Add timeline per category

nummi/plot/urls.py

@@ -5,4 +5,5 @@ from . import views
 urlpatterns = [
     path("timeline", views.timeline, name="timeline"),
     path("categories", views.categories, name="categories"),
+    path("category/<uuid>", views.category, name="category"),
 ]

nummi/plot/views.py

@@ -5,6 +5,7 @@ import matplotlib.pyplot as plt
 from matplotlib import dates as mdates
 from django.db import models
 from django.contrib.auth.decorators import login_required
+from django.shortcuts import get_object_or_404
 from django.http import HttpResponse
 from django.utils.translation import gettext as _
 
@@ -63,3 +64,35 @@ def categories(request):
     fig.savefig(_io, format="svg")
 
     return HttpResponse(_io.getvalue(), headers={"Content-Type": "image/svg+xml"})
+
+
+@login_required
+def category(request, uuid):
+    _category = get_object_or_404(Category, id=uuid)
+    _values = (
+        Transaction.objects.filter(category=_category)
+        .annotate(m=models.functions.TruncMonth("date"))
+        .values("m")
+        .annotate(sum=models.Sum("value"))
+        .order_by("m")
+    )
+
+    fig, ax = plt.subplots()
+    ax.step(
+        [v["m"] for v in _values],
+        [v["sum"] for v in _values],
+        where="post",
+    )
+    ax.xaxis.set_major_formatter(
+        mdates.ConciseDateFormatter(ax.xaxis.get_major_locator())
+    )
+    ax.autoscale(True, "x", True)
+    _ym, _yp = ax.get_ylim()
+    ax.set(ylim=(min(_ym, 0), max(_yp, 0)))
+    ax.set(ylabel=f"{_category.name} (€)")
+
+    _io = io.StringIO()
+
+    fig.savefig(_io, format="svg")
+
+    return HttpResponse(_io.getvalue(), headers={"Content-Type": "image/svg+xml"})