package main

import (
	"context"
	"encoding/json"
	"log"
	"os"
	"os/signal"
	"syscall"
	"time"

	"example.com/mqtt5-learning/internal/config"
	mqtt "example.com/mqtt5-learning/internal/mqtt"
)

func main() {
	// Convert a returned application error into a visible nonzero process exit.
	if err := run(); err != nil {
		log.Print(err)
		os.Exit(1)
	}
}

func run() error {
	// Load settings and bind cancellation to Ctrl+C or the container stop signal.
	cfg, err := config.Load(os.Args[1:])
	if err != nil {
		return err
	}
	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
	defer stop()
	// Build this device's topic namespace and bounded receive queue.
	base := "lab/v1/devices/" + cfg.MQTT.DeviceID
	inbox := make(chan mqtt.Message, 16)
	manager, err := mqtt.Start(ctx, cfg, []string{base + "/commands"}, inbox)
	if err != nil {
		return err
	}
	defer mqtt.Stop(manager)
	// Heartbeats are periodic; command handling remains active between ticks.
	ticker := time.NewTicker(3 * time.Second)
	defer ticker.Stop()
	for {
		// Handle cancellation, telemetry publication, and inbound commands together.
		select {
		case <-ctx.Done():
			return nil
		case <-ticker.C:
			payload, err := json.Marshal(struct {
				DeviceID string `json:"device_id"`
				Time     string `json:"time"`
			}{cfg.MQTT.DeviceID, time.Now().UTC().Format(time.RFC3339)})
			if err != nil {
				return err
			}
			if err := mqtt.Publish(ctx, manager, base+"/telemetry", payload); err != nil {
				log.Printf("heartbeat: %v", err)
			}
		case message := <-inbox:
			// Decode into a local command value only after rejecting retained messages.
			var command struct {
				ID      string `json:"id"`
				Command string `json:"command"`
			}
			if message.Retain {
				log.Print("ignoring retained command")
				continue
			}
			if err := json.Unmarshal(message.Payload, &command); err != nil || command.ID == "" || command.Command != "ping" {
				log.Print("ignoring malformed or unsupported command")
				continue
			}
			// Echo the command ID so the backend can associate this pong with its ping.
			response, err := json.Marshal(struct {
				ID       string `json:"id"`
				DeviceID string `json:"device_id"`
				Status   string `json:"status"`
			}{command.ID, cfg.MQTT.DeviceID, "pong"})
			if err != nil {
				return err
			}
			if err := mqtt.Publish(ctx, manager, base+"/responses", response); err != nil {
				log.Printf("response: %v", err)
			}
		}
	}
}