// Package services manages service registrations from Wild Cloud, Wild Works,
// and manual entries. Services register with Central to get DNS, gateway
// routing, TLS certificates, and optional public exposure (tunnels or direct).
//
// Registrations are stored as YAML files on disk and will later be backed by
// NATS JetStream KV for real-time coordination.
package services

import (
	"fmt"
	"log/slog"
	"os"
	"path/filepath"
	"sync"

	"gopkg.in/yaml.v3"
)

// Reach describes how a service is exposed.
type Reach string

const (
	ReachOff      Reach = "off"      // localhost only — no DNS, no proxy
	ReachInternal Reach = "internal" // LAN-visible — DNS + proxy + TLS
	ReachPublic   Reach = "public"   // internet-visible — + tunnel or direct exposure
)

// BackendType describes how the gateway handles traffic for this service.
type BackendType string

const (
	BackendTCPPassthrough BackendType = "tcp-passthrough" // L4 SNI passthrough (k8s)
	BackendHTTP           BackendType = "http"            // L7 HTTP reverse proxy
	BackendStatic         BackendType = "static"          // L7 static file serving
)

// TLSMode describes how TLS is handled for the service.
type TLSMode string

const (
	TLSTerminate   TLSMode = "terminate"   // Central terminates TLS (wildcard cert)
	TLSPassthrough TLSMode = "passthrough" // Backend handles TLS (k8s traefik)
)

// Backend describes the target for a service.
type Backend struct {
	Address string      `yaml:"address" json:"address"`             // host:port (e.g., "192.168.8.60:9001")
	Type    BackendType `yaml:"type" json:"type"`                   // how to route
	Health  string      `yaml:"health,omitempty" json:"health,omitempty"` // health check path (e.g., "/health")
}

// Service represents a registered service.
type Service struct {
	Name         string   `yaml:"name" json:"name"`
	Source       string   `yaml:"source" json:"source"`                               // "wild-cloud", "wild-works", "manual"
	SourceNode   string   `yaml:"sourceNode,omitempty" json:"sourceNode,omitempty"`   // IP of the node running this service
	Domain       string   `yaml:"domain" json:"domain"`                               // FQDN (e.g., "my-api.payne.io")
	ExtraDomains []string `yaml:"extraDomains,omitempty" json:"extraDomains,omitempty"` // additional domains
	Backend      Backend  `yaml:"backend" json:"backend"`
	Reach        Reach    `yaml:"reach" json:"reach"`
	TLS          TLSMode  `yaml:"tls,omitempty" json:"tls,omitempty"`
}

// Manager handles service registration CRUD and triggers networking reconciliation.
type Manager struct {
	dataDir     string
	mu          sync.RWMutex
	reconcileFn func() // called after service changes to update DNS/proxy/TLS
}

// NewManager creates a new service registration manager.
func NewManager(dataDir string) *Manager {
	servicesDir := filepath.Join(dataDir, "services")
	if err := os.MkdirAll(servicesDir, 0755); err != nil {
		slog.Warn("failed to create services directory", "path", servicesDir, "error", err)
	}
	return &Manager{dataDir: dataDir}
}

// SetReconcileFn sets the function called after service changes to update networking.
func (m *Manager) SetReconcileFn(fn func()) {
	m.reconcileFn = fn
}

func (m *Manager) servicesDir() string {
	return filepath.Join(m.dataDir, "services")
}

func (m *Manager) servicePath(name string) string {
	return filepath.Join(m.servicesDir(), name+".yaml")
}

// Register creates or updates a service registration.
func (m *Manager) Register(svc Service) error {
	m.mu.Lock()
	defer m.mu.Unlock()

	if svc.Name == "" {
		return fmt.Errorf("service name is required")
	}
	if svc.Domain == "" {
		return fmt.Errorf("service domain is required")
	}
	if svc.Backend.Address == "" {
		return fmt.Errorf("backend address is required")
	}

	// Default reach to internal
	if svc.Reach == "" {
		svc.Reach = ReachInternal
	}
	// Default backend type to http
	if svc.Backend.Type == "" {
		svc.Backend.Type = BackendHTTP
	}
	// Default TLS mode based on backend type
	if svc.TLS == "" {
		if svc.Backend.Type == BackendTCPPassthrough {
			svc.TLS = TLSPassthrough
		} else {
			svc.TLS = TLSTerminate
		}
	}

	data, err := yaml.Marshal(svc)
	if err != nil {
		return fmt.Errorf("marshaling service: %w", err)
	}

	if err := os.WriteFile(m.servicePath(svc.Name), data, 0644); err != nil {
		return fmt.Errorf("writing service file: %w", err)
	}

	slog.Info("service registered", "name", svc.Name, "domain", svc.Domain, "reach", svc.Reach, "source", svc.Source)

	if m.reconcileFn != nil {
		go m.reconcileFn()
	}

	return nil
}

// Deregister removes a service registration.
func (m *Manager) Deregister(name string) error {
	m.mu.Lock()
	defer m.mu.Unlock()

	path := m.servicePath(name)
	if _, err := os.Stat(path); os.IsNotExist(err) {
		return fmt.Errorf("service %q not found", name)
	}

	if err := os.Remove(path); err != nil {
		return fmt.Errorf("removing service file: %w", err)
	}

	slog.Info("service deregistered", "name", name)

	if m.reconcileFn != nil {
		go m.reconcileFn()
	}

	return nil
}

// Get retrieves a service registration by name.
func (m *Manager) Get(name string) (*Service, error) {
	m.mu.RLock()
	defer m.mu.RUnlock()

	data, err := os.ReadFile(m.servicePath(name))
	if err != nil {
		if os.IsNotExist(err) {
			return nil, fmt.Errorf("service %q not found", name)
		}
		return nil, fmt.Errorf("reading service file: %w", err)
	}

	var svc Service
	if err := yaml.Unmarshal(data, &svc); err != nil {
		return nil, fmt.Errorf("parsing service file: %w", err)
	}

	return &svc, nil
}

// List returns all registered services.
func (m *Manager) List() ([]Service, error) {
	m.mu.RLock()
	defer m.mu.RUnlock()

	entries, err := os.ReadDir(m.servicesDir())
	if err != nil {
		if os.IsNotExist(err) {
			return nil, nil
		}
		return nil, fmt.Errorf("reading services directory: %w", err)
	}

	var services []Service
	for _, entry := range entries {
		if entry.IsDir() || filepath.Ext(entry.Name()) != ".yaml" {
			continue
		}

		data, err := os.ReadFile(filepath.Join(m.servicesDir(), entry.Name()))
		if err != nil {
			slog.Warn("failed to read service file", "file", entry.Name(), "error", err)
			continue
		}

		var svc Service
		if err := yaml.Unmarshal(data, &svc); err != nil {
			slog.Warn("failed to parse service file", "file", entry.Name(), "error", err)
			continue
		}

		services = append(services, svc)
	}

	return services, nil
}

// Update applies partial updates to a service registration.
func (m *Manager) Update(name string, updates map[string]any) error {
	svc, err := m.Get(name)
	if err != nil {
		return err
	}

	// Apply known fields
	if reach, ok := updates["reach"].(string); ok {
		svc.Reach = Reach(reach)
	}
	if domain, ok := updates["domain"].(string); ok {
		svc.Domain = domain
	}
	if backend, ok := updates["backend"].(map[string]any); ok {
		if addr, ok := backend["address"].(string); ok {
			svc.Backend.Address = addr
		}
		if typ, ok := backend["type"].(string); ok {
			svc.Backend.Type = BackendType(typ)
		}
		if health, ok := backend["health"].(string); ok {
			svc.Backend.Health = health
		}
	}

	return m.Register(*svc)
}