feat(文件归并): 归并PDF封装并下沉计算逻辑

internal/codec/pdf/metadata.go

@@ -0,0 +1,51 @@
+// 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 pdf
+
+import (
+	"fmt"
+	"strings"
+	"time"
+
+	"github.com/xiaoqidun/pdfgo"
+)
+
+// MetadataDate 保留当地日历日期，PDF省略时区按GMT，XMP省略日或时区时不推算
+// 入参: text 来源日期, xmp 是否为XMP日期
+// 返回: time.Time 解析值, bool 是否精确到日, bool 是否可比较绝对时间, error 日期错误
+func MetadataDate(text string, xmp bool) (time.Time, bool, bool, error) {
+	if text == "" {
+		return time.Time{}, false, false, nil
+	}
+	if !xmp {
+		date, err := pdfgo.ParseDate(text)
+		return date, err == nil && date.Year() > 0, err == nil, err
+	}
+	if !strings.Contains(text, ",") {
+		for _, layout := range []string{time.RFC3339Nano, "2006-01-02T15:04Z07:00", "2006-01-02T15:04:05", "2006-01-02T15:04", "2006-01-02", "2006-01", "2006"} {
+			if date, err := time.Parse(layout, text); err == nil {
+				zoned := strings.Contains(layout, "Z07:00")
+				if zoned && !strings.HasSuffix(text, "Z") {
+					zone := text[len(text)-6:]
+					if zone[1:3] > "23" || zone[4:] > "59" {
+						return time.Time{}, false, false, fmt.Errorf("invalid XMP time zone")
+					}
+				}
+				return date, len(text) >= 10 && date.Year() > 0, zoned, nil
+			}
+		}
+	}
+	return time.Time{}, false, false, fmt.Errorf("invalid XMP date")
+}