// Solutions to the Advent Of Code 2024.
// Copyright (C) 2025  Stefan Müller
//
// This program is free software: you can redistribute it and/or modify it under
// the terms of the GNU General Public License as published by the Free Software
// Foundation, either version 3 of the License, or (at your option) any later
// version.
//
// 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 GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License along with
// this program.  If not, see <http://www.gnu.org/licenses/>.

#include <aoc/BridgeRepair.hpp>

#include <cmath>
#include <sstream>

#include <aoc/Math.hpp>

const std::string BridgeRepair::getPuzzleName() const
{
    return "Bridge Repair";
}

const int BridgeRepair::getPuzzleDay() const
{
    return 7;
}

void BridgeRepair::processDataLine(const std::string& line)
{
    std::istringstream stream{ line };

    long long int testValue;
    char colon;
    int calibrationNumber;
    // Calibration numbers are a pair of an actual calibration number and its precomputed smallest larger power of 10.
    // The precomputed numbers are used to facilitate the "concatenate" operator.
    std::vector<std::pair<int, int>> calibrationNumbers{};

    stream >> testValue >> colon;
    while (stream >> calibrationNumber)
    {
        // Skips the precomputation for the first calibration numbers.
        int pow10{ 0 };
        if (!calibrationNumbers.empty())
        {
            pow10 =  Math::ipow(10, static_cast<int>(floor(log10(calibrationNumber))) + 1);
        }
        calibrationNumbers.push_back({ calibrationNumber, pow10 });
    }

    if (testCalibration(testValue, calibrationNumbers, 1, false, calibrationNumbers[0].first))
    {
        part1 += testValue;
        part2 += testValue;
    }
    else if (testCalibration(testValue, calibrationNumbers, 1, true, calibrationNumbers[0].first))
    {
        part2 += testValue;
    }
}

void BridgeRepair::finish()
{
}

bool BridgeRepair::testCalibration(const long long int testValue,
    const std::vector<std::pair<int, int>>& calibrationNumbers, const size_t currentIndex,
    const bool allowConcatenation, const long long int accumulatedTestValue)
{
    if (testValue >= accumulatedTestValue && currentIndex < calibrationNumbers.size())
    {
        size_t nextIndex{ currentIndex + 1 };
        long long int nextCalibrationNumber{ calibrationNumbers[currentIndex].first };
        // Recursively tries the ||, *, and + operators.
        if ((allowConcatenation && testCalibration(testValue, calibrationNumbers, nextIndex, allowConcatenation,
                accumulatedTestValue * calibrationNumbers[currentIndex].second + calibrationNumbers[currentIndex].first)) ||
            testCalibration(testValue, calibrationNumbers, nextIndex, allowConcatenation,
                accumulatedTestValue * calibrationNumbers[currentIndex].first) ||
            testCalibration(testValue, calibrationNumbers, nextIndex, allowConcatenation,
                accumulatedTestValue + calibrationNumbers[currentIndex].first))
        {
            return true;
        }
    }
    else if (testValue == accumulatedTestValue)
    {
        return true;
    }
    return false;
}