"""Exporters for faculties, departments, and other academics components.
"""
import csv
import grok
from cStringIO import StringIO
from waeup.sirp.interfaces import ICSVExporter

class FacultyExporter(grok.GlobalUtility):
    """Exporter for faculties.
    """
    grok.implements(ICSVExporter)
    grok.name('faculties')

    #: Fieldnames considered by this exporter
    fields = ('code', 'title', 'title_prefix')

    def mangle_value(self, value, name, context=None):
        """Hook for mangling values in derived classes
        """
        if isinstance(value, unicode):
            # CSV writers like byte streams better than unicode
            value = value.encode('utf-8')
        if value is None:
            # None is not really representable in CSV files
            value = ''
        return value

    def get_csv_writer(self, filepath=None):
        """Get a CSV dict writer instance open for writing.

        Returns a tuple (<writer>, <outfile>) where ``<writer>`` is a
        :class:`csv.DictWriter` instance and outfile is the real file
        which is written to. The latter is important when writing to
        StringIO and can normally be ignored otherwise.

        The returned file will already be filled with the header row.
        """
        if filepath is None:
            outfile = StringIO()
        else:
            outfile = open(filepath, 'wb')
        writer = csv.DictWriter(outfile, self.fields)
        writer.writerow(dict(zip(self.fields, self.fields))) # header
        return writer, outfile

    def write_item(self, faculty, writer):
        """Write a row into using `writer`.
        """
        row = {}
        for name in self.fields:
            value = getattr(faculty, name, None)
            value = self.mangle_value(value, name, faculty)
            row[name] = value
        writer.writerow(row)
        return

    def close_outfile(self, filepath, outfile):
        """Close outfile.

        If filepath is None, the contents of outfile is returned.
        """
        outfile.seek(0)
        if filepath is None:
            return outfile.read()
        outfile.close()
        return

    def export(self, faculties, filepath=None):
        """Export `faculties`, an iterable, as CSV file.

        If `filepath` is ``None``, a raw string with CSV data is returned.
        """
        writer, outfile = self.get_csv_writer(filepath)
        for faculty in faculties:
            self.write_item(faculty, writer)
        return self.close_outfile(filepath, outfile)

    def export_all(self, site, filepath=None):
        """Export faculties in facultycontainer into filepath as CSV data.

        If `filepath` is ``None``, a raw string with CSV data is returned.
        """
        writer, outfile = self.get_csv_writer(filepath)
        faculties = site.get('faculties', {})
        return self.export(faculties.values(), filepath)
        for faculty in faculties.values():
            self.write_item(faculty, writer)
        return self.close_outfile(filepath, outfile)

class DepartmentExporter(FacultyExporter, grok.GlobalUtility):
    """Exporter for departments.
    """
    grok.implements(ICSVExporter)
    grok.name('departments')

    #: Fieldnames considered by this exporter
    fields = ('code', 'faculty', 'title', 'title_prefix')

    def mangle_value(self, value, name, context=None):
        """Hook for mangling values in derived classes
        """
        if name == 'faculty':
            value = getattr(
                getattr(context, '__parent__', None),
                'code', None)
        return super(DepartmentExporter, self).mangle_value(
            value, name, context)

    def export_all(self, site, filepath=None):
        """Export faculties in facultycontainer into filepath as CSV data.

        If `filepath` is ``None``, a raw string with CSV data is returned.
        """
        writer, outfile = self.get_csv_writer(filepath)
        faculties = site.get('faculties', {})
        for faculty in faculties.values():
            for department in faculty.values():
                self.write_item(department, writer)
        return self.close_outfile(filepath, outfile)


class CourseExporter(FacultyExporter, grok.GlobalUtility):
    """Exporter for courses.
    """
    grok.implements(ICSVExporter)
    grok.name('courses')

    #: Fieldnames considered by this exporter
    fields = ('code', 'faculty', 'department', 'title', 'credits',
              'passmark', 'semester')

    def mangle_value(self, value, name, context=None):
        """Hook for mangling values in derived classes
        """
        if name == 'faculty':
            try:
                value = context.__parent__.__parent__.__parent__.code
            except AttributeError:
                value = None
        elif name == 'department':
            value = getattr(
                getattr(context, '__parent__', None),
                'code', None)
        return super(CourseExporter, self).mangle_value(
            value, name, context)

    def export_all(self, site, filepath=None):
        """Export faculties in facultycontainer into filepath as CSV data.

        If `filepath` is ``None``, a raw string with CSV data is returned.
        """
        writer, outfile = self.get_csv_writer(filepath)
        faculties = site.get('faculties', {})
        for faculty in faculties.values():
            for department in faculty.values():
                for course in department.courses.values():
                    self.write_item(course, writer)
        return self.close_outfile(filepath, outfile)