import csv
import json
from io import StringIO

import yaml
from django import forms
from django.utils.translation import gettext as _

from core.forms.mixins import SyncedDataMixin
from utilities.choices import ImportFormatChoices
from utilities.forms.utils import parse_csv
from .mixins import BootstrapMixin
from ..choices import ImportMethodChoices


class BulkImportForm(BootstrapMixin, SyncedDataMixin, forms.Form):
    import_method = forms.ChoiceField(
        choices=ImportMethodChoices,
        required=False
    )
    data = forms.CharField(
        required=False,
        widget=forms.Textarea(attrs={'class': 'font-monospace'}),
        help_text=_("Enter object data in CSV, JSON or YAML format.")
    )
    upload_file = forms.FileField(
        label="Data file",
        required=False
    )
    format = forms.ChoiceField(
        choices=ImportFormatChoices,
        initial=ImportFormatChoices.AUTO
    )

    data_field = 'data'

    def clean(self):
        super().clean()

        # Determine import method
        import_method = self.cleaned_data.get('import_method') or ImportMethodChoices.DIRECT

        # Determine whether we're reading from form data or an uploaded file
        if self.cleaned_data['data'] and import_method != ImportMethodChoices.DIRECT:
            raise forms.ValidationError("Form data must be empty when uploading/selecting a file.")
        if import_method == ImportMethodChoices.UPLOAD:
            self.upload_file = 'upload_file'
            file = self.files.get('upload_file')
            data = file.read().decode('utf-8-sig')
        elif import_method == ImportMethodChoices.DATA_FILE:
            data = self.cleaned_data['data_file'].data_as_string
        else:
            data = self.cleaned_data['data']

        # Determine the data format
        if self.cleaned_data['format'] == ImportFormatChoices.AUTO:
            format = self._detect_format(data)
        else:
            format = self.cleaned_data['format']

        # Process data according to the selected format
        if format == ImportFormatChoices.CSV:
            self.cleaned_data['data'] = self._clean_csv(data)
        elif format == ImportFormatChoices.JSON:
            self.cleaned_data['data'] = self._clean_json(data)
        elif format == ImportFormatChoices.YAML:
            self.cleaned_data['data'] = self._clean_yaml(data)
        else:
            raise forms.ValidationError(f"Unknown data format: {format}")

    def _detect_format(self, data):
        """
        Attempt to automatically detect the format (CSV, JSON, or YAML) of the given data, or raise
        a ValidationError.
        """
        try:
            if data[0] in ('{', '['):
                return ImportFormatChoices.JSON
            if data.startswith('---') or data.startswith('- '):
                return ImportFormatChoices.YAML
            if ',' in data.split('\n', 1)[0]:
                return ImportFormatChoices.CSV
        except IndexError:
            pass
        raise forms.ValidationError({
            'format': _('Unable to detect data format. Please specify.')
        })

    def _clean_csv(self, data):
        """
        Clean CSV-formatted data. The first row will be treated as column headers.
        """
        stream = StringIO(data.strip())
        reader = csv.reader(stream)
        headers, records = parse_csv(reader)

        # Set CSV headers for reference by the model form
        self._csv_headers = headers

        return records

    def _clean_json(self, data):
        """
        Clean JSON-formatted data. If only a single object is defined, it will be encapsulated as a list.
        """
        try:
            data = json.loads(data)
            # Accommodate for users entering single objects
            if type(data) is not list:
                data = [data]
            return data
        except json.decoder.JSONDecodeError as err:
            raise forms.ValidationError({
                self.data_field: f"Invalid JSON data: {err}"
            })

    def _clean_yaml(self, data):
        """
        Clean YAML-formatted data. Data must be either
          a) A single document comprising a list of dictionaries (each representing an object), or
          b) Multiple documents, separated with the '---' token
        """
        records = []
        try:
            for data in yaml.load_all(data, Loader=yaml.SafeLoader):
                if type(data) == list:
                    records.extend(data)
                elif type(data) == dict:
                    records.append(data)
                else:
                    raise forms.ValidationError({
                        self.data_field: _(
                            "Invalid YAML data. Data must be in the form of multiple documents, or a single document "
                            "comprising a list of dictionaries."
                        )
                    })
        except yaml.error.YAMLError as err:
            raise forms.ValidationError({
                self.data_field: f"Invalid YAML data: {err}"
            })

        return records