Tariffs: add optional hourly averaging (#24829)

tariff/proxy_cache.go

@@ -1,30 +1,177 @@
 package tariff
 
 import (
+	"context"
 	"crypto/sha256"
+	"errors"
 	"fmt"
+	"slices"
+	"sync"
+	"time"
 
 	"github.com/evcc-io/evcc/api"
-	"github.com/evcc-io/evcc/server/db/cache"
+	"github.com/evcc-io/evcc/util"
+	"github.com/jinzhu/now"
 )
 
-type cached struct {
-	Type  api.TariffType `json:"type"`
-	Rates api.Rates      `json:"rates"`
+// cachingProxy wraps a tariff with caching
+type cachingProxy struct {
+	mu   sync.Mutex
+	hash [32]byte
+
+	key    string
+	ctx    context.Context
+	typ    string
+	config map[string]any
+
+	cached *cached
+	tariff api.Tariff
 }
 
-func cacheKey(typ string, other map[string]any) string {
-	return fmt.Sprintf("%x", sha256.Sum256(fmt.Appendf(nil, "%s-%v", typ, other)))
+var _ api.Tariff = (*cachingProxy)(nil)
+
+// NewCachedFromConfig creates a proxy that controls tariff instantiation and caching
+func NewCachedFromConfig(ctx context.Context, typ string, other map[string]any) (api.Tariff, error) {
+	tariffType := typ
+	if typ == "template" {
+		if template, ok := other["template"].(string); ok {
+			tariffType = template
+		}
+	}
+
+	p := &cachingProxy{
+		ctx:    ctx,
+		typ:    typ,
+		config: other,
+		key:    tariffType + "-" + cacheKey(typ, other),
+	}
+
+	// check if we have cached data until end of tomorrow
+	data, err := p.cacheGet(untilEndOfTomorrow())
+	if err != nil {
+		// attempt to create a new instance
+		tariff, err := NewFromConfig(ctx, typ, other)
+		if err != nil {
+			// check if we have at least data for the next 24 hours
+			atLeast2hrs, err2 := p.cacheGet(for24hrs())
+			if err2 != nil {
+				// if not available, return error
+				return nil, err
+			}
+
+			// use cached data for the next 24 hours
+			data = atLeast2hrs
+		}
+
+		// if instance creation was successful, cache it, otherwise use cached 24hrs of data
+		if err == nil {
+			p.tariff = tariff
+		}
+	}
+
+	if data != nil {
+		log := util.NewLogger("tariff")
+		log.DEBUG.Printf("using cache: %s (start: %s, end: %s)", p.key,
+			data.Rates[0].Start.Local(), data.Rates[len(data.Rates)-1].End.Local(),
+		)
+	}
+
+	return p, nil
 }
 
-func cachePut(key string, typ api.TariffType, rates api.Rates) error {
-	return cache.Put(key, &cached{
-		Type:  typ,
-		Rates: rates,
-	})
+func (p *cachingProxy) createInstance() {
+	t, err := NewFromConfig(p.ctx, p.typ, p.config)
+	if err != nil {
+		t = &proxyError{err}
+	}
+
+	p.tariff = t
 }
 
-func cacheGet(key string) (*cached, error) {
-	var res cached
-	return &res, cache.Get(key, &res)
+// Rates returns cached data until underlying tariff is created, then delegates to tariff
+func (p *cachingProxy) Rates() (api.Rates, error) {
+	p.mu.Lock()
+	defer p.mu.Unlock()
+
+	if p.tariff == nil {
+		if res, err := p.cacheGet(for24hrs()); err == nil {
+			return res.Rates, nil
+		}
+
+		p.createInstance()
+	}
+
+	res, err := p.tariff.Rates()
+	if err != nil {
+		return nil, err
+	}
+
+	if p.dynamicTariff() {
+		err = p.cachePut(p.tariff.Type(), res)
+	}
+
+	return res, err
+}
+
+// Type returns the tariff type
+func (p *cachingProxy) Type() api.TariffType {
+	p.mu.Lock()
+	defer p.mu.Unlock()
+
+	if p.tariff == nil {
+		if res, err := p.cacheGet(for24hrs()); err == nil {
+			return res.Type
+		}
+
+		p.createInstance()
+	}
+
+	return p.tariff.Type()
+}
+
+func (p *cachingProxy) dynamicTariff() bool {
+	return slices.Contains([]api.TariffType{
+		api.TariffTypePriceForecast,
+		api.TariffTypeCo2,
+		api.TariffTypeSolar,
+	}, p.tariff.Type())
+}
+
+func (p *cachingProxy) cacheGet(until time.Time) (*cached, error) {
+	if p.cached == nil {
+		res, err := cacheGet(p.key)
+		if err != nil {
+			return nil, err
+		}
+
+		p.cached = res
+	}
+
+	if !ratesValid(p.cached.Rates, until) {
+		return nil, errors.New("not enough rates")
+	}
+
+	return p.cached, nil
+}
+
+func (p *cachingProxy) cachePut(typ api.TariffType, rates api.Rates) error {
+	hash := sha256.Sum256(fmt.Append(nil, rates))
+	if hash == p.hash {
+		return nil
+	}
+
+	p.hash = hash
+	return cachePut(p.key, typ, rates)
+}
+
+func for24hrs() time.Time {
+	return time.Now().Add(24 * time.Hour)
+}
+
+func untilEndOfTomorrow() time.Time {
+	return now.BeginningOfDay().AddDate(0, 0, 2)
+}
+
+func ratesValid(rr api.Rates, until time.Time) bool {
+	return len(rr) > 0 && !rr[len(rr)-1].End.Before(until)
 }