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

internal/infrastructure/useCases/purgePlan.go

@@ -0,0 +1,162 @@
+package useCases
+
+import (
+	"RenewCMS/internal/domain/article"
+	"RenewCMS/internal/domain/image"
+	"crypto/sha256"
+	"encoding/hex"
+	"slices"
+	"strconv"
+	"strings"
+)
+
+type purgeGroup struct {
+	kept      image.Image
+	keptUsage int
+	mergedIds []uint32
+}
+
+type purgePlan struct {
+	groups      []purgeGroup
+	copies      int
+	articles    int
+	fingerprint string
+}
+
+type purgePlanner struct {
+	imageRepository   image.Repository
+	articleRepository article.Repository
+}
+
+func (p *purgePlanner) plan() (purgePlan, error) {
+	duplicates, err := p.imageRepository.ListDuplicates()
+	if err != nil {
+		return purgePlan{}, err
+	}
+	articles, err := p.articleRepository.FindByFilters(article.Filters{})
+	if err != nil {
+		return purgePlan{}, err
+	}
+
+	groups := []purgeGroup{}
+	copies := 0
+	touched := map[uint32]bool{}
+	for _, members := range groupByHash(duplicates) {
+		group, planned := planGroup(members, articles)
+		if !planned {
+			continue
+		}
+		groups = append(groups, group)
+		copies += len(group.mergedIds)
+		for _, id := range articlesUsingCopies(group, members, articles) {
+			touched[id] = true
+		}
+	}
+	slices.SortFunc(groups, func(a, b purgeGroup) int { return int(a.kept.ID) - int(b.kept.ID) })
+
+	return purgePlan{groups: groups, copies: copies, articles: len(touched), fingerprint: fingerprintOf(groups)}, nil
+}
+
+func groupByHash(images []image.Image) [][]image.Image {
+	byHash := map[string][]image.Image{}
+	hashes := []string{}
+	for _, img := range images {
+		if img.SHA256 == "" {
+			continue
+		}
+		if _, seen := byHash[img.SHA256]; !seen {
+			hashes = append(hashes, img.SHA256)
+		}
+		byHash[img.SHA256] = append(byHash[img.SHA256], img)
+	}
+	groups := make([][]image.Image, 0, len(hashes))
+	for _, hash := range hashes {
+		groups = append(groups, byHash[hash])
+	}
+	return groups
+}
+
+func usageOf(img image.Image, articles []article.Article) int {
+	storedName := image.StoredName(img.Path)
+	used := 0
+	for _, a := range articles {
+		if strings.Contains(a.Body, storedName) {
+			used++
+		}
+	}
+	return used
+}
+
+func planGroup(members []image.Image, articles []article.Article) (purgeGroup, bool) {
+	usage := make(map[uint32]int, len(members))
+	anyUsed := false
+	for _, member := range members {
+		usage[member.ID] = usageOf(member, articles)
+		anyUsed = anyUsed || usage[member.ID] > 0
+	}
+	if !anyUsed {
+		return purgeGroup{}, false
+	}
+
+	kept := members[0]
+	for _, member := range members[1:] {
+		if isBetterToKeep(member, kept, usage) {
+			kept = member
+		}
+	}
+
+	mergedIds := []uint32{}
+	for _, member := range members {
+		if member.ID != kept.ID {
+			mergedIds = append(mergedIds, member.ID)
+		}
+	}
+	slices.Sort(mergedIds)
+	return purgeGroup{kept: kept, keptUsage: usage[kept.ID], mergedIds: mergedIds}, true
+}
+
+func isBetterToKeep(candidate, current image.Image, usage map[uint32]int) bool {
+	if usage[candidate.ID] != usage[current.ID] {
+		return usage[candidate.ID] > usage[current.ID]
+	}
+	if !candidate.CreatedAt.Equal(current.CreatedAt) {
+		return candidate.CreatedAt.Before(current.CreatedAt)
+	}
+	return candidate.ID < current.ID
+}
+
+func articlesUsingCopies(group purgeGroup, members []image.Image, articles []article.Article) []uint32 {
+	mergedNames := []string{}
+	for _, member := range members {
+		if member.ID != group.kept.ID {
+			mergedNames = append(mergedNames, image.StoredName(member.Path))
+		}
+	}
+	ids := []uint32{}
+	for _, a := range articles {
+		for _, name := range mergedNames {
+			if strings.Contains(a.Body, name) {
+				ids = append(ids, a.ID)
+				break
+			}
+		}
+	}
+	return ids
+}
+
+func fingerprintOf(groups []purgeGroup) string {
+	var builder strings.Builder
+	for _, group := range groups {
+		builder.WriteString(strconv.FormatUint(uint64(group.kept.ID), 10))
+		builder.WriteString(":")
+		for position, id := range group.mergedIds {
+			if position > 0 {
+				builder.WriteString(",")
+			}
+			builder.WriteString(strconv.FormatUint(uint64(id), 10))
+		}
+		builder.WriteString(";")
+	}
+	sum := sha256.Sum256([]byte(builder.String()))
+	return hex.EncodeToString(sum[:])
+}