package filesystem

import (
	"bytes"
	"fmt"
	"io"
	"os"

	"gopkg.in/src-d/go-git.v4/core"
	"gopkg.in/src-d/go-git.v4/formats/objfile"
	"gopkg.in/src-d/go-git.v4/formats/packfile"
	"gopkg.in/src-d/go-git.v4/storage/filesystem/internal/dotgit"
	"gopkg.in/src-d/go-git.v4/storage/filesystem/internal/index"
	"gopkg.in/src-d/go-git.v4/utils/fs"
)

// ObjectStorage is an implementation of core.ObjectStorage that stores
// data on disk in the standard git format (this is, the .git directory).
//
// Zero values of this type are not safe to use, see the New function below.
//
// Currently only reads are supported, no writting.
//
// Also values from this type are not yet able to track changes on disk, this is,
// Gitdir values will get outdated as soon as repositories change on disk.
type ObjectStorage struct {
	dir   *dotgit.DotGit
	index index.Index
}

func (s *ObjectStorage) NewObject() core.Object {
	return &core.MemoryObject{}
}

// Writer method not supported on Memory storage
func (o *ObjectStorage) Writer() (io.WriteCloser, error) {
	file := bytes.NewBuffer(nil)
	return newPackWrite(o, file), nil
}

type packWriter struct {
	writer     io.Writer
	pipeReader io.ReadCloser
	pipeWriter io.WriteCloser
	file       io.Writer
	result     chan error
}

func newPackWrite(o *ObjectStorage, file io.Writer) io.WriteCloser {
	r, w := io.Pipe()

	ch := make(chan error)
	go func(r io.ReadCloser) {
		defer r.Close()
		index, err := index.NewFromPackfileInMemory(r)
		o.index = index

		ch <- err
	}(r)

	return &packWriter{
		writer:     io.MultiWriter(w, file),
		pipeReader: r,
		pipeWriter: w,
		file:       file,
		result:     ch,
	}

}

func (w *packWriter) Write(p []byte) (int, error) {
	return w.writer.Write(p)
}

func (w *packWriter) Close() error {
	defer func() {
		close(w.result)
	}()

	if err := w.pipeWriter.Close(); err != nil {
		return err
	}

	return <-w.result
}

// Set adds a new object to the storage. As this functionality is not
// yet supported, this method always returns a "not implemented yet"
// error an zero hash.
func (s *ObjectStorage) Set(core.Object) (core.Hash, error) {
	return core.ZeroHash, fmt.Errorf("not implemented yet")
}

// Get returns the object with the given hash, by searching for it in
// the packfile and the git object directories.
func (s *ObjectStorage) Get(t core.ObjectType, h core.Hash) (core.Object, error) {
	obj, err := s.getFromUnpacked(t, h)
	if err == dotgit.ErrObjfileNotFound {
		if s.index == nil {
			return nil, core.ErrObjectNotFound
		}
		return s.getFromPackfile(t, h)
	}

	return obj, err
}

func (s *ObjectStorage) getFromUnpacked(t core.ObjectType, h core.Hash) (obj core.Object, err error) {
	fs, path, err := s.dir.Objectfile(h)
	if err != nil {
		return nil, err
	}

	f, err := fs.Open(path)
	if err != nil {
		return nil, err
	}

	defer func() {
		errClose := f.Close()
		if err == nil {
			err = errClose
		}
	}()

	obj = s.NewObject()
	objReader, err := objfile.NewReader(f)
	if err != nil {
		return nil, err
	}
	defer func() {
		errClose := objReader.Close()
		if err == nil {
			err = errClose
		}
	}()

	err = objReader.FillObject(obj)
	if err != nil {
		return nil, err
	}
	if core.AnyObject != t && obj.Type() != t {
		return nil, core.ErrObjectNotFound
	}
	return obj, nil
}

// Get returns the object with the given hash, by searching for it in
// the packfile.
func (s *ObjectStorage) getFromPackfile(t core.ObjectType, h core.Hash) (obj core.Object, err error) {
	offset, err := s.index.Get(h)
	if err != nil {
		return nil, err
	}

	fs, path, err := s.dir.Packfile()
	if err != nil {
		return nil, err
	}

	f, err := fs.Open(path)
	if err != nil {
		return nil, err
	}

	defer func() {
		errClose := f.Close()
		if err == nil {
			err = errClose
		}
	}()

	_, err = f.Seek(offset, os.SEEK_SET)
	if err != nil {
		return nil, err
	}

	r := packfile.NewSeekable(f)
	r.HashToOffset = map[core.Hash]int64(s.index)
	p := packfile.NewParser(r)

	obj = s.NewObject()
	err = p.FillObject(obj)
	if err != nil {
		return nil, err
	}
	if core.AnyObject != t && obj.Type() != t {
		return nil, core.ErrObjectNotFound
	}
	return obj, nil
}

// Iter returns an iterator for all the objects in the packfile with the
// given type.
func (s *ObjectStorage) Iter(t core.ObjectType) (core.ObjectIter, error) {
	var objects []core.Object

	_, hashes, err := s.dir.Objectfiles()
	if err != nil {
		return nil, err
	}

	for _, hash := range hashes {
		object, err := s.getFromUnpacked(core.AnyObject, hash)
		if err != nil {
			return nil, err
		}
		if object.Type() == t {
			objects = append(objects, object)
		}
	}

	for hash := range s.index {
		object, err := s.getFromPackfile(core.AnyObject, hash)
		if err != nil {
			return nil, err
		}
		if t == core.AnyObject || object.Type() == t {
			objects = append(objects, object)
		}
	}

	return core.NewObjectSliceIter(objects), nil
}

func buildIndex(dir *dotgit.DotGit) (index.Index, error) {
	fs, idxfile, err := dir.Idxfile()
	if err != nil {
		if err == dotgit.ErrIdxNotFound {
			return buildIndexFromPackfile(dir)
		}
		return nil, err
	}

	return buildIndexFromIdxfile(fs, idxfile)
}

func buildIndexFromPackfile(dir *dotgit.DotGit) (index.Index, error) {
	fs, packfile, err := dir.Packfile()
	if err != nil {
		return nil, err
	}

	f, err := fs.Open(packfile)
	if err != nil {
		return nil, err
	}

	defer func() {
		errClose := f.Close()
		if err == nil {
			err = errClose
		}
	}()

	return index.NewFromPackfile(f)
}

func buildIndexFromIdxfile(fs fs.FS, path string) (index.Index, error) {
	f, err := fs.Open(path)
	if err != nil {
		return nil, err
	}

	defer func() {
		errClose := f.Close()
		if err == nil {
			err = errClose
		}
	}()

	return index.NewFromIdx(f)
}
func (o *ObjectStorage) Begin() core.TxObjectStorage {
	return &TxObjectStorage{}
}

type TxObjectStorage struct{}

func (tx *TxObjectStorage) Set(obj core.Object) (core.Hash, error) {
	return core.ZeroHash, fmt.Errorf("not implemented yet")
}

func (tx *TxObjectStorage) Commit() error {
	return fmt.Errorf("not implemented yet")
}

func (tx *TxObjectStorage) Rollback() error {
	return fmt.Errorf("not implemented yet")
}