// 22_error_comparison.cpp
// 错误处理对比实战演练：错误码、std::optional、std::expected 三种写法（C++23）

#include <cstdio>
#include <expected>
#include <optional>
#include <string>

// ========== 方式一：错误码 ==========

constexpr int kErrDivisionByZero = -1;
constexpr int kErrSuccess = 0;

int divide_error_code(int a, int b, int* out) {
    if (b == 0) {
        return kErrDivisionByZero;
    }
    *out = a / b;
    return kErrSuccess;
}

// ========== 方式二：std::optional ==========

std::optional<int> divide_optional(int a, int b) {
    if (b == 0) {
        return std::nullopt;
    }
    return a / b;
}

// ========== 方式三：std::expected ==========

enum class MathError {
    DivisionByZero,
};

std::expected<int, MathError> divide_expected(int a, int b) {
    if (b == 0) {
        return std::unexpected(MathError::DivisionByZero);
    }
    return a / b;
}

// ========== 测试 ==========

int main() {
    struct TestCase {
        int a;
        int b;
        const char* label;
    };

    TestCase cases[] = {
        {10, 3, "10 / 3"},
        {10, 0, "10 / 0 (error)"},
        {7, 2, "7 / 2"},
    };

    for (const auto& tc : cases) {
        std::printf("--- Test: %s ---\n", tc.label);

        // 错误码版本
        int result_code = 0;
        int err = divide_error_code(tc.a, tc.b, &result_code);
        if (err == kErrSuccess) {
            std::printf("  [ErrorCode]  result = %d\n", result_code);
        } else {
            std::printf("  [ErrorCode]  error: division by zero\n");
        }

        // optional 版本
        auto result_opt = divide_optional(tc.a, tc.b);
        if (result_opt.has_value()) {
            std::printf("  [Optional]   result = %d\n", result_opt.value());
        } else {
            std::printf("  [Optional]   error: no value\n");
        }

        // expected 版本
        auto result_exp = divide_expected(tc.a, tc.b);
        if (result_exp.has_value()) {
            std::printf("  [Expected]   result = %d\n", result_exp.value());
        } else {
            switch (result_exp.error()) {
                case MathError::DivisionByZero:
                    std::printf("  [Expected]   error: DivisionByZero\n");
                    break;
            }
        }
    }

    return 0;
}