package check

import (
	"context"
	"errors"
)

// ErrConflict is what a KV answers when a Create finds the key or an Update finds another revision than the one given.
var ErrConflict = errors.New("the key exists or changed")

// KV is one of the checker's buckets: read, create and compare-and-set, each write answering the key's new revision. Only
// the checker's credential writes them (ADR 0444 clause 5, ADR 0484 clause 2).
type KV interface {
	Get(ctx context.Context, key string) (value []byte, revision uint64, found bool, err error)
	Create(ctx context.Context, key string, value []byte) (uint64, error)
	Update(ctx context.Context, key string, value []byte, revision uint64) (uint64, error)
	// Keys are every key of the bucket.
	Keys(ctx context.Context) ([]string, error)
}