package main

import (
	"context"
	"crypto/subtle"
	"errors"
	"fmt"
	"io"
	"log"
	"net"
	"net/http"
	"os"
	"path/filepath"
	"strings"
	"sync"
	"syscall"

	"github.com/mholt/archives"
	"github.com/otiai10/copy"
)

var (
	authenticationKey       = os.Getenv("AUTH_KEY")
	subPath                 = strings.Trim(os.Getenv("SUBPATH"), "/")
	targetDirectory         = os.Getenv("TARGET_DIR")
	port                    = os.Getenv("PORT")
	maxUploadSize     int64 = 1 << 30 // 1GB

	deployLock sync.Mutex
)

func main() {
	if authenticationKey == "" || targetDirectory == "" {
		log.Fatal("AUTH_KEY and TARGET_DIR must be set")
	}

	if port == "" {
		port = "8080"
	}

	basePath := "/"
	if subPath != "" {
		basePath = "/" + subPath
	}

	log.Printf("starting server on :%s, endpoint %q, target directory %q", port, basePath, targetDirectory)
	http.HandleFunc(basePath, withRecovery(handle))
	log.Fatal(http.ListenAndServe(":"+port, nil))
}

func handle(w http.ResponseWriter, r *http.Request) {
	remoteIP := realIP(r)

	log.Printf("incoming %q request on %q from %s", r.Method, r.URL.Path, remoteIP)

	if r.Method != http.MethodPost {
		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
		return
	}

	auth := r.Header.Get("Authorization")
	if subtle.ConstantTimeCompare([]byte(auth), []byte(authenticationKey)) != 1 {
		log.Printf("unauthorized request from %s", remoteIP)
		http.Error(w, "unauthorized", http.StatusUnauthorized)
		return
	}

	r.Body = http.MaxBytesReader(w, r.Body, maxUploadSize)

	uploadDir, err := os.MkdirTemp("", "upload-*")
	if err != nil {
		http.Error(w, "internal error", http.StatusInternalServerError)
		return
	}
	defer os.RemoveAll(uploadDir)

	uploadFilePath := filepath.Join(uploadDir, "file")
	uploadFile, err := os.Create(uploadFilePath)
	if err != nil {
		http.Error(w, "internal error", http.StatusInternalServerError)
		return
	}
	defer uploadFile.Close()

	if _, err := io.Copy(uploadFile, r.Body); err != nil {
		http.Error(w, "bad archive", http.StatusBadRequest)
		return
	}

	uploadFile.Seek(0, io.SeekStart)
	defer uploadFile.Close()

	ctx := context.Background()

	format, archiveStream, err := archives.Identify(ctx, uploadFilePath, uploadFile)
	if err != nil {
		http.Error(w, "cannot detect archive", http.StatusBadRequest)
		return
	}

	extractor, ok := format.(archives.Extractor)
	if !ok {
		http.Error(w, "unsupported archive type", http.StatusBadRequest)
		return
	}

	extractDir, err := os.MkdirTemp("", "extract-*")
	if err != nil {
		http.Error(w, "internal error", http.StatusInternalServerError)
		return
	}
	defer os.RemoveAll(extractDir)

	if err := extractor.Extract(ctx, archiveStream, extract(extractDir)); err != nil {
		log.Printf("failed to extract archive: %v", err)
		http.Error(w, "bad archive", http.StatusBadRequest)
		return
	}

	deployLock.Lock()
	defer deployLock.Unlock()

	if err := removeContents(targetDirectory); err != nil {
		http.Error(w, "internal error", http.StatusInternalServerError)
		return
	}

	if err := renameOrCopyContents(extractDir); err != nil {
		http.Error(w, "internal error", http.StatusInternalServerError)
		return
	}

	w.WriteHeader(http.StatusOK)
	log.Printf("upload successful from %s", remoteIP)
}

func realIP(r *http.Request) string {
	if xff := r.Header.Get("X-Forwarded-For"); xff != "" {
		parts := strings.Split(xff, ",")
		return strings.TrimSpace(parts[0])
	}
	if xrip := r.Header.Get("X-Real-IP"); xrip != "" {
		return xrip
	}
	host, _, err := net.SplitHostPort(r.RemoteAddr)
	if err != nil {
		return r.RemoteAddr
	}
	return host
}

func extract(base string) archives.FileHandler {
	return func(ctx context.Context, f archives.FileInfo) error {
		if f.Mode()&os.ModeSymlink != 0 {
			return fmt.Errorf("refusing to extract symlink: %s", f.NameInArchive)
		}

		targetPath := filepath.Join(base, f.NameInArchive)
		if !strings.HasPrefix(filepath.Clean(targetPath), filepath.Clean(base)+string(os.PathSeparator)) {
			return fmt.Errorf("invalid path: %s", f.NameInArchive)
		}

		if f.IsDir() {
			return os.MkdirAll(targetPath, os.FileMode(f.Mode()))
		}

		if err := os.MkdirAll(filepath.Dir(targetPath), 0755); err != nil {
			return err
		}

		in, err := f.Open()
		if err != nil {
			return err
		}
		defer in.Close()

		out, err := os.OpenFile(targetPath, os.O_CREATE|os.O_RDWR|os.O_TRUNC, os.FileMode(f.Mode()))
		if err != nil {
			return err
		}
		defer out.Close()

		_, err = io.Copy(out, in)
		return err
	}
}

func removeContents(directory string) error {
	entries, err := os.ReadDir(directory)
	if err != nil {
		return fmt.Errorf("failed to read dir %s: %w", directory, err)
	}

	for _, entry := range entries {
		err := os.RemoveAll(filepath.Join(directory, entry.Name()))
		if err != nil {
			return err
		}
	}

	return nil
}

func renameOrCopyContents(sourceDirectory string) error {
	entries, err := os.ReadDir(sourceDirectory)
	if err != nil {
		return fmt.Errorf("failed to read dir %s: %w", sourceDirectory, err)
	}

	for _, entry := range entries {
		srcPath := filepath.Join(sourceDirectory, entry.Name())
		dstPath := filepath.Join(targetDirectory, entry.Name())

		if err := os.Rename(srcPath, dstPath); err != nil {
			if isCrossDeviceErr(err) {
				if err := copy.Copy(srcPath, dstPath); err != nil {
					return err
				}
				_ = os.RemoveAll(srcPath)
			} else {
				return err
			}
		}
	}

	return nil
}

func isCrossDeviceErr(err error) bool {
	var linkErr *os.LinkError
	return errors.As(err, &linkErr) && linkErr.Err == syscall.EXDEV
}

func withRecovery(next http.HandlerFunc) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		defer func() {
			if v := recover(); v != nil {
				log.Printf("panic: %v", v)
				http.Error(w, "internal error", http.StatusInternalServerError)
			}
		}()
		next(w, r)
	}
}