silo/internal/api/servermode.go

package api

import (
	"context"
	"sync"
	"time"

	"github.com/kindredsystems/silo/internal/storage"
	"github.com/rs/zerolog"
)

// ServerMode represents the operational mode of the server.
type ServerMode string

const (
	ModeNormal   ServerMode = "normal"
	ModeReadOnly ServerMode = "read-only"
	ModeDegraded ServerMode = "degraded"
)

const storageCheckInterval = 30 * time.Second

// ServerState tracks the server's current operational mode.
type ServerState struct {
	logger    zerolog.Logger
	mu        sync.RWMutex
	readOnly  bool
	storageOK bool
	storage   storage.FileStore
	broker    *Broker
	done      chan struct{}
}

// NewServerState creates a new server state tracker.
func NewServerState(logger zerolog.Logger, store storage.FileStore, broker *Broker) *ServerState {
	return &ServerState{
		logger:    logger.With().Str("component", "server-state").Logger(),
		storageOK: store != nil, // assume healthy if configured
		storage:   store,
		broker:    broker,
		done:      make(chan struct{}),
	}
}

// Mode returns the current effective server mode.
// Priority: explicit read-only > storage unhealthy (degraded) > normal.
func (ss *ServerState) Mode() ServerMode {
	ss.mu.RLock()
	defer ss.mu.RUnlock()
	if ss.readOnly {
		return ModeReadOnly
	}
	if ss.storage != nil && !ss.storageOK {
		return ModeDegraded
	}
	return ModeNormal
}

// IsReadOnly returns true if the server should reject writes.
// Only explicit read-only mode blocks writes; degraded is informational.
func (ss *ServerState) IsReadOnly() bool {
	ss.mu.RLock()
	defer ss.mu.RUnlock()
	return ss.readOnly
}

// SetReadOnly sets the explicit read-only flag and broadcasts a state change.
func (ss *ServerState) SetReadOnly(ro bool) {
	ss.mu.Lock()
	old := ss.mode()
	ss.readOnly = ro
	new := ss.mode()
	ss.mu.Unlock()

	if old != new {
		ss.logger.Info().Str("mode", string(new)).Msg("server mode changed")
		ss.broker.Publish("server.state", mustMarshal(map[string]string{"mode": string(new)}))
	}
}

// ToggleReadOnly flips the read-only flag.
func (ss *ServerState) ToggleReadOnly() {
	ss.mu.RLock()
	current := ss.readOnly
	ss.mu.RUnlock()
	ss.SetReadOnly(!current)
}

// StartStorageHealthCheck launches a periodic check of storage reachability.
// Updates storageOK and broadcasts server.state on transitions.
func (ss *ServerState) StartStorageHealthCheck() {
	if ss.storage == nil {
		return
	}
	go func() {
		ticker := time.NewTicker(storageCheckInterval)
		defer ticker.Stop()
		for {
			select {
			case <-ticker.C:
				ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
				err := ss.storage.Ping(ctx)
				cancel()

				ss.mu.Lock()
				old := ss.mode()
				ss.storageOK = err == nil
				new := ss.mode()
				ss.mu.Unlock()

				if old != new {
					ss.logger.Info().Str("mode", string(new)).Err(err).Msg("server mode changed")
					ss.broker.Publish("server.state", mustMarshal(map[string]string{"mode": string(new)}))
				}
			case <-ss.done:
				return
			}
		}
	}()
}

// Shutdown stops the health check loop.
func (ss *ServerState) Shutdown() {
	close(ss.done)
}

// mode returns the current mode. Must be called with mu held.
func (ss *ServerState) mode() ServerMode {
	if ss.readOnly {
		return ModeReadOnly
	}
	if ss.storage != nil && !ss.storageOK {
		return ModeDegraded
	}
	return ModeNormal
}