/*
 * libfud
 * Copyright 2024 Dominick Allen
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifndef FUD_STRING_CONVERT_HPP
#define FUD_STRING_CONVERT_HPP

#include "fud_algorithm.hpp"
#include "fud_option.hpp"
#include "fud_result.hpp"
#include "fud_status.hpp"
#include "fud_string.hpp"
#include "fud_string_view.hpp"

#include <cmath>
#include <cstdint>

namespace fud {

enum class Radix : uint8_t
{
    Binary = 2,
    Octal = 8,
    Decimal = 10,
    Hexadecimal = 16,
};

constexpr uint8_t RadixMax = 36;

template <typename T>
struct ConvertValue {
    size_t nextIndex;
    T value;
};

template <typename T>
using StringConvertResult = Result<ConvertValue<T>, FudStatus>;

template <typename T>
StringConvertResult<T> fromString(StringView inputView, Option<uint8_t> specifiedRadixOption = NullOpt);

template <typename T>
StringConvertResult<T> fromString(StringView inputView, Radix specifiedRadixOption);

template <typename T>
StringConvertResult<T> fromString(const String& inputView, Option<uint8_t> specifiedRadixOption = NullOpt);

namespace impl {
constexpr Array<int8_t, 256> AsciiLookup{
    {-1, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2,
     -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, -2, 0,  1,  2,  3,  4,  5,  6,  7,  8,  9,
     -2, -2, -2, -2, -2, -2, -2, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31,
     32, 33, 34, 35, -2, -2, -2, -2, -2, -2, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28,
     29, 30, 31, 32, 33, 34, 35, -2, -2, -2, -2, -2, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3,
     -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3,
     -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3,
     -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3,
     -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3, -3}};

// NOLINTBEGIN(readability-magic-numbers)
static_assert(AsciiLookup[static_cast<size_t>('0')] == 0);
static_assert(AsciiLookup[static_cast<size_t>('1')] == 1);
static_assert(AsciiLookup[static_cast<size_t>('2')] == 2);
static_assert(AsciiLookup[static_cast<size_t>('3')] == 3);
static_assert(AsciiLookup[static_cast<size_t>('4')] == 4);
static_assert(AsciiLookup[static_cast<size_t>('5')] == 5);
static_assert(AsciiLookup[static_cast<size_t>('6')] == 6);
static_assert(AsciiLookup[static_cast<size_t>('7')] == 7);
static_assert(AsciiLookup[static_cast<size_t>('8')] == 8);
static_assert(AsciiLookup[static_cast<size_t>('9')] == 9);
static_assert(AsciiLookup[static_cast<size_t>('a')] == 10);
static_assert(AsciiLookup[static_cast<size_t>('b')] == 11);
static_assert(AsciiLookup[static_cast<size_t>('c')] == 12);
static_assert(AsciiLookup[static_cast<size_t>('d')] == 13);
static_assert(AsciiLookup[static_cast<size_t>('e')] == 14);
static_assert(AsciiLookup[static_cast<size_t>('f')] == 15);
static_assert(AsciiLookup[static_cast<size_t>('A')] == 10);
static_assert(AsciiLookup[static_cast<size_t>('B')] == 11);
static_assert(AsciiLookup[static_cast<size_t>('C')] == 12);
static_assert(AsciiLookup[static_cast<size_t>('D')] == 13);
static_assert(AsciiLookup[static_cast<size_t>('E')] == 14);
static_assert(AsciiLookup[static_cast<size_t>('F')] == 15);
static_assert(AsciiLookup[127] == -2);
static_assert(AsciiLookup[128] == -3);
// NOLINTEND(readability-magic-numbers)

FudStatus checkPlusSigned(StringView& view, size_t& skipIndex);

Result<Radix, FudStatus> determineRadix(StringView input, size_t& index);

Result<bool, FudStatus> checkNegative(StringView& view, size_t& skipIndex);

Result<uint8_t, FudStatus> getRadix(StringView& view, size_t& skipIndex, Option<uint8_t> specifiedRadixOption);

template <typename T>
StringConvertResult<T> unsignedFromString(StringView nextView, size_t skipIndex, Option<uint8_t> specifiedRadixOption)
{
    static_assert(std::is_unsigned_v<T> && std::is_integral_v<T>);
    auto status = checkPlusSigned(nextView, skipIndex);
    if (status != FudStatus::Success) {
        return FudStatus::ArgumentInvalid;
    }

    auto radixResult = impl::getRadix(nextView, skipIndex, specifiedRadixOption);
    if (radixResult.isError()) {
        return radixResult.takeError();
    }
    auto radix = radixResult.takeOkay();

    T num = 0;
    size_t digitIndex = 0;

    while (digitIndex < nextView.length()) {
        auto digitResult = impl::AsciiLookup[nextView.data()[digitIndex]];
        if (digitResult >= radix || digitResult < 0) {
            break;
        }

        auto digit = static_cast<uint8_t>(digitResult);
        if (std::numeric_limits<T>::max() / radix < num) {
            return FudStatus::RangeError;
        }
        num *= radix;
        if (std::numeric_limits<T>::max() - digit < num) {
            return FudStatus::RangeError;
        }
        num += digit;
        digitIndex++;
    }
    if (digitIndex < 1) {
        return FudStatus::ArgumentInvalid;
    }

    return ConvertValue{skipIndex + digitIndex, num};
}

template <typename T>
FudStatus signedPositiveFromString(StringView view, uint8_t radix, size_t& digitIndex, T& num)
{
    digitIndex = 0;
    while (digitIndex < view.length()) {
        int8_t digitResult = impl::AsciiLookup[view.data()[digitIndex]];
        if (digitResult >= radix || digitResult < 0) {
            break;
        }

        auto digit = static_cast<uint8_t>(digitResult);
        if (std::numeric_limits<T>::max() / radix < num) {
            return FudStatus::RangeError;
        }
        num = static_cast<T>(num * radix);
        if (std::numeric_limits<T>::max() - digit < num) {
            return FudStatus::RangeError;
        }
        num = static_cast<T>(num + digit);
        digitIndex++;
    }

    return FudStatus::Success;
}

template <typename T>
FudStatus signedNegativeFromString(StringView view, uint8_t radix, size_t& digitIndex, T& num)
{
    digitIndex = 0;
    while (digitIndex < view.length()) {
        int8_t digitResult = impl::AsciiLookup[view.data()[digitIndex]];
        if (digitResult >= radix || digitResult < 0) {
            break;
        }

        auto digit = static_cast<uint8_t>(digitResult);
        if ((std::numeric_limits<T>::min() / radix > num)) {
            return FudStatus::RangeError;
        }
        num = static_cast<T>(num * radix);
        if (std::numeric_limits<T>::min() + digit > num) {
            return FudStatus::RangeError;
        }
        num = static_cast<T>(num - digit);
        digitIndex++;
    }

    return FudStatus::Success;
}

template <typename T>
StringConvertResult<T> signedFromString(StringView nextView, size_t skipIndex, Option<uint8_t> specifiedRadixOption)
{
    static_assert(std::is_signed_v<T> && std::is_integral_v<T>);
    auto status = impl::checkPlusSigned(nextView, skipIndex);
    if (status != FudStatus::Success) {
        return FudStatus::ArgumentInvalid;
    }

    auto radixResult = impl::getRadix(nextView, skipIndex, specifiedRadixOption);
    if (radixResult.isError()) {
        return radixResult.takeError();
    }
    auto radix = radixResult.takeOkay();

    T num = 0;
    size_t digitIndex = 0;

    auto isNegativeResult = checkNegative(nextView, skipIndex);
    if (isNegativeResult.isError()) {
        return isNegativeResult.takeError();
    }
    const auto isNegative = isNegativeResult.takeOkay();

    if (isNegative) {
        status = signedNegativeFromString(nextView, radix, digitIndex, num);
    } else {
        status = signedPositiveFromString(nextView, radix, digitIndex, num);
    }

    if (status != FudStatus::Success) {
        return status;
    }

    if (digitIndex < 1) {
        return FudStatus::ArgumentInvalid;
    }

    return ConvertValue{skipIndex + digitIndex, num};
}

template <typename T>
bool isNanOrInf(T& num, StringView& view, T& sign, size_t& digitIndex)
{
    if (view.length() >= 3) {
        Array<uint8_t, 3> letters{{view.data()[0], view.data()[1], view.data()[2]}};
        forEach(letters.span(), charToLower);
        if (letters[0] == 'i' && letters[1] == 'n' && letters[2] == 'f') {
            num = sign * std::numeric_limits<T>::infinity();
            digitIndex = 3;
            return true;
        }
        if (letters[0] == 'n' && letters[1] == 'a' && letters[2] == 'n') {
            num = std::numeric_limits<T>::quiet_NaN();
            digitIndex = 3;
            return true;
        }
    }
    return false;
}

template <typename T>
FudStatus getWhole(
    const StringView view,
    size_t& digitIndex,
    T& num,
    T sign,
    uint8_t radix,
    bool& foundDecimal,
    bool& foundExponent)
{
    while (digitIndex < view.length()) {
        auto nextChar = view.data()[digitIndex];
        if (nextChar == '.') {
            foundDecimal = true;
            digitIndex++;
            break;
        }

        if (radix == static_cast<uint8_t>(Radix::Decimal) && (nextChar == 'e' || nextChar == 'E')) {
            foundExponent = true;
            digitIndex++;
            break;
        }

        auto digitResult = impl::AsciiLookup[nextChar];
        if (digitResult >= radix) {
            return FudStatus::ArgumentInvalid;
        }
        if (digitResult < 0) {
            break;
        }
        auto digit = static_cast<T>(digitResult) * sign;
        num *= static_cast<T>(radix);

        num += digit;
        digitIndex++;
    }
    return FudStatus::Success;
}

template <typename T>
FudStatus getExponent(StringView view, size_t& digitIndex, T& num, uint8_t radix)
{
    StringView tempView{view.length() - digitIndex, view.data() + digitIndex};
    size_t exponentLength{};
    auto convertResult = signedFromString<int32_t>(tempView, exponentLength, static_cast<uint8_t>(Radix::Decimal));
    if (convertResult.isError()) {
        return convertResult.takeError();
    }
    auto convertValue = convertResult.takeOkay();
    digitIndex += convertValue.nextIndex + exponentLength;
    num = num * std::pow(static_cast<T>(radix), static_cast<T>(convertValue.value));
    return FudStatus::Success;
}

template <typename T>
FudStatus getFraction(const StringView view, size_t& digitIndex, T& num, T sign, uint8_t radix, bool& foundExponent)
{
    auto radixDiv = static_cast<T>(1) / static_cast<T>(radix);
    while (digitIndex < view.length()) {
        auto nextChar = view.data()[digitIndex];
        if (radix == static_cast<uint8_t>(Radix::Decimal) && (nextChar == 'e' || nextChar == 'E')) {
            foundExponent = true;
            digitIndex++;
            break;
        }

        auto digitResult = impl::AsciiLookup[nextChar];
        if (digitResult >= radix) {
            return FudStatus::ArgumentInvalid;
        }
        if (digitResult < 0) {
            break;
        }
        auto digit = static_cast<T>(digitResult) * sign;
        num += digit * radixDiv;
        radixDiv /= static_cast<T>(radix);
        digitIndex++;
    }
    return FudStatus::Success;
}

template <typename T>
StringConvertResult<T> floatFromString(StringView nextView, size_t skipIndex, Option<uint8_t> specifiedRadixOption)
{
    static_assert(std::is_floating_point_v<T>);
    if (nextView.length() < 1) {
        return FudStatus::ArgumentInvalid;
    }

    auto isNegativeResult = checkNegative(nextView, skipIndex);
    if (isNegativeResult.isError()) {
        return isNegativeResult.takeError();
    }
    const auto isNegative = isNegativeResult.takeOkay();

    if (!isNegative) {
        auto status = checkPlusSigned(nextView, skipIndex);
        if (status != FudStatus::Success) {
            return FudStatus::ArgumentInvalid;
        }
    }
    T sign = isNegative ? -1.0 : 1.0;

    T num = 0;
    size_t digitIndex = 0;

    auto retSuccess = [&]() { return ConvertValue{skipIndex + digitIndex, num}; };

    if (impl::isNanOrInf(num, nextView, sign, digitIndex)) {
        return retSuccess();
    }

    auto radixResult = impl::getRadix(nextView, skipIndex, specifiedRadixOption);
    if (radixResult.isError()) {
        return radixResult.takeError();
    }
    auto radix = radixResult.takeOkay();

    bool foundDecimal = false;
    bool foundExponent = false;
    auto status = getWhole(nextView, digitIndex, num, sign, radix, foundDecimal, foundExponent);

    if (status == FudStatus::Success && foundExponent) {
        status = getExponent(nextView, digitIndex, num, radix);
    }

    if (status != FudStatus::Success) {
        return status;
    }

    if (!foundDecimal) {
        if (digitIndex < 1) {
            return FudStatus::ArgumentInvalid;
        }

        return retSuccess();
    }

    status = getFraction(nextView, digitIndex, num, sign, radix, foundExponent);

    if (foundExponent) {
        status = getExponent(nextView, digitIndex, num, radix);
        if (status != FudStatus::Success) {
            return status;
        }
    }

    if (digitIndex < 1) {
        return FudStatus::ArgumentInvalid;
    }

    if (std::isinf(num) || std::isnan(num)) // isnan is dubious here - likely unreachable
    {
        return FudStatus::RangeError;
    }

    return retSuccess();
}

} // namespace impl

template <typename T>
StringConvertResult<T> fromString(StringView inputView, Radix specifiedRadixOption)
{
    return fromString<T>(inputView, static_cast<uint8_t>(specifiedRadixOption));
}

template <typename T>
StringConvertResult<T> fromString(StringView inputView, Option<uint8_t> specifiedRadixOption)
{
    if (inputView.data() == nullptr) {
        return FudStatus::NullPointer;
    }

    StringView nextView{inputView};
    auto skipResult = nextView.skipWhitespace();
    if (skipResult.isError()) {
        return skipResult.takeError();
    }
    size_t skipIndex = skipResult.takeOkay();

    if constexpr (std::is_unsigned_v<T> && std::is_integral_v<T>) {
        return impl::unsignedFromString<T>(nextView, skipIndex, specifiedRadixOption);
    } else if constexpr (std::is_signed_v<T> && std::is_integral_v<T>) {
        return impl::signedFromString<T>(nextView, skipIndex, specifiedRadixOption);
    } else if constexpr (std::is_floating_point_v<T>) {
        return impl::floatFromString<T>(nextView, skipIndex, specifiedRadixOption);
    } else {
        return FudStatus::NotImplemented;
    }
}

} // namespace fud

#endif