package main

import (
	"bufio"
	"bytes"
	"crypto/sha256"
	"encoding/base64"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"io"
	"io/ioutil"
	"log"
	"net/http"
	"net/http/httptest"
	"net/textproto"
	"os"
	"os/exec"
	"regexp"
	"strings"
	"sync"
)

var (
	repoDir      string
	largeObjects = newLfsStorage()
	server       *httptest.Server
	serveBatch   = true
)

func main() {
	repoDir = os.Getenv("LFSTEST_DIR")

	mux := http.NewServeMux()
	server = httptest.NewServer(mux)
	stopch := make(chan bool)

	mux.HandleFunc("/startbatch", func(w http.ResponseWriter, r *http.Request) {
		serveBatch = true
	})

	mux.HandleFunc("/stopbatch", func(w http.ResponseWriter, r *http.Request) {
		serveBatch = false
	})

	mux.HandleFunc("/shutdown", func(w http.ResponseWriter, r *http.Request) {
		stopch <- true
	})

	mux.HandleFunc("/storage/", storageHandler)
	mux.HandleFunc("/redirect307/", redirect307Handler)
	mux.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		if strings.Contains(r.URL.Path, "/info/lfs") {
			if !skipIfBadAuth(w, r) {
				lfsHandler(w, r)
			}

			return
		}

		log.Printf("git http-backend %s %s\n", r.Method, r.URL)
		gitHandler(w, r)
	})

	urlname := os.Getenv("LFSTEST_URL")
	if len(urlname) == 0 {
		urlname = "lfstest-gitserver"
	}

	file, err := os.Create(urlname)
	if err != nil {
		log.Fatalln(err)
	}

	file.Write([]byte(server.URL))
	file.Close()
	log.Println(server.URL)

	defer func() {
		os.RemoveAll(urlname)
	}()

	<-stopch
	log.Println("git server done")
}

type lfsObject struct {
	Oid     string             `json:"oid,omitempty"`
	Size    int64              `json:"size,omitempty"`
	Actions map[string]lfsLink `json:"actions,omitempty"`
}

type lfsLink struct {
	Href   string            `json:"href"`
	Header map[string]string `json:"header,omitempty"`
}

// handles any requests with "{name}.server.git/info/lfs" in the path
func lfsHandler(w http.ResponseWriter, r *http.Request) {
	repo, err := repoFromLfsUrl(r.URL.Path)
	if err != nil {
		w.Write([]byte(err.Error()))
		w.WriteHeader(500)
		return
	}

	log.Printf("git lfs %s %s repo: %s\n", r.Method, r.URL, repo)
	w.Header().Set("Content-Type", "application/vnd.git-lfs+json")
	switch r.Method {
	case "POST":
		if strings.HasSuffix(r.URL.String(), "batch") {
			lfsBatchHandler(w, r, repo)
		} else {
			lfsPostHandler(w, r, repo)
		}
	case "GET":
		lfsGetHandler(w, r, repo)
	default:
		w.WriteHeader(405)
	}
}

func lfsUrl(repo, oid string) string {
	return server.URL + "/storage/" + oid + "?r=" + repo
}

func lfsPostHandler(w http.ResponseWriter, r *http.Request, repo string) {
	buf := &bytes.Buffer{}
	tee := io.TeeReader(r.Body, buf)
	obj := &lfsObject{}
	err := json.NewDecoder(tee).Decode(obj)
	io.Copy(ioutil.Discard, r.Body)
	r.Body.Close()

	log.Println("REQUEST")
	log.Println(buf.String())
	log.Printf("OID: %s\n", obj.Oid)
	log.Printf("Size: %d\n", obj.Size)

	if err != nil {
		log.Fatal(err)
	}

	res := &lfsObject{
		Oid:  obj.Oid,
		Size: obj.Size,
		Actions: map[string]lfsLink{
			"upload": lfsLink{
				Href:   lfsUrl(repo, obj.Oid),
				Header: map[string]string{},
			},
		},
	}

	if testingChunkedTransferEncoding(r) {
		res.Actions["upload"].Header["Transfer-Encoding"] = "chunked"
	}

	by, err := json.Marshal(res)
	if err != nil {
		log.Fatal(err)
	}

	log.Println("RESPONSE: 202")
	log.Println(string(by))

	w.WriteHeader(202)
	w.Write(by)
}

func lfsGetHandler(w http.ResponseWriter, r *http.Request, repo string) {
	parts := strings.Split(r.URL.Path, "/")
	oid := parts[len(parts)-1]

	by, ok := largeObjects.Get(repo, oid)
	if !ok {
		w.WriteHeader(404)
		return
	}

	obj := &lfsObject{
		Oid:  oid,
		Size: int64(len(by)),
		Actions: map[string]lfsLink{
			"download": lfsLink{
				Href: lfsUrl(repo, oid),
			},
		},
	}

	by, err := json.Marshal(obj)
	if err != nil {
		log.Fatal(err)
	}

	log.Println("RESPONSE: 200")
	log.Println(string(by))

	w.WriteHeader(200)
	w.Write(by)
}

func lfsBatchHandler(w http.ResponseWriter, r *http.Request, repo string) {
	if !serveBatch {
		w.WriteHeader(404)
		return
	}

	type batchReq struct {
		Operation string      `json:"operation"`
		Objects   []lfsObject `json:"objects"`
	}

	buf := &bytes.Buffer{}
	tee := io.TeeReader(r.Body, buf)
	var objs batchReq
	err := json.NewDecoder(tee).Decode(&objs)
	io.Copy(ioutil.Discard, r.Body)
	r.Body.Close()

	log.Println("REQUEST")
	log.Println(buf.String())

	if err != nil {
		log.Fatal(err)
	}

	res := []lfsObject{}
	testingChunked := testingChunkedTransferEncoding(r)
	for _, obj := range objs.Objects {
		_, ok := largeObjects.Get(repo, obj.Oid)
		var o lfsObject
		if ok {
			o = lfsObject{
				Oid:  obj.Oid,
				Size: obj.Size,
				Actions: map[string]lfsLink{
					"download": lfsLink{
						Href: lfsUrl(repo, obj.Oid),
					},
				},
			}
			if testingChunked {
				o.Actions["download"].Header["Transfer-Encoding"] = "chunked"
			}
		} else {
			o = lfsObject{
				Oid:  obj.Oid,
				Size: obj.Size,
				Actions: map[string]lfsLink{
					"upload": lfsLink{
						Href:   lfsUrl(repo, obj.Oid),
						Header: map[string]string{},
					},
				},
			}
			if testingChunked {
				o.Actions["upload"].Header["Transfer-Encoding"] = "chunked"
			}
		}

		res = append(res, o)
	}

	ores := map[string][]lfsObject{"objects": res}

	by, err := json.Marshal(ores)
	if err != nil {
		log.Fatal(err)
	}

	log.Println("RESPONSE: 200")
	log.Println(string(by))

	w.WriteHeader(200)
	w.Write(by)
}

// handles any /storage/{oid} requests
func storageHandler(w http.ResponseWriter, r *http.Request) {
	repo := r.URL.Query().Get("r")
	log.Printf("storage %s %s repo: %s\n", r.Method, r.URL, repo)
	switch r.Method {
	case "PUT":
		if testingChunkedTransferEncoding(r) {
			valid := false
			for _, value := range r.TransferEncoding {
				if value == "chunked" {
					valid = true
					break
				}
			}
			if !valid {
				log.Fatal("Chunked transfer encoding expected")
			}
		}

		hash := sha256.New()
		buf := &bytes.Buffer{}
		io.Copy(io.MultiWriter(hash, buf), r.Body)
		oid := hex.EncodeToString(hash.Sum(nil))
		if !strings.HasSuffix(r.URL.Path, "/"+oid) {
			w.WriteHeader(403)
			return
		}

		largeObjects.Set(repo, oid, buf.Bytes())

	case "GET":
		parts := strings.Split(r.URL.Path, "/")
		oid := parts[len(parts)-1]

		if by, ok := largeObjects.Get(repo, oid); ok {
			w.Write(by)
			return
		}

		w.WriteHeader(404)
	default:
		w.WriteHeader(405)
	}
}

func gitHandler(w http.ResponseWriter, r *http.Request) {
	defer func() {
		io.Copy(ioutil.Discard, r.Body)
		r.Body.Close()
	}()

	cmd := exec.Command("git", "http-backend")
	cmd.Env = []string{
		fmt.Sprintf("GIT_PROJECT_ROOT=%s", repoDir),
		fmt.Sprintf("GIT_HTTP_EXPORT_ALL="),
		fmt.Sprintf("PATH_INFO=%s", r.URL.Path),
		fmt.Sprintf("QUERY_STRING=%s", r.URL.RawQuery),
		fmt.Sprintf("REQUEST_METHOD=%s", r.Method),
		fmt.Sprintf("CONTENT_TYPE=%s", r.Header.Get("Content-Type")),
	}

	buffer := &bytes.Buffer{}
	cmd.Stdin = r.Body
	cmd.Stdout = buffer
	cmd.Stderr = os.Stderr

	if err := cmd.Run(); err != nil {
		log.Fatal(err)
	}

	text := textproto.NewReader(bufio.NewReader(buffer))

	code, _, _ := text.ReadCodeLine(-1)

	if code != 0 {
		w.WriteHeader(code)
	}

	headers, _ := text.ReadMIMEHeader()
	head := w.Header()
	for key, values := range headers {
		for _, value := range values {
			head.Add(key, value)
		}
	}

	io.Copy(w, text.R)
}

func redirect307Handler(w http.ResponseWriter, r *http.Request) {
	// Send a redirect to info/lfs
	// Make it either absolute or relative depending on subpath
	parts := strings.Split(r.URL.Path, "/")
	// first element is always blank since rooted
	var redirectTo string
	if parts[2] == "rel" {
		redirectTo = "/" + strings.Join(parts[3:], "/")
	} else if parts[2] == "abs" {
		redirectTo = server.URL + "/" + strings.Join(parts[3:], "/")
	} else {
		log.Fatal(fmt.Errorf("Invalid URL for redirect: %v", r.URL))
		w.WriteHeader(404)
		return
	}
	w.Header().Set("Location", redirectTo)
	w.WriteHeader(307)
}

func testingChunkedTransferEncoding(r *http.Request) bool {
	return strings.HasPrefix(r.URL.String(), "/test-chunked-transfer-encoding")
}

var lfsUrlRE = regexp.MustCompile(`\A/?([^/]+)/info/lfs`)

func repoFromLfsUrl(urlpath string) (string, error) {
	matches := lfsUrlRE.FindStringSubmatch(urlpath)
	if len(matches) != 2 {
		return "", fmt.Errorf("LFS url '%s' does not match %v", urlpath, lfsUrlRE)
	}

	repo := matches[1]
	if strings.HasSuffix(repo, ".git") {
		return repo[0 : len(repo)-4], nil
	}
	return repo, nil
}

type lfsStorage struct {
	objects map[string]map[string][]byte
	mutex   *sync.Mutex
}

func (s *lfsStorage) Get(repo, oid string) ([]byte, bool) {
	s.mutex.Lock()
	defer s.mutex.Unlock()
	repoObjects, ok := s.objects[repo]
	if !ok {
		return nil, ok
	}

	by, ok := repoObjects[oid]
	return by, ok
}

func (s *lfsStorage) Set(repo, oid string, by []byte) {
	s.mutex.Lock()
	defer s.mutex.Unlock()
	repoObjects, ok := s.objects[repo]
	if !ok {
		repoObjects = make(map[string][]byte)
		s.objects[repo] = repoObjects
	}
	repoObjects[oid] = by
}

func newLfsStorage() *lfsStorage {
	return &lfsStorage{
		objects: make(map[string]map[string][]byte),
		mutex:   &sync.Mutex{},
	}
}

func skipIfBadAuth(w http.ResponseWriter, r *http.Request) bool {
	auth := r.Header.Get("Authorization")
	if auth == "" {
		w.WriteHeader(401)
		return true
	}

	if strings.HasPrefix(auth, "Basic ") {
		decodeBy, err := base64.StdEncoding.DecodeString(auth[6:len(auth)])
		decoded := string(decodeBy)

		if err != nil {
			w.WriteHeader(403)
			log.Printf("Error decoding auth: %s\n", err)
			return true
		}

		parts := strings.SplitN(decoded, ":", 2)
		if len(parts) == 2 {
			switch parts[0] {
			case "user":
				if parts[1] == "pass" {
					return false
				}
			case "path":
				if strings.HasPrefix(r.URL.Path, "/"+parts[1]) {
					return false
				}
				log.Printf("auth attempt against: %q", r.URL.Path)
			}
		}

		log.Printf("auth does not match: %q", decoded)
	}

	w.WriteHeader(403)
	log.Printf("Bad auth: %q\n", auth)
	return true
}