feat(文档导出): 支持指定页导出，统一文件编号

ofdgo_page_range.go

@@ -0,0 +1,79 @@
+// Copyright 2025-2026 肖其顿 (XIAO QI DUN)
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package ofdgo
+
+import (
+	"fmt"
+	"slices"
+	"strconv"
+	"strings"
+)
+
+// ParsePageRange 解析一基页码及闭区间，返回升序去重的零基页面索引
+// 入参: value 页码表达式，如1-6,7,8-10, count 文档总页数
+// 返回: []int 页面索引, error 错误信息
+func ParsePageRange(value string, count int) ([]int, error) {
+	selected := make(map[int]bool)
+	for _, part := range strings.Split(strings.ReplaceAll(value, "，", ","), ",") {
+		first, last, interval := strings.Cut(strings.TrimSpace(part), "-")
+		start, err := strconv.Atoi(strings.TrimSpace(first))
+		if err != nil {
+			return nil, fmt.Errorf("invalid page range %q", part)
+		}
+		end := start
+		if interval {
+			end, err = strconv.Atoi(strings.TrimSpace(last))
+			if err != nil {
+				return nil, fmt.Errorf("invalid page range %q", part)
+			}
+		}
+		if start < 1 || end < start || end > count {
+			return nil, fmt.Errorf("page range %q outside 1-%d", part, count)
+		}
+		for index := start - 1; index < end; index++ {
+			selected[index] = true
+		}
+	}
+	indices := make([]int, 0, len(selected))
+	for index := range selected {
+		indices = append(indices, index)
+	}
+	slices.Sort(indices)
+	return indices, nil
+}
+
+// exportPageIndices 校验导出索引并按原页序去重，省略索引时选取全部页面
+// 入参: count 文档总页数, indices 零基页面索引
+// 返回: []int 页面索引, error 错误信息
+func exportPageIndices(count int, indices []int) ([]int, error) {
+	if count == 0 {
+		return nil, fmt.Errorf("no pages found")
+	}
+	if len(indices) == 0 {
+		indices = make([]int, count)
+		for index := range indices {
+			indices[index] = index
+		}
+		return indices, nil
+	}
+	for _, index := range indices {
+		if index < 0 || index >= count {
+			return nil, fmt.Errorf("page index %d out of range", index)
+		}
+	}
+	indices = slices.Clone(indices)
+	slices.Sort(indices)
+	return slices.Compact(indices), nil
+}