1 files changed, 305 insertions, 0 deletions
diff --git a/internal/events/bus.go b/internal/events/bus.go
new file mode 100644
index 0000000..4856c53
--- /dev/null
+++ b/internal/events/bus.go
@@ -0,0 +1,305 @@
+package events
+
+import "sync"
+
+// ── Handler interfaces ────────────────────────────────────────────────────────
+
+// RequestMiddleware is called synchronously for every HTTP request before
+// forwarding. Returning Drop=true causes the proxy to send a 403 and stop.
+// The implementation may modify Request and Body (e.g. intercept gate).
+type RequestMiddleware interface {
+	HandleRequest(RequestEvent) RequestResult
+}
+
+// ResponseObserver is called synchronously after every completed HTTP
+// transaction. Ordering is preserved: observers see responses in the exact
+// order the proxy received them.
+type ResponseObserver interface {
+	ObserveResponse(ResponseEvent)
+}
+
+// WebSocketConnectionObserver is called synchronously when a WebSocket
+// connection is established. It returns a uint64 connection ID that the
+// bus passes back to WebSocketFrameObservers as ConnectionID. Return 0
+// to indicate the connection should not be tracked.
+type WebSocketConnectionObserver interface {
+	ObserveWebSocketConnection(WebSocketConnectionEvent) uint64
+}
+
+// WebSocketFrameObserver is called synchronously for every WebSocket frame.
+// Ordering is preserved within a connection. The returned WebSocketFrameResult
+// carries the (possibly modified) payload to forward.
+type WebSocketFrameObserver interface {
+	ObserveWebSocketFrame(WebSocketFrameEvent) WebSocketFrameResult
+}
+
+// PluginLogObserver is called synchronously when a plugin emits a log line.
+// The store implements this to buffer lines in memory and notify the UI.
+type PluginLogObserver interface {
+	ObservePluginLog(PluginLogEvent)
+}
+
+// PluginEnabledObserver is called synchronously when the UI toggles a plugin.
+// Both the engine (to skip hooks) and the store (to persist state) implement this.
+type PluginEnabledObserver interface {
+	ObservePluginEnabled(SetPluginEnabledEvent)
+}
+
+// LoadPluginObserver is called synchronously when the user imports a new
+// plugin. The engine observes it to copy, load, and register the plugin.
+type LoadPluginObserver interface {
+	ObserveLoadPlugin(LoadPluginEvent)
+}
+
+// ProxyCommandObserver is implemented by the proxy to react to UI-initiated
+// control events. Restart starts or restarts the proxy on the given address.
+// Stop shuts the proxy down.
+type ProxyCommandObserver interface {
+	ObserveProxyRestart(ProxyRestartEvent)
+	ObserveProxyStop(ProxyStopEvent)
+}
+
+// ── Func adapters ─────────────────────────────────────────────────────────────
+// Allow main.go to register plain closures without declaring named types.
+
+type RequestMiddlewareFunc func(RequestEvent) RequestResult
+
+func (f RequestMiddlewareFunc) HandleRequest(e RequestEvent) RequestResult {
+	return f(e)
+}
+
+type ResponseObserverFunc func(ResponseEvent)
+
+func (f ResponseObserverFunc) ObserveResponse(e ResponseEvent) {
+	f(e)
+}
+
+type WebSocketConnectionObserverFunc func(WebSocketConnectionEvent) uint64
+
+func (f WebSocketConnectionObserverFunc) ObserveWebSocketConnection(e WebSocketConnectionEvent) uint64 {
+	return f(e)
+}
+
+type WebSocketFrameObserverFunc func(WebSocketFrameEvent) WebSocketFrameResult
+
+func (f WebSocketFrameObserverFunc) ObserveWebSocketFrame(e WebSocketFrameEvent) WebSocketFrameResult {
+	return f(e)
+}
+
+type PluginLogObserverFunc func(PluginLogEvent)
+
+func (f PluginLogObserverFunc) ObservePluginLog(e PluginLogEvent) {
+	f(e)
+}
+
+type PluginEnabledObserverFunc func(SetPluginEnabledEvent)
+
+func (f PluginEnabledObserverFunc) ObservePluginEnabled(e SetPluginEnabledEvent) {
+	f(e)
+}
+
+type LoadPluginObserverFunc func(LoadPluginEvent)
+
+func (f LoadPluginObserverFunc) ObserveLoadPlugin(e LoadPluginEvent) {
+	f(e)
+}
+
+// ── Bus ───────────────────────────────────────────────────────────────────────
+
+// Bus holds registered handlers and dispatches events to them.
+// All methods are safe for concurrent use. All emit methods run
+// synchronously to preserve the ordering guarantee that existed before
+// the refactor: store.Log emits to the Updates channel which the UI reads
+// in arrival order. Making observers async would break this.
+type Bus struct {
+	mu                     sync.RWMutex
+	requestMiddlewares     []RequestMiddleware
+	responseObservers      []ResponseObserver
+	wsConnObservers        []WebSocketConnectionObserver
+	wsFrameObservers       []WebSocketFrameObserver
+	pluginLogObservers     []PluginLogObserver
+	pluginEnabledObservers []PluginEnabledObserver
+	pluginLoadObservers    []LoadPluginObserver
+	proxyCommandObservers  []ProxyCommandObserver
+}
+
+// NewBus returns a ready-to-use Bus with no handlers registered.
+func NewBus() *Bus {
+	return &Bus{}
+}
+
+// Register adds a handler to the bus. The handler is matched against all
+// handler interfaces — a single type may implement multiple interfaces
+// and will be registered for each one it satisfies. Panics if h implements
+// none of the interfaces (programming error).
+func (b *Bus) Register(h any) {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+
+	matched := false
+	if v, ok := h.(RequestMiddleware); ok {
+		b.requestMiddlewares = append(b.requestMiddlewares, v)
+		matched = true
+	}
+	if v, ok := h.(ResponseObserver); ok {
+		b.responseObservers = append(b.responseObservers, v)
+		matched = true
+	}
+	if v, ok := h.(WebSocketConnectionObserver); ok {
+		b.wsConnObservers = append(b.wsConnObservers, v)
+		matched = true
+	}
+	if v, ok := h.(WebSocketFrameObserver); ok {
+		b.wsFrameObservers = append(b.wsFrameObservers, v)
+		matched = true
+	}
+	if v, ok := h.(PluginLogObserver); ok {
+		b.pluginLogObservers = append(b.pluginLogObservers, v)
+		matched = true
+	}
+	if v, ok := h.(PluginEnabledObserver); ok {
+		b.pluginEnabledObservers = append(b.pluginEnabledObservers, v)
+		matched = true
+	}
+	if v, ok := h.(LoadPluginObserver); ok {
+		b.pluginLoadObservers = append(b.pluginLoadObservers, v)
+		matched = true
+	}
+	if v, ok := h.(ProxyCommandObserver); ok {
+		b.proxyCommandObservers = append(b.proxyCommandObservers, v)
+		matched = true
+	}
+	if !matched {
+		panic("events: Register called with a type that implements no handler interface")
+	}
+}
+
+// EmitRequest runs all RequestMiddlewares in registration order.
+// The first middleware to return Drop=true short-circuits — subsequent
+// middlewares are not called. If no middleware drops the request, the
+// final Request and Body are taken from the last middleware result.
+// If no middlewares are registered the original event values are returned
+// as a pass-through result.
+func (b *Bus) EmitRequest(e RequestEvent) RequestResult {
+	b.mu.RLock()
+	mws := b.requestMiddlewares
+	b.mu.RUnlock()
+
+	result := RequestResult{Request: e.Request, Body: e.Body}
+	for _, mw := range mws {
+		result = mw.HandleRequest(RequestEvent{Request: result.Request, Body: result.Body})
+		if result.Drop {
+			return result
+		}
+	}
+	return result
+}
+
+// EmitResponse calls all ResponseObservers in registration order.
+// Runs synchronously; returns when all observers have returned.
+func (b *Bus) EmitResponse(e ResponseEvent) {
+	b.mu.RLock()
+	obs := b.responseObservers
+	b.mu.RUnlock()
+
+	for _, o := range obs {
+		o.ObserveResponse(e)
+	}
+}
+
+// EmitWebSocketConnection calls all WebSocketConnectionObservers in
+// registration order. The first non-zero uint64 returned is used as the
+// connection ID for subsequent frame events. Runs synchronously.
+func (b *Bus) EmitWebSocketConnection(e WebSocketConnectionEvent) uint64 {
+	b.mu.RLock()
+	obs := b.wsConnObservers
+	b.mu.RUnlock()
+
+	var connID uint64
+	for _, o := range obs {
+		if id := o.ObserveWebSocketConnection(e); id != 0 && connID == 0 {
+			connID = id
+		}
+	}
+	return connID
+}
+
+// EmitWebSocketFrame calls all WebSocketFrameObservers in registration order.
+// Runs synchronously to preserve per-connection frame ordering. Each observer
+// may return a modified payload — the last non-nil payload wins. The final
+// WebSocketFrameResult carries the payload to forward.
+func (b *Bus) EmitWebSocketFrame(e WebSocketFrameEvent) WebSocketFrameResult {
+	b.mu.RLock()
+	obs := b.wsFrameObservers
+	b.mu.RUnlock()
+
+	result := WebSocketFrameResult{Payload: e.Payload}
+	for _, o := range obs {
+		r := o.ObserveWebSocketFrame(e)
+		if r.Payload != nil {
+			result.Payload = r.Payload
+			e.Payload = r.Payload
+		}
+	}
+	return result
+}
+
+// EmitPluginLog calls all PluginLogObservers in registration order.
+// Runs synchronously.
+func (b *Bus) EmitPluginLog(e PluginLogEvent) {
+	b.mu.RLock()
+	obs := b.pluginLogObservers
+	b.mu.RUnlock()
+
+	for _, o := range obs {
+		o.ObservePluginLog(e)
+	}
+}
+
+// EmitSetPluginEnabled calls all PluginEnabledObservers in registration order.
+// Runs synchronously.
+func (b *Bus) EmitSetPluginEnabled(e SetPluginEnabledEvent) {
+	b.mu.RLock()
+	obs := b.pluginEnabledObservers
+	b.mu.RUnlock()
+
+	for _, o := range obs {
+		o.ObservePluginEnabled(e)
+	}
+}
+
+// EmitLoadPlugin calls all LoadPluginObservers in registration order.
+// Runs synchronously.
+func (b *Bus) EmitLoadPlugin(e LoadPluginEvent) {
+	b.mu.RLock()
+	obs := b.pluginLoadObservers
+	b.mu.RUnlock()
+
+	for _, o := range obs {
+		o.ObserveLoadPlugin(e)
+	}
+}
+
+// EmitProxyRestart calls all ProxyCommandObservers to restart on the given address.
+// Runs synchronously.
+func (b *Bus) EmitProxyRestart(e ProxyRestartEvent) {
+	b.mu.RLock()
+	obs := b.proxyCommandObservers
+	b.mu.RUnlock()
+
+	for _, o := range obs {
+		o.ObserveProxyRestart(e)
+	}
+}
+
+// EmitProxyStop calls all ProxyCommandObservers to stop the proxy.
+// Runs synchronously.
+func (b *Bus) EmitProxyStop(e ProxyStopEvent) {
+	b.mu.RLock()
+	obs := b.proxyCommandObservers
+	b.mu.RUnlock()
+
+	for _, o := range obs {
+		o.ObserveProxyStop(e)
+	}
+}