同步支持动态更新取件码长度，调整存量取件码以适配新长度并优化相关逻辑和文档。

internal/service/batch_service.go

@@ -6,8 +6,12 @@ import (
 	"FileRelay/internal/storage"
 	"context"
 	"errors"
+	"math/big"
+	"strings"
 	"time"
 
+	"crypto/rand"
+
 	"gorm.io/gorm"
 )
 
@@ -84,3 +88,85 @@ func (s *BatchService) IncrementDownloadCount(batchID string) error {
 	return s.db.Model(&model.FileBatch{}).Where("id = ?", batchID).
 		UpdateColumn("download_count", gorm.Expr("download_count + ?", 1)).Error
 }
+
+func (s *BatchService) GeneratePickupCode(length int) (string, error) {
+	const charset = "0123456789"
+	b := make([]byte, length)
+	for i := range b {
+		num, err := rand.Int(rand.Reader, big.NewInt(int64(len(charset))))
+		if err != nil {
+			return "", err
+		}
+		b[i] = charset[num.Int64()]
+	}
+	// 检查是否冲突 (排除已删除的，但包括活跃的和已过期的)
+	var count int64
+	s.db.Model(&model.FileBatch{}).Where("pickup_code = ?", string(b)).Count(&count)
+	if count > 0 {
+		return s.GeneratePickupCode(length) // 递归生成
+	}
+	return string(b), nil
+}
+
+func (s *BatchService) UpdateAllPickupCodes(newLength int) error {
+	var batches []model.FileBatch
+	// 只更新未删除的记录，包括 active 和 expired
+	if err := s.db.Find(&batches).Error; err != nil {
+		return err
+	}
+
+	return s.db.Transaction(func(tx *gorm.DB) error {
+		for _, batch := range batches {
+			oldCode := batch.PickupCode
+			if len(oldCode) == newLength {
+				continue
+			}
+
+			var newCode string
+			if len(oldCode) < newLength {
+				// 右侧补零，方便用户输入原码后通过补 0 完成输入
+				newCode = oldCode + strings.Repeat("0", newLength-len(oldCode))
+			} else {
+				// 截取前 newLength 位，保留原码头部
+				newCode = oldCode[:newLength]
+			}
+
+			// 检查冲突 (在事务中检查)
+			var count int64
+			tx.Model(&model.FileBatch{}).Where("pickup_code = ? AND id != ?", newCode, batch.ID).Count(&count)
+			if count > 0 {
+				// 如果冲突，生成一个新的随机码
+				var err error
+				newCode, err = s.generateUniquePickupCodeInTx(tx, newLength)
+				if err != nil {
+					return err
+				}
+			}
+
+			if err := tx.Model(&batch).Update("pickup_code", newCode).Error; err != nil {
+				return err
+			}
+		}
+		return nil
+	})
+}
+
+func (s *BatchService) generateUniquePickupCodeInTx(tx *gorm.DB, length int) (string, error) {
+	const charset = "0123456789"
+	for {
+		b := make([]byte, length)
+		for i := range b {
+			num, err := rand.Int(rand.Reader, big.NewInt(int64(len(charset))))
+			if err != nil {
+				return "", err
+			}
+			b[i] = charset[num.Int64()]
+		}
+
+		var count int64
+		tx.Model(&model.FileBatch{}).Where("pickup_code = ?", string(b)).Count(&count)
+		if count == 0 {
+			return string(b), nil
+		}
+	}
+}