knowyt/server/handler/sync.go

package handler

import (
	"encoding/json"
	"fmt"
	"github.com/imkira/go-observer"
	"net/http"
	"strconv"
)

type Value struct {
	VersionRef int `json:"version"`
}

func SyncFactory(obs observer.Property) HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		versionRef, err := strconv.Atoi(r.URL.Query().Get("v"))
		if err != nil {
			versionRef = -1
		}

		stream := obs.Observe()
		var value Value
		for {
			value = stream.Value().(Value)
			if value.VersionRef >= versionRef {
				break
			}

			select {
			case <-stream.Changes():
				stream.Next()
			}
		}

		jsonString, _ := json.MarshalIndent(value, "", "  ")
		w.Header().Add("Content-Type", "application/json")
		fmt.Fprintf(w, string(jsonString))
	}
}