package monitor

import (
	"encoding/json"
	"fmt"
	"log"
	"strings"
	"time"

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

// backupStaleAfter is the maximum age of the newest offsite backup before the daily
// deadline check raises expected_backup_missed. 26h covers an evening backup schedule
// (e.g. ~18:00–22:00) plus headroom, so a healthy once-daily cadence never trips the
// early-morning check.
//
// R-81 also reuses it as the ABSENCE window (see assessBackupFreshness): the existing
// threshold, anchored at first-contact, IS the newborn grace — no new knob, exactly as
// v0.73.0 reused offsite staleAfter for its never-ran anchor.
//
// ⚠️ LANDMINE — dependency on R-82 (the backup target split). This constant is applied to
// whichever tier is NEWEST, PBS or vzdump, with no tier-awareness. Today a daily vzdump
// always wins, so PBS's own age is invisible here and 26h is harmless. The moment PBS moves
// to a WEEKLY cadence, a perfectly healthy weekly snapshot is >26h old six days in seven and
// this constant alarms on it. Fixing that means per-tier thresholds, which cannot be built
// before the per-tier cadence config exists (`local_backup_target` is a single target and
// BackupCadence() a single 24h window today). Do NOT pre-build it — R-82 owns both halves.
const backupStaleAfter = 26 * time.Hour

// backupEvidenceLookback bounds how far back the hub looks for evidence that a backup ever
// happened, when the LATEST report carries none. Generous against any plausible daily cadence
// (and against an agent that stayed restarted for days), bounded so the cold path can't turn
// into a full-retention scan of every report the hub holds. Beyond this the verdict is
// "no evidence in the lookback", which is a fault in its own right once the anchor elapsed.
const backupEvidenceLookback = 7 * 24 * time.Hour

// hostReportBackups is the minimal slice of an agent host-report the deadline check
// reads to judge backup freshness (pbs_snapshots is the offsite-DR signal; backups is
// the local vzdump fallback). Mirrors the agent's hub.PBSSnapshot / hub.Backup wire
// contract for just the fields we need.
type hostReportBackups struct {
	PBSSnapshots []struct {
		BackupTime  string `json:"backup_time"`
		VerifyState string `json:"verify_state"`
	} `json:"pbs_snapshots"`
	Backups []struct {
		// TargetID is the SLICE-C discriminator: a backups[] entry belongs to whichever tier its
		// target storage belongs to, never to "the local tier" by virtue of being in this array.
		TargetID  string `json:"target_id"`
		StartedAt string `json:"started_at"`
		Success   bool   `json:"success"`
	} `json:"backups"`
	// StorageTargets carries the target TYPE, which is how a backups[] entry is attributed to a
	// tier (target_id → name → type == "pbs"). See pbsTargetSet.
	StorageTargets []struct {
		Name    string `json:"name"`
		Type    string `json:"type"`
		Content string `json:"content"`
	} `json:"storage_targets"`
}

// backupVerdict is the three-valued outcome of the freshness policy. The middle value is the
// whole point of R-81: "I have no evidence" is NOT "the backup failed".
type backupVerdict int

const (
	verdictOK      backupVerdict = iota // positive evidence of a recent backup
	verdictUnknown                      // no evidence yet, and the anchored window has not elapsed
	verdictMissed                       // positive evidence of a problem — alarm
)

// backupAssessment is the verdict for one customer's offsite backup health.
type backupAssessment struct {
	verdict backupVerdict
	reason  string // human-readable cause (event message + logs)
}

// missed reports whether this assessment should raise expected_backup_missed.
func (a backupAssessment) missed() bool { return a.verdict == verdictMissed }

// backupEvidence is the hub-history half of the freshness policy, resolved by the caller so
// assessBackupFreshness stays PURE (see its doc comment on why that matters).
type backupEvidence struct {
	// newestSeen is the newest backup evidence found across the retained host-report window
	// (PBS backup_time or successful vzdump started_at), regardless of whether the LATEST
	// report still carries it. haveSeen is false when the window held none.
	newestSeen time.Time
	haveSeen   bool

	// Per-tier window evidence (R-82 Slice C). A single "newest across everything" would let a
	// fresh daily host backup satisfy the OFFSITE tier's lookup — the same error Slice A fixed
	// agent-side. newestSeen/haveSeen above remain the pre-Slice-C combined values, used only by
	// the no-tier fallback path.
	newestHost    time.Time
	haveHost      bool
	newestOffsite time.Time
	haveOffsite   bool

	// firstReportAt is when the hub first saw ANY host-report from this customer — the
	// observation anchor. Zero when unknown, which the policy treats as "cannot defer"
	// (fail toward visibility, matching the v0.73.0 zero-anchor branch).
	firstReportAt time.Time
}

// assessBackupFreshness decides whether a customer's backups are healthy. Pure (now and the
// hub-history evidence are injected) so the policy is unit-tested — that purity is why the
// 2026-07-26 incident could be diagnosed at all, and why the fix below is provable.
//
// ── THE INVARIANT (R-81) ──────────────────────────────────────────────────────────────────
//
//	Only POSITIVE EVIDENCE OF A PROBLEM raises an alarm. ABSENCE OF A SIGNAL IS UNKNOWN,
//	and becomes a fault only once that absence has persisted beyond an ANCHORED window.
//
// This monitor family has made the same mistake three times, and it is written down here so
// the fourth is harder:
//   - hub v0.12.0 — `expected_backup_missed` fired daily for every healthy customer, because
//     it looked for a `backup_completed` event that no component emits anymore.
//   - hub v0.73.0 — `offsite_stale` fired minutes after a HEALTHY repair, because the
//     never-ran branch had no time anchor. Fixed by anchoring, not by silence.
//   - R-81 (this) — `expected_backup_missed` fired on three boxes at once on 2026-07-26,
//     because an agent restart empties the host-report `backups` array (the agent's store is
//     in-memory) and empty was read as "no backup exists". The vzdump had in fact run.
//
// Note the shape of the fix in all three: NOT silence. Silence is the opposite failure — a
// box that genuinely never backs up would then alarm never, which is strictly worse than
// crying wolf. Absence is deferred, then alarmed on, with its own distinct reason string.
//
// ── THE BRANCHES ──────────────────────────────────────────────────────────────────────────
//
//	unparseable latest report                                    → missed ("could not be parsed")
//	newest evidence (report OR window) older than staleAfter      → missed ("newest backup is Xh old")
//	newest PBS snapshot's verify_state == "failed"                → missed ("failed verification")
//	NO evidence anywhere, anchor NOT yet elapsed                  → UNKNOWN, silent + logged
//	NO evidence anywhere, anchor elapsed                          → missed ("no backup evidence in …")
//	otherwise                                                     → ok
//
// Each failure mode keeps its OWN reason string. That is not polish: the entire 2026-07-26
// diagnosis turned on reading the exact string, and collapsing them would have made it
// impossible. In particular "absence over time" and "a timestamp that is too old" are
// different faults with different causes, and must never share a message.
//
// A fresh-but-not-yet-verified snapshot (verify_state "none"/"") is NOT treated as a
// failure: PBS verification runs on its own cadence, so a snapshot taken hours before the
// 03:00 check may legitimately be unverified. Alarming on that would re-introduce exactly
// the daily false alarm the v0.12.0 repoint removed (hence "failed" only, not "≠ ok").
func assessBackupFreshness(reportJSON string, ev backupEvidence, now time.Time) backupAssessment {
	var hr hostReportBackups
	if err := json.Unmarshal([]byte(reportJSON), &hr); err != nil {
		// Unparseable report → can't confirm a backup. Surface it rather than swallow it.
		return backupAssessment{verdict: verdictMissed, reason: "latest host-report could not be parsed"}
	}

	var newestPBS time.Time
	var newestPBSVerify string
	havePBS := false
	for _, ps := range hr.PBSSnapshots {
		t, ok := parseBackupTime(ps.BackupTime)
		if !ok {
			continue
		}
		if !havePBS || t.After(newestPBS) {
			havePBS = true
			newestPBS = t
			newestPBSVerify = strings.ToLower(strings.TrimSpace(ps.VerifyState))
		}
	}

	var newestVzdump time.Time
	haveVzdump := false
	for _, b := range hr.Backups {
		if !b.Success {
			continue
		}
		t, ok := parseBackupTime(b.StartedAt)
		if !ok {
			continue
		}
		if !haveVzdump || t.After(newestVzdump) {
			haveVzdump = true
			newestVzdump = t
		}
	}

	// ── R-82 Slice C: TIER-AWARE assessment ───────────────────────────────────────────────────
	// Judge each tier against ITS OWN threshold. Falls through to the pre-Slice-C combined logic
	// below only when NEITHER tier is identifiable — an old agent whose report carries no
	// storage_targets and no target_id — so nothing regresses on a fleet mid-upgrade.
	hostView, offView := splitTiers(hr)
	if hostView.expected || offView.expected {
		var as []backupAssessment
		if hostView.expected {
			as = append(as, assessTier(tierHost, hostView, ev.newestHost, ev.haveHost, ev.firstReportAt, now))
		}
		if offView.expected {
			as = append(as, assessTier(tierOffsite, offView, ev.newestOffsite, ev.haveOffsite, ev.firstReportAt, now))
		}
		return worst(as...)
	}

	// The newest evidence the LATEST report itself carries.
	newest := newestPBS
	haveNewest := havePBS
	if haveVzdump && (!haveNewest || newestVzdump.After(newest)) {
		newest, haveNewest = newestVzdump, true
	}

	// R-81: fold in what the hub REMEMBERS. The agent's store is point-in-time and forgets
	// across a restart; the hub's retained host-reports do not. An empty array in the latest
	// report therefore says nothing on its own — the question is when evidence was last SEEN,
	// not whether this one report happens to carry it.
	if ev.haveSeen && (!haveNewest || ev.newestSeen.After(newest)) {
		newest, haveNewest = ev.newestSeen, true
	}

	if !haveNewest {
		// ABSENCE. Not a failure by itself — see the invariant above. It becomes one only
		// once it has outlived the existing threshold, counted from first contact (the point
		// at which a backup first became possible to observe).
		if ev.firstReportAt.IsZero() {
			// No anchor to defer against — fail toward visibility, as v0.73.0 does for the
			// legacy zero-anchor shape. Distinct string: this is an unanchored absence.
			return backupAssessment{
				verdict: verdictMissed,
				reason:  "no backup evidence in any retained host-report, and no first-contact anchor to defer against",
			}
		}
		watched := now.Sub(ev.firstReportAt)
		if watched <= backupStaleAfter {
			return backupAssessment{
				verdict: verdictUnknown,
				reason: fmt.Sprintf("no backup evidence yet, but only watching for %s (grace %s since first contact %s) — newborn host, not a fault",
					watched.Round(time.Hour), backupStaleAfter, ev.firstReportAt.Format(time.RFC3339)),
			}
		}
		return backupAssessment{
			verdict: verdictMissed,
			reason: fmt.Sprintf("no backup evidence in any host-report for %s (limit %s, first contact %s, lookback %s)",
				watched.Round(time.Hour), backupStaleAfter, ev.firstReportAt.Format(time.RFC3339), backupEvidenceLookback),
		}
	}

	if age := now.Sub(newest); age > backupStaleAfter {
		return backupAssessment{verdict: verdictMissed, reason: fmt.Sprintf("newest backup is %s old (limit %s)", age.Round(time.Hour), backupStaleAfter)}
	}
	if havePBS && newestPBSVerify == "failed" {
		return backupAssessment{verdict: verdictMissed, reason: "newest PBS snapshot failed verification"}
	}
	return backupAssessment{verdict: verdictOK}
}

// newestBackupEvidence scans the customer's retained host-reports (newest first) for the most
// recent backup evidence — a PBS snapshot backup_time or a SUCCESSFUL vzdump started_at —
// regardless of whether the latest report still carries it.
//
// Cost discipline: it stops as soon as it has found evidence FRESH enough that nothing older
// could change the verdict, so the healthy path reads one row. Only the genuinely-broken path
// (no fresh evidence anywhere) walks the full lookback, and that is bounded by
// backupEvidenceLookback rather than by retention.
func newestBackupEvidence(rows []store.HostReportRow, now time.Time) (time.Time, bool) {
	var newest time.Time
	have := false
	for _, r := range rows {
		var hr hostReportBackups
		if err := json.Unmarshal([]byte(r.ReportJSON), &hr); err != nil {
			continue // a single malformed retained report must not blind the scan
		}
		for _, ps := range hr.PBSSnapshots {
			if t, ok := parseBackupTime(ps.BackupTime); ok && (!have || t.After(newest)) {
				newest, have = t, true
			}
		}
		for _, b := range hr.Backups {
			if !b.Success {
				continue
			}
			if t, ok := parseBackupTime(b.StartedAt); ok && (!have || t.After(newest)) {
				newest, have = t, true
			}
		}
		// Fresh evidence found → the age branch cannot fire and nothing older matters.
		if have && now.Sub(newest) <= backupStaleAfter {
			break
		}
	}
	return newest, have
}

// parseBackupTime parses an RFC3339 timestamp from a host-report and normalizes to UTC.
func parseBackupTime(s string) (time.Time, bool) {
	s = strings.TrimSpace(s)
	if s == "" {
		return time.Time{}, false
	}
	if t, err := time.Parse(time.RFC3339, s); err == nil {
		return t.UTC(), true
	}
	return time.Time{}, false
}

// budapest returns the Europe/Budapest timezone (cached).
var budapest *time.Location

func init() {
	var err error
	budapest, err = time.LoadLocation("Europe/Budapest")
	if err != nil {
		// Fallback: UTC+1 (CET base; DST handled by OS if available)
		budapest = time.FixedZone("CET", 3600)
	}
}

// CheckBackupDeadlines checks whether active customers had their expected
// daily backups and DB dumps. Runs once daily (early morning, Budapest time).
//
// Backup half: read the agent's latest host-report and raise expected_backup_missed
// only when its PBS snapshots / vzdump backups show no fresh, verified backup (see
// assessBackupFreshness). This replaced the old backup_completed-event check, which
// fired daily for every healthy customer because no component emits that event anymore
// (the controller's disk-tier backup moved to the agent in slice 8C).
//
// DB-dump half: unchanged — the in-guest controller still emits db_dump_completed, so
// the event-based check there is correct.
//
// Customers whose nodes are "down" (no report in >1h) are skipped — they
// already have staleness events.
func CheckBackupDeadlines(s *store.Store, staleness *StalenessChecker, onEvent EventNotifyFunc, logger *log.Logger) {
	customerIDs, err := s.GetActiveCustomerIDs()
	if err != nil {
		logger.Printf("[WARN] Deadline check: failed to get active customers: %v", err)
		return
	}

	// Budapest midnight today
	now := time.Now().In(budapest)
	midnightBudapest := time.Date(now.Year(), now.Month(), now.Day(), 0, 0, 0, 0, budapest)
	sinceUTC := midnightBudapest.UTC()

	var backupMissed, dbdumpMissed, skipped, deferred, unbound int

	for _, id := range customerIDs {
		// Skip nodes that are down — they already have staleness events
		if staleness != nil && staleness.GetState(id) == "down" {
			skipped++
			continue
		}

		// Check blocked
		if s.IsCustomerBlocked(id) {
			continue
		}

		// ── R-195: a customer with NO machine EVER bound is UNKNOWN, not missed ────────────────
		//
		// Both verdicts below ask "did the thing we expect every day happen?". For a customer
		// that has never had a machine bound, nothing has ever been expected, so the honest
		// answer is UNKNOWN — the same invariant assessBackupFreshness states above, applied one
		// level up, at the question of whether there is a subject at all.
		//
		// The discriminator is "was a host EVER bound", NOT "has a report arrived". That is the
		// case this check must not break: a box that was installed, bound, and then went silent
		// has a real fault and must keep alarming. It is bound, so it is judged.
		//
		// WHY THIS WAS REACHABLE AT ALL, measured 2026-08-04: the down-skip above is what
		// protects every other silent customer, and it reads the staleness checker's state — which
		// is seeded from the `reports` table (store.GetCustomers). A customer that has NEVER
		// reported appears in no report row, so it gets no staleness state at all and GetState()
		// returns "" rather than "down". The skip misses exactly the customer it would most
		// obviously cover, and the DB-dump half below then fires every night: `david`, a
		// prospective customer whose record was created 2026-08-01 with no machine ever bound,
		// e-mailed an expected_dbdump_missed ERROR at 03:00 UTC on three consecutive days.
		//
		// Fail-open on a read error: an unreadable binding must never SUPPRESS a real alarm.
		if bound, berr := s.HasEverBoundHost(id); berr != nil {
			logger.Printf("[WARN] Deadline check: failed to read host binding for %s (judging anyway): %v", id, berr)
		} else if !bound {
			// Visible, per the v0.73.0 Part-7 precedent below: a quiet check must never be
			// indistinguishable from a check that did not run. Once daily, one line per customer.
			logger.Printf("[INFO] Deadline check: %s has no host EVER bound — all deadline verdicts UNKNOWN (no alarm)", id)
			unbound++
			continue
		}

		// Backup freshness from the agent's host-report (PBS snapshots + vzdump),
		// the authoritative offsite-backup signal post-slice-8C.
		reportJSON, rerr := s.GetLatestHostReportJSON(id)
		switch {
		case rerr != nil:
			logger.Printf("[WARN] Deadline check: failed to read host-report for %s: %v", id, rerr)
		case reportJSON == "":
			// No agent host-report at all (legacy/defunct controller-only customer).
			// Liveness is owned by the host-staleness checker; the backup deadline check
			// has no PBS data to judge here and must not emit a daily backup alarm of its
			// own. (The DB-dump half below still applies.)
		default:
			nowUTC := time.Now().UTC()

			// R-81: resolve the hub-history half BEFORE judging. A read failure here must not
			// invent a fault — it degrades to "the latest report is all I know", which is the
			// pre-R-81 behaviour, and is logged rather than swallowed.
			var ev backupEvidence
			if rows, rerr := s.GetHostReportsSince(id, nowUTC.Add(-backupEvidenceLookback)); rerr != nil {
				logger.Printf("[WARN] Deadline check: failed to read host-report window for %s: %v", id, rerr)
			} else {
				ev.newestSeen, ev.haveSeen = newestBackupEvidence(rows, nowUTC)
				// Slice C: per-tier window evidence. Which tiers to look for comes from the LATEST
				// report, so a box with no offsite tier never pays for scanning one.
				var latest hostReportBackups
				wantHost, wantOffsite := true, true
				if json.Unmarshal([]byte(reportJSON), &latest) == nil {
					h, o := splitTiers(latest)
					wantHost, wantOffsite = h.expected, o.expected
				}
				ev.newestHost, ev.haveHost, ev.newestOffsite, ev.haveOffsite =
					newestBackupEvidenceByTier(rows, wantHost, wantOffsite, nowUTC)
			}
			if first, ferr := s.GetFirstHostReportAt(id); ferr != nil {
				logger.Printf("[WARN] Deadline check: failed to read first host-report for %s: %v", id, ferr)
			} else {
				ev.firstReportAt = first
			}

			a := assessBackupFreshness(reportJSON, ev, nowUTC)
			switch a.verdict {
			case verdictMissed:
				msg := "No fresh verified backup: " + a.reason
				if _, err := s.SaveEvent(id, "expected_backup_missed", "error", msg, "{}", "hub"); err != nil {
					logger.Printf("[WARN] Failed to save expected_backup_missed for %s: %v", id, err)
				} else if onEvent != nil {
					onEvent(id, "expected_backup_missed", "error", msg, "{}", "hub")
				}
				backupMissed++
			case verdictUnknown:
				// Make the deferral VISIBLE (the v0.73.0 Part-7 precedent): a quiet check must
				// never be indistinguishable from a check that did not run. This check fires
				// once daily, so this is at most one line per customer per day — not spam, and
				// it is the line that proves the deferral happened rather than an error.
				logger.Printf("[INFO] Deadline check: %s backup verdict UNKNOWN (no alarm) — %s", id, a.reason)
				deferred++
			}
		}

		// Check db_dump_completed / db_dump_failed since midnight
		dumpOK, _ := s.GetEventsByType(id, "db_dump_completed", sinceUTC)
		dumpFailed, _ := s.GetEventsByType(id, "db_dump_failed", sinceUTC)
		if len(dumpOK) == 0 && len(dumpFailed) == 0 {
			msg := "No DB dump completed or failed since midnight"
			if _, err := s.SaveEvent(id, "expected_dbdump_missed", "error", msg, "{}", "hub"); err != nil {
				logger.Printf("[WARN] Failed to save expected_dbdump_missed for %s: %v", id, err)
			} else if onEvent != nil {
				onEvent(id, "expected_dbdump_missed", "error", msg, "{}", "hub")
			}
			dbdumpMissed++
		}
	}

	logger.Printf("[INFO] Deadline check: %d customers, %d backup missed, %d backup unknown (deferred), %d dbdump missed, %d skipped (down), %d unknown (no host ever bound)",
		len(customerIDs), backupMissed, deferred, dbdumpMissed, skipped, unbound)
}