/*
 * 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_HPP
#define FUD_STRING_HPP

#include "fud_allocator.hpp"
#include "fud_assert.hpp"
#include "fud_c_string.hpp"
#include "fud_option.hpp"
#include "fud_result.hpp"
#include "fud_status.hpp"
#include "fud_string_view.hpp"
#include "fud_utf8.hpp"

#include <climits>
#include <cstddef>

static_assert(CHAR_BIT == 8);

/** @file */

namespace fud {

struct DrainResult {
    size_t bytesWritten;
    FudStatus status;
};

/** \brief The maximum length of a string using the small string optimization
 * buffer. */
constexpr size_t SSO_BUF_LENGTH = 15;

/** \brief The size of the small string optimization buffer, to include space
 * for the null terminator. */
constexpr size_t SSO_BUF_SIZE = SSO_BUF_LENGTH + 1;

class String;

/** \brief A result containing a valid @String or the @FudStatus error
 * encountered during its creation. */
using StringResult = Result<String, FudStatus>;

/** \brief A null terminated, growable, array of utf8 code points, with a custom
 * allocator. */
class String {
  public:
    /** \brief Create a string from a C String.
     *
     * \param [in] cString a pointer to a C string to populate the String.
     *
     * \returns String on success.
     * \returns NullPointer if cString is null.
     * \returns ArgumentInvalid if the length of cString is greater than or
     * equal to SSIZE_MAX.
     * \returns FudStatus::AllocFailure if the allocator fails.
     */
    static StringResult makeFromCString(const char* cString);

    /** \brief Create a string from a C String, specifying the allocator.
     *
     * \param [in] cString a pointer to a C string to populate the String.
     * \param [in] allocator the allocator the string will use.
     *
     * \returns String on success.
     * \returns NullPointer if cString or allocator is null.
     * \returns ArgumentInvalid if the length of cString is greater than or
     * equal to SSIZE_MAX.
     * \returns FudStatus::AllocFailure if the allocator fails.
     */
    static StringResult makeFromCString(const char* cString, Allocator* allocator);

    /** \brief Create a string from concatenating multiple C Strings.
     *
     * This function uses the default globalFudAllocator.
     *
     * \tparam CStrings a parameter pack of types convertible to const char*.
     * \param [in] cStrings  pointers to C strings to concatenate into a single String.
     *
     * \returns String on success.
     * \returns NullPointer if cString or allocator is null.
     * \returns ArgumentInvalid if the length of cString is greater than or
     * equal to SSIZE_MAX.
     * \returns FudStatus::AllocFailure if the allocator fails.
     */
    template <typename... CStrings>
    static StringResult makeFromCStrings(CStrings... cStrings)
    {
        return makeFromCStringsAlloc(&globalFudAllocator, cStrings...);
    }

    /** \brief Create a string from concatenating multiple C Strings.
     *
     * \tparam CStrings a parameter pack of types convertible to const char*.
     * \param [in] cStrings  pointers to C strings to concatenate into a single String.
     * \param [in] allocator the allocator the string will use.
     *
     * \returns String on success.
     * \returns NullPointer if cString or allocator is null.
     * \returns ArgumentInvalid if the length of cString is greater than or
     * equal to SSIZE_MAX.
     * \returns FudStatus::AllocFailure if the allocator fails.
     */
    template <typename... CStrings>
    static StringResult makeFromCStringsAlloc(Allocator* allocator, CStrings... cStrings)
    {
        if (allocator == nullptr) {
            return StringResult::error(FudStatus::NullPointer);
        }

        if (!String::allocatorValid(allocator)) {
            return StringResult::error(FudStatus::ArgumentInvalid);
        }

        size_t totalLength = 0;
        Array<size_t, sizeof...(cStrings)> lengths{};
        Array<const char*, sizeof...(cStrings)> strPointers{};
        size_t index = 0;
        for (const auto* cStringItem : {cStrings...}) {
            const char* cString = nullptr;
            if constexpr (std::is_same_v<decltype(cStringItem), const char*>) {
                cString = cStringItem;
            } else if constexpr (std::is_same_v<decltype(cStringItem), const utf8*>) {
                cString = reinterpret_cast<const char*>(cStringItem);
            } else {
                static_assert(!std::is_same_v<decltype(cStringItem), const char*>);
            }
            strPointers[index] = cString;

            auto lengthResult = cStringLength(cString);
            if (lengthResult < 0 || lengthResult >= SSIZE_MAX) {
                return StringResult::error(FudStatus::ArgumentInvalid);
            }
            auto stringLength = static_cast<size_t>(lengthResult);
            if (SIZE_MAX - totalLength < stringLength) {
                return StringResult::error(FudStatus::Failure);
            }
            totalLength += stringLength;
            lengths[index] = stringLength;
            index++;
        }

        String output{};
        output.m_length = totalLength;
        output.m_allocator = allocator;
        if (output.m_length >= output.m_capacity) {
            output.m_capacity = output.m_length + 1;
            /* Avoid using compiler expansions in headers */
            auto dataResult = output.allocator()->allocate(output.m_capacity);
            if (dataResult.isError()) {
                return StringResult::error(dataResult.getError());
            }
            output.m_data = static_cast<utf8*>(dataResult.getOkay());
        }

        auto* data = output.dataMut();
        size_t cumulativeLength = 0;
        for (size_t idx = 0; idx < strPointers.size(); ++idx) {
            const auto* cString = strPointers[idx];
            auto copyStatus = copyMem(
                data + cumulativeLength,
                output.m_capacity - cumulativeLength,
                cString,
                lengths[idx]);
            fudAssert(copyStatus == FudStatus::Success);
            cumulativeLength += lengths[idx];
        }

        auto terminateStatus = output.nullTerminate();
        fudAssert(terminateStatus == FudStatus::Success);

        return StringResult::okay(std::move(output));
    }

    String() noexcept = default;

    String(const String& rhs) = delete;

    String(String&& rhs) noexcept;

    ~String();

    String& operator=(const String& rhs) = delete;

    String& operator=(String&& rhs) noexcept;

    static StringResult from(const String& rhs);

    static StringResult from(StringView view, Allocator* allocator = &globalFudAllocator);

    FudStatus copy(const String& rhs);

    /** \brief The raw length of the string's data, excluding the null terminator. */
    [[nodiscard]] constexpr size_t length() const
    {
        return m_length;
    }

    /** \brief Indicates if no characters are present in the string's data. */
    [[nodiscard]] constexpr bool empty() const
    {
        return m_length == 0;
    }

    /** \brief The total size of the string's data, including the null terminator. */
    [[nodiscard]] constexpr size_t size() const
    {
        return m_length + 1;
    }

    /** \brief The current capacity of the string, excluding the reserved slot
     * for the null terminator. */
    [[nodiscard]] constexpr size_t capacity() const
    {
        fudAssert(m_capacity > 0);
        return m_capacity - 1;
    }

    /** \brief The underlying data, guaranteed to have c string representation. */
    [[nodiscard]] constexpr const utf8* data() const
    {
        return isLarge() ? m_data : m_buffer.data();
    }

    /** \brief The underlying data as an explicit c string. */
    [[nodiscard]] inline const char* c_str() const
    {
        return reinterpret_cast<const char*>(data());
    }

    [[nodiscard]] bool utf8Valid() const;

    FudStatus reserve(size_t newCapacity);

    [[nodiscard]] Option<utf8> back();

    [[nodiscard]] constexpr size_t remainingLength() const
    {
        if (m_length >= m_capacity) {
            return 0;
        }

        return m_capacity - 1U - m_length;
    }

    [[nodiscard]] inline StringView asView() const
    {
        return StringView(*this);
    }

    FudStatus pushBack(char letter);

    FudStatus pushBack(utf8 letter);

    FudStatus pushBack(const FudUtf8& letter);

    Option<utf8> pop();

    FudStatus append(const char* source);

    FudStatus append(const String& source);

    FudStatus append(StringView source);

    DrainResult drain(const char* source);

    DrainResult drain(const String& source);

    DrainResult drain(StringView source);

    [[nodiscard]] StringResult catenate(const String& rhs) const;

    [[nodiscard]] StringResult catenate(const char* rhs) const;

    [[nodiscard]] bool compare(const String& rhs) const;

    FudStatus clear();

    const utf8* begin() const;

    const utf8* end() const;

  private:
    static constexpr uint8_t capacityMask = 0x07;

    [[nodiscard]] static bool allocatorValid(Allocator* allocator)
    {
        return ((reinterpret_cast<uintptr_t>(allocator) & capacityMask) == 0);
    }

    [[nodiscard]] bool nullTerminated() const;

    [[nodiscard]] bool valid() const;

    FudStatus nullTerminate();

    Allocator* allocator() const
    {
        constexpr uintptr_t ALLOCATOR_MASK = ~static_cast<uintptr_t>(capacityMask);
        const auto allocptr = reinterpret_cast<uintptr_t>(m_allocator);
        return reinterpret_cast<Allocator*>(allocptr & ALLOCATOR_MASK);
    }

    /** \brief The underlying data, guaranteed to have c string
     * representation. */
    [[nodiscard]] constexpr utf8* dataMut()
    {
        return isLarge() ? m_data : m_buffer.data();
    }

    void cleanup();

    FudStatus resize(size_t newCapacity);

    [[nodiscard]] bool optIsLarge() const
    {
        return (reinterpret_cast<uintptr_t>(m_allocator) & capacityMask) != 0;
    }

  public:
    static constexpr size_t OptBufSize = 2 * sizeof(size_t) + sizeof(utf8*) - 1;
    using OptBufType = Array<utf8, OptBufSize>;
    size_t optLength() const
    {
        if (optIsLarge()) {
            return m_large.optLength;
        }
        return m_small.optLength;
    }

    size_t optCapacity() const
    {
        if (optIsLarge()) {
            return m_large.optCapacity;
        }
        return OptBufSize - 1U;
    }

  private:
    void setLength(size_t newLength)
    {
        m_length = newLength;
        if (optIsLarge()) {
            m_large.optLength = newLength;
        } else {
            m_small.optLength = static_cast<uint8_t>(newLength);
        }
    }

    /** \brief The allocator used to get storage for characters when the string
     * is large. */
    Allocator* m_allocator{&globalFudAllocator};

    union {
        struct {
            size_t optLength;
            size_t optCapacity;
            utf8* optData;
        } m_large;
        struct {
            uint8_t optLength;
            OptBufType optBuffer;
        } m_small;
    };

    using BufType = Array<utf8, SSO_BUF_SIZE>;
    union {
        /** \brief The storage for string characters when using SSO. */
        BufType m_buffer{BufType::constFill(0)};
        /** \brief The storage for string characters when the string is
         * large. */
        utf8* m_data;
    };

    /** \brief The length of the string excluding the null terminator. */
    size_t m_length{0};

    /** \brief The capacity of the string, including the null terminator. */
    size_t m_capacity{SSO_BUF_SIZE};

    /** \brief Whether or not the string must use its allocator for storage. */
    [[nodiscard]] constexpr bool isLarge() const
    {
        return m_capacity > SSO_BUF_SIZE;
    }
};

} // namespace fud

#endif