/*

 * Authored by Alex Hultman, 2018-2022.

 * Intellectual property of third-party.

 * 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 UWS_CHUNKEDENCODING_H

#define UWS_CHUNKEDENCODING_H

/* Independent chunked encoding parser, used by HttpParser. */

#include <string>

#include <cstring>

#include <algorithm>

#include <string_view>

#include "MoveOnlyFunction.h"

#include <optional>

namespace uWS {

    constexpr uint32_t STATE_HAS_SIZE = 0x80000000;

    constexpr uint32_t STATE_IS_CHUNKED = 0x40000000;

    constexpr uint32_t STATE_SIZE_MASK = 0x3FFFFFFF;

    constexpr uint32_t STATE_IS_ERROR = 0xFFFFFFFF;

    constexpr uint32_t STATE_SIZE_OVERFLOW = 0x0F000000;

    inline unsigned int chunkSize(unsigned int state) {

        return state & STATE_SIZE_MASK;

    }

    /* Reads hex number until CR or out of data to consume. Updates state. Returns bytes consumed. */

    inline void consumeHexNumber(std::string_view &data, unsigned int &state) {

        /* Consume everything higher than 32 */

        while (data.length() && data.data()[0] > 32) {

            unsigned char digit = (unsigned char)data.data()[0];

            if (digit >= 'a') {

                digit = (unsigned char) (digit - ('a' - ':'));

            } else if (digit >= 'A') {

                digit = (unsigned char) (digit - ('A' - ':'));

            }

            unsigned int number = ((unsigned int) digit - (unsigned int) '0');

            if (number > 16 || (chunkSize(state) & STATE_SIZE_OVERFLOW)) {

                state = STATE_IS_ERROR;

                return;

            }

            // extract state bits

            unsigned int bits = /*state &*/ STATE_IS_CHUNKED;

            state = (state & STATE_SIZE_MASK) * 16u + number;

            state |= bits;

            data.remove_prefix(1);

        }

        /* Consume everything not /n */

        while (data.length() && data.data()[0] != '\n') {

            data.remove_prefix(1);

        }

        /* Now we stand on \n so consume it and enable size */

        if (data.length()) {

            state += 2; // include the two last /r/n

            state |= STATE_HAS_SIZE | STATE_IS_CHUNKED;

            data.remove_prefix(1);

        }

    }

    inline void decChunkSize(unsigned int &state, unsigned int by) {

        //unsigned int bits = state & STATE_IS_CHUNKED;

        state = (state & ~STATE_SIZE_MASK) | (chunkSize(state) - by);

        //state |= bits;

    }

    inline bool hasChunkSize(unsigned int state) {

        return state & STATE_HAS_SIZE;

    }

    /* Are we in the middle of parsing chunked encoding? */

    inline bool isParsingChunkedEncoding(unsigned int state) {

        return state & ~STATE_SIZE_MASK;

    }

    inline bool isParsingInvalidChunkedEncoding(unsigned int state) {

        return state == STATE_IS_ERROR;

    }

    /* Returns next chunk (empty or not), or if all data was consumed, nullopt is returned. */

    static std::optional<std::string_view> getNextChunk(std::string_view &data, unsigned int &state, bool trailer = false) {

        while (data.length()) {

            // if in "drop trailer mode", just drop up to what we have as size

            if (((state & STATE_IS_CHUNKED) == 0) && hasChunkSize(state) && chunkSize(state)) {

                //printf("Parsing trailer now\n");

                while(data.length() && chunkSize(state)) {

                    data.remove_prefix(1);

                    decChunkSize(state, 1);

                    if (chunkSize(state) == 0) {

                        /* This is an actual place where we need 0 as state */

                        state = 0;

                        /* The parser MUST stop consuming here */

                        return std::nullopt;

                    }

                }

                continue;

            }

            if (!hasChunkSize(state)) {

                consumeHexNumber(data, state);

                if (isParsingInvalidChunkedEncoding(state)) {

                    return std::nullopt;

                }

                if (hasChunkSize(state) && chunkSize(state) == 2) {

                    //printf("Setting state to trailer-parsing and emitting empty chunk\n");

                    // set trailer state and increase size to 4

                    if (trailer) {

                        state = 4 /*| STATE_IS_CHUNKED*/ | STATE_HAS_SIZE;

                    } else {

                        state = 2 /*| STATE_IS_CHUNKED*/ | STATE_HAS_SIZE;

                    }

                    return std::string_view(nullptr, 0);

                }

                continue;

            }

            // do we have data to emit all?

            if (data.length() >= chunkSize(state)) {

                // emit all but 2 bytes then reset state to 0 and goto beginning

                // not fin

                std::string_view emitSoon;

                bool shouldEmit = false;

                if (chunkSize(state) > 2) {

                    emitSoon = std::string_view(data.data(), chunkSize(state) - 2);

                    shouldEmit = true;

                }

                data.remove_prefix(chunkSize(state));

                state = STATE_IS_CHUNKED;

                if (shouldEmit) {

                    return emitSoon;

                }

                continue;

            } else {

                /* We will consume all our input data */

                std::string_view emitSoon;

                if (chunkSize(state) > 2) {

                    unsigned int maximalAppEmit = chunkSize(state) - 2;

                    if (data.length() > maximalAppEmit) {

                        emitSoon = data.substr(0, maximalAppEmit);

                    } else {

                        //cb(data);

                        emitSoon = data;

                    }

                }

                decChunkSize(state, (unsigned int) data.length());

                state |= STATE_IS_CHUNKED;

                // new: decrease data by its size (bug)

                data.remove_prefix(data.length()); // ny bug fix för getNextChunk

                if (emitSoon.length()) {

                    return emitSoon;

                } else {

                    return std::nullopt;

                }

            }

        }

        return std::nullopt;

    }

    /* This is really just a wrapper for convenience */

    struct ChunkIterator {

        std::string_view *data;

        std::optional<std::string_view> chunk;

        unsigned int *state;

        bool trailer;

        ChunkIterator(std::string_view *data, unsigned int *state, bool trailer = false) : data(data), state(state), trailer(trailer) {

            chunk = uWS::getNextChunk(*data, *state, trailer);

        }

        ChunkIterator() {

        }

        ChunkIterator begin() {

            return *this;

        }

        ChunkIterator end() {

            return ChunkIterator();

        }

        std::string_view operator*() {

            if (!chunk.has_value()) {

                std::abort();

            }

            return chunk.value();

        }

        bool operator!=(const ChunkIterator &other) const {

            return other.chunk.has_value() != chunk.has_value();

        }

        ChunkIterator &operator++() {

            chunk = uWS::getNextChunk(*data, *state, trailer);

            return *this;

        }

    };

}

#endif // UWS_CHUNKEDENCODING_H