package server

import (
	"encoding/json"
	"errors"
	"fmt"
	"io/fs"
	"os"
	"path/filepath"
	"sync"
	"time"
)

// storedCert is one issued certificate. With the local issuer, issuance is
// synchronous, so a bound CSR always has its certificate populated.
type storedCert struct {
	ID          string `json:"id"`
	CSR         string `json:"csr"`
	Certificate string `json:"certificate"`
	Chain       string `json:"chain"`
	Expiry      string `json:"expiry"`
}

type storedTunnel struct {
	ID          string      `json:"id"`
	Hostname    string      `json:"hostname"`
	TokenHash   string      `json:"tokenHash"`
	Certificate *storedCert `json:"certificate,omitempty"`
}

// storeData is the on-disk shape. The CA key is a secret, so the file is
// written 0600.
type storeData struct {
	CAKeyPEM  string                  `json:"caKeyPem"`
	CACertPEM string                  `json:"caCertPEM"`
	ServerKey string                  `json:"serverKey"`
	ServerCrt string                  `json:"serverCrt"`
	Tunnels   map[string]storedTunnel `json:"tunnels"`
}

// Store is a JSON-file-backed tunnel store: adequate for a single-node
// self-hosted deployment, and the one writer this server has.
type Store struct {
	mu   sync.Mutex
	path string
	data storeData
}

// openStore loads path, or initializes it (with a fresh local CA) when it
// does not exist. An empty path keeps state in memory only.
func OpenStore(path string) (*Store, error) {
	s := &Store{path: path, data: storeData{Tunnels: map[string]storedTunnel{}}}
	if path != "" {
		if raw, err := os.ReadFile(path); err == nil {
			if err := json.Unmarshal(raw, &s.data); err != nil {
				return nil, fmt.Errorf("reading %s: %w", path, err)
			}
			if s.data.Tunnels == nil {
				s.data.Tunnels = map[string]storedTunnel{}
			}
		} else if !errors.Is(err, fs.ErrNotExist) {
			return nil, err
		}
	}
	if s.data.CAKeyPEM == "" {
		ca, err := newLocalCA()
		if err != nil {
			return nil, err
		}
		keyPEM, err := ca.keyPEM()
		if err != nil {
			return nil, err
		}
		s.data.CAKeyPEM = string(keyPEM)
		s.data.CACertPEM = string(ca.certPEM)
		if err := s.saveLocked(); err != nil {
			return nil, err
		}
	}
	return s, nil
}

// ca returns the store's local CA, loading it from the stored PEM.
func (s *Store) ca() (*localCA, error) {
	s.mu.Lock()
	defer s.mu.Unlock()
	return loadLocalCA([]byte(s.data.CAKeyPEM), []byte(s.data.CACertPEM))
}

// CACertPEM is the CA certificate clients should trust.
func (s *Store) CACertPEM() string {
	s.mu.Lock()
	defer s.mu.Unlock()
	return s.data.CACertPEM
}

// serverCertificate returns the API domain's key and certificate PEM,
// issuing one with the CA when missing.
func (s *Store) ServerCertificate(domain string) (certPEM, keyPEM []byte, err error) {
	s.mu.Lock()
	defer s.mu.Unlock()
	if s.data.ServerCrt != "" {
		return []byte(s.data.ServerCrt), []byte(s.data.ServerKey), nil
	}
	ca, err := loadLocalCA([]byte(s.data.CAKeyPEM), []byte(s.data.CACertPEM))
	if err != nil {
		return nil, nil, err
	}
	certPEM, keyPEM, err = ca.issue(domain)
	if err != nil {
		return nil, nil, err
	}
	s.data.ServerCrt = string(certPEM)
	s.data.ServerKey = string(keyPEM)
	if err := s.saveLocked(); err != nil {
		return nil, nil, err
	}
	return certPEM, keyPEM, nil
}

// createTunnel stores a new tunnel and returns it with its bearer token, the
// only time the token is visible.
func (s *Store) createTunnel(domain string) (storedTunnel, string, error) {
	token := newToken()
	t := storedTunnel{
		ID:        slug(),
		TokenHash: hashToken(token),
	}
	t.Hostname = t.ID + "." + domain
	s.mu.Lock()
	defer s.mu.Unlock()
	s.data.Tunnels[t.ID] = t
	return t, token, s.saveLocked()
}

// get returns the tunnel with id, or false.
func (s *Store) get(id string) (storedTunnel, bool) {
	s.mu.Lock()
	defer s.mu.Unlock()
	t, ok := s.data.Tunnels[id]
	return t, ok
}

// bindCSR records the issued certificate for the tunnel. The CSR is kept so a
// renewal (and a resumed provision) can be answered without a new bind.
func (s *Store) bindCertificate(id string, cert storedCert) error {
	s.mu.Lock()
	defer s.mu.Unlock()
	t, ok := s.data.Tunnels[id]
	if !ok {
		return errors.New("tunnel not found")
	}
	t.Certificate = &cert
	s.data.Tunnels[id] = t
	return s.saveLocked()
}

// remove deletes the tunnel.
func (s *Store) remove(id string) error {
	s.mu.Lock()
	defer s.mu.Unlock()
	if _, ok := s.data.Tunnels[id]; !ok {
		return errors.New("tunnel not found")
	}
	delete(s.data.Tunnels, id)
	return s.saveLocked()
}

// saveLocked writes the data file atomically (0600); a no-op for an
// in-memory store.
func (s *Store) saveLocked() error {
	if s.path == "" {
		return nil
	}
	raw, err := json.MarshalIndent(s.data, "", "  ")
	if err != nil {
		return err
	}
	tmp := s.path + ".tmp"
	if err := os.MkdirAll(filepath.Dir(s.path), 0o700); err != nil {
		return err
	}
	if err := os.WriteFile(tmp, raw, 0o600); err != nil {
		return err
	}
	return os.Rename(tmp, s.path)
}

// expiryString formats a time as the reference does: ISO 8601 UTC with
// milliseconds, e.g. 2026-10-03T00:00:00.000Z.
func expiryString(t time.Time) string {
	return t.UTC().Format("2006-01-02T15:04:05.000Z")
}