package filesystem

import (
	"io"
	"os"
	"time"

	"gopkg.in/src-d/go-git.v4/plumbing"
	"gopkg.in/src-d/go-git.v4/plumbing/cache"
	"gopkg.in/src-d/go-git.v4/plumbing/format/idxfile"
	"gopkg.in/src-d/go-git.v4/plumbing/format/objfile"
	"gopkg.in/src-d/go-git.v4/plumbing/format/packfile"
	"gopkg.in/src-d/go-git.v4/plumbing/storer"
	"gopkg.in/src-d/go-git.v4/storage/filesystem/dotgit"
	"gopkg.in/src-d/go-git.v4/storage/memory"
	"gopkg.in/src-d/go-git.v4/utils/ioutil"

	"gopkg.in/src-d/go-billy.v4"
)

type ObjectStorage struct {
	// deltaBaseCache is an object cache uses to cache delta's bases when
	deltaBaseCache cache.Object

	dir   *dotgit.DotGit
	index map[plumbing.Hash]*packfile.Index
}

// NewObjectStorage creates a new ObjectStorage with the given .git directory.
func NewObjectStorage(dir *dotgit.DotGit) (ObjectStorage, error) {
	s := ObjectStorage{
		deltaBaseCache: cache.NewObjectLRUDefault(),
		dir:            dir,
	}

	return s, nil
}

func (s *ObjectStorage) requireIndex() error {
	if s.index != nil {
		return nil
	}

	s.index = make(map[plumbing.Hash]*packfile.Index)
	packs, err := s.dir.ObjectPacks()
	if err != nil {
		return err
	}

	for _, h := range packs {
		if err := s.loadIdxFile(h); err != nil {
			return err
		}
	}

	return nil
}

func (s *ObjectStorage) loadIdxFile(h plumbing.Hash) (err error) {
	f, err := s.dir.ObjectPackIdx(h)
	if err != nil {
		return err
	}

	defer ioutil.CheckClose(f, &err)
	idxf := idxfile.NewIdxfile()
	d := idxfile.NewDecoder(f)
	if err = d.Decode(idxf); err != nil {
		return err
	}

	s.index[h] = packfile.NewIndexFromIdxFile(idxf)
	return err
}

func (s *ObjectStorage) NewEncodedObject() plumbing.EncodedObject {
	return &plumbing.MemoryObject{}
}

func (s *ObjectStorage) PackfileWriter() (io.WriteCloser, error) {
	if err := s.requireIndex(); err != nil {
		return nil, err
	}

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

	w.Notify = func(h plumbing.Hash, idx *packfile.Index) {
		s.index[h] = idx
	}

	return w, nil
}

// SetEncodedObject adds a new object to the storage.
func (s *ObjectStorage) SetEncodedObject(o plumbing.EncodedObject) (h plumbing.Hash, err error) {
	if o.Type() == plumbing.OFSDeltaObject || o.Type() == plumbing.REFDeltaObject {
		return plumbing.ZeroHash, plumbing.ErrInvalidType
	}

	ow, err := s.dir.NewObject()
	if err != nil {
		return plumbing.ZeroHash, err
	}

	defer ioutil.CheckClose(ow, &err)

	or, err := o.Reader()
	if err != nil {
		return plumbing.ZeroHash, err
	}

	defer ioutil.CheckClose(or, &err)

	if err = ow.WriteHeader(o.Type(), o.Size()); err != nil {
		return plumbing.ZeroHash, err
	}

	if _, err = io.Copy(ow, or); err != nil {
		return plumbing.ZeroHash, err
	}

	return o.Hash(), err
}

// HasEncodedObject returns nil if the object exists, without actually
// reading the object data from storage.
func (s *ObjectStorage) HasEncodedObject(h plumbing.Hash) (err error) {
	// Check unpacked objects
	f, err := s.dir.Object(h)
	if err != nil {
		if !os.IsNotExist(err) {
			return err
		}
		// Fall through to check packed objects.
	} else {
		defer ioutil.CheckClose(f, &err)
		return nil
	}

	// Check packed objects.
	if err := s.requireIndex(); err != nil {
		return err
	}
	_, _, offset := s.findObjectInPackfile(h)
	if offset == -1 {
		return plumbing.ErrObjectNotFound
	}
	return nil
}

// EncodedObject returns the object with the given hash, by searching for it in
// the packfile and the git object directories.
func (s *ObjectStorage) EncodedObject(t plumbing.ObjectType, h plumbing.Hash) (plumbing.EncodedObject, error) {
	obj, err := s.getFromUnpacked(h)
	if err == plumbing.ErrObjectNotFound {
		obj, err = s.getFromPackfile(h, false)
	}

	// If the error is still object not found, check if it's a shared object
	// repository.
	if err == plumbing.ErrObjectNotFound {
		dotgits, e := s.dir.Alternates()
		if e == nil {
			// Create a new object storage with the DotGit(s) and check for the
			// required hash object. Skip when not found.
			for _, dg := range dotgits {
				o, oe := NewObjectStorage(dg)
				if oe != nil {
					continue
				}
				enobj, enerr := o.EncodedObject(t, h)
				if enerr != nil {
					continue
				}
				return enobj, nil
			}
		}
	}

	if err != nil {
		return nil, err
	}

	if plumbing.AnyObject != t && obj.Type() != t {
		return nil, plumbing.ErrObjectNotFound
	}

	return obj, nil
}

// DeltaObject returns the object with the given hash, by searching for
// it in the packfile and the git object directories.
func (s *ObjectStorage) DeltaObject(t plumbing.ObjectType,
	h plumbing.Hash) (plumbing.EncodedObject, error) {
	obj, err := s.getFromUnpacked(h)
	if err == plumbing.ErrObjectNotFound {
		obj, err = s.getFromPackfile(h, true)
	}

	if err != nil {
		return nil, err
	}

	if plumbing.AnyObject != t && obj.Type() != t {
		return nil, plumbing.ErrObjectNotFound
	}

	return obj, nil
}

func (s *ObjectStorage) getFromUnpacked(h plumbing.Hash) (obj plumbing.EncodedObject, err error) {
	f, err := s.dir.Object(h)
	if err != nil {
		if os.IsNotExist(err) {
			return nil, plumbing.ErrObjectNotFound
		}

		return nil, err
	}

	defer ioutil.CheckClose(f, &err)

	obj = s.NewEncodedObject()
	r, err := objfile.NewReader(f)
	if err != nil {
		return nil, err
	}

	defer ioutil.CheckClose(r, &err)

	t, size, err := r.Header()
	if err != nil {
		return nil, err
	}

	obj.SetType(t)
	obj.SetSize(size)
	w, err := obj.Writer()
	if err != nil {
		return nil, err
	}

	_, err = io.Copy(w, r)
	return obj, err
}

// Get returns the object with the given hash, by searching for it in
// the packfile.
func (s *ObjectStorage) getFromPackfile(h plumbing.Hash, canBeDelta bool) (
	plumbing.EncodedObject, error) {

	if err := s.requireIndex(); err != nil {
		return nil, err
	}

	pack, hash, offset := s.findObjectInPackfile(h)
	if offset == -1 {
		return nil, plumbing.ErrObjectNotFound
	}

	f, err := s.dir.ObjectPack(pack)
	if err != nil {
		return nil, err
	}

	defer ioutil.CheckClose(f, &err)

	idx := s.index[pack]
	if canBeDelta {
		return s.decodeDeltaObjectAt(f, idx, offset, hash)
	}

	return s.decodeObjectAt(f, idx, offset)
}

func (s *ObjectStorage) decodeObjectAt(
	f billy.File,
	idx *packfile.Index,
	offset int64) (plumbing.EncodedObject, error) {
	if _, err := f.Seek(0, io.SeekStart); err != nil {
		return nil, err
	}

	p := packfile.NewScanner(f)

	d, err := packfile.NewDecoderWithCache(p, memory.NewStorage(),
		s.deltaBaseCache)
	if err != nil {
		return nil, err
	}

	d.SetIndex(idx)
	obj, err := d.DecodeObjectAt(offset)
	return obj, err
}

func (s *ObjectStorage) decodeDeltaObjectAt(
	f billy.File,
	idx *packfile.Index,
	offset int64,
	hash plumbing.Hash) (plumbing.EncodedObject, error) {
	if _, err := f.Seek(0, io.SeekStart); err != nil {
		return nil, err
	}

	p := packfile.NewScanner(f)
	if _, err := p.SeekFromStart(offset); err != nil {
		return nil, err
	}

	header, err := p.NextObjectHeader()
	if err != nil {
		return nil, err
	}

	var (
		base plumbing.Hash
	)

	switch header.Type {
	case plumbing.REFDeltaObject:
		base = header.Reference
	case plumbing.OFSDeltaObject:
		e, ok := idx.LookupOffset(uint64(header.OffsetReference))
		if !ok {
			return nil, plumbing.ErrObjectNotFound
		}

		base = e.Hash
	default:
		return s.decodeObjectAt(f, idx, offset)
	}

	obj := &plumbing.MemoryObject{}
	obj.SetType(header.Type)
	w, err := obj.Writer()
	if err != nil {
		return nil, err
	}

	if _, _, err := p.NextObject(w); err != nil {
		return nil, err
	}

	return newDeltaObject(obj, hash, base, header.Length), nil
}

func (s *ObjectStorage) findObjectInPackfile(h plumbing.Hash) (plumbing.Hash, plumbing.Hash, int64) {
	for packfile, index := range s.index {
		if e, ok := index.LookupHash(h); ok {
			return packfile, e.Hash, int64(e.Offset)
		}
	}

	return plumbing.ZeroHash, plumbing.ZeroHash, -1
}

// IterEncodedObjects returns an iterator for all the objects in the packfile
// with the given type.
func (s *ObjectStorage) IterEncodedObjects(t plumbing.ObjectType) (storer.EncodedObjectIter, error) {
	objects, err := s.dir.Objects()
	if err != nil {
		return nil, err
	}

	seen := make(map[plumbing.Hash]struct{})
	var iters []storer.EncodedObjectIter
	if len(objects) != 0 {
		iters = append(iters, &objectsIter{s: s, t: t, h: objects})
		seen = hashListAsMap(objects)
	}

	packi, err := s.buildPackfileIters(t, seen)
	if err != nil {
		return nil, err
	}

	iters = append(iters, packi)
	return storer.NewMultiEncodedObjectIter(iters), nil
}

func (s *ObjectStorage) buildPackfileIters(t plumbing.ObjectType, seen map[plumbing.Hash]struct{}) (storer.EncodedObjectIter, error) {
	if err := s.requireIndex(); err != nil {
		return nil, err
	}

	packs, err := s.dir.ObjectPacks()
	if err != nil {
		return nil, err
	}
	return &lazyPackfilesIter{
		hashes: packs,
		open: func(h plumbing.Hash) (storer.EncodedObjectIter, error) {
			pack, err := s.dir.ObjectPack(h)
			if err != nil {
				return nil, err
			}
			return newPackfileIter(pack, t, seen, s.index[h], s.deltaBaseCache)
		},
	}, nil
}

type lazyPackfilesIter struct {
	hashes []plumbing.Hash
	open   func(h plumbing.Hash) (storer.EncodedObjectIter, error)
	cur    storer.EncodedObjectIter
}

func (it *lazyPackfilesIter) Next() (plumbing.EncodedObject, error) {
	for {
		if it.cur == nil {
			if len(it.hashes) == 0 {
				return nil, io.EOF
			}
			h := it.hashes[0]
			it.hashes = it.hashes[1:]

			sub, err := it.open(h)
			if err == io.EOF {
				continue
			} else if err != nil {
				return nil, err
			}
			it.cur = sub
		}
		ob, err := it.cur.Next()
		if err == io.EOF {
			it.cur.Close()
			it.cur = nil
			continue
		} else if err != nil {
			return nil, err
		}
		return ob, nil
	}
}

func (it *lazyPackfilesIter) ForEach(cb func(plumbing.EncodedObject) error) error {
	return storer.ForEachIterator(it, cb)
}

func (it *lazyPackfilesIter) Close() {
	if it.cur != nil {
		it.cur.Close()
		it.cur = nil
	}
	it.hashes = nil
}

type packfileIter struct {
	f billy.File
	d *packfile.Decoder
	t plumbing.ObjectType

	seen     map[plumbing.Hash]struct{}
	position uint32
	total    uint32
}

func NewPackfileIter(f billy.File, t plumbing.ObjectType) (storer.EncodedObjectIter, error) {
	return newPackfileIter(f, t, make(map[plumbing.Hash]struct{}), nil, nil)
}

func newPackfileIter(f billy.File, t plumbing.ObjectType, seen map[plumbing.Hash]struct{},
	index *packfile.Index, cache cache.Object) (storer.EncodedObjectIter, error) {
	s := packfile.NewScanner(f)
	_, total, err := s.Header()
	if err != nil {
		return nil, err
	}

	d, err := packfile.NewDecoderForType(s, memory.NewStorage(), t, cache)
	if err != nil {
		return nil, err
	}

	d.SetIndex(index)

	return &packfileIter{
		f: f,
		d: d,
		t: t,

		total: total,
		seen:  seen,
	}, nil
}

func (iter *packfileIter) Next() (plumbing.EncodedObject, error) {
	for {
		if iter.position >= iter.total {
			return nil, io.EOF
		}

		obj, err := iter.d.DecodeObject()
		if err != nil {
			return nil, err
		}

		iter.position++
		if obj == nil {
			continue
		}

		if _, ok := iter.seen[obj.Hash()]; ok {
			return iter.Next()
		}

		return obj, nil
	}
}

// ForEach is never called since is used inside of a MultiObjectIterator
func (iter *packfileIter) ForEach(cb func(plumbing.EncodedObject) error) error {
	return nil
}

func (iter *packfileIter) Close() {
	iter.f.Close()
	iter.d.Close()
}

type objectsIter struct {
	s *ObjectStorage
	t plumbing.ObjectType
	h []plumbing.Hash
}

func (iter *objectsIter) Next() (plumbing.EncodedObject, error) {
	if len(iter.h) == 0 {
		return nil, io.EOF
	}

	obj, err := iter.s.getFromUnpacked(iter.h[0])
	iter.h = iter.h[1:]

	if err != nil {
		return nil, err
	}

	if iter.t != plumbing.AnyObject && iter.t != obj.Type() {
		return iter.Next()
	}

	return obj, err
}

// ForEach is never called since is used inside of a MultiObjectIterator
func (iter *objectsIter) ForEach(cb func(plumbing.EncodedObject) error) error {
	return nil
}

func (iter *objectsIter) Close() {
	iter.h = []plumbing.Hash{}
}

func hashListAsMap(l []plumbing.Hash) map[plumbing.Hash]struct{} {
	m := make(map[plumbing.Hash]struct{}, len(l))
	for _, h := range l {
		m[h] = struct{}{}
	}
	return m
}

func (s *ObjectStorage) ForEachObjectHash(fun func(plumbing.Hash) error) error {
	err := s.dir.ForEachObjectHash(fun)
	if err == storer.ErrStop {
		return nil
	}
	return err
}

func (s *ObjectStorage) LooseObjectTime(hash plumbing.Hash) (time.Time, error) {
	fi, err := s.dir.ObjectStat(hash)
	if err != nil {
		return time.Time{}, err
	}
	return fi.ModTime(), nil
}

func (s *ObjectStorage) DeleteLooseObject(hash plumbing.Hash) error {
	return s.dir.ObjectDelete(hash)
}

func (s *ObjectStorage) ObjectPacks() ([]plumbing.Hash, error) {
	return s.dir.ObjectPacks()
}

func (s *ObjectStorage) DeleteOldObjectPackAndIndex(h plumbing.Hash, t time.Time) error {
	return s.dir.DeleteOldObjectPackAndIndex(h, t)
}