feat(eventstore): sdk (#39)

* sdk

* fix(sdk): return correct error type

* AppendEventError instead of Aggregater error

* fix(tests): tests

* fix(tests): wantErr to is error func

internal/eventstore/sdk/sdk.go

@@ -0,0 +1,72 @@
+package sdk
+
+import (
+	"context"
+
+	"github.com/caos/zitadel/internal/errors"
+	"github.com/caos/zitadel/internal/eventstore/models"
+	es_models "github.com/caos/zitadel/internal/eventstore/models"
+)
+
+type filterFunc func(context.Context, *es_models.SearchQuery) ([]*es_models.Event, error)
+type appendFunc func(...*es_models.Event) error
+type aggregateFunc func(context.Context) (*es_models.Aggregate, error)
+type pushFunc func(context.Context, ...*es_models.Aggregate) error
+
+func Filter(ctx context.Context, filter filterFunc, appender appendFunc, query *es_models.SearchQuery) error {
+	events, err := filter(ctx, query)
+	if err != nil {
+		return err
+	}
+	if len(events) == 0 {
+		return errors.ThrowNotFound(nil, "EVENT-8due3", "no events found")
+	}
+	err = appender(events...)
+	if err != nil{
+		return ThrowAppendEventError(err, "SDK-awiWK", "appender failed")
+	}
+	return nil
+}
+
+// Push creates the aggregates from aggregater
+// and pushes the aggregates to the given pushFunc
+// the given events are appended by the appender
+func Push(ctx context.Context, push pushFunc, appender appendFunc, aggregaters ...aggregateFunc) (err error) {
+	if len(aggregaters) < 1 {
+		return errors.ThrowPreconditionFailed(nil, "SDK-q9wjp", "no aggregaters passed")
+	}
+
+	aggregates, err := makeAggregates(ctx, aggregaters)
+	if err != nil {
+		return err
+	}
+
+	err = push(ctx, aggregates...)
+	if err != nil {
+		return err
+	}
+	
+
+	return appendAggregates(appender, aggregates)
+}
+
+func appendAggregates(appender appendFunc, aggregates []*models.Aggregate) error {
+	for _, aggregate := range aggregates {
+		err := appender(aggregate.Events...)
+		if err != nil {
+			return ThrowAppendEventError(err, "SDK-o6kzK", "aggregator failed")
+		}
+	}
+	return nil
+}
+
+func makeAggregates(ctx context.Context, aggregaters []aggregateFunc) (aggregates []*models.Aggregate, err error) {
+	aggregates = make([]*models.Aggregate, len(aggregaters))
+	for i, aggregater := range aggregaters {
+		aggregates[i], err = aggregater(ctx)
+		if err != nil {
+			return nil, err
+		}
+	}
+	return aggregates, nil
+}