// Package utils provides some common utility methods
package utils

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/ecdsa"
	"crypto/ed25519"
	"crypto/elliptic"
	"crypto/rand"
	"crypto/rsa"
	"crypto/tls"
	"crypto/x509"
	"encoding/hex"
	"encoding/pem"
	"errors"
	"fmt"
	"html/template"
	"io"
	"net"
	"net/http"
	"os"
	"path"
	"path/filepath"
	"runtime"
	"strings"
	"time"

	"github.com/rs/xid"
	"golang.org/x/crypto/ssh"

	"github.com/drakkan/sftpgo/logger"
)

const (
	logSender = "utils"
)

// IsStringInSlice searches a string in a slice and returns true if the string is found
func IsStringInSlice(obj string, list []string) bool {
	for _, v := range list {
		if v == obj {
			return true
		}
	}
	return false
}

// IsStringPrefixInSlice searches a string prefix in a slice and returns true
// if a matching prefix is found
func IsStringPrefixInSlice(obj string, list []string) bool {
	for _, v := range list {
		if strings.HasPrefix(obj, v) {
			return true
		}
	}
	return false
}

// RemoveDuplicates returns a new slice removing any duplicate element from the initial one
func RemoveDuplicates(obj []string) []string {
	if len(obj) == 0 {
		return obj
	}
	result := make([]string, 0, len(obj))
	seen := make(map[string]bool)
	for _, item := range obj {
		if _, ok := seen[item]; !ok {
			result = append(result, item)
		}
		seen[item] = true
	}
	return result
}

// GetTimeAsMsSinceEpoch returns unix timestamp as milliseconds from a time struct
func GetTimeAsMsSinceEpoch(t time.Time) int64 {
	return t.UnixNano() / 1000000
}

// GetTimeFromMsecSinceEpoch return a time struct from a unix timestamp with millisecond precision
func GetTimeFromMsecSinceEpoch(msec int64) time.Time {
	return time.Unix(0, msec*1000000)
}

// GetDurationAsString returns a string representation for a time.Duration
func GetDurationAsString(d time.Duration) string {
	d = d.Round(time.Second)
	h := d / time.Hour
	d -= h * time.Hour
	m := d / time.Minute
	d -= m * time.Minute
	s := d / time.Second
	if h > 0 {
		return fmt.Sprintf("%02d:%02d:%02d", h, m, s)
	}
	return fmt.Sprintf("%02d:%02d", m, s)
}

// ByteCountSI returns humanized size in SI (decimal) format
func ByteCountSI(b int64) string {
	return byteCount(b, 1000)
}

// ByteCountIEC returns humanized size in IEC (binary) format
func ByteCountIEC(b int64) string {
	return byteCount(b, 1024)
}

func byteCount(b int64, unit int64) string {
	if b < unit {
		return fmt.Sprintf("%d B", b)
	}
	div, exp := unit, 0
	for n := b / unit; n >= unit; n /= unit {
		div *= unit
		exp++
	}
	if unit == 1000 {
		return fmt.Sprintf("%.1f %cB",
			float64(b)/float64(div), "KMGTPE"[exp])
	}
	return fmt.Sprintf("%.1f %ciB",
		float64(b)/float64(div), "KMGTPE"[exp])
}

// GetIPFromRemoteAddress returns the IP from the remote address.
// If the given remote address cannot be parsed it will be returned unchanged
func GetIPFromRemoteAddress(remoteAddress string) string {
	ip, _, err := net.SplitHostPort(remoteAddress)
	if err == nil {
		return ip
	}
	return remoteAddress
}

// NilIfEmpty returns nil if the input string is empty
func NilIfEmpty(s string) *string {
	if len(s) == 0 {
		return nil
	}
	return &s
}

// EncryptData encrypts data using the given key
func EncryptData(data string) (string, error) {
	var result string
	key := make([]byte, 16)
	if _, err := io.ReadFull(rand.Reader, key); err != nil {
		return result, err
	}
	keyHex := hex.EncodeToString(key)
	block, err := aes.NewCipher([]byte(keyHex))
	if err != nil {
		return result, err
	}
	gcm, err := cipher.NewGCM(block)
	if err != nil {
		return result, err
	}
	nonce := make([]byte, gcm.NonceSize())
	if _, err = io.ReadFull(rand.Reader, nonce); err != nil {
		return result, err
	}
	ciphertext := gcm.Seal(nonce, nonce, []byte(data), nil)
	result = fmt.Sprintf("$aes$%s$%x", keyHex, ciphertext)
	return result, err
}

// RemoveDecryptionKey returns encrypted data without the decryption key
func RemoveDecryptionKey(encryptData string) string {
	vals := strings.Split(encryptData, "$")
	if len(vals) == 4 {
		return fmt.Sprintf("$%v$%v", vals[1], vals[3])
	}
	return encryptData
}

// DecryptData decrypts data encrypted using EncryptData
func DecryptData(data string) (string, error) {
	var result string
	vals := strings.Split(data, "$")
	if len(vals) != 4 {
		return "", errors.New("data to decrypt is not in the correct format")
	}
	key := vals[2]
	encrypted, err := hex.DecodeString(vals[3])
	if err != nil {
		return result, err
	}
	block, err := aes.NewCipher([]byte(key))
	if err != nil {
		return result, err
	}
	gcm, err := cipher.NewGCM(block)
	if err != nil {
		return result, err
	}
	nonceSize := gcm.NonceSize()
	if len(encrypted) < nonceSize {
		return result, errors.New("malformed ciphertext")
	}
	nonce, ciphertext := encrypted[:nonceSize], encrypted[nonceSize:]
	plaintext, err := gcm.Open(nil, nonce, ciphertext, nil)
	if err != nil {
		return result, err
	}
	return string(plaintext), nil
}

// GenerateRSAKeys generate rsa private and public keys and write the
// private key to specified file and the public key to the specified
// file adding the .pub suffix
func GenerateRSAKeys(file string) error {
	if err := createDirPathIfMissing(file, 0700); err != nil {
		return err
	}
	key, err := rsa.GenerateKey(rand.Reader, 4096)
	if err != nil {
		return err
	}

	o, err := os.OpenFile(file, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0600)
	if err != nil {
		return err
	}
	defer o.Close()

	priv := &pem.Block{
		Type:  "RSA PRIVATE KEY",
		Bytes: x509.MarshalPKCS1PrivateKey(key),
	}

	if err := pem.Encode(o, priv); err != nil {
		return err
	}

	pub, err := ssh.NewPublicKey(&key.PublicKey)
	if err != nil {
		return err
	}
	return os.WriteFile(file+".pub", ssh.MarshalAuthorizedKey(pub), 0600)
}

// GenerateECDSAKeys generate ecdsa private and public keys and write the
// private key to specified file and the public key to the specified
// file adding the .pub suffix
func GenerateECDSAKeys(file string) error {
	if err := createDirPathIfMissing(file, 0700); err != nil {
		return err
	}
	key, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
	if err != nil {
		return err
	}

	keyBytes, err := x509.MarshalECPrivateKey(key)
	if err != nil {
		return err
	}
	priv := &pem.Block{
		Type:  "EC PRIVATE KEY",
		Bytes: keyBytes,
	}

	o, err := os.OpenFile(file, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0600)
	if err != nil {
		return err
	}
	defer o.Close()

	if err := pem.Encode(o, priv); err != nil {
		return err
	}

	pub, err := ssh.NewPublicKey(&key.PublicKey)
	if err != nil {
		return err
	}
	return os.WriteFile(file+".pub", ssh.MarshalAuthorizedKey(pub), 0600)
}

// GenerateEd25519Keys generate ed25519 private and public keys and write the
// private key to specified file and the public key to the specified
// file adding the .pub suffix
func GenerateEd25519Keys(file string) error {
	pubKey, privKey, err := ed25519.GenerateKey(rand.Reader)
	if err != nil {
		return err
	}
	keyBytes, err := x509.MarshalPKCS8PrivateKey(privKey)
	if err != nil {
		return err
	}
	priv := &pem.Block{
		Type:  "PRIVATE KEY",
		Bytes: keyBytes,
	}
	o, err := os.OpenFile(file, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0600)
	if err != nil {
		return err
	}
	defer o.Close()

	if err := pem.Encode(o, priv); err != nil {
		return err
	}
	pub, err := ssh.NewPublicKey(pubKey)
	if err != nil {
		return err
	}
	return os.WriteFile(file+".pub", ssh.MarshalAuthorizedKey(pub), 0600)
}

// GetDirsForSFTPPath returns all the directory for the given path in reverse order
// for example if the path is: /1/2/3/4 it returns:
// [ "/1/2/3/4", "/1/2/3", "/1/2", "/1", "/" ]
func GetDirsForSFTPPath(p string) []string {
	sftpPath := CleanPath(p)
	dirsForPath := []string{sftpPath}
	for {
		if sftpPath == "/" {
			break
		}
		sftpPath = path.Dir(sftpPath)
		dirsForPath = append(dirsForPath, sftpPath)
	}
	return dirsForPath
}

// CleanPath returns a clean POSIX (/) absolute path to work with
func CleanPath(p string) string {
	p = filepath.ToSlash(p)
	if !path.IsAbs(p) {
		p = "/" + p
	}
	return path.Clean(p)
}

// LoadTemplate wraps a call to a function returning (*Template, error)
// it is just like template.Must but it writes a log before exiting
func LoadTemplate(t *template.Template, err error) *template.Template {
	if err != nil {
		logger.ErrorToConsole("error loading required template: %v", err)
		logger.Error(logSender, "", "error loading required template: %v", err)
		panic(err)
	}
	return t
}

// IsFileInputValid returns true this is a valid file name.
// This method must be used before joining a file name, generally provided as
// user input, with a directory
func IsFileInputValid(fileInput string) bool {
	cleanInput := filepath.Clean(fileInput)
	if cleanInput == "." || cleanInput == ".." {
		return false
	}
	return true
}

// CleanDirInput sanitizes user input for directories.
// On Windows it removes any trailing `"`.
// We try to help windows users that set an invalid path such as "C:\ProgramData\SFTPGO\".
// This will only help if the invalid path is the last argument, for example in this command:
// sftpgo.exe serve -c "C:\ProgramData\SFTPGO\" -l "sftpgo.log"
// the -l flag will be ignored and the -c flag will get the value `C:\ProgramData\SFTPGO" -l sftpgo.log`
// since the backslash after SFTPGO escape the double quote. This is definitely a bad user input
func CleanDirInput(dirInput string) string {
	if runtime.GOOS == "windows" {
		for strings.HasSuffix(dirInput, "\"") {
			dirInput = strings.TrimSuffix(dirInput, "\"")
		}
	}
	return filepath.Clean(dirInput)
}

func createDirPathIfMissing(file string, perm os.FileMode) error {
	dirPath := filepath.Dir(file)
	if _, err := os.Stat(dirPath); os.IsNotExist(err) {
		err = os.MkdirAll(dirPath, perm)
		if err != nil {
			return err
		}
	}
	return nil
}

// GenerateRandomBytes generates the secret to use for JWT auth
func GenerateRandomBytes(length int) []byte {
	b := make([]byte, length)
	_, err := io.ReadFull(rand.Reader, b)
	if err != nil {
		return b
	}

	b = xid.New().Bytes()
	for len(b) < length {
		b = append(b, xid.New().Bytes()...)
	}

	return b[:length]
}

// HTTPListenAndServe is a wrapper for ListenAndServe that support both tcp
// and Unix-domain sockets
func HTTPListenAndServe(srv *http.Server, address string, port int, isTLS bool, logSender string) error {
	var listener net.Listener
	var err error

	if filepath.IsAbs(address) && runtime.GOOS != "windows" {
		if !IsFileInputValid(address) {
			return fmt.Errorf("invalid socket address %#v", address)
		}
		err = createDirPathIfMissing(address, os.ModePerm)
		if err != nil {
			logger.ErrorToConsole("error creating Unix-domain socket parent dir: %v", err)
			logger.Error(logSender, "", "error creating Unix-domain socket parent dir: %v", err)
		}
		os.Remove(address)

		listener, err = net.Listen("unix", address)
	} else {
		listener, err = net.Listen("tcp", fmt.Sprintf("%s:%d", address, port))
	}
	if err != nil {
		return err
	}

	logger.Info(logSender, "", "server listener registered, address: %v TLS enabled: %v", listener.Addr().String(), isTLS)

	defer listener.Close()

	if isTLS {
		return srv.ServeTLS(listener, "", "")
	}
	return srv.Serve(listener)
}

// GetTLSCiphersFromNames returns the TLS ciphers from the specified names
func GetTLSCiphersFromNames(cipherNames []string) []uint16 {
	var ciphers []uint16

	for _, name := range RemoveDuplicates(cipherNames) {
		for _, c := range tls.CipherSuites() {
			if c.Name == strings.TrimSpace(name) {
				ciphers = append(ciphers, c.ID)
			}
		}
	}

	return ciphers
}