package prom

import (
	"fmt"
	"regexp"
	"strconv"
	"time"
)

const DefaultBeylaJobSelector = `job=~".*beyla.*|.*alloy.*"`

type RequestSource string

const (
	RequestSourceBeyla RequestSource = "beyla"
	RequestSourceIstio RequestSource = "istio"
)

type RequestQueries struct {
	Rate                string
	Errors              string
	P50                 string
	P95                 string
	HistogramCoverage   string
	StatusCoverage      string
	ObservedPods        string
	Population          string
	HistogramUniformity string
}

var beylaJobMatcher = regexp.MustCompile(`^job\s*(=|=~)\s*("(?:[^"\\]|\\.)*")$`)

func BuildRequestQueries(step time.Duration, sel PodSelection, scope WorkloadMetricsScope, source RequestSource, jobSelector string) (RequestQueries, error) {
	cluster, err := scope.Matchers()
	if err != nil {
		return RequestQueries{}, err
	}
	return buildRequestQueries(step, sel, cluster, source, jobSelector, nil, nil)
}

func BuildIdentityRequestQueries(step time.Duration, sel PodSelection, pods []WorkloadPodIdentity, source RequestSource, jobSelector string) (RequestQueries, error) {
	branches, err := buildWorkloadIdentityFilter(pods, source)
	if err != nil {
		return RequestQueries{}, err
	}
	return buildRequestQueries(step, sel, "", source, jobSelector, branches, nil)
}

func BuildHistoryRequestQueries(step time.Duration, history WorkloadHistory, source RequestSource, jobSelector string) (RequestQueries, error) {
	if _, err := history.OwnerQuery(); err != nil {
		return RequestQueries{}, err
	}
	cluster, _ := history.Scope.Matchers()
	if jobSelector == "" {
		jobSelector = `job=~".+"`
	}
	return buildRequestQueries(step, PodSelection{Namespace: history.Namespace}, cluster, source, jobSelector, nil, &history)
}

func buildRequestQueries(step time.Duration, sel PodSelection, cluster string, source RequestSource, jobSelector string, branches *workloadIdentityFilter, history *WorkloadHistory) (RequestQueries, error) {
	if history == nil && sel.IsEmpty() {
		return RequestQueries{}, fmt.Errorf("no current pods")
	}
	var metric, target, status, podLabel string
	unitScale := ""
	switch source {
	case RequestSourceBeyla:
		if jobSelector == "" {
			jobSelector = DefaultBeylaJobSelector
		}
		match := beylaJobMatcher.FindStringSubmatch(jobSelector)
		if match == nil {
			return RequestQueries{}, fmt.Errorf("the configured Beyla job filter must be one job equality or regex matcher for workload charts; Live Traffic accepts wider fragments")
		}
		value, err := strconv.Unquote(match[2])
		if err != nil {
			return RequestQueries{}, fmt.Errorf("invalid Beyla job matcher: %w", err)
		}
		if match[1] == "=~" {
			if _, err := regexp.Compile(value); err != nil {
				return RequestQueries{}, fmt.Errorf("invalid Beyla job regex: %w", err)
			}
		}
		metric = "http_server_request_duration_seconds"
		target = fmt.Sprintf(`%s,k8s_namespace_name=%s,k8s_pod_name=~'%s'`, jobSelector, strconv.Quote(sel.Namespace), exactSetPattern(sel.Pods))
		if history != nil {
			target = fmt.Sprintf(`%s,k8s_namespace_name=%s,k8s_pod_name!=""`, jobSelector, strconv.Quote(sel.Namespace))
		}
		status = "http_response_status_code"
		podLabel = "k8s_pod_name"
	case RequestSourceIstio:
		metric = "istio_request_duration_milliseconds"
		// A destination reporter's scrape Pod is the observed Pod. A waypoint's
		// scrape Pod is the proxy, not its target; it cannot use this attribution.
		target = fmt.Sprintf(`reporter="destination",request_protocol="http",destination_workload_namespace=%s,namespace=%s%s`, strconv.Quote(sel.Namespace), strconv.Quote(sel.Namespace), scopeClause(sel))
		if history != nil {
			target = fmt.Sprintf(`reporter="destination",request_protocol="http",destination_workload_namespace=%s,namespace=%s,destination_workload=%s`, strconv.Quote(sel.Namespace), strconv.Quote(sel.Namespace), strconv.Quote(history.Name))
		}
		status = "response_code"
		podLabel = "pod"
		unitScale = " / 1000"
	default:
		return RequestQueries{}, fmt.Errorf("unsupported request source %q", source)
	}
	expression := func(metric, extra string) string {
		if history != nil {
			query, _ := history.expression(metric, target+extra, WorkloadRateWindow(step).String(), source == RequestSourceBeyla)
			return query
		}
		return workloadMetricExpression(metric, cluster, target+extra, branches, WorkloadRateWindow(step).String())
	}
	countMetric := metric + "_count"
	if source == RequestSourceIstio {
		countMetric = "istio_requests_total"
	}
	rate := func(metric, extra string) string {
		return "sum(max without (job,instance) (" + expression(metric, extra) + "))"
	}
	total := rate(countMetric, "")
	errors := rate(countMetric, fmt.Sprintf(`,%s=~"5.."`, status))
	bucketRates := "max without (job,instance) (" + expression(metric+"_bucket", "") + ")"
	buckets := "sum by (le) (" + bucketRates + ")"
	bucketPopulation := "count by (le) (" + bucketRates + ")"
	quantile := func(q string) string {
		return "histogram_quantile(" + q + ", " + buckets + ")" + unitScale
	}
	histogramCoverage := rate(metric+"_bucket", `,le="+Inf"`)
	populationMetrics := expression(countMetric, "") + " or " + expression(metric+"_bucket", "")
	if source == RequestSourceIstio {
		populationMetrics += " or " + expression(metric+"_count", "")
		counter := "max without (job,instance) (" + expression(countMetric, "") + ")"
		histogramCount := "max without (job,instance) (" + expression(metric+"_count", "") + ")"
		infinity := "max without (job,instance,le) (" + expression(metric+"_bucket", `,le="+Inf"`) + ")"
		// Envoy merges histograms asynchronously from request counters. Match
		// their complete label populations, but compare values within the histogram.
		population := "count(" + counter + " and " + histogramCount + ") == bool count(" + counter + " or " + histogramCount + ")"
		consistent := "count(" + histogramCount + " == " + infinity + ") == bool count(" + histogramCount + " or " + infinity + ")"
		noForeignBuckets := "((count(" + bucketRates + " unless ignoring(le) " + histogramCount + ") or vector(0)) == bool 0)"
		histogramCoverage = "(" + population + ") * (" + consistent + ") * " + noForeignBuckets
	}
	return RequestQueries{
		Rate:                total,
		Errors:              errors,
		P50:                 quantile("0.50"),
		P95:                 quantile("0.95"),
		HistogramCoverage:   histogramCoverage,
		HistogramUniformity: "min(" + bucketPopulation + ") / max(" + bucketPopulation + ")",
		StatusCoverage:      rate(countMetric, fmt.Sprintf(`,%s=~"0|[1-5][0-9][0-9]"`, status)),
		ObservedPods:        "count(count by (" + podLabel + ") (" + expression(countMetric, "") + "))",
		Population:          "count(count by (job,replica,prometheus_replica,__replica__) (" + populationMetrics + "))",
	}, nil
}