//
// Created by Grant Horner on 12/4/25.
//

#include <ranges>
#include <string>
#include <vector>

#include "doctest.h"
#include "utils.h"

namespace day4 {
const std::string sample =
        "..@@.@@@@.\n"
        "@@@.@.@.@@\n"
        "@@@@@.@.@@\n"
        "@.@@@@..@.\n"
        "@@.@@@@.@@\n"
        ".@@@@@@@.@\n"
        ".@.@.@.@@@\n"
        "@.@@@.@@@@\n"
        ".@@@@@@@@.\n"
        "@.@.@@@.@.\n";

enum class Point : char {
    Paper = '@',
    Empty = '.',
};

template<typename T>
std::array<char, 8> get_surrounding(const std::vector<T> &lines, size_t x, size_t y) noexcept {
    std::array<char, 8> points = {};
    size_t i = 0;
    for (int dy = -1; dy < 2; ++dy) {
        if (y + dy < 0 || y + dy >= lines.size()) { continue; }
        for (int dx = -1; dx < 2; ++dx) {
            if (x + dx < 0 || x + dx >= lines[0].size()) { continue; }
            if (dx == 0 && dy == 0) continue;

            points[i] = lines[y + dy][x + dx];
            i++;
        }
    }

    return points;
}

uint32_t solve_first(const std::string_view input) noexcept {
    const auto lines = std::string_view{input}
                       | std::views::split('\n')
                       | std::views::transform(to_string_view)
                       | std::views::filter([](const auto s) { return !s.empty(); })
                       | std::ranges::to<std::vector>();

    uint32_t accessible = 0;

    for (size_t y = 0; y < lines.size(); ++y) {
        for (size_t x = 0; x < lines[0].size(); ++x) {
            const auto c = lines[y][x];
            if (c != '@') continue;
            size_t num_paper = 0;
            for (const char p: get_surrounding(lines, x, y)) {
                if (p == '@') {
                    num_paper++;
                }
                if (num_paper == 4) {
                    break;
                }
            }

            if (num_paper < 4) {
                accessible++;
            }
        }
    }

    return accessible;
}

template<typename T>
std::vector<std::tuple<size_t, size_t> > remove_paper(const std::vector<T> &lines) {
    std::vector<std::tuple<size_t, size_t> > removable = {};

    for (size_t y = 0; y < lines.size(); ++y) {
        for (size_t x = 0; x < lines[0].size(); ++x) {
            const auto c = lines[y][x];
            if (c != '@') continue;
            size_t num_paper = 0;
            for (const char p: get_surrounding(lines, x, y)) {
                if (p == '@') {
                    num_paper++;
                }
                if (num_paper == 4) {
                    break;
                }
            }

            if (num_paper < 4) {
                removable.emplace_back(x, y);
            }
        }
    }

    return removable;
}

uint32_t solve_second(const std::string_view input) {
    std::vector<std::string> lines = std::string_view{input}
                                     | std::views::split('\n')
                                     | std::views::transform([](const auto r) {
                                         return std::string(r.data(), r.size());
                                     })
                                     | std::views::filter([](const auto &s) { return !s.empty(); })
                                     | std::ranges::to<std::vector>();
    bool removed = false;
    uint32_t total_removed = 0;
    do {
        removed = false;
        const auto removable = remove_paper(lines);
        if (!removable.empty()) {
            removed = true;
        }
        for (auto [x, y]: removable) {
            lines[y][x] = '.';
            total_removed++;
        }
    } while (removed);

    return total_removed;
}

TEST_SUITE_BEGIN("Day 4");

TEST_CASE("solves first sample") {
    CHECK(solve_first(sample) == 13);
}

TEST_CASE("solves first puzzle") {
    CHECK(solve_first(read_file("day4input.txt")) == 1626);
}


TEST_CASE("solves second sample") {
    CHECK(solve_second(sample) == 43);
}

TEST_CASE("solves second puzzle") {
    CHECK(solve_second(read_file("day4input.txt")) == 9173);
}

TEST_SUITE_END();
}