usd2brl.go

package main

import (
    "encoding/json"
    "fmt"
    "io/ioutil"
    "log"
    "net/http"
    "os"
    "strconv"
    "time"
)

type RequestResult struct {
    Query struct {
        Count   int    `json:"count"`
        Created string `json:"created"`
        Lang    string `json:"lang"`
        Results string `json:"results"`
    } `json:"query"`
}

const URL = "http://query.yahooapis.com/v1/public/yql?q=select%20*%20from%20html%20where%20url%3D%27www.google.com%2Ffinance%2Fconverter%3Fa%3D1%26from%3DUSD%26to%3DBRL%27%20and%20xpath%3D%27%2F%2F*%5B%40id%3D\"currency_converter_result\"%5D%2Fspan%2Ftext()%27&format=json&callback="

// Make the request and return the content of body
func Checker() (string, error) {
    if resp, err := http.Get(URL); err != nil {
        return "", err
    } else {
        defer resp.Body.Close()
        if contents, err := ioutil.ReadAll(resp.Body); err != nil {
            return "", err
        } else {
            return string(contents), nil
        }
    }
}

// Parses the json and get only the value Results
func ParseJSON(jsonResult string) string {
    log.Println("JSON REQUEST", jsonResult)
    result := new(RequestResult)

    err := json.Unmarshal([]byte(jsonResult), result)

    if err != nil {
        log.Println(err)
    }

    log.Println(result)

    return result.Query.Results
}

// Checking the webservice each 30 minutes
func Pool() chan string {
    ch := make(chan string)
    go func() {
        for {
            if res, err := Checker(); err == nil {
                if jsonRes := ParseJSON(res); jsonRes != "" {
                    ch <- jsonRes
                    time.Sleep(time.Minute * 30)
                }
            }
        }
    }()
    return ch
}

func main() {
    // Get the first value
    checkerPool := Pool()
    latestResult := <-checkerPool

    // To deploy at heroku :D
    env := os.Getenv("GO_ENV")
    host := "127.0.0.1"
    port := 9000

    if env == "PRODUCTION" {
        host = ""
        port, _ = strconv.Atoi(os.Getenv("PORT"))
    }

    address := fmt.Sprintf("%s:%d", host, port)
    log.Println("Ready to serve at", address)

    http.HandleFunc("/", func(rw http.ResponseWriter, req *http.Request) {
        log.Println(len(checkerPool))

        // Check if chan res a value waiting
        if len(checkerPool) >= 1 {
            latestResult = <-checkerPool
        }

        rw.Write([]byte(latestResult))
    })

    if err := http.ListenAndServe(address, nil); err != nil {
        log.Fatal("Failed to serve to address", address, err)
    }
}