Import EK channels from USB if present

This is a first step to import the content from USB if present instead
of from network, without importing the content, just the metadata.

The list of channels is getted from the network right now, waiting for
the metadata.json definition that could be present in the
KOLIBRI_DATA/content folder:
learningequality/kolibri#9460

https://phabricator.endlessm.com/T33526

kolibri_explore_plugin/views.py

@@ -6,6 +6,7 @@
 import os
 
 import requests
+from django.core.management import call_command
 from django.http import FileResponse
 from django.http import Http404
 from django.http import HttpResponse
@@ -17,6 +18,9 @@
 from django.views.generic.base import View
 from kolibri.core.content.api import cache_forever
 from kolibri.core.content.api import RemoteChannelViewSet
+from kolibri.core.content.models import ContentNode
+from kolibri.core.content.models import LocalFile
+from kolibri.core.content.utils import paths
 from kolibri.core.content.zip_wsgi import add_security_headers
 from kolibri.core.content.zip_wsgi import get_embedded_file
 from kolibri.core.decorators import cache_no_user_data
@@ -109,6 +113,31 @@ def get(self, request, app):
             return HttpResponse(json_file, content_type="application/json")
 
 
+def _import_channel_from_usb(channel_id, directory):
+    """
+    Imports the specified channel from the content directory
+    and then make all the content available.
+
+    This function doesn't import the actual content, just the channel
+    metadata, the content should exists and be present in the
+    KOLIBRI_CONTENT_FALLBACK_DIRS configuration, in other case the
+    imported content with this method won't work correctly.
+
+    Function to be called as a background call adding it to a task queue
+    """
+    call_command(
+        "importchannel",
+        "disk",
+        channel_id,
+        directory,
+    )
+    # Enable the content after import
+    nodes = ContentNode.objects.filter(channel_id=channel_id)
+    files = LocalFile.objects.filter(files__contentnode__channel_id=channel_id)
+    nodes.update(available=True)
+    files.update(available=True)
+
+
 @method_decorator(csrf_exempt, name="dispatch")
 class EndlessLearningCollection(View):
     COLLECTION_TOKEN = "totoj-jupak"
@@ -144,10 +173,37 @@ def get(self, request):
             json.dumps(jobs_response), content_type="application/json"
         )
 
+    def import_job(self, task):
+        content_fallback = paths.get_content_fallback_paths()
+        if content_fallback:
+            task.update({"type": "DISKIMPORT"})
+            # Just getting the first one
+            directory = os.path.dirname(content_fallback[0])
+            job_id = queue.enqueue(
+                _import_channel_from_usb,
+                task["channel_id"],
+                directory,
+                extra_metadata=task,
+                track_progress=True,
+            )
+        else:
+            task.update({"type": "REMOTEIMPORT"})
+            job_id = queue.enqueue(
+                _remoteimport,
+                task["channel_id"],
+                task["baseurl"],
+                extra_metadata=task,
+                track_progress=True,
+                cancellable=True,
+            )
+
+        return job_id
+
     def post(self, request):
         token = self.COLLECTION_TOKEN
 
         channel_viewset = RemoteChannelViewSet()
+        # TODO: get the list of channels from USB if exists
         channels = channel_viewset._make_channel_endpoint_request(
             identifier=token
         )
@@ -161,18 +217,9 @@ def post(self, request):
                 "channel_name": channel["name"],
                 "baseurl": self.BASE_URL,
                 "started_by_username": "endless",
-                "type": "REMOTEIMPORT",
                 "PID": pid,
             }
-
-            job_id = queue.enqueue(
-                _remoteimport,
-                task["channel_id"],
-                task["baseurl"],
-                extra_metadata=task,
-                track_progress=True,
-                cancellable=True,
-            )
+            job_id = self.import_job(task)
             job_ids.append(job_id)
 
         request.session["job_ids"] = job_ids