feedkit: split the former maximumdirect.net/weatherd project in two.

feedkit now contains a reusable core, while weatherfeeder is a concrete implementation that includes weather-specific functions.

pipeline/pipeline.go

@@ -0,0 +1,43 @@
+package pipeline
+
+import (
+	"context"
+	"fmt"
+
+	"gitea.maximumdirect.net/ejr/feedkit/event"
+)
+
+// Processor can mutate/drop events (dedupe, rate-limit, normalization tweaks).
+type Processor interface {
+	Process(ctx context.Context, in event.Event) (out *event.Event, err error)
+}
+
+type Pipeline struct {
+	Processors []Processor
+}
+
+func (p *Pipeline) Process(ctx context.Context, e event.Event) (*event.Event, error) {
+	if err := e.Validate(); err != nil {
+		return nil, fmt.Errorf("pipeline: invalid input event: %w", err)
+	}
+
+	cur := &e
+
+	for _, proc := range p.Processors {
+		out, err := proc.Process(ctx, *cur)
+		if err != nil {
+			return nil, err
+		}
+		if out == nil {
+			// Dropped by policy.
+			return nil, nil
+		}
+		cur = out
+	}
+
+	if err := cur.Validate(); err != nil {
+		return nil, fmt.Errorf("pipeline: invalid output event: %w", err)
+	}
+
+	return cur, nil
+}