From 64037f9a53928ef3fb8b468d7abc2d15ecd1a28c Mon Sep 17 00:00:00 2001
From: Robin Krahl <me@robin-krahl.de>
Date: Fri, 9 Mar 2018 19:26:54 +0100
Subject: Extract DOI from PDF text using a regex

---
 bibtool/extract.py | 31 ++++++++++++++++++++++++++-----
 setup.py           |  2 +-
 2 files changed, 27 insertions(+), 6 deletions(-)

diff --git a/bibtool/extract.py b/bibtool/extract.py
index 6409f1b..6955dbe 100644
--- a/bibtool/extract.py
+++ b/bibtool/extract.py
@@ -2,15 +2,37 @@
 # SPDX-License-Identifier: MIT
 
 import mimetypes
+import re
 import urllib.request
 
 import bibtexparser
+import pdftotext
 import PyPDF2.pdf
 
 
 PDF_INFO_DOI = '/doi'
 
 
+def _extract_doi(filename):
+    with open(filename, 'rb') as f:
+        reader = PyPDF2.pdf.PdfFileReader(f)
+        if PDF_INFO_DOI in reader.documentInfo:
+            return reader.documentInfo[PDF_INFO_DOI]
+
+    with open(filename, 'rb') as f:
+        pdf = pdftotext.PDF(f)
+
+    if len(pdf):
+        text = pdf[0]
+
+        pattern = re.compile(r'\b(10\.\d{4,}(?:\.\d+)*/(?:(?!["&\'<>])\S)+)\b')
+        m = pattern.search(text)
+        if m:
+            return m.group(1)
+
+    return None
+
+
 def _get_data_for_doi(doi):
     url = 'http://dx.doi.org/{}'.format(doi)
     headers = {'Accept': 'text/bibliography; style=bibtex'}
@@ -21,11 +43,10 @@ def _get_data_for_doi(doi):
 
 
 def _handle_pdf(filename):
-    with open(filename, 'rb') as f:
-        reader = PyPDF2.pdf.PdfFileReader(f)
-        if PDF_INFO_DOI not in reader.documentInfo:
-            raise Exception('PDF file does not have doi header')
-        doi = reader.documentInfo[PDF_INFO_DOI]
+    doi = _extract_doi(filename)
+
+    if not doi:
+        raise Exception('Could not extract a DOI from the PDF file')
 
     return _get_data_for_doi(doi)
 
diff --git a/setup.py b/setup.py
index d871b5c..9333697 100644
--- a/setup.py
+++ b/setup.py
@@ -17,7 +17,7 @@ setuptools.setup(
             'Programming Language :: Python :: 3',
         ],
         packages=['bibtool'],
-        install_requires=['bibtexparser', 'click', 'PyPDF2'],
+        install_requires=['bibtexparser', 'click', 'pdftotext', 'PyPDF2'],
         extras_require={
             'checkstyle': ['flake8'],
         },
-- 
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