package rules

import (
	"context"
	"fmt"
	"sync"
	"time"

	"github.com/go-kit/log"
	"github.com/go-kit/log/level"
	"go.uber.org/zap"

	plabels "github.com/prometheus/prometheus/pkg/labels"
	pql "github.com/prometheus/prometheus/promql"
	"go.signoz.io/signoz/pkg/query-service/model"
	qslabels "go.signoz.io/signoz/pkg/query-service/utils/labels"
	"go.signoz.io/signoz/pkg/query-service/utils/times"
	"go.signoz.io/signoz/pkg/query-service/utils/timestamp"
	yaml "gopkg.in/yaml.v2"
)

type PromRuleOpts struct {
	// SendAlways will send alert irresepective of resendDelay
	// or other params
	SendAlways bool
}

type PromRule struct {
	id            string
	name          string
	source        string
	ruleCondition *RuleCondition

	evalWindow   time.Duration
	holdDuration time.Duration
	labels       plabels.Labels
	annotations  plabels.Labels

	preferredChannels []string

	mtx                 sync.Mutex
	evaluationDuration  time.Duration
	evaluationTimestamp time.Time

	health RuleHealth

	lastError error

	// map of active alerts
	active map[uint64]*Alert

	logger log.Logger
	opts   PromRuleOpts
}

func NewPromRule(
	id string,
	postableRule *PostableRule,
	logger log.Logger,
	opts PromRuleOpts,
) (*PromRule, error) {

	if postableRule.RuleCondition == nil {
		return nil, fmt.Errorf("no rule condition")
	} else if !postableRule.RuleCondition.IsValid() {
		return nil, fmt.Errorf("invalid rule condition")
	}

	p := PromRule{
		id:                id,
		name:              postableRule.Alert,
		source:            postableRule.Source,
		ruleCondition:     postableRule.RuleCondition,
		evalWindow:        time.Duration(postableRule.EvalWindow),
		labels:            plabels.FromMap(postableRule.Labels),
		annotations:       plabels.FromMap(postableRule.Annotations),
		preferredChannels: postableRule.PreferredChannels,
		health:            HealthUnknown,
		active:            map[uint64]*Alert{},
		logger:            logger,
		opts:              opts,
	}

	if int64(p.evalWindow) == 0 {
		p.evalWindow = 5 * time.Minute
	}
	query, err := p.getPqlQuery()

	if err != nil {
		// can not generate a valid prom QL query
		return nil, err
	}

	zap.S().Info("msg:", "creating new alerting rule", "\t name:", p.name, "\t condition:", p.ruleCondition.String(), "\t query:", query)

	return &p, nil
}

func (r *PromRule) Name() string {
	return r.name
}

func (r *PromRule) ID() string {
	return r.id
}

func (r *PromRule) Condition() *RuleCondition {
	return r.ruleCondition
}

func (r *PromRule) Type() RuleType {
	return RuleTypeProm
}

func (r *PromRule) GeneratorURL() string {
	return prepareRuleGeneratorURL(r.ID(), r.source)
}

func (r *PromRule) PreferredChannels() []string {
	return r.preferredChannels
}

func (r *PromRule) SetLastError(err error) {
	r.mtx.Lock()
	defer r.mtx.Unlock()
	r.lastError = err
}

func (r *PromRule) LastError() error {
	r.mtx.Lock()
	defer r.mtx.Unlock()
	return r.lastError
}

func (r *PromRule) SetHealth(health RuleHealth) {
	r.mtx.Lock()
	defer r.mtx.Unlock()
	r.health = health
}

func (r *PromRule) Health() RuleHealth {
	r.mtx.Lock()
	defer r.mtx.Unlock()
	return r.health
}

// SetEvaluationDuration updates evaluationDuration to the duration it took to evaluate the rule on its last evaluation.
func (r *PromRule) SetEvaluationDuration(dur time.Duration) {
	r.mtx.Lock()
	defer r.mtx.Unlock()
	r.evaluationDuration = dur
}

func (r *PromRule) HoldDuration() time.Duration {
	return r.holdDuration
}

func (r *PromRule) EvalWindow() time.Duration {
	return r.evalWindow
}

// Labels returns the labels of the alerting rule.
func (r *PromRule) Labels() qslabels.BaseLabels {
	return r.labels
}

// Annotations returns the annotations of the alerting rule.
func (r *PromRule) Annotations() qslabels.BaseLabels {
	return r.annotations
}

func (r *PromRule) sample(alert *Alert, ts time.Time) pql.Sample {
	lb := plabels.NewBuilder(r.labels)

	alertLabels := alert.Labels.(plabels.Labels)
	for _, l := range alertLabels {
		lb.Set(l.Name, l.Value)
	}

	lb.Set(qslabels.MetricNameLabel, alertMetricName)
	lb.Set(qslabels.AlertNameLabel, r.name)
	lb.Set(qslabels.AlertStateLabel, alert.State.String())

	s := pql.Sample{
		Metric: lb.Labels(),
		Point:  pql.Point{T: timestamp.FromTime(ts), V: 1},
	}
	return s
}

// GetEvaluationDuration returns the time in seconds it took to evaluate the alerting rule.
func (r *PromRule) GetEvaluationDuration() time.Duration {
	r.mtx.Lock()
	defer r.mtx.Unlock()
	return r.evaluationDuration
}

// SetEvaluationTimestamp updates evaluationTimestamp to the timestamp of when the rule was last evaluated.
func (r *PromRule) SetEvaluationTimestamp(ts time.Time) {
	r.mtx.Lock()
	defer r.mtx.Unlock()
	r.evaluationTimestamp = ts
}

// GetEvaluationTimestamp returns the time the evaluation took place.
func (r *PromRule) GetEvaluationTimestamp() time.Time {
	r.mtx.Lock()
	defer r.mtx.Unlock()
	return r.evaluationTimestamp
}

// State returns the maximum state of alert instances for this rule.
// StateFiring > StatePending > StateInactive
func (r *PromRule) State() AlertState {
	r.mtx.Lock()
	defer r.mtx.Unlock()

	maxState := StateInactive
	for _, a := range r.active {
		if a.State > maxState {
			maxState = a.State
		}
	}
	return maxState
}

func (r *PromRule) currentAlerts() []*Alert {
	r.mtx.Lock()
	defer r.mtx.Unlock()

	alerts := make([]*Alert, 0, len(r.active))

	for _, a := range r.active {
		anew := *a
		alerts = append(alerts, &anew)
	}
	return alerts
}

func (r *PromRule) ActiveAlerts() []*Alert {
	var res []*Alert
	for _, a := range r.currentAlerts() {
		if a.ResolvedAt.IsZero() {
			res = append(res, a)
		}
	}
	return res
}

// ForEachActiveAlert runs the given function on each alert.
// This should be used when you want to use the actual alerts from the ThresholdRule
// and not on its copy.
// If you want to run on a copy of alerts then don't use this, get the alerts from 'ActiveAlerts()'.
func (r *PromRule) ForEachActiveAlert(f func(*Alert)) {
	r.mtx.Lock()
	defer r.mtx.Unlock()

	for _, a := range r.active {
		f(a)
	}
}

func (r *PromRule) SendAlerts(ctx context.Context, ts time.Time, resendDelay time.Duration, interval time.Duration, notifyFunc NotifyFunc) {
	alerts := []*Alert{}
	r.ForEachActiveAlert(func(alert *Alert) {
		if r.opts.SendAlways || alert.needsSending(ts, resendDelay) {
			alert.LastSentAt = ts
			// Allow for two Eval or Alertmanager send failures.
			delta := resendDelay
			if interval > resendDelay {
				delta = interval
			}
			alert.ValidUntil = ts.Add(4 * delta)
			anew := *alert
			alerts = append(alerts, &anew)
		}
	})
	notifyFunc(ctx, "", alerts...)
}

func (r *PromRule) getPqlQuery() (string, error) {

	if r.ruleCondition.CompositeMetricQuery.QueryType == model.PROM {
		if len(r.ruleCondition.CompositeMetricQuery.PromQueries) > 0 {
			if promQuery, ok := r.ruleCondition.CompositeMetricQuery.PromQueries["A"]; ok {
				query := promQuery.Query
				if query == "" {
					return query, fmt.Errorf("a promquery needs to be set for this rule to function")
				}
				if r.ruleCondition.Target != nil && r.ruleCondition.CompareOp != CompareOpNone {
					query = fmt.Sprintf("%s %s %f", query, ResolveCompareOp(r.ruleCondition.CompareOp), *r.ruleCondition.Target)
					return query, nil
				} else {
					return query, nil
				}
			}
		}
	}

	return "", fmt.Errorf("invalid promql rule query")
}

func (r *PromRule) Eval(ctx context.Context, ts time.Time, queriers *Queriers) (interface{}, error) {

	q, err := r.getPqlQuery()
	if err != nil {
		return nil, err
	}
	zap.S().Info("rule:", r.Name(), "\t evaluating promql query: ", q)
	res, err := queriers.PqlEngine.RunAlertQuery(ctx, q, ts)
	if err != nil {
		r.SetHealth(HealthBad)
		r.SetLastError(err)
		return nil, err
	}

	r.mtx.Lock()
	defer r.mtx.Unlock()

	resultFPs := map[uint64]struct{}{}

	var alerts = make(map[uint64]*Alert, len(res))

	for _, smpl := range res {
		l := make(map[string]string, len(smpl.Metric))
		for _, lbl := range smpl.Metric {
			l[lbl.Name] = lbl.Value
		}

		tmplData := AlertTemplateData(l, smpl.V)
		// Inject some convenience variables that are easier to remember for users
		// who are not used to Go's templating system.
		defs := "{{$labels := .Labels}}{{$value := .Value}}"

		expand := func(text string) string {

			tmpl := NewTemplateExpander(
				ctx,
				defs+text,
				"__alert_"+r.Name(),
				tmplData,
				times.Time(timestamp.FromTime(ts)),
				nil,
			)
			result, err := tmpl.Expand()
			if err != nil {
				result = fmt.Sprintf("<error expanding template: %s>", err)
				level.Warn(r.logger).Log("msg", "Expanding alert template failed", "err", err, "data", tmplData)
			}
			return result
		}

		lb := plabels.NewBuilder(smpl.Metric).Del(plabels.MetricName)

		for _, l := range r.labels {
			lb.Set(l.Name, expand(l.Value))
		}

		lb.Set(qslabels.AlertNameLabel, r.Name())
		lb.Set(qslabels.AlertRuleIdLabel, r.ID())
		lb.Set(qslabels.RuleSourceLabel, r.GeneratorURL())

		annotations := make(plabels.Labels, 0, len(r.annotations))
		for _, a := range r.annotations {
			annotations = append(annotations, plabels.Label{Name: a.Name, Value: expand(a.Value)})
		}

		lbs := lb.Labels()
		h := lbs.Hash()
		resultFPs[h] = struct{}{}

		if _, ok := alerts[h]; ok {
			err = fmt.Errorf("vector contains metrics with the same labelset after applying alert labels")
			// We have already acquired the lock above hence using SetHealth and
			// SetLastError will deadlock.
			r.health = HealthBad
			r.lastError = err
			return nil, err
		}

		alerts[h] = &Alert{
			Labels:       lbs,
			Annotations:  annotations,
			ActiveAt:     ts,
			State:        StatePending,
			Value:        smpl.V,
			GeneratorURL: r.GeneratorURL(),
			Receivers:    r.preferredChannels,
		}
	}

	// alerts[h] is ready, add or update active list now
	for h, a := range alerts {
		// Check whether we already have alerting state for the identifying label set.
		// Update the last value and annotations if so, create a new alert entry otherwise.
		if alert, ok := r.active[h]; ok && alert.State != StateInactive {
			alert.Value = a.Value
			alert.Annotations = a.Annotations
			alert.Receivers = r.preferredChannels
			continue
		}

		r.active[h] = a

	}

	// Check if any pending alerts should be removed or fire now. Write out alert timeseries.
	for fp, a := range r.active {
		if _, ok := resultFPs[fp]; !ok {
			// If the alert was previously firing, keep it around for a given
			// retention time so it is reported as resolved to the AlertManager.
			if a.State == StatePending || (!a.ResolvedAt.IsZero() && ts.Sub(a.ResolvedAt) > resolvedRetention) {
				delete(r.active, fp)
			}
			if a.State != StateInactive {
				a.State = StateInactive
				a.ResolvedAt = ts
			}
			continue
		}

		if a.State == StatePending && ts.Sub(a.ActiveAt) >= r.holdDuration {
			a.State = StateFiring
			a.FiredAt = ts
		}

	}
	r.health = HealthGood
	r.lastError = err

	return len(r.active), nil
}

func (r *PromRule) String() string {

	ar := PostableRule{
		Alert:             r.name,
		RuleCondition:     r.ruleCondition,
		EvalWindow:        Duration(r.evalWindow),
		Labels:            r.labels.Map(),
		Annotations:       r.annotations.Map(),
		PreferredChannels: r.preferredChannels,
	}

	byt, err := yaml.Marshal(ar)
	if err != nil {
		return fmt.Sprintf("error marshaling alerting rule: %s", err.Error())
	}

	return string(byt)
}