import abc
import itertools
from collections import defaultdict
from typing import Any, Dict, List

from django.conf import settings

from api.models import Example, Project
from label_types.models import CategoryType, SpanType
from .exceptions import FileParseException
from .readers import BaseReader


class Writer(abc.ABC):

    @abc.abstractmethod
    def save(self, reader: BaseReader, project: Project, user, cleaner):
        """Save the read contents to DB."""
        raise NotImplementedError('Please implement this method in the subclass.')

    def errors(self) -> List[Dict[Any, Any]]:
        """Return errors."""
        raise NotImplementedError('Please implement this method in the subclass.')


def group_by_class(instances):
    groups = defaultdict(list)
    for instance in instances:
        groups[instance.__class__].append(instance)
    return groups


class Examples:

    def __init__(self, buffer_size: int = settings.IMPORT_BATCH_SIZE):
        self.buffer_size = buffer_size
        self.buffer = []

    def __len__(self):
        return len(self.buffer)

    @property
    def data(self):
        return self.buffer

    def add(self, data):
        self.buffer.append(data)

    def clear(self):
        self.buffer = []

    def is_full(self):
        return len(self) >= self.buffer_size

    def is_empty(self):
        return len(self) == 0

    def save_label(self, project: Project):
        labels = list(itertools.chain.from_iterable([example.create_label(project) for example in self.buffer]))
        labels = list(filter(None, labels))
        groups = group_by_class(labels)
        for klass, instances in groups.items():
            klass.objects.bulk_create(instances, ignore_conflicts=True)

    def save_data(self, project: Project) -> List[Example]:
        examples = [example.create_data(project) for example in self.buffer]
        return Example.objects.bulk_create(examples)

    def save_annotation(self, project: Project, user, examples):
        # mapping = {label.text: label for label in project.labels.all()}
        # Todo: move annotation class
        mapping = {}
        for model in [CategoryType, SpanType]:
            for label in model.objects.all():
                mapping[label.text] = label
        annotations = list(itertools.chain.from_iterable([
            data.create_annotation(user, example, mapping) for data, example in zip(self.buffer, examples)
        ]))
        groups = group_by_class(annotations)
        for klass, instances in groups.items():
            klass.objects.bulk_create(instances)


class BulkWriter(Writer):

    def __init__(self, batch_size: int):
        self.examples = Examples(batch_size)
        self._errors = []

    def save(self, reader: BaseReader, project: Project, user, cleaner):
        it = iter(reader)
        while True:
            try:
                example = next(it)
            except StopIteration:
                break
            try:
                example.clean(cleaner)
            except FileParseException as err:
                self._errors.append(err)

            self.examples.add(example)
            if self.examples.is_full():
                self.create(project, user)
                self.examples.clear()
        if not self.examples.is_empty():
            self.create(project, user)
            self.examples.clear()
        self._errors.extend(reader.errors)

    @property
    def errors(self) -> List[Dict[Any, Any]]:
        self._errors.sort(key=lambda e: e.line_num)
        return [error.dict() for error in self._errors]

    def create(self, project: Project, user):
        self.examples.save_label(project)
        ids = self.examples.save_data(project)
        self.examples.save_annotation(project, user, ids)