
		return fmt.Errorf("failed to check if vault exists: %w", err)
	}

	if !exists {
		return fmt.Errorf("vault %s %w", name, ErrVaultNotFound)
	}

	// Create or replace the currentvault file with just the vault name. It
	// is replaced in one rename, so it never goes missing.
	currentVaultPath := filepath.Join(stateDir, "currentvault")

	secret.Debug("Writing currentvault file", "vault_name", name)

	err = secret.WriteFileAtomic(fs, currentVaultPath, []byte(name))
	if err != nil {
		return fmt.Errorf("failed to select vault: %w", err)
	}

	secret.Debug("Successfully selected vault", "vault_name", name)

	return nil
}