package storage

import (
	"context"
	"log/slog"
	"os"
	"path/filepath"
	"strings"

	"gitea.dooplex.hu/admin/felhom-agent/internal/hub"
)

// RegistryKnownTargets sources the watchdog's known-drive set from the drive INTENT registry + the
// Felhom `.mount` units — NOT from PVE storages (Observe). Impl-2a decoupling: a drive tracked this way
// needs NO PVE dir-storage (which is what hid registry-only drives from health/detect, the 3b-fix class).
// Real PVE storages (local/local-lvm/pbs) are NOT drives and are handled elsewhere via Observe.
//
// A unit is included iff its drive's intent is not `new` (enrolled/ejected/decommissioned are all
// "known" = health-tracked; the watchdog's IntentReader gate then decides whether to RE-MOUNT — only
// `enrolled` is remounted). A `new`-intent unit (should not normally exist) is excluded so it never
// auto-mounts.
type RegistryKnownTargets struct {
	unitDir string
	intent  IntentReader
	logger  *slog.Logger
}

// NewRegistryKnownTargets builds the provider. unitDir is the systemd unit dir the Felhom `.mount`
// units live in (e.g. /etc/systemd/system); intent is the durable-id → intent store (may be nil →
// every Felhom unit is treated as known, matching the legacy ungated behaviour).
func NewRegistryKnownTargets(unitDir string, intent IntentReader, logger *slog.Logger) *RegistryKnownTargets {
	if logger == nil {
		logger = slog.Default()
	}
	return &RegistryKnownTargets{unitDir: unitDir, intent: intent, logger: logger}
}

// Known enumerates the Felhom drive units under unitDir and returns one KnownTarget per enrolled/
// tracked drive. It mirrors ReassertEnrolledMounts's enumeration (read dir → parseFelhomMountUnit).
func (r *RegistryKnownTargets) Known(ctx context.Context) ([]KnownTarget, error) {
	entries, err := os.ReadDir(r.unitDir)
	if err != nil {
		return nil, err // let the caching layer keep the last good set; the watchdog logs + skips a cycle
	}
	var out []KnownTarget
	for _, e := range entries {
		if !strings.HasSuffix(e.Name(), ".mount") {
			continue
		}
		data, rerr := os.ReadFile(filepath.Join(r.unitDir, e.Name()))
		if rerr != nil {
			continue
		}
		spec, ok := parseFelhomMountUnit(string(data))
		if !ok {
			continue // not one of our by-uuid drive units (netmount units are excluded by the parser)
		}
		durableID := "uuid:" + spec.UUID // the same scheme enroll records in the intent store
		if r.intent != nil && r.intent.Get(durableID) == IntentNew {
			// A unit with no recorded intent — not enrolled/ejected/decommissioned. Do NOT track it
			// (and the watchdog must not auto-mount it): a genuine drive must be enrolled first.
			continue
		}
		out = append(out, KnownTarget{
			Name:        spec.Name,
			Type:        hub.StorageTypeUSB, // a Felhom drive; MountBacked is what the watchdog keys on
			DurableID:   durableID,
			UUID:        spec.UUID,
			MountBacked: true,
			MountPath:   spec.Where,
			// BackingDevice left "" — HostLiveness resolves the device by UUID (by-uuid symlink).
		})
	}
	return out, nil
}

// ReconcileExistingDrives migrates drives enrolled before Impl-2a into the intent-registry model so the
// registry-sourced Known() tracks them without depending on their (legacy) PVE dir-storage: for each
// Felhom `.mount` unit whose drive is currently mounted, ensure the intent registry records it
// `enrolled`. Idempotent (an already-enrolled drive is a no-op) and non-destructive — it creates no PVE
// storage and removes nothing. Best-effort per drive. Call once at agent start.
func ReconcileExistingDrives(unitDir string, mounts []Mount, intent *IntentStore, logger *slog.Logger) {
	if intent == nil || logger == nil {
		return
	}
	mounted := make(map[string]bool, len(mounts))
	for _, m := range mounts {
		mounted[m.MountPoint] = true
	}
	entries, err := os.ReadDir(unitDir)
	if err != nil {
		logger.Warn("migrate: cannot read unit dir — existing-drive reconcile skipped", "dir", unitDir, "err", err)
		return
	}
	for _, e := range entries {
		if !strings.HasSuffix(e.Name(), ".mount") {
			continue
		}
		data, rerr := os.ReadFile(filepath.Join(unitDir, e.Name()))
		if rerr != nil {
			continue
		}
		spec, ok := parseFelhomMountUnit(string(data))
		if !ok || !mounted[spec.Where] {
			continue // only migrate currently-active Felhom drives
		}
		durableID := "uuid:" + spec.UUID
		if intent.Get(durableID) != IntentNew {
			continue // already tracked (enrolled/ejected/decommissioned) — idempotent no-op
		}
		if serr := intent.SetEnrolled(durableID); serr != nil {
			logger.Warn("migrate: could not record enrolled intent", "drive", spec.Name, "err", serr)
		} else {
			logger.Info("migrate: recorded existing drive as enrolled", "drive", spec.Name, "durable_id", durableID)
		}
	}
}