package platform

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/hmac"
	"crypto/rand"
	"crypto/sha256"
	"crypto/subtle"
	"encoding/base64"
	"errors"
	"fmt"
	"strconv"
	"strings"
)

const passwordIterations = 210_000

type Vault struct {
	key []byte
}

func NewVault(encoded string) (*Vault, error) {
	encoded = strings.TrimSpace(encoded)
	if encoded == "" {
		return nil, errors.New("LICENSE_MASTER_KEY is required")
	}
	key, err := base64.RawStdEncoding.DecodeString(encoded)
	if err != nil {
		key, err = base64.StdEncoding.DecodeString(encoded)
	}
	if err != nil || len(key) != 32 {
		return nil, errors.New("LICENSE_MASTER_KEY must be a base64-encoded 32-byte key")
	}
	return &Vault{key: key}, nil
}

func (v *Vault) Encrypt(plaintext string) (string, error) {
	block, err := aes.NewCipher(v.key)
	if err != nil {
		return "", err
	}
	gcm, err := cipher.NewGCM(block)
	if err != nil {
		return "", err
	}
	nonce := make([]byte, gcm.NonceSize())
	if _, err := rand.Read(nonce); err != nil {
		return "", err
	}
	sealed := gcm.Seal(nil, nonce, []byte(plaintext), nil)
	payload := append(nonce, sealed...)
	return "v1." + base64.RawURLEncoding.EncodeToString(payload), nil
}

func (v *Vault) Decrypt(ciphertext string) (string, error) {
	parts := strings.SplitN(strings.TrimSpace(ciphertext), ".", 2)
	if len(parts) != 2 || parts[0] != "v1" {
		return "", errors.New("unsupported encrypted value")
	}
	payload, err := base64.RawURLEncoding.DecodeString(parts[1])
	if err != nil {
		return "", err
	}
	block, err := aes.NewCipher(v.key)
	if err != nil {
		return "", err
	}
	gcm, err := cipher.NewGCM(block)
	if err != nil {
		return "", err
	}
	if len(payload) < gcm.NonceSize() {
		return "", errors.New("encrypted value is truncated")
	}
	plain, err := gcm.Open(nil, payload[:gcm.NonceSize()], payload[gcm.NonceSize():], nil)
	if err != nil {
		return "", errors.New("encrypted value authentication failed")
	}
	return string(plain), nil
}

func HashPassword(password string) (string, error) {
	if len(password) < 12 {
		return "", errors.New("password must contain at least 12 characters")
	}
	if len(password) > 1024 {
		return "", errors.New("password is too long")
	}
	salt := make([]byte, 16)
	if _, err := rand.Read(salt); err != nil {
		return "", err
	}
	dk := pbkdf2SHA256([]byte(password), salt, passwordIterations, 32)
	return fmt.Sprintf("pbkdf2-sha256$%d$%s$%s", passwordIterations, base64.RawStdEncoding.EncodeToString(salt), base64.RawStdEncoding.EncodeToString(dk)), nil
}

func VerifyPassword(encoded, password string) bool {
	parts := strings.Split(encoded, "$")
	if len(parts) != 4 || parts[0] != "pbkdf2-sha256" {
		return false
	}
	iterations, err := strconv.Atoi(parts[1])
	if err != nil || iterations < 100_000 || iterations > 2_000_000 {
		return false
	}
	salt, err1 := base64.RawStdEncoding.DecodeString(parts[2])
	expected, err2 := base64.RawStdEncoding.DecodeString(parts[3])
	if err1 != nil || err2 != nil || len(expected) == 0 {
		return false
	}
	actual := pbkdf2SHA256([]byte(password), salt, iterations, len(expected))
	return subtle.ConstantTimeCompare(actual, expected) == 1
}

func pbkdf2SHA256(password, salt []byte, iterations, keyLen int) []byte {
	hLen := sha256.Size
	blocks := (keyLen + hLen - 1) / hLen
	out := make([]byte, 0, blocks*hLen)
	for i := 1; i <= blocks; i++ {
		mac := hmac.New(sha256.New, password)
		mac.Write(salt)
		mac.Write([]byte{byte(i >> 24), byte(i >> 16), byte(i >> 8), byte(i)})
		u := mac.Sum(nil)
		t := append([]byte(nil), u...)
		for j := 1; j < iterations; j++ {
			mac = hmac.New(sha256.New, password)
			mac.Write(u)
			u = mac.Sum(nil)
			for k := range t {
				t[k] ^= u[k]
			}
		}
		out = append(out, t...)
	}
	return out[:keyLen]
}

func randomToken(bytes int) (string, error) {
	buf := make([]byte, bytes)
	if _, err := rand.Read(buf); err != nil {
		return "", err
	}
	return base64.RawURLEncoding.EncodeToString(buf), nil
}

func tokenHash(value string) string {
	sum := sha256.Sum256([]byte(value))
	return base64.RawURLEncoding.EncodeToString(sum[:])
}

func constantTokenEqual(expected, actual string) bool {
	if expected == "" || actual == "" {
		return false
	}
	return subtle.ConstantTimeCompare([]byte(tokenHash(expected)), []byte(tokenHash(actual))) == 1
}