1 files changed, 201 insertions, 0 deletions
diff --git a/internal/showcase/rank_history.go b/internal/showcase/rank_history.go
new file mode 100644
index 0000000..92c0c33
--- /dev/null
+++ b/internal/showcase/rank_history.go
@@ -0,0 +1,201 @@
+package showcase
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+	"sort"
+	"strings"
+	"time"
+)
+
+const (
+	rankHistoryFilename = ".gitsyncer-showcase-rank-history.json"
+	rankHistoryPoints   = 5
+	rankHistoryVersion  = 1
+)
+
+// RankSnapshot stores ranking spots for all repositories on one day.
+type RankSnapshot struct {
+	Date  string         `json:"date"`
+	Ranks map[string]int `json:"ranks"`
+}
+
+// RankHistoryStore stores all ranking snapshots used for weekly history.
+type RankHistoryStore struct {
+	Version   int            `json:"version"`
+	Snapshots []RankSnapshot `json:"snapshots"`
+}
+
+// RepoRankHistory represents one history point for a repository.
+type RepoRankHistory struct {
+	Spot         int    `json:"spot"`
+	Anchor       string `json:"anchor"`
+	SnapshotDate string `json:"snapshotDate,omitempty"`
+	Arrow        string `json:"arrow"`
+}
+
+func newRankHistoryStore() *RankHistoryStore {
+	return &RankHistoryStore{
+		Version:   rankHistoryVersion,
+		Snapshots: []RankSnapshot{},
+	}
+}
+
+func loadRankHistory(path string) (*RankHistoryStore, error) {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return newRankHistoryStore(), nil
+		}
+		return nil, fmt.Errorf("read rank history file: %w", err)
+	}
+
+	var store RankHistoryStore
+	if err := json.Unmarshal(data, &store); err != nil {
+		return nil, fmt.Errorf("parse rank history file: %w", err)
+	}
+
+	if store.Version == 0 {
+		store.Version = rankHistoryVersion
+	}
+	if store.Snapshots == nil {
+		store.Snapshots = []RankSnapshot{}
+	}
+
+	sort.Slice(store.Snapshots, func(i, j int) bool {
+		return store.Snapshots[i].Date < store.Snapshots[j].Date
+	})
+
+	return &store, nil
+}
+
+func saveRankHistory(path string, store *RankHistoryStore) error {
+	data, err := json.MarshalIndent(store, "", "  ")
+	if err != nil {
+		return fmt.Errorf("marshal rank history: %w", err)
+	}
+	if err := os.WriteFile(path, data, 0644); err != nil {
+		return fmt.Errorf("write rank history file: %w", err)
+	}
+	return nil
+}
+
+func buildCurrentRanks(sorted []ProjectSummary) map[string]int {
+	ranks := make(map[string]int, len(sorted))
+	for i, summary := range sorted {
+		ranks[summary.Name] = i + 1
+	}
+	return ranks
+}
+
+func upsertSnapshotForDate(store *RankHistoryStore, anchorDate time.Time, ranks map[string]int) {
+	day := anchorDate.Format("2006-01-02")
+	clonedRanks := make(map[string]int, len(ranks))
+	for repo, rank := range ranks {
+		clonedRanks[repo] = rank
+	}
+
+	for i := range store.Snapshots {
+		if store.Snapshots[i].Date == day {
+			store.Snapshots[i].Ranks = clonedRanks
+			return
+		}
+	}
+
+	store.Snapshots = append(store.Snapshots, RankSnapshot{
+		Date:  day,
+		Ranks: clonedRanks,
+	})
+	sort.Slice(store.Snapshots, func(i, j int) bool {
+		return store.Snapshots[i].Date < store.Snapshots[j].Date
+	})
+}
+
+func applyRankHistoryToSummaries(summaries []ProjectSummary, store *RankHistoryStore, anchorDate time.Time, points int) {
+	for i := range summaries {
+		summaries[i].RankHistory = computeRepoHistory(store, summaries[i].Name, anchorDate, points)
+	}
+}
+
+func computeRepoHistory(store *RankHistoryStore, repo string, anchorDate time.Time, points int) []RepoRankHistory {
+	history := make([]RepoRankHistory, 0, points)
+	for i := 0; i < points; i++ {
+		target := anchorDate.AddDate(0, 0, -7*i)
+		targetDate := target.Format("2006-01-02")
+		snapshot := latestSnapshotAtOrBefore(store, targetDate)
+
+		item := RepoRankHistory{
+			Anchor: anchorLabel(i),
+			Arrow:  "·",
+		}
+		if snapshot != nil {
+			item.SnapshotDate = snapshot.Date
+			if spot, ok := snapshot.Ranks[repo]; ok {
+				item.Spot = spot
+			}
+		}
+		if i > 0 {
+			item.Arrow = movementArrow(history[i-1].Spot, item.Spot)
+		}
+
+		history = append(history, item)
+	}
+
+	return history
+}
+
+func latestSnapshotAtOrBefore(store *RankHistoryStore, targetDate string) *RankSnapshot {
+	var latest *RankSnapshot
+	for i := range store.Snapshots {
+		snapshot := &store.Snapshots[i]
+		if snapshot.Date <= targetDate {
+			if latest == nil || snapshot.Date > latest.Date {
+				latest = snapshot
+			}
+		}
+	}
+	return latest
+}
+
+func movementArrow(currentSpot, olderSpot int) string {
+	if currentSpot <= 0 || olderSpot <= 0 {
+		return "·"
+	}
+	if currentSpot == olderSpot {
+		return "→"
+	}
+	if currentSpot < olderSpot {
+		return "↑"
+	}
+	return "↓"
+}
+
+func formatRankHistoryForHeader(history []RepoRankHistory) string {
+	if len(history) == 0 {
+		return ""
+	}
+
+	tokens := make([]string, 0, len(history))
+	for i, point := range history {
+		spot := fmt.Sprintf("#%d", point.Spot)
+		if point.Spot <= 0 {
+			spot = "n/a"
+		}
+
+		if i == 0 {
+			tokens = append(tokens, fmt.Sprintf("%s(%s)", spot, point.Anchor))
+			continue
+		}
+		tokens = append(tokens, fmt.Sprintf("%s%s(%s)", point.Arrow, spot, point.Anchor))
+	}
+
+	return " [" + strings.Join(tokens, " ") + "]"
+}
+
+func anchorLabel(i int) string {
+	if i == 0 {
+		return "now"
+	}
+	return fmt.Sprintf("%dw", i)
+}