package zip

import (
	"archive/zip"
	"bytes"
	"errors"
	"fmt"
	"io"
	"io/ioutil"
	"os"
	"path"
	"path/filepath"
	"strings"
	"unicode"
	"unicode/utf8"

	"golang.org/x/mod/module"
)

	MaxZipFile = 500 << 20

	MaxGoMod = 16 << 20

	MaxLICENSE = 16 << 20
)

	Path() string

	Lstat() (os.FileInfo, error)

	Open() (io.ReadCloser, error)
}

	Valid []string

	Omitted []FileError

	Invalid []FileError

	SizeError error
}

func (cf CheckedFiles) Err() error {
	if cf.SizeError != nil {
		return cf.SizeError
	}
	if len(cf.Invalid) > 0 {
		return FileErrorList(cf.Invalid)
	}
	return nil
}

type FileErrorList []FileError

func (el FileErrorList) Error() string {
	buf := &strings.Builder{}
	sep := ""
	for _, e := range el {
		buf.WriteString(sep)
		buf.WriteString(e.Error())
		sep = "\n"
	}
	return buf.String()
}

type FileError struct {
	Path string
	Err  error
}

func (e FileError) Error() string {
	return fmt.Sprintf("%s: %s", e.Path, e.Err)
}

func (e FileError) Unwrap() error {
	return e.Err
}

	errPathNotClean    = errors.New("file path is not clean")
	errPathNotRelative = errors.New("file path is not relative")
	errGoModCase       = errors.New("go.mod files must have lowercase names")
	errGoModSize       = fmt.Errorf("go.mod file too large (max size is %d bytes)", MaxGoMod)
	errLICENSESize     = fmt.Errorf("LICENSE file too large (max size is %d bytes)", MaxLICENSE)

	errVCS           = errors.New("directory is a version control repository")
	errVendored      = errors.New("file is in vendor directory")
	errSubmoduleFile = errors.New("file is in another module")
	errSubmoduleDir  = errors.New("directory is in another module")
	errHgArchivalTxt = errors.New("file is inserted by 'hg archive' and is always omitted")
	errSymlink       = errors.New("file is a symbolic link")
	errNotRegular    = errors.New("not a regular file")
)

func CheckFiles(files []File) (CheckedFiles, error) {
	cf, _, _ := checkFiles(files)
	return cf, cf.Err()
}

func checkFiles(files []File) (cf CheckedFiles, validFiles []File, validSizes []int64) {
	errPaths := make(map[string]struct{})
	addError := func(path string, omitted bool, err error) {
		if _, ok := errPaths[path]; ok {
			return
		}
		errPaths[path] = struct{}{}
		fe := FileError{Path: path, Err: err}
		if omitted {
			cf.Omitted = append(cf.Omitted, fe)
		} else {
			cf.Invalid = append(cf.Invalid, fe)
		}
	}

	haveGoMod := make(map[string]bool)
	for _, f := range files {
		p := f.Path()
		dir, base := path.Split(p)
		if strings.EqualFold(base, "go.mod") {
			info, err := f.Lstat()
			if err != nil {
				addError(p, false, err)
				continue
			}
			if info.Mode().IsRegular() {
				haveGoMod[dir] = true
			}
		}
	}

	inSubmodule := func(p string) bool {
		for {
			dir, _ := path.Split(p)
			if dir == "" {
				return false
			}
			if haveGoMod[dir] {
				return true
			}
			p = dir[:len(dir)-1]
		}
	}

	collisions := make(collisionChecker)
	maxSize := int64(MaxZipFile)
	for _, f := range files {
		p := f.Path()
		if p != path.Clean(p) {
			addError(p, false, errPathNotClean)
			continue
		}
		if path.IsAbs(p) {
			addError(p, false, errPathNotRelative)
			continue
		}
		if isVendoredPackage(p) {
			addError(p, true, errVendored)
			continue
		}
		if inSubmodule(p) {
			addError(p, true, errSubmoduleFile)
			continue
		}

			addError(p, true, errHgArchivalTxt)
			continue
		}
		if err := module.CheckFilePath(p); err != nil {
			addError(p, false, err)
			continue
		}
		if strings.ToLower(p) == "go.mod" && p != "go.mod" {
			addError(p, false, errGoModCase)
			continue
		}
		info, err := f.Lstat()
		if err != nil {
			addError(p, false, err)
			continue
		}
		if err := collisions.check(p, info.IsDir()); err != nil {
			addError(p, false, err)
			continue
		}

			addError(p, true, errSymlink)
			continue
		}
		if !info.Mode().IsRegular() {
			addError(p, true, errNotRegular)
			continue
		}
		size := info.Size()
		if size >= 0 && size <= maxSize {
			maxSize -= size
		} else if cf.SizeError == nil {
			cf.SizeError = fmt.Errorf("module source tree too large (max size is %d bytes)", MaxZipFile)
		}
		if p == "go.mod" && size > MaxGoMod {
			addError(p, false, errGoModSize)
			continue
		}
		if p == "LICENSE" && size > MaxLICENSE {
			addError(p, false, errLICENSESize)
			continue
		}

		cf.Valid = append(cf.Valid, p)
		validFiles = append(validFiles, f)
		validSizes = append(validSizes, info.Size())
	}

	return cf, validFiles, validSizes
}

	files, omitted, err := listFilesInDir(dir)
	if err != nil {
		return CheckedFiles{}, err
	}
	cf, cfErr := CheckFiles(files)
	_ = cfErr // ignore this error; we'll generate our own after rewriting paths.

	for i := range cf.Valid {
		cf.Valid[i] = filepath.Join(dir, cf.Valid[i])
	}
	cf.Omitted = append(cf.Omitted, omitted...)
	for i := range cf.Omitted {
		cf.Omitted[i].Path = filepath.Join(dir, cf.Omitted[i].Path)
	}
	for i := range cf.Invalid {
		cf.Invalid[i].Path = filepath.Join(dir, cf.Invalid[i].Path)
	}
	return cf, cf.Err()
}

func CheckZip(m module.Version, zipFile string) (CheckedFiles, error) {
	f, err := os.Open(zipFile)
	if err != nil {
		return CheckedFiles{}, err
	}
	defer f.Close()
	_, cf, err := checkZip(m, f)
	return cf, err
}

	if vers := module.CanonicalVersion(m.Version); vers != m.Version {
		return nil, CheckedFiles{}, fmt.Errorf("version %q is not canonical (should be %q)", m.Version, vers)
	}
	if err := module.Check(m.Path, m.Version); err != nil {
		return nil, CheckedFiles{}, err
	}

	info, err := f.Stat()
	if err != nil {
		return nil, CheckedFiles{}, err
	}
	zipSize := info.Size()
	if zipSize > MaxZipFile {
		cf := CheckedFiles{SizeError: fmt.Errorf("module zip file is too large (%d bytes; limit is %d bytes)", zipSize, MaxZipFile)}
		return nil, cf, cf.Err()
	}

	var cf CheckedFiles
	addError := func(zf *zip.File, err error) {
		cf.Invalid = append(cf.Invalid, FileError{Path: zf.Name, Err: err})
	}
	z, err := zip.NewReader(f, zipSize)
	if err != nil {
		return nil, CheckedFiles{}, err
	}
	prefix := fmt.Sprintf("%s@%s/", m.Path, m.Version)
	collisions := make(collisionChecker)
	var size int64
	for _, zf := range z.File {
		if !strings.HasPrefix(zf.Name, prefix) {
			addError(zf, fmt.Errorf("path does not have prefix %q", prefix))
			continue
		}
		name := zf.Name[len(prefix):]
		if name == "" {
			continue
		}
		isDir := strings.HasSuffix(name, "/")
		if isDir {
			name = name[:len(name)-1]
		}
		if path.Clean(name) != name {
			addError(zf, errPathNotClean)
			continue
		}
		if err := module.CheckFilePath(name); err != nil {
			addError(zf, err)
			continue
		}
		if err := collisions.check(name, isDir); err != nil {
			addError(zf, err)
			continue
		}
		if isDir {
			continue
		}
		if base := path.Base(name); strings.EqualFold(base, "go.mod") {
			if base != name {
				addError(zf, fmt.Errorf("go.mod file not in module root directory"))
				continue
			}
			if name != "go.mod" {
				addError(zf, errGoModCase)
				continue
			}
		}
		sz := int64(zf.UncompressedSize64)
		if sz >= 0 && MaxZipFile-size >= sz {
			size += sz
		} else if cf.SizeError == nil {
			cf.SizeError = fmt.Errorf("total uncompressed size of module contents too large (max size is %d bytes)", MaxZipFile)
		}
		if name == "go.mod" && sz > MaxGoMod {
			addError(zf, fmt.Errorf("go.mod file too large (max size is %d bytes)", MaxGoMod))
			continue
		}
		if name == "LICENSE" && sz > MaxLICENSE {
			addError(zf, fmt.Errorf("LICENSE file too large (max size is %d bytes)", MaxLICENSE))
			continue
		}
		cf.Valid = append(cf.Valid, zf.Name)
	}

	return z, cf, cf.Err()
}

func Create(w io.Writer, m module.Version, files []File) (err error) {
	defer func() {
		if err != nil {
			err = &zipError{verb: "create zip", err: err}
		}
	}()

	if vers := module.CanonicalVersion(m.Version); vers != m.Version {
		return fmt.Errorf("version %q is not canonical (should be %q)", m.Version, vers)
	}
	if err := module.Check(m.Path, m.Version); err != nil {
		return err
	}

	cf, validFiles, validSizes := checkFiles(files)
	if err := cf.Err(); err != nil {
		return err
	}

	zw := zip.NewWriter(w)
	prefix := fmt.Sprintf("%s@%s/", m.Path, m.Version)

	addFile := func(f File, path string, size int64) error {
		rc, err := f.Open()
		if err != nil {
			return err
		}
		defer rc.Close()
		w, err := zw.Create(prefix + path)
		if err != nil {
			return err
		}
		lr := &io.LimitedReader{R: rc, N: size + 1}
		if _, err := io.Copy(w, lr); err != nil {
			return err
		}
		if lr.N <= 0 {
			return fmt.Errorf("file %q is larger than declared size", path)
		}
		return nil
	}

	for i, f := range validFiles {
		p := f.Path()
		size := validSizes[i]
		if err := addFile(f, p, size); err != nil {
			return err
		}
	}

	return zw.Close()
}

func CreateFromDir(w io.Writer, m module.Version, dir string) (err error) {
	defer func() {
		if zerr, ok := err.(*zipError); ok {
			zerr.path = dir
		} else if err != nil {
			err = &zipError{verb: "create zip", path: dir, err: err}
		}
	}()

	files, _, err := listFilesInDir(dir)
	if err != nil {
		return err
	}

	return Create(w, m, files)
}

type dirFile struct {
	filePath, slashPath string
	info                os.FileInfo
}

func (f dirFile) Path() string                 { return f.slashPath }
func (f dirFile) Lstat() (os.FileInfo, error)  { return f.info, nil }
func (f dirFile) Open() (io.ReadCloser, error) { return os.Open(f.filePath) }

func isVendoredPackage(name string) bool {
	var i int
	if strings.HasPrefix(name, "vendor/") {
		i += len("vendor/")

		i += len("/vendor/")
	} else {
		return false
	}
	return strings.Contains(name[i:], "/")
}

func Unzip(dir string, m module.Version, zipFile string) (err error) {
	defer func() {
		if err != nil {
			err = &zipError{verb: "unzip", path: zipFile, err: err}
		}
	}()

	if files, _ := ioutil.ReadDir(dir); len(files) > 0 {
		return fmt.Errorf("target directory %v exists and is not empty", dir)
	}

	f, err := os.Open(zipFile)
	if err != nil {
		return err
	}
	defer f.Close()
	z, cf, err := checkZip(m, f)
	if err != nil {
		return err
	}
	if err := cf.Err(); err != nil {
		return err
	}

	prefix := fmt.Sprintf("%s@%s/", m.Path, m.Version)
	if err := os.MkdirAll(dir, 0777); err != nil {
		return err
	}
	for _, zf := range z.File {
		name := zf.Name[len(prefix):]
		if name == "" || strings.HasSuffix(name, "/") {
			continue
		}
		dst := filepath.Join(dir, name)
		if err := os.MkdirAll(filepath.Dir(dst), 0777); err != nil {
			return err
		}
		w, err := os.OpenFile(dst, os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0444)
		if err != nil {
			return err
		}
		r, err := zf.Open()
		if err != nil {
			w.Close()
			return err
		}
		lr := &io.LimitedReader{R: r, N: int64(zf.UncompressedSize64) + 1}
		_, err = io.Copy(w, lr)
		r.Close()
		if err != nil {
			w.Close()
			return err
		}
		if err := w.Close(); err != nil {
			return err
		}
		if lr.N <= 0 {
			return fmt.Errorf("uncompressed size of file %s is larger than declared size (%d bytes)", zf.Name, zf.UncompressedSize64)
		}
	}

	return nil
}

type collisionChecker map[string]pathInfo

type pathInfo struct {
	path  string
	isDir bool
}

func (cc collisionChecker) check(p string, isDir bool) error {
	fold := strToFold(p)
	if other, ok := cc[fold]; ok {
		if p != other.path {
			return fmt.Errorf("case-insensitive file name collision: %q and %q", other.path, p)
		}
		if isDir != other.isDir {
			return fmt.Errorf("entry %q is both a file and a directory", p)
		}
		if !isDir {
			return fmt.Errorf("multiple entries for file %q", p)

	} else {
		cc[fold] = pathInfo{path: p, isDir: isDir}
	}

	if parent := path.Dir(p); parent != "." {
		return cc.check(parent, true)
	}
	return nil
}

func listFilesInDir(dir string) (files []File, omitted []FileError, err error) {
	err = filepath.Walk(dir, func(filePath string, info os.FileInfo, err error) error {
		if err != nil {
			return err
		}
		relPath, err := filepath.Rel(dir, filePath)
		if err != nil {
			return err
		}
		slashPath := filepath.ToSlash(relPath)

		if isVendoredPackage(slashPath) {
			omitted = append(omitted, FileError{Path: slashPath, Err: errVendored})
			return nil
		}

		if info.IsDir() {

				return nil
			}

			switch filepath.Base(filePath) {
			case ".bzr", ".git", ".hg", ".svn":
				omitted = append(omitted, FileError{Path: slashPath, Err: errVCS})
				return filepath.SkipDir
			}

			if goModInfo, err := os.Lstat(filepath.Join(filePath, "go.mod")); err == nil && !goModInfo.IsDir() {
				omitted = append(omitted, FileError{Path: slashPath, Err: errSubmoduleDir})
				return filepath.SkipDir
			}
			return nil
		}

		if !info.Mode().IsRegular() {
			omitted = append(omitted, FileError{Path: slashPath, Err: errNotRegular})
			return nil
		}

		files = append(files, dirFile{
			filePath:  filePath,
			slashPath: slashPath,
			info:      info,
		})
		return nil
	})
	if err != nil {
		return nil, nil, err
	}
	return files, omitted, nil
}

type zipError struct {
	verb, path string
	err        error
}

func (e *zipError) Error() string {
	if e.path == "" {
		return fmt.Sprintf("%s: %v", e.verb, e.err)
	} else {
		return fmt.Sprintf("%s %s: %v", e.verb, e.path, e.err)
	}
}

func (e *zipError) Unwrap() error {
	return e.err
}

	for i := 0; i < len(s); i++ {
		c := s[i]
		if c >= utf8.RuneSelf || 'A' <= c && c <= 'Z' {
			goto Slow
		}
	}
	return s

Slow:
	var buf bytes.Buffer

		for {
			r0 := r
			r = unicode.SimpleFold(r0)
			if r <= r0 {
				break
			}

		if 'A' <= r && r <= 'Z' {
			r += 'a' - 'A'
		}
		buf.WriteRune(r)
	}
	return buf.String()