첫 커밋: 로컬 프로젝트 업로드

baron-sso/backend/internal/pagination/cursor.go

@@ -0,0 +1,103 @@
+package pagination
+
+import (
+	"encoding/base64"
+	"encoding/json"
+	"errors"
+	"sort"
+	"strings"
+	"time"
+
+	"gorm.io/gorm"
+)
+
+type Cursor struct {
+	Timestamp time.Time `json:"timestamp"`
+	ID        string    `json:"id"`
+}
+
+func Encode(timestamp time.Time, id string) string {
+	if timestamp.IsZero() || strings.TrimSpace(id) == "" {
+		return ""
+	}
+	payload, err := json.Marshal(Cursor{
+		Timestamp: timestamp.UTC(),
+		ID:        id,
+	})
+	if err != nil {
+		return ""
+	}
+	return base64.RawURLEncoding.EncodeToString(payload)
+}
+
+func Decode(raw string) (*Cursor, error) {
+	raw = strings.TrimSpace(raw)
+	if raw == "" {
+		return nil, nil
+	}
+	decoded, err := base64.RawURLEncoding.DecodeString(raw)
+	if err != nil {
+		return nil, err
+	}
+	var cursor Cursor
+	if err := json.Unmarshal(decoded, &cursor); err != nil {
+		return nil, err
+	}
+	if cursor.Timestamp.IsZero() || strings.TrimSpace(cursor.ID) == "" {
+		return nil, errors.New("invalid cursor")
+	}
+	return &cursor, nil
+}
+
+func ComesAfter(timestamp time.Time, id string, cursor *Cursor) bool {
+	if cursor == nil {
+		return true
+	}
+	if timestamp.Before(cursor.Timestamp) {
+		return true
+	}
+	return timestamp.Equal(cursor.Timestamp) && id < cursor.ID
+}
+
+func SortByKeyDesc[T any](items []T, key func(T) (time.Time, string)) {
+	sort.SliceStable(items, func(i, j int) bool {
+		leftTime, leftID := key(items[i])
+		rightTime, rightID := key(items[j])
+		if !leftTime.Equal(rightTime) {
+			return leftTime.After(rightTime)
+		}
+		return leftID > rightID
+	})
+}
+
+func PageByCursor[T any](items []T, limit int, cursorRaw string, key func(T) (time.Time, string)) ([]T, string, error) {
+	cursor, err := Decode(cursorRaw)
+	if err != nil {
+		return nil, "", err
+	}
+	filtered := make([]T, 0, len(items))
+	for _, item := range items {
+		timestamp, id := key(item)
+		if ComesAfter(timestamp, id, cursor) {
+			filtered = append(filtered, item)
+		}
+	}
+	if len(filtered) <= limit {
+		return filtered, "", nil
+	}
+	page := filtered[:limit]
+	lastTimestamp, lastID := key(page[len(page)-1])
+	return page, Encode(lastTimestamp, lastID), nil
+}
+
+func ApplyCreatedAtIDCursor(db *gorm.DB, cursor *Cursor, createdAtColumn string, idColumn string) *gorm.DB {
+	if cursor == nil {
+		return db
+	}
+	return db.Where(
+		createdAtColumn+" < ? OR ("+createdAtColumn+" = ? AND "+idColumn+" < ?)",
+		cursor.Timestamp,
+		cursor.Timestamp,
+		cursor.ID,
+	)
+}