package broker

import (
	"encoding/json"
	"sync"
)

// Event is a JSON-serialisable message pushed to WebSocket clients.
type Event struct {
	Type    string `json:"type"`
	AgentID string `json:"agent_id,omitempty"`
	Payload any    `json:"payload"`
}

type subscriber chan []byte

// Broker fan-outs events to all registered WebSocket subscribers.
type Broker struct {
	mu   sync.RWMutex
	subs map[subscriber]struct{}
}

func New() *Broker {
	return &Broker{subs: make(map[subscriber]struct{})}
}

func (b *Broker) Subscribe() subscriber {
	ch := make(subscriber, 32)
	b.mu.Lock()
	b.subs[ch] = struct{}{}
	b.mu.Unlock()
	return ch
}

func (b *Broker) Unsubscribe(ch subscriber) {
	b.mu.Lock()
	delete(b.subs, ch)
	b.mu.Unlock()
	close(ch)
}

func (b *Broker) Publish(evt Event) {
	data, err := json.Marshal(evt)
	if err != nil {
		return
	}
	b.mu.RLock()
	defer b.mu.RUnlock()
	for ch := range b.subs {
		select {
		case ch <- data:
		default: // drop if subscriber is slow
		}
	}
}