package backup

import (
	"encoding/json"
	"os"
	"path/filepath"
	"sort"
	"strconv"
	"sync"
	"time"

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

// BackupSuccessState persists the newest SUCCESSFUL whole-guest backup per tier and guest (R-894).
//
// Why it exists. The due-check (`localapi` handleBackupDue) asks the tier's storage when a backup last
// landed (R-84) and falls back to the in-memory record when the storage cannot be read. The in-memory
// record is empty after an agent restart (Store, R-348), so "storage unreadable" right after a restart
// read as "no record — DUE". Measured 2026-10-05 on demo-hp: the agent restarted at 04:57, the off-site
// storage answered "Can't connect" at 06:25, the 7-day tier — last copy 2026-10-01 — read DUE, the
// controller asked, and vzdump failed. This file is the last known copy the fallback reads instead.
//
// It is read ONLY when the storage cannot be read. A storage that answers is the ground truth and wins,
// in both directions: an archive found there counts, and an archive absent there is absent even when
// this file remembers a success (a pruned or deleted archive must make the tier due — the same reason
// R-84 chose the storage over a persisted record). Pinned by
// TestBackupDue_R894_SavedCopyIgnoredWhenStorageAnswers.
//
// Only SUCCESSES are written (the RestoreTestState rule): a failure must stay due and be retried, so a
// record of a failure has no reader.
type BackupSuccessState struct {
	path string
	mu   sync.Mutex
	last map[string]savedSuccess // key(target, vmid) → the newest success
}

type savedSuccess struct {
	target string
	vmid   int
	at     time.Time
}

// backupSuccessJSON is one entry on disk.
type backupSuccessJSON struct {
	Target    string `json:"target"`
	VMID      int    `json:"vmid"`
	StartedAt string `json:"started_at"`
}

func backupStateKey(target string, vmid int) string { return target + "/" + strconv.Itoa(vmid) }

// NewBackupSuccessState opens (or creates) the state at path. A missing or unreadable file degrades to
// "nothing known" — the pre-R-894 behaviour, which is DUE — and never wedges the daemon.
func NewBackupSuccessState(path string) *BackupSuccessState {
	s := &BackupSuccessState{path: path, last: map[string]savedSuccess{}}
	data, err := os.ReadFile(path)
	if err != nil {
		return s
	}
	var entries []backupSuccessJSON
	if json.Unmarshal(data, &entries) != nil {
		return s
	}
	for _, e := range entries {
		t, perr := time.Parse(time.RFC3339, e.StartedAt)
		if perr != nil {
			continue // one unreadable entry must not lose the others
		}
		s.last[backupStateKey(e.Target, e.VMID)] = savedSuccess{target: e.Target, vmid: e.VMID, at: t.UTC()}
	}
	return s
}

// RecordBackupSuccess saves b when it is a success newer than the one on file. target is the tier the
// job ran on (the due-check's key); a failure or an unparseable time is ignored.
func (s *BackupSuccessState) RecordBackupSuccess(target string, b hub.Backup) error {
	if s == nil || !b.Success {
		return nil
	}
	t, err := time.Parse(time.RFC3339, b.StartedAt)
	if err != nil {
		return nil
	}
	s.mu.Lock()
	defer s.mu.Unlock()
	k := backupStateKey(target, b.VMID)
	if old, ok := s.last[k]; ok && !t.After(old.at) {
		return nil
	}
	s.last[k] = savedSuccess{target: target, vmid: b.VMID, at: t.UTC()}
	return s.saveLocked()
}

// LastKnownSuccess returns the newest saved success for this tier and guest (ok=false = none on file).
func (s *BackupSuccessState) LastKnownSuccess(target string, vmid int) (time.Time, bool) {
	if s == nil {
		return time.Time{}, false
	}
	s.mu.Lock()
	defer s.mu.Unlock()
	e, ok := s.last[backupStateKey(target, vmid)]
	return e.at, ok
}

func (s *BackupSuccessState) saveLocked() error {
	entries := make([]backupSuccessJSON, 0, len(s.last))
	for _, e := range s.last {
		entries = append(entries, backupSuccessJSON{Target: e.target, VMID: e.vmid, StartedAt: e.at.Format(time.RFC3339)})
	}
	// Deterministic file content (Go's map order is random).
	sort.Slice(entries, func(i, j int) bool {
		if entries[i].Target != entries[j].Target {
			return entries[i].Target < entries[j].Target
		}
		return entries[i].VMID < entries[j].VMID
	})
	data, err := json.MarshalIndent(entries, "", "  ")
	if err != nil {
		return err
	}
	if err := os.MkdirAll(filepath.Dir(s.path), 0o755); err != nil {
		return err
	}
	tmp := s.path + ".tmp"
	if err := os.WriteFile(tmp, data, 0o600); err != nil {
		os.Remove(tmp)
		return err
	}
	return os.Rename(tmp, s.path)
}