import type { ColumnDefaultValue, SQLExpression } from './model.js';
/** Legacy spelling of an expression default: `'fn:now()'` ≡ `{ expression: 'now()' }`. */
export declare const LEGACY_EXPRESSION_PREFIX = "fn:";
export type ParsedColumnDefault = {
    kind: 'expression';
    sql: string;
} | {
    kind: 'literal';
    value: string | number | boolean;
};
/**
 * Classifies a column default. `{ expression }` and a legacy `'fn:'` string
 * are SQL expressions, trimmed with their comments kept (an empty `# ` comment
 * at the end is trimmed like whitespace); every other value is a literal.
 * Canonical definitions, which snapshots and plugin hooks see, always use the
 * `fn:` spelling, so read defaults through this function rather than
 * inspecting the raw value.
 */
export declare function parseColumnDefault(value: ColumnDefaultValue): ParsedColumnDefault;
/**
 * Snapshot form of a default: an expression in either spelling becomes the
 * trimmed `fn:` string (`{ expression: ' now() ' }` and `'fn: now()'` both give
 * `'fn:now()'`), so switching spellings plans nothing. Literals are unchanged.
 */
export declare function canonicalizeColumnDefault(value: ColumnDefaultValue): string | number | boolean;
/**
 * SQL for a column default, whatever its `defaultKind`. An expression is its
 * SQL without comments: chkit renders it on the column's line, where a `--`
 * comment would swallow the `,`, COMMENT, CODEC or `;` that follows (#234). A
 * string is a quoted literal with quotes and backslashes escaped; numbers and
 * booleans render as written.
 */
export declare function renderDefault(value: ColumnDefaultValue): string;
export declare function isSQLExpression(value: unknown): value is SQLExpression;
/** Whether a quoted string literal is a valid value of `type`, whatever its Nullable or LowCardinality wrappers. */
export declare function columnTypeAcceptsStringLiteral(type: string): boolean;
/**
 * Whether ClickHouse accepts any quoted string as a default of the rendered
 * column type `type` and stores NULL when the text does not parse: a Nullable
 * number, decimal, date, time, UUID or IP address. SimpleAggregateFunction
 * defers to its value type, as ClickHouse does.
 */
export declare function storesUnparsableLiteralAsNull(type: string): boolean;
/**
 * storesUnparsableLiteralAsNull for an EPHEMERAL default, which ClickHouse
 * reads but never stores, so it skips the checks for stored column types.
 * LowCardinality around a Nullable number, date, time, UUID or IP address
 * then reads NULL too, where a DEFAULT column of that type is refused; a type
 * that LowCardinality rejects (decimals, DateTime64, Time64) still fails.
 * Verified on ClickHouse 26.3 (#234).
 */
export declare function readsUnparsableEphemeralLiteralAsNull(type: string): boolean;
/** Text that starts with a function call, e.g. `now()` or `toDate(ts) + 1`. */
export declare function startsWithFunctionCall(value: string): boolean;
/**
 * Trims an expression. ClickHouse reads `#` as a comment only before a space
 * or `!`, so trimming the space of an empty `# ` comment at the end would
 * leave a bare `#`, a syntax error. That comment is trimmed with the
 * whitespace instead.
 */
export declare function trimExpression(sql: string): string;
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