package client

import (
	"context"
	"crypto/tls"
	"errors"
	"fmt"
	"log"
	"os"
	"sync"
	"sync/atomic"
	"time"
)

// Service is one provisioning + serving lifecycle for a config file.
type Service struct {
	ConfigPath string
	Paths      Paths
	Config     *Config
	API        *APIClient
	Log        *log.Logger
	Version    string

	cert atomic.Pointer[tls.Certificate]

	mu       sync.RWMutex // guards Config and API during the renewal poller
	statusMu sync.RWMutex
	handler  func(Status)
	status   atomic.Value
}

// Status is a snapshot of the bridge connection for UIs.
type Status struct {
	Connected       bool
	Session         string
	Routes          []string
	LastError       string
	LastConnectedAt time.Time
}

// SetStatusHandler registers a callback invoked whenever the status changes.
func (s *Service) SetStatusHandler(handler func(Status)) {
	s.statusMu.Lock()
	s.handler = handler
	s.statusMu.Unlock()
}

// SetConfig replaces the loaded config and API client, used by the desktop UI.
func (s *Service) SetConfig(cfg *Config) {
	s.mu.Lock()
	defer s.mu.Unlock()
	s.Config = cfg
	s.API = NewAPIClient(cfg.API)
}

// CurrentStatus returns the latest bridge status.
func (s *Service) CurrentStatus() Status {
	if value := s.status.Load(); value != nil {
		return value.(Status)
	}
	return Status{}
}

func (s *Service) report(status Status) {
	s.status.Store(status)
	s.statusMu.RLock()
	handler := s.handler
	s.statusMu.RUnlock()
	if handler != nil {
		handler(status)
	}
}

// NewService loads a config (which may not exist yet).
func NewService(configPath, version string, logger *log.Logger) (*Service, error) {
	cfg, err := Load(configPath)
	if err != nil {
		return nil, err
	}
	if logger == nil {
		logger = log.New(os.Stderr, "", log.LstdFlags)
	}
	s := &Service{
		ConfigPath: configPath,
		Paths:      ConfigPaths(configPath),
		Config:     cfg,
		Log:        logger,
		Version:    version,
	}
	if cfg.API != "" {
		s.API = NewAPIClient(cfg.API)
	}
	return s, nil
}

// Ensure creates the tunnel if needed, makes the local key/CSR, and makes
// sure a usable certificate is cached.
func (s *Service) Ensure(ctx context.Context) error {
	cfg, err := Load(s.ConfigPath)
	if err != nil {
		return err
	}
	if cfg.API == "" {
		return errors.New("no API configured; run: tunnel config set-api https://your-server")
	}
	s.Paths = ConfigPaths(s.ConfigPath)
	s.mu.Lock()
	s.Config = cfg
	s.API = NewAPIClient(cfg.API)
	s.mu.Unlock()

	if cfg.TunnelID == "" || cfg.Token == "" {
		ctx, cancel := context.WithTimeout(ctx, 60*time.Second)
		tunnel, token, err := s.API.CreateTunnel(ctx)
		cancel()
		if err != nil {
			return fmt.Errorf("create tunnel: %w", err)
		}
		cfg.TunnelID, cfg.Hostname, cfg.Token = tunnel.ID, tunnel.Hostname, token
		// Persist the identity before binding, so an interrupted provision
		// can resume with the same token and hostname.
		if err := cfg.Save(s.ConfigPath); err != nil {
			return err
		}
		s.Log.Printf("created tunnel %s (%s)", cfg.TunnelID, cfg.Hostname)
	}

	info, err := s.API.GetTunnel(ctx, cfg.TunnelID, cfg.Token)
	if err != nil {
		var apiErr *APIError
		if errors.As(err, &apiErr) && apiErr.Status == 404 {
			return fmt.Errorf("tunnel %s no longer exists on the server", cfg.TunnelID)
		}
		if errors.As(err, &apiErr) && apiErr.Status == 401 {
			return fmt.Errorf("the server rejected the saved token for tunnel %s", cfg.TunnelID)
		}
		return fmt.Errorf("get tunnel: %w", err)
	}
	if info.Hostname != "" && info.Hostname != cfg.Hostname {
		cfg.Hostname = info.Hostname
		if err := cfg.Save(s.ConfigPath); err != nil {
			return err
		}
	}
	if cfg.Hostname == "" {
		return errors.New("server did not return a tunnel hostname")
	}

	keyPEM, csrPEM, err := EnsureIdentity(s.Paths, cfg.Hostname)
	if err != nil {
		return err
	}
	return s.ensureCertificate(ctx, keyPEM, csrPEM)
}

func (s *Service) ensureCertificate(ctx context.Context, keyPEM, csrPEM []byte) error {
	cfg := s.Config
	localCert, localExpiry, localErr := LoadCertificate(s.Paths, cfg.Hostname)

	info, err := s.API.GetCertificate(ctx, cfg.TunnelID, cfg.Token)
	if err != nil {
		var apiErr *APIError
		if errors.As(err, &apiErr) && apiErr.Status == 404 {
			return s.bindAndWait(ctx, keyPEM, csrPEM)
		}
		if localErr == nil {
			s.Log.Printf("certificate check failed (%v); using saved certificate expiring %s", err, localExpiry.Format(time.RFC3339))
			s.cert.Store(&localCert)
			return nil
		}
		return fmt.Errorf("get certificate: %w", err)
	}

	switch info.State.Type {
	case "ready":
		return s.useReadyCertificate(keyPEM, localCert, localExpiry, localErr, info)
	case "failed":
		return s.bindAndWait(ctx, keyPEM, csrPEM)
	case "issuing":
		return s.waitForCertificate(ctx, keyPEM)
	default:
		return s.bindAndWait(ctx, keyPEM, csrPEM)
	}
}

func (s *Service) useReadyCertificate(keyPEM []byte, localCert tls.Certificate, localExpiry time.Time, localErr error, info CertificateInfo) error {
	serverExpiry, err := CertificateExpiry(info.State.Expiry)
	if err != nil {
		return fmt.Errorf("server certificate expiry: %w", err)
	}
	if localErr == nil && !localExpiry.Before(serverExpiry) && sameExpiry(s.Config.CertificateExpiry, serverExpiry) {
		s.cert.Store(&localCert)
		return nil
	}
	cert, expiry, err := SaveCertificate(s.Paths, []byte(info.State.Certificate), []byte(info.State.Chain), keyPEM, s.Config.Hostname)
	if err != nil {
		return fmt.Errorf("save certificate: %w", err)
	}
	s.cert.Store(&cert)
	s.setExpiry(expiry)
	s.Log.Printf("certificate ready (expires %s)", expiry.Format(time.RFC3339))
	return nil
}

func (s *Service) bindAndWait(ctx context.Context, keyPEM, csrPEM []byte) error {
	s.Log.Printf("requesting certificate for %s", s.Config.Hostname)
	info, err := s.API.BindCertificate(ctx, s.Config.TunnelID, s.Config.Token, string(csrPEM))
	if err != nil {
		var apiErr *APIError
		if !errors.As(err, &apiErr) || apiErr.Status != 409 {
			return fmt.Errorf("bind certificate: %w", err)
		}
	}
	if info.State.Type == "ready" {
		return s.storeReady(keyPEM, info)
	}
	if info.State.Type == "failed" {
		return fmt.Errorf("certificate issuance failed: %s", info.State.Reason)
	}
	return s.waitForCertificate(ctx, keyPEM)
}

func (s *Service) waitForCertificate(ctx context.Context, keyPEM []byte) error {
	ctx, cancel := context.WithTimeout(ctx, 10*time.Minute)
	defer cancel()
	ticker := time.NewTicker(2 * time.Second)
	defer ticker.Stop()
	for {
		info, err := s.API.GetCertificate(ctx, s.Config.TunnelID, s.Config.Token)
		if err != nil {
			return fmt.Errorf("poll certificate: %w", err)
		}
		switch info.State.Type {
		case "ready":
			return s.storeReady(keyPEM, info)
		case "failed":
			return fmt.Errorf("certificate issuance failed: %s", info.State.Reason)
		}
		select {
		case <-ctx.Done():
			return fmt.Errorf("certificate not ready: %w", ctx.Err())
		case <-ticker.C:
		}
	}
}

func (s *Service) storeReady(keyPEM []byte, info CertificateInfo) error {
	cert, expiry, err := SaveCertificate(s.Paths, []byte(info.State.Certificate), []byte(info.State.Chain), keyPEM, s.Config.Hostname)
	if err != nil {
		return fmt.Errorf("save certificate: %w", err)
	}
	s.cert.Store(&cert)
	s.setExpiry(expiry)
	s.Log.Printf("certificate ready (expires %s)", expiry.Format(time.RFC3339))
	return nil
}

func (s *Service) setExpiry(expiry time.Time) {
	s.mu.Lock()
	defer s.mu.Unlock()
	s.Config.CertificateExpiry = expiry.UTC().Format(time.RFC3339)
	if err := s.Config.Save(s.ConfigPath); err != nil {
		s.Log.Printf("save config: %v", err)
	}
}

func sameExpiry(stored string, expiry time.Time) bool {
	parsed, err := CertificateExpiry(stored)
	return err == nil && parsed.Equal(expiry)
}

// RefreshCertificate checks the server for a renewed certificate. A transient
// failure leaves the current certificate serving.
func (s *Service) RefreshCertificate(ctx context.Context) {
	s.mu.RLock()
	cfg := *s.Config
	api := s.API
	s.mu.RUnlock()
	info, err := api.GetCertificate(ctx, cfg.TunnelID, cfg.Token)
	if err != nil {
		s.Log.Printf("certificate refresh check: %v", err)
		return
	}
	if info.State.Type != "ready" {
		if info.State.Type == "failed" {
			s.Log.Printf("certificate renewal failed on the server: %s", info.State.Reason)
		}
		return
	}
	expiry, err := CertificateExpiry(info.State.Expiry)
	if err != nil {
		s.Log.Printf("certificate expiry: %v", err)
		return
	}
	if sameExpiry(cfg.CertificateExpiry, expiry) {
		return
	}
	keyPEM, err := os.ReadFile(s.Paths.Key)
	if err != nil {
		s.Log.Printf("read key: %v", err)
		return
	}
	cert, expiry, err := SaveCertificate(s.Paths, []byte(info.State.Certificate), []byte(info.State.Chain), keyPEM, cfg.Hostname)
	if err != nil {
		s.Log.Printf("save renewed certificate: %v", err)
		return
	}
	s.cert.Store(&cert)
	s.setExpiry(expiry)
	s.Log.Printf("certificate renewed (expires %s)", expiry.Format(time.RFC3339))
}

func (s *Service) refreshLoop(ctx context.Context) {
	for {
		interval := 12 * time.Hour
		s.mu.RLock()
		expiryText := s.Config.CertificateExpiry
		s.mu.RUnlock()
		if expiry, err := CertificateExpiry(expiryText); err == nil {
			if time.Until(expiry) < 30*24*time.Hour {
				interval = time.Minute
			}
		}
		timer := time.NewTimer(interval)
		select {
		case <-ctx.Done():
			timer.Stop()
			return
		case <-timer.C:
			s.RefreshCertificate(ctx)
		}
	}
}

// Run keeps the bridge connected, reloading routes when the config changes.
func (s *Service) Run(ctx context.Context) error {
	s.report(Status{Connected: false})
	if err := s.Ensure(ctx); err != nil {
		s.report(Status{Connected: false, LastError: err.Error()})
		return err
	}
	go s.refreshLoop(ctx)

	reload := make(chan struct{}, 1)
	go watchConfig(ctx, s.ConfigPath, reload)

	delay := 250 * time.Millisecond
	for {
		cfg, err := s.reload(ctx)
		if err != nil {
			s.Log.Printf("config: %v", err)
			s.report(Status{Connected: false, LastError: err.Error()})
			if !wait(ctx, delay) {
				return ctx.Err()
			}
			delay = nextBackoff(delay)
			continue
		}
		sess, err := s.connect(ctx, cfg)
		if err != nil {
			s.Log.Printf("bridge: %v", err)
			if errors.Is(err, errFatalAttach) {
				return err
			}
			if !wait(ctx, delay) {
				return ctx.Err()
			}
			delay = nextBackoff(delay)
			continue
		}
		delay = 250 * time.Millisecond
		select {
		case <-ctx.Done():
			sess.close("shutdown")
			s.report(Status{Connected: false})
			return ctx.Err()
		case <-reload:
			s.Log.Printf("config changed; reconnecting")
			sess.close("config changed")
			s.report(Status{Connected: false})
		case <-sess.done:
			s.report(Status{Connected: false})
		}
	}
}

func (s *Service) reload(ctx context.Context) (*Config, error) {
	cfg, err := Load(s.ConfigPath)
	if err != nil {
		return nil, err
	}
	if cfg.API == "" {
		return nil, errors.New("no API configured; run: tunnel config set-api https://your-server")
	}
	if cfg.TunnelID == "" || cfg.Token == "" || cfg.Hostname == "" || s.cert.Load() == nil {
		if err := s.Ensure(ctx); err != nil {
			return nil, err
		}
		s.mu.RLock()
		cfg = s.Config
		s.mu.RUnlock()
	}
	s.mu.Lock()
	s.Config = cfg
	s.API = NewAPIClient(cfg.API)
	s.mu.Unlock()
	return cfg, nil
}

// TLSConfig serves the current certificate and supports hot renewal.
func (s *Service) TLSConfig() *tls.Config {
	return &tls.Config{
		MinVersion: tls.VersionTLS12,
		NextProtos: []string{"http/1.1"},
		GetCertificate: func(*tls.ClientHelloInfo) (*tls.Certificate, error) {
			cert := s.cert.Load()
			if cert == nil {
				return nil, errors.New("no certificate loaded")
			}
			return cert, nil
		},
	}
}

func watchConfig(ctx context.Context, path string, changed chan<- struct{}) {
	var last time.Time
	if info, err := os.Stat(path); err == nil {
		last = info.ModTime()
	}
	ticker := time.NewTicker(2 * time.Second)
	defer ticker.Stop()
	for {
		select {
		case <-ctx.Done():
			return
		case <-ticker.C:
			info, err := os.Stat(path)
			if err != nil || !info.ModTime().After(last) {
				continue
			}
			last = info.ModTime()
			select {
			case changed <- struct{}{}:
			default:
			}
		}
	}
}

func wait(ctx context.Context, d time.Duration) bool {
	timer := time.NewTimer(d)
	defer timer.Stop()
	select {
	case <-ctx.Done():
		return false
	case <-timer.C:
		return true
	}
}

func nextBackoff(d time.Duration) time.Duration {
	d *= 2
	if d > 30*time.Second {
		return 30 * time.Second
	}
	return d
}