feat(backend): add root cause calculation

backend/cmd/main.go

@@ -110,7 +110,7 @@ func main() {
 	if graphPath == "" {
 		graphPath = "/etc/hellreign/services.yaml"
 	}
-	graphHandlers := handlers.NewGraphHandlers(graphPath)
+	graphHandlers := handlers.NewGraphHandlers(graphPath, coll)
 
 	agents := handlers.NewAgentsGroup(h, coll)
 	auth := handlers.AuthGroup{Handlers: h}
@@ -226,6 +226,7 @@ func main() {
 			graphGroup.PUT("", graphHandlers.UpdateYAML)
 			graphGroup.GET("/order", graphHandlers.StartupOrder)
 			graphGroup.GET("/cycle", graphHandlers.CycleCheck)
+			graphGroup.GET("/failure", graphHandlers.GetFailureRootCause)
 		}
 
 		// Agent registration

backend/internal/handlers/graph.go

@@ -5,23 +5,26 @@ import (
 	"log"
 	"net/http"
 	"os"
+	"strings"
 	"sync"
 
 	"gitea.d3m0k1d.ru/d3m0k1d/HellreigN/backend/internal/graph"
+	"gitea.d3m0k1d.ru/d3m0k1d/HellreigN/backend/internal/grpcsrv/collector"
 	"github.com/gin-gonic/gin"
 )
 
 // GraphHandlers manages the service dependency graph.
 type GraphHandlers struct {
-	path     string
-	mu       sync.RWMutex
-	yamlData []byte
-	loaded   *graph.Graph
+	path      string
+	mu        sync.RWMutex
+	yamlData  []byte
+	loaded    *graph.Graph
+	collector *collector.Collector
 }
 
 // NewGraphHandlers loads the graph from the given YAML file path.
-func NewGraphHandlers(yamlPath string) *GraphHandlers {
-	h := &GraphHandlers{path: yamlPath}
+func NewGraphHandlers(yamlPath string, coll *collector.Collector) *GraphHandlers {
+	h := &GraphHandlers{path: yamlPath, collector: coll}
 	if err := h.reload(); err != nil {
 		if _, ok := err.(*os.PathError); ok {
 			log.Printf("[graph] no graph file at %q, starting with empty graph", yamlPath)
@@ -147,3 +150,209 @@ func (h *GraphHandlers) CycleCheck(c *gin.Context) {
 
 	c.JSON(http.StatusOK, gin.H{"has_cycle": g.HasCycle()})
 }
+
+// ServiceStatusOut represents a service and its current status.
+type ServiceStatusOut struct {
+	NodeID  string `json:"node_id"`
+	Name    string `json:"name"`
+	Status  string `json:"status"`
+	Healthy bool   `json:"healthy"`
+}
+
+// FailureRootCauseOut represents the result of a failure analysis.
+type FailureRootCauseOut struct {
+	Affected   ServiceStatusOut `json:"affected"`
+	RootCause  *ServiceStatusOut `json:"root_cause,omitempty"`
+	DependencyChain []string    `json:"dependency_chain,omitempty"`
+}
+
+// GetFailureRootCause analyzes the dependency graph and current service
+// statuses to find the root cause of a service failure.
+// If the specified service is unhealthy, it traverses its dependencies
+// to find the first unhealthy dependency — the one that is the root cause.
+// @Summary Find failure root cause
+// @Description Analyzes dependencies and service statuses to find the root cause of a failure
+// @Tags graph
+// @Param node_id query string false "Node ID (agent label)"
+// @Param service query string true "Service name"
+// @Produce json
+// @Success 200 {object} FailureRootCauseOut
+// @Failure 400 {object} map[string]string
+// @Security Bearer
+// @Router /graph/failure [get]
+func (h *GraphHandlers) GetFailureRootCause(c *gin.Context) {
+	nodeID := c.Query("node_id")
+	svcName := c.Query("service")
+	if svcName == "" {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "service query param is required"})
+		return
+	}
+
+	h.mu.RLock()
+	g := h.loaded
+	h.mu.RUnlock()
+
+	if g == nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "no graph loaded"})
+		return
+	}
+
+	// Build a map of service statuses from all agents
+	svcStatus := h.buildServiceStatusMap()
+
+	// If no node specified, search all nodes for the service
+	if nodeID == "" {
+		for _, node := range g.Nodes() {
+			if _, ok := g.GetService(node.ID, svcName); ok {
+				nodeID = node.ID
+				break
+			}
+		}
+	}
+
+	if nodeID == "" {
+		c.JSON(http.StatusNotFound, gin.H{"error": "service not found in graph"})
+		return
+	}
+
+	if _, ok := g.GetService(nodeID, svcName); !ok {
+		c.JSON(http.StatusNotFound, gin.H{"error": "service not found in node"})
+		return
+	}
+
+	// Get current status
+	status := svcStatus[nodeID+":"+svcName]
+	affected := ServiceStatusOut{
+		NodeID:  nodeID,
+		Name:    svcName,
+		Status:  status.status,
+		Healthy: status.healthy,
+	}
+
+	// If the service is healthy, no failure to analyze
+	if status.healthy {
+		c.JSON(http.StatusOK, FailureRootCauseOut{
+			Affected: affected,
+		})
+		return
+	}
+
+	// Find root cause: traverse dependencies to find the first unhealthy one
+	rootCause, chain := findRootCause(g, nodeID, svcName, svcStatus)
+
+	out := FailureRootCauseOut{
+		Affected:        affected,
+		DependencyChain: chain,
+	}
+	if rootCause != nil {
+		out.RootCause = rootCause
+	}
+
+	c.JSON(http.StatusOK, out)
+}
+
+// svcStatusEntry holds parsed status info.
+type svcStatusEntry struct {
+	status  string
+	healthy bool
+}
+
+// buildServiceStatusMap creates a map of "nodeID:serviceName" → status.
+// Matches graph nodes to agent labels in the collector.
+func (h *GraphHandlers) buildServiceStatusMap() map[string]svcStatusEntry {
+	result := make(map[string]svcStatusEntry)
+
+	h.mu.RLock()
+	nodes := h.loaded.Nodes()
+	h.mu.RUnlock()
+
+	for _, agent := range h.collector.Agents() {
+		for _, svc := range agent.Services {
+			healthy := isHealthyStatus(svc.Status)
+			entry := svcStatusEntry{status: svc.Status, healthy: healthy}
+
+			// Try exact node match first
+			key := agent.Label + ":" + svc.Name
+			result[key] = entry
+
+			// Also register under all nodes that don't have a status yet
+			for _, node := range nodes {
+				nodeKey := node.ID + ":" + svc.Name
+				if _, exists := result[nodeKey]; !exists {
+					result[nodeKey] = entry
+				}
+			}
+		}
+	}
+
+	return result
+}
+
+// findRootCause traverses the dependency graph to find the first unhealthy dependency.
+func findRootCause(g *graph.Graph, nodeID, svcName string, statusMap map[string]svcStatusEntry) (*ServiceStatusOut, []string) {
+	visited := make(map[string]bool)
+	var chain []string
+
+	var dfs func(string, string) *ServiceStatusOut
+	dfs = func(nid, sname string) *ServiceStatusOut {
+		key := nid + ":" + sname
+		chain = append(chain, key)
+		visited[key] = true
+
+		svc, ok := g.GetService(nid, sname)
+		if !ok {
+			return nil
+		}
+
+		// Check each dependency
+		for _, dep := range svc.Dependencies {
+			depNodeID := dep.Target.NodeID
+			if depNodeID == "" {
+				depNodeID = nid
+			}
+			depKey := depNodeID + ":" + dep.Target.Name
+
+			if visited[depKey] {
+				continue // avoid loops
+			}
+
+			depStatus := statusMap[depKey]
+
+			if !depStatus.healthy {
+				// This dependency is unhealthy — check if IT has an unhealthy dependency
+				// (to find the true root cause)
+				if deeper := dfs(depNodeID, dep.Target.Name); deeper != nil {
+					return deeper
+				}
+				// This is the root cause
+				return &ServiceStatusOut{
+					NodeID:  depNodeID,
+					Name:    dep.Target.Name,
+					Status:  depStatus.status,
+					Healthy: false,
+				}
+			}
+		}
+
+		return nil
+	}
+
+	root := dfs(nodeID, svcName)
+
+	// Deduplicate chain
+	seen := make(map[string]bool)
+	var deduped []string
+	for _, k := range chain {
+		if !seen[k] {
+			seen[k] = true
+			deduped = append(deduped, k)
+		}
+	}
+
+	return root, deduped
+}
+
+func isHealthyStatus(status string) bool {
+	s := strings.ToLower(status)
+	return s == "running" || s == "up" || s == "healthy"
+}