Add dashboard statistics module and refactor views for metrics handling

- Introduced a new `stats.py` module to encapsulate dashboard statistics building and cache key constants.
- Refactored `views.py` to utilize the new `build_stats` function for constructing metrics context, improving code organization and readability.
- Updated Prometheus query handling to streamline metrics fetching with a new `fetch_dashboard_metrics` function.
- Enhanced test cases to reflect changes in metrics fetching and context building, ensuring accurate functionality.
- Added new HTML templates for displaying detailed resource allocation and flavor statistics on the dashboard.

dashboard/stats.py

@@ -0,0 +1,76 @@
+"""Dashboard statistics building and cache key constants."""
+
+# Cache keys used by views
+CACHE_KEY_STATS = "dashboard_stats"
+CACHE_KEY_AUDITS = "dashboard_audits"
+CACHE_KEY_CURRENT_CLUSTER = "dashboard_current_cluster"
+CACHE_KEY_SOURCE_STATUS = "dashboard_source_status"
+
+# Empty structures for skeleton context (same shape as build_stats output)
+EMPTY_FLAVORS = {
+    "first_common_flavor": {"name": "—", "count": 0},
+    "second_common_flavor": None,
+    "third_common_flavor": None,
+}
+
+
+def build_stats(metrics: dict, region_name: str, flavors: dict) -> dict:
+    """
+    Build stats dict from raw metrics and OpenStack-derived data.
+    Returns region, pcpu, vcpu, pram, vram, vm, flavors (no audits/current_cluster).
+    """
+    hosts_total = metrics.get("hosts_total") or 1
+    pcpu_total = metrics.get("pcpu_total", 0)
+    pcpu_usage = metrics.get("pcpu_usage", 0)
+    vcpu_allocated = metrics.get("vcpu_allocated", 0)
+    vcpu_overcommit_max = metrics.get("vcpu_overcommit_max", 0)
+    pram_total = metrics.get("pram_total", 0)
+    pram_usage = metrics.get("pram_usage", 0)
+    vram_allocated = metrics.get("vram_allocated", 0)
+    vram_overcommit_max = metrics.get("vram_overcommit_max", 0)
+    vm_count = metrics.get("vm_count", 0)
+    vm_active = metrics.get("vm_active", 0)
+
+    vcpu_total = pcpu_total * vcpu_overcommit_max
+    vram_total = pram_total * vram_overcommit_max
+
+    return {
+        "region": {"name": region_name, "hosts_total": hosts_total},
+        "pcpu": {
+            "total": pcpu_total,
+            "usage": pcpu_usage,
+            "free": pcpu_total - pcpu_usage,
+            "used_percentage": (pcpu_usage / pcpu_total * 100) if pcpu_total else 0,
+        },
+        "vcpu": {
+            "total": vcpu_total,
+            "allocated": vcpu_allocated,
+            "free": vcpu_total - vcpu_allocated,
+            "allocated_percentage": (vcpu_allocated / vcpu_total * 100) if vcpu_total else 0,
+            "overcommit_ratio": (vcpu_allocated / pcpu_total) if pcpu_total else 0,
+            "overcommit_max": vcpu_overcommit_max,
+        },
+        "pram": {
+            "total": pram_total,
+            "usage": pram_usage,
+            "free": pram_total - pram_usage,
+            "used_percentage": (pram_usage / pram_total * 100) if pram_total else 0,
+        },
+        "vram": {
+            "total": vram_total,
+            "allocated": vram_allocated,
+            "free": vram_total - vram_allocated,
+            "allocated_percentage": (vram_allocated / vram_total * 100) if vram_total else 0,
+            "overcommit_ratio": (vram_allocated / pram_total) if pram_total else 0,
+            "overcommit_max": vram_overcommit_max,
+        },
+        "vm": {
+            "count": vm_count,
+            "active": vm_active,
+            "stopped": vm_count - vm_active,
+            "avg_cpu": vcpu_allocated / vm_count if vm_count else 0,
+            "avg_ram": vram_allocated / vm_count if vm_count else 0,
+            "density": vm_count / hosts_total if hosts_total else 0,
+        },
+        "flavors": flavors,
+    }