package bootstrap

import (
	"context"
	"sync"
	"time"

	"go.uber.org/fx"
	"go.uber.org/zap"

	"iop/apps/node/internal/transport"
	"iop/packages/go/config"
)

// runtimeSupervisor owns the node's single active edge connection across its
// entire lifetime. A single supervisor goroutine serially performs the initial
// dial, waits for the established session to end, and reconnects, so at most one
// in-flight dial and one active session exist at any time. The mutex guards
// current across the supervisor goroutine and the OnStop hook.
type runtimeSupervisor struct {
	cfg            *config.NodeConfig
	logger         *zap.Logger
	dialer         DialFunc
	sleeper        func(ctx context.Context, d time.Duration)
	metricsStarter func(port int) error
	shutdowner     fx.Shutdowner

	mu               sync.Mutex
	current          *runtimeOwner
	cancelSupervisor context.CancelFunc
	done             chan struct{}
}

// start launches the metrics server and the single supervisor goroutine, then
// returns immediately. Establishing the initial connection is the supervisor's
// responsibility, so a transient Edge outage at startup no longer fails the fx
// OnStart hook (SDD S16).
func (s *runtimeSupervisor) start(_ context.Context) error {
	supCtx, cancel := context.WithCancel(context.Background())
	s.cancelSupervisor = cancel
	s.done = make(chan struct{})

	go func() {
		defer close(s.done)
		s.run(supCtx)
	}()

	if s.cfg.Metrics.Port > 0 {
		go func() {
			if err := s.metricsStarter(s.cfg.Metrics.Port); err != nil {
				s.logger.Warn("metrics server exited", zap.Error(err))
			}
		}()
	}
	return nil
}

// run drives the full connectivity lifecycle: connect (initial), wait for the
// active session to end, then reconnect, repeating until the supervisor is
// cancelled, a fatal error occurs, finite attempts are exhausted, or a local
// shutdown ends the session.
func (s *runtimeSupervisor) run(supCtx context.Context) {
	owner := s.connect(supCtx, true)
	if owner == nil {
		return
	}

	for {
		select {
		case <-supCtx.Done():
			return
		case <-owner.sess.Done():
		}

		// Guard against supervisor cancellation racing with disconnect.
		select {
		case <-supCtx.Done():
			return
		default:
		}

		if owner.sess.IsLocalShutdown() {
			return
		}

		owner = s.connect(supCtx, false)
		if owner == nil {
			return
		}
	}
}

// connect runs the bounded connect/retry loop shared by the initial dial and
// established-session reconnect. On success it installs the new owner and
// returns it. It returns nil after supervisor cancellation, a fatal
// (non-retryable) failure, or finite attempt exhaustion; the latter two request
// a node shutdown with exit code 1 before returning.
//
// The reconnect path sleeps before every attempt; the initial path issues its
// first dial immediately for fast startup and sleeps only before retries. A
// finite policy (max_attempts>0) makes exactly max_attempts attempts before
// exhausting; an unlimited policy (max_attempts=0) retries until cancelled.
func (s *runtimeSupervisor) connect(supCtx context.Context, initial bool) *runtimeOwner {
	maxAttempts := s.cfg.Reconnect.MaxAttempts
	intervalSec := s.cfg.Reconnect.IntervalSec
	unlimited := maxAttempts == 0

	for attempt := 1; unlimited || attempt <= maxAttempts; attempt++ {
		if attempt > 1 || !initial {
			s.sleeper(supCtx, time.Duration(intervalSec)*time.Second)
		}
		if supCtx.Err() != nil {
			return nil
		}

		s.logger.Info("connecting to edge",
			zap.Bool("initial", initial),
			zap.Int("attempt", attempt),
			zap.Int("max_attempts", maxAttempts),
			zap.Bool("unlimited", unlimited),
			zap.Int("interval_sec", intervalSec),
		)

		dialCtx, dialCancel := context.WithTimeout(supCtx, 30*time.Second)
		owner, err := connectRuntime(dialCtx, s.cfg, s.logger, s.dialer)
		dialCancel()
		// Local shutdown wins when a dial completes concurrently with supervisor
		// cancellation. A dialer may observe cancellation and still return a late
		// success or fatal result; never install that owner or turn it into exit 1.
		if supCtx.Err() != nil {
			if owner != nil {
				owner.close()
			}
			return nil
		}
		if err == nil {
			s.swapOwner(owner)
			return owner
		}

		if transport.IsFatalConnectError(err) {
			s.fatal(err)
			return nil
		}

		s.logger.Warn("connect attempt failed",
			zap.Bool("initial", initial),
			zap.Int("attempt", attempt),
			zap.Int("max_attempts", maxAttempts),
			zap.Error(err),
		)
	}

	// A local shutdown that lands on the final finite attempt falls out of the
	// loop; treat it as cancellation rather than exhaustion.
	if supCtx.Err() != nil {
		return nil
	}
	s.exhaust(maxAttempts)
	return nil
}

// swapOwner installs owner as the current connection and closes the previous one.
func (s *runtimeSupervisor) swapOwner(owner *runtimeOwner) {
	s.mu.Lock()
	prev := s.current
	s.current = owner
	s.mu.Unlock()
	if prev != nil {
		prev.close()
	}
}

// fatal clears the current owner, logs the non-retryable failure, and requests a
// node shutdown with a non-zero exit code.
func (s *runtimeSupervisor) fatal(err error) {
	s.clearCurrent()
	s.logger.Error("connect failed with non-retryable error, shutting down node",
		zap.Error(err),
	)
	_ = s.shutdowner.Shutdown(fx.ExitCode(1))
}

// exhaust clears the current owner, logs the exhaustion, and requests a node
// shutdown with a non-zero exit code.
func (s *runtimeSupervisor) exhaust(maxAttempts int) {
	s.clearCurrent()
	s.logger.Error("reconnect exhausted, shutting down node",
		zap.Int("max_attempts", maxAttempts),
	)
	_ = s.shutdowner.Shutdown(fx.ExitCode(1))
}

// clearCurrent detaches and closes the current owner, if any.
func (s *runtimeSupervisor) clearCurrent() {
	s.mu.Lock()
	prev := s.current
	s.current = nil
	s.mu.Unlock()
	if prev != nil {
		prev.close()
	}
}

// stop cancels the supervisor goroutine, waits for it to exit, and closes the
// current connection. Waiting guarantees no retry sleep or dial survives the
// shutdown and no additional attempt runs afterward.
func (s *runtimeSupervisor) stop() {
	if s.cancelSupervisor != nil {
		s.cancelSupervisor()
	}
	if s.done != nil {
		<-s.done
	}
	s.clearCurrent()
}