Show average run times for imports

This should give users a sense of when to start wondering if their
import isn't running after all.

bookwyrm/views/imports/import_data.py

@@ -1,10 +1,14 @@
 """ import books from another app """
 from io import TextIOWrapper
+import datetime
 
 from django.contrib.auth.decorators import login_required
+from django.db.models import Avg, ExpressionWrapper, F, fields
+from django.core.paginator import Paginator
 from django.http import HttpResponseBadRequest
 from django.shortcuts import redirect
 from django.template.response import TemplateResponse
+from django.utils import timezone
 from django.utils.decorators import method_decorator
 from django.utils.translation import gettext_lazy as _
 from django.views import View
@@ -17,6 +21,7 @@ from bookwyrm.importers import (
     StorygraphImporter,
     OpenLibraryImporter,
 )
+from bookwyrm.settings import PAGE_LENGTH
 
 # pylint: disable= no-self-use
 @method_decorator(login_required, name="dispatch")
@@ -25,16 +30,39 @@ class Import(View):
 
     def get(self, request):
         """load import page"""
-        return TemplateResponse(
-            request,
-            "import/import.html",
-            {
-                "import_form": forms.ImportForm(),
-                "jobs": models.ImportJob.objects.filter(user=request.user).order_by(
-                    "-created_date"
-                ),
-            },
+        jobs = models.ImportJob.objects.filter(user=request.user).order_by(
+            "-created_date"
         )
+        paginated = Paginator(jobs, PAGE_LENGTH)
+        page = paginated.get_page(request.GET.get("page"))
+        data = {
+            "import_form": forms.ImportForm(),
+            "jobs": page,
+            "page_range": paginated.get_elided_page_range(
+                page.number, on_each_side=2, on_ends=1
+            ),
+        }
+
+        last_week = timezone.now() - datetime.timedelta(days=7)
+        recent_avg = (
+            models.ImportJob.objects.filter(created_date__gte=last_week, complete=True)
+            .annotate(
+                runtime=ExpressionWrapper(
+                    F("updated_date") - F("created_date"),
+                    output_field=fields.DurationField(),
+                )
+            )
+            .aggregate(Avg("runtime"))
+            .get("runtime__avg")
+        )
+        if recent_avg:
+            seconds = recent_avg.total_seconds()
+            if seconds > 60**2:
+                data["recent_avg_hours"] = recent_avg.seconds / (60**2)
+            else:
+                data["recent_avg_minutes"] = recent_avg.seconds / 60
+
+        return TemplateResponse(request, "import/import.html", data)
 
     def post(self, request):
         """ingest a goodreads csv"""