// Copyright (C) 2019 Marius Schellenberger

package main

import (
	"encoding/json"
	"fmt"
	"io/ioutil"
	"log"
	"net"
	"net/http"
	"net/url"
	"reflect"
	"strconv"
	"strings"
	"time"

	//corev1 "k8s.io/api/core/v1"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/client-go/kubernetes"
	typedcorev1 "k8s.io/client-go/kubernetes/typed/core/v1"
	"k8s.io/client-go/rest"
)

var debug = false

const (
	prAction      = "X-Interceptor-Pr-Action"
	pushAction    = "X-Interceptor-Push-Action"
	commentAction = "X-Interceptor-Comment-Action"

	contentType = "Content-Type"
	jsonType    = "application/json"

	githubEvent = "X-GitHub-Event"
	giteaEvent  = "X-Gitea-Event"

	issueHeader  = "Issue"
	commitHeader = "Commit"

	secretName = "git-auth"
)

func init() {
	log.SetFlags(log.Flags() | log.Lshortfile)
}

func (h *Handler) getSecret(host string) (username, password string, err error) {
	sec, err := h.sec.Get(secretName, metav1.GetOptions{})
	if err != nil {
		return
	}
	s, ok := sec.Data[host]
	if !ok {
		err = fmt.Errorf("no key found for host %s in secret %s/%s", host, sec.Namespace, sec.Name)
		return
	}
	a := strings.SplitN(string(s), ":", 2)
	if len(a) < 2 {
		err = fmt.Errorf("missing credentials for host %s in secret %s/%s", host, sec.Namespace, sec.Name)
		return
	}
	username = a[0]
	password = a[1]
	return
}

func (h *Handler) getPullRequest(repo Repository, api, id string) (*PullRequest, error) {
	u, err := url.Parse(repo.CloneURL)
	if err != nil {
		return nil, err
	}
	u.Path = strings.Join([]string{api, "repos",
		repo.Owner.Login, repo.Name,
		"pulls", id}, "/")
	req, err := http.NewRequest("GET", u.String(), nil)
	if err != nil {
		return nil, err
	}
	req.Header.Set(contentType, jsonType)

	user, pass, err := h.getSecret(u.Host)
	if err != nil {
		return nil, err
	}
	req.SetBasicAuth(user, pass)

	resp, err := h.cl.Do(req)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()
	pr := new(PullRequest)
	err = json.NewDecoder(resp.Body).Decode(pr)
	if err != nil {
		return nil, err
	}
	return pr, nil
}

type Handler struct {
	sec typedcorev1.SecretInterface
	cl  *http.Client
}

func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	event := r.Header.Get(githubEvent)
	switch event {
	case "pull_request":
		h.prHandler(w, r)
	case "push":
		h.pushHandler(w, r)
	case "issue_comment":
		h.commentHandler(w, r)
	default:
		h.dumpHandler(w, r)
	}
	status := int(reflect.Indirect(reflect.ValueOf(w)).FieldByName("status").Int())
	log.Printf("%s %s %s event:%s status:%d", r.RemoteAddr, r.Method, r.URL, event, status)
}

func (h *Handler) prHandler(w http.ResponseWriter, r *http.Request) {
	var prb PullRequestBody
	body, err := readBody(r, &prb)
	if err != nil {
		logError(w, err.Error())
		return
	}
	if contains(r.Header[prAction], prb.Action) {
		h := w.Header()
		h.Set(issueHeader, strconv.FormatInt(prb.Number, 10))
		h.Set(commitHeader, prb.PullRequest.Head.SHA)
		w.Write(body)
		return
	}
	w.WriteHeader(http.StatusBadRequest)
}

func (h *Handler) pushHandler(w http.ResponseWriter, r *http.Request) {
	var pb PushBody
	body, err := readBody(r, &pb)
	if err != nil {
		logError(w, err.Error())
		return
	}
	if contains(r.Header[pushAction], pb.Ref) {
		h := w.Header()
		h.Set(commitHeader, pb.After)
		w.Write(body)
		return
	}
	w.WriteHeader(http.StatusBadRequest)
}

func (h *Handler) commentHandler(w http.ResponseWriter, r *http.Request) {
	var cb CommentBody
	body, err := readBody(r, &cb)
	if err != nil {
		logError(w, err.Error())
		return
	}
	//if label := r.Header.Get(labelHeader); label != "" {
	//}
	if contains(r.Header[commentAction], cb.Comment.Body) {
		issue := strconv.FormatInt(cb.Issue.Number, 10)
		api := detectAPI(r)
		if api == "" {
			logError(w, "unable to detect git provider API")
			return
		}
		pr, err := h.getPullRequest(cb.Repository, api, issue)
		if err != nil {
			logError(w, err.Error())
			return
		}

		h := w.Header()
		h.Set(issueHeader, issue)
		h.Set(commitHeader, pr.Head.SHA)
		w.Write(body)
		return
	}
	w.WriteHeader(http.StatusBadRequest)
}

func (h *Handler) dumpHandler(w http.ResponseWriter, r *http.Request) {
	defer r.Body.Close()
	if debug {
		body, err := ioutil.ReadAll(r.Body)
		if err != nil {
			logError(w, err.Error())
			return
		}
		log.Printf("debug headers: %#v", r.Header)
		log.Printf("debug: %s", string(body))
	}
	w.WriteHeader(http.StatusBadRequest)
}

func main() {
	cfg, err := rest.InClusterConfig()
	if err != nil {
		log.Fatalf("error configuring kube client: %s\n", err)
	}
	cl, err := kubernetes.NewForConfig(cfg)
	if err != nil {
		log.Fatalf("error creating new kube client: %s\n", err)
	}
	ns, err := getNS()
	if err != nil {
		log.Fatalf("error getting current namespace %s\n", err)
	}
	h := &Handler{
		sec: cl.CoreV1().Secrets(ns),
		cl: &http.Client{Transport: &http.Transport{
			DialContext: (&net.Dialer{
				Timeout: 30 * time.Second,
			}).DialContext,
		}},
	}

	http.Handle("/", h)
	s := &http.Server{
		ReadTimeout:  5 * time.Second,
		WriteTimeout: 10 * time.Second,
		IdleTimeout:  120 * time.Second,
		Addr:         ":8080",
	}
	log.Println("started webhook listener")
	log.Fatal(s.ListenAndServe())
}