// package blockstore implements a thin wrapper over a datastore, giving a
// clean interface for Getting and Putting block objects.
package blockstore

import (
	"errors"

	ds "github.com/jbenet/go-ipfs/Godeps/_workspace/src/github.com/jbenet/go-datastore"
	dsns "github.com/jbenet/go-ipfs/Godeps/_workspace/src/github.com/jbenet/go-datastore/namespace"
	dsq "github.com/jbenet/go-ipfs/Godeps/_workspace/src/github.com/jbenet/go-datastore/query"
	mh "github.com/jbenet/go-ipfs/Godeps/_workspace/src/github.com/jbenet/go-multihash"

	blocks "github.com/jbenet/go-ipfs/blocks"
	u "github.com/jbenet/go-ipfs/util"
)

// BlockPrefix namespaces blockstore datastores
var BlockPrefix = ds.NewKey("blocks")

var ValueTypeMismatch = errors.New("The retrieved value is not a Block")

var ErrNotFound = errors.New("blockstore: block not found")

// Blockstore wraps a ThreadSafeDatastore
type Blockstore interface {
	DeleteBlock(u.Key) error
	Has(u.Key) (bool, error)
	Get(u.Key) (*blocks.Block, error)
	Put(*blocks.Block) error
	AllKeys(offset int, limit int) ([]u.Key, error)
}

func NewBlockstore(d ds.ThreadSafeDatastore) Blockstore {
	dd := dsns.Wrap(d, BlockPrefix)
	return &blockstore{
		datastore: dd,
	}
}

type blockstore struct {
	datastore ds.Datastore
	// cant be ThreadSafeDatastore cause namespace.Datastore doesnt support it.
	// we do check it on `NewBlockstore` though.
}

func (bs *blockstore) Get(k u.Key) (*blocks.Block, error) {
	maybeData, err := bs.datastore.Get(k.DsKey())
	if err == ds.ErrNotFound {
		return nil, ErrNotFound
	}
	if err != nil {
		return nil, err
	}
	bdata, ok := maybeData.([]byte)
	if !ok {
		return nil, ValueTypeMismatch
	}

	return blocks.NewBlockWithHash(bdata, mh.Multihash(k))
}

func (bs *blockstore) Put(block *blocks.Block) error {
	// Has is cheaper than
	k := block.Key().DsKey()
	exists, err := bs.datastore.Has(k)
	if err != nil && exists {
		return nil // already stored.
	}
	return bs.datastore.Put(k, block.Data)
}

func (bs *blockstore) Has(k u.Key) (bool, error) {
	return bs.datastore.Has(k.DsKey())
}

func (s *blockstore) DeleteBlock(k u.Key) error {
	return s.datastore.Delete(k.DsKey())
}

// AllKeys runs a query for keys from the blockstore.
// this is very simplistic, in the future, take dsq.Query as a param?
// if offset and limit are 0, they are ignored.
func (bs *blockstore) AllKeys(offset int, limit int) ([]u.Key, error) {
	var keys []u.Key

	// TODO make async inside ds/leveldb.Query
	// KeysOnly, because that would be _a lot_ of data.
	q := dsq.Query{KeysOnly: true, Offset: offset, Limit: limit}
	res, err := bs.datastore.Query(q)
	if err != nil {
		return nil, err
	}

	for e := range res.Entries() {
		// need to convert to u.Key using u.KeyFromDsKey.
		k := u.KeyFromDsKey(ds.NewKey(e.Key))
		keys = append(keys, k)
	}
	return keys, nil
}