package repository

import (
	"context"
	"encoding/json"
	"errors"
	"sync"
	"time"

	"evobgp/internal/store"

	"github.com/jackc/pgx/v5"
)

// asnCacheRowExistsOnce caches the schema check for the process lifetime (see moduleSnapshotRowTableExists).
var (
	asnCacheRowExistsOnce   sync.Once
	asnCacheRowExistsCached bool
)

func asnCacheRowTableExists(ctx context.Context, q queryRower) bool {
	asnCacheRowExistsOnce.Do(func() {
		var n int
		err := q.QueryRow(ctx, `
			SELECT 1 FROM information_schema.tables
			WHERE table_schema = 'public' AND table_name = 'asn_prefix_cache_row'
			LIMIT 1`).Scan(&n)
		if err != nil {
			asnCacheRowExistsOnce = sync.Once{}
			return
		}
		asnCacheRowExistsCached = true
	})
	return asnCacheRowExistsCached
}

func (p *Postgres) GetASNPrefixCache(asn int64) (*store.ASNPrefixCacheEntry, bool, error) {
	ctx := context.Background()
	var holder string
	var fetchedAt time.Time
	err := p.pool.QueryRow(ctx, `
		SELECT holder, fetched_at FROM asn_prefix_cache WHERE asn = $1`, asn).
		Scan(&holder, &fetchedAt)
	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return nil, false, nil
		}
		return nil, false, err
	}
	var prefixes []string
	if asnCacheRowTableExists(ctx, p.pool) {
		rows, qerr := p.pool.Query(ctx, `
			SELECT prefix::text FROM asn_prefix_cache_row WHERE asn = $1 ORDER BY prefix`, asn)
		if qerr != nil {
			return nil, false, qerr
		}
		defer rows.Close()
		for rows.Next() {
			var s string
			if err := rows.Scan(&s); err != nil {
				continue
			}
			prefixes = append(prefixes, s)
		}
	} else {
		var raw []byte
		if err := p.pool.QueryRow(ctx, `SELECT prefixes_json FROM asn_prefix_cache WHERE asn = $1`, asn).Scan(&raw); err == nil && len(raw) > 0 {
			_ = json.Unmarshal(raw, &prefixes)
		}
	}
	return &store.ASNPrefixCacheEntry{
		ASN:       asn,
		Holder:    holder,
		Prefixes:  prefixes,
		FetchedAt: fetchedAt.UTC(),
	}, true, nil
}

func (p *Postgres) SetASNPrefixCache(asn int64, holder string, prefixes []string) error {
	ctx := context.Background()
	tx, err := p.pool.Begin(ctx)
	if err != nil {
		return err
	}
	defer func() { _ = tx.Rollback(ctx) }()
	_, err = tx.Exec(ctx, `
		INSERT INTO asn_prefix_cache (asn, holder, fetched_at)
		VALUES ($1, $2, now())
		ON CONFLICT (asn) DO UPDATE SET
			holder = EXCLUDED.holder,
			fetched_at = EXCLUDED.fetched_at`, asn, holder)
	if err != nil {
		return err
	}
	if asnCacheRowTableExists(ctx, tx) {
		if _, err := tx.Exec(ctx, `DELETE FROM asn_prefix_cache_row WHERE asn = $1`, asn); err != nil {
			return err
		}
		for _, pfx := range prefixes {
			if _, err := tx.Exec(ctx, `
				INSERT INTO asn_prefix_cache_row (asn, prefix) VALUES ($1, $2::cidr)`, asn, pfx); err != nil {
				return err
			}
		}
	} else {
		raw, err := json.Marshal(prefixes)
		if err != nil {
			return err
		}
		if _, err := tx.Exec(ctx, `
			UPDATE asn_prefix_cache SET prefixes_json = $2::jsonb WHERE asn = $1`, asn, string(raw)); err != nil {
			return err
		}
	}
	return tx.Commit(ctx)
}