package sender

import (
	"context"
	"crypto/sha256"
	"errors"
	"fmt"
	"net/url"
	"path"
	"sort"
	"sync"
	"time"

	"github.com/benbjohnson/clock"
	"github.com/prometheus/client_golang/prometheus"

	"github.com/grafana/grafana/pkg/api/datasource"
	"github.com/grafana/grafana/pkg/infra/log"
	"github.com/grafana/grafana/pkg/services/datasources"
	"github.com/grafana/grafana/pkg/services/featuremgmt"
	"github.com/grafana/grafana/pkg/services/ngalert/api/tooling/definitions"
	"github.com/grafana/grafana/pkg/services/ngalert/models"
	"github.com/grafana/grafana/pkg/services/ngalert/notifier"
	"github.com/grafana/grafana/pkg/services/ngalert/store"
	"github.com/grafana/grafana/pkg/services/secrets"
)

// AlertsRouter handles alerts generated during alert rule evaluation.
// Based on rule's orgID and the configuration for that organization,
// it determines whether an alert needs to be sent to an external Alertmanager and\or internal notifier.Alertmanager
//
// After creating a AlertsRouter, you must call Run to keep the AlertsRouter's
// state synchronized with the alerting configuration.
type AlertsRouter struct {
	logger           log.Logger
	clock            clock.Clock
	adminConfigStore store.AdminConfigurationStore

	// externalAlertmanagers help us send alerts to external Alertmanagers.
	adminConfigMtx               sync.RWMutex
	sendAlertsTo                 map[int64]models.AlertmanagersChoice
	externalAlertmanagers        map[int64]*ExternalAlertmanager
	externalAlertmanagersCfgHash map[int64]string

	multiOrgNotifier *notifier.MultiOrgAlertmanager

	appURL                  *url.URL
	disabledOrgs            map[int64]struct{}
	adminConfigPollInterval time.Duration

	datasourceService datasources.DataSourceService
	secretService     secrets.Service
	featureManager    featuremgmt.FeatureToggles
}

func NewAlertsRouter(multiOrgNotifier *notifier.MultiOrgAlertmanager, store store.AdminConfigurationStore,
	clk clock.Clock, appURL *url.URL, disabledOrgs map[int64]struct{}, configPollInterval time.Duration,
	datasourceService datasources.DataSourceService, secretService secrets.Service, featureManager featuremgmt.FeatureToggles) *AlertsRouter {
	d := &AlertsRouter{
		logger:           log.New("ngalert.sender.router"),
		clock:            clk,
		adminConfigStore: store,

		adminConfigMtx:               sync.RWMutex{},
		externalAlertmanagers:        map[int64]*ExternalAlertmanager{},
		externalAlertmanagersCfgHash: map[int64]string{},
		sendAlertsTo:                 map[int64]models.AlertmanagersChoice{},

		multiOrgNotifier: multiOrgNotifier,

		appURL:                  appURL,
		disabledOrgs:            disabledOrgs,
		adminConfigPollInterval: configPollInterval,

		datasourceService: datasourceService,
		secretService:     secretService,
		featureManager:    featureManager,
	}
	return d
}

// SyncAndApplyConfigFromDatabase looks for the admin configuration in the database
// and adjusts the sender(s) and alert handling mechanism accordingly.
func (d *AlertsRouter) SyncAndApplyConfigFromDatabase(ctx context.Context) error {
	cfgs, err := d.adminConfigStore.GetAdminConfigurations()
	if err != nil {
		return err
	}

	d.logger.Debug("Attempting to sync admin configs", "count", len(cfgs))

	disableExternal := d.featureManager.IsEnabled(ctx, featuremgmt.FlagAlertingDisableSendAlertsExternal)

	orgsFound := make(map[int64]struct{}, len(cfgs))
	d.adminConfigMtx.Lock()
	for _, cfg := range cfgs {
		_, isDisabledOrg := d.disabledOrgs[cfg.OrgID]
		if isDisabledOrg {
			continue
		}

		if disableExternal && cfg.SendAlertsTo != models.InternalAlertmanager {
			d.logger.Warn("Alertmanager choice in configuration will be ignored due to feature flags", "org", cfg.OrgID, "choice", cfg.SendAlertsTo)
			cfg.SendAlertsTo = models.InternalAlertmanager
		}

		// Update the Alertmanagers choice for the organization.
		d.sendAlertsTo[cfg.OrgID] = cfg.SendAlertsTo

		orgsFound[cfg.OrgID] = struct{}{} // keep track of the which externalAlertmanagers we need to keep.

		existing, ok := d.externalAlertmanagers[cfg.OrgID]

		//  We have no running sender and alerts are handled internally, no-op.
		if !ok && cfg.SendAlertsTo == models.InternalAlertmanager {
			d.logger.Debug("Grafana is configured to send alerts to the internal alertmanager only. Skipping synchronization with external alertmanager", "org", cfg.OrgID)
			continue
		}

		alertmanagers, err := d.alertmanagersFromDatasources(cfg.OrgID)
		if err != nil {
			d.logger.Error("Failed to get alertmanagers from datasources", "org", cfg.OrgID, "error", err)
			continue
		}

		// We have no running sender and no Alertmanager(s) configured, no-op.
		if !ok && len(alertmanagers) == 0 {
			d.logger.Debug("No external alertmanagers configured", "org", cfg.OrgID)
			continue
		}

		// We have a running sender but no Alertmanager(s) configured, shut it down.
		if ok && len(alertmanagers) == 0 {
			d.logger.Info("No external alertmanager(s) configured, sender will be stopped", "org", cfg.OrgID)
			delete(orgsFound, cfg.OrgID)
			continue
		}

		// Avoid logging sensitive data
		redactedAMs := buildRedactedAMs(d.logger, alertmanagers, cfg.OrgID)
		d.logger.Debug("Alertmanagers found in the configuration", "alertmanagers", redactedAMs)

		var hashes []string
		for _, cfg := range alertmanagers {
			hashes = append(hashes, cfg.SHA256())
		}
		// We have a running sender, check if we need to apply a new config.
		amHash := asSHA256(hashes)
		if ok {
			if d.externalAlertmanagersCfgHash[cfg.OrgID] == amHash {
				d.logger.Debug("Sender configuration is the same as the one running, no-op", "org", cfg.OrgID, "alertmanagers", redactedAMs)
				continue
			}

			d.logger.Info("Applying new configuration to sender", "org", cfg.OrgID, "alertmanagers", redactedAMs, "cfg", cfg.ID)
			err := existing.ApplyConfig(cfg.OrgID, cfg.ID, alertmanagers)
			if err != nil {
				d.logger.Error("Failed to apply configuration", "error", err, "org", cfg.OrgID)
				continue
			}
			d.externalAlertmanagersCfgHash[cfg.OrgID] = amHash
			continue
		}

		// No sender and have Alertmanager(s) to send to - start a new one.
		d.logger.Info("Creating new sender for the external alertmanagers", "org", cfg.OrgID, "alertmanagers", redactedAMs)
		senderLogger := log.New("ngalert.sender.external-alertmanager")
		s := NewExternalAlertmanagerSender(senderLogger, prometheus.NewRegistry())
		d.externalAlertmanagers[cfg.OrgID] = s
		s.Run()

		err = s.ApplyConfig(cfg.OrgID, cfg.ID, alertmanagers)
		if err != nil {
			d.logger.Error("Failed to apply configuration", "error", err, "org", cfg.OrgID)
			continue
		}

		d.externalAlertmanagersCfgHash[cfg.OrgID] = amHash
	}

	sendersToStop := map[int64]*ExternalAlertmanager{}

	for orgID, s := range d.externalAlertmanagers {
		if _, exists := orgsFound[orgID]; !exists {
			sendersToStop[orgID] = s
			delete(d.externalAlertmanagers, orgID)
			delete(d.externalAlertmanagersCfgHash, orgID)
		}
	}
	d.adminConfigMtx.Unlock()

	// We can now stop these external Alertmanagers w/o having to hold a lock.
	for orgID, s := range sendersToStop {
		d.logger.Info("Stopping sender", "org", orgID)
		s.Stop()
		d.logger.Info("Stopped sender", "org", orgID)
	}

	d.logger.Debug("Finish of admin configuration sync")

	return nil
}

func buildRedactedAMs(l log.Logger, alertmanagers []ExternalAMcfg, ordId int64) []string {
	var redactedAMs []string
	for _, am := range alertmanagers {
		parsedAM, err := url.Parse(am.URL)
		if err != nil {
			l.Error("Failed to parse alertmanager string", "org", ordId, "error", err)
			continue
		}
		redactedAMs = append(redactedAMs, parsedAM.Redacted())
	}
	return redactedAMs
}

func asSHA256(strings []string) string {
	h := sha256.New()
	sort.Strings(strings)
	_, _ = h.Write([]byte(fmt.Sprintf("%v", strings)))
	return fmt.Sprintf("%x", h.Sum(nil))
}

func (d *AlertsRouter) alertmanagersFromDatasources(orgID int64) ([]ExternalAMcfg, error) {
	var (
		alertmanagers []ExternalAMcfg
	)
	// We might have alertmanager datasources that are acting as external
	// alertmanager, let's fetch them.
	query := &datasources.GetDataSourcesByTypeQuery{
		OrgID: orgID,
		Type:  datasources.DS_ALERTMANAGER,
	}
	ctx, cancel := context.WithTimeout(context.Background(), time.Second*5)
	defer cancel()
	dataSources, err := d.datasourceService.GetDataSourcesByType(ctx, query)
	if err != nil {
		return nil, fmt.Errorf("failed to fetch datasources for org: %w", err)
	}
	for _, ds := range dataSources {
		if !ds.JsonData.Get(definitions.HandleGrafanaManagedAlerts).MustBool(false) {
			continue
		}
		amURL, err := d.buildExternalURL(ds)
		if err != nil {
			d.logger.Error("Failed to build external alertmanager URL",
				"org", ds.OrgID,
				"uid", ds.UID,
				"error", err)
			continue
		}
		ctx, cancel := context.WithTimeout(context.Background(), time.Second*10)
		headers, err := d.datasourceService.CustomHeaders(ctx, ds)
		cancel()
		if err != nil {
			d.logger.Error("Failed to get headers for external alertmanager",
				"org", ds.OrgID,
				"uid", ds.UID,
				"error", err)
			continue
		}
		alertmanagers = append(alertmanagers, ExternalAMcfg{
			URL:     amURL,
			Headers: headers,
		})
	}
	return alertmanagers, nil
}

func (d *AlertsRouter) buildExternalURL(ds *datasources.DataSource) (string, error) {
	// We re-use the same parsing logic as the datasource to make sure it matches whatever output the user received
	// when doing the healthcheck.
	parsed, err := datasource.ValidateURL(datasources.DS_ALERTMANAGER, ds.URL)
	if err != nil {
		return "", fmt.Errorf("failed to parse alertmanager datasource url: %w", err)
	}

	// If this is a Mimir or Cortex implementation, the Alert API is under a different path than config API
	if ds.JsonData != nil {
		impl := ds.JsonData.Get("implementation").MustString("")
		switch impl {
		case "mimir", "cortex":
			if parsed.Path == "" {
				parsed.Path = "/"
			}
			lastSegment := path.Base(parsed.Path)
			if lastSegment != "alertmanager" {
				parsed = parsed.JoinPath("/alertmanager")
			}
		default:
		}
	}

	// If basic auth is enabled we need to build the url with basic auth baked in.
	if ds.BasicAuth {
		password := d.secretService.GetDecryptedValue(context.Background(), ds.SecureJsonData, "basicAuthPassword", "")
		if password == "" {
			return "", fmt.Errorf("basic auth enabled but no password set")
		}
		parsed.User = url.UserPassword(ds.BasicAuthUser, password)
	}

	return parsed.String(), nil
}

func (d *AlertsRouter) Send(ctx context.Context, key models.AlertRuleKey, alerts definitions.PostableAlerts) {
	logger := d.logger.New(key.LogContext()...)
	if len(alerts.PostableAlerts) == 0 {
		logger.Info("No alerts to notify about")
		return
	}
	// Send alerts to local notifier if they need to be handled internally
	// or if no external AMs have been discovered yet.
	var localNotifierExist, externalNotifierExist bool
	if d.sendAlertsTo[key.OrgID] == models.ExternalAlertmanagers && len(d.AlertmanagersFor(key.OrgID)) > 0 {
		logger.Debug("All alerts for the given org should be routed to external notifiers only. skipping the internal notifier.")
	} else {
		logger.Info("Sending alerts to local notifier", "count", len(alerts.PostableAlerts))
		n, err := d.multiOrgNotifier.AlertmanagerFor(key.OrgID)
		if err == nil {
			localNotifierExist = true
			if err := n.PutAlerts(ctx, alerts); err != nil {
				logger.Error("Failed to put alerts in the local notifier", "count", len(alerts.PostableAlerts), "error", err)
			}
		} else {
			if errors.Is(err, notifier.ErrNoAlertmanagerForOrg) {
				logger.Debug("Local notifier was not found")
			} else {
				logger.Error("Local notifier is not available", "error", err)
			}
		}
	}

	// Send alerts to external Alertmanager(s) if we have a sender for this organization
	// and alerts are not being handled just internally.
	d.adminConfigMtx.RLock()
	defer d.adminConfigMtx.RUnlock()
	s, ok := d.externalAlertmanagers[key.OrgID]
	if ok && d.sendAlertsTo[key.OrgID] != models.InternalAlertmanager {
		logger.Info("Sending alerts to external notifier", "count", len(alerts.PostableAlerts))
		s.SendAlerts(alerts)
		externalNotifierExist = true
	}

	if !localNotifierExist && !externalNotifierExist {
		logger.Error("No external or internal notifier - alerts not delivered", "count", len(alerts.PostableAlerts))
	}
}

// AlertmanagersFor returns all the discovered Alertmanager(s) for a particular organization.
func (d *AlertsRouter) AlertmanagersFor(orgID int64) []*url.URL {
	d.adminConfigMtx.RLock()
	defer d.adminConfigMtx.RUnlock()
	s, ok := d.externalAlertmanagers[orgID]
	if !ok {
		return []*url.URL{}
	}
	return s.Alertmanagers()
}

// DroppedAlertmanagersFor returns all the dropped Alertmanager(s) for a particular organization.
func (d *AlertsRouter) DroppedAlertmanagersFor(orgID int64) []*url.URL {
	d.adminConfigMtx.RLock()
	defer d.adminConfigMtx.RUnlock()
	s, ok := d.externalAlertmanagers[orgID]
	if !ok {
		return []*url.URL{}
	}

	return s.DroppedAlertmanagers()
}

// Run starts regular updates of the configuration.
func (d *AlertsRouter) Run(ctx context.Context) error {
	for {
		select {
		case <-time.After(d.adminConfigPollInterval):
			if err := d.SyncAndApplyConfigFromDatabase(ctx); err != nil {
				d.logger.Error("Unable to sync admin configuration", "error", err)
			}
		case <-ctx.Done():
			// Stop sending alerts to all external Alertmanager(s).
			d.adminConfigMtx.Lock()
			for orgID, s := range d.externalAlertmanagers {
				delete(d.externalAlertmanagers, orgID) // delete before we stop to make sure we don't accept any more alerts.
				s.Stop()
			}
			d.adminConfigMtx.Unlock()

			return nil
		}
	}
}