package web

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"net"
	"net/http"
	"strconv"
	"strings"
	"time"

	"github.com/yuanyuanxiang/SimpleRemoter/server/go/hub"
	"github.com/yuanyuanxiang/SimpleRemoter/server/go/logger"
	"github.com/yuanyuanxiang/SimpleRemoter/server/go/wsauth"
)

// Server serves the web remote desktop UI: the embedded index.html, xterm.js
// static assets, the PWA manifest, and JSON APIs backed by the device hub.
// WebSocket signaling and screen streaming will be wired up in later phases.
type Server struct {
	port              int
	log               *logger.Logger
	srv               *http.Server
	hub               *hub.Hub
	auth              *wsauth.Authenticator
	ws                *wsHub
	allowedOrigins    []string // for WS Origin allowlist; empty = same-origin only
	loginIPLimit      *wsauth.RateLimiter
	loginUserLimit    *wsauth.RateLimiter
	trustForwardedFor bool // honor X-Forwarded-For (behind trusted proxy only)
}

// Config tunes the server's exposed-on-public-HTTPS hardening knobs.
// All fields are optional; zero values pick reasonable defaults.
type Config struct {
	// AllowedOrigins is the comma-separated list of Origin header values
	// the WebSocket upgrade will accept in addition to same-origin
	// requests. Empty (default) → only same-origin upgrades are allowed,
	// which is correct when the web UI and the WS endpoint are served
	// from the same host.
	AllowedOrigins []string
	// LoginIPLimit / LoginUserLimit throttle the get_salt + login flow
	// per source IP and per username respectively. Pass nil to disable
	// either dimension (e.g. dev mode).
	LoginIPLimit   *wsauth.RateLimiter
	LoginUserLimit *wsauth.RateLimiter
	// TrustForwardedFor switches client-IP extraction from RemoteAddr
	// (default) to the last entry of X-Forwarded-For. Set true only when
	// running behind a reverse proxy that you control; on direct
	// exposure the header is client-controlled and would let attackers
	// evade per-IP rate limits.
	TrustForwardedFor bool
}

// New creates an HTTP server bound to the given port. port=0 disables the server.
// The hub provides read access to the online-device registry; the authenticator
// owns user accounts and session tokens.
func New(port int, log *logger.Logger, h *hub.Hub, auth *wsauth.Authenticator) *Server {
	return &Server{port: port, log: log, hub: h, auth: auth}
}

// WithConfig applies hardening configuration. Returns the receiver for
// chainable setup. Safe to call before Start; ignored thereafter.
func (s *Server) WithConfig(cfg Config) *Server {
	s.allowedOrigins = cfg.AllowedOrigins
	s.loginIPLimit = cfg.LoginIPLimit
	s.loginUserLimit = cfg.LoginUserLimit
	s.trustForwardedFor = cfg.TrustForwardedFor
	return s
}

// Start launches the server in a goroutine and returns immediately.
// If port is 0, returns nil without starting anything.
func (s *Server) Start() error {
	if s.port == 0 {
		s.log.Info("HTTP server disabled (-http-port=0)")
		return nil
	}

	s.ws = newWSHub(s.auth, s.hub, s.log).
		withOriginAllowlist(s.allowedOrigins).
		withLoginRateLimiters(s.loginIPLimit, s.loginUserLimit).
		withTrustForwardedFor(s.trustForwardedFor)

	mux := http.NewServeMux()
	mux.HandleFunc("/", s.handleIndex)
	mux.HandleFunc("/health", s.handleHealth)
	mux.HandleFunc("/manifest.json", s.handleManifest)
	mux.HandleFunc("/api/devices", s.requireBearer(s.handleDevices))
	mux.HandleFunc("/ws", s.ws.serve)
	mux.HandleFunc("/static/xterm.js", staticHandler(xtermJS, "application/javascript; charset=utf-8"))
	mux.HandleFunc("/static/xterm.css", staticHandler(xtermCSS, "text/css; charset=utf-8"))
	mux.HandleFunc("/static/xterm-fit.js", staticHandler(xtermFitJS, "application/javascript; charset=utf-8"))

	s.srv = &http.Server{
		Addr:              ":" + strconv.Itoa(s.port),
		Handler:           mux,
		ReadHeaderTimeout: 10 * time.Second,
	}

	// Bind synchronously so port-in-use / permission errors propagate to the
	// caller instead of being lost inside the goroutine after a misleading
	// "started" log line.
	ln, err := net.Listen("tcp", s.srv.Addr)
	if err != nil {
		return fmt.Errorf("listen on :%d: %w", s.port, err)
	}
	s.log.Info("HTTP server started on :%d", s.port)
	go func() {
		if err := s.srv.Serve(ln); err != nil && !errors.Is(err, http.ErrServerClosed) {
			s.log.Error("HTTP server stopped: %v", err)
		}
	}()
	return nil
}

// Stop gracefully shuts the server down.
func (s *Server) Stop() {
	if s.ws != nil {
		s.ws.stop()
	}
	if s.srv == nil {
		return
	}
	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
	defer cancel()
	_ = s.srv.Shutdown(ctx)
}

func (s *Server) handleIndex(w http.ResponseWriter, r *http.Request) {
	if r.URL.Path != "/" && r.URL.Path != "/index.html" {
		http.NotFound(w, r)
		return
	}
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	w.Header().Set("Cache-Control", "no-cache")
	_, _ = w.Write(IndexHTML)
}

func (s *Server) handleHealth(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("Content-Type", "application/json")
	_, _ = w.Write([]byte(`{"status":"ok"}`))
}

// handleDevices returns a JSON snapshot of currently-online devices. Empty
// array (not null) when no clients are connected — matches what the front-end
// will eventually expect. Auth-gated via requireBearer.
func (s *Server) handleDevices(w http.ResponseWriter, r *http.Request) {
	devices := s.hub.ListDevices()
	w.Header().Set("Content-Type", "application/json; charset=utf-8")
	w.Header().Set("Cache-Control", "no-store")
	if err := json.NewEncoder(w).Encode(devices); err != nil {
		s.log.Error("encode /api/devices: %v", err)
	}
}

// requireBearer wraps a handler with `Authorization: Bearer <token>` auth
// against the same session-token store the WebSocket uses. Returns 401 on
// missing / invalid / expired tokens. Used to gate REST endpoints that
// previously fell through with no auth (notably /api/devices, which
// otherwise leaks the full online-device list to anyone on the internet).
func (s *Server) requireBearer(next http.HandlerFunc) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		const prefix = "Bearer "
		hdr := r.Header.Get("Authorization")
		if !strings.HasPrefix(hdr, prefix) {
			s.unauthorized(w)
			return
		}
		token := strings.TrimSpace(hdr[len(prefix):])
		if token == "" {
			s.unauthorized(w)
			return
		}
		if _, err := s.auth.ValidateToken(token); err != nil {
			s.unauthorized(w)
			return
		}
		next(w, r)
	}
}

func (s *Server) unauthorized(w http.ResponseWriter) {
	w.Header().Set("WWW-Authenticate", `Bearer realm="yama"`)
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(http.StatusUnauthorized)
	_, _ = w.Write([]byte(`{"error":"unauthorized"}`))
}

// PWA manifest. Referenced by <link rel="manifest"> in index.html.
// Static JSON, no template needed.
const manifestJSON = `{
  "name": "SimpleRemoter",
  "short_name": "Remoter",
  "start_url": "/",
  "display": "standalone",
  "orientation": "any",
  "background_color": "#1a1a2e",
  "theme_color": "#1a1a2e"
}`

func (s *Server) handleManifest(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("Content-Type", "application/manifest+json")
	w.Header().Set("Cache-Control", "public, max-age=86400")
	_, _ = w.Write([]byte(manifestJSON))
}

// staticHandler returns an http.HandlerFunc that serves a fixed byte slice
// with the given content-type. Used for embedded third-party assets (xterm.js etc.)
// that change infrequently — 1-day browser cache is fine.
func staticHandler(body []byte, contentType string) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Content-Type", contentType)
		w.Header().Set("Cache-Control", "public, max-age=86400")
		_, _ = w.Write(body)
	}
}