fiatrates: Implement a fiat rate oracle for tatanka (#2736)

* fiatrates: implement a fiat rate oracle for tatanka

Signed-off-by: Philemon Ukane <ukanephilemon@gmail.com>

dex/fiatrates/fiatrates.go

@@ -91,11 +91,22 @@ func FetchCoinpaprikaRates(ctx context.Context, assets []*CoinpaprikaAsset, log
 }
 
 func getRates(ctx context.Context, url string, thing any) error {
+	return getRatesWithHeader(ctx, url, thing, nil)
+}
+
+func getRatesWithHeader(ctx context.Context, url string, thing any, header map[string]string) error {
+	ctx, cancel := context.WithTimeout(ctx, fiatRequestTimeout)
+	defer cancel()
+
 	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
 	if err != nil {
 		return err
 	}
 
+	for key, value := range header {
+		req.Header.Add(key, value)
+	}
+
 	resp, err := http.DefaultClient.Do(req)
 	if err != nil {
 		return err

dex/fiatrates/oracle.go

@@ -0,0 +1,282 @@
+package fiatrates
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"strings"
+	"sync"
+	"time"
+
+	"decred.org/dcrdex/dex"
+)
+
+const (
+	// FiatRateDataExpiry : Any data older than FiatRateDataExpiry will be
+	// discarded.
+	FiatRateDataExpiry = 60 * time.Minute
+
+	// averageRateRefreshInterval is how long it'll take before a fresh fiat
+	// average rate is calculated.
+	averageRateRefreshInterval = defaultRefreshInterval + time.Minute
+)
+
+// Oracle manages and retrieves fiat rate information from all enabled rate
+// sources.
+type Oracle struct {
+	log      dex.Logger
+	sources  []*source
+	ratesMtx sync.RWMutex
+	rates    map[string]*FiatRateInfo
+
+	listenersMtx sync.RWMutex
+	listeners    map[string]chan<- map[string]*FiatRateInfo
+}
+
+func NewFiatOracle(cfg Config, tickerSymbols string, log dex.Logger) (*Oracle, error) {
+	fiatOracle := &Oracle{
+		log:       log,
+		rates:     make(map[string]*FiatRateInfo),
+		sources:   fiatSources(cfg),
+		listeners: make(map[string]chan<- map[string]*FiatRateInfo),
+	}
+
+	tickers := strings.Split(tickerSymbols, ",")
+	for _, ticker := range tickers {
+		_, ok := dex.BipSymbolID(strings.ToLower(ticker))
+		if !ok {
+			return nil, fmt.Errorf("unknown asset %s", ticker)
+		}
+
+		// Initialize entry for this asset.
+		fiatOracle.rates[parseTicker(ticker)] = new(FiatRateInfo)
+	}
+
+	if len(fiatOracle.rates) == 0 {
+		return nil, errors.New("a minimum of one ticker is expected to configure fiat oracle")
+	}
+
+	return fiatOracle, nil
+}
+
+// tickers retrieves all tickers that data can be fetched for.
+func (o *Oracle) tickers() []string {
+	o.ratesMtx.RLock()
+	defer o.ratesMtx.RUnlock()
+	var tickers []string
+	for ticker := range o.rates {
+		tickers = append(tickers, ticker)
+	}
+	return tickers
+}
+
+// Rates returns the current fiat rates. Returns an empty map if there are no
+// valid rates.
+func (o *Oracle) Rates() map[string]*FiatRateInfo {
+	o.ratesMtx.RLock()
+	defer o.ratesMtx.RUnlock()
+	rates := make(map[string]*FiatRateInfo, len(o.rates))
+	for ticker, rate := range o.rates {
+		if rate.Value > 0 && time.Since(rate.LastUpdate) < FiatRateDataExpiry {
+			r := *rate
+			rates[ticker] = &r
+		}
+	}
+	return rates
+}
+
+// Run starts goroutines that refresh fiat rates every source.refreshInterval.
+// This should be called in a goroutine as it's blocking.
+func (o *Oracle) Run(ctx context.Context) {
+	var wg sync.WaitGroup
+	var sourcesEnabled int
+	for i := range o.sources {
+		fiatSource := o.sources[i]
+		if fiatSource.isDisabled() {
+			o.log.Infof("Fiat rate source %q is disabled...", fiatSource.name)
+			continue
+		}
+
+		o.fetchFromSource(ctx, fiatSource, &wg)
+		sourcesEnabled++
+
+		// Fetch rates now.
+		newRates, err := fiatSource.getRates(ctx, o.tickers(), o.log)
+		if err != nil {
+			o.log.Errorf("failed to retrieve rate from %s: %v", fiatSource.name, err)
+			continue
+		}
+
+		fiatSource.mtx.Lock()
+		fiatSource.rates = newRates
+		fiatSource.lastRefresh = time.Now()
+		fiatSource.mtx.Unlock()
+	}
+
+	// Calculate average fiat rate now.
+	o.calculateAverageRate()
+
+	if sourcesEnabled > 0 {
+		// Start a goroutine to generate an average fiat rate based on fresh
+		// data from all enabled sources. This is done every
+		// averageRateRefreshInterval.
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			ticker := time.NewTicker(averageRateRefreshInterval)
+			defer ticker.Stop()
+
+			for {
+				select {
+				case <-ctx.Done():
+					return
+				case <-ticker.C:
+					reActivatedSources := o.calculateAverageRate()
+					for _, index := range reActivatedSources {
+						s := o.sources[index]
+						// Start a new goroutine for this source.
+						o.fetchFromSource(ctx, s, &wg)
+					}
+				}
+			}
+		}()
+	}
+
+	wg.Wait()
+
+	o.listenersMtx.Lock()
+	for id, rateChan := range o.listeners {
+		close(rateChan) // we are done sending fiat rates
+		delete(o.listeners, id)
+	}
+	o.listenersMtx.Unlock()
+}
+
+// AddFiatRateListener adds a new fiat rate listener for the provided uniqueID.
+// Overrides existing rateChan if uniqueID already exists.
+func (o *Oracle) AddFiatRateListener(uniqueID string, ratesChan chan<- map[string]*FiatRateInfo) {
+	o.listenersMtx.Lock()
+	defer o.listenersMtx.Unlock()
+	o.listeners[uniqueID] = ratesChan
+}
+
+// RemoveFiatRateListener removes a fiat rate listener. no-op if there's no
+// listener for the provided uniqueID. The fiat rate chan will be closed to
+// signal to readers that we are done sending.
+func (o *Oracle) RemoveFiatRateListener(uniqueID string) {
+	o.listenersMtx.Lock()
+	defer o.listenersMtx.Unlock()
+	rateChan, ok := o.listeners[uniqueID]
+	if !ok {
+		return
+	}
+
+	delete(o.listeners, uniqueID)
+	close(rateChan) // we are done sending.
+}
+
+// notifyListeners sends the provided rates to all listener.
+func (o *Oracle) notifyListeners(rates map[string]*FiatRateInfo) {
+	o.listenersMtx.RLock()
+	defer o.listenersMtx.RUnlock()
+	for _, rateChan := range o.listeners {
+		rateChan <- rates
+	}
+}
+
+// calculateAverageRate is a shared function to support fiat average rate
+// calculations before and after averageRateRefreshInterval.
+func (o *Oracle) calculateAverageRate() []int {
+	var reActivatedSourceIndexes []int
+	newRatesInfo := make(map[string]*fiatRateAndSourceCount)
+	for i := range o.sources {
+		s := o.sources[i]
+		if s.isDisabled() {
+			if s.checkIfSourceCanReactivate() {
+				reActivatedSourceIndexes = append(reActivatedSourceIndexes, i)
+			}
+			continue
+		}
+
+		s.mtx.RLock()
+		sourceRates := s.rates
+		s.mtx.RUnlock()
+
+		for ticker, rate := range sourceRates {
+			if rate == 0 {
+				continue
+			}
+
+			info, ok := newRatesInfo[ticker]
+			if !ok {
+				info = new(fiatRateAndSourceCount)
+				newRatesInfo[ticker] = info
+			}
+
+			info.sources++
+			info.totalFiatRate += rate
+		}
+	}
+
+	now := time.Now()
+	broadcastRates := make(map[string]*FiatRateInfo)
+	o.ratesMtx.Lock()
+	for ticker := range o.rates {
+		rateInfo := newRatesInfo[ticker]
+		if rateInfo != nil {
+			newRate := rateInfo.totalFiatRate / float64(rateInfo.sources)
+			if newRate > 0 {
+				o.rates[ticker].Value = newRate
+				o.rates[ticker].LastUpdate = now
+				rate := *o.rates[ticker] // copy
+				broadcastRates[ticker] = &rate
+			}
+		}
+	}
+	o.ratesMtx.Unlock()
+
+	if len(broadcastRates) > 0 {
+		o.notifyListeners(broadcastRates)
+	}
+
+	return reActivatedSourceIndexes
+}
+
+// fetchFromSource starts a goroutine that retrieves fiat rate from the provided
+// source.
+func (o *Oracle) fetchFromSource(ctx context.Context, s *source, wg *sync.WaitGroup) {
+	wg.Add(1)
+	go func(s *source) {
+		defer wg.Done()
+		ticker := time.NewTicker(s.requestInterval)
+		defer ticker.Stop()
+
+		for {
+			select {
+			case <-ctx.Done():
+				return
+			case <-ticker.C:
+				if s.isDisabled() { // nothing to fetch.
+					continue
+				}
+
+				if s.hasTicker() && s.isExpired() {
+					s.deactivate()
+					o.log.Errorf("Fiat rate source %q has been disabled due to lack of fresh data. It will be re-enabled after %d hours.", s.name, reactivateDuration.Hours())
+					return
+				}
+
+				newRates, err := s.getRates(ctx, o.tickers(), o.log)
+				if err != nil {
+					o.log.Errorf("%s.getRates error: %v", s.name, err)
+					continue
+				}
+
+				s.mtx.Lock()
+				s.rates = newRates
+				s.lastRefresh = time.Now()
+				s.mtx.Unlock()
+			}
+		}
+	}(s)
+}