Extract Spreadsheet model from app/utils.py

`app/utils.py` is a bit of a dumping ground for things we don’t have a
better place for.

We now have a place and structure for storing ‘model’ code (‘model’ in
the model, view, controller (MVC) sense of the word).

This commit moves the spreadsheet model to that place.

app/models/spreadsheet.py

@@ -0,0 +1,105 @@
+import csv
+from io import BytesIO, StringIO
+from os import path
+
+import pyexcel
+import pyexcel_xlsx
+
+
+class Spreadsheet():
+
+    ALLOWED_FILE_EXTENSIONS = ('csv', 'xlsx', 'xls', 'ods', 'xlsm', 'tsv')
+
+    def __init__(self, csv_data=None, rows=None, filename=''):
+
+        self.filename = filename
+
+        if csv_data and rows:
+            raise TypeError('Spreadsheet must be created from either rows or CSV data')
+
+        self._csv_data = csv_data or ''
+        self._rows = rows or []
+
+    @property
+    def as_dict(self):
+        return {
+            'file_name': self.filename,
+            'data': self.as_csv_data
+        }
+
+    @property
+    def as_csv_data(self):
+        if not self._csv_data:
+            with StringIO() as converted:
+                output = csv.writer(converted)
+                for row in self._rows:
+                    output.writerow(row)
+                self._csv_data = converted.getvalue()
+        return self._csv_data
+
+    @classmethod
+    def can_handle(cls, filename):
+        return cls.get_extension(filename) in cls.ALLOWED_FILE_EXTENSIONS
+
+    @staticmethod
+    def get_extension(filename):
+        return path.splitext(filename)[1].lower().lstrip('.')
+
+    @staticmethod
+    def normalise_newlines(file_content):
+        return '\r\n'.join(file_content.read().decode('utf-8').splitlines())
+
+    @classmethod
+    def from_rows(cls, rows, filename=''):
+        return cls(rows=rows, filename=filename)
+
+    @classmethod
+    def from_dict(cls, dictionary, filename=''):
+        return cls.from_rows(
+            zip(
+                *sorted(dictionary.items(), key=lambda pair: pair[0])
+            ),
+            filename=filename,
+        )
+
+    @classmethod
+    def from_file(cls, file_content, filename=''):
+        extension = cls.get_extension(filename)
+
+        if extension == 'csv':
+            return cls(csv_data=Spreadsheet.normalise_newlines(file_content), filename=filename)
+
+        if extension == 'tsv':
+            file_content = StringIO(
+                Spreadsheet.normalise_newlines(file_content))
+
+        instance = cls.from_rows(
+            pyexcel.iget_array(
+                file_type=extension,
+                file_stream=file_content),
+            filename)
+        pyexcel.free_resources()
+        return instance
+
+    @classmethod
+    def from_file_form(cls, form):
+        return cls.from_file(
+            form.file.data,
+            filename=form.file.data.filename,
+        )
+
+    @property
+    def as_rows(self):
+        if not self._rows:
+            self._rows = list(csv.reader(
+                StringIO(self._csv_data),
+                quoting=csv.QUOTE_MINIMAL,
+                skipinitialspace=True,
+            ))
+        return self._rows
+
+    @property
+    def as_excel_file(self):
+        io = BytesIO()
+        pyexcel_xlsx.save_data(io, {'Sheet 1': self.as_rows})
+        return io.getvalue()