package stacks

import (
	"context"
	"fmt"
	"os"
	"path/filepath"
	"strconv"
	"strings"
	"time"

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

// ── The undo (09 §3 decision 15, v0.263.0) ─────────────────────────────────────────────────────────
//
// WHAT IT REPLACES. Until v0.262.1 a failed health check after `up` stopped the app and HELD it, and
// the household's only way back was a restore from a backup tier (§6.1, "THE ABORT DECISION"). Decision
// 15 replaced that: the box puts the old version back ITSELF, together with the data exactly as it was
// seconds before the update, and holds only if that undo fails too.
//
// WHY THE OLD RULING DOES NOT BIND THIS. The old version refuses to start on data the new one migrated
// (Nextcloud, docmost, RomM — §4, and the 2026-09-23 spike). The undo does not put the old image on
// migrated data: it puts back the PRE-MIGRATION data too, so the old version meets the data it knows.
// Measured by hand on docmost, romm and vikunja before a line of this was written
// (felhom.eu/documentation/audits/update-rulings-2026-09-23/ and undo-bakeoff-2026-09-23/).
//
// THE COPY IS A FOLDER COPY, chosen by the bake-off (decision 19). After the pull and just before
// `up` — where the app is stopped anyway to be recreated — every NAMED volume the app owns is copied
// with `cp -a` into a sibling volume by a helper container, which writes a finished-marker LAST. The
// dump-and-load route passed too, but an app with no database server gets no dump at all, so it would
// have needed this copy anyway.
//
// THREE RULES, each earned by a measurement:
//
//  1. FILES ON DISK ARE NEVER TOUCHED. Only named volumes are copied and put back. A bind-mounted
//     folder — photos, documents, the household's drive — is never in the copy and never moved by an
//     undo. An app whose data is only in such folders gets its old version back and nothing else.
//  2. A COPY COUNTS ONLY WITH ITS FINISHED-MARKER. Killing `docker run` does not stop the copy (the
//     container runs on — measured on docmost, undo-bakeoff docmost-60); a copy container killed
//     mid-way leaves fewer bytes and no marker. The marker is written after `cp -a` and `sync` both
//     succeed, so its presence is the only evidence the copy is whole. Pinned by
//     TestUndo_CutOffCopyIsRefusedBeforeAnythingMoves.
//  3. THE UNDO READS ITS OWN COPIES, NEVER THE RECOVERY UNIT. Measured 2026-09-23: ten seconds after
//     a hold was lifted, the unit was re-captured with the NEW definition (R-645); a pin-back that read
//     it started the new version on the restored data. The previous compose, applied definition, pin
//     AND `.felhom.yml` are kept in the stack dir until the undo is over (R-639).
//
// And the old version is checked with the OLD `.felhom.yml` probe: the new one may name a port the
// old version never answers. Pinned by TestUndo_UsesTheOldProbe.

// Undo phases and outcomes.
const (
	UpdatePhaseCopying = "copying"
	UpdatePhaseUndoing = "undoing"
	UpdatePhaseUndone  = "undone"

	// UndoState* is what a FAILED undo left the data as — carried to the hold so the household is
	// told the truth about it. "" means the undo was not attempted (an update journaled by an older
	// controller, resumed after an upgrade).
	UndoStateUntouched  = "untouched"   // the copy was unusable; nothing was put back
	UndoStateHalf       = "half"        // putting the copy back stopped part-way; the copy is kept
	UndoStateNotStarted = "not_started" // data and definition put back; the old version did not come up
)

// undoCopyLabel marks every copy volume with the app it belongs to, so a removal can find and delete
// it (a copy carries no compose-project label, deliberately: it must never be mistaken for the app's
// own volume by the backup legs or the removal's volume accounting).
const undoCopyLabel = "felhom.undo-copy-of"

// undoCopyMarker is written last into a copy volume, beside the data (never inside it).
const undoCopyMarker = "felhom-undo-complete"

// preUpdateMetaDir holds the previous .felhom.yml. A DIRECTORY, so LoadMetadata can read it; the
// syncer copies only two files into the stack dir's root and never touches a subdirectory.
const preUpdateMetaDir = "pre-update-meta"

// undoHelperImage is the helper the backup legs already use for volume tars (backup.go, restore.go),
// so no new image is introduced onto a box.
const undoHelperImage = "alpine"

// undoCopy pairs an app volume with its last-second copy.
type undoCopy struct {
	Volume string `json:"volume"`
	Copy   string `json:"copy"`
}

// UpdateUndone is app.yaml's record of the last update the box undid (decision 15: no automatic
// retry until the catalog moves; the button stays usable for a person). Written only by a
// successful undo; cleared by the next successful update.
type UpdateUndone struct {
	To  map[string]string `yaml:"to" json:"to"`
	At  string            `yaml:"at" json:"at"`
	Why string            `yaml:"why,omitempty" json:"why,omitempty"`
}

// volumeCopier is the process boundary of the undo's copy. Production is dockerVolumeCopier; tests
// inject a fake and never touch docker.
type volumeCopier interface {
	ProjectVolumes(project string) ([]string, error)
	VolumeBytes(vol string) (int64, error)
	Copy(src, dst, app string) error
	Complete(copyVol string) bool
	Restore(copyVol, vol string) error
	Remove(vol string) error
	CopiesOf(app string) []string
}

func (m *Manager) copier() volumeCopier {
	if m.undoCopier != nil {
		return m.undoCopier
	}
	return dockerVolumeCopier{m: m}
}

type dockerVolumeCopier struct{ m *Manager }

func (d dockerVolumeCopier) ProjectVolumes(project string) ([]string, error) {
	out, err := d.m.execCommand("docker", "volume", "ls", "--filter", "label=com.docker.compose.project="+project, "--format", "{{.Name}}")
	if err != nil {
		return nil, err
	}
	var vols []string
	for _, l := range strings.Split(out, "\n") {
		if l = strings.TrimSpace(l); l != "" {
			vols = append(vols, l)
		}
	}
	return vols, nil
}

func (d dockerVolumeCopier) VolumeBytes(vol string) (int64, error) {
	out, err := d.m.execCommand("docker", "run", "--rm", "-v", vol+":/v:ro", undoHelperImage, "du", "-sb", "/v")
	if err != nil {
		return 0, err
	}
	f := strings.Fields(out)
	if len(f) == 0 {
		return 0, fmt.Errorf("du printed nothing for %s", vol)
	}
	return strconv.ParseInt(f[0], 10, 64)
}

// Copy runs in the FOREGROUND so the helper container's own exit status is the answer; the marker is
// written only after cp and sync both succeed.
func (d dockerVolumeCopier) Copy(src, dst, app string) error {
	if _, err := d.m.execCommand("docker", "volume", "create", "--label", undoCopyLabel+"="+app, dst); err != nil {
		return err
	}
	_, err := d.m.execCommand("docker", "run", "--rm", "-v", src+":/from:ro", "-v", dst+":/to", undoHelperImage,
		"sh", "-c", "mkdir -p /to/data && cp -a /from/. /to/data/ && sync && touch /to/"+undoCopyMarker)
	return err
}

func (d dockerVolumeCopier) Complete(copyVol string) bool {
	_, err := d.m.execCommand("docker", "run", "--rm", "-v", copyVol+":/c:ro", undoHelperImage, "test", "-f", "/c/"+undoCopyMarker)
	return err == nil
}

// Restore empties the app's volume and copies the data back. The marker is checked again INSIDE the
// same helper, so a copy that lost it between the check and the restore is never poured in.
func (d dockerVolumeCopier) Restore(copyVol, vol string) error {
	_, err := d.m.execCommand("docker", "run", "--rm", "-v", copyVol+":/from:ro", "-v", vol+":/to", undoHelperImage,
		"sh", "-c", "test -f /from/"+undoCopyMarker+" && find /to -mindepth 1 -delete && cp -a /from/data/. /to/ && sync")
	return err
}

func (d dockerVolumeCopier) Remove(vol string) error {
	_, err := d.m.execCommand("docker", "volume", "rm", "-f", vol)
	return err
}

func (d dockerVolumeCopier) CopiesOf(app string) []string {
	out, err := d.m.execCommand("docker", "volume", "ls", "-q", "--filter", "label="+undoCopyLabel+"="+app)
	if err != nil {
		return nil
	}
	var vols []string
	for _, l := range strings.Split(out, "\n") {
		if l = strings.TrimSpace(l); l != "" {
			vols = append(vols, l)
		}
	}
	return vols
}

// undoCopyName is `<volume>.pre-update-<stamp>` — a legal Docker volume name, unique per update.
func undoCopyName(vol string, at time.Time) string {
	return vol + ".pre-update-" + at.UTC().Format("20060102T150405Z")
}

// undoMsg renders a born-as-key sentence of the update job. Hungarian, like every other sentence the
// job writes today (R-606 localises them together).
func undoMsg(key string, args ...interface{}) string { return util.Text("hu", key, args...) }

// planUndoCopies lists the app's named volumes and refuses — before anything moves — when their copy
// would breach the disk floor the update already keeps (decision 19's disk limit).
func (m *Manager) planUndoCopies(name string) ([]string, error) {
	vols, err := m.copier().ProjectVolumes(name)
	if err != nil {
		return nil, fmt.Errorf("listing the app's volumes: %w", err)
	}
	var total int64
	for _, v := range vols {
		b, err := m.copier().VolumeBytes(v)
		if err != nil {
			return nil, fmt.Errorf("sizing volume %s: %w", v, err)
		}
		total += b
	}
	needGiB := float64(total) / (1 << 30)
	if free, known := m.updateDiskFree(); known && free-needGiB < updateDiskFloorGiB {
		return nil, &undoSpaceError{need: needGiB, free: free}
	}
	m.logger.Printf("[INFO] [stacks] update %s: the undo copy will hold %d named volume(s), %.1f MiB", name, len(vols), float64(total)/(1<<20))
	return vols, nil
}

type undoSpaceError struct{ need, free float64 }

func (e *undoSpaceError) Error() string {
	return fmt.Sprintf("the undo copy needs %.2f GiB and %.2f GiB is free (floor %.0f GiB)", e.need, e.free, updateDiskFloorGiB)
}

// makeUndoCopies stops the app and copies every volume. The copies are journaled BEFORE each copy
// starts, so a power cut mid-copy leaves a journal that names every volume to clean up.
func (m *Manager) makeUndoCopies(name, dir string, env []string, vols []string, entry *updateJournalEntry) error {
	if _, err := m.updateCompose(dir, env, "stop"); err != nil {
		return fmt.Errorf("stopping the app for the copy: %w", err)
	}
	stamp := m.now()
	for _, v := range vols {
		c := undoCopy{Volume: v, Copy: undoCopyName(v, stamp)}
		entry.UndoCopies = append(entry.UndoCopies, c)
		if !m.enterUpdatePhase(name, entry, UpdatePhaseCopying) {
			return fmt.Errorf("journal write failed before copying %s", v)
		}
		t0 := time.Now()
		if err := m.copier().Copy(c.Volume, c.Copy, name); err != nil {
			return fmt.Errorf("copying %s: %w", v, err)
		}
		m.logger.Printf("[INFO] [stacks] update %s: copied %s → %s in %s", name, c.Volume, c.Copy, time.Since(t0).Round(time.Millisecond))
	}
	entry.Copied = true
	return nil
}

func (m *Manager) removeUndoCopies(name string, copies []undoCopy) {
	for _, c := range copies {
		if err := m.copier().Remove(c.Copy); err != nil {
			m.logger.Printf("[WARN] [stacks] update %s: could not remove the undo copy %s: %v", name, c.Copy, err)
		}
	}
}

// RemoveUndoCopies deletes every undo copy an app still has — the removal path's hook, so a copy kept
// by a failed undo does not outlive the app.
func (m *Manager) RemoveUndoCopies(name string) int {
	n := 0
	for _, v := range m.copier().CopiesOf(name) {
		if err := m.copier().Remove(v); err != nil {
			m.logger.Printf("[WARN] [stacks] remove %s: could not delete the undo copy %s: %v", name, v, err)
			continue
		}
		n++
	}
	return n
}

// savePreUpdateMeta keeps the previous .felhom.yml for the undo's health check.
func savePreUpdateMeta(dir string) (string, error) {
	src, err := os.ReadFile(filepath.Join(dir, ".felhom.yml"))
	if err != nil {
		return "", err
	}
	md := filepath.Join(dir, preUpdateMetaDir)
	if err := os.MkdirAll(md, 0o755); err != nil {
		return "", err
	}
	return md, os.WriteFile(filepath.Join(md, ".felhom.yml"), src, 0o644)
}

func (m *Manager) undoHealth(ctx context.Context, name string, timeout time.Duration, meta *Metadata) (bool, string) {
	if m.updateUndoHealthFn != nil {
		return m.updateUndoHealthFn(ctx, name, timeout, meta)
	}
	// A test that injects only the update's health seam gets the same answer for the undo (production
	// injects neither and always takes waitUpdateHealthyMeta).
	if m.updateHealthFn != nil {
		return m.updateHealthFn(ctx, name, timeout)
	}
	return m.waitUpdateHealthyMeta(ctx, name, timeout, meta)
}

// tryUndo puts the pre-update data and definition back and checks the old version with its own probe.
// It returns "" when the app is healthy on its old version again, else the state the data is in.
//
// ORDER IS THE DESIGN: every copy is validated BEFORE any is poured back (a cut-off copy leaves the
// data exactly as the new version left it — UndoStateUntouched); the definition is put back only after
// the data (so a failure in between reads "half" with the pin still naming the new version, which is
// what ran on that data).
func (m *Manager) tryUndo(ctx context.Context, name, dir, why string, entry *updateJournalEntry) string {
	start := m.now()
	if !m.enterUpdatePhase(name, entry, UpdatePhaseUndoing) {
		m.logger.Printf("[ERROR] [stacks] update %s: could not journal the undo — undoing anyway", name)
	}
	m.logger.Printf("[WARN] [stacks] update %s: UNDO — putting back the previous version and its %d volume copy(ies) (reason: %s)", name, len(entry.UndoCopies), why)
	if _, err := m.updateCompose(dir, m.stackEnv(dir), "down"); err != nil {
		m.logger.Printf("[ERROR] [stacks] update %s: stopping the new version before the undo failed: %v", name, err)
	}
	for _, c := range entry.UndoCopies {
		if !m.copier().Complete(c.Copy) {
			m.logger.Printf("[ERROR] [stacks] update %s: the undo copy %s has no finished-marker — it is cut off or missing; NOTHING is put back", name, c.Copy)
			return UndoStateUntouched
		}
	}
	for _, c := range entry.UndoCopies {
		if err := m.copier().Restore(c.Copy, c.Volume); err != nil {
			m.logger.Printf("[ERROR] [stacks] update %s: putting %s back from %s FAILED: %v — the data is mixed; the copies are kept", name, c.Volume, c.Copy, err)
			return UndoStateHalf
		}
	}
	m.restoreDefinition(name, dir, *entry)
	env := m.stackEnv(dir)
	if _, err := m.updateCompose(dir, env, "up", "-d", "--remove-orphans"); err != nil {
		m.logger.Printf("[ERROR] [stacks] update %s: starting the previous version failed: %v", name, err)
		m.captureHoldLogs(name, dir, env)
		_, _ = m.updateCompose(dir, env, "down")
		return UndoStateNotStarted
	}
	meta := LoadMetadata(dir)
	if entry.PrevMeta != "" {
		if _, err := os.Stat(filepath.Join(entry.PrevMeta, ".felhom.yml")); err == nil {
			meta = LoadMetadata(entry.PrevMeta)
		} else {
			m.logger.Printf("[WARN] [stacks] update %s: the previous .felhom.yml is missing (%v) — checking with the current one", name, err)
		}
	}
	healthy, detail := m.undoHealth(ctx, name, m.healthTimeout(), &meta)
	if !healthy {
		m.logger.Printf("[ERROR] [stacks] update %s: the previous version did not come up after the undo: %s", name, detail)
		m.captureHoldLogs(name, dir, env)
		_, _ = m.updateCompose(dir, env, "down")
		return UndoStateNotStarted
	}

	m.recordInstalledImages(name, dir, env)
	m.removeUndoCopies(name, entry.UndoCopies)
	m.recordUpdateUndone(name, dir, &UpdateUndone{To: entry.NewPin, At: start.UTC().Format(time.RFC3339), Why: why})
	m.removePreUpdateCopies(dir)
	_ = m.RefreshStatus()
	m.clearJournal(name)
	m.finishUpdate(name, UpdatePhaseUndone, "")
	m.logger.Printf("[INFO] [stacks] update %s: UNDONE in %s — the previous version is running on the data from before the update (%s)", name, m.now().Sub(start).Round(time.Second), detail)
	return ""
}

// recordUpdateUndone writes (or, with nil, clears) app.yaml's last_update_undone. A failed write is
// logged and never fails the undo — it is a record, and the app is already back.
func (m *Manager) recordUpdateUndone(name, dir string, u *UpdateUndone) {
	cfg := LoadAppConfig(dir)
	if cfg == nil || (u == nil && cfg.LastUpdateUndone == nil) {
		return
	}
	cfg.LastUpdateUndone = u
	meta := LoadMetadata(dir)
	if err := SaveAppConfig(dir, cfg, m.encKey, SensitiveEnvVars(&meta)); err != nil {
		m.logger.Printf("[ERROR] [stacks] update %s: recording last_update_undone failed: %v", name, err)
		return
	}
	m.mu.Lock()
	if st, ok := m.stacks[name]; ok && st.AppConfig != nil {
		st.AppConfig.LastUpdateUndone = u
	}
	m.mu.Unlock()
}