Added a dedupe processor, and moved processor packages under processors/*

processors/dedupe/processor.go

@@ -0,0 +1,89 @@
+package dedupe
+
+import (
+	"container/list"
+	"context"
+	"fmt"
+	"strings"
+	"sync"
+
+	"gitea.maximumdirect.net/ejr/feedkit/event"
+	"gitea.maximumdirect.net/ejr/feedkit/processors"
+)
+
+// Processor drops duplicate events by Event.ID using an in-memory LRU.
+type Processor struct {
+	maxEntries int
+
+	mu    sync.Mutex
+	order *list.List               // most-recent at front, least-recent at back
+	byID  map[string]*list.Element // id -> list element (element.Value is string id)
+}
+
+var _ processors.Processor = (*Processor)(nil)
+
+// NewProcessor constructs a dedupe processor with a required max entry count.
+func NewProcessor(maxEntries int) (*Processor, error) {
+	if maxEntries <= 0 {
+		return nil, fmt.Errorf("dedupe: maxEntries must be > 0, got %d", maxEntries)
+	}
+
+	return &Processor{
+		maxEntries: maxEntries,
+		order:      list.New(),
+		byID:       make(map[string]*list.Element, maxEntries),
+	}, nil
+}
+
+// Factory returns a processors.Factory that constructs Processor instances.
+func Factory(maxEntries int) processors.Factory {
+	return func() (processors.Processor, error) {
+		return NewProcessor(maxEntries)
+	}
+}
+
+// Process implements processors.Processor.
+func (p *Processor) Process(_ context.Context, in event.Event) (*event.Event, error) {
+	if p == nil {
+		return nil, fmt.Errorf("dedupe: processor is nil")
+	}
+	if p.maxEntries <= 0 {
+		return nil, fmt.Errorf("dedupe: processor maxEntries must be > 0")
+	}
+
+	id := strings.TrimSpace(in.ID)
+	if id == "" {
+		return nil, fmt.Errorf("dedupe: event ID is required")
+	}
+
+	p.mu.Lock()
+
+	if p.order == nil || p.byID == nil {
+		p.mu.Unlock()
+		return nil, fmt.Errorf("dedupe: processor is not initialized")
+	}
+
+	if elem, exists := p.byID[id]; exists {
+		p.order.MoveToFront(elem)
+		p.mu.Unlock()
+		return nil, nil
+	}
+
+	elem := p.order.PushFront(id)
+	p.byID[id] = elem
+
+	if p.order.Len() > p.maxEntries {
+		oldest := p.order.Back()
+		if oldest != nil {
+			p.order.Remove(oldest)
+			if oldestID, ok := oldest.Value.(string); ok {
+				delete(p.byID, oldestID)
+			}
+		}
+	}
+
+	p.mu.Unlock()
+
+	out := in
+	return &out, nil
+}