package control

import (
	"sync"
	"time"

	offpkg "github.com/jan/fm-rds-tx/internal/offline"
)

type TelemetryMessage struct {
	Type string                     `json:"type"`
	TS   time.Time                  `json:"ts"`
	Seq  uint64                     `json:"seq"`
	Data *offpkg.MeasurementSnapshot `json:"data,omitempty"`
}

type telemetrySubscriber struct {
	ch chan TelemetryMessage
}

type TelemetryHub struct {
	mu          sync.Mutex
	subscribers map[*telemetrySubscriber]struct{}
}

func NewTelemetryHub() *TelemetryHub {
	return &TelemetryHub{subscribers: make(map[*telemetrySubscriber]struct{})}
}

func (h *TelemetryHub) Subscribe() (*telemetrySubscriber, func()) {
	sub := &telemetrySubscriber{ch: make(chan TelemetryMessage, 1)}
	h.mu.Lock()
	h.subscribers[sub] = struct{}{}
	h.mu.Unlock()
	return sub, func() {
		h.mu.Lock()
		if _, ok := h.subscribers[sub]; ok {
			delete(h.subscribers, sub)
			close(sub.ch)
		}
		h.mu.Unlock()
	}
}

func (h *TelemetryHub) PublishMeasurement(snapshot *offpkg.MeasurementSnapshot) {
	if h == nil || snapshot == nil {
		return
	}
	msg := TelemetryMessage{
		Type: "measurement",
		TS:   snapshot.Timestamp,
		Seq:  snapshot.Sequence,
		Data: snapshot,
	}

	h.mu.Lock()
	subs := make([]*telemetrySubscriber, 0, len(h.subscribers))
	for sub := range h.subscribers {
		subs = append(subs, sub)
	}
	h.mu.Unlock()

	for _, sub := range subs {
		select {
		case sub.ch <- msg:
		default:
			select {
			case <-sub.ch:
			default:
			}
			select {
			case sub.ch <- msg:
			default:
			}
		}
	}
}