// Copyright (c) 2019-2025 The Bitcoin developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
#include <rpc/blockchain.h>

#include <chain.h>

#include <test/setup_common.h>

#include <boost/test/unit_test.hpp>

#include <cstdlib>
#include <memory>

/**
 * Equality between doubles is imprecise. Comparison should be done
 * with a small threshold of tolerance, rather than exact equality.
 */
static bool DoubleEquals(double a, double b, double epsilon) {
    return std::abs(a - b) < epsilon;
}

using CBlockIndexPtr = std::unique_ptr<CBlockIndex>;

static CBlockIndexPtr CreateBlockIndexWithNbits(uint32_t nbits) {
    CBlockIndexPtr block_index = std::make_unique<CBlockIndex>();
    block_index->nHeight = 46367;
    block_index->nTime = 1269211443;
    block_index->nBits = nbits;
    return block_index;
}

static void RejectDifficultyMismatch(double difficulty,
                                     double expected_difficulty) {
    BOOST_CHECK_MESSAGE(DoubleEquals(difficulty, expected_difficulty, 0.00001),
                        "Difficulty was " + std::to_string(difficulty) +
                            " but was expected to be " +
                            std::to_string(expected_difficulty));
}

/**
 * Given a BlockIndex with the provided nbits,
 * verify that the expected difficulty results.
 */
static void TestDifficulty(uint32_t nbits, double expected_difficulty) {
    CBlockIndexPtr block_index = CreateBlockIndexWithNbits(nbits);
    double difficulty = GetDifficulty(block_index.get());

    RejectDifficultyMismatch(difficulty, expected_difficulty);
}

BOOST_FIXTURE_TEST_SUITE(blockchain_tests, BasicTestingSetup)

BOOST_AUTO_TEST_CASE(get_difficulty_for_very_low_target) {
    TestDifficulty(0x1f111111, 0.000001);
}

BOOST_AUTO_TEST_CASE(get_difficulty_for_low_target) {
    TestDifficulty(0x1ef88f6f, 0.000016);
}

BOOST_AUTO_TEST_CASE(get_difficulty_for_mid_target) {
    TestDifficulty(0x1df88f6f, 0.004023);
}

BOOST_AUTO_TEST_CASE(get_difficulty_for_high_target) {
    TestDifficulty(0x1cf88f6f, 1.029916);
}

BOOST_AUTO_TEST_CASE(get_difficulty_for_very_high_target) {
    TestDifficulty(0x12345678, 5913134931067755359633408.0);
}

BOOST_AUTO_TEST_SUITE_END()
