/*
Copyright 2024 Adora Laura Kalb <adora@lila.network>

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

	http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package main

import (
	"net/http"
	"net/netip"
	"os"
	"time"

	"github.com/alecthomas/kingpin/v2"
	"github.com/go-kit/log"
	"github.com/go-kit/log/level"
	"github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/client_golang/prometheus/promauto"
	"github.com/prometheus/client_golang/prometheus/promhttp"
	"github.com/prometheus/common/promlog"
	"github.com/prometheus/common/promlog/flag"
	"github.com/prometheus/common/version"
	"github.com/prometheus/exporter-toolkit/web"
	webflag "github.com/prometheus/exporter-toolkit/web/kingpinflag"
	"golang.adora.codes/ntppool-exporter/collector"
)

const (
	namespace = "ntppool"
)

var (
	metricsPath = kingpin.Flag(
		"web.telemetry-path",
		"Path under which to expose metrics.",
	).Default("/metrics").String()
	//appListenIP  = kingpin.Flag("web.listen-address", "Addresses on which to expose metrics and web interface").Default(":43609").String()
	toolkitFlags = webflag.AddFlags(kingpin.CommandLine, ":43609")

	// Metrics about the SNMP exporter itself.
	ntppoolRequestErrors = promauto.NewCounter(
		prometheus.CounterOpts{
			Namespace: namespace,
			Name:      "request_errors_total",
			Help:      "Errors in requests to the SNMP exporter",
		},
	)
)

func handler(w http.ResponseWriter, r *http.Request, logger log.Logger, exporterMetrics collector.Metrics) {

	// /metrics&target=2003%3Adb8%3A%3A1
	// /metrics&target=1.2.3.4
	query := r.URL.Query()

	target := query.Get("target")
	if len(query["target"]) != 1 || target == "" {
		http.Error(w, "'target' parameter must be specified once", http.StatusBadRequest)
		ntppoolRequestErrors.Inc()
		return
	}

	targetIP, ipError := netip.ParseAddr(target)
	if ipError != nil {
		http.Error(w, "'target' parameter must be a valid IPv4/IPv6 address", http.StatusBadRequest)
		ntppoolRequestErrors.Inc()
		return
	}

	logger = log.With(logger, "target", target)
	registry := prometheus.NewRegistry()
	c := collector.New(r.Context(), targetIP, logger, exporterMetrics)
	registry.MustRegister(c)
	// Delegate http serving to Prometheus client library, which will call collector.Collect.
	h := promhttp.HandlerFor(registry, promhttp.HandlerOpts{})
	h.ServeHTTP(w, r)
}

func main() {
	promlogConfig := &promlog.Config{}
	flag.AddFlags(kingpin.CommandLine, promlogConfig)
	kingpin.Version(version.Print("ntppool_exporter"))
	kingpin.HelpFlag.Short('h')
	kingpin.Parse()
	logger := promlog.New(promlogConfig)

	level.Info(logger).Log("msg", "Starting ntppool_exporter", "version", version.Info())
	level.Info(logger).Log("build_context", version.BuildContext())

	exporterMetrics := collector.Metrics{
		NtpppolServerScore: promauto.NewGauge(
			prometheus.GaugeOpts{
				Namespace: namespace,
				Name:      "server_score",
				Help:      "Current ntppool server score",
			},
		),
	}

	http.HandleFunc(*metricsPath, func(w http.ResponseWriter, r *http.Request) {
		handler(w, r, logger, exporterMetrics)
	})

	metricsPathValue := *metricsPath

	if *metricsPath != "/" && *metricsPath != "" {
		landingConfig := web.LandingConfig{
			Name:        "ntppool Exporter",
			Description: "Prometheus Exporter for SNMP targets",
			Version:     version.Info(),
			Form: web.LandingForm{
				Action: metricsPathValue,
				Inputs: []web.LandingFormInput{
					{
						Label:       "Target",
						Type:        "text",
						Name:        "target",
						Placeholder: "X.X.X.X/[::X]",
						Value:       "::1",
					},
				},
			},
			Links: []web.LandingLinks{
				{
					Address: *metricsPath,
					Text:    "Metrics",
				},
			},
		}

		landingPage, err := web.NewLandingPage(landingConfig)
		if err != nil {
			level.Error(logger).Log("err", err)
			os.Exit(1)
		}
		http.Handle("/", landingPage)
	}

	srv := &http.Server{
		ReadHeaderTimeout: 15 * time.Second,
		ReadTimeout:       15 * time.Second,
		WriteTimeout:      10 * time.Second,
		IdleTimeout:       30 * time.Second,
	}
	if err := web.ListenAndServe(srv, toolkitFlags, logger); err != nil {
		level.Error(logger).Log("msg", "Error starting HTTP server", "err", err)
		os.Exit(1)
	}
}