package notifiers

import (
	"context"
	"fmt"
	"regexp"
	"strings"
	"time"

	"github.com/grafana/grafana/pkg/bus"
	"github.com/grafana/grafana/pkg/components/simplejson"
	"github.com/grafana/grafana/pkg/infra/log"
	"github.com/grafana/grafana/pkg/models"
	"github.com/grafana/grafana/pkg/services/alerting"
)

func init() {
	alerting.RegisterNotifier(&alerting.NotifierPlugin{
		Type:        "prometheus-alertmanager",
		Name:        "Prometheus Alertmanager",
		Description: "Sends alert to Prometheus Alertmanager",
		Heading:     "Alertmanager settings",
		Factory:     NewAlertmanagerNotifier,
		Options: []alerting.NotifierOption{
			{
				Label:        "Url",
				Element:      alerting.ElementTypeInput,
				InputType:    alerting.InputTypeText,
				Description:  "As specified in Alertmanager documentation, do not specify a load balancer here. Enter all your Alertmanager URLs comma-separated.",
				Placeholder:  "http://localhost:9093",
				PropertyName: "url",
				Required:     true,
			},
			{
				Label:        "Basic Auth User",
				Element:      alerting.ElementTypeInput,
				InputType:    alerting.InputTypeText,
				PropertyName: "basicAuthUser",
			},
			{
				Label:        "Basic Auth Password",
				Element:      alerting.ElementTypeInput,
				InputType:    alerting.InputTypePassword,
				PropertyName: "basicAuthPassword",
				Secure:       true,
			},
		},
	})
}

// NewAlertmanagerNotifier returns a new Alertmanager notifier
func NewAlertmanagerNotifier(model *models.AlertNotification) (alerting.Notifier, error) {
	urlString := model.Settings.Get("url").MustString()
	if urlString == "" {
		return nil, alerting.ValidationError{Reason: "Could not find url property in settings"}
	}

	var url []string
	for _, u := range strings.Split(urlString, ",") {
		u = strings.TrimSpace(u)
		if u != "" {
			url = append(url, u)
		}
	}
	basicAuthUser := model.Settings.Get("basicAuthUser").MustString()
	basicAuthPassword := model.DecryptedValue("basicAuthPassword", model.Settings.Get("basicAuthPassword").MustString())

	return &AlertmanagerNotifier{
		NotifierBase:      NewNotifierBase(model),
		URL:               url,
		BasicAuthUser:     basicAuthUser,
		BasicAuthPassword: basicAuthPassword,
		log:               log.New("alerting.notifier.prometheus-alertmanager"),
	}, nil
}

// AlertmanagerNotifier sends alert notifications to the alert manager
type AlertmanagerNotifier struct {
	NotifierBase
	URL               []string
	BasicAuthUser     string
	BasicAuthPassword string
	log               log.Logger
}

// ShouldNotify returns true if the notifiers should be used depending on state
func (am *AlertmanagerNotifier) ShouldNotify(ctx context.Context, evalContext *alerting.EvalContext, notificationState *models.AlertNotificationState) bool {
	am.log.Debug("Should notify", "ruleId", evalContext.Rule.ID, "state", evalContext.Rule.State, "previousState", evalContext.PrevAlertState)

	// Do not notify when we become OK for the first time.
	if (evalContext.PrevAlertState == models.AlertStatePending) && (evalContext.Rule.State == models.AlertStateOK) {
		return false
	}

	// Notify on Alerting -> OK to resolve before alertmanager timeout.
	if (evalContext.PrevAlertState == models.AlertStateAlerting) && (evalContext.Rule.State == models.AlertStateOK) {
		return true
	}

	return evalContext.Rule.State == models.AlertStateAlerting
}

func (am *AlertmanagerNotifier) createAlert(evalContext *alerting.EvalContext, match *alerting.EvalMatch, ruleURL string) *simplejson.Json {
	alertJSON := simplejson.New()
	alertJSON.Set("startsAt", evalContext.StartTime.UTC().Format(time.RFC3339))
	if evalContext.Rule.State == models.AlertStateOK {
		alertJSON.Set("endsAt", time.Now().UTC().Format(time.RFC3339))
	}
	alertJSON.Set("generatorURL", ruleURL)

	// Annotations (summary and description are very commonly used).
	alertJSON.SetPath([]string{"annotations", "summary"}, evalContext.Rule.Name)
	description := ""
	if evalContext.Rule.Message != "" {
		description += evalContext.Rule.Message
	}
	if evalContext.Error != nil {
		if description != "" {
			description += "\n"
		}
		description += "Error: " + evalContext.Error.Error()
	}
	if description != "" {
		alertJSON.SetPath([]string{"annotations", "description"}, description)
	}
	if evalContext.ImagePublicURL != "" {
		alertJSON.SetPath([]string{"annotations", "image"}, evalContext.ImagePublicURL)
	}

	// Labels (from metrics tags + AlertRuleTags + mandatory alertname).
	tags := make(map[string]string)
	if match != nil {
		if len(match.Tags) == 0 {
			tags["metric"] = match.Metric
		} else {
			for k, v := range match.Tags {
				tags[replaceIllegalCharsInLabelname(k)] = v
			}
		}
	}
	for _, tag := range evalContext.Rule.AlertRuleTags {
		tags[tag.Key] = tag.Value
	}
	tags["alertname"] = evalContext.Rule.Name
	alertJSON.Set("labels", tags)
	return alertJSON
}

// Notify sends alert notifications to the alert manager
func (am *AlertmanagerNotifier) Notify(evalContext *alerting.EvalContext) error {
	am.log.Info("Sending Alertmanager alert", "ruleId", evalContext.Rule.ID, "notification", am.Name)

	ruleURL, err := evalContext.GetRuleURL()
	if err != nil {
		am.log.Error("Failed get rule link", "error", err)
		return err
	}

	// Send one alert per matching series.
	alerts := make([]interface{}, 0)
	for _, match := range evalContext.EvalMatches {
		alert := am.createAlert(evalContext, match, ruleURL)
		alerts = append(alerts, alert)
	}

	// This happens on ExecutionError or NoData
	if len(alerts) == 0 {
		alert := am.createAlert(evalContext, nil, ruleURL)
		alerts = append(alerts, alert)
	}

	bodyJSON := simplejson.NewFromAny(alerts)
	body, _ := bodyJSON.MarshalJSON()
	errCnt := 0

	for _, url := range am.URL {
		cmd := &models.SendWebhookSync{
			Url:        strings.TrimSuffix(url, "/") + "/api/v1/alerts",
			User:       am.BasicAuthUser,
			Password:   am.BasicAuthPassword,
			HttpMethod: "POST",
			Body:       string(body),
		}

		if err := bus.DispatchCtx(evalContext.Ctx, cmd); err != nil {
			am.log.Error("Failed to send alertmanager", "error", err, "alertmanager", am.Name, "url", url)
			errCnt++
		}
	}

	// This happens when every dispatch return error
	if errCnt == len(am.URL) {
		return fmt.Errorf("failed to send alert to alertmanager")
	}

	return nil
}

// regexp that matches all none valid label name characters
// https://prometheus.io/docs/concepts/data_model/#metric-names-and-labels
var labelNamePattern = regexp.MustCompile(`[^a-zA-Z0-9_]`)

func replaceIllegalCharsInLabelname(input string) string {
	return labelNamePattern.ReplaceAllString(input, "_")
}