package main

import (
	"fmt"
	"log/slog"
	"net/http"
	"os"
	"strings"

	"github.com/alecthomas/kingpin/v2"
	"github.com/prometheus/client_golang/prometheus"
	versioncollector "github.com/prometheus/client_golang/prometheus/collectors/version"
	"github.com/prometheus/client_golang/prometheus/promhttp"
	"github.com/prometheus/common/promslog"
	promslogflag "github.com/prometheus/common/promslog/flag"
	"github.com/prometheus/exporter-toolkit/web"
	"github.com/prometheus/exporter-toolkit/web/kingpinflag"

	"github.com/dsgeis/pve-exporter/collector"
)

func main() {
	var (
		pveHosts = kingpin.Flag(
			"pve.host",
			"PVE host base URL (e.g. https://pve1:8006). May be repeated for failover.",
		).Required().Strings()
		pveAPIToken = kingpin.Flag(
			"pve.api-token",
			"PVE API token (USER@REALM!TOKENID=SECRET).",
		).String()
		pveTokenFile = kingpin.Flag(
			"pve.token-file",
			"Path to file containing the PVE API token.",
		).String()
		pveTLSInsecure = kingpin.Flag(
			"pve.tls-insecure",
			"Disable TLS certificate verification for PVE API.",
		).Default("false").Bool()
		pveMaxConcurrent = kingpin.Flag(
			"pve.max-concurrent",
			"Maximum number of concurrent API requests to PVE.",
		).Default("5").Int()
		metricsPath = kingpin.Flag(
			"web.telemetry-path",
			"Path under which to expose metrics.",
		).Default("/metrics").String()
		toolkitFlags = kingpinflag.AddFlags(kingpin.CommandLine, ":9221")
	)

	promslogConfig := &promslog.Config{}
	promslogflag.AddFlags(kingpin.CommandLine, promslogConfig)
	kingpin.HelpFlag.Short('h')
	kingpin.Parse()
	logger := promslog.New(promslogConfig)

	token, err := resolveToken(*pveAPIToken, *pveTokenFile)
	if err != nil {
		logger.Error("failed to resolve API token", "err", err)
		os.Exit(1)
	}

	client := collector.NewClient(*pveHosts, token, *pveTLSInsecure, *pveMaxConcurrent)
	pveCollector := collector.NewPVECollector(client, logger)

	registry := prometheus.NewRegistry()
	registry.MustRegister(versioncollector.NewCollector("pve_exporter"))
	registry.MustRegister(pveCollector)

	http.Handle(*metricsPath, promhttp.HandlerFor(
		registry,
		promhttp.HandlerOpts{
			ErrorLog:            slog.NewLogLogger(logger.Handler(), slog.LevelError),
			ErrorHandling:       promhttp.ContinueOnError,
			MaxRequestsInFlight: 5,
		},
	))

	if *metricsPath != "/" {
		landingConfig := web.LandingConfig{
			Name:        "PVE Exporter",
			Description: "Prometheus Exporter for Proxmox VE",
			Links: []web.LandingLinks{
				{
					Address: *metricsPath,
					Text:    "Metrics",
				},
			},
		}
		landingPage, err := web.NewLandingPage(landingConfig)
		if err != nil {
			logger.Error("failed to create landing page", "err", err)
			os.Exit(1)
		}
		http.Handle("/", landingPage)
	}

	server := &http.Server{}
	if err := web.ListenAndServe(server, toolkitFlags, logger); err != nil {
		logger.Error("HTTP server error", "err", err)
		os.Exit(1)
	}
}

// resolveToken determines the API token from flags or environment.
// Exactly one of apiToken or tokenFile may be set; if neither is set,
// the PVE_API_TOKEN environment variable is used as a fallback.
func resolveToken(apiToken, tokenFile string) (string, error) {
	if apiToken != "" && tokenFile != "" {
		return "", fmt.Errorf("--pve.api-token and --pve.token-file are mutually exclusive")
	}

	if apiToken != "" {
		return apiToken, nil
	}

	if tokenFile != "" {
		data, err := os.ReadFile(tokenFile)
		if err != nil {
			return "", fmt.Errorf("reading token file: %w", err)
		}
		token := strings.TrimSpace(string(data))
		if token == "" {
			return "", fmt.Errorf("token file %s is empty", tokenFile)
		}
		return token, nil
	}

	if envToken := os.Getenv("PVE_API_TOKEN"); envToken != "" {
		return envToken, nil
	}

	return "", fmt.Errorf("no API token provided: use --pve.api-token, --pve.token-file, or PVE_API_TOKEN env var")
}