// Adding a file directly to index (stage area), without using working tree.
//
// $ go build index-add.go && yes | mv index-add ~/code/workspace/bin
// $ mkdir -p /tmp/sample && cd /tmp/sample
// $ index-add
package main

import (
	"bytes"
	"fmt"
	"path"
	"sort"
	"strconv"
	"strings"
	"time"

	"golang.org/x/crypto/openpgp"
	"gopkg.in/src-d/go-billy.v4"
	"gopkg.in/src-d/go-billy.v4/osfs"
	"gopkg.in/src-d/go-git.v4"
	. "gopkg.in/src-d/go-git.v4/_examples"
	"gopkg.in/src-d/go-git.v4/plumbing"
	"gopkg.in/src-d/go-git.v4/plumbing/filemode"
	"gopkg.in/src-d/go-git.v4/plumbing/format/index"
	"gopkg.in/src-d/go-git.v4/plumbing/object"
	"gopkg.in/src-d/go-git.v4/storage"
	fsfs "gopkg.in/src-d/go-git.v4/storage/filesystem"
)

// 获取git log
func gitLog(r *git.Repository) {
	// ... retrieves the branch pointed by HEAD
	ref, err := r.Head()
	CheckIfError(err)

	// ... retrieves the commit history
	cIter, err := r.Log(&git.LogOptions{From: ref.Hash()})
	CheckIfError(err)

	// ... just iterates over the commits, printing it
	err = cIter.ForEach(func(c *object.Commit) error {
		fmt.Println(c)
		return nil
	})
	CheckIfError(err)
}

// 创建一个新的 bare repository
func gitInit(repoPath string) *git.Repository {
	s := fsfs.NewStorage(osfs.New(repoPath), nil)
	r, err := git.Init(s, nil)
	CheckIfError(err)
	return r
}

// 打开一个已经存在的 repository
func gitPlainOpen(repoPath string) *git.Repository {

	r, err := git.PlainOpen(repoPath)
	CheckIfError(err)
	return r
}

// 添加文件到 index cache
func gitAdd(r *git.Repository, path string, content []byte) {
	// Find index from Storer, here we are using filesystem.
	idx, err := r.Storer.Index()
	CheckIfError(err)

	// Get an object, write data into the object, then save to object storage.
	obj := r.Storer.NewEncodedObject()
	obj.SetType(plumbing.BlobObject)
	obj.SetSize(int64(len(content)))

	// The implementation of "obj.Writer.Write()" is MemoryObject, which
	// makes a copy of the object.
	writer, err := obj.Writer()
	CheckIfError(err)
	_, err = writer.Write(content)
	CheckIfError(err)
	writer.Close()

	// Here we again copy the object from "obj" to underline storage. Once
	// saved, it is officially considered part of git database.
	// ** Improvement Needed to avoid Double Copy**
	h, err := r.Storer.SetEncodedObject(obj)
	CheckIfError(err)

	e := idx.Add(path)

	// Add a new entry (we can use "idx.Entry(path)" to check if path exists).
	e.Hash = h
	e.Mode = filemode.Regular
	// Set index, which will be translated to tree object once we commit.
	r.Storer.SetIndex(idx)
}

func gitDelete(r *git.Repository, filePath string) {
	// Find index from Storer, here we are using filesystem.
	idx, err := r.Storer.Index()
	CheckIfError(err)

	_, err = idx.Remove(filePath)
	CheckIfError(err)

	err = r.Storer.SetIndex(idx)
	CheckIfError(err)
}

// 发布变更
func gitCommit(r *git.Repository, msg string, opts *git.CommitOptions) (plumbing.Hash, error) {
	if err := opts.Validate(r); err != nil {
		return plumbing.ZeroHash, err
	}

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

	h := &buildTreeHelper{
		s: r.Storer,
	}

	tree, err := h.BuildTree(idx)
	if err != nil {
		return plumbing.ZeroHash, err
	}

	commit, err := buildCommitObject(r, msg, opts, tree)
	if err != nil {
		return plumbing.ZeroHash, err
	}

	// updateHEAD
	head, err := r.Storer.Reference(plumbing.HEAD)
	if err != nil {
		return commit, err
	}

	name := plumbing.HEAD
	if head.Type() != plumbing.HashReference {
		name = head.Target()
	}

	ref := plumbing.NewHashReference(name, commit)
	return commit, r.Storer.SetReference(ref)
}

func main() {
	// repoPath = "/tmp/interesting"
	// gitInit or gitPlainOpen
	r := gitInit("/tmp/interesting")

	// gitAdd
	for i := 0; i < 10; i++ {
		content := []byte(strconv.Itoa(i))
		filePath := strconv.Itoa(i)
		gitAdd(r, filePath, content)
	}

	// gitCommit
	_, err := gitCommit(r, "add files", &git.CommitOptions{
		Author: &object.Signature{
			Name:  "John Doe",
			Email: "john@doe.org",
			When:  time.Now(),
		},
		Parents: []plumbing.Hash{},
	})
	CheckIfError(err)

	// gitDelete
	gitDelete(r, "3")

	// gitCommit
	_, err = gitCommit(r, "remove file", &git.CommitOptions{
		Author: &object.Signature{
			Name:  "John Doe",
			Email: "john@doe.org",
			When:  time.Now(),
		},
		Parents: []plumbing.Hash{},
	})
	CheckIfError(err)

	// gitLog
	gitLog(r)
}

/////////////////////////////////////////////////////////////////////
/////////////////                                     ///////////////
/////////////////  The following copy from work tree  ///////////////
/////////////////                                     ///////////////
/////////////////////////////////////////////////////////////////////

// buildTreeHelper converts a given index.Index file into multiple git objects
// reading the blobs from the given filesystem and creating the trees from the
// index structure. The created objects are pushed to a given Storer.
type buildTreeHelper struct {
	fs billy.Filesystem
	s  storage.Storer

	trees   map[string]*object.Tree
	entries map[string]*object.TreeEntry
}

// BuildTree builds the tree objects and push its to the storer, the hash
// of the root tree is returned.
func (h *buildTreeHelper) BuildTree(idx *index.Index) (plumbing.Hash, error) {
	const rootNode = ""
	h.trees = map[string]*object.Tree{rootNode: {}}
	h.entries = map[string]*object.TreeEntry{}

	for _, e := range idx.Entries {
		if err := h.commitIndexEntry(e); err != nil {
			return plumbing.ZeroHash, err
		}
	}

	return h.copyTreeToStorageRecursive(rootNode, h.trees[rootNode])
}

func (h *buildTreeHelper) commitIndexEntry(e *index.Entry) error {
	parts := strings.Split(e.Name, "/")

	var fullpath string
	for _, part := range parts {
		parent := fullpath
		fullpath = path.Join(fullpath, part)

		h.doBuildTree(e, parent, fullpath)
	}

	return nil
}

func (h *buildTreeHelper) doBuildTree(e *index.Entry, parent, fullpath string) {
	if _, ok := h.trees[fullpath]; ok {
		return
	}

	if _, ok := h.entries[fullpath]; ok {
		return
	}

	te := object.TreeEntry{Name: path.Base(fullpath)}

	if fullpath == e.Name {
		te.Mode = e.Mode
		te.Hash = e.Hash
	} else {
		te.Mode = filemode.Dir
		h.trees[fullpath] = &object.Tree{}
	}

	h.trees[parent].Entries = append(h.trees[parent].Entries, te)
}

type sortableEntries []object.TreeEntry

func (sortableEntries) sortName(te object.TreeEntry) string {
	if te.Mode == filemode.Dir {
		return te.Name + "/"
	}
	return te.Name
}
func (se sortableEntries) Len() int               { return len(se) }
func (se sortableEntries) Less(i int, j int) bool { return se.sortName(se[i]) < se.sortName(se[j]) }
func (se sortableEntries) Swap(i int, j int)      { se[i], se[j] = se[j], se[i] }

func (h *buildTreeHelper) copyTreeToStorageRecursive(parent string, t *object.Tree) (plumbing.Hash, error) {
	sort.Sort(sortableEntries(t.Entries))
	for i, e := range t.Entries {
		if e.Mode != filemode.Dir && !e.Hash.IsZero() {
			continue
		}

		path := path.Join(parent, e.Name)

		var err error
		e.Hash, err = h.copyTreeToStorageRecursive(path, h.trees[path])
		if err != nil {
			return plumbing.ZeroHash, err
		}

		t.Entries[i] = e
	}

	o := h.s.NewEncodedObject()
	if err := t.Encode(o); err != nil {
		return plumbing.ZeroHash, err
	}

	return h.s.SetEncodedObject(o)
}

func buildCommitObject(r *git.Repository, msg string, opts *git.CommitOptions, tree plumbing.Hash) (plumbing.Hash, error) {
	commit := &object.Commit{
		Author:       *opts.Author,
		Committer:    *opts.Committer,
		Message:      msg,
		TreeHash:     tree,
		ParentHashes: opts.Parents,
	}

	if opts.SignKey != nil {
		sig, err := buildCommitSignature(commit, opts.SignKey)
		if err != nil {
			return plumbing.ZeroHash, err
		}
		commit.PGPSignature = sig
	}

	obj := r.Storer.NewEncodedObject()
	if err := commit.Encode(obj); err != nil {
		return plumbing.ZeroHash, err
	}
	return r.Storer.SetEncodedObject(obj)
}

func buildCommitSignature(commit *object.Commit, signKey *openpgp.Entity) (string, error) {
	encoded := &plumbing.MemoryObject{}
	if err := commit.Encode(encoded); err != nil {
		return "", err
	}
	r, err := encoded.Reader()
	if err != nil {
		return "", err
	}
	var b bytes.Buffer
	if err := openpgp.ArmoredDetachSign(&b, signKey, r, nil); err != nil {
		return "", err
	}
	return b.String(), nil
}