package metric

import (
	"crypto/md5"
	"encoding/binary"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"math"
	"os"

	"repositories.action2quare.com/ayo/gocommon/logger"
)

const (
	METRIC_HEAD_INLINE = byte(1)
	METRIC_TAIL_INLINE = byte(2)
)

type MetricType int

const (
	MetricCounter   = MetricType(1)
	MetricGuage     = MetricType(2)
	metric_key_size = 8
)

type MetricDescription struct {
	Key         string
	Type        MetricType
	Name        string            `json:",omitempty"`
	Help        string            `json:",omitempty"`
	ConstLabels map[string]string `json:",omitempty"`
}

type writeRequest struct {
	key string
	val float64
}

type metricCollection struct {
	writerChan chan *writeRequest
}

var mc = metricCollection{
	writerChan: make(chan *writeRequest, 100),
}

type MetricWriter func(float64)

func (mc *metricCollection) metricWriter() {
	// head + metric_key_size + 8byte + tail + cr = 19
	var buff [20]byte
	buff[0] = METRIC_HEAD_INLINE
	buff[17] = METRIC_TAIL_INLINE
	buff[18] = '\n'

	for req := range mc.writerChan {
		copy(buff[1:], []byte(req.key))
		binary.BigEndian.PutUint64(buff[9:], math.Float64bits(req.val))
		os.Stdout.Write(buff[:])
	}
}

var NewMetric func(MetricType, string, string, map[string]string) MetricWriter

func init() {
	NewMetric = func(MetricType, string, string, map[string]string) MetricWriter {
		return func(val float64) {}
	}

	ppid := os.Getppid()
	if parent, _ := os.FindProcess(ppid); parent != nil {
		filename := fmt.Sprintf(`/proc/%d/stat`, os.Getppid())
		if fn, err := os.ReadFile(filename); err == nil {
			if string(fn) == "houston" {
				logger.Println("metrics are activated for houston")
				go mc.metricWriter()
				NewMetric = newMetricImpl
			} else {
				logger.Println("metrics are NOT activated")
			}
		} else {
			logger.Println("metrics are NOT activated")
		}
	} else {
		logger.Println("metrics are NOT activated")
	}
}

func newMetricImpl(mt MetricType, name string, help string, constLabels map[string]string) (writer MetricWriter) {
	hash := md5.New()
	hash.Write([]byte(name))

	key := hex.EncodeToString(hash.Sum(nil))[:metric_key_size]
	temp, _ := json.Marshal(MetricDescription{
		Key:         key,
		Type:        mt,
		Name:        name,
		Help:        help,
		ConstLabels: constLabels,
	})

	writer = func(val float64) {
		mc.writerChan <- &writeRequest{
			key: key,
			val: val,
		}
	}

	output := append([]byte{METRIC_HEAD_INLINE}, temp...)
	output = append(output, METRIC_TAIL_INLINE, '\n')
	os.Stdout.Write(output)

	return
}