package server

import (
	"fmt"
	"net/http"
	"sort"
	"strings"
	"sync"
	"time"

	"scm.bstein.dev/bstein/soteria/internal/api"
)

type metricSample struct {
	labels map[string]string
	value  float64
}

type telemetry struct {
	mu                      sync.RWMutex
	backupRequests          map[string]metricSample
	restoreRequests         map[string]metricSample
	authzDenials            map[string]metricSample
	inventoryRefreshFailure float64
	inventoryRefreshTime    float64
	pvcBackupAgeHours       map[string]metricSample
	pvcBackupHealth         map[string]metricSample
	pvcBackupLastSuccess    map[string]metricSample
	pvcBackupCount          map[string]metricSample
}

func newTelemetry() *telemetry {
	return &telemetry{
		backupRequests:       map[string]metricSample{},
		restoreRequests:      map[string]metricSample{},
		authzDenials:         map[string]metricSample{},
		pvcBackupAgeHours:    map[string]metricSample{},
		pvcBackupHealth:      map[string]metricSample{},
		pvcBackupLastSuccess: map[string]metricSample{},
		pvcBackupCount:       map[string]metricSample{},
	}
}

func (t *telemetry) Handler() http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
		w.Header().Set("Content-Type", "text/plain; version=0.0.4; charset=utf-8")
		_, _ = w.Write([]byte(t.render()))
	})
}

func (t *telemetry) RecordBackupRequest(driver, result string) {
	t.mu.Lock()
	defer t.mu.Unlock()
	incMetric(t.backupRequests, map[string]string{"driver": driver, "result": result})
}

func (t *telemetry) RecordRestoreRequest(driver, result string) {
	t.mu.Lock()
	defer t.mu.Unlock()
	incMetric(t.restoreRequests, map[string]string{"driver": driver, "result": result})
}

func (t *telemetry) RecordAuthzDenied(reason string) {
	t.mu.Lock()
	defer t.mu.Unlock()
	incMetric(t.authzDenials, map[string]string{"reason": reason})
}

func (t *telemetry) RecordInventoryFailure() {
	t.mu.Lock()
	defer t.mu.Unlock()
	t.inventoryRefreshFailure++
}

func (t *telemetry) RecordInventory(inv api.InventoryResponse) {
	t.mu.Lock()
	defer t.mu.Unlock()

	t.pvcBackupAgeHours = map[string]metricSample{}
	t.pvcBackupHealth = map[string]metricSample{}
	t.pvcBackupLastSuccess = map[string]metricSample{}
	t.pvcBackupCount = map[string]metricSample{}

	for _, namespace := range inv.Namespaces {
		for _, pvc := range namespace.PVCs {
			labels := map[string]string{
				"namespace": pvc.Namespace,
				"pvc":       pvc.PVC,
				"volume":    pvc.Volume,
				"driver":    pvc.Driver,
			}
			setMetric(t.pvcBackupCount, labels, float64(pvc.BackupCount))
			if pvc.Healthy {
				setMetric(t.pvcBackupHealth, labels, 1)
			} else {
				setMetric(t.pvcBackupHealth, labels, 0)
			}
			if pvc.LastBackupAt == "" {
				continue
			}
			setMetric(t.pvcBackupAgeHours, labels, pvc.LastBackupAgeHours)
			if ts, ok := parseBackupTime(pvc.LastBackupAt); ok {
				setMetric(t.pvcBackupLastSuccess, labels, float64(ts.Unix()))
			}
		}
	}

	t.inventoryRefreshTime = float64(time.Now().Unix())
}

func (t *telemetry) render() string {
	t.mu.RLock()
	defer t.mu.RUnlock()

	var b strings.Builder
	writeMetricFamily(&b, "soteria_backup_requests_total", "counter", "Backup requests handled by Soteria.", metricValues(t.backupRequests))
	writeMetricFamily(&b, "soteria_restore_requests_total", "counter", "Restore requests handled by Soteria.", metricValues(t.restoreRequests))
	writeMetricFamily(&b, "soteria_authz_denials_total", "counter", "Authorization denials emitted by Soteria.", metricValues(t.authzDenials))
	writeMetricFamily(&b, "soteria_inventory_refresh_failures_total", "counter", "Inventory refresh failures while computing PVC backup telemetry.", []metricSample{{value: t.inventoryRefreshFailure}})
	writeMetricFamily(&b, "soteria_inventory_refresh_timestamp_seconds", "gauge", "Unix timestamp of the last successful inventory refresh.", []metricSample{{value: t.inventoryRefreshTime}})
	writeMetricFamily(&b, "pvc_backup_age_hours", "gauge", "Age in hours of the latest successful PVC backup known to Soteria.", metricValues(t.pvcBackupAgeHours))
	writeMetricFamily(&b, "pvc_backup_health", "gauge", "PVC backup health according to Soteria: 1=fresh backup within policy, 0=missing/stale/error.", metricValues(t.pvcBackupHealth))
	writeMetricFamily(&b, "pvc_backup_last_success_timestamp_seconds", "gauge", "Unix timestamp of the latest successful PVC backup known to Soteria.", metricValues(t.pvcBackupLastSuccess))
	writeMetricFamily(&b, "pvc_backup_count", "gauge", "Count of backup records discovered for a PVC.", metricValues(t.pvcBackupCount))
	return b.String()
}

func metricValues(source map[string]metricSample) []metricSample {
	keys := make([]string, 0, len(source))
	for key := range source {
		keys = append(keys, key)
	}
	sort.Strings(keys)
	values := make([]metricSample, 0, len(keys))
	for _, key := range keys {
		values = append(values, source[key])
	}
	return values
}

func writeMetricFamily(b *strings.Builder, name, metricType, help string, samples []metricSample) {
	b.WriteString("# HELP ")
	b.WriteString(name)
	b.WriteString(" ")
	b.WriteString(help)
	b.WriteString("\n")
	b.WriteString("# TYPE ")
	b.WriteString(name)
	b.WriteString(" ")
	b.WriteString(metricType)
	b.WriteString("\n")
	for _, sample := range samples {
		b.WriteString(name)
		b.WriteString(renderLabels(sample.labels))
		b.WriteString(" ")
		b.WriteString(fmt.Sprintf("%g", sample.value))
		b.WriteString("\n")
	}
}

func renderLabels(labels map[string]string) string {
	if len(labels) == 0 {
		return ""
	}
	keys := make([]string, 0, len(labels))
	for key := range labels {
		keys = append(keys, key)
	}
	sort.Strings(keys)
	parts := make([]string, 0, len(keys))
	for _, key := range keys {
		parts = append(parts, fmt.Sprintf("%s=%q", key, labels[key]))
	}
	return "{" + strings.Join(parts, ",") + "}"
}

func metricKey(labels map[string]string) string {
	return renderLabels(labels)
}

func incMetric(target map[string]metricSample, labels map[string]string) {
	key := metricKey(labels)
	sample, ok := target[key]
	if !ok {
		target[key] = metricSample{labels: cloneLabels(labels), value: 1}
		return
	}
	sample.value++
	target[key] = sample
}

func setMetric(target map[string]metricSample, labels map[string]string, value float64) {
	key := metricKey(labels)
	target[key] = metricSample{labels: cloneLabels(labels), value: value}
}

func cloneLabels(labels map[string]string) map[string]string {
	out := make(map[string]string, len(labels))
	for key, value := range labels {
		out[key] = value
	}
	return out
}