updates

type Channel struct {
	// Name is the user-facing identifier for a graph of updates.
	Name string `json:"name"`

	// Metadata contains any additional properties about the channel.
	// For example, the applicable datastore is stored as metadata.
	Metadata map[string]string `json:"metadata,omitempty"`

	// Edges are the transitions between states in the update graph.
	Edges EdgeSet `json:"edges,omitempty"`

	// Nodes are the possible states in an update graph.
	Nodes []State `json:"nodes,omitempty"`
}

type EdgeSet map[string][]string

type MemorySource struct {
	// OrderedNodes is an ordered list of all nodes. Lower index == newer currentVersion.
	OrderedNodes []State
	// Nodes is a helper to lookup a node by id
	Nodes NodeSet
	// Edges contains the edgeset for this source.
	Edges EdgeSet
}

type NodeSet map[string]int

type Source interface {
	// NextVersionWithoutMigrations returns the newest currentVersion that has an edge that
	// does not require any migrations.
	NextVersionWithoutMigrations(from string) string

	// NextVersion returns the newest currentVersion that has an edge.
	// This currentVersion might include migrations.
	NextVersion(from string) string

	// LatestVersion returns the newest currentVersion that has some path through the
	// graph.
	//
	// If no path exists, returns the empty string.
	//
	// If different from `NextVersion`, that means multiple steps are
	// required (i.e. a multi-phase migration, or a required stopping point
	// in a series of updates).
	LatestVersion(from string) string

	// State returns the information that is required to update to the provided
	// node.
	State(id string) State

	// Subgraph returns a new Source that is a subgraph of the current source,
	// but where `head` is set to the provided node.
	Subgraph(head string) (Source, error)
}

type State struct {
	ID        string `json:"id"`
	Tag       string `json:"tag,omitempty"`
	Migration string `json:"migration,omitempty"`
	Phase     string `json:"phase,omitempty"`
	Digest    string `json:"digest,omitempty"`
}

type UpdateGraph struct {
	Channels []Channel `json:"channels,omitempty"`
}