/**
 * Boot-time gate: verify the ClickHouse `_schema_migrations` audit table's
 * most recently applied row matches the expected version baked into the
 * deployed image. Companion to the SQL-side helper
 * `verifyExpectedSchemaVersion` from `@fjall/util/migration` — together they
 * close the asymmetry where a webapp's boot gate checks Postgres but blindly
 * trusts ClickHouse.
 *
 * The audit table is owned by the migration runner: see the canonical DDL
 * recorded by `ensureSchemaMigrationsTable` in the webapp's migration-runner
 * (columns `version`, `applied_at`, `snapshot_arn`, `prisma_version`,
 * `ch_version`). This helper reads a single configurable column (default
 * `ch_version`) so callers can pin to whichever the image's expected env
 * carries (overall migration hash via `version`, Prisma-side via
 * `prisma_version`, or ClickHouse-side via `ch_version`).
 *
 * Returns `{ matches, expected, actual }` rather than throwing on mismatch:
 * the consumer's boot script owns the exit-code / log shape.
 *
 * `matches` tolerates expand-only rollback via the shared
 * `isSchemaVersionSatisfied` (same comparator the Postgres gate uses, so the
 * two can't drift): the default `ch_version` field is an orderable `.sql`
 * filename, so `actual >= expected` passes; the non-orderable audit fields
 * (`version` sha256 hash, `prisma_version` constant) fall back to strict
 * identity.
 */
import type { MigrationLogger } from "./logger.js";
declare const ALLOWED_FIELDS: readonly ["version", "ch_version", "prisma_version"];
type AllowedField = (typeof ALLOWED_FIELDS)[number];
/**
 * The slice of `ClickHouseClient` this check needs. Structural so a caller
 * holding a narrower handle (the schema-gate container's injectable
 * `SchemaGateChHandle`) passes it without a cast; `@clickhouse/client`
 * satisfies it directly.
 */
export interface SchemaVersionQueryClient {
    query(params: {
        query: string;
        format: "JSONEachRow";
        abort_signal?: AbortSignal;
    }): Promise<{
        json(): Promise<unknown>;
    }>;
}
export interface VerifyExpectedClickHouseSchemaVersionOpts {
    client: SchemaVersionQueryClient;
    /** Expected version (typically read from an env var baked into the image). */
    expected: string;
    /** Database holding the audit table. Defaults to `"analytics"`. */
    database?: string;
    /** Audit-table name. Defaults to `"_schema_migrations"`. */
    table?: string;
    /** Column whose latest value to compare. Defaults to `"ch_version"`. */
    field?: AllowedField;
    signal?: AbortSignal;
    logger?: MigrationLogger;
}
export interface VerifyExpectedClickHouseSchemaVersionResult {
    matches: boolean;
    expected: string;
    /** `null` when the audit table is empty (no migrations applied yet). */
    actual: string | null;
}
export declare function verifyExpectedClickHouseSchemaVersion(opts: VerifyExpectedClickHouseSchemaVersionOpts): Promise<VerifyExpectedClickHouseSchemaVersionResult>;
export {};