package backup

import (
	"context"
	"errors"
	"fmt"
	"os"
	"os/exec"
	"path/filepath"
	"strings"
	"time"

	"gitea.dooplex.hu/admin/felhom-controller/internal/settings"
	"gitea.dooplex.hu/admin/felhom-controller/internal/system"
)

// Tier 2 = an off-drive (different physical disk) copy of an HDD app's recovery unit + bulk userdata.
// It is the ONLY off-drive protection that browsable HDD userdata can get — PBS can't reach bind
// mounts. Auto-enabled for every HDD app; the target is auto-picked: prefer another registered
// user-data drive (can hold bulk), else the internal SSD for SMALL units only — and the SSD is the
// guest rootfs (~8 GB), so we REFUSE rather than fill it (a size-aware headroom guard). When no
// off-drive target fits, we record an honest "needs a 2nd HDD" status instead of silently doing
// nothing useful.

const gibibyte = 1024 * 1024 * 1024

var (
	errNoOffDiskTarget = errors.New("no off-drive target (single drive, app already on the system disk)")
	errSSDNoHeadroom   = errors.New("the internal SSD lacks headroom for this app's data — a 2nd drive is required for off-drive backup")
)

// Tier2Target is a resolved off-drive destination for an app's Tier 2 copy.
type Tier2Target struct {
	NamespaceRoot string // felhom-data namespace root on the target drive
	Label         string // human label (UI)
	IsSystemDrive bool   // target is the internal SSD/system drive (DB/config only)
	Reason        string // why this target (Hungarian, for UI/logs)
}

// tier2FitsHeadroom reports whether a unit of unitGB fits on a system/rootfs drive while leaving a
// reserve free. Reserve = max(2 GB, 20% of total) — this is what protects the small (~8 GB) guest
// rootfs from being filled by a Tier 2 copy. Pure function (unit-tested).
func tier2FitsHeadroom(availGB, totalGB, unitGB float64) bool {
	reserve := totalGB * 0.20
	if reserve < 2.0 {
		reserve = 2.0
	}
	return (availGB - unitGB) >= reserve
}

// selectTier2Target picks the off-drive destination for an app's Tier 2 copy. A customer-pinned
// target (PreferredTarget, set from the config panel) wins when it is still valid; otherwise it
// auto-picks: another user-data drive, else the internal SSD for small units (headroom-guarded).
func (m *Manager) selectTier2Target(stackName string, unitSizeBytes int64) (*Tier2Target, error) {
	sourceDrive := m.GetAppDrivePath(stackName)
	if sourceDrive == "" {
		return nil, fmt.Errorf("no source drive for %s", stackName)
	}

	// 0. Honor a customer-pinned target if it is still valid (registered, schedulable, off-disk).
	//    An invalid pin (gone / same physical disk) silently falls through to the auto-pick.
	if m.settings != nil {
		if cd := m.settings.GetCrossDriveConfig(stackName); cd != nil && cd.PreferredTarget != "" {
			for _, sp := range m.settings.GetSchedulableStoragePaths() {
				if sp.Path != cd.PreferredTarget {
					continue
				}
				if sp.Path == sourceDrive || system.SamePhysicalDevice(sourceDrive, sp.Path) {
					break // pinned target is on the same physical disk — not off-drive; fall through
				}
				label := sp.Label
				if label == "" {
					label = filepath.Base(sp.Path)
				}
				return &Tier2Target{
					NamespaceRoot: NamespaceRoot(sp.Path, true),
					Label:         label,
					IsSystemDrive: false,
					Reason:        "kézi választás",
				}, nil
			}
		}
	}

	// 1. Prefer another registered user-data drive on a DIFFERENT physical disk (can hold bulk userdata).
	if m.settings != nil {
		for _, sp := range m.settings.GetSchedulableStoragePaths() {
			if sp.Path == sourceDrive || system.SamePhysicalDevice(sourceDrive, sp.Path) {
				continue
			}
			label := sp.Label
			if label == "" {
				label = filepath.Base(sp.Path)
			}
			return &Tier2Target{
				NamespaceRoot: NamespaceRoot(sp.Path, true), // Model A: in-guest mount IS the namespace root
				Label:         label,
				IsSystemDrive: false,
				Reason:        "másik adatmeghajtó",
			}, nil
		}
	}

	// 2. Fall back to the internal SSD (system data path) — SMALL units only.
	sys := m.systemDataPath
	if sys == "" || system.SamePhysicalDevice(sourceDrive, sys) {
		return nil, errNoOffDiskTarget // single drive / app already on the system disk
	}
	if !m.tier2FitsSystemDrive(sys, unitSizeBytes) {
		return nil, errSSDNoHeadroom // would fill the ~8 GB rootfs — refuse, don't fill
	}
	return &Tier2Target{
		NamespaceRoot: NamespaceRoot(sys, false), // system path is a real root → felhom-data appended
		Label:         "belső SSD (rendszer)",
		IsSystemDrive: true,
		Reason:        "nincs 2. adatmeghajtó — csak az adatbázis/konfiguráció fér a belső SSD-re; a nagy fájlokhoz 2. meghajtó kell",
	}, nil
}

// tier2FitsSystemDrive checks the size-aware rootfs-headroom guard for the SSD target.
func (m *Manager) tier2FitsSystemDrive(sys string, unitSizeBytes int64) bool {
	di := system.GetDiskUsage(sys)
	if di == nil {
		return false // can't determine free space → refuse (fail-closed for the rootfs)
	}
	return tier2FitsHeadroom(di.AvailGB, di.TotalGB, float64(unitSizeBytes)/gibibyte)
}

// RunTier2 makes/refreshes the off-drive copy of a single HDD app's recovery unit + userdata.
// Best-effort and idempotent (rsync mirror). Records status into settings for the UI; returns an
// error only on an actual copy failure (no valid target is a recorded status, not an error).
func (m *Manager) RunTier2(stackName string) error {
	// Customer turned Tier 2 off for this app (config panel) — skip without touching status.
	if m.settings != nil {
		if cd := m.settings.GetCrossDriveConfig(stackName); cd != nil && cd.UserDisabled {
			m.logger.Printf("[INFO] [backup] Tier 2 for %s skipped — disabled by customer", stackName)
			return nil
		}
	}
	sourceDrive := m.GetAppDrivePath(stackName)
	if sourceDrive == "" {
		return fmt.Errorf("no source drive for %s", stackName)
	}
	sourceNsRoot := m.namespaceRoot(sourceDrive)
	unitDir := RecoveryUnitPath(sourceNsRoot, stackName)
	appDataDir := AppDataDir(sourceNsRoot, stackName)
	if _, err := os.Stat(unitDir); err != nil {
		return nil // no recovery unit yet — nothing to copy
	}

	unitSize := dirSizeBytes(unitDir) + dirSizeBytes(appDataDir)

	target, err := m.selectTier2Target(stackName, unitSize)
	if err != nil {
		reason := tier2NoTargetReason(err)
		m.recordTier2NoTarget(stackName, reason)
		m.logger.Printf("[INFO] [backup] Tier 2 for %s: no off-drive target — %s", stackName, reason)
		return nil
	}
	// Defense-in-depth off-drive guard (selection already enforced it).
	if system.SamePhysicalDevice(sourceDrive, target.NamespaceRoot) {
		m.recordTier2NoTarget(stackName, "a kiválasztott cél ugyanazon a fizikai lemezen van")
		return nil
	}

	destBase := filepath.Join(target.NamespaceRoot, "backups", "secondary", stackName)
	start := time.Now()

	if err := rsyncMirror(unitDir, filepath.Join(destBase, "recovery-unit")); err != nil {
		m.recordTier2Failure(stackName, target, err)
		if m.tier2Notify != nil {
			m.tier2Notify(stackName, target.Label, time.Since(start), err)
		}
		return fmt.Errorf("tier2 rsync unit for %s: %w", stackName, err)
	}
	if _, e := os.Stat(appDataDir); e == nil {
		if err := rsyncMirror(appDataDir, filepath.Join(destBase, "appdata")); err != nil {
			m.recordTier2Failure(stackName, target, err)
			if m.tier2Notify != nil {
				m.tier2Notify(stackName, target.Label, time.Since(start), err)
			}
			return fmt.Errorf("tier2 rsync appdata for %s: %w", stackName, err)
		}
	}

	dur := time.Since(start)
	m.recordTier2Success(stackName, target, unitSize, dur)
	if m.tier2Notify != nil {
		m.tier2Notify(stackName, target.Label, dur, nil)
	}
	m.logger.Printf("[INFO] [backup] Tier 2 copied %s → %s (%s, %s)%s",
		stackName, destBase, humanizeBytes(unitSize), dur.Round(time.Second),
		map[bool]string{true: " [SSD: DB/config only]", false: ""}[target.IsSystemDrive])
	return nil
}

// RunAllTier2 runs Tier 2 for every deployed HDD app (apps whose data lives on an external drive —
// non-HDD apps live on the rootfs and are already inside the PBS whole-guest snapshot).
func (m *Manager) RunAllTier2() {
	if m.stackProvider == nil {
		return
	}
	var n int
	for _, stack := range m.stackProvider.ListDeployedStacks() {
		if m.stackProvider.GetStackHDDPath(stack.Name) == "" {
			continue // not an HDD app — its data is on the rootfs, covered by PBS
		}
		if m.settings != nil && (m.settings.IsDisconnected(m.GetAppDrivePath(stack.Name)) ||
			m.settings.IsDecommissioned(m.GetAppDrivePath(stack.Name))) {
			continue
		}
		if err := m.RunTier2(stack.Name); err != nil {
			m.logger.Printf("[WARN] [backup] Tier 2 failed for %s: %v", stack.Name, err)
		}
		n++
	}
	m.logger.Printf("[INFO] [backup] Tier 2 run complete: %d HDD app(s) processed", n)
}

// --- per-app config-panel view (drives the Tier-2 "Beállítás" page) ---

// Tier2Option is one selectable off-drive destination in the config panel.
type Tier2Option struct {
	Path  string // registered storage path (the value persisted as PreferredTarget)
	Label string // human label for the dropdown
}

// Tier2Info is the per-app Tier-2 view the config panel renders. It exposes the effective target
// (pinned or auto), whether that is the size-limited internal SSD, the honest no-target reason, and
// the off-disk drives the customer may pin — so the control is meaningful even with a single target.
type Tier2Info struct {
	IsHDDApp       bool   // false = the app lives on the rootfs (already inside the PBS whole-guest snapshot)
	SourceDrive    string // where the app's data currently lives
	Disabled       bool   // customer turned Tier 2 off
	Preferred      string // customer-pinned target path ("" = automatic)
	EffectiveLabel string // label of the target that WOULD be used right now
	EffectiveIsSSD bool   // the effective target is the internal SSD (DB/config only)
	EffectiveDesc  string // why this target (Hungarian)
	NoTarget       bool   // no off-drive target fits at all
	NoTargetReason string // honest reason when NoTarget
	Alternatives   []Tier2Option
}

// Tier2Info builds the config-panel view for one app. Read-only (no status writes).
func (m *Manager) Tier2Info(stackName string) Tier2Info {
	var info Tier2Info
	if m.stackProvider != nil {
		info.IsHDDApp = m.stackProvider.GetStackHDDPath(stackName) != ""
	}
	source := m.GetAppDrivePath(stackName)
	info.SourceDrive = source

	if m.settings != nil {
		if cd := m.settings.GetCrossDriveConfig(stackName); cd != nil {
			info.Disabled = cd.UserDisabled
			info.Preferred = cd.PreferredTarget
		}
		// Eligible alternative drives: registered, schedulable, on a DIFFERENT physical disk.
		for _, sp := range m.settings.GetSchedulableStoragePaths() {
			if sp.Path == source || system.SamePhysicalDevice(source, sp.Path) {
				continue
			}
			label := sp.Label
			if label == "" {
				label = filepath.Base(sp.Path)
			}
			info.Alternatives = append(info.Alternatives, Tier2Option{Path: sp.Path, Label: label})
		}
	}

	// Resolve what the runner WOULD pick right now (real unit size feeds the SSD headroom guard).
	sourceNsRoot := m.namespaceRoot(source)
	unitSize := dirSizeBytes(RecoveryUnitPath(sourceNsRoot, stackName)) + dirSizeBytes(AppDataDir(sourceNsRoot, stackName))
	target, err := m.selectTier2Target(stackName, unitSize)
	if err != nil {
		info.NoTarget = true
		info.NoTargetReason = tier2NoTargetReason(err)
		return info
	}
	info.EffectiveLabel = target.Label
	info.EffectiveIsSSD = target.IsSystemDrive
	info.EffectiveDesc = target.Reason
	return info
}

// --- status persistence (drives the "2. mentés" UI card) ---

// withTier2Prefs carries the customer-preference fields (UserDisabled/PreferredTarget) from any
// existing config into a freshly-built status struct, so a runner status write never clobbers them.
func (m *Manager) withTier2Prefs(stackName string, cfg *settings.CrossDriveBackup) *settings.CrossDriveBackup {
	if m.settings != nil {
		if existing := m.settings.GetCrossDriveConfig(stackName); existing != nil {
			cfg.UserDisabled = existing.UserDisabled
			cfg.PreferredTarget = existing.PreferredTarget
		}
	}
	return cfg
}

func (m *Manager) recordTier2Success(stackName string, target *Tier2Target, sizeBytes int64, dur time.Duration) {
	if m.settings == nil {
		return
	}
	_ = m.settings.SetCrossDriveConfig(stackName, m.withTier2Prefs(stackName, &settings.CrossDriveBackup{
		Enabled:         true,
		Method:          "rsync",
		DestinationPath: target.NamespaceRoot,
		Schedule:        "daily",
		LastRun:         time.Now().Format(time.RFC3339),
		LastStatus:      "ok",
		LastDuration:    dur.Round(time.Second).String(),
		LastSizeHuman:   humanizeBytes(sizeBytes),
	}))
}

func (m *Manager) recordTier2Failure(stackName string, target *Tier2Target, cause error) {
	if m.settings == nil {
		return
	}
	_ = m.settings.SetCrossDriveConfig(stackName, m.withTier2Prefs(stackName, &settings.CrossDriveBackup{
		Enabled:         true,
		Method:          "rsync",
		DestinationPath: target.NamespaceRoot,
		Schedule:        "daily",
		LastRun:         time.Now().Format(time.RFC3339),
		LastStatus:      "error",
		LastError:       cause.Error(),
	}))
}

func (m *Manager) recordTier2NoTarget(stackName, reason string) {
	if m.settings == nil {
		return
	}
	_ = m.settings.SetCrossDriveConfig(stackName, m.withTier2Prefs(stackName, &settings.CrossDriveBackup{
		Enabled:    false,
		Method:     "rsync",
		Schedule:   "daily",
		LastStatus: "no_target",
		LastError:  reason,
	}))
}

func tier2NoTargetReason(err error) string {
	switch {
	case errors.Is(err, errSSDNoHeadroom):
		return "nincs elég hely a belső SSD-n — a nagy fájlok off-drive mentéséhez 2. meghajtó (vagy távoli tárhely) szükséges"
	case errors.Is(err, errNoOffDiskTarget):
		return "nincs másik fizikai meghajtó — a 2. mentéshez 2. meghajtó szükséges"
	default:
		return err.Error()
	}
}

// --- helpers ---

// rsyncMirror mirrors src→dst with rsync -a --delete (exact copy, browsable on disk, no versioning).
func rsyncMirror(src, dst string) error {
	if err := os.MkdirAll(dst, 0755); err != nil {
		return fmt.Errorf("mkdir %s: %w", dst, err)
	}
	ctx, cancel := context.WithTimeout(context.Background(), 60*time.Minute)
	defer cancel()
	// Trailing slashes: copy the CONTENTS of src into dst.
	cmd := exec.CommandContext(ctx, "rsync", "-a", "--delete", strings.TrimRight(src, "/")+"/", strings.TrimRight(dst, "/")+"/")
	out, err := cmd.CombinedOutput()
	if err != nil {
		return fmt.Errorf("%v: %s", err, strings.TrimSpace(string(out)))
	}
	return nil
}

// dirSizeBytes returns the total size of a directory via `du -sb` (0 if absent/error).
func dirSizeBytes(dir string) int64 {
	if _, err := os.Stat(dir); err != nil {
		return 0
	}
	ctx, cancel := context.WithTimeout(context.Background(), 60*time.Second)
	defer cancel()
	out, err := exec.CommandContext(ctx, "du", "-sb", dir).Output()
	if err != nil {
		return 0
	}
	fields := strings.Fields(string(out))
	if len(fields) == 0 {
		return 0
	}
	var size int64
	if _, err := fmt.Sscanf(fields[0], "%d", &size); err != nil {
		return 0
	}
	return size
}