package metric

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

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 metricWriterFlag sync.Once

func NewMetric(mt MetricType, name string, help string, constLabel ...string) (writer MetricWriter) {
	metricWriterFlag.Do(func() {
		go mc.metricWriter()
	})

	hash := md5.New()
	hash.Write([]byte(name))

	var constLabels map[string]string
	if len(constLabel) > 0 {
		constLabels = make(map[string]string)
		for i := 0; i < len(constLabel); i = i + 2 {
			constLabels[constLabel[i]] = ""
			hash.Write([]byte(constLabel[i]))
		}

		for i := 1; i < len(constLabel); i = i + 2 {
			constLabels[constLabel[i-1]] = constLabel[i]
			hash.Write([]byte(constLabel[i]))
		}
	}

	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
}