package web

import (
	"context"
	"errors"
	"io/fs"
	"net"
	"net/http"
	"path"
	"strings"
	"time"
)

var (
	errBadCredentials  = errors.New("invalid password")
	errTooManyAttempts = errors.New("too many failed attempts, try again later")
	errInternal        = errors.New("internal error")
)

// Rule is the JSON representation of a single ruleset rule. The YAML tags
// mirror the rule file format, so the same struct can be written back out.
type Rule struct {
	Name     string        `json:"name" yaml:"name"`
	Action   string        `json:"action,omitempty" yaml:"action,omitempty"`
	Log      bool          `json:"log,omitempty" yaml:"log,omitempty"`
	Modifier *RuleModifier `json:"modifier,omitempty" yaml:"modifier,omitempty"`
	Expr     string        `json:"expr" yaml:"expr"`
}

// RuleModifier is the modifier attached to a `modify` rule.
type RuleModifier struct {
	Name string                 `json:"name" yaml:"name"`
	Args map[string]interface{} `json:"args,omitempty" yaml:"args,omitempty"`
}

// RuleManager gives the web server access to the running ruleset. The
// implementation lives in the cmd package, which owns both the rule file and
// the engine.
type RuleManager interface {
	// Path returns the path of the rule file.
	Path() string
	// Load reads the rule file and returns its raw content and parsed rules.
	Load() (string, []Rule, error)
	// Validate parses and compiles the given YAML without applying it.
	Validate(raw string) ([]Rule, error)
	// Marshal serializes structured rules back to YAML.
	Marshal(rules []Rule) (string, error)
	// Apply validates the given YAML, writes it to the rule file and hot
	// reloads the engine.
	Apply(raw string) ([]Rule, error)
}

// Info is the static information about the running instance shown by the UI.
type Info struct {
	Version   string       `json:"version"`
	Commit    string       `json:"commit,omitempty"`
	Platform  string       `json:"platform"`
	GoVersion string       `json:"goVersion"`
	Hostname  string       `json:"hostname"`
	RuleFile  string       `json:"ruleFile"`
	Config    ConfigDigest `json:"config"`
}

// ConfigDigest is a read-only summary of the engine configuration.
type ConfigDigest struct {
	IOQueueSize   uint32 `json:"ioQueueSize"`
	IOLocal       bool   `json:"ioLocal"`
	IORST         bool   `json:"ioRST"`
	Workers       int    `json:"workers"`
	WorkerQueue   int    `json:"workerQueueSize"`
	UDPMaxStreams int    `json:"udpMaxStreams"`
	GeoIP         string `json:"geoip,omitempty"`
	GeoSite       string `json:"geosite,omitempty"`
}

// MetaInfo describes what the engine is capable of. The rule editor uses it
// for autocompletion and validation hints.
type MetaInfo struct {
	Analyzers []AnalyzerInfo `json:"analyzers"`
	Modifiers []string       `json:"modifiers"`
	Actions   []string       `json:"actions"`
	Functions []string       `json:"functions"`
}

// AnalyzerInfo describes a single analyzer.
type AnalyzerInfo struct {
	Name  string `json:"name"`
	Proto string `json:"proto"`
}

// Config is the web server configuration.
type Config struct {
	// Listen is the address to listen on, e.g. ":8080".
	Listen string
	// Secret is the password required to log in. Must not be empty.
	Secret string
	// CertFile / KeyFile enable HTTPS when both are set.
	CertFile string
	KeyFile  string

	Hub   *Hub
	Rules RuleManager
	Meta  MetaInfo
	Info  func() Info

	// Logf is used for the few messages the server produces. Optional.
	Logf func(format string, args ...interface{})
}

// Server serves the web UI and its API.
type Server struct {
	config Config
	auth   *authenticator
	mux    *http.ServeMux
	static http.Handler
}

// NewServer creates a new web UI server.
func NewServer(config Config) (*Server, error) {
	if config.Hub == nil {
		return nil, errors.New("web: hub is required")
	}
	if config.Secret == "" {
		return nil, errors.New("web: secret is required")
	}
	if config.Listen == "" {
		config.Listen = ":8080"
	}
	if config.Logf == nil {
		config.Logf = func(string, ...interface{}) {}
	}
	s := &Server{
		config: config,
		auth:   newAuthenticator(config.Secret),
		mux:    http.NewServeMux(),
		static: staticHandler(),
	}
	s.routes()
	return s, nil
}

// Secret returns the password in use, which is useful when it was generated.
func (s *Server) Secret() string { return s.config.Secret }

// Addr returns the address the server listens on.
func (s *Server) Addr() string { return s.config.Listen }

// TLS reports whether the server serves HTTPS.
func (s *Server) TLS() bool { return s.config.CertFile != "" && s.config.KeyFile != "" }

func (s *Server) routes() {
	s.mux.HandleFunc("/api/v1/login", s.handleLogin)
	s.mux.HandleFunc("/api/v1/logout", s.guard(s.handleLogout, true))
	s.mux.HandleFunc("/api/v1/info", s.guard(s.handleInfo, false))
	s.mux.HandleFunc("/api/v1/meta", s.guard(s.handleMeta, false))
	s.mux.HandleFunc("/api/v1/metrics", s.guard(s.handleMetrics, false))
	s.mux.HandleFunc("/api/v1/events", s.guard(s.handleEvents, false))
	s.mux.HandleFunc("/api/v1/live", s.guard(s.handleLive, false))
	s.mux.HandleFunc("/api/v1/rules", s.guard(s.handleRules, false))
	s.mux.HandleFunc("/api/v1/rules/validate", s.guard(s.handleRulesValidate, true))
	s.mux.HandleFunc("/", s.handleStatic)
}

// Run starts the server and blocks until the context is cancelled.
func (s *Server) Run(ctx context.Context) error {
	srv := &http.Server{
		Handler:           s.securityHeaders(s.mux),
		ReadHeaderTimeout: 10 * time.Second,
		BaseContext:       func(net.Listener) context.Context { return ctx },
	}
	ln, err := net.Listen("tcp", s.config.Listen)
	if err != nil {
		return err
	}
	errChan := make(chan error, 1)
	go func() {
		if s.TLS() {
			errChan <- srv.ServeTLS(ln, s.config.CertFile, s.config.KeyFile)
		} else {
			errChan <- srv.Serve(ln)
		}
	}()
	select {
	case <-ctx.Done():
		shutdownCtx, cancel := context.WithTimeout(context.Background(), 3*time.Second)
		defer cancel()
		_ = srv.Shutdown(shutdownCtx)
		return nil
	case err := <-errChan:
		if errors.Is(err, http.ErrServerClosed) {
			return nil
		}
		return err
	}
}

// guard wraps a handler with authentication. When mutating is true, a bearer
// token is required (a session cookie alone is not enough), which makes the
// endpoint immune to cross-site request forgery.
func (s *Server) guard(next http.HandlerFunc, mutating bool) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		token := bearerToken(r)
		if token == "" && !mutating && r.Method == http.MethodGet {
			token = cookieToken(r)
		}
		if !s.auth.valid(token) {
			writeError(w, http.StatusUnauthorized, "unauthorized")
			return
		}
		next(w, r)
	}
}

func (s *Server) securityHeaders(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		h := w.Header()
		h.Set("X-Content-Type-Options", "nosniff")
		h.Set("X-Frame-Options", "DENY")
		h.Set("Referrer-Policy", "no-referrer")
		next.ServeHTTP(w, r)
	})
}

func (s *Server) handleStatic(w http.ResponseWriter, r *http.Request) {
	if strings.HasPrefix(r.URL.Path, "/api/") {
		writeError(w, http.StatusNotFound, "not found")
		return
	}
	s.static.ServeHTTP(w, r)
}

// staticHandler serves the embedded single page application, falling back to
// index.html so that client side routing works on a hard refresh.
func staticHandler() http.Handler {
	sub, err := fs.Sub(distFS, "dist")
	if err != nil {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			http.Error(w, "web UI is not built", http.StatusNotImplemented)
		})
	}
	files := http.FileServer(http.FS(sub))
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		name := strings.TrimPrefix(path.Clean(r.URL.Path), "/")
		if name == "" || name == "." {
			name = "index.html"
		}
		if _, err := fs.Stat(sub, name); err != nil {
			// Unknown path: let the SPA router handle it.
			r = r.Clone(r.Context())
			r.URL.Path = "/"
			w.Header().Set("Cache-Control", "no-store")
			files.ServeHTTP(w, r)
			return
		}
		if strings.HasPrefix(name, "assets/") {
			w.Header().Set("Cache-Control", "public, max-age=31536000, immutable")
		} else {
			w.Header().Set("Cache-Control", "no-cache")
		}
		files.ServeHTTP(w, r)
	})
}