//go:build linux || freebsd
// +build linux freebsd

package crypto

import (
	"bytes"
	"fmt"
	"io"
	"os"
	"strings"

	// Deprecated: golang.org/x/crypto/openpgp is frozen; no more security fixes.
	// Will be replaced with an alternative in a future release.
	"golang.org/x/crypto/openpgp"
	"golang.org/x/crypto/openpgp/armor"
	"golang.org/x/crypto/openpgp/clearsign"
)

// PGPConfig configures PGP operations
type PGPConfig struct {
	// Path to private key
	PrivateKeyPath string

	// Path to public key
	PublicKeyPath string

	// Passphrase for private key
	Passphrase string

	// Armor output (ASCII vs binary)
	Armor bool

	// KeyRing for verification
	KeyRing openpgp.EntityList
}

// DefaultPGPConfig returns the default configuration
func DefaultPGPConfig() *PGPConfig {
	return &PGPConfig{
		Armor: true,
	}
}

// PGPDecryptor decrypts PGP encrypted data
type PGPDecryptor struct {
	config *PGPConfig
}

// NewPGPDecryptor creates a new PGP decryptor
func NewPGPDecryptor(cfg *PGPConfig) *PGPDecryptor {
	if cfg == nil {
		cfg = DefaultPGPConfig()
	}
	return &PGPDecryptor{config: cfg}
}

// Decrypt decrypts PGP encrypted data
func (pd *PGPDecryptor) Decrypt(r io.Reader, w io.Writer) error {
	var keyring openpgp.EntityList
	var err error

	// Load private key if configured
	if pd.config.PrivateKeyPath != "" {
		keyring, err = loadPrivateKeyRing(pd.config.PrivateKeyPath, []byte(pd.config.Passphrase))
		if err != nil {
			return fmt.Errorf("failed to load private key: %w", err)
		}
	}

	// Check if input is armored
	buf := make([]byte, 64)
	n, err := io.ReadFull(r, buf)
	if err != nil && err != io.ErrUnexpectedEOF {
		return fmt.Errorf("failed to read input: %w", err)
	}

	input := io.MultiReader(bytes.NewReader(buf[:n]), r)

	// Try to decode armor
	if bytes.HasPrefix(bytes.TrimSpace(buf[:n]), []byte("-----BEGIN PGP")) {
		armoredBlock, err := armor.Decode(input)
		if err != nil {
			return fmt.Errorf("failed to decode pgp armor: %w", err)
		}
		input = armoredBlock.Body
	}

	// Decrypt the data
	md, err := openpgp.ReadMessage(input, keyring, pd.config.passphrasePrompt(), nil)
	if err != nil {
		return fmt.Errorf("failed to decrypt message: %w", err)
	}

	// Read all decrypted data
	_, err = io.Copy(w, md.UnverifiedBody)
	readErr := err

	// Close the body (this also verifies the signature if present)
	// UnverifiedBody is actually a ReadCloser, but declared as io.Reader
	if closer, ok := md.UnverifiedBody.(io.Closer); ok {
		closeErr := closer.Close()
		if closeErr != nil {
			if readErr == nil {
				return fmt.Errorf("signature verification failed: %w", closeErr)
			}
		}
	}

	if readErr != nil {
		return fmt.Errorf("failed to read decrypted data: %w", readErr)
	}

	// Verify signature if present
	if md.IsSigned && md.SignedBy != nil {
		// Message was signed and verified
	}

	return nil
}

// DecryptFile decrypts a PGP encrypted file
func (pd *PGPDecryptor) DecryptFile(inputPath, outputPath string) error {
	inputFile, err := os.Open(inputPath)
	if err != nil {
		return fmt.Errorf("failed to open input file: %w", err)
	}
	defer inputFile.Close()

	outputFile, err := os.Create(outputPath)
	if err != nil {
		return fmt.Errorf("failed to create output file: %w", err)
	}
	defer outputFile.Close()

	return pd.Decrypt(inputFile, outputFile)
}

// PGPEncryptor encrypts data using PGP
type PGPEncryptor struct {
	config *PGPConfig
}

// NewPGPEncryptor creates a new PGP encryptor
func NewPGPEncryptor(cfg *PGPConfig) *PGPEncryptor {
	if cfg == nil {
		cfg = DefaultPGPConfig()
	}
	return &PGPEncryptor{config: cfg}
}

// Encrypt encrypts data using PGP
func (pe *PGPEncryptor) Encrypt(r io.Reader, w io.Writer) error {
	// Load public key
	if pe.config.PublicKeyPath == "" {
		return fmt.Errorf("public key path is required for encryption")
	}

	entity, err := loadPublicKey(pe.config.PublicKeyPath)
	if err != nil {
		return fmt.Errorf("failed to load public key: %w", err)
	}

	// Prepare hints
	hints := &openpgp.FileHints{
		IsBinary: true,
		FileName: "", // Don't store filename
	}

	var out io.WriteCloser
	if pe.config.Armor {
		out, err = armor.Encode(w, "PGP MESSAGE", nil)
		if err != nil {
			return fmt.Errorf("failed to create armor encoder: %w", err)
		}
	} else {
		out = nopWriteCloser{w}
	}

	// Encrypt the data
	plaintext, err := openpgp.Encrypt(out, []*openpgp.Entity{entity}, nil, hints, nil)
	if err != nil {
		if out != nil {
			out.Close()
		}
		return fmt.Errorf("failed to encrypt: %w", err)
	}

	_, err = io.Copy(plaintext, r)
	if err != nil {
		plaintext.Close()
		if out != nil {
			out.Close()
		}
		return fmt.Errorf("failed to write encrypted data: %w", err)
	}

	plaintext.Close()
	if pe.config.Armor && out != nil {
		out.Close()
	}

	return nil
}

// EncryptFile encrypts a file using PGP
func (pe *PGPEncryptor) EncryptFile(inputPath, outputPath string) error {
	inputFile, err := os.Open(inputPath)
	if err != nil {
		return fmt.Errorf("failed to open input file: %w", err)
	}
	defer inputFile.Close()

	outputFile, err := os.Create(outputPath)
	if err != nil {
		return fmt.Errorf("failed to create output file: %w", err)
	}
	defer outputFile.Close()

	return pe.Encrypt(inputFile, outputFile)
}

// PGPVerifier verifies PGP signatures
type PGPVerifier struct {
	config *PGPConfig
}

// NewPGPVerifier creates a new PGP verifier
func NewPGPVerifier(cfg *PGPConfig) *PGPVerifier {
	if cfg == nil {
		cfg = DefaultPGPConfig()
	}
	return &PGPVerifier{config: cfg}
}

// Verify verifies a PGP signature (detached signature)
func (pv *PGPVerifier) Verify(data io.Reader, signature []byte) (bool, string, error) {
	// Load keyring
	var keyring openpgp.EntityList
	var err error

	if pv.config.PublicKeyPath != "" {
		keyring, err = loadPublicKeyRing(pv.config.PublicKeyPath)
		if err != nil {
			return false, "", fmt.Errorf("failed to load public key: %w", err)
		}
	} else if pv.config.KeyRing != nil {
		keyring = pv.config.KeyRing
	} else {
		// Use empty keyring - will try to verify with any available key
		keyring = openpgp.EntityList{}
	}

	// Check if signature is armored
	sigReader := bytes.NewReader(signature)
	var sigInput io.Reader = sigReader

	if bytes.HasPrefix(bytes.TrimSpace(signature), []byte("-----BEGIN PGP")) {
		armoredBlock, err := armor.Decode(sigReader)
		if err != nil {
			return false, "", fmt.Errorf("failed to decode signature armor: %w", err)
		}
		sigInput = armoredBlock.Body
	}

	// Verify the signature
	signer, err := openpgp.CheckDetachedSignature(keyring, data, sigInput)
	if err != nil {
		return false, "", fmt.Errorf("signature verification failed: %w", err)
	}

	if signer == nil {
		return false, "", fmt.Errorf("no valid signature found")
	}

	// Get signer identity
	identity := ""
	for _, id := range signer.Identities {
		if identity == "" {
			identity = id.Name
		}
		if id.SelfSignature != nil {
			identity = id.Name
			break
		}
	}

	if identity == "" {
		identity = "Unknown"
	}

	return true, identity, nil
}

// VerifyFile verifies PGP signature of a file (detached signature)
func (pv *PGPVerifier) VerifyFile(filePath string, signaturePath string) (bool, string, error) {
	// Read signature file
	sigData, err := os.ReadFile(signaturePath)
	if err != nil {
		return false, "", fmt.Errorf("failed to read signature file: %w", err)
	}

	// Open data file
	dataFile, err := os.Open(filePath)
	if err != nil {
		return false, "", fmt.Errorf("failed to open data file: %w", err)
	}
	defer dataFile.Close()

	return pv.Verify(dataFile, sigData)
}

// VerifyClearsign verifies a clearsigned message
func (pv *PGPVerifier) VerifyClearsign(data []byte) (bool, string, []byte, error) {
	// Check if it's a clearsigned message
	if !bytes.Contains(data, []byte("-----BEGIN PGP SIGNED MESSAGE-----")) {
		return false, "", nil, fmt.Errorf("not a clearsigned message")
	}

	// Load keyring
	var keyring openpgp.EntityList
	var err error

	if pv.config.PublicKeyPath != "" {
		keyring, err = loadPublicKeyRing(pv.config.PublicKeyPath)
		if err != nil {
			return false, "", nil, fmt.Errorf("failed to load public key: %w", err)
		}
	} else if pv.config.KeyRing != nil {
		keyring = pv.config.KeyRing
	}

	block, rest := clearsign.Decode(data)
	if len(rest) > 0 {
		// There's additional data after the clearsigned block
	}

	signer, err := openpgp.CheckDetachedSignature(keyring, bytes.NewReader(block.Bytes), block.ArmoredSignature.Body)
	if err != nil {
		return false, "", nil, fmt.Errorf("signature verification failed: %w", err)
	}

	if signer == nil {
		return false, "", nil, fmt.Errorf("no valid signature found")
	}

	// Get signer identity
	identity := "Unknown"
	for _, id := range signer.Identities {
		if id.SelfSignature != nil {
			identity = id.Name
			break
		}
	}

	return true, identity, block.Bytes, nil
}

// IsPGPEncrypted determines whether data is PGP encrypted
func IsPGPEncrypted(data []byte) bool {
	if len(data) < 10 {
		return false
	}

	// Check for ASCII armor header
	header := string(data[:min(len(data), 50)])
	if strings.Contains(header, "-----BEGIN PGP MESSAGE-----") ||
		strings.Contains(header, "-----BEGIN PGP PUBLIC KEY BLOCK-----") ||
		strings.Contains(header, "-----BEGIN PGP PRIVATE KEY BLOCK-----") ||
		strings.Contains(header, "-----BEGIN PGP SIGNATURE-----") {
		return true
	}

	// Check for binary PGP packet tags
	// PGP binary packets start with specific byte patterns
	if len(data) >= 2 {
		firstByte := data[0]
		// Check for old format packet tag (bits 7-6 = 1, bit 5 = 0)
		if (firstByte&0x80) != 0 && (firstByte&0x40) == 0 {
			return true
		}
		// Check for new format packet tag (bits 7-6 = 1, bit 5 = 1)
		if (firstByte & 0xC0) == 0xC0 {
			return true
		}
	}

	return false
}

// IsPGPSignature determines whether data is a PGP signature
func IsPGPSignature(data []byte) bool {
	if len(data) < 10 {
		return false
	}

	header := string(data[:min(len(data), 50)])
	return strings.Contains(header, "-----BEGIN PGP SIGNATURE-----")
}

// IsClearsignedMessage determines whether a message is clearsigned
func IsClearsignedMessage(data []byte) bool {
	if len(data) < 10 {
		return false
	}

	header := string(data[:min(len(data), 50)])
	return strings.Contains(header, "-----BEGIN PGP SIGNED MESSAGE-----")
}

// passphrasePrompt returns a function to prompt for passphrase
func (c *PGPConfig) passphrasePrompt() func(keys []openpgp.Key, symmetric bool) ([]byte, error) {
	return func(keys []openpgp.Key, symmetric bool) ([]byte, error) {
		if c.Passphrase != "" {
			return []byte(c.Passphrase), nil
		}
		// If no passphrase configured, try empty passphrase
		return nil, nil
	}
}

// loadPrivateKeyRing loads a keyring from a private key
func loadPrivateKeyRing(path string, passphrase []byte) (openpgp.EntityList, error) {
	file, err := os.Open(path)
	if err != nil {
		return nil, err
	}
	defer file.Close()

	keyring, err := openpgp.ReadKeyRing(file)
	if err != nil {
		return nil, fmt.Errorf("failed to parse keyring: %w", err)
	}

	// Unlock private keys
	for _, entity := range keyring {
		if entity.PrivateKey != nil && entity.PrivateKey.Encrypted {
			err := entity.PrivateKey.Decrypt(passphrase)
			if err != nil {
				return nil, fmt.Errorf("failed to decrypt private key: %w", err)
			}
		}
		for _, subkey := range entity.Subkeys {
			if subkey.PrivateKey != nil && subkey.PrivateKey.Encrypted {
				err := subkey.PrivateKey.Decrypt(passphrase)
				if err != nil {
					return nil, fmt.Errorf("failed to decrypt subkey: %w", err)
				}
			}
		}
	}

	return keyring, nil
}

// loadPublicKeyRing loads a keyring from a public key
func loadPublicKeyRing(path string) (openpgp.EntityList, error) {
	file, err := os.Open(path)
	if err != nil {
		return nil, err
	}
	defer file.Close()

	keyring, err := openpgp.ReadKeyRing(file)
	if err != nil {
		return nil, fmt.Errorf("failed to parse keyring: %w", err)
	}

	return keyring, nil
}

// loadPublicKey loads a public key
func loadPublicKey(path string) (*openpgp.Entity, error) {
	file, err := os.Open(path)
	if err != nil {
		return nil, err
	}
	defer file.Close()

	keyring, err := openpgp.ReadKeyRing(file)
	if err != nil {
		return nil, fmt.Errorf("failed to parse public key: %w", err)
	}

	if len(keyring) == 0 {
		return nil, fmt.Errorf("no keys found in key file")
	}

	// Return first key
	return keyring[0], nil
}

// nopWriteCloser helper for non-closing writer
type nopWriteCloser struct {
	io.Writer
}

func (nwc nopWriteCloser) Close() error {
	return nil
}