stock.go

/*
  Package stock allows to use yahoo finance api to get historical quotes data
  It uses YQL pointing to yahoo.finance.historicaldata to get the necessary info
*/
package yahoofinance

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

const (
	YQL_HISTORICAL_DATA = "select Date, Close from yahoo.finance.historicaldata where symbol=\"%s\" and startDate=\"%s\" and endDate=\"%s\""
	YQL_WEB_SERVICE_URL = "http://query.yahooapis.com/v1/public/yql?format=json&diagnostics=false&callback=&%s"
)

// Aux struct to unmarshal API Response
type rootResult struct {
	Query queryInfo
}

// Aux struct to unmarshal API Response
type queryInfo struct {
	Results resultsInfo
}

// Aux struct to unmarshal API Response
type resultsInfo struct {
	Quote []quoteInfo
}

// Aux struct to unmarshal API Response
type quoteInfo struct {
	Close string
	Date  string
}

type Quote struct {
	Close float64
	Date  time.Time
	Avg   float64
	Top   float64
	Bottom float64
}

// Set the correct data types to allow to work with quotes and reverse order
func normalize(quotesOriginal []quoteInfo) (quotes []Quote) {
        var length = len(quotesOriginal)
	quotes = make([]Quote, length)
	for i, q := range quotesOriginal {
		close, err := strconv.ParseFloat(q.Close, 64)
		perror(err)
		date, err := time.Parse("2006-01-02", q.Date)
		perror(err)
		quotes[length - i - 1] = Quote{Close: close, Date: date}
	}
	return
}

func perror(err error) {
	if err != nil {
		panic(err)
	}
}

func HistoricalPrices(symbol string, start, end time.Time) []Quote {
	yql := fmt.Sprintf(YQL_HISTORICAL_DATA, symbol, start.Format("2006-01-02"), end.Format("2006-01-02")) // Replace dynamic info for q Param
	v := url.Values{}                                                                                     //I use v to hack reserved symbols to be encoded before API call
	v.Set("q", yql)
	v.Add("env", "store://datatables.org/alltableswithkeys")
	yqlUrl := fmt.Sprintf(YQL_WEB_SERVICE_URL, v.Encode())

	resp, err := http.Get(yqlUrl) //Call to Yahoo API
	perror(err)
	defer resp.Body.Close()                //Automatic close resp after use it
	body, err := ioutil.ReadAll(resp.Body) //Get reponse
	perror(err)

	var data rootResult
	err = json.Unmarshal(body, &data) //Fill aux struct with API response
	perror(err)

	return normalize(data.Query.Results.Quote) //Return quotes
}