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#pragma once
#include <Core/Block.h>
#include <Core/Field.h>
#include <Interpreters/Context_fwd.h>
#include <Parsers/IAST.h>
#include <memory>
#include <optional>
namespace DB
{
class ExpressionActions;
class IDataType;
using ExpressionActionsPtr = std::shared_ptr<ExpressionActions>;
/** Evaluate constant expression and its type.
* Used in rare cases - for elements of set for IN, for data to INSERT.
* Throws exception if it's not a constant expression.
* Quite suboptimal.
*/
std::pair<Field, std::shared_ptr<const IDataType>> evaluateConstantExpression(const ASTPtr & node, const ContextPtr & context);
/** Evaluate constant expression and returns ASTLiteral with its value.
*/
ASTPtr evaluateConstantExpressionAsLiteral(const ASTPtr & node, const ContextPtr & context);
/** Evaluate constant expression and returns ASTLiteral with its value.
* Also, if AST is identifier, then return string literal with its name.
* Useful in places where some name may be specified as identifier, or as result of a constant expression.
*/
ASTPtr evaluateConstantExpressionOrIdentifierAsLiteral(const ASTPtr & node, const ContextPtr & context);
/** The same as evaluateConstantExpressionOrIdentifierAsLiteral(...),
* but if result is an empty string, replace it with current database name
* or default database name.
*/
ASTPtr evaluateConstantExpressionForDatabaseName(const ASTPtr & node, const ContextPtr & context);
/** Try to fold condition to countable set of constant values.
* @param node a condition that we try to fold.
* @param target_expr expression evaluated over a set of constants.
* @param limit limit for number of values
* @return optional blocks each with a single row and a single column for target expression,
* or empty blocks if condition is always false,
* or nothing if condition can't be folded to a set of constants.
*/
std::optional<Blocks> evaluateExpressionOverConstantCondition(const ASTPtr & node, const ExpressionActionsPtr & target_expr, size_t & limit);
}
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