mycurrencynet/mycurrencynet.go

package mycurrencynet

import (
	"bytes"
	"fmt"
	"strconv"
	"strings"
	"sync"
	"time"

	"github.com/PuerkitoBio/goquery"
	"github.com/go-resty/resty/v2"

	"git.gensokyo.cafe/kkyy/mycurrencynet/iso"
)

var (
	updateUrl = "https://www.mycurrency.net/=US"

	client = resty.New()
)

type Currency struct {
	Code      string
	Name      string
	Countries []string // TODO fill this
	Rate      float64
}

func (c *Currency) To(t *Currency) float64 {
	if c == nil || t == nil || c.Rate == 0 {
		return 0
	}
	return t.Rate / c.Rate
}

func init() {
	client.
		SetTimeout(5*time.Second).
		SetRetryCount(1).
		SetHeader("User-Agent", "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Firefox/102.0")
}

func fetch() (html []byte, err error) {
	resp, err := client.R().Get(updateUrl)
	if err != nil {
		return
	}
	if resp.StatusCode() != 200 {
		return nil, fmt.Errorf("HTTP %d %s: %q", resp.StatusCode(), resp.Status(), resp.String())
	}

	return resp.Body(), nil
}

func parse(body []byte) (map[string]*Currency, error) {
	doc, err := goquery.NewDocumentFromReader(bytes.NewReader(body))
	if err != nil {
		return nil, err
	}
	ret := make(map[string]*Currency)

	doc.Find("tr.country").Each(func(_ int, s *goquery.Selection) {
		var (
			c    Currency
			isoC iso.ISOCurrency
			ok   bool
			err  error
			rate string
		)
		if c.Code, ok = s.Attr("data-currency-code"); !ok {
			return
		}
		if _, exist := ret[c.Code]; exist {
			return
		}

		if isoC, ok = iso.Currencies[c.Code]; !ok {
			return
		}
		c.Name = isoC.Name

		if rate, ok = s.Find(".money[data-rate]").Attr("data-rate"); !ok {
			return
		}
		if c.Rate, err = strconv.ParseFloat(rate, 64); err != nil {
			return
		}

		ret[c.Code] = &c
	})

	return ret, nil
}

func Fetch() (map[string]*Currency, error) {
	html, err := fetch()
	if err != nil {
		return nil, err
	}
	rates, err := parse(html)
	if err != nil {
		return nil, err
	}
	// add base currency
	rates["USD"] = &Currency{
		Code: "USD",
		Name: iso.Currencies["USD"].Name,
		Rate: 1,
	}
	return rates, nil
}

type MyCurrencyNet struct {
	rates      map[string]*Currency
	lastUpdate time.Time

	mu sync.RWMutex
}

func New() *MyCurrencyNet {
	return &MyCurrencyNet{}
}

func (m *MyCurrencyNet) Get(codes ...string) ([]*Currency, error) {
	if m.rates == nil {
		return nil, fmt.Errorf("not initialized.")
	}

	ret := make([]*Currency, len(codes))
	m.mu.RLock()
	defer m.mu.RUnlock()

	var (
		errors []string
		err    error = nil
	)
	for i, code := range codes {
		rate, ok := m.rates[strings.ToUpper(code)]
		if !ok {
			errors = append(errors, "unknown currency code: "+code)
			continue
		}
		var cp Currency = *rate
		ret[i] = &cp
	}
	if len(errors) > 0 {
		err = fmt.Errorf(strings.Join(errors, ", "))
	}
	return ret, err
}

func (m *MyCurrencyNet) Update() error {
	currencies, err := Fetch()
	if err != nil {
		return err
	}

	m.mu.Lock()
	defer m.mu.Unlock()
	m.rates = currencies
	m.lastUpdate = time.Now()

	return nil
}

func (m *MyCurrencyNet) UpdateEvery(interval time.Duration, onErr func(error), onSuccess func()) {
	for {
		<-time.After(interval)

		if err := m.Update(); err != nil {
			if onErr != nil {
				onErr(err)
			}
		} else {
			if onSuccess != nil {
				onSuccess()
			}
		}
	}
}