package cdp

import (
	"encoding/hex"
	"strconv"
	"strings"
	"time"
)

// EndpointMessage is a generic message
type EndpointMessage struct {
	Reports []EndpointMessageReport `json:"reports"`
}

// EndpointMessageReportTime for custom time
type EndpointMessageReportTime struct {
	time.Time
}

// ResourcePathUplinkMsgData is the resource path for uplink messages
const ResourcePathUplinkMsgData = "uplinkMsg/0/data"

// EndpointMessageReport is a single device report
type EndpointMessageReport struct {
	SerialNumber   SerialNumber              `json:"serialNumber"`
	Timestamp      EndpointMessageReportTime `json:"timestamp"`
	SubscriptionID string                    `json:"subscriptionId"`
	ResourcePath   string                    `json:"resourcePath"`
	Value          string                    `json:"value"`
}

// UnmarshalJSON for converting from UNIX milliseconds to time.Time
func (t *EndpointMessageReportTime) UnmarshalJSON(b []byte) error {
	ms, err := strconv.Atoi(string(b))
	if err != nil {
		return err
	}
	s := ms / 1e3
	ns := (ms - s*1e3) * 1e6
	t.Time = time.Unix(int64(s), int64(ns))
	return nil
}

// SerialNumber attribute from EndpointMessageReport
type SerialNumber string

// IMEI calculates the IMEI from the SerialNumber it returns an empty string when not valid
func (sn SerialNumber) IMEI() string {
	const imeiPrefix = "IMEI:"
	if strings.HasPrefix(string(sn), imeiPrefix) {
		return strings.TrimPrefix(string(sn), imeiPrefix)
	}
	return ""
}

//NewEndpointMessage creates a new endpoint message containing a single report.
//The single report wraps the CRM payload given.
func NewEndpointMessage(payload []byte, timestamp time.Time) *EndpointMessageReport {
	hexPayload := hex.EncodeToString(payload)

	return &EndpointMessageReport{
		SerialNumber:   "",
		Timestamp:      EndpointMessageReportTime{timestamp},
		SubscriptionID: "",
		ResourcePath:   "",
		Value:          hexPayload,
	}
}