feat: media duplicate purge, part 1 of 3: persisted purge settings and the purge API

internal/infrastructure/useCases/PreviewPurge.go

@@ -0,0 +1,61 @@
+package useCases
+
+import (
+	"RenewCMS/internal/domain/article"
+	"RenewCMS/internal/domain/image"
+)
+
+const purgePreviewListLimit = 5
+
+type PurgePreviewGroup struct {
+	KeepID   uint32
+	Filename string
+	URL      string
+	UsedIn   int
+	Merged   int
+}
+
+type PurgePreview struct {
+	Groups      int
+	Copies      int
+	Articles    int
+	List        []PurgePreviewGroup
+	More        int
+	Fingerprint string
+}
+
+type PreviewPurgeUseCase struct {
+	planner *purgePlanner
+}
+
+func NewPreviewPurgeUseCase(imageRepository image.Repository, articleRepository article.Repository) *PreviewPurgeUseCase {
+	return &PreviewPurgeUseCase{&purgePlanner{imageRepository, articleRepository}}
+}
+
+func (u *PreviewPurgeUseCase) Preview() (PurgePreview, error) {
+	plan, err := u.planner.plan()
+	if err != nil {
+		return PurgePreview{}, err
+	}
+
+	shown := min(len(plan.groups), purgePreviewListLimit)
+	list := make([]PurgePreviewGroup, 0, shown)
+	for _, group := range plan.groups[:shown] {
+		list = append(list, PurgePreviewGroup{
+			KeepID:   group.kept.ID,
+			Filename: group.kept.Filename,
+			URL:      group.kept.Path,
+			UsedIn:   group.keptUsage,
+			Merged:   len(group.mergedIds),
+		})
+	}
+
+	return PurgePreview{
+		Groups:      len(plan.groups),
+		Copies:      plan.copies,
+		Articles:    plan.articles,
+		List:        list,
+		More:        len(plan.groups) - shown,
+		Fingerprint: plan.fingerprint,
+	}, nil
+}