//----------------------------------------------------------------------------- 
//     ___                      __ _       _
//    / _ \__ _ _ __ ___  ___  / /(_)_ __ | | __
//   / /_)/ _` | '__/ __|/ _ \/ / | | '_ \| |/ /
//  / ___/ (_| | |  \__ \  __/ /__| | | | |   <
//  \/    \__,_|_|  |___/\___\____/_|_| |_|_|\_\ .
//
//----------------------------------------------------------------------------- 
// Author: Kurt Sassenrath
// Module: msgpack
//
// Token-based reader for unpacking MessagePack data. Ensure lifetime of the
// MessagePack buffer exceeds the lifetime of parsed tokens.
//
// TBD: How best to handle arrays and maps.
//
// Copyright (c) 2023 Kurt Sassenrath.
//
// License TBD.
//----------------------------------------------------------------------------- 
#ifndef msgpack_token_reader_8daff350a0b1a519
#define msgpack_token_reader_8daff350a0b1a519

#include "type.h"

#include <tl/expected.hpp>

namespace msgpack {

class token_reader {
public:

    enum class error {
        end_of_message,
        incomplete_message
    };

    constexpr token_reader(std::span<std::byte const> src) noexcept :
        data_(src), end_(src.size()) {}

    // Read the next token. If the reader currently points to the end of the
    // byte buffer, then end_of_message is returned, and if there is still
    // some data present in the buffer, then incomplete_message is returned,
    // potentially hinting that further buffering is required.
    constexpr tl::expected<token, error> read_one() noexcept;

    // Read multiple tokens from the byte buffer. The number of tokens parsed
    // can be surmised from the returned span of tokens. If the reader
    // currently points to the end of the byte buffer, then
    // error::end_of_message is returned, and if there is not enough data to
    // fully parse a token, then incomplete_message is returned.
    constexpr tl::expected<std::span<token>, error> read_some(
            std::span<token> token_buffer) noexcept;
private:
    std::span<std::byte const> data_;
    std::size_t curr_;
    std::size_t end_;
};

} // namespace msgpack

#endif // msgpack_token_reader_8daff350a0b1a519