/*
Volt Ingress — Native reverse proxy and API gateway.

Provides hostname/path-based routing of external traffic to containers,
with TLS termination and rate limiting.

Architecture:
  - Go-native HTTP reverse proxy (net/http/httputil)
  - Route configuration stored at /etc/volt/ingress/routes.json
  - TLS via autocert (Let's Encrypt ACME) or user-provided certs
  - Rate limiting via token bucket per route
  - Runs as volt-ingress systemd service

Copyright (c) Armored Gates LLC. All rights reserved.
AGPSL v5 — Source-available. Anti-competition clauses apply.
*/
package ingress

import (
	"encoding/json"
	"fmt"
	"net"
	"net/http"
	"net/http/httputil"
	"net/url"
	"os"
	"strings"
	"sync"
	"time"
)

// ── Constants ────────────────────────────────────────────────────────────────

const (
	IngressConfigDir  = "/etc/volt/ingress"
	RoutesFile        = "/etc/volt/ingress/routes.json"
	CertsDir          = "/etc/volt/ingress/certs"
	DefaultHTTPPort   = 80
	DefaultHTTPSPort  = 443
)

// ── Route ────────────────────────────────────────────────────────────────────

// Route defines a hostname/path → backend mapping.
type Route struct {
	ID          string            `json:"id"`
	Domain      string            `json:"domain"`         // hostname to match
	Path        string            `json:"path"`           // path prefix (default: "/")
	Target      string            `json:"target"`         // container name or IP:port
	TargetPort  int               `json:"target_port"`    // backend port
	TLS         bool              `json:"tls"`            // enable TLS termination
	TLSCertFile string            `json:"tls_cert_file,omitempty"` // custom cert path
	TLSKeyFile  string            `json:"tls_key_file,omitempty"`  // custom key path
	AutoTLS     bool              `json:"auto_tls"`       // use Let's Encrypt
	RateLimit   int               `json:"rate_limit"`     // requests per second (0 = unlimited)
	Headers     map[string]string `json:"headers,omitempty"` // custom headers to add
	HealthCheck string            `json:"health_check,omitempty"` // health check path
	Enabled     bool              `json:"enabled"`
	CreatedAt   string            `json:"created_at"`
}

// ── Route Store ──────────────────────────────────────────────────────────────

// RouteStore manages ingress route configuration.
type RouteStore struct {
	Routes []Route `json:"routes"`
	mu     sync.RWMutex
}

// LoadRoutes reads routes from disk.
func LoadRoutes() (*RouteStore, error) {
	store := &RouteStore{}
	data, err := os.ReadFile(RoutesFile)
	if err != nil {
		if os.IsNotExist(err) {
			return store, nil
		}
		return nil, fmt.Errorf("failed to read routes: %w", err)
	}
	if err := json.Unmarshal(data, store); err != nil {
		return nil, fmt.Errorf("failed to parse routes: %w", err)
	}
	return store, nil
}

// Save writes routes to disk.
func (s *RouteStore) Save() error {
	s.mu.Lock()
	defer s.mu.Unlock()

	os.MkdirAll(IngressConfigDir, 0755)
	data, err := json.MarshalIndent(s, "", "  ")
	if err != nil {
		return err
	}
	return os.WriteFile(RoutesFile, data, 0644)
}

// AddRoute adds a new route.
func (s *RouteStore) AddRoute(route Route) error {
	s.mu.Lock()
	defer s.mu.Unlock()

	// Check for duplicate domain+path
	for _, existing := range s.Routes {
		if existing.Domain == route.Domain && existing.Path == route.Path {
			return fmt.Errorf("route for %s%s already exists (id: %s)", route.Domain, route.Path, existing.ID)
		}
	}

	s.Routes = append(s.Routes, route)
	return nil
}

// RemoveRoute removes a route by ID or domain.
func (s *RouteStore) RemoveRoute(idOrDomain string) (*Route, error) {
	s.mu.Lock()
	defer s.mu.Unlock()

	var remaining []Route
	var removed *Route
	for i := range s.Routes {
		if s.Routes[i].ID == idOrDomain || s.Routes[i].Domain == idOrDomain {
			r := s.Routes[i]
			removed = &r
		} else {
			remaining = append(remaining, s.Routes[i])
		}
	}

	if removed == nil {
		return nil, fmt.Errorf("route %q not found", idOrDomain)
	}

	s.Routes = remaining
	return removed, nil
}

// FindRoute matches a request to a route based on Host header and path.
func (s *RouteStore) FindRoute(host, path string) *Route {
	s.mu.RLock()
	defer s.mu.RUnlock()

	// Strip port from host if present
	if h, _, err := net.SplitHostPort(host); err == nil {
		host = h
	}

	var bestMatch *Route
	bestPathLen := -1

	for i := range s.Routes {
		r := &s.Routes[i]
		if !r.Enabled {
			continue
		}
		if r.Domain != host && r.Domain != "*" {
			continue
		}
		routePath := r.Path
		if routePath == "" {
			routePath = "/"
		}
		if strings.HasPrefix(path, routePath) && len(routePath) > bestPathLen {
			bestMatch = r
			bestPathLen = len(routePath)
		}
	}

	return bestMatch
}

// ── Reverse Proxy ────────────────────────────────────────────────────────────

// IngressProxy is the HTTP reverse proxy engine.
type IngressProxy struct {
	routes     *RouteStore
	rateLimits map[string]*rateLimiter
	mu         sync.RWMutex
}

// NewIngressProxy creates a new proxy with the given route store.
func NewIngressProxy(routes *RouteStore) *IngressProxy {
	return &IngressProxy{
		routes:     routes,
		rateLimits: make(map[string]*rateLimiter),
	}
}

// ServeHTTP implements http.Handler — the main request routing logic.
func (p *IngressProxy) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	route := p.routes.FindRoute(r.Host, r.URL.Path)
	if route == nil {
		http.Error(w, "502 Bad Gateway — no route found", http.StatusBadGateway)
		return
	}

	// Rate limiting
	if route.RateLimit > 0 {
		limiter := p.getRateLimiter(route.ID, route.RateLimit)
		if !limiter.allow() {
			http.Error(w, "429 Too Many Requests", http.StatusTooManyRequests)
			return
		}
	}

	// Resolve backend address
	backendAddr := resolveBackend(route.Target, route.TargetPort)
	if backendAddr == "" {
		http.Error(w, "502 Bad Gateway — backend unavailable", http.StatusBadGateway)
		return
	}

	// Build target URL
	targetURL, err := url.Parse(fmt.Sprintf("http://%s", backendAddr))
	if err != nil {
		http.Error(w, "502 Bad Gateway — invalid backend", http.StatusBadGateway)
		return
	}

	// Create reverse proxy
	proxy := httputil.NewSingleHostReverseProxy(targetURL)
	proxy.ErrorHandler = func(rw http.ResponseWriter, req *http.Request, err error) {
		http.Error(rw, fmt.Sprintf("502 Bad Gateway — %v", err), http.StatusBadGateway)
	}

	// Add custom headers
	for k, v := range route.Headers {
		r.Header.Set(k, v)
	}

	// Set X-Forwarded headers
	r.Header.Set("X-Forwarded-Host", r.Host)
	r.Header.Set("X-Forwarded-Proto", "https")
	if clientIP, _, err := net.SplitHostPort(r.RemoteAddr); err == nil {
		r.Header.Set("X-Real-IP", clientIP)
		existing := r.Header.Get("X-Forwarded-For")
		if existing != "" {
			r.Header.Set("X-Forwarded-For", existing+", "+clientIP)
		} else {
			r.Header.Set("X-Forwarded-For", clientIP)
		}
	}

	proxy.ServeHTTP(w, r)
}

// resolveBackend resolves a container name or IP to a backend address.
func resolveBackend(target string, port int) string {
	if port == 0 {
		port = 80
	}

	// If target already contains ":", it's an IP:port
	if strings.Contains(target, ":") {
		return target
	}

	// If it looks like an IP, just add port
	if net.ParseIP(target) != nil {
		return fmt.Sprintf("%s:%d", target, port)
	}

	// Try to resolve as container name via machinectl
	out, err := runCommandSilent("machinectl", "show", target, "-p", "Addresses", "--value")
	if err == nil {
		addr := strings.TrimSpace(out)
		for _, a := range strings.Fields(addr) {
			if net.ParseIP(a) != nil {
				return fmt.Sprintf("%s:%d", a, port)
			}
		}
	}

	// Fallback: assume it's a hostname
	return fmt.Sprintf("%s:%d", target, port)
}

func runCommandSilent(name string, args ...string) (string, error) {
	out, err := execCommand(name, args...)
	return strings.TrimSpace(out), err
}

func execCommand(name string, args ...string) (string, error) {
	cmd := newCommand(name, args...)
	out, err := cmd.Output()
	return string(out), err
}

// ── Rate Limiting ────────────────────────────────────────────────────────────

type rateLimiter struct {
	tokens     float64
	maxTokens  float64
	refillRate float64 // tokens per second
	lastRefill time.Time
	mu         sync.Mutex
}

func newRateLimiter(rps int) *rateLimiter {
	return &rateLimiter{
		tokens:     float64(rps),
		maxTokens:  float64(rps),
		refillRate: float64(rps),
		lastRefill: time.Now(),
	}
}

func (rl *rateLimiter) allow() bool {
	rl.mu.Lock()
	defer rl.mu.Unlock()

	now := time.Now()
	elapsed := now.Sub(rl.lastRefill).Seconds()
	rl.tokens += elapsed * rl.refillRate
	if rl.tokens > rl.maxTokens {
		rl.tokens = rl.maxTokens
	}
	rl.lastRefill = now

	if rl.tokens >= 1 {
		rl.tokens--
		return true
	}
	return false
}

func (p *IngressProxy) getRateLimiter(routeID string, rps int) *rateLimiter {
	p.mu.Lock()
	defer p.mu.Unlock()

	if rl, exists := p.rateLimits[routeID]; exists {
		return rl
	}
	rl := newRateLimiter(rps)
	p.rateLimits[routeID] = rl
	return rl
}

// ── Route ID Generation ─────────────────────────────────────────────────────

// GenerateRouteID creates a deterministic route ID from domain and path.
func GenerateRouteID(domain, path string) string {
	id := strings.ReplaceAll(domain, ".", "-")
	if path != "" && path != "/" {
		id += "-" + strings.Trim(strings.ReplaceAll(path, "/", "-"), "-")
	}
	return id
}