package handlers

import (
	"io"
	"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
	collector *collector.Collector
}

// NewGraphHandlers loads the graph from the given YAML file path.
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)
			h.loaded = graph.New()
			h.yamlData = []byte("nodes: {}\n")
		} else {
			log.Fatalf("[graph] failed to load graph from %q: %v", yamlPath, err)
		}
	}
	return h
}

func (h *GraphHandlers) reload() error {
	data, err := os.ReadFile(h.path)
	if err != nil {
		return err
	}
	g, err := graph.ParseYAML(data)
	if err != nil {
		return err
	}
	h.mu.Lock()
	h.yamlData = data
	h.loaded = g
	h.mu.Unlock()
	return nil
}

// GetGraph returns the current parsed graph.
func (h *GraphHandlers) GetGraph() *graph.Graph {
	h.mu.RLock()
	defer h.mu.RUnlock()
	return h.loaded
}

// GetYAML returns the raw YAML content.
// @Summary Get dependency graph YAML
// @Description Returns the service dependency graph as raw YAML text
// @Tags graph
// @Produce plain
// @Success 200 {string} string "YAML content"
// @Security Bearer
// @Router /graph [get]
func (h *GraphHandlers) GetYAML(c *gin.Context) {
	h.mu.RLock()
	defer h.mu.RUnlock()
	c.Data(http.StatusOK, "text/yaml", h.yamlData)
}

// UpdateYAML updates the graph from new YAML text.
// @Summary Update dependency graph YAML
// @Description Replaces the service dependency graph YAML and reloads it
// @Tags graph
// @Accept plain
// @Produce json
// @Param body body string true "New YAML content"
// @Success 200 {object} map[string]string
// @Failure 400 {object} map[string]string
// @Security Bearer
// @Router /graph [put]
func (h *GraphHandlers) UpdateYAML(c *gin.Context) {
	body, err := io.ReadAll(c.Request.Body)
	if err != nil {
		c.JSON(http.StatusBadRequest, gin.H{"error": "failed to read body"})
		return
	}

	g, err := graph.ParseYAML(body)
	if err != nil {
		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
		return
	}

	if err := os.WriteFile(h.path, body, 0o644); err != nil {
		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to write graph file"})
		return
	}

	h.mu.Lock()
	h.yamlData = body
	h.loaded = g
	h.mu.Unlock()

	log.Printf("[graph] updated graph from admin, saved to %s", h.path)
	c.JSON(http.StatusOK, gin.H{"message": "graph updated"})
}

// StartupOrder returns the computed service startup order.
// @Summary Get startup order
// @Description Returns the topologically sorted service startup order
// @Tags graph
// @Produce json
// @Success 200 {array} string
// @Failure 400 {object} map[string]string
// @Security Bearer
// @Router /graph/order [get]
func (h *GraphHandlers) StartupOrder(c *gin.Context) {
	h.mu.RLock()
	g := h.loaded
	h.mu.RUnlock()

	order, err := g.TopologicalSort()
	if err != nil {
		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
		return
	}

	c.JSON(http.StatusOK, order)
}

// CycleCheck checks if the graph has cycles.
// @Summary Check for cycles
// @Description Returns whether the dependency graph contains cycles
// @Tags graph
// @Produce json
// @Success 200 {object} map[string]bool
// @Security Bearer
// @Router /graph/cycle [get]
func (h *GraphHandlers) CycleCheck(c *gin.Context) {
	h.mu.RLock()
	g := h.loaded
	h.mu.RUnlock()

	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"
}