from django.db import transaction
import datetime
import hashlib
import logging
import os
import re
import uuid

from django.conf import settings
from django.utils import timezone
from paperless.db import GnuPG
from .classifier import DocumentClassifier

from .models import Document, FileInfo, Tag
from .parsers import ParseError
from .signals import (
    document_consumer_declaration,
    document_consumption_finished,
    document_consumption_started
)


class ConsumerError(Exception):
    pass


class Consumer:
    """
    Loop over every file found in CONSUMPTION_DIR and:
      1. Convert it to a greyscale pnm
      2. Use tesseract on the pnm
      3. Store the document in the MEDIA_ROOT with optional encryption
      4. Store the OCR'd text in the database
      5. Delete the document and image(s)
    """

    def __init__(self, consume=settings.CONSUMPTION_DIR,
                 scratch=settings.SCRATCH_DIR):

        self.logger = logging.getLogger(__name__)
        self.logging_group = None

        self.consume = consume
        self.scratch = scratch

        self.classifier = DocumentClassifier()

        os.makedirs(self.scratch, exist_ok=True)

        self.storage_type = Document.STORAGE_TYPE_UNENCRYPTED
        if settings.PASSPHRASE:
            self.storage_type = Document.STORAGE_TYPE_GPG

        if not self.consume:
            raise ConsumerError(
                "The CONSUMPTION_DIR settings variable does not appear to be "
                "set."
            )

        if not os.path.exists(self.consume):
            raise ConsumerError(
                "Consumption directory {} does not exist".format(self.consume))

        self.parsers = []
        for response in document_consumer_declaration.send(self):
            self.parsers.append(response[1])

        if not self.parsers:
            raise ConsumerError(
                "No parsers could be found, not even the default.  "
                "This is a problem."
            )

    def log(self, level, message):
        getattr(self.logger, level)(message, extra={
            "group": self.logging_group
        })

    @transaction.atomic
    def try_consume_file(self, file):
        """
        Return True if file was consumed
        """

        if not re.match(FileInfo.REGEXES["title"], file):
            return False

        doc = file

        if self._is_duplicate(doc):
            self.log(
                "warning",
                "Skipping {} as it appears to be a duplicate".format(doc)
            )
            return False

        self.log("info", "Consuming {}".format(doc))

        parser_class = self._get_parser_class(doc)
        if not parser_class:
            self.log(
                "error", "No parsers could be found for {}".format(doc))
            return False

        self.logging_group = uuid.uuid4()


        document_consumption_started.send(
            sender=self.__class__,
            filename=doc,
            logging_group=self.logging_group
        )

        document_parser = parser_class(doc, self.logging_group)

        try:
            thumbnail = document_parser.get_optimised_thumbnail()
            date = document_parser.get_date()
            document = self._store(
                document_parser.get_text(),
                doc,
                thumbnail,
                date
            )
        except ParseError as e:
            self.log("fatal", "PARSE FAILURE for {}: {}".format(doc, e))
            document_parser.cleanup()
            return False
        else:
            document_parser.cleanup()
            self._cleanup_doc(doc)

            self.log(
                "info",
                "Document {} consumption finished".format(document)
            )

            classifier = None

            try:
                self.classifier.reload()
                classifier = self.classifier
            except FileNotFoundError:
                self.log("warning", "Cannot classify documents, classifier "
                                    "model file was not found. Consider "
                                    "running python manage.py "
                                    "document_create_classifier.")

            document_consumption_finished.send(
                sender=self.__class__,
                document=document,
                logging_group=self.logging_group,
                classifier=classifier
            )
            return True

    def _get_parser_class(self, doc):
        """
        Determine the appropriate parser class based on the file
        """

        options = []
        for parser in self.parsers:
            result = parser(doc)
            if result:
                options.append(result)

        self.log(
            "info",
            "Parsers available: {}".format(
                ", ".join([str(o["parser"].__name__) for o in options])
            )
        )

        if not options:
            return None

        # Return the parser with the highest weight.
        return sorted(
            options, key=lambda _: _["weight"], reverse=True)[0]["parser"]

    def _store(self, text, doc, thumbnail, date):

        file_info = FileInfo.from_path(doc)

        stats = os.stat(doc)

        self.log("debug", "Saving record to database")

        created = file_info.created or date or timezone.make_aware(
                    datetime.datetime.fromtimestamp(stats.st_mtime))

        with open(doc, "rb") as f:
            document = Document.objects.create(
                correspondent=file_info.correspondent,
                title=file_info.title,
                content=text,
                file_type=file_info.extension,
                checksum=hashlib.md5(f.read()).hexdigest(),
                created=created,
                modified=created,
                storage_type=self.storage_type
            )

        relevant_tags = set(file_info.tags)
        if relevant_tags:
            tag_names = ", ".join([t.slug for t in relevant_tags])
            self.log("debug", "Tagging with {}".format(tag_names))
            document.tags.add(*relevant_tags)

        self._write(document, doc, document.source_path)
        self._write(document, thumbnail, document.thumbnail_path)

        document.save()

        self.log("debug", "Completed")

        return document

    def _write(self, document, source, target):
        with open(source, "rb") as read_file:
            with open(target, "wb") as write_file:
                if document.storage_type == Document.STORAGE_TYPE_UNENCRYPTED:
                    write_file.write(read_file.read())
                    return
                self.log("debug", "Encrypting")
                write_file.write(GnuPG.encrypted(read_file))

    def _cleanup_doc(self, doc):
        self.log("debug", "Deleting document {}".format(doc))
        os.unlink(doc)

    @staticmethod
    def _is_duplicate(doc):
        with open(doc, "rb") as f:
            checksum = hashlib.md5(f.read()).hexdigest()
        return Document.objects.filter(checksum=checksum).exists()