package app

import (
	"fmt"
	"sort"
	"strings"
	"time"
)

func runTransportPolicyHealthCheck(clients []TransportClient, plan TransportPolicyCompilePlan, now time.Time) (TransportPolicyHealthCheck, []TransportClient, bool) {
	updated := append([]TransportClient(nil), clients...)
	clientIDs := collectTransportPolicyHealthCheckClientIDs(plan)
	items := make([]TransportPolicyHealthCheckItem, 0, len(clientIDs))
	itemByClientID := make(map[string]TransportPolicyHealthCheckItem, len(clientIDs))
	checkedCount := 0
	failedCount := 0
	changed := false

	for _, clientID := range clientIDs {
		idx := findTransportClientIndex(updated, clientID)
		if idx < 0 {
			item := TransportPolicyHealthCheckItem{
				ClientID: clientID,
				Required: true,
				OK:       false,
				Code:     "TRANSPORT_CLIENT_NOT_FOUND",
				Message:  "client not found during health-check",
			}
			items = append(items, item)
			itemByClientID[clientID] = item
			checkedCount++
			failedCount++
			continue
		}

		current := updated[idx]
		required := transportPolicyHealthCheckRequired(current)
		item := TransportPolicyHealthCheckItem{
			ClientID: current.ID,
			Kind:     string(current.Kind),
			Required: required,
			OK:       true,
			Status:   string(normalizeTransportStatus(current.Status)),
		}
		if !required {
			item.Message = "skipped inactive draft client"
			items = append(items, item)
			itemByClientID[current.ID] = item
			continue
		}

		checkedCount++
		backend := selectTransportBackend(current)
		probe := backend.Health(current)
		next := applyTransportHealthProbeSnapshot(current, backend.ID(), probe, now)
		updated[idx] = next
		if transportHealthChanged(current, next) || transportShouldPersistHealthSnapshot(current, next, now) {
			changed = true
		}

		item.Status = string(normalizeTransportStatus(next.Status))
		item.Code = strings.TrimSpace(probe.Code)
		if probe.OK && next.Status != TransportClientDown {
			item.Message = "ok"
			items = append(items, item)
			itemByClientID[current.ID] = item
			continue
		}

		item.OK = false
		if item.Code == "" && next.Status == TransportClientDown {
			item.Code = "TRANSPORT_POLICY_HEALTH_DOWN"
		}
		msg := strings.TrimSpace(probe.Message)
		if msg == "" && next.Status == TransportClientDown {
			msg = "transport client is down after apply"
		}
		if msg == "" {
			msg = "transport policy health-check failed"
		}
		item.Message = msg
		items = append(items, item)
		itemByClientID[current.ID] = item
		failedCount++
	}

	clientByID := make(map[string]TransportClient, len(updated))
	for _, client := range updated {
		clientByID[client.ID] = client
	}
	interfaces := buildTransportPolicyHealthCheckInterfaces(plan, itemByClientID, clientByID, now)

	resp := TransportPolicyHealthCheck{
		OK:             failedCount == 0,
		CheckedCount:   checkedCount,
		FailedCount:    failedCount,
		InterfaceCount: len(interfaces),
		Interfaces:     interfaces,
		Items:          items,
	}
	switch {
	case checkedCount == 0:
		resp.OK = true
		resp.Message = "health-check skipped: no active transport clients in policy"
	case failedCount == 0:
		resp.Message = fmt.Sprintf("health-check passed for %d client(s)", checkedCount)
	default:
		resp.Message = fmt.Sprintf("health-check failed for %d of %d client(s)", failedCount, checkedCount)
	}
	return resp, updated, changed
}

func buildTransportPolicyHealthCheckInterfaces(
	plan TransportPolicyCompilePlan,
	itemByClientID map[string]TransportPolicyHealthCheckItem,
	clientByID map[string]TransportClient,
	now time.Time,
) []TransportPolicyHealthCheckInterface {
	if len(plan.Interfaces) == 0 {
		return nil
	}
	out := make([]TransportPolicyHealthCheckInterface, 0, len(plan.Interfaces))
	for _, iface := range plan.Interfaces {
		summary := TransportPolicyHealthCheckInterface{
			IfaceID:      normalizeTransportIfaceID(iface.IfaceID),
			Mode:         strings.TrimSpace(iface.Mode),
			RuntimeIface: strings.TrimSpace(iface.RuntimeIface),
			NetnsName:    strings.TrimSpace(iface.NetnsName),
			RoutingTable: strings.TrimSpace(iface.RoutingTable),
			Status:       string(TransportClientDown),
			OK:           true,
		}
		seen := map[string]struct{}{}
		members := make([]TransportClient, 0, len(iface.ClientIDs))
		for _, rawClientID := range iface.ClientIDs {
			clientID := sanitizeID(rawClientID)
			if clientID == "" {
				continue
			}
			if _, ok := seen[clientID]; ok {
				continue
			}
			seen[clientID] = struct{}{}
			summary.ClientIDs = append(summary.ClientIDs, clientID)
			summary.ClientCount++
			if client, ok := clientByID[clientID]; ok {
				members = append(members, client)
			}
			item, ok := itemByClientID[clientID]
			if !ok {
				continue
			}
			if item.Required {
				summary.CheckedCount++
				if !item.OK {
					summary.FailedCount++
				}
				continue
			}
			summary.SkippedCount++
		}
		if len(members) > 0 {
			counters := buildTransportRuntimeObservabilityCounters(members)
			summary.Status = string(aggregateTransportRuntimeObservabilityStatus(counters))
			if primary, ok := selectTransportRuntimeObservabilityPrimaryClient(members); ok {
				summary.ActiveClientID = primary.ID
				summary.LatencyMS = primary.Health.LatencyMS
				if summary.RuntimeIface == "" {
					summary.RuntimeIface = strings.TrimSpace(primary.Iface)
				}
				if summary.NetnsName == "" && transportNetnsEnabled(primary) {
					summary.NetnsName = transportNetnsName(primary)
				}
				if summary.RoutingTable == "" {
					summary.RoutingTable = strings.TrimSpace(primary.RoutingTable)
				}
			}
			if errClient, ok := selectTransportRuntimeObservabilityErrorClient(members); ok {
				summary.LastError = transportRuntimeObservabilityClientError(errClient, now)
			}
		}
		switch {
		case summary.ClientCount == 0:
			summary.Message = "health-check skipped: no compiled clients on interface"
		case summary.CheckedCount == 0:
			summary.Message = "health-check skipped: no active transport clients on interface"
		case summary.FailedCount == 0:
			summary.Message = fmt.Sprintf("health-check passed for %d client(s) on interface", summary.CheckedCount)
		default:
			summary.OK = false
			summary.Message = fmt.Sprintf(
				"health-check failed for %d of %d client(s) on interface",
				summary.FailedCount,
				summary.CheckedCount,
			)
		}
		out = append(out, summary)
	}
	return out
}

func collectTransportPolicyHealthCheckClientIDs(plan TransportPolicyCompilePlan) []string {
	seen := map[string]struct{}{}
	out := make([]string, 0, plan.RuleCount)
	for _, iface := range plan.Interfaces {
		for _, clientID := range iface.ClientIDs {
			id := sanitizeID(clientID)
			if id == "" {
				continue
			}
			if _, ok := seen[id]; ok {
				continue
			}
			seen[id] = struct{}{}
			out = append(out, id)
		}
	}
	sort.Strings(out)
	return out
}

func transportPolicyHealthCheckRequired(client TransportClient) bool {
	if client.Enabled {
		return true
	}
	return normalizeTransportStatus(client.Status) != TransportClientDown
}