package backupgood

import (
	"encoding/json"
	"fmt"
	"time"
)

// **Each item's last good night** (novox/hq ADR 0571 clause 3, ADR 0564 §6; the lead, 2026-10-29): the node-backup holder
// restic keeps, from its tools bundle through the runtime on the night's file event (its night's process runs as the
// operator's account and holds no bus account, ADR 0436 §1-2), its own state `good`, one key `<node>.<module>.<item>` for every item a module
// declares that a backup path covers, written when it changes: the item, the path whose snapshot keeps it and the newest
// good night of its module (zero before the first). The self-check's probe of a stale backup reads it there. The package is restic's own, published by its series (ADR 0634 §4); the readers import it.
const (
	ResticModule = "restic"
	GoodState    = "good"
	GoodBucket   = ResticModule + "_" + GoodState
	GoodRead     = ResticModule + "." + GoodState
	GoodVersion  = 1
)

// GoodRow is one key of restic's `good`.
type GoodRow struct {
	V         int       `json:"v"`
	Node      string    `json:"node"`
	Module    string    `json:"module"`
	Item      string    `json:"item"`
	CoveredBy string    `json:"covered_by"`
	LastGood  time.Time `json:"last_good,omitzero"`
}

// GoodKey is a row's key: `<node>.<module>.<item>`, as a disk-load reading's.
func GoodKey(node, module, item string) string { return node + "." + module + "." + item }

// DecodeGoodRow reads a row; it refuses another version.
func DecodeGoodRow(raw []byte) (GoodRow, error) {
	var g GoodRow
	if err := json.Unmarshal(raw, &g); err != nil {
		return GoodRow{}, fmt.Errorf("backupgood: a last good night is not readable: %w", err)
	}
	if g.V != GoodVersion {
		return GoodRow{}, fmt.Errorf("backupgood: a last good night of version %d, and this reads %d", g.V, GoodVersion)
	}
	return g, nil
}