package stacks

import (
	"fmt"
	"sort"
	"strings"

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

// ── Controller image retention (R-745, `09` §3 decision 56) ───────────────────────────────────────────
//
// Decision 53's app sweep never touches the controller's own repository (deleteUnkeptImages skips it), so every
// release a box ever ran stayed: ~80 controller images on demo-hp's guest on 2026-10-01. The ruling: a box keeps the
// controller image it RUNS and the one BEFORE it; older ones are deleted by the same in-use rule as decision 53.
//
// MEASURED before building (2026-10-01, `audits/rulings-2026-10-01/B/`):
//   - the agent's swap rolls back to whatever /etc/felhom-controller-image named when the swap began — the RUNNING
//     image (felhom-agent internal/localapi/controllerswap.go Swap/rollback). The controller does NOT hand it a
//     previous image; SwapController carries the target only. So the self-update's own roll-back needs only the
//     running image, which a container uses and is never a candidate. "The previous" is kept for a hand roll-back.
//   - the bootstrap unit `docker run`s the image the file names at every guest boot; the file always names the
//     running image after a swap (done or rolled back). The golden's baked image is the running one until the first
//     swap, and nothing reads it after that.
//   - a whole-guest restore brings /var/lib/docker back with the guest (mp0 backup=1), so the image it ran then.
//
// THE KEEP SET (rebuilt at every pass): every image a container uses (the running controller among them); the tag
// of the running version; the PREVIOUS — the self-update's own record (update-state.json previous_image of a swap
// that ended on the running version), or, when there is no such record or its image is gone, the highest version
// below the running one (logged as "by version order"); every version ABOVE the running one (a pulled target the
// swap has not taken yet); every tag that is not a plain X.Y.Z (latest, -rc) — left alone, logged. A candidate is an
// untagged (<none>) controller image or one whose every tag is a version below the previous. Deleted by exact
// name/ID, never forced, never by prune; an ID that also carries another repository's name is left alone. NOTHING is
// deleted while the controller is swapping itself (selfUpdatingNow). Registry tags are never touched.
// Pinned by internal/stacks/controller_image_retention_test.go.

// ControllerImageRecord is what the caller knows about the controller's own images.
type ControllerImageRecord struct {
	Repo     string // the controller repository, no tag (cfg.SelfUpdate.Image)
	Running  string // this process's version
	Previous string // the self-update's record: the image before Running ("" when none)
}

// RetainControllerImages applies decision 56 once. Returns the names it deleted.
func (m *Manager) RetainControllerImages(rec ControllerImageRecord) ([]string, error) {
	imageRetentionMu.Lock()
	defer imageRetentionMu.Unlock()
	running, err := util.ParseVersion(rec.Running)
	if err != nil || rec.Repo == "" {
		m.logger.Printf("[INFO] [stacks] controller image retention: skipped — running version %q is not a release (or no repository)", rec.Running)
		return nil, nil
	}
	if m.selfUpdatingNow() {
		m.logger.Printf("[INFO] [stacks] controller image retention: skipped — the controller is swapping itself (the target it pulled is named by nothing yet)")
		return nil, nil
	}
	imgs, err := listLocalImages()
	if err != nil {
		return nil, err
	}
	used, err := imagesUsedByContainers()
	if err != nil {
		m.logger.Printf("[WARN] [stacks] controller image retention: the containers could not be read (%v) — NOTHING is deleted", err)
		return nil, err
	}
	repo := normRepo(rec.Repo)
	byID := map[string][]localImage{}
	for _, im := range imgs {
		byID[im.ID] = append(byID[im.ID], im)
	}

	// The previous: the swap's own record first, version order only when the record names nothing present.
	prevTag, prevHow := "", ""
	if rec.Previous != "" {
		if r, t, _ := splitRepoTag(rec.Previous); normRepo(r) == repo {
			for _, im := range imgs {
				if im.Repo == repo && im.Tag == t {
					prevTag, prevHow = t, "the self-update's record"
					break
				}
			}
		}
	}
	if prevTag == "" {
		var best *util.Version
		for _, im := range imgs {
			if im.Repo != repo {
				continue
			}
			if v, err := util.ParseVersion(im.Tag); err == nil && v.Compare(running) < 0 && (best == nil || v.Compare(*best) > 0) {
				vv := v
				best = &vv
			}
		}
		if best != nil {
			prevTag, prevHow = best.Raw, "by version order (no swap record names one present)"
		}
	}
	var prev *util.Version
	if prevTag != "" {
		if v, err := util.ParseVersion(prevTag); err == nil {
			prev = &v
		}
	}

	ids := make([]string, 0, len(byID))
	for id := range byID {
		ids = append(ids, id)
	}
	sort.Strings(ids)
	var deleted []string
	considered, candidates := 0, 0
	defer func() {
		// ONE line per pass, whatever it did — the positive observable that the pass ran (R-96 rule 3).
		m.logger.Printf("[INFO] [stacks] controller image retention: pass over %d controller image(s) — running %s, previous %q (%s), %d candidate(s), %d deleted, the rest kept",
			considered, rec.Running, prevTag, prevHow, candidates, len(deleted))
	}()
	for _, id := range ids {
		group := byID[id]
		var mine []localImage
		other := false
		for _, im := range group {
			if im.Repo == repo {
				mine = append(mine, im)
			} else {
				other = true
			}
		}
		if len(mine) == 0 {
			continue
		}
		considered++
		if used[id] {
			continue
		}
		deletable, odd := true, ""
		var names []string
		for _, im := range mine {
			if im.Tag == "<none>" || im.Tag == "" {
				continue
			}
			names = append(names, im.Repo+":"+im.Tag)
			v, err := util.ParseVersion(im.Tag)
			switch {
			case err != nil:
				deletable, odd = false, im.Tag // latest, -rc: not ours to judge
			case v.Compare(running) >= 0:
				deletable = false // the running one, or a pulled target not swapped to yet
			case prev == nil || v.Compare(*prev) >= 0:
				deletable = false // the previous (or nothing to call previous: keep)
			}
		}
		if !deletable {
			if odd != "" {
				m.logger.Printf("[INFO] [stacks] controller image retention: %s carries a tag that is not a version (%s) — left alone", shortID(id), odd)
			}
			continue
		}
		candidates++
		if other {
			m.logger.Printf("[INFO] [stacks] controller image retention: %s also carries another repository's name — left alone", shortID(id))
			continue
		}
		// A tagged image is removed by its names (rmi by ID refuses an ID with several tags); an untagged one by ID.
		targets := names
		if len(targets) == 0 {
			targets = []string{id}
		}
		ok := true
		for _, t := range targets {
			if out, err := imageDocker("rmi", t); err != nil {
				m.logger.Printf("[WARN] [stacks] controller image retention: docker refused to delete %s (%s): %s", t, shortID(id), truncateStr(strings.TrimSpace(out), 160))
				ok = false
				break
			}
		}
		if !ok {
			continue
		}
		label := strings.Join(names, ",")
		if label == "" {
			label = repo + ":<none>"
		}
		m.logger.Printf("[INFO] [stacks] controller image retention: deleted %s (%s, %s) — older than the previous controller and no container uses it (decision 56)", label, shortID(id), mine[0].Size)
		deleted = append(deleted, fmt.Sprintf("%s@%s", label, shortID(id)))
	}
	return deleted, nil
}