package credentials

// Package credentials stores platform secrets outside the SQL account model.
// Files are encrypted with AES-256-GCM and keyed by workspace/account IDs so a
// leaked account row or browser event never contains cookies.

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"encoding/base64"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"strconv"
	"sync"
)

var errInvalidID = errors.New("workspace and account IDs must be positive")

// Store is a process-safe encrypted credential store.
type Store struct {
	root string
	key  []byte
	mu   sync.Mutex
}

// Open creates or loads a 32-byte master key in root. The key file is never
// returned by an API and is permission-restricted to the current user.
func Open(root string) (*Store, error) {
	if root == "" {
		return nil, errors.New("credential directory is empty")
	}
	if err := os.MkdirAll(root, 0o700); err != nil {
		return nil, err
	}
	keyPath := filepath.Join(root, "master.key")
	key, err := os.ReadFile(keyPath)
	if errors.Is(err, os.ErrNotExist) {
		key = make([]byte, 32)
		if _, err = io.ReadFull(rand.Reader, key); err != nil {
			return nil, err
		}
		if err = writePrivate(keyPath, key); err != nil {
			return nil, err
		}
	} else if err != nil {
		return nil, err
	}
	if len(key) != 32 {
		return nil, errors.New("credential master key must be 32 bytes")
	}
	return &Store{root: root, key: append([]byte(nil), key...)}, nil
}

func (s *Store) path(workspaceID, accountID uint64) (string, error) {
	if workspaceID == 0 || accountID == 0 {
		return "", errInvalidID
	}
	dir := filepath.Join(s.root, strconv.FormatUint(workspaceID, 10))
	return filepath.Join(dir, strconv.FormatUint(accountID, 10)+".enc"), nil
}

// Save encrypts value and atomically replaces the account file.
func (s *Store) Save(workspaceID, accountID uint64, value []byte) error {
	path, err := s.path(workspaceID, accountID)
	if err != nil {
		return err
	}
	block, err := aes.NewCipher(s.key)
	if err != nil {
		return err
	}
	gcm, err := cipher.NewGCM(block)
	if err != nil {
		return err
	}
	nonce := make([]byte, gcm.NonceSize())
	if _, err = io.ReadFull(rand.Reader, nonce); err != nil {
		return err
	}
	ciphertext := gcm.Seal(nil, nonce, value, nil)
	payload := struct {
		Nonce string `json:"nonce"`
		Data  string `json:"data"`
	}{base64.RawStdEncoding.EncodeToString(nonce), base64.RawStdEncoding.EncodeToString(ciphertext)}
	raw, err := json.Marshal(payload)
	if err != nil {
		return err
	}
	s.mu.Lock()
	defer s.mu.Unlock()
	if err = os.MkdirAll(filepath.Dir(path), 0o700); err != nil {
		return err
	}
	tmp, err := os.CreateTemp(filepath.Dir(path), ".credential-*")
	if err != nil {
		return err
	}
	tmpName := tmp.Name()
	defer os.Remove(tmpName)
	if err = tmp.Chmod(0o600); err == nil {
		_, err = tmp.Write(raw)
	}
	if closeErr := tmp.Close(); err == nil {
		err = closeErr
	}
	if err != nil {
		return err
	}
	return os.Rename(tmpName, path)
}

// Load decrypts credentials for one workspace/account pair.
func (s *Store) Load(workspaceID, accountID uint64) ([]byte, error) {
	path, err := s.path(workspaceID, accountID)
	if err != nil {
		return nil, err
	}
	s.mu.Lock()
	raw, err := os.ReadFile(path)
	s.mu.Unlock()
	if err != nil {
		return nil, err
	}
	var payload struct {
		Nonce string `json:"nonce"`
		Data  string `json:"data"`
	}
	if err = json.Unmarshal(raw, &payload); err != nil {
		return nil, fmt.Errorf("credential envelope: %w", err)
	}
	nonce, err := base64.RawStdEncoding.DecodeString(payload.Nonce)
	if err != nil {
		return nil, fmt.Errorf("credential nonce: %w", err)
	}
	ciphertext, err := base64.RawStdEncoding.DecodeString(payload.Data)
	if err != nil {
		return nil, fmt.Errorf("credential data: %w", err)
	}
	block, err := aes.NewCipher(s.key)
	if err != nil {
		return nil, err
	}
	gcm, err := cipher.NewGCM(block)
	if err != nil {
		return nil, err
	}
	if len(nonce) != gcm.NonceSize() {
		return nil, errors.New("credential nonce has invalid size")
	}
	plain, err := gcm.Open(nil, nonce, ciphertext, nil)
	if err != nil {
		return nil, errors.New("credential authentication failed")
	}
	return plain, nil
}

// Delete removes credentials. Missing files are treated as success.
func (s *Store) Delete(workspaceID, accountID uint64) error {
	path, err := s.path(workspaceID, accountID)
	if err != nil {
		return err
	}
	s.mu.Lock()
	defer s.mu.Unlock()
	if err = os.Remove(path); errors.Is(err, os.ErrNotExist) {
		return nil
	}
	return err
}

func writePrivate(path string, value []byte) error {
	tmp, err := os.CreateTemp(filepath.Dir(path), ".master-*")
	if err != nil {
		return err
	}
	tmpName := tmp.Name()
	defer os.Remove(tmpName)
	if err = tmp.Chmod(0o600); err == nil {
		_, err = tmp.Write(value)
	}
	if closeErr := tmp.Close(); err == nil {
		err = closeErr
	}
	if err != nil {
		return err
	}
	return os.Rename(tmpName, path)
}