Add website analytics

A Tianji-style Websites section: a small tracking script, a public collection endpoint, and a
page per website with visitors, page views, visits, bounce rate, a chart and top lists for pages,
referrers, browsers, systems, devices, countries, languages and events. No cookies and no stored
IP address or user agent. SANDBAR_TRUST_PROXY makes the client address come from the proxy.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

internal/sandbar/server.go

@@ -23,8 +23,10 @@ type Options struct {
 	MasterKey    string
 	MetricsToken string
 	SMTP         SMTPConfig
-	MessageDays  int // how long topic messages are kept (default 30)
-	CheckDays    int // how long monitor results are kept (default 30)
+	MessageDays  int  // how long topic messages are kept (default 30)
+	CheckDays    int  // how long monitor results are kept (default 30)
+	HitDays      int  // how long website analytics are kept (default 365)
+	TrustProxy   bool // take the client address from X-Forwarded-For, for use behind a reverse proxy
 
 	// Self-update (see update.go). Version is the running release, such as v0.2.0; anything else
 	// ("dev") never updates. Restart is called after a new binary is installed and should close
@@ -55,6 +57,10 @@ type Server struct {
 
 	upd updateState
 
+	anaMu     sync.Mutex // website analytics: the visitor salt and a per-address rate limit
+	anaSecret string
+	anaTry    map[string][]time.Time
+
 	stop chan struct{}
 	wg   sync.WaitGroup
 }
@@ -66,7 +72,10 @@ func New(opts Options, st *Store) *Server {
 	if opts.CheckDays <= 0 {
 		opts.CheckDays = 30
 	}
-	return &Server{opts: opts, st: st, hub: newHub(), running: map[string]bool{}, loginTry: map[string][]time.Time{}, stop: make(chan struct{})}
+	if opts.HitDays <= 0 {
+		opts.HitDays = 365
+	}
+	return &Server{opts: opts, st: st, hub: newHub(), running: map[string]bool{}, loginTry: map[string][]time.Time{}, anaTry: map[string][]time.Time{}, stop: make(chan struct{})}
 }
 
 func (s *Server) now() time.Time {
@@ -80,7 +89,7 @@ func (s *Server) now() time.Time {
 func (s *Server) Start() {
 	s.every(time.Second, func() { s.runDueMonitors(s.now()) })
 	s.every(5*time.Second, func() { s.escalate(s.now()) })
-	s.every(time.Hour, func() { s.st.prune(s.now(), s.opts.MessageDays, s.opts.CheckDays) })
+	s.every(time.Hour, func() { s.st.prune(s.now(), s.opts.MessageDays, s.opts.CheckDays, s.opts.HitDays) })
 }
 
 func (s *Server) Close() {