package mqtt

import (
	"encoding/json"
	"time"
)

// Envelope MQTT 消息通用外层（协议文档 §4）
//
//	{
//	  "requestId": "req-uuid" | null,
//	  "dockId":    "dock-...",
//	  "droneSn":   "..." | null,
//	  "timestamp": 1784700000000,
//	  "payload":   { ... }
//	}
type Envelope struct {
	RequestID string          `json:"requestId"`
	EventID   string          `json:"eventId"`
	Version   int64           `json:"version"`
	DockID    string          `json:"dockId"`
	DroneSN   string          `json:"droneSn"`
	Timestamp int64           `json:"timestamp"`
	Payload   json.RawMessage `json:"payload"`
}

// ParseEnvelope 解析通用外层；payload 缺失（无外层的历史扁平消息）时把整个消息体当作 payload。
func ParseEnvelope(data []byte) *Envelope {
	var env Envelope
	if err := json.Unmarshal(data, &env); err != nil {
		return &Envelope{Payload: data}
	}
	if len(env.Payload) == 0 {
		env.Payload = data
	}
	return &env
}

// NewEnvelope 构造下行外层；payload 为业务字段（内部自动 marshal），timestamp 取当前毫秒。
func NewEnvelope(requestID, dockID, droneSN string, payload any) *Envelope {
	var raw json.RawMessage
	if payload != nil {
		if b, err := json.Marshal(payload); err == nil {
			raw = b
		}
	}
	return &Envelope{
		RequestID: requestID,
		DockID:    dockID,
		DroneSN:   droneSN,
		Timestamp: time.Now().UnixMilli(),
		Payload:   raw,
	}
}