// Package service 提供管理系统/App 与 IoT 设备链路之间的稳定上下行 HTTP 边界。
package service

import (
	"bytes"
	"context"
	"crypto/subtle"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"time"

	"git.apinb.com/heqiapp/platforms/backend/iot-gateway/internal/config"
)

type Service struct {
	cfg    config.Config
	client *http.Client
	http   *http.Server
}
type Command struct {
	Identity       string    `json:"identity"`
	IdempotencyKey string    `json:"idempotency_key"`
	DeviceID       string    `json:"device_id"`
	Action         string    `json:"action"`
	ExpiresAt      time.Time `json:"expires_at"`
	KeyID          byte      `json:"key_id"`
	DeviceKind     byte      `json:"device_kind"`
	DeviceType     byte      `json:"device_type"`
	DeviceModel    [3]byte   `json:"device_model"`
	Controller     byte      `json:"controller"`
	Loop           byte      `json:"loop"`
	Component      byte      `json:"component"`
}
type deviceEnvelope struct {
	Type, Topic, DeviceID, ReceivedAt, PayloadHex string
	Frame                                         json.RawMessage `json:"frame,omitempty"`
}

func New(cfg config.Config) *Service {
	return &Service{cfg: cfg, client: &http.Client{Timeout: 12 * time.Second}}
}
func (s *Service) Run(ctx context.Context) error {
	mux := http.NewServeMux()
	mux.HandleFunc("/health", func(w http.ResponseWriter, _ *http.Request) { w.WriteHeader(http.StatusNoContent) })
	mux.HandleFunc("/v1/device-commands", s.commands)
	mux.HandleFunc("/internal/v1/device-messages", s.deviceMessage)
	s.http = &http.Server{Addr: s.cfg.HTTP.Address, Handler: mux, ReadHeaderTimeout: 5 * time.Second}
	go func() {
		<-ctx.Done()
		shutdown, cancel := context.WithTimeout(context.Background(), 10*time.Second)
		defer cancel()
		_ = s.http.Shutdown(shutdown)
	}()
	err := s.http.ListenAndServe()
	if err == http.ErrServerClosed {
		return nil
	}
	return err
}
func (s *Service) commands(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodPost {
		http.Error(w, "method not allowed", 405)
		return
	}
	if !s.authorized(r) {
		http.Error(w, "unauthorized", 401)
		return
	}
	var cmd Command
	if err := json.NewDecoder(io.LimitReader(r.Body, 64<<10)).Decode(&cmd); err != nil {
		http.Error(w, "invalid json", 400)
		return
	}
	if cmd.Identity == "" || cmd.IdempotencyKey == "" || cmd.DeviceID == "" || (cmd.Action != "open_valve" && cmd.Action != "close_valve") {
		http.Error(w, "invalid command", 422)
		return
	}
	if cmd.ExpiresAt.IsZero() {
		cmd.ExpiresAt = time.Now().Add(30 * time.Second)
	}
	if time.Now().After(cmd.ExpiresAt) {
		http.Error(w, "command expired", 422)
		return
	}
	status, packet, err := s.dispatch(r.Context(), cmd)
	if err != nil {
		writeJSON(w, http.StatusBadGateway, map[string]any{"identity": cmd.Identity, "status": "dispatch_failed", "error_code": "IOT_DISPATCH_FAILED"})
		return
	}
	writeJSON(w, http.StatusAccepted, map[string]any{"identity": cmd.Identity, "status": status, "packet_number": packet})
}
func (s *Service) deviceMessage(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodPost || !s.authorized(r) {
		http.Error(w, "unauthorized", 401)
		return
	}
	data, err := io.ReadAll(io.LimitReader(r.Body, 1<<20))
	if err != nil {
		http.Error(w, "invalid body", 400)
		return
	}
	var envelope deviceEnvelope
	if json.Unmarshal(data, &envelope) != nil || envelope.ReceivedAt == "" {
		http.Error(w, "invalid envelope", 422)
		return
	}
	request, err := http.NewRequestWithContext(r.Context(), http.MethodPost, s.cfg.Upstream.PlatformAPIURL+"/heqi/internal/v1/iot/device-messages", bytes.NewReader(data))
	if err != nil {
		http.Error(w, "upstream request failed", 502)
		return
	}
	request.Header.Set("Content-Type", "application/json")
	request.Header.Set("X-Heqi-Iot-Token", s.cfg.Upstream.Token)
	response, err := s.client.Do(request)
	if err != nil {
		http.Error(w, "platform api unavailable", 502)
		return
	}
	defer response.Body.Close()
	if response.StatusCode >= 300 {
		http.Error(w, "platform api rejected message", 502)
		return
	}
	w.WriteHeader(http.StatusAccepted)
}
func (s *Service) dispatch(ctx context.Context, cmd Command) (string, uint16, error) {
	data, _ := json.Marshal(cmd)
	request, err := http.NewRequestWithContext(ctx, http.MethodPost, s.cfg.Upstream.IoTServerURL+"/internal/v1/commands", bytes.NewReader(data))
	if err != nil {
		return "", 0, err
	}
	request.Header.Set("Content-Type", "application/json")
	request.Header.Set("X-Heqi-Iot-Token", s.cfg.Upstream.Token)
	response, err := s.client.Do(request)
	if err != nil {
		return "", 0, err
	}
	defer response.Body.Close()
	if response.StatusCode != http.StatusAccepted {
		body, _ := io.ReadAll(io.LimitReader(response.Body, 4096))
		return "", 0, fmt.Errorf("iot server %d: %s", response.StatusCode, body)
	}
	var result struct {
		Status       string `json:"status"`
		PacketNumber uint16 `json:"packet_number"`
	}
	if err = json.NewDecoder(response.Body).Decode(&result); err != nil {
		return "", 0, err
	}
	return result.Status, result.PacketNumber, nil
}
func (s *Service) authorized(r *http.Request) bool {
	value := r.Header.Get("X-Heqi-Iot-Token")
	expected := s.cfg.HTTP.InternalToken
	return len(value) == len(expected) && subtle.ConstantTimeCompare([]byte(value), []byte(expected)) == 1
}
func writeJSON(w http.ResponseWriter, status int, value any) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	_ = json.NewEncoder(w).Encode(value)
}