feat: 新增编码预览功能

- 后端新增 /rpc-api/base/code-gen/preview 接口
- SequenceAllocator.preview 查询序号但不消耗
- 前端操作列新增预览按钮，弹窗展示下一个编码

nl-module-base/nl-module-base-server/src/main/java/cn/code/nl/module/base/controller/api/CodeGenController.java

@@ -8,9 +8,11 @@ import io.swagger.v3.oas.annotations.tags.Tag;
 import jakarta.annotation.Resource;
 import jakarta.validation.Valid;
 import org.springframework.validation.annotation.Validated;
+import org.springframework.web.bind.annotation.GetMapping;
 import org.springframework.web.bind.annotation.PostMapping;
 import org.springframework.web.bind.annotation.RequestBody;
 import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RequestParam;
 import org.springframework.web.bind.annotation.RestController;
 
 import static cn.code.nl.framework.common.pojo.CommonResult.success;
@@ -39,4 +41,11 @@ public class CodeGenController {
         return success(code);
     }
 
+    @GetMapping("/preview")
+    @Operation(summary = "预览下一个编码（不消耗序号）")
+    public CommonResult<String> preview(@RequestParam("ruleCode") String ruleCode) {
+        String code = codeGenService.preview(ruleCode);
+        return success(code);
+    }
+
 }

nl-module-base/nl-module-base-server/src/main/java/cn/code/nl/module/base/service/codegen/CodeGenService.java

@@ -15,4 +15,12 @@ public interface CodeGenService {
      */
     String generate(String ruleCode);
 
+    /**
+     * 预览下一个编码（不消耗序号）
+     *
+     * @param ruleCode 规则编码
+     * @return 预览的编码
+     */
+    String preview(String ruleCode);
+
 }

nl-module-base/nl-module-base-server/src/main/java/cn/code/nl/module/base/service/codegen/CodeGenServiceImpl.java

@@ -54,6 +54,26 @@ public class CodeGenServiceImpl implements CodeGenService {
         return postProcess(sb.toString(), rule);
     }
 
+    @Override
+    public String preview(String ruleCode) {
+        // 1. 获取规则配置
+        CodeRuleDO rule = codeRuleService.getRuleByCode(ruleCode);
+
+        // 2. 遍历分段，SEQUENCE 段用 preview（不消耗序号）
+        List<SegmentConfig> segments = rule.getSegmentConfig();
+        StringBuilder sb = new StringBuilder();
+        for (int i = 0; i < segments.size(); i++) {
+            String segmentValue = buildPreviewSegment(rule, segments.get(i));
+            sb.append(segmentValue);
+            if (i < segments.size() - 1 && StrUtil.isNotBlank(rule.getSeparator())) {
+                sb.append(rule.getSeparator());
+            }
+        }
+
+        // 3. 后处理
+        return postProcess(sb.toString(), rule);
+    }
+
     /**
      * 根据段类型分发处理，生成段值
      */
@@ -66,6 +86,18 @@ public class CodeGenServiceImpl implements CodeGenService {
         };
     }
 
+    /**
+     * 预览模式分发（SEQUENCE 段不消耗序号）
+     */
+    private String buildPreviewSegment(CodeRuleDO rule, SegmentConfig segment) {
+        return switch (segment.getType()) {
+            case "PREFIX" -> buildPrefixSegment(segment);
+            case "DATE" -> buildDateSegment(segment);
+            case "SEQUENCE" -> sequenceAllocator.preview(rule.getId(), segment);
+            default -> throw new IllegalArgumentException("不支持的段类型: " + segment.getType());
+        };
+    }
+
     /**
      * 生成固定前缀段
      */

nl-module-base/nl-module-base-server/src/main/java/cn/code/nl/module/base/service/codegen/SequenceAllocator.java

@@ -189,4 +189,19 @@ public class SequenceAllocator {
         return paddingChar.repeat(paddingLen - raw.length()) + raw;
     }
 
+    /**
+     * 预览下一个序号（不实际分配，不更新数据库）
+     *
+     * @param ruleId  规则ID
+     * @param segment 序号段配置
+     * @return 格式化后的序号字符串
+     */
+    public String preview(Long ruleId, SegmentConfig segment) {
+        String resetKey = buildResetKey(segment.getResetBy());
+        CodeSequenceDO seq = codeSequenceMapper.selectByRuleIdAndResetKey(ruleId, resetKey);
+        Long startAt = segment.getStartAt() != null ? segment.getStartAt() : 1L;
+        long nextValue = (seq != null) ? seq.getCurrentValue() + 1 : startAt;
+        return formatSequence(nextValue, segment);
+    }
+
 }