from django import forms
from django.utils.translation import ugettext_lazy as _

class UploadedFileInMemoryError(Exception):
	pass
	
class DocField(forms.FileField):
	"""
	This is form field for PDF or Microsoft Word Document (both .doc and .docx)
	It will validate the file uploaded as a valid PDF and MS Word Document.
	~~~~~~~~~
	Usage:
	import DocField
	doc = models.DocField()	
	~~~~~~~~~
	It extends a forms.FileField, so you can put all the arguments relevant to FileField.
	
	IMPORTANT NOTE: The method of validation is actually run thru *nix OS shell command 'file', 
				    therefore, 1. only *nix system can use this class. 
				               2. The file uploaded must be saved on disk, meaning you need to set your upload handler to use TempoaryFileUploadHandler Only.
 	
    # (i.e. put this in your settings.py) 
	FILE_UPLOAD_HANDLERS = (
 		"django.core.files.uploadhandler.TemporaryFileUploadHandler",
 	)
	
	"""
	default_error_messages = {
		'invalid': _(u"No file was submitted. Check the encoding type on the form."),
		'missing': _(u"No file was submitted."),
		'empty': _(u"The submitted file is empty."),
		'not_doc': _(u"Upload a valid document. The file you uploaded was not a acceptable document or a corrupted document."),
	}

	def clean(self, data, initial=None):
		super(DocField, self).clean(initial or data)

		#before save check if the writing sample is valid
		import os, re
		from django.forms.util import ValidationError

		match = r'PDF document|Microsoft Office Document|Zip archive data'

		if hasattr(data, 'temporary_file_path'):
			file = data.temporary_file_path()
		else:
			# throw an error because uploaded file in memory 
			raise UploadedFileInMemoryError('The file uploaded is stored in memory instead of disk and the validation cannot be performed.')
						
		out = os.popen('file %s' % file)
		ck = re.search(match, out.read())
		if ck == None:
			raise ValidationError(self.error_messages['not_doc'])
		#  check further for docx file as it's zip file
		if ck.group(0)[0] == 'Z':
			import zipfile
			docx = 'word/document.xml'
			if not zipfile.is_zipfile(file):
				raise ValidationError(self.error_messages['not_doc'])

			zf = zipfile.ZipFile(file)
			if not docx in zf.namelist():
				raise ValidationError(self.error_messages['not_doc'])
		return data