package keytransform

import (
	ds "github.com/jbenet/go-datastore"
	dsq "github.com/jbenet/go-datastore/query"
)

type Pair struct {
	Convert KeyMapping
	Invert  KeyMapping
}

func (t *Pair) ConvertKey(k ds.Key) ds.Key {
	return t.Convert(k)
}

func (t *Pair) InvertKey(k ds.Key) ds.Key {
	return t.Invert(k)
}

// ktds keeps a KeyTransform function
type ktds struct {
	child ds.Datastore

	KeyTransform
}

// Children implements ds.Shim
func (d *ktds) Children() []ds.Datastore {
	return []ds.Datastore{d.child}
}

// Put stores the given value, transforming the key first.
func (d *ktds) Put(key ds.Key, value interface{}) (err error) {
	return d.child.Put(d.ConvertKey(key), value)
}

// Get returns the value for given key, transforming the key first.
func (d *ktds) Get(key ds.Key) (value interface{}, err error) {
	return d.child.Get(d.ConvertKey(key))
}

// Has returns whether the datastore has a value for a given key, transforming
// the key first.
func (d *ktds) Has(key ds.Key) (exists bool, err error) {
	return d.child.Has(d.ConvertKey(key))
}

// Delete removes the value for given key
func (d *ktds) Delete(key ds.Key) (err error) {
	return d.child.Delete(d.ConvertKey(key))
}

// Query implements Query, inverting keys on the way back out.
func (d *ktds) Query(q dsq.Query) (dsq.Results, error) {
	qr, err := d.child.Query(q)
	if err != nil {
		return nil, err
	}

	ch := make(chan dsq.Result)
	go func() {
		defer close(ch)
		defer qr.Close()

		for r := range qr.Next() {
			if r.Error == nil {
				r.Entry.Key = d.InvertKey(ds.NewKey(r.Entry.Key)).String()
			}
			ch <- r
		}
	}()

	return dsq.DerivedResults(qr, ch), nil
}

func (d *ktds) Batch() ds.Batch {
	return &transformBatch{
		dst: d.child.Batch(),
		f:   d.ConvertKey,
	}
}

type transformBatch struct {
	dst ds.Batch

	f KeyMapping
}

func (t *transformBatch) Put(key ds.Key, val interface{}) error {
	return t.dst.Put(t.f(key), val)
}

func (t *transformBatch) Delete(key ds.Key) error {
	return t.dst.Delete(t.f(key))
}

func (t *transformBatch) Commit() error {
	return t.dst.Commit()
}