from __future__ import unicode_literals

from django.db import models
from django.contrib.postgres import fields
from django.utils import timezone
from django.dispatch import receiver
from .api_client import ApiClient
import json
from django.db.models import signals
from requests.exceptions import ConnectionError
from .exceptions import ProcessingException

def api(func):
    """
    Catches JSON decoding errors that might happen when the server
    answers unexpectedly
    """
    def wrapper(*args,**kwargs):
        try:
            return func(*args, **kwargs)
        except json.decoder.JSONDecodeError as e:
            raise ProcessingException(str(e))

    return wrapper

class ProcessingNode(models.Model):
    hostname = models.CharField(max_length=255, help_text="Hostname where the node is located (can be an internal hostname as well)")
    port = models.PositiveIntegerField(help_text="Port that connects to the node's API")
    api_version = models.CharField(max_length=32, null=True, help_text="API version used by the node")
    last_refreshed = models.DateTimeField(null=True, help_text="When was the information about this node last retrieved?")
    queue_count = models.PositiveIntegerField(default=0, help_text="Number of tasks currently being processed by this node (as reported by the node itself)")
    available_options = fields.JSONField(default=dict(), help_text="Description of the options that can be used for processing")
    
    def __str__(self):
        return '{}:{}'.format(self.hostname, self.port)

    @api
    def update_node_info(self):
        """
        Retrieves information and options from the node API
        and saves it into the database.

        :returns: True if information could be updated, False otherwise
        """
        api_client = self.api_client()
        try:
            info = api_client.info()
            self.api_version = info['version']
            self.queue_count = info['taskQueueCount']

            options = api_client.options()
            self.available_options = options
            self.last_refreshed = timezone.now()
            self.save()
            return True
        except ConnectionError:
            return False

    def api_client(self):
        return ApiClient(self.hostname, self.port)

    def get_available_options_json(self, pretty=False):
        """
        :returns available options in JSON string format
        """
        kwargs = dict(indent=4, separators=(',', ": ")) if pretty else dict() 
        return json.dumps(self.available_options, **kwargs)

    @api
    def process_new_task(self, images, name=None, options=[]):
        """
        Sends a set of images (and optional GCP file) via the API
        to start processing.

        :param images: list of path images
        :param name: name of the task
        :param options: options to be used for processing ([{'name': optionName, 'value': optionValue}, ...])

        :returns UUID of the newly created task
        """
        if len(images) < 2: raise ProcessingException("Need at least 2 images")

        api_client = self.api_client()
        result = api_client.new_task(images, name, options)
        if result['uuid']:
            return result['uuid']
        elif result['error']:
            raise ProcessingException(result['error'])

    @api
    def get_task_info(self, uuid):
        """
        Gets information about this task, such as name, creation date, 
        processing time, status, command line options and number of 
        images being processed.
        """
        api_client = self.api_client()
        result = api_client.task_info(uuid)
        if isinstance(result, dict) and 'uuid' in result:
            return result
        elif isinstance(result, dict) and 'error' in result:
            raise ProcessingException(result['error'])
        else:
            raise ProcessingException("Unknown result from task info: {}".format(result))

    @api
    def get_task_console_output(self, uuid, line):
        """
        Retrieves the console output of the OpenDroneMap's process.
        Useful for monitoring execution and to provide updates to the user.
        """
        api_client = self.api_client()
        result = api_client.task_output(uuid, line)
        if isinstance(result, dict) and 'error' in result:
            raise ProcessingException(result['error'])
        elif isinstance(result, list):
            return "".join(result)
        else:
            raise ProcessingException("Unknown response for console output: {}".format(result))

    @api
    def cancel_task(self, uuid):
        """
        Cancels a task (stops its execution, or prevents it from being executed)
        """
        api_client = self.api_client()
        return self.handle_generic_post_response(api_client.task_cancel(uuid))

    @api
    def remove_task(self, uuid):
        """
        Removes a task and deletes all of its assets
        """
        api_client = self.api_client()
        return self.handle_generic_post_response(api_client.task_remove(uuid))

    @api
    def download_task_asset(self, uuid, asset):
        """
        Downloads a task asset
        """
        api_client = self.api_client()
        res = api_client.task_download(uuid, asset)
        if isinstance(res, dict) and 'error' in res:
            raise ProcessingException(res['error'])
        else:
            return res

    @api
    def restart_task(self, uuid):
        """
        Restarts a task that was previously canceled or that had failed to process
        """
        api_client = self.api_client()
        return self.handle_generic_post_response(api_client.task_restart(uuid))

    @staticmethod
    def handle_generic_post_response(result):
        """
        Handles a POST response that has either a "success" flag, or an error message.
        This is a common response in node-OpenDroneMap POST calls.
        :param result: result of API call
        :return: True on success, raises ProcessingException otherwise
        """
        if isinstance(result, dict) and 'error' in result:
            raise ProcessingException(result['error'])
        elif isinstance(result, dict) and 'success' in result:
            return True
        else:
            raise ProcessingException("Unknown response: {}".format(result))

# First time a processing node is created, automatically try to update
@receiver(signals.post_save, sender=ProcessingNode, dispatch_uid="update_processing_node_info")
def auto_update_node_info(sender, instance, created, **kwargs):
    if created:
        instance.update_node_info()