Add date validation

I'm only concerned with validating issue dates here. In DSpace they
are generally always YYYY, YYY-MM, or YYYY-MM-DD (though in theory
they could be any valid ISO8601 format).

This also checks for cases where the date is missing and where the
metadata has specified multiple dates like "1990||1991", as this is
valid, but there is no practical value for it in our system.

csv_metadata_quality/app.py

@@ -1,6 +1,7 @@
 import csv_metadata_quality.check as check
 import csv_metadata_quality.fix as fix
 import pandas as pd
+import re
 
 def main():
     # Read all fields as strings so dates don't get converted from 1998 to 1998.0
@@ -22,5 +23,10 @@ def main():
         if column == 'dc.identifier.isbn':
             df[column] = df[column].apply(check.isbn)
 
+        # check if column is a date column like dc.date.issued
+        match = re.match(r'^.*?date.*$', column)
+        if match is not None:
+            df[column] = df[column].apply(check.date)
+
     # Write
     df.to_csv('/tmp/test.fixed.csv', index=False)

csv_metadata_quality/check.py

@@ -73,3 +73,54 @@ def separators(field):
 
 
     return field
+
+
+def date(field):
+    """Check if a date is valid.
+
+    In DSpace the issue date is usually 1990, 1990-01, or 1990-01-01, but it
+    could technically even include time as long as it is ISO8601.
+
+    Also checks for other invalid cases like missing and multiple dates.
+
+    Prints the date if invalid.
+    """
+    from datetime import datetime
+
+    if pd.isna(field):
+        print(f'Missing date.')
+
+        return
+
+    # Try to split multi-value field on "||" separator
+    multiple_dates = field.split('||')
+
+    # We don't allow multi-value date fields
+    if len(multiple_dates) > 1:
+        print(f'Multiple dates not allowed: {field}')
+
+        return field
+
+    try:
+        # Check if date is valid YYYY format
+        datetime.strptime(field, '%Y')
+
+        return field
+    except ValueError:
+        pass
+
+    try:
+        # Check if date is valid YYYY-MM format
+        datetime.strptime(field, '%Y-%m')
+
+        return field
+    except ValueError:
+        pass
+
+    try:
+        # Check if date is valid YYYY-MM-DD format
+        datetime.strptime(field, '%Y-%m-%d')
+
+        return field
+    except ValueError:
+        print(f'Invalid date: {field}')

tests/test_check.py

@@ -62,3 +62,46 @@ def test_check_valid_separators():
     result = check.separators(value)
 
     assert result == value
+
+
+def test_check_missing_date(capsys):
+    '''Test checking missing date.'''
+
+    value = None
+
+    check.date(value)
+
+    captured = capsys.readouterr()
+    assert captured.out == f'Missing date.\n'
+
+
+def test_check_multiple_dates(capsys):
+    '''Test checking multiple dates.'''
+
+    value = '1990||1991'
+
+    check.date(value)
+
+    captured = capsys.readouterr()
+    assert captured.out == f'Multiple dates not allowed: {value}\n'
+
+
+def test_check_invalid_date(capsys):
+    '''Test checking invalid ISO8601 date.'''
+
+    value = '1990-0'
+
+    check.date(value)
+
+    captured = capsys.readouterr()
+    assert captured.out == f'Invalid date: {value}\n'
+
+
+def test_check_valid_date():
+    '''Test checking valid ISO8601 date.'''
+
+    value = '1990'
+
+    result = check.date(value)
+
+    assert result == value