package backup

import (
	"context"
	"encoding/json"
	"errors"
	"sort"
	"time"
)

// R-193 Part 3 — WHAT IS IN THERE. After a successful unlock the customer is shown the contents of the
// repository they just opened: which apps, from when, how big.
//
// READ-ONLY, AND THAT IS THE POINT. This restores nothing, puts nothing back, and compares nothing
// against live data. Unlocking and restoring are separate (operator ruling, 2026-08-05): restore is
// already per-app and already lives in the backups area, and a screen that unlocks and then offers to
// overwrite is two decisions wearing one button.
//
// WHY A LISTING AT ALL, rather than a success message: "unlocked" with nothing shown is
// indistinguishable from having unlocked an EMPTY store, and the customer has no way to tell whether
// what came back is the right thing. Seeing their own app names and dates is how they know.

// errNoOffsiteTarget is returned when the repository cannot even be addressed — no off-site target is
// configured on this box yet. Distinguished from a read failure because the remedy differs: this one
// resolves by itself once the tier is re-applied.
var errNoOffsiteTarget = errors.New("no off-site target is configured on this box yet")

// ErrNoOffsiteTarget reports whether err is the not-yet-configured case, so a caller can say the right
// thing rather than showing a generic failure.
func ErrNoOffsiteTarget(err error) bool { return errors.Is(err, errNoOffsiteTarget) }

// OffsiteInventoryApp is one app's presence in the opened repository. Non-secret throughout.
type OffsiteInventoryApp struct {
	App       string    // the restic tag == the stack name
	LatestAt  time.Time // the newest snapshot's time for this app
	SizeBytes int64     // restore size of that newest snapshot (0 = could not be determined)
}

// OffsiteInventory is the whole answer, including the EMPTY case stated explicitly.
type OffsiteInventory struct {
	Apps []OffsiteInventoryApp
	// Empty is true when the repository opened cleanly and holds no snapshots. It is a real and
	// confusing outcome — a bare list there reads as a broken page — so it is named rather than
	// inferred from len(Apps)==0, which is also what a failed read looks like.
	Empty bool
}

// OffsiteInventoryList opens the repository and reports what is in it, grouped per app. One
// `snapshots --json` call for the whole repo, then one `stats` per app for the newest snapshot's size.
//
// A per-app size failure is NOT fatal: the app is still listed, with SizeBytes 0, because knowing an
// app is in there matters more than knowing how big it is, and dropping it would under-report the
// customer's own data.
func (m *Manager) OffsiteInventoryList(ctx context.Context) (OffsiteInventory, error) {
	var inv OffsiteInventory
	// A box can hold a recovered key and still have no off-site COORDINATES — the pristine rebuilt
	// shape, before its target is re-applied. Reading the repository is impossible then, and saying so
	// is the honest answer; without this guard offboxBaseArgs nil-derefs on the missing target.
	if !m.OffboxConfigured() {
		return inv, errNoOffsiteTarget
	}
	t := m.settings.GetOffboxTarget()
	base, env := m.offboxBaseArgs(t)
	sctx, cancel := context.WithTimeout(ctx, offboxProbeTimeout)
	defer cancel()
	out, err := m.runner()(sctx, env, append(append([]string{}, base...), "snapshots", "--json")...)
	if err != nil {
		return inv, err
	}
	var snaps []struct {
		ShortID string    `json:"short_id"`
		ID      string    `json:"id"`
		Time    time.Time `json:"time"`
		Tags    []string  `json:"tags"`
	}
	if uerr := json.Unmarshal(out, &snaps); uerr != nil {
		return inv, uerr
	}
	if len(snaps) == 0 {
		inv.Empty = true
		return inv, nil
	}
	// Newest snapshot per tag. A snapshot may carry several tags; each names an app it belongs to.
	newest := map[string]struct {
		id string
		at time.Time
	}{}
	for _, s := range snaps {
		id := s.ShortID
		if id == "" {
			id = s.ID
		}
		for _, tag := range s.Tags {
			if tag == "" {
				continue
			}
			if cur, ok := newest[tag]; !ok || s.Time.After(cur.at) {
				newest[tag] = struct {
					id string
					at time.Time
				}{id: id, at: s.Time}
			}
		}
	}
	if len(newest) == 0 {
		// Snapshots exist but carry no tags — not "empty", and saying so would be a lie. Report an
		// empty app list without the Empty flag; the page renders the honest in-between wording.
		return inv, nil
	}
	for tag, n := range newest {
		app := OffsiteInventoryApp{App: tag, LatestAt: n.at}
		if size, serr := m.offboxSnapshotSize(ctx, n.id); serr == nil {
			app.SizeBytes = size
		} else {
			m.logger.Printf("[WARN] [offbox] inventory: size of %s's newest snapshot unknown: %v (listing it anyway)", tag, serr)
		}
		inv.Apps = append(inv.Apps, app)
	}
	sort.Slice(inv.Apps, func(i, j int) bool { return inv.Apps[i].App < inv.Apps[j].App })
	return inv, nil
}

// HumanizeBytes exposes the shared byte formatter to the web layer so the recovery page renders sizes
// the same way every other surface does.
func HumanizeBytes(n int64) string { return humanizeBytes(n) }