package metrics

import (
	"context"
	"fmt"
	"net/http"
	"runtime"
	"sync/atomic"
	"time"
)

var startedAt = time.Now()
var submitAccepted atomic.Uint64
var submitFailed atomic.Uint64
var submitDurationNanoseconds atomic.Uint64

type Snapshot struct {
	UpstreamDesired       int
	UpstreamConnected     int
	DownstreamConnected   int
	SubmitWorkerUp        bool
	QueueAvailable        bool
	QueuePending          int64
	QueueLag              int64
	QueueOldestAgeSeconds float64
}

type SnapshotFunc func(context.Context) Snapshot

func ObserveSubmit(accepted bool, duration time.Duration) {
	if accepted {
		submitAccepted.Add(1)
	} else {
		submitFailed.Add(1)
	}
	submitDurationNanoseconds.Add(uint64(max(duration, 0)))
}

func Handler(load SnapshotFunc) http.Handler {
	return http.HandlerFunc(func(response http.ResponseWriter, request *http.Request) {
		if request.Method != http.MethodGet || request.URL.Path != "/metrics" {
			response.WriteHeader(http.StatusNotFound)
			return
		}
		ctx, cancel := context.WithTimeout(request.Context(), time.Second)
		defer cancel()
		snapshot := Snapshot{}
		if load != nil {
			snapshot = load(ctx)
		}
		var memory runtime.MemStats
		runtime.ReadMemStats(&memory)
		accepted := submitAccepted.Load()
		failed := submitFailed.Load()
		count := accepted + failed
		response.Header().Set("Content-Type", "text/plain; version=0.0.4; charset=utf-8")
		response.Header().Set("Cache-Control", "no-store")
		fmt.Fprintf(response, "# HELP cmpp_gateway_process_uptime_seconds Gateway process uptime.\n# TYPE cmpp_gateway_process_uptime_seconds gauge\ncmpp_gateway_process_uptime_seconds %f\n", time.Since(startedAt).Seconds())
		fmt.Fprintf(response, "# HELP cmpp_gateway_go_goroutines Current goroutine count.\n# TYPE cmpp_gateway_go_goroutines gauge\ncmpp_gateway_go_goroutines %d\n", runtime.NumGoroutine())
		fmt.Fprintf(response, "# HELP cmpp_gateway_go_heap_alloc_bytes Current Go heap allocation.\n# TYPE cmpp_gateway_go_heap_alloc_bytes gauge\ncmpp_gateway_go_heap_alloc_bytes %d\n", memory.HeapAlloc)
		fmt.Fprintf(response, "# HELP cmpp_gateway_submit_total Upstream submit attempts by bounded result.\n# TYPE cmpp_gateway_submit_total counter\ncmpp_gateway_submit_total{result=\"accepted\"} %d\ncmpp_gateway_submit_total{result=\"failed\"} %d\n", accepted, failed)
		fmt.Fprintf(response, "# HELP cmpp_gateway_submit_duration_seconds_sum Total upstream submit duration.\n# TYPE cmpp_gateway_submit_duration_seconds_sum counter\ncmpp_gateway_submit_duration_seconds_sum %f\n", float64(submitDurationNanoseconds.Load())/float64(time.Second))
		fmt.Fprintf(response, "# HELP cmpp_gateway_submit_duration_seconds_count Total measured upstream submits.\n# TYPE cmpp_gateway_submit_duration_seconds_count counter\ncmpp_gateway_submit_duration_seconds_count %d\n", count)
		fmt.Fprintf(response, "# HELP cmpp_gateway_upstream_connections Desired and live supplier connections.\n# TYPE cmpp_gateway_upstream_connections gauge\ncmpp_gateway_upstream_connections{state=\"desired\"} %d\ncmpp_gateway_upstream_connections{state=\"connected\"} %d\n", snapshot.UpstreamDesired, snapshot.UpstreamConnected)
		fmt.Fprintf(response, "# HELP cmpp_gateway_downstream_connections Authenticated client connections.\n# TYPE cmpp_gateway_downstream_connections gauge\ncmpp_gateway_downstream_connections %d\n", snapshot.DownstreamConnected)
		fmt.Fprintf(response, "# HELP cmpp_gateway_submit_worker_up Whether the submit worker was initialized.\n# TYPE cmpp_gateway_submit_worker_up gauge\ncmpp_gateway_submit_worker_up %d\n", boolNumber(snapshot.SubmitWorkerUp))
		if snapshot.QueueAvailable {
			fmt.Fprintf(response, "# HELP cmpp_gateway_submit_queue_pending Pending entries owned by the consumer group.\n# TYPE cmpp_gateway_submit_queue_pending gauge\ncmpp_gateway_submit_queue_pending %d\n", snapshot.QueuePending)
			fmt.Fprintf(response, "# HELP cmpp_gateway_submit_queue_lag Undelivered entries for the consumer group.\n# TYPE cmpp_gateway_submit_queue_lag gauge\ncmpp_gateway_submit_queue_lag %d\n", snapshot.QueueLag)
			fmt.Fprintf(response, "# HELP cmpp_gateway_submit_queue_oldest_pending_age_seconds Age of the oldest pending entry.\n# TYPE cmpp_gateway_submit_queue_oldest_pending_age_seconds gauge\ncmpp_gateway_submit_queue_oldest_pending_age_seconds %f\n", snapshot.QueueOldestAgeSeconds)
		}
	})
}

func boolNumber(value bool) int {
	if value {
		return 1
	}
	return 0
}