package backup

import (
	"context"
	"encoding/json"
	"fmt"
	"os"
	"os/exec"
	"path/filepath"
	"strings"
	"time"
)

// Offsite restore rework (Task 3a §7). With mandatory userdata now in snapshots, restore needs three
// changes over the old dump-to-rootfs-scratch:
//   1. scratch relocated off the ~8 GB guest rootfs onto a data drive, behind a headroom gate (F-A1);
//   2. a unit-only DEFAULT restore (`--include <absolute-unit-path>`, SP-3.2) — full is a deliberate,
//      size-gated second action;
//   3. place-to-live = a missing-only merge (never --delete) so the SQ3 immich case is restorable
//      from offsite alone.
// ID-first everywhere (§3): `restic stats --tag` is UNPROVEN on 0.14.0, so the size lookup resolves the
// snapshot ID via `snapshots latest --tag` and calls `stats <ID>`.

const (
	// offboxUnitOnlyFreeFloor — a unit-only restore needs at least this much free on the scratch drive.
	// Catalog recovery units are MB–1 GB (SQ4); 2 GiB is a safe floor without a per-snapshot size probe.
	offboxUnitOnlyFreeFloor = int64(2) << 30
)

// SetOffboxFreeFn overrides the restore free-space probe (tests; the Windows go-test host has no df).
func (m *Manager) SetOffboxFreeFn(fn func(path string) int64) { m.offboxFreeFn = fn }

// offboxFree returns the free-space probe (nil seam → the real diskFreeBytes).
func (m *Manager) offboxFree() func(string) int64 {
	if m.offboxFreeFn != nil {
		return m.offboxFreeFn
	}
	return diskFreeBytes
}

// diskFreeBytes returns available bytes on the filesystem holding path (0 on any error). Mirrors
// appexport.DiskFree; kept local so the backup package needs no cross-package dependency.
func diskFreeBytes(path string) int64 {
	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
	defer cancel()
	out, err := exec.CommandContext(ctx, "df", "--output=avail", "-B1", path).Output()
	if err != nil {
		return 0
	}
	lines := strings.Split(strings.TrimSpace(string(out)), "\n")
	if len(lines) < 2 {
		return 0
	}
	var size int64
	fmt.Sscanf(strings.TrimSpace(lines[1]), "%d", &size)
	return size
}

// offboxUnitPathOf returns the snapshot path that is the recovery unit for stack (suffix
// backups/primary/<stack>), or "" if none is present.
func offboxUnitPathOf(paths []string, stack string) string {
	suffix := "/backups/primary/" + stack
	for _, p := range paths {
		if strings.HasSuffix(p, suffix) {
			return p
		}
	}
	return ""
}

// offboxLatestSnapshot resolves the newest snapshot for stack: its short ID + captured paths, via
// `snapshots latest --tag <stack> --json`. When the tag spans more than one group (old unit-only shape
// + new enlarged shape), it returns the newest by time.
func (m *Manager) offboxLatestSnapshot(ctx context.Context, stack string) (id string, paths []string, err error) {
	t := m.settings.GetOffboxTarget()
	base, env := m.offboxBaseArgs(t)
	sctx, cancel := context.WithTimeout(ctx, offboxProbeTimeout)
	defer cancel()
	out, serr := m.runner()(sctx, env, append(append([]string{}, base...), "snapshots", "latest", "--tag", stack, "--json")...)
	if serr != nil {
		return "", nil, fmt.Errorf("offbox snapshots %s: %w: %s", stack, serr, truncate(out))
	}
	var snaps []struct {
		ShortID string    `json:"short_id"`
		ID      string    `json:"id"`
		Time    time.Time `json:"time"`
		Paths   []string  `json:"paths"`
	}
	if json.Unmarshal(out, &snaps) != nil || len(snaps) == 0 {
		return "", nil, fmt.Errorf("offbox: nincs pillanatkép a(z) %s alkalmazáshoz", stack)
	}
	best := 0
	for i := 1; i < len(snaps); i++ {
		if snaps[i].Time.After(snaps[best].Time) {
			best = i
		}
	}
	id = snaps[best].ShortID
	if id == "" {
		id = snaps[best].ID
	}
	return id, snaps[best].Paths, nil
}

// offboxSnapshotSize returns the restore-size (logical bytes) of ONE snapshot via `stats <ID> --json`
// (default mode — for a single snapshot ID this is exactly that snapshot's on-disk-when-restored size,
// the correct headroom meaning; SP-1). ID-first: never `stats --tag` (unproven on 0.14.0).
func (m *Manager) offboxSnapshotSize(ctx context.Context, id string) (int64, error) {
	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...), "stats", id, "--json")...)
	if err != nil {
		return 0, fmt.Errorf("offbox stats %s: %w: %s", id, err, truncate(out))
	}
	var st struct {
		TotalSize int64 `json:"total_size"`
	}
	if json.Unmarshal(out, &st) != nil || st.TotalSize <= 0 {
		return 0, fmt.Errorf("offbox: a(z) %s pillanatkép mérete ismeretlen", id)
	}
	return st.TotalSize, nil
}

// offboxRestoreScratchDir returns the on-DATA-DRIVE scratch dir for an app's offsite restore
// (<nsRoot>/backups/offsite-restore/<app>) plus the namespace root (an existing dir, for the free-space
// probe). NEVER cfg.Paths.DataDir (the rootfs — the F-A1 filler). App's HDD drive first; else the first
// schedulable storage path; else a Hungarian refusal.
func (m *Manager) offboxRestoreScratchDir(stack string) (scratch, nsRoot string, err error) {
	// offsiteRestoreRootFor is THE place `backups/offsite-restore` is spelled (offbox_verify_copies.go)
	// — the listing/delete surface must resolve byte-identical paths to the ones written here.
	scratchFor := func(root string) (string, string) {
		return filepath.Join(m.offsiteRestoreRootFor(root), stack), m.namespaceRoot(root)
	}
	isNet := func(path string) bool { return m.settings != nil && m.settings.IsNetworkStoragePath(path) }
	// (1) the app's own drive — preferred, but ONLY if it is not NETWORK storage (F-3afix-1). restic
	//     restores uid/gid/setgid fully onto a LOCAL fs (SP-3.3); a squashed network scratch would feed
	//     PlaceOffsiteRestore wrong-owner files — the F-6C-1 silently-broken-restore class, offsite-side.
	if m.stackProvider != nil {
		if hdd := strings.TrimSpace(m.stackProvider.GetStackHDDPath(stack)); hdd != "" && !isNet(hdd) {
			s, nr := scratchFor(hdd)
			return s, nr, nil
		}
	}
	// (2) the first NON-network schedulable path.
	if m.settings != nil {
		for _, sp := range m.settings.GetSchedulableStoragePaths() {
			if strings.TrimSpace(sp.Path) != "" && !sp.IsNetwork() {
				s, nr := scratchFor(sp.Path)
				return s, nr, nil
			}
		}
		// (3) last resort ONLY: any schedulable path, with a loud WARN — a network scratch cannot
		//     guarantee ownership fidelity under root_squash.
		for _, sp := range m.settings.GetSchedulableStoragePaths() {
			if strings.TrimSpace(sp.Path) != "" {
				m.logger.Printf("[WARN] [offbox] %s: restore scratch on network storage %s — ownership fidelity not guaranteed under squash", stack, sp.Path)
				s, nr := scratchFor(sp.Path)
				return s, nr, nil
			}
		}
	}
	return "", "", fmt.Errorf("nincs elérhető adatmeghajtó a visszaállításhoz")
}

// RestoreOffboxScratch restores an app's latest offsite snapshot to an on-data-drive scratch dir
// (non-destructive — never overwrites live data). full=false (the default) restores the recovery UNIT
// only (`--include <absolute-unit-path>`, SP-3.2); full=true restores the whole snapshot (unit +
// mandatory userdata) behind a size×1.1 headroom gate. Fail-closed: an unknown snapshot size refuses a
// full restore.
func (m *Manager) RestoreOffboxScratch(ctx context.Context, stack string, full bool) error {
	if !m.OffboxConfigured() {
		return fmt.Errorf("off-box backup not configured")
	}
	if !isSafeStackName(stack) {
		return fmt.Errorf("invalid stack name")
	}
	id, paths, err := m.offboxLatestSnapshot(ctx, stack)
	if err != nil {
		return err
	}
	unitPath := offboxUnitPathOf(paths, stack)
	if unitPath == "" {
		return fmt.Errorf("a(z) %s pillanatképében nincs mentési egység — a visszaállítás nem indítható", stack)
	}
	scratch, nsRoot, err := m.offboxRestoreScratchDir(stack)
	if err != nil {
		return err
	}
	// Headroom gate (F-A1) — probed on the namespace root (an existing dir).
	free := m.offboxFree()(nsRoot)
	if full {
		size, serr := m.offboxSnapshotSize(ctx, id)
		if serr != nil {
			// SizeUnknown never renders as fits — fail closed.
			return fmt.Errorf("A mentés mérete nem állapítható meg — a teljes visszaállítás biztonsági okból nem indítható.")
		}
		need := size + size/10 // ×1.1
		if free < need {
			return fmt.Errorf("Nincs elég szabad hely a visszaállításhoz (%s szükséges, %s szabad).", humanizeBytes(need), humanizeBytes(free))
		}
	} else if free < offboxUnitOnlyFreeFloor {
		return fmt.Errorf("Nincs elég szabad hely a visszaállításhoz (%s szükséges, %s szabad).", humanizeBytes(offboxUnitOnlyFreeFloor), humanizeBytes(free))
	}
	// F-A1 hygiene: drop the legacy rootfs scratch (DataDir/offbox-restore/<app>) best-effort.
	legacy := filepath.Join(m.cfg.Paths.DataDir, "offbox-restore", stack)
	if _, sErr := os.Stat(legacy); sErr == nil {
		if rmErr := os.RemoveAll(legacy); rmErr != nil {
			m.logger.Printf("[WARN] [offbox] could not remove legacy rootfs restore scratch %s: %v", legacy, rmErr)
		} else {
			m.logger.Printf("[INFO] [offbox] removed legacy rootfs restore scratch %s", legacy)
		}
	}
	if err := os.MkdirAll(scratch, 0o755); err != nil {
		return fmt.Errorf("restore dir: %w", err)
	}
	t := m.settings.GetOffboxTarget()
	base, env := m.offboxBaseArgs(t)
	rctx, cancel := context.WithTimeout(ctx, offboxBackupTimeout)
	defer cancel()
	m.unlockStale(rctx, base, env) // pre-restore hygiene
	args := []string{"restore", id, "--target", scratch}
	if !full {
		args = append(args, "--include", unitPath) // SP-3.2: absolute snapshot unit path = unit-only
	}
	out, rerr := m.resticStep(rctx, env, base, "restore:"+stack, args...)
	if rerr != nil {
		return fmt.Errorf("offbox restore %s: %w: %s", stack, rerr, truncate(out))
	}
	m.logger.Printf("[INFO] [offbox] restored %s (%s, full=%v) → %s", stack, id, full, scratch)
	return nil
}

// OffboxRestorePrepareFull resolves the latest snapshot's restore-size and verifies scratch headroom
// for a FULL restore WITHOUT starting it (the two-step size-first gate). Returns the human size on
// success, or a Hungarian error to flash on refusal (size unknown / no headroom — fail-closed).
func (m *Manager) OffboxRestorePrepareFull(ctx context.Context, stack string) (string, error) {
	if !m.OffboxConfigured() {
		return "", fmt.Errorf("off-box backup not configured")
	}
	if !isSafeStackName(stack) {
		return "", fmt.Errorf("invalid stack name")
	}
	id, _, err := m.offboxLatestSnapshot(ctx, stack)
	if err != nil {
		return "", err
	}
	size, serr := m.offboxSnapshotSize(ctx, id)
	if serr != nil {
		return "", fmt.Errorf("A mentés mérete nem állapítható meg — a teljes visszaállítás biztonsági okból nem indítható.")
	}
	_, nsRoot, derr := m.offboxRestoreScratchDir(stack)
	if derr != nil {
		return "", derr
	}
	need := size + size/10
	if free := m.offboxFree()(nsRoot); free < need {
		return "", fmt.Errorf("Nincs elég szabad hely a visszaállításhoz (%s szükséges, %s szabad).", humanizeBytes(need), humanizeBytes(free))
	}
	return humanizeBytes(size), nil
}

// OffboxFullScratchReady reports whether a (non-empty) full-restore scratch exists for stack — the gate
// for showing the place-to-live action. PlaceOffsiteRestore re-validates per-path completeness.
func (m *Manager) OffboxFullScratchReady(stack string) bool {
	if !isSafeStackName(stack) {
		return false
	}
	scratch, _, err := m.offboxRestoreScratchDir(stack)
	if err != nil {
		return false
	}
	if fi, sErr := os.Stat(scratch); sErr != nil || !fi.IsDir() {
		return false
	}
	entries, _ := os.ReadDir(scratch)
	return len(entries) > 0
}

// placement is one source→dest pair for place-to-live: src is the reconstructed absolute path under the
// scratch (SP-3.1), dst is the live location under the app's current namespace root.
type placement struct {
	src    string
	dst    string
	isUnit bool
}

// mapOffsiteRestorePaths maps a completed full-scratch restore to live placements (pure). The anchor
// oldNs is derived by trimming backups/primary/<stack> off the unit path (the snapshot may come from a
// DIFFERENT drive after churn — liveNsRoot is where it goes). Refuses the WHOLE placement (no partial
// writes) on: no unit path; a path outside oldNs (escape); a `..` segment; a non-unit path in the
// reserved backups/ zone.
func mapOffsiteRestorePaths(snapPaths []string, stack, scratch, liveNsRoot string) ([]placement, error) {
	unitSuffix := "/backups/primary/" + stack
	oldNs := ""
	for _, p := range snapPaths {
		if strings.HasSuffix(p, unitSuffix) {
			oldNs = strings.TrimSuffix(p, unitSuffix)
			break
		}
	}
	if oldNs == "" {
		return nil, fmt.Errorf("a pillanatképben nincs mentési egység (backups/primary/%s)", stack)
	}
	out := make([]placement, 0, len(snapPaths))
	for _, p := range snapPaths {
		// Every captured path must be a STRICT descendant of oldNs. Requiring the trailing "/" also
		// catches p == oldNs (the namespace root itself — F-3a-3), which would otherwise map to a junk
		// placement nesting the whole old namespace under the live root.
		if !strings.HasPrefix(p, oldNs+"/") {
			return nil, fmt.Errorf("a pillanatkép egy útvonala a névtéren kívülre mutat: %s", p)
		}
		rel := strings.TrimPrefix(p, oldNs+"/")
		for _, seg := range strings.Split(rel, "/") {
			if seg == ".." {
				return nil, fmt.Errorf("a pillanatkép egy útvonala érvénytelen (..): %s", p)
			}
		}
		isUnit := rel == "backups/primary/"+stack
		if !isUnit && (rel == "backups" || strings.HasPrefix(rel, "backups/")) {
			return nil, fmt.Errorf("nem-egység útvonal a fenntartott backups zónában: %s", p)
		}
		out = append(out, placement{
			src:    filepath.Join(scratch, p), // SP-3.1: abs source reconstructed under the target
			dst:    filepath.Join(liveNsRoot, rel),
			isUnit: isUnit,
		})
	}
	return out, nil
}

// placeCopier returns the place-to-live missing-only merge (nil seam → rsyncRestoreMissing, the
// `-a --ignore-existing` additive copy). NEVER rsyncMirror (--delete).
func (m *Manager) placeCopier() func(src, dst string) (int, error) {
	if m.offboxPlaceCopier != nil {
		return m.offboxPlaceCopier
	}
	return rsyncRestoreMissing
}

// PlaceOffsiteRestore places a COMPLETED full-scratch restore into the app's live locations via a
// missing-only merge (§7.3), so the SQ3 immich case is restorable from offsite alone. The recovery
// unit is placed ONLY if the live unit is ABSENT (never overwrites a local unit); every other path is
// merged missing-only. Does NOT deploy/start anything — RecreateStackFromUnit / the restore flow owns
// that. Single-flight. Requires a completed full scratch (deterministic path + existence check).
func (m *Manager) PlaceOffsiteRestore(ctx context.Context, stack string) error {
	if !m.OffboxConfigured() {
		return fmt.Errorf("off-box backup not configured")
	}
	if !isSafeStackName(stack) {
		return fmt.Errorf("invalid stack name")
	}
	if err := m.acquireRunning(); err != nil {
		return fmt.Errorf("egy másik mentési/visszaállítási művelet már fut")
	}
	defer m.releaseRunning()

	scratch, _, err := m.offboxRestoreScratchDir(stack)
	if err != nil {
		return err
	}
	if _, sErr := os.Stat(scratch); sErr != nil {
		return fmt.Errorf("nincs előkészített teljes visszaállítás — futtass előbb egy teljes visszaállítást")
	}
	id, paths, err := m.offboxLatestSnapshot(ctx, stack)
	if err != nil {
		return err
	}
	_ = id
	// F-3a-1a: the live target uses the RAW HDD path (mirrors offboxCaptureSet). NOT AppNamespaceRoot —
	// its systemDataPath fallback would merge userdata onto the SSD system namespace. Empty HDD ⇒
	// undeployed ⇒ refuse: the app must be restored first, then its data placed under its live drive.
	hdd := ""
	if m.stackProvider != nil {
		hdd = strings.TrimSpace(m.stackProvider.GetStackHDDPath(stack))
	}
	if hdd == "" {
		return fmt.Errorf("a(z) %s nincs telepítve — előbb állítsd helyre az alkalmazást, utána az adatokat", stack)
	}
	liveNs := m.namespaceRoot(hdd)
	// F-3a-1b: headroom gate — a missing-only merge copies at most the scratch size; refuse before any
	// copy if the live drive lacks that (conservative — scratch and live often share a drive).
	if free, need := m.offboxFree()(liveNs), m.offboxSize()(scratch); free < need {
		return fmt.Errorf("Nincs elég szabad hely a visszaállításhoz (%s szükséges, %s szabad).", humanizeBytes(need), humanizeBytes(free))
	}
	placements, err := mapOffsiteRestorePaths(paths, stack, scratch, liveNs)
	if err != nil {
		return err // whole-placement refusal (no partial writes)
	}
	// F-3a-4: stat pre-pass over EVERY placement BEFORE the first copy — an incomplete scratch (e.g. a
	// unit-only restore, userdata srcs absent) refuses with ZERO copies, making "no partial writes" true.
	for _, pl := range placements {
		if _, sErr := os.Stat(pl.src); sErr != nil {
			return fmt.Errorf("a teljes visszaállítás hiányos (%s nincs meg) — futtass előbb egy teljes visszaállítást", filepath.Base(pl.src))
		}
	}
	copier := m.placeCopier()
	var placed int
	for _, pl := range placements {
		if pl.isUnit {
			if _, liveErr := os.Stat(pl.dst); liveErr == nil {
				m.logger.Printf("[INFO] [offbox] place %s: live recovery unit present — not overwriting", stack)
				continue // never overwrite a local unit
			}
		}
		n, cErr := copier(pl.src, pl.dst)
		if cErr != nil {
			return fmt.Errorf("a(z) %s helyreállítása sikertelen: %w", stack, cErr) // scratch KEPT for retry
		}
		placed += n
	}
	// F-3a-2: on FULL success, remove the scratch best-effort (OffboxFullScratchReady then turns false →
	// the place button disappears). A failed placement returned above, keeping the scratch for a retry.
	if rmErr := os.RemoveAll(scratch); rmErr != nil {
		m.logger.Printf("[WARN] [offbox] place %s: scratch cleanup failed (harmless): %v", stack, rmErr)
	} else {
		m.logger.Printf("[INFO] [offbox] place %s: scratch removed after successful placement", stack)
	}
	m.logger.Printf("[INFO] [offbox] placed %s from offsite scratch: %d file(s) merged (missing-only)", stack, placed)
	return nil
}