package auth

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"crypto/sha256"
	"database/sql"
	"encoding/base64"
	"errors"
	"fmt"

	"git.noroutes.net/NoRoutes/vibetunes/internal/database"
)

// The legacy Subsonic protocol's token authentication scheme
// (t = md5(password + salt)) can only be verified by a server that
// knows the plaintext password. VibeSonic's native login hashes
// passwords with Argon2id, which is one-way by design and cannot answer
// that check. Every Subsonic-compatible server that supports token auth
// solves this the same way: keep a second, reversible copy of the
// password around specifically for this purpose, encrypted at rest
// (never plaintext) with a server-side key.
//
// EncryptionKey resolves that key: the operator-configured
// VIBESONIC_SESSION_SECRET if set (sha256'd to the right size), or
// otherwise a random 32-byte key generated once and persisted in the
// settings table.

const settingsKeyAuthKey = "subsonic_auth_encryption_key"

func EncryptionKey(db *sql.DB, configuredSecret string) ([]byte, error) {
	if configuredSecret != "" {
		sum := sha256.Sum256([]byte(configuredSecret))
		return sum[:], nil
	}
	if existing := database.GetSetting(db, settingsKeyAuthKey, ""); existing != "" {
		key, err := base64.StdEncoding.DecodeString(existing)
		if err == nil && len(key) == 32 {
			return key, nil
		}
	}
	key := make([]byte, 32)
	if _, err := rand.Read(key); err != nil {
		return nil, err
	}
	if err := database.SetSetting(db, settingsKeyAuthKey, base64.StdEncoding.EncodeToString(key)); err != nil {
		return nil, err
	}
	return key, nil
}

// EncryptPassword returns an AES-256-GCM encrypted, base64-encoded copy
// of plaintext for storage in users.subsonic_auth_secret.
func EncryptPassword(key []byte, plaintext string) (string, error) {
	block, err := aes.NewCipher(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
	}
	ciphertext := gcm.Seal(nonce, nonce, []byte(plaintext), nil)
	return base64.StdEncoding.EncodeToString(ciphertext), nil
}

var ErrCannotDecrypt = errors.New("cannot decrypt stored password")

// DecryptPassword reverses EncryptPassword.
func DecryptPassword(key []byte, encoded string) (string, error) {
	raw, err := base64.StdEncoding.DecodeString(encoded)
	if err != nil {
		return "", ErrCannotDecrypt
	}
	block, err := aes.NewCipher(key)
	if err != nil {
		return "", err
	}
	gcm, err := cipher.NewGCM(block)
	if err != nil {
		return "", err
	}
	if len(raw) < gcm.NonceSize() {
		return "", ErrCannotDecrypt
	}
	nonce, ciphertext := raw[:gcm.NonceSize()], raw[gcm.NonceSize():]
	plaintext, err := gcm.Open(nil, nonce, ciphertext, nil)
	if err != nil {
		return "", fmt.Errorf("%w: %v", ErrCannotDecrypt, err)
	}
	return string(plaintext), nil
}