ClickHouse/dbms/src/Functions/FunctionHelpers.h

#pragma once

#include <Common/typeid_cast.h>
#include <Common/assert_cast.h>
#include <DataTypes/IDataType.h>
#include <Columns/IColumn.h>
#include <Columns/ColumnArray.h>
#include <Columns/ColumnConst.h>
#include <Core/Block.h>
#include <Core/ColumnNumbers.h>
#include <Core/callOnTypeIndex.h>


namespace DB
{

class IFunction;

/// Methods, that helps dispatching over real column types.

template <typename Type>
const Type * checkAndGetDataType(const IDataType * data_type)
{
    return typeid_cast<const Type *>(data_type);
}

template <typename Type>
const ColumnConst * checkAndGetColumnConst(const IColumn * column)
{
    if (!column || !isColumnConst(*column))
        return {};

    const ColumnConst * res = assert_cast<const ColumnConst *>(column);

    if (!checkColumn<Type>(&res->getDataColumn()))
        return {};

    return res;
}

template <typename Type>
const Type * checkAndGetColumnConstData(const IColumn * column)
{
    const ColumnConst * res = checkAndGetColumnConst<Type>(column);

    if (!res)
        return {};

    return static_cast<const Type *>(&res->getDataColumn());
}

template <typename Type>
bool checkColumnConst(const IColumn * column)
{
    return checkAndGetColumnConst<Type>(column);
}

/// Returns non-nullptr if column is ColumnConst with ColumnString or ColumnFixedString inside.
const ColumnConst * checkAndGetColumnConstStringOrFixedString(const IColumn * column);


/// Transform anything to Field.
template <typename T>
inline std::enable_if_t<!IsDecimalNumber<T>, Field> toField(const T & x)
{
    return Field(NearestFieldType<T>(x));
}

template <typename T>
inline std::enable_if_t<IsDecimalNumber<T>, Field> toField(const T & x, UInt32 scale)
{
    return Field(NearestFieldType<T>(x, scale));
}


Columns convertConstTupleToConstantElements(const ColumnConst & column);


/// Returns the copy of a given block in which each column specified in
/// the "arguments" parameter is replaced with its respective nested
/// column if it is nullable.
Block createBlockWithNestedColumns(const Block & block, const ColumnNumbers & args);

/// Similar function as above. Additionally transform the result type if needed.
Block createBlockWithNestedColumns(const Block & block, const ColumnNumbers & args, size_t result);

/// Checks argument type at specified index with predicate.
/// throws if there is no argument at specified index or if predicate returns false.
void validateArgumentType(const IFunction & func, const DataTypes & arguments,
        size_t argument_index, bool (* validator_func)(const IDataType &),
        const char * expected_type_description);

// Simple validator that is used in conjunction with validateFunctionArgumentTypes() to check if function arguments are as expected.
struct FunctionArgumentDescriptor
{
    const char * argument_name;

    bool (* type_validator_func)(const IDataType &);
    bool (* column_validator_func)(const IColumn &);

    const char * expected_type_description;

    bool isValid(const DataTypePtr & data_type, const ColumnPtr & column) const;
};

using FunctionArgumentDescriptors = std::vector<FunctionArgumentDescriptor>;

/** Validate that function arguments match specification.
 *
 * Designed to simplify argument validation
 * for functions with variable arguments (e.g. depending on result type or other trait).
 * first, checks that mandatory args present and have valid type.
 * second, checks optional arguents types, skipping ones that are missing.
 *
 * Please note that if you have several optional arguments, like f([a, b, c]),
 * only these calls are considered valid:
 *  f(a)
 *  f(a, b)
 *  f(a, b, c)
 *
 * But NOT these: f(a, c), f(b, c)
 * In other words you can't skip
 *
 * If any mandatory arg is missing, throw an exception, with explicit description of expected arguments.
 */
void validateFunctionArgumentTypes(const IFunction & func, const ColumnsWithTypeAndName & arguments,
                                   const FunctionArgumentDescriptors & mandatory_args,
                                   const FunctionArgumentDescriptors & optional_args = {});

/// Checks if a list of array columns have equal offsets. Return a pair of nested columns and offsets if true, otherwise throw.
std::pair<std::vector<const IColumn *>, const ColumnArray::Offset *>
checkAndGetNestedArrayOffset(const IColumn ** columns, size_t num_arguments);

}