package admin

import (
	"crypto/subtle"
	"log/slog"
	"net/http"
	"os"
	"strings"
	"time"

	"github.com/Wei-Shaw/sub2api/internal/pkg/response"
	"github.com/Wei-Shaw/sub2api/internal/service"
	"github.com/gin-gonic/gin"
)

// ============================================================
// Alertmanager Webhook Handler
//
// 将 Prometheus Alertmanager 告警桥接到现有 ops_alert_events 表，
// 复用现有的邮件通知、静默检查等基础设施。
//
// Alertmanager 中配置 webhook receiver 指向该接口:
//
//	receivers:
//	  - name: 'ops-bridge'
//	    webhook_configs:
//	      - url: 'http://localhost:8080/admin/ops/prometheus-alerts'
//	        send_resolved: true
//	        http_config:
//	          bearer_token: '<INTERNAL_TOKEN>'
//
// ============================================================

// alertmanagerPayload is the JSON body sent by Alertmanager.
type alertmanagerPayload struct {
	Receiver string              `json:"receiver"`
	Status   string              `json:"status"` // "firing" | "resolved"
	Alerts   []alertmanagerAlert `json:"alerts"`

	GroupLabels       map[string]string `json:"groupLabels"`
	CommonLabels      map[string]string `json:"commonLabels"`
	CommonAnnotations map[string]string `json:"commonAnnotations"`

	ExternalURL string `json:"externalURL"`
	Version     string `json:"version"`
}

type alertmanagerAlert struct {
	Status string `json:"status"` // "firing" | "resolved"

	Labels      map[string]string `json:"labels"`
	Annotations map[string]string `json:"annotations"`

	StartsAt     time.Time  `json:"startsAt"`
	EndsAt       time.Time  `json:"endsAt"`
	GeneratorURL string     `json:"generatorURL"`
	Fingerprint  string     `json:"fingerprint"`
}

// PromAlertsBridgeHandler receives Alertmanager webhook and writes to ops_alert_events.
//
// POST /admin/ops/prometheus-alerts
//
// Security: This endpoint is NOT protected by JWT (it's called by Alertmanager).
// It validates the Authorization header against INTERNAL_WEBHOOK_TOKEN env var
// using constant-time comparison to prevent timing attacks.
func (h *OpsHandler) PromAlertsBridgeHandler(c *gin.Context) {
	// Validate bearer token against INTERNAL_WEBHOOK_TOKEN env var
	expectedToken := os.Getenv("INTERNAL_WEBHOOK_TOKEN")
	if expectedToken == "" {
		slog.Error("INTERNAL_WEBHOOK_TOKEN not configured, rejecting prometheus webhook")
		response.Error(c, http.StatusServiceUnavailable, "webhook token not configured")
		return
	}

	authHeader := c.GetHeader("Authorization")
	const prefix = "Bearer "
	if !strings.HasPrefix(authHeader, prefix) {
		response.Error(c, http.StatusUnauthorized, "missing or invalid authorization header")
		return
	}
	token := strings.TrimPrefix(authHeader, prefix)

	// Constant-time comparison to prevent timing attacks
	if subtle.ConstantTimeCompare([]byte(token), []byte(expectedToken)) != 1 {
		slog.Warn("invalid webhook token received", "remote_ip", c.ClientIP())
		response.Error(c, http.StatusUnauthorized, "invalid token")
		return
	}

	var payload alertmanagerPayload
	if err := c.ShouldBindJSON(&payload); err != nil {
		response.Error(c, http.StatusBadRequest, "invalid payload: "+err.Error())
		return
	}

	if len(payload.Alerts) == 0 {
		c.Status(http.StatusNoContent)
		return
	}

	var successCount, failCount int

	for _, alert := range payload.Alerts {
		event := convertAlertToEvent(alert)
		if err := h.opsService.CreateExternalAlertEvent(c.Request.Context(), event); err != nil {
			slog.Warn("failed to persist prometheus alert event",
				"fingerprint", alert.Fingerprint,
				"alertname", alert.Labels["alertname"],
				"err", err,
			)
			failCount++
			continue
		}
		successCount++
	}

	slog.Info("prometheus alerts bridged",
		"total", len(payload.Alerts),
		"success", successCount,
		"failed", failCount,
	)

	c.JSON(http.StatusOK, gin.H{
		"total":   len(payload.Alerts),
		"success": successCount,
		"failed":  failCount,
	})
}

// convertAlertToEvent maps an Alertmanager alert to an OpsAlertEvent.
// We use a synthetic rule_id=0 to distinguish Prometheus-sourced events
// from native evaluator-sourced events.
func convertAlertToEvent(a alertmanagerAlert) *service.OpsAlertEvent {
	// Map Alertmanager severity to internal severity levels
	severity := mapSeverity(a.Labels["severity"])

	// Map status
	status := service.OpsAlertStatusFiring
	if a.Status == "resolved" {
		status = service.OpsAlertStatusResolved
	}

	title := a.Annotations["summary"]
	if title == "" {
		title = a.Labels["alertname"]
	}

	description := a.Annotations["description"]
	if description == "" {
		description = a.Annotations["message"]
	}

	firedAt := a.StartsAt
	if firedAt.IsZero() {
		firedAt = time.Now()
	}

	var resolvedAt *time.Time
	if a.Status == "resolved" && !a.EndsAt.IsZero() {
		t := a.EndsAt
		resolvedAt = &t
	}

	// Collect useful label dimensions to store in Dimensions
	dimensions := make(map[string]any)
	for k, v := range a.Labels {
		if k != "alertname" && k != "severity" {
			dimensions[k] = v
		}
	}
	// Add Prometheus-specific metadata
	dimensions["source"] = "prometheus"
	dimensions["fingerprint"] = a.Fingerprint
	if runbook := a.Annotations["runbook_url"]; runbook != "" {
		dimensions["runbook_url"] = runbook
	}

	return &service.OpsAlertEvent{
		// RuleID = 0 indicates an externally-sourced alert (Prometheus)
		RuleID:      0,
		Severity:    severity,
		Status:      status,
		Title:       title,
		Description: description,
		Dimensions:  dimensions,
		FiredAt:     firedAt,
		ResolvedAt:  resolvedAt,
	}
}

// mapSeverity converts Prometheus severity labels to internal levels.
func mapSeverity(s string) string {
	switch strings.ToLower(s) {
	case "critical":
		return "P0"
	case "high":
		return "P1"
	case "warning", "medium":
		return "P2"
	default:
		return "P3"
	}
}