package handler

import (
	"context"
	"encoding/json"
	"net/http"
	"time"

	"github.com/shankar0123/certctl/internal/api/middleware"
)

// MetricsService defines the service interface for metrics collection.
type MetricsService interface {
	GetDashboardSummary(ctx context.Context) (interface{}, error)
}

// MetricsHandler handles HTTP requests for Prometheus-style metrics.
// In V2, returns JSON metrics (not Prometheus format).
// Prometheus format can be added in V3 when observability becomes a paid feature.
type MetricsHandler struct {
	svc           MetricsService
	serverStarted time.Time
}

// NewMetricsHandler creates a new MetricsHandler with a service dependency.
// serverStarted is used to calculate uptime_seconds.
func NewMetricsHandler(svc MetricsService, serverStarted time.Time) MetricsHandler {
	return MetricsHandler{
		svc:           svc,
		serverStarted: serverStarted,
	}
}

// MetricsResponse represents the JSON metrics response for V2.
type MetricsResponse struct {
	Gauge   MetricsGauge   `json:"gauge"`
	Counter MetricsCounter `json:"counter"`
	Uptime  UptimeMetric   `json:"uptime"`
}

// MetricsGauge represents gauge metrics (point-in-time values).
type MetricsGauge struct {
	CertificateTotal       int64   `json:"certificate_total"`
	CertificateActive      int64   `json:"certificate_active"`
	CertificateExpiringSoon int64  `json:"certificate_expiring_soon"` // Within 30d
	CertificateExpired     int64   `json:"certificate_expired"`
	CertificateRevoked     int64   `json:"certificate_revoked"`
	AgentTotal             int64   `json:"agent_total"`
	AgentOnline            int64   `json:"agent_online"`
	JobPending             int64   `json:"job_pending"`
}

// MetricsCounter represents counter metrics (cumulative values).
type MetricsCounter struct {
	JobCompletedTotal int64 `json:"job_completed_total"`
	JobFailedTotal    int64 `json:"job_failed_total"`
}

// UptimeMetric represents server uptime information.
type UptimeMetric struct {
	UptimeSeconds int64     `json:"uptime_seconds"`
	ServerStarted time.Time `json:"server_started"`
	MeasuredAt    time.Time `json:"measured_at"`
}

// GetMetrics returns JSON metrics (aggregated from dashboard summary).
// GET /api/v1/metrics
func (h MetricsHandler) GetMetrics(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodGet {
		Error(w, http.StatusMethodNotAllowed, "Method not allowed")
		return
	}

	requestID := middleware.GetRequestID(r.Context())

	summary, err := h.svc.GetDashboardSummary(r.Context())
	if err != nil {
		ErrorWithRequestID(w, http.StatusInternalServerError, "Failed to collect metrics", requestID)
		return
	}

	// Extract fields from summary via JSON round-trip (avoids cross-package type assertion)
	jsonBytes, err := json.Marshal(summary)
	if err != nil {
		ErrorWithRequestID(w, http.StatusInternalServerError, "Failed to marshal metrics data", requestID)
		return
	}
	var dashboardSummary DashboardSummary
	if err := json.Unmarshal(jsonBytes, &dashboardSummary); err != nil {
		ErrorWithRequestID(w, http.StatusInternalServerError, "Invalid metrics data", requestID)
		return
	}

	// Build metrics response
	metricsResp := MetricsResponse{
		Gauge: MetricsGauge{
			CertificateTotal:      dashboardSummary.TotalCertificates,
			CertificateActive:     dashboardSummary.TotalCertificates - dashboardSummary.ExpiringCertificates - dashboardSummary.ExpiredCertificates - dashboardSummary.RevokedCertificates,
			CertificateExpiringSoon: dashboardSummary.ExpiringCertificates,
			CertificateExpired:    dashboardSummary.ExpiredCertificates,
			CertificateRevoked:    dashboardSummary.RevokedCertificates,
			AgentTotal:            dashboardSummary.TotalAgents,
			AgentOnline:           dashboardSummary.ActiveAgents,
			JobPending:            dashboardSummary.PendingJobs,
		},
		Counter: MetricsCounter{
			JobCompletedTotal: dashboardSummary.CompleteJobs,
			JobFailedTotal:    dashboardSummary.FailedJobs,
		},
		Uptime: UptimeMetric{
			UptimeSeconds: int64(time.Since(h.serverStarted).Seconds()),
			ServerStarted: h.serverStarted,
			MeasuredAt:    time.Now(),
		},
	}

	JSON(w, http.StatusOK, metricsResp)
}

// DashboardSummary mirrors the service.DashboardSummary for JSON unmarshaling.
// JSON tags must match the service-layer struct exactly.
type DashboardSummary struct {
	TotalCertificates    int64     `json:"total_certificates"`
	ExpiringCertificates int64     `json:"expiring_certificates"`
	ExpiredCertificates  int64     `json:"expired_certificates"`
	RevokedCertificates  int64     `json:"revoked_certificates"`
	ActiveAgents         int64     `json:"active_agents"`
	OfflineAgents        int64     `json:"offline_agents"`
	TotalAgents          int64     `json:"total_agents"`
	PendingJobs          int64     `json:"pending_jobs"`
	FailedJobs           int64     `json:"failed_jobs"`
	CompleteJobs         int64     `json:"complete_jobs"`
	CompletedAt          time.Time `json:"completed_at"`
}