package concurrency

import (
    "fmt"

    v3 "github.com/coreos/etcd/clientv3"
    "github.com/coreos/etcd/mvcc/mvccpb"
    "golang.org/x/net/context"
)

func waitDelete(ctx context.Context, client *v3.Client, key string, rev int64) error {
    cctx, cancel := context.WithCancel(ctx)
    defer cancel()

    var wr v3.WatchResponse
    wch := client.Watch(cctx, key, v3.WithRev(rev))
    for wr = range wch {
        for _, ev := range wr.Events {
            if ev.Type == mvccpb.DELETE {
                return nil
            }
        }
    }
    if err := wr.Err(); err != nil {
        return err
    }
    if err := ctx.Err(); err != nil {
        return err
    }
    return fmt.Errorf("lost watcher waiting for delete")
}

// waitDeletes efficiently waits until all keys matching the prefix and no greater
// than the create revision.
func waitDeletes(ctx context.Context, client *v3.Client, pfx string, maxCreateRev int64) error {
    getOpts := append(v3.WithLastCreate(), v3.WithMaxCreateRev(maxCreateRev))
    for {
        resp, err := client.Get(ctx, pfx, getOpts...)
        if err != nil {
            return err
        }
        if len(resp.Kvs) == 0 {
            return nil
        }
        lastKey := string(resp.Kvs[0].Key)
        if err = waitDelete(ctx, client, lastKey, resp.Header.Revision); err != nil {
            return err
        }
    }
}