package gus

import(
        `github.com/0xor1/sus`
        `github.com/qedus/nds`
        `golang.org/x/net/context`
        `google.golang.org/appengine/datastore`
)

// Creates and configures a store that stores entities in Google AppEngines memcache and datastore.
// github.com/qedus/nds is used for strongly consistent automatic caching.
func NewGaeStore(kind string, ctx context.Context, idf sus.IdFactory, vf sus.VersionFactory) sus.Store {
        getKey := func(ctx context.Context, id string) *datastore.Key {
                return datastore.NewKey(ctx, kind, id, 0, nil)
        }

        getMulti := func(ids []string) (vs []sus.Version, err error) {
                count := len(ids)
                vs = make([]sus.Version, count, count)
                ks := make([]*datastore.Key, count, count)
                for i := 0; i < count; i++ {
                        vs[i] = vf()
                        ks[i] = getKey(ctx, ids[i])
                }
                err = nds.GetMulti(ctx, ks, vs)
                return
        }

        putMulti := func(ids []string, vs []sus.Version) (err error) {
                count := len(ids)
                ks := make([]*datastore.Key, count, count)
                for i := 0; i < count; i++ {
                        ks[i] = getKey(ctx, ids[i])
                }
                _, err = nds.PutMulti(ctx, ks, vs)
                return
        }

        delMulti := func(ids []string) error {
                count := len(ids)
                ks := make([]*datastore.Key, count, count)
                for i := 0; i < count; i++ {
                        ks[i] = getKey(ctx, ids[i])
                }
                return nds.DeleteMulti(ctx, ks)
        }

        isNonExtantError := func(err error) bool {
                return err.Error() == datastore.ErrNoSuchEntity.Error()
        }

        rit := func(tran sus.Transaction) error {
                return nds.RunInTransaction(ctx, func(ctx context.Context)error{
                        return tran()
                }, &datastore.TransactionOptions{XG:true})
        }

        return sus.NewStore(getMulti, putMulti, delMulti, idf, vf, isNonExtantError,rit)
}