/**
 *    Copyright (C) 2018-present MongoDB, Inc.
 *
 *    This program is free software: you can redistribute it and/or modify
 *    it under the terms of the Server Side Public License, version 1,
 *    as published by MongoDB, Inc.
 *
 *    This program is distributed in the hope that it will be useful,
 *    but WITHOUT ANY WARRANTY; without even the implied warranty of
 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *    Server Side Public License for more details.
 *
 *    You should have received a copy of the Server Side Public License
 *    along with this program. If not, see
 *    <http://www.mongodb.com/licensing/server-side-public-license>.
 *
 *    As a special exception, the copyright holders give permission to link the
 *    code of portions of this program with the OpenSSL library under certain
 *    conditions as described in each individual source file and distribute
 *    linked combinations including the program with the OpenSSL library. You
 *    must comply with the Server Side Public License in all respects for
 *    all of the code used other than as permitted herein. If you modify file(s)
 *    with this exception, you may extend this exception to your version of the
 *    file(s), but you are not obligated to do so. If you do not wish to do so,
 *    delete this exception statement from your version. If you delete this
 *    exception statement from all source files in the program, then also delete
 *    it in the license file.
 */

#include "mongo/platform/basic.h"

#include "mongo/util/itoa.h"

#include <cstdint>
#include <type_traits>

#include "mongo/base/string_data.h"
#include "mongo/platform/bits.h"
#include "mongo/util/assert_util.h"
#include "mongo/util/itoa_table_4.h"  // Generated by generate_itoa_table.py

namespace mongo {
namespace {

constexpr std::size_t kTableDigits = 4;

constexpr std::size_t pow10(std::size_t n) {
    return n ? 10 * pow10(n - 1) : 1;
}

constexpr std::size_t kTableSize = pow10(kTableDigits);

// Cheesing gTable initializer out to Python and CPP due to compiler-imposed constexpr
// complexity restrictions (clang, msvc). C'est la vie.  See `generate_itoa_table.py`.
constexpr struct {
    std::uint8_t n;
    char s[kTableDigits];
} gTable[] = {
#define EXPAND_PACK_(...) __VA_ARGS__
#define MAKE_ENTRY_(n, digitPack) \
    { n, EXPAND_PACK_ digitPack }
#define COMMA_ ,
    ITOA_TABLE_EXPAND_4(MAKE_ENTRY_, COMMA_)
#undef COMMA_
#undef MAKE_ENTRY_
#undef EXPAND_PACK_
};
static_assert(std::extent_v<decltype(gTable)> == kTableSize, "gTable has correct size.");

}  // namespace

ItoA::ItoA(std::uint64_t val) {
    if (val < kTableSize) {
        const auto& e = gTable[val];
        std::size_t n = e.n;
        _str = StringData(std::end(e.s) - n, n);
        return;
    }
    char* p = std::end(_buf);
    while (val >= kTableSize) {
        std::size_t idx = val % kTableSize;
        val /= kTableSize;
        const auto& e = gTable[idx];
        p -= kTableDigits;
        memcpy(p, std::end(e.s) - kTableDigits, kTableDigits);
    }
    const auto& e = gTable[val];
    auto n = e.n;
    p -= n;
    memcpy(p, std::end(e.s) - n, n);
    _str = StringData(p, std::end(_buf) - p);
}

}  // namespace mongo