[templates] Fix navigation and add AGENTS file

vrobbler/apps/charts/views.py

@@ -414,4 +414,145 @@ class ChartRecordView(TemplateView):
                 ),
             }
 
+        context["chart_years"] = self.get_available_years(user)
+        context["period_type"] = self.get_period_type()
+        context["prev_period"] = self.get_prev_period_url(user)
+        context["next_period"] = self.get_next_period_url(user)
+
         return context
+
+    def get_available_years(self, user):
+        return list(
+            ChartRecord.objects.filter(user=user)
+            .values_list("year", flat=True)
+            .distinct()
+            .order_by("-year")
+        )
+
+    def get_period_type(self):
+        date_param = self.request.GET.get("date")
+        if not date_param:
+            return "current"
+        parts = date_param.split("-")
+        if len(parts) >= 3 and not parts[2].startswith("W"):
+            return "day"
+        if len(parts) >= 2 and parts[1].startswith("W"):
+            return "week"
+        if len(parts) >= 2:
+            return "month"
+        return "year"
+
+    def parse_date_params(self):
+        date_param = self.request.GET.get("date")
+        if not date_param:
+            return None, None, None, None
+
+        parts = date_param.split("-")
+        year = int(parts[0])
+        week = None
+        month = None
+        day = None
+
+        if len(parts) >= 2 and parts[1].startswith("W"):
+            week = int(parts[1].lstrip("W"))
+        elif len(parts) >= 2:
+            try:
+                month = int(parts[1])
+            except ValueError:
+                pass
+
+        if len(parts) >= 3:
+            if parts[2].startswith("W"):
+                week = int(parts[2].lstrip("W"))
+            else:
+                day = int(parts[2])
+
+        return year, month, week, day
+
+    def get_prev_period_url(self, user):
+        period_type = self.get_period_type()
+
+        if period_type == "current":
+            return None
+
+        year, month, week, day = self.parse_date_params()
+        if year is None:
+            return None
+
+        available_years = self.get_available_years(user)
+
+        if period_type == "day" and month and day:
+            if month == 1:
+                prev_month = 12
+                prev_year = year - 1
+            else:
+                prev_month = month - 1
+                prev_year = year
+            return f"/charts/?date={prev_year}-{prev_month:02d}"
+        elif period_type == "month" and month:
+            if month == 1:
+                prev_month = 12
+                prev_year = year - 1
+            else:
+                prev_month = month - 1
+                prev_year = year
+            return f"/charts/?date={prev_year}-{prev_month:02d}"
+        elif period_type == "week" and week:
+            if week == 1:
+                prev_week = 52
+                prev_year = year - 1
+            else:
+                prev_week = week - 1
+                prev_year = year
+            return f"/charts/?date={prev_year}-W{prev_week:02d}"
+        elif period_type == "year":
+            if year in available_years:
+                idx = available_years.index(year)
+                if idx + 1 < len(available_years):
+                    return f"/charts/?date={available_years[idx + 1]}"
+            return f"/charts/?date={year - 1}"
+        return None
+
+    def get_next_period_url(self, user):
+        period_type = self.get_period_type()
+
+        if period_type == "current":
+            return None
+
+        year, month, week, day = self.parse_date_params()
+        if year is None:
+            return None
+
+        available_years = self.get_available_years(user)
+
+        if period_type == "day" and month and day:
+            if month == 12:
+                next_month = 1
+                next_year = year + 1
+            else:
+                next_month = month + 1
+                next_year = year
+            return f"/charts/?date={next_year}-{next_month:02d}"
+        elif period_type == "month" and month:
+            if month == 12:
+                next_month = 1
+                next_year = year + 1
+            else:
+                next_month = month + 1
+                next_year = year
+            return f"/charts/?date={next_year}-{next_month:02d}"
+        elif period_type == "week" and week:
+            if week == 52:
+                next_week = 1
+                next_year = year + 1
+            else:
+                next_week = week + 1
+                next_year = year
+            return f"/charts/?date={next_year}-W{next_week:02d}"
+        elif period_type == "year":
+            if year in available_years:
+                idx = available_years.index(year)
+                if idx > 0:
+                    return f"/charts/?date={available_years[idx - 1]}"
+            return f"/charts/?date={year + 1}"
+        return None