// Copyright (c) 2009-2010 Satoshi Nakamoto
// Copyright (c) 2009-present The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.

#ifndef BITCOIN_UINT256_H
#define BITCOIN_UINT256_H

#include <crypto/common.h>
#include <span.h>
#include <util/strencodings.h>

#include <algorithm>
#include <array>
#include <cassert>
#include <cstdint>
#include <cstring>
#include <optional>
#include <string>

/** Template base class for fixed-sized opaque blobs. */
template<unsigned int BITS>
class base_blob
{
protected:
    static constexpr int WIDTH = BITS / 8;
    static_assert(BITS % 8 == 0, "base_blob currently only supports whole bytes.");
    std::array<uint8_t, WIDTH> m_data;
    static_assert(WIDTH == sizeof(m_data), "Sanity check");

public:
    /* construct 0 value by default */
    constexpr base_blob() : m_data() {}

    /* constructor for constants between 1 and 255 */
    constexpr explicit base_blob(uint8_t v) : m_data{v} {}

    constexpr explicit base_blob(Span<const unsigned char> vch)
    {
        assert(vch.size() == WIDTH);
        std::copy(vch.begin(), vch.end(), m_data.begin());
    }

    constexpr bool IsNull() const
    {
        return std::all_of(m_data.begin(), m_data.end(), [](uint8_t val) {
            return val == 0;
        });
    }

    constexpr void SetNull()
    {
        std::fill(m_data.begin(), m_data.end(), 0);
    }

    constexpr int Compare(const base_blob& other) const { return std::memcmp(m_data.data(), other.m_data.data(), WIDTH); }

    friend constexpr bool operator==(const base_blob& a, const base_blob& b) { return a.Compare(b) == 0; }
    friend constexpr bool operator!=(const base_blob& a, const base_blob& b) { return a.Compare(b) != 0; }
    friend constexpr bool operator<(const base_blob& a, const base_blob& b) { return a.Compare(b) < 0; }

    // Hex string representations are little-endian.
    std::string GetHex() const;
    /** Unlike FromHex this accepts any invalid input, thus it is fragile and deprecated */
    void SetHexDeprecated(std::string_view str);
    std::string ToString() const;

    constexpr const unsigned char* data() const { return m_data.data(); }
    constexpr unsigned char* data() { return m_data.data(); }

    constexpr unsigned char* begin() { return m_data.data(); }
    constexpr unsigned char* end() { return m_data.data() + WIDTH; }

    constexpr const unsigned char* begin() const { return m_data.data(); }
    constexpr const unsigned char* end() const { return m_data.data() + WIDTH; }

    static constexpr unsigned int size() { return WIDTH; }

    constexpr uint64_t GetUint64(int pos) const { return ReadLE64(m_data.data() + pos * 8); }

    template<typename Stream>
    void Serialize(Stream& s) const
    {
        s << Span(m_data);
    }

    template<typename Stream>
    void Unserialize(Stream& s)
    {
        s.read(MakeWritableByteSpan(m_data));
    }
};

namespace detail {
/**
 * Writes the hex string (treated as little-endian) into a new uintN_t object
 * and only returns a value iff all of the checks pass:
 *   - Input length is uintN_t::size()*2
 *   - All characters are hex
 */
template <class uintN_t>
std::optional<uintN_t> FromHex(std::string_view str)
{
    if (uintN_t::size() * 2 != str.size() || !IsHex(str)) return std::nullopt;
    uintN_t rv;
    rv.SetHexDeprecated(str);
    return rv;
}
} // namespace detail

/** 160-bit opaque blob.
 * @note This type is called uint160 for historical reasons only. It is an opaque
 * blob of 160 bits and has no integer operations.
 */
class uint160 : public base_blob<160> {
public:
    static std::optional<uint160> FromHex(std::string_view str) { return detail::FromHex<uint160>(str); }
    constexpr uint160() = default;
    constexpr explicit uint160(Span<const unsigned char> vch) : base_blob<160>(vch) {}
};

/** 256-bit opaque blob.
 * @note This type is called uint256 for historical reasons only. It is an
 * opaque blob of 256 bits and has no integer operations. Use arith_uint256 if
 * those are required.
 */
class uint256 : public base_blob<256> {
public:
    static std::optional<uint256> FromHex(std::string_view str) { return detail::FromHex<uint256>(str); }
    constexpr uint256() = default;
    constexpr explicit uint256(uint8_t v) : base_blob<256>(v) {}
    constexpr explicit uint256(Span<const unsigned char> vch) : base_blob<256>(vch) {}
    static const uint256 ZERO;
    static const uint256 ONE;
};

/* uint256 from std::string_view, treated as little-endian.
 * DEPRECATED. Unlike FromHex this accepts any invalid input, thus it is fragile and deprecated!
 */
inline uint256 uint256S(std::string_view str)
{
    uint256 rv;
    rv.SetHexDeprecated(str);
    return rv;
}

#endif // BITCOIN_UINT256_H
