package service

import (
	"atsflare/model"
	"errors"
	"sort"
	"time"

	"gorm.io/gorm"
)

type DashboardOverviewView struct {
	GeneratedAt  time.Time             `json:"generated_at"`
	Summary      DashboardSummary      `json:"summary"`
	Traffic      DashboardTraffic      `json:"traffic"`
	Capacity     DashboardCapacity     `json:"capacity"`
	Config       DashboardConfig       `json:"config"`
	Nodes        []DashboardNodeHealth `json:"nodes"`
	ActiveAlerts []DashboardAlert      `json:"active_alerts"`
}

type DashboardSummary struct {
	TotalNodes     int `json:"total_nodes"`
	OnlineNodes    int `json:"online_nodes"`
	OfflineNodes   int `json:"offline_nodes"`
	PendingNodes   int `json:"pending_nodes"`
	UnhealthyNodes int `json:"unhealthy_nodes"`
	ActiveAlerts   int `json:"active_alerts"`
	LaggingNodes   int `json:"lagging_nodes"`
}

type DashboardTraffic struct {
	RequestCount   int64   `json:"request_count"`
	UniqueVisitors int64   `json:"unique_visitors"`
	ErrorCount     int64   `json:"error_count"`
	EstimatedQPS   float64 `json:"estimated_qps"`
	ReportedNodes  int     `json:"reported_nodes"`
}

type DashboardCapacity struct {
	AverageCPUUsagePercent    float64 `json:"average_cpu_usage_percent"`
	AverageMemoryUsagePercent float64 `json:"average_memory_usage_percent"`
	HighCPUNodes              int     `json:"high_cpu_nodes"`
	HighMemoryNodes           int     `json:"high_memory_nodes"`
	HighStorageNodes          int     `json:"high_storage_nodes"`
}

type DashboardConfig struct {
	ActiveVersion string `json:"active_version"`
	LaggingNodes  int    `json:"lagging_nodes"`
	PendingNodes  int    `json:"pending_nodes"`
}

type DashboardNodeHealth struct {
	ID                  uint      `json:"id"`
	NodeID              string    `json:"node_id"`
	Name                string    `json:"name"`
	Status              string    `json:"status"`
	OpenrestyStatus     string    `json:"openresty_status"`
	CurrentVersion      string    `json:"current_version"`
	LastSeenAt          time.Time `json:"last_seen_at"`
	ActiveEventCount    int       `json:"active_event_count"`
	CPUUsagePercent     float64   `json:"cpu_usage_percent"`
	MemoryUsagePercent  float64   `json:"memory_usage_percent"`
	StorageUsagePercent float64   `json:"storage_usage_percent"`
	RequestCount        int64     `json:"request_count"`
	ErrorCount          int64     `json:"error_count"`
	UniqueVisitorCount  int64     `json:"unique_visitor_count"`
}

type DashboardAlert struct {
	NodeID          string    `json:"node_id"`
	NodeName        string    `json:"node_name"`
	EventType       string    `json:"event_type"`
	Severity        string    `json:"severity"`
	Message         string    `json:"message"`
	LastTriggeredAt time.Time `json:"last_triggered_at"`
	Status          string    `json:"status"`
}

func GetDashboardOverview() (*DashboardOverviewView, error) {
	now := time.Now()
	since := now.Add(-24 * time.Hour)

	nodes, err := model.ListNodes()
	if err != nil {
		return nil, err
	}

	activeVersion := ""
	if version, versionErr := model.GetActiveConfigVersion(); versionErr == nil {
		activeVersion = version.Version
	} else if !errors.Is(versionErr, gorm.ErrRecordNotFound) {
		return nil, versionErr
	}

	view := &DashboardOverviewView{
		GeneratedAt: now,
		Nodes:       make([]DashboardNodeHealth, 0, len(nodes)),
	}

	var cpuNodeCount int
	var memoryNodeCount int

	for _, node := range nodes {
		computedStatus := computeNodeStatus(node)
		switch computedStatus {
		case NodeStatusOnline:
			view.Summary.OnlineNodes++
		case NodeStatusOffline:
			view.Summary.OfflineNodes++
		case NodeStatusPending:
			view.Summary.PendingNodes++
		}
		if node.OpenrestyStatus == OpenrestyStatusUnhealthy {
			view.Summary.UnhealthyNodes++
		}
		if activeVersion != "" && node.CurrentVersion != "" && node.CurrentVersion != activeVersion {
			view.Summary.LaggingNodes++
		}
		if activeVersion != "" && node.CurrentVersion == "" && computedStatus != NodeStatusPending {
			view.Summary.LaggingNodes++
		}

		latestSnapshot := latestMetricSnapshotForNode(node.NodeID, since)
		latestTraffic := latestTrafficReportForNode(node.NodeID, since)
		activeEvents, eventErr := model.ListNodeHealthEvents(node.NodeID, true, 20)
		if eventErr != nil {
			return nil, eventErr
		}

		nodeHealth := DashboardNodeHealth{
			ID:               node.ID,
			NodeID:           node.NodeID,
			Name:             node.Name,
			Status:           computedStatus,
			OpenrestyStatus:  node.OpenrestyStatus,
			CurrentVersion:   node.CurrentVersion,
			LastSeenAt:       node.LastSeenAt,
			ActiveEventCount: len(activeEvents),
		}

		for _, event := range activeEvents {
			view.ActiveAlerts = append(view.ActiveAlerts, DashboardAlert{
				NodeID:          node.NodeID,
				NodeName:        node.Name,
				EventType:       event.EventType,
				Severity:        event.Severity,
				Message:         event.Message,
				LastTriggeredAt: event.LastTriggeredAt,
				Status:          event.Status,
			})
		}

		if latestSnapshot != nil {
			nodeHealth.CPUUsagePercent = latestSnapshot.CPUUsagePercent
			nodeHealth.MemoryUsagePercent = percentage(latestSnapshot.MemoryUsedBytes, latestSnapshot.MemoryTotalBytes)
			nodeHealth.StorageUsagePercent = percentage(latestSnapshot.StorageUsedBytes, latestSnapshot.StorageTotalBytes)
			if latestSnapshot.CPUUsagePercent > 0 {
				view.Capacity.AverageCPUUsagePercent += latestSnapshot.CPUUsagePercent
				cpuNodeCount++
			}
			if nodeHealth.MemoryUsagePercent > 0 {
				view.Capacity.AverageMemoryUsagePercent += nodeHealth.MemoryUsagePercent
				memoryNodeCount++
			}
			if latestSnapshot.CPUUsagePercent >= 80 {
				view.Capacity.HighCPUNodes++
			}
			if nodeHealth.MemoryUsagePercent >= 85 {
				view.Capacity.HighMemoryNodes++
			}
			if nodeHealth.StorageUsagePercent >= 85 {
				view.Capacity.HighStorageNodes++
			}
		}

		if latestTraffic != nil {
			nodeHealth.RequestCount = latestTraffic.RequestCount
			nodeHealth.ErrorCount = latestTraffic.ErrorCount
			nodeHealth.UniqueVisitorCount = latestTraffic.UniqueVisitorCount
			view.Traffic.RequestCount += latestTraffic.RequestCount
			view.Traffic.UniqueVisitors += latestTraffic.UniqueVisitorCount
			view.Traffic.ErrorCount += latestTraffic.ErrorCount
			if duration := latestTraffic.WindowEndedAt.Sub(latestTraffic.WindowStartedAt).Seconds(); duration > 0 {
				view.Traffic.EstimatedQPS += float64(latestTraffic.RequestCount) / duration
			}
			view.Traffic.ReportedNodes++
		}

		view.Summary.ActiveAlerts += len(activeEvents)
		view.Nodes = append(view.Nodes, nodeHealth)
	}

	view.Summary.TotalNodes = len(nodes)
	view.Config.ActiveVersion = activeVersion
	view.Config.LaggingNodes = view.Summary.LaggingNodes
	view.Config.PendingNodes = view.Summary.PendingNodes

	if cpuNodeCount > 0 {
		view.Capacity.AverageCPUUsagePercent /= float64(cpuNodeCount)
	}
	if memoryNodeCount > 0 {
		view.Capacity.AverageMemoryUsagePercent /= float64(memoryNodeCount)
	}

	sort.Slice(view.ActiveAlerts, func(i int, j int) bool {
		if severityWeight(view.ActiveAlerts[i].Severity) == severityWeight(view.ActiveAlerts[j].Severity) {
			return view.ActiveAlerts[i].LastTriggeredAt.After(view.ActiveAlerts[j].LastTriggeredAt)
		}
		return severityWeight(view.ActiveAlerts[i].Severity) > severityWeight(view.ActiveAlerts[j].Severity)
	})

	sort.Slice(view.Nodes, func(i int, j int) bool {
		if view.Nodes[i].ActiveEventCount == view.Nodes[j].ActiveEventCount {
			return view.Nodes[i].CPUUsagePercent > view.Nodes[j].CPUUsagePercent
		}
		return view.Nodes[i].ActiveEventCount > view.Nodes[j].ActiveEventCount
	})

	if len(view.ActiveAlerts) > 8 {
		view.ActiveAlerts = view.ActiveAlerts[:8]
	}

	return view, nil
}

func latestMetricSnapshotForNode(nodeID string, since time.Time) *model.NodeMetricSnapshot {
	snapshots, err := model.ListNodeMetricSnapshots(nodeID, since, 1)
	if err != nil || len(snapshots) == 0 {
		return nil
	}
	return snapshots[0]
}

func latestTrafficReportForNode(nodeID string, since time.Time) *model.NodeRequestReport {
	reports, err := model.ListNodeRequestReports(nodeID, since, 1)
	if err != nil || len(reports) == 0 {
		return nil
	}
	return reports[0]
}

func percentage(used int64, total int64) float64 {
	if used <= 0 || total <= 0 {
		return 0
	}
	return (float64(used) / float64(total)) * 100
}

func severityWeight(severity string) int {
	switch severity {
	case NodeHealthSeverityCritical:
		return 3
	case NodeHealthSeverityWarning:
		return 2
	default:
		return 1
	}
}