// Package domains manages domain registrations from Wild Cloud, Wild Works,
// and manual entries. Domains register with Central to get DNS, gateway
// routing, TLS certificates, and optional public exposure via DDNS.
//
// Each registration is keyed by its domain — one registration per domain.
// Central registers its own UI domain here on startup (source: "central").
package domains

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

	"gopkg.in/yaml.v3"
)

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

const (
	BackendTCPPassthrough BackendType = "tcp-passthrough" // L4 SNI passthrough (k8s)
	BackendHTTP           BackendType = "http"            // L7 HTTP reverse proxy
	BackendDNSOnly        BackendType = "dns-only"        // DNS resolution only, no gateway
)

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

const (
	TLSTerminate   TLSMode = "terminate"   // Central terminates TLS
	TLSPassthrough TLSMode = "passthrough" // Backend handles TLS (k8s traefik)
	TLSNone        TLSMode = "none"        // No TLS (dns-only)
)

// Backend describes the target for a domain.
type Backend struct {
	Address string      `yaml:"address" json:"address"` // host:port
	Type    BackendType `yaml:"type" json:"type"`       // tcp-passthrough or http
	Health  string      `yaml:"health,omitempty" json:"health,omitempty"`
}

// HeaderConfig describes custom request/response headers for L7 HTTP domains.
type HeaderConfig struct {
	Request  map[string]string `yaml:"request,omitempty" json:"request,omitempty"`
	Response map[string]string `yaml:"response,omitempty" json:"response,omitempty"`
}

// Route describes one path→backend mapping within a domain.
// Routes are evaluated in order — first match wins.
// A route with empty Paths is a catch-all (should be last).
type Route struct {
	Paths   []string      `yaml:"paths,omitempty" json:"paths,omitempty"`     // path prefixes (empty = catch-all)
	Backend Backend       `yaml:"backend" json:"backend"`                     // where to route
	Headers *HeaderConfig `yaml:"headers,omitempty" json:"headers,omitempty"` // per-route headers
	IPAllow []string      `yaml:"ipAllow,omitempty" json:"ipAllow,omitempty"` // per-route CIDR whitelist
}

// AuthConfig describes forward-auth protection for an L7 HTTP domain.
// Only applicable to domains with backend type "http" (L7 TLS termination).
type AuthConfig struct {
	Enabled bool   `yaml:"enabled,omitempty" json:"enabled,omitempty"`
	Policy  string `yaml:"policy,omitempty" json:"policy,omitempty"` // one_factor, two_factor, bypass
}

// Domain represents a registered domain. The Domain field is the unique key.
//
// Simple domains use Backend directly. Multi-backend domains use Routes
// for path-based splitting (Backend is ignored when Routes is present).
type Domain struct {
	DomainName string  `yaml:"domain" json:"domain"`                             // FQDN — unique key
	Source     string  `yaml:"source,omitempty" json:"source,omitempty"`         // who registered: wild-cloud, wild-works, manual
	Backend    Backend `yaml:"backend,omitempty" json:"backend,omitempty"`       // single backend (simple case)
	Subdomains bool    `yaml:"subdomains,omitempty" json:"subdomains,omitempty"` // also match *.domain
	Public     bool    `yaml:"public,omitempty" json:"public,omitempty"`         // true = internet-visible (DDNS + external), false = LAN only
	TLS        TLSMode `yaml:"tls,omitempty" json:"tls,omitempty"`              // passthrough or terminate
	Auth       *AuthConfig `yaml:"auth,omitempty" json:"auth,omitempty"`        // forward-auth protection (L7 HTTP only)

	// Multi-backend path routing. When present, Backend is ignored.
	// Each route maps path prefixes to a specific backend with its own L7 options.
	Routes []Route `yaml:"routes,omitempty" json:"routes,omitempty"`
}

// EffectiveRoutes returns the domain's routing as a normalized []Route.
// Simple domains (Backend, no Routes) are wrapped in a single-element slice.
func (d *Domain) EffectiveRoutes() []Route {
	if len(d.Routes) > 0 {
		return d.Routes
	}
	if d.Backend.Address == "" {
		return nil
	}
	return []Route{{Backend: d.Backend}}
}

// EffectiveBackendAddress returns the primary backend address for DNS/DDNS purposes.
// For multi-route domains, returns the first route's backend.
func (d *Domain) EffectiveBackendAddress() string {
	if len(d.Routes) > 0 {
		return d.Routes[0].Backend.Address
	}
	return d.Backend.Address
}

// EffectiveBackendType returns the backend type for routing decisions.
func (d *Domain) EffectiveBackendType() BackendType {
	if len(d.Routes) > 0 {
		return d.Routes[0].Backend.Type
	}
	return d.Backend.Type
}

// Manager handles domain registration CRUD and triggers networking reconciliation.
type Manager struct {
	dataDir     string
	mu          sync.RWMutex
	reconcileFn func()
}

// NewManager creates a new domain registration manager.
func NewManager(dataDir string) *Manager {
	domainsDir := filepath.Join(dataDir, "domains")
	oldServicesDir := filepath.Join(dataDir, "services")

	// Migrate from old "services" directory if it exists
	if _, err := os.Stat(oldServicesDir); err == nil {
		if _, err := os.Stat(domainsDir); os.IsNotExist(err) {
			if err := os.Rename(oldServicesDir, domainsDir); err != nil {
				slog.Warn("failed to migrate services dir to domains", "error", err)
			} else {
				slog.Info("migrated data directory", "from", oldServicesDir, "to", domainsDir)
			}
		}
	}

	if err := os.MkdirAll(domainsDir, 0755); err != nil {
		slog.Warn("failed to create domains directory", "path", domainsDir, "error", err)
	}
	return &Manager{dataDir: dataDir}
}

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

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

// domainToFilename converts a domain to a filesystem-safe filename.
func domainToFilename(domain string) string {
	return strings.ReplaceAll(domain, ".", "_") + ".yaml"
}

func (m *Manager) domainPath(domain string) string {
	return filepath.Join(m.domainsDir(), domainToFilename(domain))
}

// Register creates or updates a domain registration.
func (m *Manager) Register(dom Domain) error {
	m.mu.Lock()
	defer m.mu.Unlock()

	if dom.DomainName == "" {
		return fmt.Errorf("domain is required")
	}

	hasBackend := dom.Backend.Address != ""
	hasRoutes := len(dom.Routes) > 0

	if hasBackend && hasRoutes {
		return fmt.Errorf("domain must use backend or routes, not both")
	}
	if !hasBackend && !hasRoutes {
		return fmt.Errorf("backend address or routes required")
	}

	if hasRoutes {
		for i, r := range dom.Routes {
			if r.Backend.Address == "" {
				return fmt.Errorf("route %d: backend address is required", i)
			}
			if r.Backend.Type == "" {
				return fmt.Errorf("route %d: backend type is required", i)
			}
		}
	} else {
		if dom.Backend.Type == "" {
			return fmt.Errorf("backend type is required")
		}
	}

	// Default TLS mode based on backend type
	if dom.TLS == "" {
		switch dom.EffectiveBackendType() {
		case BackendTCPPassthrough:
			dom.TLS = TLSPassthrough
		case BackendDNSOnly:
			dom.TLS = TLSNone
		default:
			dom.TLS = TLSTerminate
		}
	}

	// Default source
	if dom.Source == "" {
		dom.Source = "manual"
	}

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

	if err := os.WriteFile(m.domainPath(dom.DomainName), data, 0644); err != nil {
		return fmt.Errorf("writing domain file: %w", err)
	}

	slog.Info("domain registered", "domain", dom.DomainName, "public", dom.Public, "source", dom.Source, "subdomains", dom.Subdomains)

	if m.reconcileFn != nil {
		go func() {
			defer func() {
				if r := recover(); r != nil {
					slog.Error("reconcile panicked", "error", r)
				}
			}()
			m.reconcileFn()
		}()
	}

	return nil
}

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

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

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

	slog.Info("domain deregistered", "domain", domain)

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

	return nil
}

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

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

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

	return &dom, nil
}

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

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

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

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

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

		doms = append(doms, dom)
	}

	return doms, nil
}

// DeregisterBySource removes all registrations from a given source that match
// a backend address. Used by consumers to clean up before re-registering.
func (m *Manager) DeregisterBySource(source, backendAddress string) error {
	doms, err := m.List()
	if err != nil {
		return err
	}

	for _, dom := range doms {
		if dom.Source == source && dom.EffectiveBackendAddress() == backendAddress {
			if err := m.Deregister(dom.DomainName); err != nil {
				slog.Warn("failed to deregister domain during cleanup", "domain", dom.DomainName, "error", err)
			}
		}
	}

	return nil
}

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

	if public, ok := updates["public"].(bool); ok {
		dom.Public = public
	}
	if sub, ok := updates["subdomains"].(bool); ok {
		dom.Subdomains = sub
	}
	if backend, ok := updates["backend"].(map[string]any); ok {
		if addr, ok := backend["address"].(string); ok {
			dom.Backend.Address = addr
		}
		if typ, ok := backend["type"].(string); ok {
			dom.Backend.Type = BackendType(typ)
		}
		if health, ok := backend["health"].(string); ok {
			dom.Backend.Health = health
		}
	}
	if tls, ok := updates["tls"].(string); ok {
		dom.TLS = TLSMode(tls)
	}
	if auth, ok := updates["auth"].(map[string]any); ok {
		if dom.Auth == nil {
			dom.Auth = &AuthConfig{}
		}
		if enabled, ok := auth["enabled"].(bool); ok {
			dom.Auth.Enabled = enabled
		}
		if policy, ok := auth["policy"].(string); ok {
			dom.Auth.Policy = policy
		}
		// Clear auth if disabled and no policy
		if !dom.Auth.Enabled && dom.Auth.Policy == "" {
			dom.Auth = nil
		}
	}

	return m.Register(*dom)
}