pow.go

package main

import (
        "crypto/sha256"
        "encoding/hex"
        "encoding/json"
        "fmt"
        "io"
        "log"
        "net/http"
        "os"
        "strconv"
        "strings"
        "sync"
        "time"

        "github.com/davecgh/go-spew/spew"
        "github.com/gorilla/mux"
        "github.com/joho/godotenv"
)



/* Decalres the variables */
const difficulty = 1
type Block struct {
        Index      int
        Timestamp  string
        BPM        int
        Hash       string
        PrevHash   string
        Difficulty int
        Nonce      string
}
var Blockchain []Block

type Message struct {
        BPM int
}
var mutex = &sync.Mutex{}

/* create the webserver using Mux Router and the get the PORT ADDR ="8080" from the .env file*/
func run() error {
	mux := makeMuxRouter()
	httpAddr := os.Getenv("ADDR")
	log.Println("Listening on ", os.Getenv("ADDR"))
	s := &http.Server{
			Addr:           ":" + httpAddr,
			Handler:        mux,
			ReadTimeout:    10 * time.Second,
			WriteTimeout:   10 * time.Second,
			MaxHeaderBytes: 1 << 20,
	}

	if err := s.ListenAndServe(); err != nil {
			return err
	}

	return nil
}

/* Its web server call method to get the blocks details and for wrting the blocks */
func makeMuxRouter() http.Handler {
	muxRouter := mux.NewRouter()
	muxRouter.HandleFunc("/", handleGetBlockchain).Methods("GET")
	muxRouter.HandleFunc("/", handleWriteBlock).Methods("POST")
	return muxRouter
}


/* Get the all the blocks */
func handleGetBlockchain(w http.ResponseWriter, r *http.Request) {
	bytes, err := json.MarshalIndent(Blockchain, "", "  ")
	if err != nil {
			http.Error(w, err.Error(), http.StatusInternalServerError)
			return
	}
	io.WriteString(w, string(bytes))
}

func respondWithJSON(w http.ResponseWriter, r *http.Request, code int, payload interface{}) {
	w.Header().Set("Content-Type", "application/json")
	response, err := json.MarshalIndent(payload, "", "  ")
	if err != nil {
			w.WriteHeader(http.StatusInternalServerError)
			w.Write([]byte("HTTP 500: Internal Server Error"))
			return
	}
	w.WriteHeader(code)
	w.Write(response)
}

/* Write Block */
func handleWriteBlock(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("Content-Type", "application/json")
	var m Message

	decoder := json.NewDecoder(r.Body)
	if err := decoder.Decode(&m); err != nil {
			respondWithJSON(w, r, http.StatusBadRequest, r.Body)
			return
	}   
	defer r.Body.Close()

	//ensure atomicity when creating new block
	mutex.Lock()
	newBlock := generateBlock(Blockchain[len(Blockchain)-1], m.BPM)
	mutex.Unlock()

	if isBlockValid(newBlock, Blockchain[len(Blockchain)-1]) {
			Blockchain = append(Blockchain, newBlock)
			spew.Dump(Blockchain)
	}   

	respondWithJSON(w, r, http.StatusCreated, newBlock)

}

/* Check the created block is valid*/
func isBlockValid(newBlock, oldBlock Block) bool {
	if oldBlock.Index+1 != newBlock.Index {
			return false
	}

	if oldBlock.Hash != newBlock.PrevHash {
			return false
	}

	if calculateHash(newBlock) != newBlock.Hash {
			return false
	}

	return true
}

/* calculateHash create the current block hash*/
func calculateHash(block Block) string {
	record := strconv.Itoa(block.Index) + block.Timestamp + strconv.Itoa(block.BPM) + block.PrevHash + block.Nonce
	h := sha256.New()
	h.Write([]byte(record))
	hashed := h.Sum(nil)
	return hex.EncodeToString(hashed)
}


/* isHashValid check the created hash and diffculty level */
func isHashValid(hash string, difficulty int) bool {
	prefix := strings.Repeat("0", difficulty)
	return strings.HasPrefix(hash, prefix)
}


/* Genetrate function require oldblocks value and BPM value  */
/* Calculate generate the nonce */
func generateBlock(oldBlock Block, BPM int) Block {
	var newBlock Block

	t := time.Now()

	newBlock.Index = oldBlock.Index + 1
	newBlock.Timestamp = t.String()
	newBlock.BPM = BPM
	newBlock.PrevHash = oldBlock.Hash
	newBlock.Difficulty = difficulty

	for i := 0; ; i++ {
			hex := fmt.Sprintf("%x", i)
			newBlock.Nonce = hex
			if !isHashValid(calculateHash(newBlock), newBlock.Difficulty) {
					fmt.Println(calculateHash(newBlock), " do more work!")
					time.Sleep(time.Second)
					continue
			} else {
					fmt.Println(calculateHash(newBlock), " work done!")
					newBlock.Hash = calculateHash(newBlock)
					break
			}

	}
	return newBlock
}


/* Function main create the genesisBlock and (run) function to evoke the Webserver */
func main() {
	err := godotenv.Load()
	if err != nil {
			log.Fatal(err)
	}   

	go func() {
			t := time.Now()
			genesisBlock := Block{}
			genesisBlock = Block{0, t.String(), 0, calculateHash(genesisBlock), "", difficulty, ""} 
			spew.Dump(genesisBlock)

			mutex.Lock()
			Blockchain = append(Blockchain, genesisBlock)
			mutex.Unlock()
	}() 
	log.Fatal(run())

}