package handler

import (
	"encoding/json"
	"fmt"
	"sync"
)

// Hub 按 runId 分组的 SSE 订阅中心
type Hub struct {
	mu   sync.Mutex
	subs map[string]map[chan []byte]struct{}
}

func NewHub() *Hub {
	return &Hub{subs: make(map[string]map[chan []byte]struct{})}
}

func (h *Hub) Subscribe(runId string) chan []byte {
	ch := make(chan []byte, 64)
	h.mu.Lock()
	defer h.mu.Unlock()
	if h.subs[runId] == nil {
		h.subs[runId] = make(map[chan []byte]struct{})
	}
	h.subs[runId][ch] = struct{}{}
	return ch
}

func (h *Hub) Unsubscribe(runId string, ch chan []byte) {
	h.mu.Lock()
	defer h.mu.Unlock()
	if set := h.subs[runId]; set != nil {
		delete(set, ch)
		if len(set) == 0 {
			delete(h.subs, runId)
		}
	}
}

// Publish 向 runId 的所有订阅者推送一条 SSE 帧（event + data）
func (h *Hub) Publish(runId, event string, payload any) {
	data, err := json.Marshal(payload)
	if err != nil {
		return
	}
	frame := []byte(fmt.Sprintf("event: %s\ndata: %s\n\n", event, data))
	h.mu.Lock()
	defer h.mu.Unlock()
	for ch := range h.subs[runId] {
		select {
		case ch <- frame:
		default: // 订阅者消费过慢则丢弃，避免阻塞模拟引擎
		}
	}
}