#include <Columns/ColumnConst.h>
#include <Functions/FunctionHelpers.h>
#include <Functions/FunctionTokens.h>
#include <Functions/FunctionFactory.h>
#include <Common/StringUtils/StringUtils.h>
#include <Common/assert_cast.h>


namespace DB
{

namespace ErrorCodes
{
    extern const int ILLEGAL_COLUMN;
}


/** Functions that split strings into an array of strings or vice versa.
  *
  * splitByString(sep, s[, max_substrings])
  */
namespace
{

using Pos = const char *;

class SplitByStringImpl
{
private:
    Pos pos;
    Pos end;
    String separator;
    std::optional<size_t> max_splits;
    size_t splits;
    bool max_substrings_includes_remaining_string;

public:
    static constexpr auto name = "splitByString";
    static bool isVariadic() { return true; }
    static size_t getNumberOfArguments() { return 0; }

    static ColumnNumbers getArgumentsThatAreAlwaysConstant() { return {0, 2}; }

    static void checkArguments(const IFunction & func, const ColumnsWithTypeAndName & arguments)
    {
        checkArgumentsWithSeparatorAndOptionalMaxSubstrings(func, arguments);
    }

    static constexpr auto strings_argument_position = 1uz;

    void init(const ColumnsWithTypeAndName & arguments, bool max_substrings_includes_remaining_string_)
    {
        const ColumnConst * col = checkAndGetColumnConstStringOrFixedString(arguments[0].column.get());

        if (!col)
            throw Exception(ErrorCodes::ILLEGAL_COLUMN, "Illegal column {} of first argument of function {}. "
                "Must be constant string.", arguments[0].column->getName(), name);

        separator = col->getValue<String>();

        max_substrings_includes_remaining_string = max_substrings_includes_remaining_string_;
        max_splits = extractMaxSplits(arguments, 2);
    }

    /// Called for each next string.
    void set(Pos pos_, Pos end_)
    {
        pos = pos_;
        end = end_;
        splits = 0;
    }

    /// Get the next token, if any, or return false.
    bool get(Pos & token_begin, Pos & token_end)
    {
        if (separator.empty())
        {
            if (pos == end)
                return false;

            token_begin = pos;

            if (max_splits)
            {
                if (max_substrings_includes_remaining_string)
                {
                    if (splits == *max_splits - 1)
                    {
                        token_end = end;
                        pos = end;
                        return true;
                    }
                }
                else
                    if (splits == *max_splits)
                        return false;
            }

            pos += 1;
            token_end = pos;
            ++splits;
        }
        else
        {
            if (!pos)
                return false;

            token_begin = pos;

            if (max_splits)
            {
                if (max_substrings_includes_remaining_string)
                {
                    if (splits == *max_splits - 1)
                    {
                        token_end = end;
                        pos = nullptr;
                        return true;
                    }
                }
                else
                    if (splits == *max_splits)
                        return false;
            }

            pos = reinterpret_cast<Pos>(memmem(pos, end - pos, separator.data(), separator.size()));
            if (pos)
            {
                token_end = pos;
                pos += separator.size();
                ++splits;
            }
            else
                token_end = end;
        }

        return true;
    }
};

using FunctionSplitByString = FunctionTokens<SplitByStringImpl>;

}

REGISTER_FUNCTION(SplitByString)
{
    factory.registerFunction<FunctionSplitByString>();
}

}