package secret

import (
	"encoding/json"
	"errors"
	"fmt"
	"log/slog"
	"path/filepath"
	"slices"
	"sort"
	"strings"
	"time"

	"filippo.io/age"
	"github.com/awnumar/memguard"
	"github.com/oklog/ulid/v2"
	"github.com/spf13/afero"
)

const (
	versionNameParts  = 2
	maxVersionsPerDay = 999
)

var (
	errMaxVersionsPerDay = errors.New("exceeded maximum versions per day (999)")
	errNilValueBuffer    = errors.New("value buffer is nil")
)

// VersionMetadata contains information about a secret version
type VersionMetadata struct {
	ID        string     `json:"id"`                  // ULID
	CreatedAt *time.Time `json:"createdAt,omitempty"` // When version was created
	NotBefore *time.Time `json:"notBefore,omitempty"` // When this version becomes active
	NotAfter  *time.Time `json:"notAfter,omitempty"`  // Expiry (nil = current)
}

// Version represents a version of a secret
type Version struct {
	SecretName string
	Version    string
	Directory  string
	Metadata   VersionMetadata
	vault      VaultInterface
}

// NewVersion creates a new Version instance
func NewVersion(vault VaultInterface, secretName string, version string) *Version {
	DebugWith("Creating new secret version instance",
		slog.String("secret_name", secretName),
		slog.String("version", version),
		slog.String("vault_name", vault.GetName()),
	)

	vaultDir, _ := vault.GetDirectory()
	storageName := strings.ReplaceAll(secretName, "/", "%")
	versionDir := filepath.Join(vaultDir, "secrets.d", storageName, "versions", version)

	DebugWith("Secret version storage details",
		slog.String("secret_name", secretName),
		slog.String("version", version),
		slog.String("version_dir", versionDir),
	)

	now := time.Now()

	return &Version{
		SecretName: secretName,
		Version:    version,
		Directory:  versionDir,
		vault:      vault,
		Metadata: VersionMetadata{
			ID:        ulid.Make().String(),
			CreatedAt: &now,
		},
	}
}

// GenerateVersionName generates a new version name in YYYYMMDD.NNN format
func GenerateVersionName(fs afero.Fs, secretDir string) (string, error) {
	today := time.Now().Format("20060102")
	versionsDir := filepath.Join(secretDir, "versions")

	// Ensure versions directory exists
	err := fs.MkdirAll(versionsDir, DirPerms)
	if err != nil {
		return "", fmt.Errorf("failed to create versions directory: %w", err)
	}

	// Find the highest serial number for today
	entries, err := afero.ReadDir(fs, versionsDir)
	if err != nil {
		return "", fmt.Errorf("failed to read versions directory: %w", err)
	}

	maxSerial := 0
	prefix := today + "."

	for _, entry := range entries {
		// Skip non-directories and those without correct prefix
		if !entry.IsDir() || !strings.HasPrefix(entry.Name(), prefix) {
			continue
		}

		// Extract serial number
		parts := strings.Split(entry.Name(), ".")
		if len(parts) != versionNameParts {
			continue
		}

		var serial int

		_, err := fmt.Sscanf(parts[1], "%03d", &serial)
		if err != nil {
			Warn("Skipping malformed version directory name",
				"name", entry.Name(), "error", err)

			continue
		}

		if serial > maxSerial {
			maxSerial = serial
		}
	}

	// Generate new version name
	newSerial := maxSerial + 1
	if newSerial > maxVersionsPerDay {
		return "", errMaxVersionsPerDay
	}

	return fmt.Sprintf("%s.%03d", today, newSerial), nil
}

// Save saves the version metadata and value. The files are written into a
// temporary directory that is renamed to sv.Directory once all of them are
// complete, so the version directory is either whole or absent, even if the
// process dies part-way.
func (sv *Version) Save(value *memguard.LockedBuffer) error {
	if value == nil {
		return errNilValueBuffer
	}

	DebugWith("Saving secret version",
		slog.String("secret_name", sv.SecretName),
		slog.String("version", sv.Version),
		slog.Int("value_length", value.Size()),
	)

	fs := sv.vault.GetFilesystem()

	// Create the versions directory the finished version is renamed into
	err := fs.MkdirAll(filepath.Dir(sv.Directory), DirPerms)
	if err != nil {
		Debug("Failed to create versions directory", "error", err, "dir", sv.Directory)

		return fmt.Errorf("failed to create versions directory: %w", err)
	}

	tmpDir, err := TempDirFor(fs, sv.Directory)
	if err != nil {
		return err
	}

	// Once the rename below has moved it into place, this finds nothing.
	defer func() { _ = fs.RemoveAll(tmpDir) }()

	// Generate a new keypair for this version
	Debug("Generating version-specific keypair", "version", sv.Version)

	versionIdentity, err := age.GenerateX25519Identity()
	if err != nil {
		Debug("Failed to generate version keypair", "error", err, "version", sv.Version)

		return fmt.Errorf("failed to generate version keypair: %w", err)
	}

	// Store private key in memguard buffer immediately
	versionPrivateKeyBuffer := memguard.NewBufferFromBytes(
		[]byte(versionIdentity.String()))
	defer versionPrivateKeyBuffer.Destroy()

	DebugWith("Generated version keypair",
		slog.String("version", sv.Version),
		slog.String("public_key", versionIdentity.Recipient().String()),
	)

	err = sv.writePublicKeyAndValue(fs, tmpDir, versionIdentity, value)
	if err != nil {
		return err
	}

	err = sv.writeEncryptedPrivateKey(fs, tmpDir, versionPrivateKeyBuffer)
	if err != nil {
		return err
	}

	err = sv.writeEncryptedMetadata(fs, tmpDir, versionIdentity)
	if err != nil {
		return err
	}

	err = fs.Rename(tmpDir, sv.Directory)
	if err != nil {
		Debug("Failed to move version into place", "error", err, "dir", sv.Directory)

		return fmt.Errorf("failed to move version into place: %w", err)
	}

	Debug("Successfully saved secret version",
		"version", sv.Version, "secret_name", sv.SecretName)

	return nil
}

// LoadMetadata loads and decrypts the version metadata
func (sv *Version) LoadMetadata(ltIdentity *age.X25519Identity) error {
	DebugWith("Loading version metadata",
		slog.String("secret_name", sv.SecretName),
		slog.String("version", sv.Version),
	)

	fs := sv.vault.GetFilesystem()

	// Step 1: Read encrypted version private key
	encryptedPrivKeyPath := filepath.Join(sv.Directory, "priv.age")

	encryptedPrivKey, err := afero.ReadFile(fs, encryptedPrivKeyPath)
	if err != nil {
		Debug("Failed to read encrypted version private key",
			"error", err, "path", encryptedPrivKeyPath)

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

	// Step 2: Decrypt version private key using long-term key
	versionPrivKeyBuffer, err := DecryptWithIdentity(encryptedPrivKey, ltIdentity)
	if err != nil {
		Debug("Failed to decrypt version private key", "error", err, "version", sv.Version)

		return fmt.Errorf("failed to decrypt version private key: %w", err)
	}
	defer versionPrivKeyBuffer.Destroy()

	// Step 3: Parse version private key
	versionIdentity, err := age.ParseX25519Identity(versionPrivKeyBuffer.String())
	if err != nil {
		Debug("Failed to parse version private key", "error", err, "version", sv.Version)

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

	// Step 4: Read encrypted metadata
	encryptedMetadataPath := filepath.Join(sv.Directory, "metadata.age")

	encryptedMetadata, err := afero.ReadFile(fs, encryptedMetadataPath)
	if err != nil {
		Debug("Failed to read encrypted version metadata",
			"error", err, "path", encryptedMetadataPath)

		return fmt.Errorf("failed to read encrypted version metadata: %w", err)
	}

	// Step 5: Decrypt metadata using version key
	metadataBuffer, err := DecryptWithIdentity(encryptedMetadata, versionIdentity)
	if err != nil {
		Debug("Failed to decrypt version metadata", "error", err, "version", sv.Version)

		return fmt.Errorf("failed to decrypt version metadata: %w", err)
	}
	defer metadataBuffer.Destroy()

	// Step 6: Unmarshal metadata
	var metadata VersionMetadata

	err = json.Unmarshal(metadataBuffer.Bytes(), &metadata)
	if err != nil {
		Debug("Failed to unmarshal version metadata", "error", err, "version", sv.Version)

		return fmt.Errorf("failed to unmarshal version metadata: %w", err)
	}

	sv.Metadata = metadata

	Debug("Successfully loaded version metadata", "version", sv.Version)

	return nil
}

// GetValue retrieves and decrypts the version value
func (sv *Version) GetValue(
	ltIdentity *age.X25519Identity,
) (*memguard.LockedBuffer, error) {
	DebugWith("Getting version value",
		slog.String("secret_name", sv.SecretName),
		slog.String("version", sv.Version),
	)

	// Debug: Log the directory and long-term key info
	Debug("SecretVersion GetValue debug info",
		"secret_name", sv.SecretName,
		"version", sv.Version,
		"directory", sv.Directory,
		"lt_identity_public_key", ltIdentity.Recipient().String())

	fs := sv.vault.GetFilesystem()

	// Step 1: Read encrypted version private key
	encryptedPrivKeyPath := filepath.Join(sv.Directory, "priv.age")
	Debug("Reading encrypted version private key", "path", encryptedPrivKeyPath)

	encryptedPrivKey, err := afero.ReadFile(fs, encryptedPrivKeyPath)
	if err != nil {
		Debug("Failed to read encrypted version private key",
			"error", err, "path", encryptedPrivKeyPath)

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

	Debug("Successfully read encrypted version private key",
		"path", encryptedPrivKeyPath, "size", len(encryptedPrivKey))

	// Step 2: Decrypt version private key using long-term key
	Debug("Decrypting version private key with long-term identity", "version", sv.Version)

	versionPrivKeyBuffer, err := DecryptWithIdentity(encryptedPrivKey, ltIdentity)
	if err != nil {
		Debug("Failed to decrypt version private key", "error", err, "version", sv.Version)

		return nil, fmt.Errorf("failed to decrypt version private key: %w", err)
	}
	defer versionPrivKeyBuffer.Destroy()

	Debug("Successfully decrypted version private key",
		"version", sv.Version, "size", versionPrivKeyBuffer.Size())

	// Step 3: Parse version private key
	versionIdentity, err := age.ParseX25519Identity(versionPrivKeyBuffer.String())
	if err != nil {
		Debug("Failed to parse version private key", "error", err, "version", sv.Version)

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

	// Step 4: Read encrypted value
	encryptedValuePath := filepath.Join(sv.Directory, "value.age")
	Debug("Reading encrypted value", "path", encryptedValuePath)

	encryptedValue, err := afero.ReadFile(fs, encryptedValuePath)
	if err != nil {
		Debug("Failed to read encrypted version value",
			"error", err, "path", encryptedValuePath)

		return nil, fmt.Errorf("failed to read encrypted version value: %w", err)
	}

	Debug("Successfully read encrypted value",
		"path", encryptedValuePath, "size", len(encryptedValue))

	// Step 5: Decrypt value using version key
	Debug("Decrypting value with version identity", "version", sv.Version)

	valueBuffer, err := DecryptWithIdentity(encryptedValue, versionIdentity)
	if err != nil {
		Debug("Failed to decrypt version value", "error", err, "version", sv.Version)

		return nil, fmt.Errorf("failed to decrypt version value: %w", err)
	}

	Debug("Successfully retrieved version value",
		"version", sv.Version,
		"value_length", valueBuffer.Size(),
		"is_empty", valueBuffer.Size() == 0)

	return valueBuffer, nil
}

// writePublicKeyAndValue stores the version's public key and the value
// encrypted to it in dir.
func (sv *Version) writePublicKeyAndValue(
	fs afero.Fs,
	dir string,
	versionIdentity *age.X25519Identity,
	value *memguard.LockedBuffer,
) error {
	versionPublicKey := versionIdentity.Recipient().String()
	pubKeyPath := filepath.Join(dir, "pub.age")
	Debug("Writing version public key", "path", pubKeyPath)

	err := WriteFileAtomic(fs, pubKeyPath, []byte(versionPublicKey))
	if err != nil {
		Debug("Failed to write version public key", "error", err, "path", pubKeyPath)

		return fmt.Errorf("failed to write version public key: %w", err)
	}

	// Encrypt the value to the version's public key
	Debug("Encrypting value to version's public key", "version", sv.Version)

	encryptedValue, err := EncryptToRecipient(value, versionIdentity.Recipient())
	if err != nil {
		Debug("Failed to encrypt version value", "error", err, "version", sv.Version)

		return fmt.Errorf("failed to encrypt version value: %w", err)
	}

	valuePath := filepath.Join(dir, "value.age")
	Debug("Writing encrypted version value", "path", valuePath)

	err = WriteFileAtomic(fs, valuePath, encryptedValue)
	if err != nil {
		Debug("Failed to write encrypted version value", "error", err, "path", valuePath)

		return fmt.Errorf("failed to write encrypted version value: %w", err)
	}

	return nil
}

// writeEncryptedPrivateKey encrypts the version's private key to the
// vault's long-term public key and stores it in dir.
func (sv *Version) writeEncryptedPrivateKey(
	fs afero.Fs,
	dir string,
	versionPrivateKeyBuffer *memguard.LockedBuffer,
) error {
	vaultDir, _ := sv.vault.GetDirectory()
	ltPubKeyPath := filepath.Join(vaultDir, "pub.age")
	Debug("Reading long-term public key", "path", ltPubKeyPath)

	ltPubKeyData, err := afero.ReadFile(fs, ltPubKeyPath)
	if err != nil {
		Debug("Failed to read long-term public key", "error", err, "path", ltPubKeyPath)

		return fmt.Errorf("failed to read long-term public key: %w", err)
	}

	Debug("Parsing long-term public key")

	ltRecipient, err := age.ParseX25519Recipient(string(ltPubKeyData))
	if err != nil {
		Debug("Failed to parse long-term public key", "error", err)

		return fmt.Errorf("failed to parse long-term public key: %w", err)
	}

	Debug("Encrypting version private key to long-term public key",
		"version", sv.Version)

	encryptedPrivKey, err := EncryptToRecipient(versionPrivateKeyBuffer, ltRecipient)
	if err != nil {
		Debug("Failed to encrypt version private key",
			"error", err, "version", sv.Version)

		return fmt.Errorf("failed to encrypt version private key: %w", err)
	}

	privKeyPath := filepath.Join(dir, "priv.age")
	Debug("Writing encrypted version private key", "path", privKeyPath)

	err = WriteFileAtomic(fs, privKeyPath, encryptedPrivKey)
	if err != nil {
		Debug("Failed to write encrypted version private key",
			"error", err, "path", privKeyPath)

		return fmt.Errorf("failed to write encrypted version private key: %w", err)
	}

	return nil
}

// writeEncryptedMetadata encrypts the version metadata to the version's
// public key and stores it in dir.
func (sv *Version) writeEncryptedMetadata(
	fs afero.Fs,
	dir string,
	versionIdentity *age.X25519Identity,
) error {
	Debug("Encrypting version metadata", "version", sv.Version)

	metadataBytes, err := json.MarshalIndent(sv.Metadata, "", "  ")
	if err != nil {
		Debug("Failed to marshal version metadata", "error", err)

		return fmt.Errorf("failed to marshal version metadata: %w", err)
	}

	// Encrypt metadata to the version's public key
	metadataBuffer := memguard.NewBufferFromBytes(metadataBytes)
	defer metadataBuffer.Destroy()

	encryptedMetadata, err := EncryptToRecipient(
		metadataBuffer, versionIdentity.Recipient())
	if err != nil {
		Debug("Failed to encrypt version metadata", "error", err, "version", sv.Version)

		return fmt.Errorf("failed to encrypt version metadata: %w", err)
	}

	metadataPath := filepath.Join(dir, "metadata.age")
	Debug("Writing encrypted version metadata", "path", metadataPath)

	err = WriteFileAtomic(fs, metadataPath, encryptedMetadata)
	if err != nil {
		Debug("Failed to write encrypted version metadata",
			"error", err, "path", metadataPath)

		return fmt.Errorf("failed to write encrypted version metadata: %w", err)
	}

	return nil
}

// ListVersions lists all versions of a secret
func ListVersions(fs afero.Fs, secretDir string) ([]string, error) {
	versionsDir := filepath.Join(secretDir, "versions")

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

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

	// List all version directories
	entries, err := afero.ReadDir(fs, versionsDir)
	if err != nil {
		return nil, fmt.Errorf("failed to read versions directory: %w", err)
	}

	var versions []string

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

	// Sort versions in reverse chronological order
	sort.Sort(sort.Reverse(sort.StringSlice(versions)))

	return versions, nil
}

// VersionExists reports whether version is one of the versions ListVersions
// lists for the secret in secretDir. It only compares names, so a version
// the user typed can be checked with it before any path is built from it.
func VersionExists(fs afero.Fs, secretDir string, version string) (bool, error) {
	versions, err := ListVersions(fs, secretDir)
	if err != nil {
		return false, err
	}

	return slices.Contains(versions, version), nil
}

// GetCurrentVersion returns the version that the "current" file points to
// The file contains just the version name (e.g., "20231215.001")
func GetCurrentVersion(fs afero.Fs, secretDir string) (string, error) {
	currentPath := filepath.Join(secretDir, "current")

	fileData, err := afero.ReadFile(fs, currentPath)
	if err != nil {
		return "", fmt.Errorf("failed to read current version file: %w", err)
	}

	version := strings.TrimSpace(string(fileData))

	return version, nil
}

// SetCurrentVersion updates the "current" file to point to a specific version
// The file contains just the version name (e.g., "20231215.001"). It is
// replaced in one rename, so once written it always exists.
func SetCurrentVersion(fs afero.Fs, secretDir string, version string) error {
	currentPath := filepath.Join(secretDir, "current")

	err := WriteFileAtomic(fs, currentPath, []byte(version))
	if err != nil {
		return fmt.Errorf("failed to create current version file: %w", err)
	}

	return nil
}