package buscompose

import (
	"fmt"
)

// The mesh's caps on a bucket, the same for every module: a value is a piece of state, not a file,
// and a bucket that grew without bound would be one module filling the bus's disk for everyone.
const (
	StateMaxValueBytes = 256 * 1024
)

// A Bucket is one module's declared state as the bus holds it.
type Bucket struct {
	Module string
	Name   string
	// History is how many values a key keeps; zero is one.
	History int
	// TTLSeconds is how long a value lives; zero is until replaced or deleted.
	TTLSeconds int
	// PerMachine says each machine's instance writes only the key named for its machine (novox/hq ADR
	// 0260), and is granted that key and no other.
	PerMachine bool
	// KeyTTL says the bucket allows a time to live per key (novox/hq ADR 0433 §1): its owner writes each key with its
	// own, and the server writes a delete marker, kept KeyTTLMarkerTTL, when it ends.
	KeyTTL bool
}

// BucketName is the bucket a module's state lives in: the module and the local name joined by an
// underscore, which neither may contain, so two modules can never derive one bucket.
func BucketName(module, name string) string { return module + "_" + name }

// Bucket is this bucket's name on the bus.
func (b Bucket) Bucket() string { return BucketName(b.Module, b.Name) }

// Why is carried into the server's description of the bucket, so somebody reading the server's
// own state finds whose it is and why it is kept.
func (b Bucket) Why() string {
	return fmt.Sprintf("%s's state %q (novox/hq ADR 0201): its current value per key, written by %s, "+
		"read by whatever declares it reads it; kept when %s is unassigned, because it is data",
		b.Module, b.Name, b.Module, b.Module)
}

// KeyedRead is one key of another module's state a principal reads, and no other key of it.
type KeyedRead struct {
	Read string `json:"read"`
	Key  string `json:"key"`
}

// ResolvedBucket is mesh-config's state of resolved values, keyed `<node>.<module>.<key>`.
const ResolvedBucket = "mesh-config_resolved"