Display playtime graph on session list

Fixes #29

src/web/common/util/plots.py

@@ -0,0 +1,64 @@
+import pandas as pd
+import matplotlib.pyplot as plt
+from matplotlib.dates import date2num
+import base64
+from io import BytesIO
+from tracker.models import Session
+from django.db.models import Sum, IntegerField, F
+from django.db.models.functions import TruncDay
+import logging
+from datetime import datetime
+from django.db.models import QuerySet
+
+
+def key_value_to_value_value(data):
+    return {data["date"]: data["hours"]}
+
+
+def playtime_over_time_chart(queryset: QuerySet = Session.objects):
+    microsecond_in_second = 1000000
+    result = (
+        queryset.annotate(date=TruncDay("timestamp_start"))
+        .values("date")
+        .annotate(
+            hours=Sum(
+                F("duration_calculated") + F("duration_manual"),
+                output_field=IntegerField(),
+            )
+        )
+        .values("date", "hours")
+    )
+    keys = []
+    values = []
+    running_total = int(0)
+    for item in result:
+        date_value = datetime.strftime(item["date"], "%d-%m-%Y")
+        keys.append(date_value)
+        running_total += int(item["hours"] / (3600 * microsecond_in_second))
+        values.append(running_total)
+    data = [keys, values]
+    return get_chart(data, title="Playtime over time", xlabel="Date", ylabel="Hours")
+
+
+def get_graph():
+    buffer = BytesIO()
+    plt.savefig(buffer, format="svg", transparent=True)
+    buffer.seek(0)
+    image_png = buffer.getvalue()
+    graph = base64.b64encode(image_png)
+    graph = graph.decode("utf-8")
+    buffer.close()
+    return graph
+
+
+def get_chart(data, title="", xlabel="", ylabel=""):
+    plt.style.use("dark_background")
+    plt.switch_backend("SVG")
+    fig = plt.figure(figsize=(10, 4))
+    plt.plot(data[0], data[1])
+    plt.title(title)
+    plt.xlabel(xlabel)
+    plt.ylabel(ylabel)
+    plt.tight_layout()
+    chart = get_graph()
+    return chart