gocryptotrader/currency.go

package main

import (
	"net/http"
	"net/url"
	"fmt"
	"io/ioutil"
	"encoding/json"
	"strings"
	"time"
	"errors"
	"log"
)

type Rate struct {
	Id string `json:"id"`
	Name string `json:"Name"`
	Rate float64 `json:",string"`
	Date string `json:"Date"`
	Time string `json:"Time"`
	Ask float64 `json:",string"`
	Bid float64 `json:",string"`
}

type YahooJSONResponseInfo struct {
	Count int `json:"count"`
	Created time.Time `json:"created"`
	Lang string `json:"lang"`
}

type YahooJSONResponse struct {
	Query struct {
		YahooJSONResponseInfo
		Results struct {
			Rate []Rate `json:"rate"`
		}
	}
}

const (
	YAHOO_YQL_URL = "http://query.yahooapis.com/v1/public/yql"
	YAHOO_DATABASE = "store://datatables.org/alltableswithkeys"
	CURRENCIES = "USD,CNY,AUD,EUR"

)

var (
	CurrencyStore YahooJSONResponse
	ErrCurrencyDataNotFetched = errors.New("Yahoo currency data has not been fetched yet.")
	ErrCurrencyNotFound = errors.New("Unable to find specified currency.")
)

func MakeCurrencyPairs() (string) {
	currencies := strings.Split(CURRENCIES, ",")
	pairs := ""
	count := len(currencies)
	for i := 0; i < count; i++ {
		currency := currencies[i]
		for j := 0; j < count; j++ {
			if currency != currencies[j] {
				pairs += currency + currencies[j] + ","
			}
		}
	}
	return pairs[0:len(pairs)-1]
}

func ConvertCurrency(amount float64, from, to string) (float64, error) {
	if CurrencyStore.Query.YahooJSONResponseInfo.Count == 0 {
		return 0, ErrCurrencyDataNotFetched
	}

	currency := strings.ToUpper(from + to)
	for i := 0; i < CurrencyStore.Query.YahooJSONResponseInfo.Count; i++ {
		if CurrencyStore.Query.Results.Rate[i].Id == currency {
			return amount * CurrencyStore.Query.Results.Rate[i].Rate, nil
		}
	}
	return 0, ErrCurrencyNotFound
}

func QueryYahooCurrencyValues() (error) {
	currencyPairs := MakeCurrencyPairs()
	log.Printf("Supported currency pairs: %s\n", currencyPairs)

	values := url.Values{}
	values.Set("q", fmt.Sprintf("SELECT * from yahoo.finance.xchange WHERE pair in (\"%s\")", currencyPairs))
	values.Set("format", "json")
	values.Set("env", YAHOO_DATABASE)
	path := YAHOO_YQL_URL+"?"+values.Encode()
	log.Println("Sending request to: " + path)
	req, err := http.NewRequest("GET", path, strings.NewReader(""))

	if err != nil {
		return err
	}

	req.Header.Add("Content-Type", "application/x-www-form-urlencoded")

	client := &http.Client{}
	resp, err := client.Do(req)

	if err != nil {
		return err
	}

	contents, _ := ioutil.ReadAll(resp.Body)
	err = json.Unmarshal(contents, &CurrencyStore)

	if err != nil {
		return err
	}

	resp.Body.Close()
	return nil
}