package main

import (
	"embed"
	"flag"
	"fmt"
	"io/fs"
	"log"
	"net/http"
	"os"
	"regexp"
	"time"

	"github.com/dgraph-io/badger/v2"
	"github.com/gojp/goreportcard/handlers"

	"github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/client_golang/prometheus/promhttp"
)

var (
	addr = flag.String("http", ":8000", "HTTP listen address")

	databasePath = flag.String("db", getEnv("GRC_DATABASE_PATH", "/usr/local/badger"), "path to local badger database")

	//go:embed assets/*
	embedFS embed.FS
)

func makeHandler(db *badger.DB, name string, fn func(http.ResponseWriter, *http.Request, *badger.DB, string)) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		validPath := regexp.MustCompile(fmt.Sprintf(`^/%s/([a-zA-Z0-9\-_\/\.~]+)$`, name))

		m := validPath.FindStringSubmatch(r.URL.Path)
		if m == nil {
			http.NotFound(w, r)
			return
		}
		if len(m) < 1 || m[1] == "" {
			http.Error(w, "Please enter a repository", http.StatusBadRequest)
			return
		}

		repo := m[1]

		// for backwards-compatibility, we must support URLs formatted as
		//   /report/[org]/[repo]
		// and they will be assumed to be github.com URLs. This is because
		// at first Go Report Card only supported github.com URLs, and
		// took only the org name and repo name as parameters. This is no longer the
		// case, but we do not want external links to break.
		oldFormat := regexp.MustCompile(fmt.Sprintf(`^/%s/([a-zA-Z0-9\-_]+)/([a-zA-Z0-9\-_]+)$`, name))
		m2 := oldFormat.FindStringSubmatch(r.URL.Path)
		if m2 != nil {
			// old format is being used
			repo = "github.com/" + repo
			log.Printf("Assuming intended repo is %q, redirecting", repo)
			http.Redirect(w, r, fmt.Sprintf("/%s/%s", name, repo), http.StatusMovedPermanently)
			return
		}

		fn(w, r, db, repo)
	}
}

func injectBadgerHandler(db *badger.DB, fn func(http.ResponseWriter, *http.Request, *badger.DB)) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		fn(w, r, db)
	}
}

// metrics provides functionality for monitoring the application status
type metrics struct {
	responseTimes *prometheus.SummaryVec
}

// setupMetrics creates custom Prometheus metrics for monitoring
// application statistics.
func setupMetrics() *metrics {
	m := &metrics{}
	m.responseTimes = prometheus.NewSummaryVec(
		prometheus.SummaryOpts{
			Name: "response_time_ms",
			Help: "Time to serve requests",
		},
		[]string{"endpoint"},
	)

	prometheus.MustRegister(m.responseTimes)
	return m
}

// recordDuration records the length of a request from start to now
func (m metrics) recordDuration(start time.Time, name string) {
	elapsed := time.Since(start)
	m.responseTimes.WithLabelValues(name).Observe(float64(elapsed.Milliseconds()))
	log.Printf("Served %s in %s", name, elapsed)
}

// instrument adds metric instrumentation to the handler passed in as argument
func (m metrics) instrument(path string, h http.HandlerFunc) (string, http.HandlerFunc) {
	return path, func(w http.ResponseWriter, r *http.Request) {
		defer m.recordDuration(time.Now(), r.URL.Path)
		h.ServeHTTP(w, r)
	}
}

func getEnv(name, def string) string {
	got := os.Getenv(name)
	if got == "" {
		return def
	}
	return got
}

func main() {
	flag.Parse()
	if err := os.MkdirAll("_repos/src/github.com", 0755); err != nil && !os.IsExist(err) {
		log.Fatal("ERROR: could not create repos dir: ", err)
	}

	db, err := badger.Open(badger.DefaultOptions(*databasePath).WithTruncate(true))
	if err != nil {
		log.Fatal("ERROR: could not open badger db: ", err)
	}

	assetsFS, err := fs.Sub(embedFS, "assets")
	if err != nil {
		log.Fatal(err)
	}

	gh := handlers.GRCHandler{AssetsFS: http.FS(assetsFS)}

	defer db.Close()

	m := setupMetrics()

	http.HandleFunc(m.instrument("/assets/", http.StripPrefix("/assets/", http.FileServer(http.FS(assetsFS))).ServeHTTP))
	http.HandleFunc(m.instrument("/checks", injectBadgerHandler(db, handlers.CheckHandler)))
	http.HandleFunc(m.instrument("/report/", makeHandler(db, "report", gh.ReportHandler)))
	http.HandleFunc(m.instrument("/badge/", makeHandler(db, "badge", handlers.BadgeHandler)))
	http.HandleFunc(m.instrument("/high_scores/", injectBadgerHandler(db, gh.HighScoresHandler)))
	http.HandleFunc(m.instrument("/supporters/", gh.SupportersHandler))
	http.HandleFunc(m.instrument("/about/", gh.AboutHandler))
	http.HandleFunc(m.instrument("/", injectBadgerHandler(db, gh.HomeHandler)))

	http.Handle("/metrics", promhttp.Handler())

	log.Printf("Running on %s ...", *addr)
	log.Fatal(http.ListenAndServe(*addr, nil))
}
