package tasks

import (
	"context"
	"database/sql"
	"log/slog"
	"time"

	"vctp/db"

	"github.com/jmoiron/sqlx"
)

// presenceKeys builds lookup keys for vm presence comparison.
func presenceKeys(vmID, vmUUID, name string) []string {
	keys := make([]string, 0, 3)
	if vmID != "" {
		keys = append(keys, "id:"+vmID)
	}
	if vmUUID != "" {
		keys = append(keys, "uuid:"+vmUUID)
	}
	if name != "" {
		keys = append(keys, "name:"+name)
	}
	return keys
}

// backfillLifecycleDeletionsToday looks for VMs in the lifecycle cache that are not in the current inventory,
// have no DeletedAt, and determines their deletion time from today's hourly snapshots, optionally checking the next snapshot (next day) to confirm.
func backfillLifecycleDeletionsToday(ctx context.Context, logger *slog.Logger, dbConn *sqlx.DB, vcenter string, snapshotTime time.Time, present map[string]InventorySnapshotRow) error {
	dayStart := truncateDate(snapshotTime)
	dayEnd := dayStart.Add(24 * time.Hour)

	candidates, err := loadLifecycleCandidates(ctx, dbConn, vcenter, present)
	if err != nil || len(candidates) == 0 {
		return err
	}

	tables, err := listHourlyTablesForDay(ctx, dbConn, dayStart, dayEnd)
	if err != nil {
		return err
	}
	if len(tables) == 0 {
		return nil
	}

	nextPresence := make(map[string]struct{})
	if nextTable, nextErr := nextSnapshotAfter(ctx, dbConn, dayEnd, vcenter); nextErr == nil && nextTable != "" {
		nextPresence = loadPresenceKeys(ctx, dbConn, nextTable, vcenter)
	}

	for _, cand := range candidates {
		deletion, firstMiss := findDeletionInTables(ctx, dbConn, tables, vcenter, cand)
		if deletion == 0 && len(nextPresence) > 0 && firstMiss > 0 {
			if !isPresent(nextPresence, cand) {
				// Single miss at end of day, confirmed by next-day absence.
				deletion = firstMiss
				logger.Debug("cross-day deletion inferred from next snapshot", "vcenter", vcenter, "vm_id", cand.vmID, "vm_uuid", cand.vmUUID, "name", cand.name, "deletion", deletion)
			}
		}
		if deletion > 0 {
			if err := db.MarkVmDeletedWithDetails(ctx, dbConn, vcenter, cand.vmID, cand.vmUUID, cand.name, cand.cluster, deletion); err != nil {
				logger.Warn("lifecycle backfill mark deleted failed", "vcenter", vcenter, "vm_id", cand.vmID, "vm_uuid", cand.vmUUID, "name", cand.name, "cluster", cand.cluster, "deletion", deletion, "error", err)
				continue
			}
			logger.Debug("lifecycle backfill applied", "vcenter", vcenter, "vm_id", cand.vmID, "vm_uuid", cand.vmUUID, "name", cand.name, "cluster", cand.cluster, "deletion", deletion)
		}
	}
	return nil
}

type lifecycleCandidate struct {
	vmID    string
	vmUUID  string
	name    string
	cluster string
}

func loadLifecycleCandidates(ctx context.Context, dbConn *sqlx.DB, vcenter string, present map[string]InventorySnapshotRow) ([]lifecycleCandidate, error) {
	rows, err := dbConn.QueryxContext(ctx, `
SELECT "VmId","VmUuid","Name","Cluster"
FROM vm_lifecycle_cache
WHERE "Vcenter" = ? AND ("DeletedAt" IS NULL OR "DeletedAt" = 0)
`, vcenter)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var cands []lifecycleCandidate
	for rows.Next() {
		var vmID, vmUUID, name, cluster sql.NullString
		if scanErr := rows.Scan(&vmID, &vmUUID, &name, &cluster); scanErr != nil {
			continue
		}
		if vmID.String == "" {
			continue
		}
		if _, ok := present[vmID.String]; ok {
			continue // still present, skip
		}
		cands = append(cands, lifecycleCandidate{
			vmID:    vmID.String,
			vmUUID:  vmUUID.String,
			name:    name.String,
			cluster: cluster.String,
		})
	}
	return cands, nil
}

type snapshotTable struct {
	Table string `db:"table_name"`
	Time  int64  `db:"snapshot_time"`
}

func listHourlyTablesForDay(ctx context.Context, dbConn *sqlx.DB, dayStart, dayEnd time.Time) ([]snapshotTable, error) {
	rows, err := dbConn.QueryxContext(ctx, `
SELECT table_name, snapshot_time
FROM snapshot_registry
WHERE snapshot_type = 'hourly' AND snapshot_time >= ? AND snapshot_time < ?
ORDER BY snapshot_time ASC
`, dayStart.Unix(), dayEnd.Unix())
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var tables []snapshotTable
	for rows.Next() {
		var t snapshotTable
		if err := rows.StructScan(&t); err != nil {
			continue
		}
		if err := db.ValidateTableName(t.Table); err != nil {
			continue
		}
		hasRows, err := db.TableHasRows(ctx, dbConn, t.Table)
		if err != nil || !hasRows {
			continue
		}
		tables = append(tables, t)
	}
	return tables, nil
}

func nextSnapshotAfter(ctx context.Context, dbConn *sqlx.DB, after time.Time, vcenter string) (string, error) {
	rows, err := dbConn.QueryxContext(ctx, `
SELECT table_name
FROM snapshot_registry
WHERE snapshot_type = 'hourly' AND snapshot_time >= ?
ORDER BY snapshot_time ASC
LIMIT 1
`, after.Unix())
	if err != nil {
		return "", err
	}
	defer rows.Close()
	for rows.Next() {
		var name string
		if err := rows.Scan(&name); err != nil {
			continue
		}
		if err := db.ValidateTableName(name); err != nil {
			continue
		}
		// ensure the snapshot table actually has entries for this vcenter
		vrows, qerr := querySnapshotRows(ctx, dbConn, name, []string{"VmId"}, `"Vcenter" = ? LIMIT 1`, vcenter)
		if qerr != nil {
			continue
		}
		hasVcenter := vrows.Next()
		vrows.Close()
		if hasVcenter {
			return name, nil
		}
	}
	return "", nil
}

func loadPresenceKeys(ctx context.Context, dbConn *sqlx.DB, table, vcenter string) map[string]struct{} {
	out := make(map[string]struct{})
	rows, err := querySnapshotRows(ctx, dbConn, table, []string{"VmId", "VmUuid", "Name"}, `"Vcenter" = ?`, vcenter)
	if err != nil {
		return out
	}
	defer rows.Close()
	for rows.Next() {
		var vmId, vmUuid, name sql.NullString
		if err := rows.Scan(&vmId, &vmUuid, &name); err == nil {
			for _, k := range presenceKeys(vmId.String, vmUuid.String, name.String) {
				out[k] = struct{}{}
			}
		}
	}
	return out
}

func isPresent(presence map[string]struct{}, cand lifecycleCandidate) bool {
	for _, k := range presenceKeys(cand.vmID, cand.vmUUID, cand.name) {
		if _, ok := presence[k]; ok {
			return true
		}
	}
	return false
}

func findDeletionInTables(ctx context.Context, dbConn *sqlx.DB, tables []snapshotTable, vcenter string, cand lifecycleCandidate) (int64, int64) {
	var lastSeen int64
	var firstMiss int64
	for i, tbl := range tables {
		rows, err := querySnapshotRows(ctx, dbConn, tbl.Table, []string{"VmId", "VmUuid", "Name", "Cluster"}, `"Vcenter" = ? AND "VmId" = ?`, vcenter, cand.vmID)
		if err == nil {
			if rows.Next() {
				var vmId, vmUuid, name, cluster sql.NullString
				if scanErr := rows.Scan(&vmId, &vmUuid, &name, &cluster); scanErr == nil {
					lastSeen = tbl.Time
					if cand.name == "" && name.Valid {
						cand.name = name.String
					}
					if cand.cluster == "" && cluster.Valid {
						cand.cluster = cluster.String
					}
				}
			}
			rows.Close()
		}
		if lastSeen > 0 && tbl.Time > lastSeen {
			// first table after last seen -> first miss
			if seen, _ := candSeenInTable(ctx, dbConn, tbl.Table, vcenter, cand.vmID); !seen {
				firstMiss = tbl.Time
				// need two consecutive misses
				if i+1 < len(tables) {
					if seen2, _ := candSeenInTable(ctx, dbConn, tables[i+1].Table, vcenter, cand.vmID); !seen2 {
						return firstMiss, firstMiss
					}
				}
			}
		}
	}
	return 0, firstMiss
}

func candSeenInTable(ctx context.Context, dbConn *sqlx.DB, table, vcenter, vmID string) (bool, error) {
	rows, err := querySnapshotRows(ctx, dbConn, table, []string{"VmId"}, `"Vcenter" = ? AND "VmId" = ? LIMIT 1`, vcenter, vmID)
	if err != nil {
		return false, err
	}
	defer rows.Close()
	return rows.Next(), nil
}