/*

 * Copyright (c) 2022, Lucas Chollet <lucas.chollet@free.fr>

 *

 * SPDX-License-Identifier: BSD-2-Clause

 */

#pragma once

#include <AK/ByteBuffer.h>

#include <AK/Error.h>

#include <AK/HashMap.h>

#include <AK/Noncopyable.h>

#include <AK/Vector.h>

namespace AK {

class CircularBuffer {

    AK_MAKE_NONCOPYABLE(CircularBuffer);

    AK_MAKE_DEFAULT_MOVABLE(CircularBuffer);

public:

    static ErrorOr<CircularBuffer> create_empty(size_t size);

    static ErrorOr<CircularBuffer> create_initialized(ByteBuffer);

    ~CircularBuffer() = default;

    size_t write(ReadonlyBytes bytes);

    Bytes read(Bytes bytes);

    ErrorOr<void> discard(size_t discarded_bytes);

    ErrorOr<size_t> fill_from_stream(Stream&);

    ErrorOr<size_t> flush_to_stream(Stream&);

    /// Compared to `read()`, this starts reading from an offset that is `distance` bytes

    /// before the current write pointer and allows for reading already-read data.

    ErrorOr<Bytes> read_with_seekback(Bytes bytes, size_t distance) const;

    ErrorOr<size_t> copy_from_seekback(size_t distance, size_t length);

    [[nodiscard]] size_t empty_space() const;

    [[nodiscard]] size_t used_space() const;

    [[nodiscard]] size_t capacity() const;

    [[nodiscard]] size_t seekback_limit() const;

    Optional<size_t> offset_of(StringView needle, Optional<size_t> from = {}, Optional<size_t> until = {}) const;

    void clear();

protected:

    CircularBuffer(ByteBuffer);

    [[nodiscard]] bool is_wrapping_around() const;

    [[nodiscard]] Bytes next_write_span();

    [[nodiscard]] ReadonlyBytes next_read_span(size_t offset = 0) const;

    [[nodiscard]] ReadonlyBytes next_seekback_span(size_t distance) const;

    ByteBuffer m_buffer {};

    size_t m_reading_head {};

    size_t m_used_space {};

    size_t m_seekback_limit {};

};

class SearchableCircularBuffer : public CircularBuffer {

public:

    static ErrorOr<SearchableCircularBuffer> create_empty(size_t size);

    static ErrorOr<SearchableCircularBuffer> create_initialized(ByteBuffer);

    [[nodiscard]] size_t search_limit() const;

    // These functions update the read pointer, so we need to hash any data that we have processed.

    ErrorOr<Bytes> read(Bytes bytes);

    ErrorOr<void> discard(size_t discarded_bytes);

    ErrorOr<size_t> flush_to_stream(Stream& stream);

    struct Match {

        size_t distance;

        size_t length;

    };

    /// This searches the seekback buffer (between read head and limit) for occurrences where it matches the next `length` bytes from the read buffer.

    /// Supplying any hints will only consider those distances, in case existing offsets need to be validated.

    /// Note that, since we only start searching at the read head, the length between read head and write head is excluded from the distance.

    Optional<Match> find_copy_in_seekback(size_t maximum_length, size_t minimum_length = 2);

    Optional<Match> find_copy_in_seekback(ReadonlySpan<size_t> distances, size_t maximum_length, size_t minimum_length = 2) const;

    // The chunk size for which the hash table holds hashes.

    // This is nice for users to know, as picking a minimum match length that is

    // equal or greater than this allows us to completely skip a slow memory search.

    static constexpr size_t HASH_CHUNK_SIZE = 3;

private:

    // Note: This function has a similar purpose as next_seekback_span, but they differ in their reference point.

    //       Seekback operations start counting their distance at the write head, while search operations start counting their distance at the read head.

    [[nodiscard]] ReadonlyBytes next_search_span(size_t distance) const;

    SearchableCircularBuffer(ByteBuffer);

    size_t m_hash_head {};

    HashMap<unsigned, size_t> m_hash_location_map;

    HashMap<size_t, size_t> m_location_chain_map;

    ErrorOr<void> insert_location_hash(ReadonlyBytes value, size_t raw_offset);

    ErrorOr<void> hash_new_bytes();

};

}