package git

import (
	"bytes"
	"errors"
	"io"
	"os"
	"path"
	"path/filepath"

	"github.com/go-git/go-billy/v5/util"
	"github.com/go-git/go-git/v5/plumbing"
	"github.com/go-git/go-git/v5/plumbing/filemode"
	"github.com/go-git/go-git/v5/plumbing/format/gitignore"
	"github.com/go-git/go-git/v5/plumbing/format/index"
	"github.com/go-git/go-git/v5/plumbing/object"
	"github.com/go-git/go-git/v5/utils/ioutil"
	"github.com/go-git/go-git/v5/utils/merkletrie"
	"github.com/go-git/go-git/v5/utils/merkletrie/filesystem"
	mindex "github.com/go-git/go-git/v5/utils/merkletrie/index"
	"github.com/go-git/go-git/v5/utils/merkletrie/noder"
)

var (
	// ErrDestinationExists in an Move operation means that the target exists on
	// the worktree.
	ErrDestinationExists = errors.New("destination exists")
	// ErrGlobNoMatches in an AddGlob if the glob pattern does not match any
	// files in the worktree.
	ErrGlobNoMatches = errors.New("glob pattern did not match any files")
)

// Status returns the working tree status.
func (w *Worktree) Status() (Status, error) {
	var hash plumbing.Hash

	ref, err := w.r.Head()
	if err != nil && err != plumbing.ErrReferenceNotFound {
		return nil, err
	}

	if err == nil {
		hash = ref.Hash()
	}

	return w.status(hash)
}

func (w *Worktree) status(commit plumbing.Hash) (Status, error) {
	s := make(Status)

	left, err := w.diffCommitWithStaging(commit, false)
	if err != nil {
		return nil, err
	}

	for _, ch := range left {
		a, err := ch.Action()
		if err != nil {
			return nil, err
		}

		fs := s.File(nameFromAction(&ch))
		fs.Worktree = Unmodified

		switch a {
		case merkletrie.Delete:
			s.File(ch.From.String()).Staging = Deleted
		case merkletrie.Insert:
			s.File(ch.To.String()).Staging = Added
		case merkletrie.Modify:
			s.File(ch.To.String()).Staging = Modified
		}
	}

	right, err := w.diffStagingWithWorktree(false)
	if err != nil {
		return nil, err
	}

	for _, ch := range right {
		a, err := ch.Action()
		if err != nil {
			return nil, err
		}

		fs := s.File(nameFromAction(&ch))
		if fs.Staging == Untracked {
			fs.Staging = Unmodified
		}

		switch a {
		case merkletrie.Delete:
			fs.Worktree = Deleted
		case merkletrie.Insert:
			fs.Worktree = Untracked
			fs.Staging = Untracked
		case merkletrie.Modify:
			fs.Worktree = Modified
		}
	}

	return s, nil
}

func nameFromAction(ch *merkletrie.Change) string {
	name := ch.To.String()
	if name == "" {
		return ch.From.String()
	}

	return name
}

func (w *Worktree) diffStagingWithWorktree(reverse bool) (merkletrie.Changes, error) {
	idx, err := w.r.Storer.Index()
	if err != nil {
		return nil, err
	}

	from := mindex.NewRootNode(idx)
	submodules, err := w.getSubmodulesStatus()
	if err != nil {
		return nil, err
	}

	to := filesystem.NewRootNode(w.Filesystem, submodules)

	var c merkletrie.Changes
	if reverse {
		c, err = merkletrie.DiffTree(to, from, diffTreeIsEquals)
	} else {
		c, err = merkletrie.DiffTree(from, to, diffTreeIsEquals)
	}

	if err != nil {
		return nil, err
	}

	return w.excludeIgnoredChanges(c), nil
}

func (w *Worktree) excludeIgnoredChanges(changes merkletrie.Changes) merkletrie.Changes {
	patterns, err := gitignore.ReadPatterns(w.Filesystem, nil)
	if err != nil {
		return changes
	}

	patterns = append(patterns, w.Excludes...)

	if len(patterns) == 0 {
		return changes
	}

	m := gitignore.NewMatcher(patterns)

	var res merkletrie.Changes
	for _, ch := range changes {
		var path []string
		for _, n := range ch.To {
			path = append(path, n.Name())
		}
		if len(path) == 0 {
			for _, n := range ch.From {
				path = append(path, n.Name())
			}
		}
		if len(path) != 0 {
			isDir := (len(ch.To) > 0 && ch.To.IsDir()) || (len(ch.From) > 0 && ch.From.IsDir())
			if m.Match(path, isDir) {
				continue
			}
		}
		res = append(res, ch)
	}
	return res
}

func (w *Worktree) getSubmodulesStatus() (map[string]plumbing.Hash, error) {
	o := map[string]plumbing.Hash{}

	sub, err := w.Submodules()
	if err != nil {
		return nil, err
	}

	status, err := sub.Status()
	if err != nil {
		return nil, err
	}

	for _, s := range status {
		if s.Current.IsZero() {
			o[s.Path] = s.Expected
			continue
		}

		o[s.Path] = s.Current
	}

	return o, nil
}

func (w *Worktree) diffCommitWithStaging(commit plumbing.Hash, reverse bool) (merkletrie.Changes, error) {
	var t *object.Tree
	if !commit.IsZero() {
		c, err := w.r.CommitObject(commit)
		if err != nil {
			return nil, err
		}

		t, err = c.Tree()
		if err != nil {
			return nil, err
		}
	}

	return w.diffTreeWithStaging(t, reverse)
}

func (w *Worktree) diffTreeWithStaging(t *object.Tree, reverse bool) (merkletrie.Changes, error) {
	var from noder.Noder
	if t != nil {
		from = object.NewTreeRootNode(t)
	}

	idx, err := w.r.Storer.Index()
	if err != nil {
		return nil, err
	}

	to := mindex.NewRootNode(idx)

	if reverse {
		return merkletrie.DiffTree(to, from, diffTreeIsEquals)
	}

	return merkletrie.DiffTree(from, to, diffTreeIsEquals)
}

var emptyNoderHash = make([]byte, 24)

// diffTreeIsEquals is a implementation of noder.Equals, used to compare
// noder.Noder, it compare the content and the length of the hashes.
//
// Since some of the noder.Noder implementations doesn't compute a hash for
// some directories, if any of the hashes is a 24-byte slice of zero values
// the comparison is not done and the hashes are take as different.
func diffTreeIsEquals(a, b noder.Hasher) bool {
	hashA := a.Hash()
	hashB := b.Hash()

	if bytes.Equal(hashA, emptyNoderHash) || bytes.Equal(hashB, emptyNoderHash) {
		return false
	}

	return bytes.Equal(hashA, hashB)
}

// Add adds the file contents of a file in the worktree to the index. if the
// file is already staged in the index no error is returned. If a file deleted
// from the Workspace is given, the file is removed from the index. If a
// directory given, adds the files and all his sub-directories recursively in
// the worktree to the index. If any of the files is already staged in the index
// no error is returned. When path is a file, the blob.Hash is returned.
func (w *Worktree) Add(path string) (plumbing.Hash, error) {
	// TODO(mcuadros): remove plumbing.Hash from signature at v5.
	s, err := w.Status()
	if err != nil {
		return plumbing.ZeroHash, err
	}

	idx, err := w.r.Storer.Index()
	if err != nil {
		return plumbing.ZeroHash, err
	}

	var h plumbing.Hash
	var added bool

	fi, err := w.Filesystem.Lstat(path)
	if err != nil || !fi.IsDir() {
		added, h, err = w.doAddFile(idx, s, path)
	} else {
		added, err = w.doAddDirectory(idx, s, path)
	}

	if err != nil {
		return h, err
	}

	if !added {
		return h, nil
	}

	return h, w.r.Storer.SetIndex(idx)
}

func (w *Worktree) doAddDirectory(idx *index.Index, s Status, directory string) (added bool, err error) {
	files, err := w.Filesystem.ReadDir(directory)
	if err != nil {
		return false, err
	}

	for _, file := range files {
		name := path.Join(directory, file.Name())

		var a bool
		if file.IsDir() {
			if file.Name() == GitDirName {
				// ignore special git directory
				continue
			}
			a, err = w.doAddDirectory(idx, s, name)
		} else {
			a, _, err = w.doAddFile(idx, s, name)
		}

		if err != nil {
			return
		}

		if !added && a {
			added = true
		}
	}

	return
}

// AddGlob adds all paths, matching pattern, to the index. If pattern matches a
// directory path, all directory contents are added to the index recursively. No
// error is returned if all matching paths are already staged in index.
func (w *Worktree) AddGlob(pattern string) error {
	files, err := util.Glob(w.Filesystem, pattern)
	if err != nil {
		return err
	}

	if len(files) == 0 {
		return ErrGlobNoMatches
	}

	s, err := w.Status()
	if err != nil {
		return err
	}

	idx, err := w.r.Storer.Index()
	if err != nil {
		return err
	}

	var saveIndex bool
	for _, file := range files {
		fi, err := w.Filesystem.Lstat(file)
		if err != nil {
			return err
		}

		var added bool
		if fi.IsDir() {
			added, err = w.doAddDirectory(idx, s, file)
		} else {
			added, _, err = w.doAddFile(idx, s, file)
		}

		if err != nil {
			return err
		}

		if !saveIndex && added {
			saveIndex = true
		}
	}

	if saveIndex {
		return w.r.Storer.SetIndex(idx)
	}

	return nil
}

// doAddFile create a new blob from path and update the index, added is true if
// the file added is different from the index.
func (w *Worktree) doAddFile(idx *index.Index, s Status, path string) (added bool, h plumbing.Hash, err error) {
	if s.File(path).Worktree == Unmodified {
		return false, h, nil
	}

	h, err = w.copyFileToStorage(path)
	if err != nil {
		if os.IsNotExist(err) {
			added = true
			h, err = w.deleteFromIndex(idx, path)
		}

		return
	}

	if err := w.addOrUpdateFileToIndex(idx, path, h); err != nil {
		return false, h, err
	}

	return true, h, err
}

func (w *Worktree) copyFileToStorage(path string) (hash plumbing.Hash, err error) {
	fi, err := w.Filesystem.Lstat(path)
	if err != nil {
		return plumbing.ZeroHash, err
	}

	obj := w.r.Storer.NewEncodedObject()
	obj.SetType(plumbing.BlobObject)
	obj.SetSize(fi.Size())

	writer, err := obj.Writer()
	if err != nil {
		return plumbing.ZeroHash, err
	}

	defer ioutil.CheckClose(writer, &err)

	if fi.Mode()&os.ModeSymlink != 0 {
		err = w.fillEncodedObjectFromSymlink(writer, path, fi)
	} else {
		err = w.fillEncodedObjectFromFile(writer, path, fi)
	}

	if err != nil {
		return plumbing.ZeroHash, err
	}

	return w.r.Storer.SetEncodedObject(obj)
}

func (w *Worktree) fillEncodedObjectFromFile(dst io.Writer, path string, fi os.FileInfo) (err error) {
	src, err := w.Filesystem.Open(path)
	if err != nil {
		return err
	}

	defer ioutil.CheckClose(src, &err)

	if _, err := io.Copy(dst, src); err != nil {
		return err
	}

	return err
}

func (w *Worktree) fillEncodedObjectFromSymlink(dst io.Writer, path string, fi os.FileInfo) error {
	target, err := w.Filesystem.Readlink(path)
	if err != nil {
		return err
	}

	_, err = dst.Write([]byte(target))
	return err
}

func (w *Worktree) addOrUpdateFileToIndex(idx *index.Index, filename string, h plumbing.Hash) error {
	e, err := idx.Entry(filename)
	if err != nil && err != index.ErrEntryNotFound {
		return err
	}

	if err == index.ErrEntryNotFound {
		return w.doAddFileToIndex(idx, filename, h)
	}

	return w.doUpdateFileToIndex(e, filename, h)
}

func (w *Worktree) doAddFileToIndex(idx *index.Index, filename string, h plumbing.Hash) error {
	return w.doUpdateFileToIndex(idx.Add(filename), filename, h)
}

func (w *Worktree) doUpdateFileToIndex(e *index.Entry, filename string, h plumbing.Hash) error {
	info, err := w.Filesystem.Lstat(filename)
	if err != nil {
		return err
	}

	e.Hash = h
	e.ModifiedAt = info.ModTime()
	e.Mode, err = filemode.NewFromOSFileMode(info.Mode())
	if err != nil {
		return err
	}

	if e.Mode.IsRegular() {
		e.Size = uint32(info.Size())
	}

	fillSystemInfo(e, info.Sys())
	return nil
}

// Remove removes files from the working tree and from the index.
func (w *Worktree) Remove(path string) (plumbing.Hash, error) {
	// TODO(mcuadros): remove plumbing.Hash from signature at v5.
	idx, err := w.r.Storer.Index()
	if err != nil {
		return plumbing.ZeroHash, err
	}

	var h plumbing.Hash

	fi, err := w.Filesystem.Lstat(path)
	if err != nil || !fi.IsDir() {
		h, err = w.doRemoveFile(idx, path)
	} else {
		_, err = w.doRemoveDirectory(idx, path)
	}
	if err != nil {
		return h, err
	}

	return h, w.r.Storer.SetIndex(idx)
}

func (w *Worktree) doRemoveDirectory(idx *index.Index, directory string) (removed bool, err error) {
	files, err := w.Filesystem.ReadDir(directory)
	if err != nil {
		return false, err
	}

	for _, file := range files {
		name := path.Join(directory, file.Name())

		var r bool
		if file.IsDir() {
			r, err = w.doRemoveDirectory(idx, name)
		} else {
			_, err = w.doRemoveFile(idx, name)
			if err == index.ErrEntryNotFound {
				err = nil
			}
		}

		if err != nil {
			return
		}

		if !removed && r {
			removed = true
		}
	}

	err = w.removeEmptyDirectory(directory)
	return
}

func (w *Worktree) removeEmptyDirectory(path string) error {
	files, err := w.Filesystem.ReadDir(path)
	if err != nil {
		return err
	}

	if len(files) != 0 {
		return nil
	}

	return w.Filesystem.Remove(path)
}

func (w *Worktree) doRemoveFile(idx *index.Index, path string) (plumbing.Hash, error) {
	hash, err := w.deleteFromIndex(idx, path)
	if err != nil {
		return plumbing.ZeroHash, err
	}

	return hash, w.deleteFromFilesystem(path)
}

func (w *Worktree) deleteFromIndex(idx *index.Index, path string) (plumbing.Hash, error) {
	e, err := idx.Remove(path)
	if err != nil {
		return plumbing.ZeroHash, err
	}

	return e.Hash, nil
}

func (w *Worktree) deleteFromFilesystem(path string) error {
	err := w.Filesystem.Remove(path)
	if os.IsNotExist(err) {
		return nil
	}

	return err
}

// RemoveGlob removes all paths, matching pattern, from the index. If pattern
// matches a directory path, all directory contents are removed from the index
// recursively.
func (w *Worktree) RemoveGlob(pattern string) error {
	idx, err := w.r.Storer.Index()
	if err != nil {
		return err
	}

	entries, err := idx.Glob(pattern)
	if err != nil {
		return err
	}

	for _, e := range entries {
		file := filepath.FromSlash(e.Name)
		if _, err := w.Filesystem.Lstat(file); err != nil && !os.IsNotExist(err) {
			return err
		}

		if _, err := w.doRemoveFile(idx, file); err != nil {
			return err
		}

		dir, _ := filepath.Split(file)
		if err := w.removeEmptyDirectory(dir); err != nil {
			return err
		}
	}

	return w.r.Storer.SetIndex(idx)
}

// Move moves or rename a file in the worktree and the index, directories are
// not supported.
func (w *Worktree) Move(from, to string) (plumbing.Hash, error) {
	// TODO(mcuadros): support directories and/or implement support for glob
	if _, err := w.Filesystem.Lstat(from); err != nil {
		return plumbing.ZeroHash, err
	}

	if _, err := w.Filesystem.Lstat(to); err == nil {
		return plumbing.ZeroHash, ErrDestinationExists
	}

	idx, err := w.r.Storer.Index()
	if err != nil {
		return plumbing.ZeroHash, err
	}

	hash, err := w.deleteFromIndex(idx, from)
	if err != nil {
		return plumbing.ZeroHash, err
	}

	if err := w.Filesystem.Rename(from, to); err != nil {
		return hash, err
	}

	if err := w.addOrUpdateFileToIndex(idx, to, hash); err != nil {
		return hash, err
	}

	return hash, w.r.Storer.SetIndex(idx)
}
