from __future__ import unicode_literals

from django.core.exceptions import ImproperlyConfigured
from django.http import HttpResponse

try:
    from tablib import Dataset
except ImportError:  # pragma: no cover
    raise ImproperlyConfigured(
        'You must have tablib installed in order to use the django-tables2 export functionality'
    )


class TableExport(object):
    '''
    Export data from a table to the filetype specified.

    Argumenents:
        export_format (str): one of `csv, json, latex, ods, tsv, xls, xlsx, yml`
        table (`~.Table`): instance of the table to export the data from
        exclude_columns (iterable): list of column names to exclude from the export
    '''
    CSV = 'csv'
    JSON = 'json'
    LATEX = 'latex'
    ODS = 'ods'
    TSV = 'tsv'
    XLS = 'xls'
    XLSX = 'xlsx'
    YAML = 'yml'

    FORMATS = {
        CSV: 'text/csv; charset=utf-8',
        JSON: 'application/json',
        LATEX: 'text/plain',
        ODS: 'application/vnd.oasis.opendocument.spreadsheet',
        TSV: 'text/tsv; charset=utf-8',
        XLS: 'application/vnd.ms-excel',
        XLSX: 'application/vnd.ms-excel',
        YAML: 'text/yml; charset=utf-8',
    }

    def __init__(self, export_format, table, exclude_columns=None):
        if not self.is_valid_format(export_format):
            raise TypeError('Export format "{}" is not supported.'.format(export_format))

        self.format = export_format

        self.dataset = Dataset()
        for i, row in enumerate(table.as_values(exclude_columns=exclude_columns)):
            if i == 0:
                self.dataset.headers = row
            else:
                self.dataset.append(row)

    @classmethod
    def is_valid_format(self, export_format):
        '''
        Returns true if `export_format` is one of the supported export formats
        '''
        return (
            export_format is not None and
            export_format in TableExport.FORMATS.keys()
        )

    def content_type(self):
        '''
        Returns the content type for the current export format
        '''
        return self.FORMATS[self.format]

    def export(self):
        '''
        Returns the string/bytes for the current export format
        '''
        return getattr(self.dataset, self.format)

    def response(self, filename=None):
        '''
        Builds and returns a `HttpResponse` containing the exported data

        Arguments:
            filename (str): if not `None`,
        '''
        response = HttpResponse(content_type=self.content_type())
        if filename is not None:
            response['Content-Disposition'] = 'attachment; filename="{}"'.format(
                filename
            )

        response.write(self.export())
        return response