package routes

import (
	"crypto/sha256"
	"encoding/hex"
	"errors"
	"io"
	"io/fs"
	"mime/multipart"
	"os"
)

// saveTemp writes an uploaded file to a new temp file in dir and returns its
// path and SHA-256.
func saveTemp(fh *multipart.FileHeader, dir string) (path, sum string, err error) {

	src, err := fh.Open()
	if err != nil {
		return "", "", err
	}
	defer src.Close()

	dst, err := os.CreateTemp(dir, "upload-*.apk")
	if err != nil {
		return "", "", err
	}

	hash := sha256.New()
	_, err = io.Copy(io.MultiWriter(dst, hash), src)
	if cerr := dst.Close(); err == nil {
		err = cerr
	}
	if err != nil {
		os.Remove(dst.Name())
		return "", "", err
	}

	return dst.Name(), hex.EncodeToString(hash.Sum(nil)), nil
}

// moveFile moves src to dst without ever overwriting an existing dst. It
// falls back to a copy when they are on different filesystems (the tmp and
// uploads directories are separate volumes).
func moveFile(src, dst string) error {

	// Unlike rename, link fails when dst exists, so a concurrent upload can never replace a published APK
	if err := os.Link(src, dst); err == nil {
		return os.Remove(src)
	} else if errors.Is(err, fs.ErrExist) {
		return err
	}

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

	out, err := os.OpenFile(dst, os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0644)
	if err != nil {
		return err
	}

	_, err = io.Copy(out, in)
	if cerr := out.Close(); err == nil {
		err = cerr
	}
	if err != nil {
		os.Remove(dst)
		return err
	}

	return os.Remove(src)
}