#include "problems.h"

#include <print>

#include <leveldb/db.h>
#include <leveldb/write_batch.h>

#include <nlohmann/json.hpp>
#include <string>

using leveldb_ptr = leveldb::DB*;

auto problems_db    = leveldb_ptr{nullptr};
auto max_problem_id = 0;


extern "C"
{
    int open_problems_db()
    {
        auto opts = leveldb::Options{};

        opts.create_if_missing = true;

        auto status = leveldb::DB::Open(opts, "db/problems", &problems_db);

        if (!status.ok()) {
            std::println(stderr, "Failed to open problems database: {}", status.ToString());
            return 0;
        }

        auto value = std::string{};
        status     = problems_db->Get(leveldb::ReadOptions{}, "@", &value);
        if (status.ok()) {
            auto json = nlohmann::json::parse(value);
            json["max_problem_id"].get_to(max_problem_id);
        } else if (status.IsNotFound()) {
            auto json = nlohmann::json{
                {"max_problem_id", 0}
            };
            status = problems_db->Put(leveldb::WriteOptions{}, "@", json.dump());
            return 1;
        } else {
            std::println(stderr, "Failed to get max problem id: {}", status.ToString());
            delete problems_db;
            return 0;
        }
        return 1;
    }

    void close_problems_db()
    {
        delete problems_db;
    }

    int add_problem(const char* problem, const char* answer, const char* check_error, int* result)
    {
        auto batch = leveldb::WriteBatch{};
        ++max_problem_id;
        auto json = nlohmann::json{
            {"max_problem_id", max_problem_id}
        };
        batch.Put("@", json.dump());
        json = nlohmann::json{
            {"content", problem    },
            {"answer",  answer     },
            {"error",   check_error}
        };
        batch.Put(std::to_string(max_problem_id), json.dump());
        auto status = problems_db->Write(leveldb::WriteOptions{}, &batch);
        if (!status.ok()) {
            std::println(stderr, "Failed to add a problem: {}", status.ToString());
            return 0;
        }
        *result = max_problem_id;
        return 1;
    }

    int delete_problems(int problems_id)
    {
        auto batch  = leveldb::WriteBatch{};
        auto status = problems_db->Delete(leveldb::WriteOptions{}, std::to_string(problems_id));
        if (!status.ok()) {
            std::println(stderr, "Failed to delete a problem: {}", status.ToString());
            return 0;
        }
        return 1;
    }

    int get_problem(int id, char** result1, char** result2, char** result3)
    {
        auto value = std::string{};

        auto status = problems_db->Get(leveldb::ReadOptions{}, std::to_string(id), &value);
        if (!status.ok()) {
            std::println(stderr, "Failed to get a problem: {}", status.ToString());
            return 0;
        }

        auto json = nlohmann::json::parse(value);
        if (result1) {
            json["content"].get_to(value);
            *result1 = strdup(value.data());
        }
        if (result2) {
            json["answer"].get_to(value);
            *result2 = strdup(value.data());
        }
        if (result3) {
            json["error"].get_to(value);
            *result3 = strdup(value.data());
        }

        return 1;
    }

    int modify_problem(int problems_id, const char* problem, const char* answer, const char* check_error)
    {
        auto json = nlohmann::json{
            {"content", problem    },
            {"answer",  answer     },
            {"error",   check_error}
        };
        auto status = problems_db->Put(leveldb::WriteOptions{}, std::to_string(problems_id), json.dump());
        if (!status.ok()) {
            std::println(stderr, "Failed to modify a problem: {}", status.ToString());
            return 0;
        }
        return 1;
    }

    int check_answer(int problems_id, const char* answer, int* result)
    {
        auto value = std::string{};

        auto status = problems_db->Get(leveldb::ReadOptions{}, std::to_string(problems_id), &value);
        if (!status.ok()) {
            std::println(stderr, "Failed to check the answer: {}", status.ToString());
            return 0;
        }

        auto value2 = std::string{};
        auto json   = nlohmann::json::parse(value);

        json["answer"].get_to(value);
        json["error"].get_to(value2);

        if (value2.empty()) {
            *result = value == answer;
        } else {
            auto error       = std::stod(value2);
            auto std_answer  = std::stod(value);
            auto user_answer = std::stod(answer);
            *result          = std::fabs(std_answer - user_answer) <= error;
        }
        return 1;
    }

    int has_problem(int problems_id, int* result)
    {
        auto value = std::string{};

        auto status = problems_db->Get(leveldb::ReadOptions{}, std::to_string(problems_id), &value);
        if (status.ok()) {
            *result = 1;
        } else if (status.IsNotFound()) {
            *result = 0;
        } else {
            std::println(stderr, "Failed to check problem existence: {}", status.ToString());
            return 0;
        }
        return 1;
    }

    int all_problems(char** result)
    {
        auto problems = std::vector<int>{};

        leveldb::Iterator* it = problems_db->NewIterator(leveldb::ReadOptions());
        for (it->SeekToFirst(); it->Valid(); it->Next()) {
            if (!it->key().compare("@")) continue;
            problems.emplace_back(std::stoi(it->key().ToString()));
        }

        if (!it->status().ok()) {
            std::println(stderr, "Failed to get all problems: {}", it->status().ToString());
            return 0;
        }
        auto json = nlohmann::json(problems);

        *result = strdup(json.dump().c_str());
        return 1;
    }
}