type Identifier interface {
	// Scheme returns the scheme of the identifier so that it can be routed back
	// to an appropriate Source.
	Scheme() string

	// Capture records the provenance of the identifier.
	Capture(dest *provenance.Capture, pin string) error
}

type Manager struct {
	// contains filtered or unexported fields
}

type Source interface {
	// Schemes returns a list of SourceOp identifier schemes that this source
	// should match.
	Schemes() []string

	// Identifier constructs an Identifier from the given scheme, ref, and attrs,
	// all of which come from a SourceOp.
	Identifier(scheme, ref string, attrs map[string]string, platform *pb.Platform) (Identifier, error)

	// Resolve constructs an instance of the source from an Identifier.
	Resolve(ctx context.Context, id Identifier, sm *session.Manager, vtx solver.Vertex) (SourceInstance, error)
}

type SourceInstance interface {
	// CacheKey returns the cache key for the instance.
	CacheKey(ctx context.Context, g session.Group, index int) (key, pin string, opts solver.CacheOpts, done bool, err error)

	// Snapshot creates a cache ref for the instance. May return a nil ref if source points to empty content, e.g. image without any layers.
	Snapshot(ctx context.Context, g session.Group) (cache.ImmutableRef, error)
}