package depot

import "context"

type ProbeState int

const (
	Present ProbeState = iota
	Absent
	Unconfirmed
)

// Backend defines the interface for blob storage backends.
type Backend interface {
	// Name returns the backend name.
	Name() string
	// Probe returns the existence state of one sha. transient=true means a
	// retry might change the answer (feeds the serial confirm loop).
	Probe(ctx context.Context, sha string) (state ProbeState, transient bool, err error)
	// Get fetches sha into dest (temp file + rename), re-hashes, deletes on mismatch.
	Get(ctx context.Context, sha, dest string) error
	// Put uploads bytes from src for sha. Read-only backends return an error.
	Put(ctx context.Context, sha, src string) error
}