uri_parser.h

#pragma once

#ifndef SIMPLE_URI_PARSER_LIBRARY_H
#define SIMPLE_URI_PARSER_LIBRARY_H

#include <string>
#include <unordered_map>
#include <algorithm>

#ifndef simple_uri_CPLUSPLUS
# if defined(_MSVC_LANG ) && !defined(__clang__)
#  define simple_uri_CPLUSPLUS (_MSC_VER == 1900 ? 201103L : _MSVC_LANG )
# else
#  define simple_uri_CPLUSPLUS __cplusplus
# endif
#endif

#define simple_uri_CPP17_OR_GREATER  ( simple_uri_CPLUSPLUS >= 201703L )

namespace uri {

#if simple_uri_CPP17_OR_GREATER
  using string_view_type = std::string_view;
  using string_arg_type = std::string_view;
  constexpr auto npos = std::string_view::npos;
#else
  using string_view_type = std::string;
  using string_arg_type = const std::string&;
  constexpr auto npos = std::string::npos;
#endif

using query_type = std::unordered_map<std::string, std::string>;

enum class Error {
    None,
    InvalidScheme,
    InvalidPort,
};

struct Authority {
    std::string authority;
    std::string userinfo;
    std::string host;
    long port = 0;
};

struct Uri {
    Error error;
    std::string scheme;
    Authority authority = {};
    std::string path;
    query_type query = {};
    std::string query_string;
    std::string fragment;

    explicit Uri(Error error) : error(error) {}
    Uri(std::string scheme, Authority authority, std::string path, query_type query, std::string query_string, std::string fragment)
        : error(Error::None)
        , scheme(std::move(scheme))
        , authority(std::move(authority))
        , path(std::move(path))
        , query(std::move(query))
        , query_string(std::move(query_string))
        , fragment(std::move(fragment))
        {}
};

}

namespace {

bool valid_scheme(uri::string_arg_type scheme) {
    if (scheme.empty()) {
        return false;
    }
    auto pos = std::find_if_not(scheme.begin(), scheme.end(), [&](char c){
        return std::isalnum(c) || c == '+' || c == '.' || c == '-';
    });
    return pos == scheme.end();
}

std::tuple<std::string, uri::Error, uri::string_view_type> parse_scheme(uri::string_arg_type uri) {
    auto pos = uri.find(':');
    if (pos == uri::npos) {
        return { "", uri::Error::InvalidScheme, uri };
    }

    auto scheme = uri.substr(0, pos);
    if (!::valid_scheme(scheme)) {
        return { "", uri::Error::InvalidScheme, uri };
    }
    std::string scheme_string{ scheme };
    std::transform(scheme_string.begin(), scheme_string.end(), scheme_string.begin(),
                   [](unsigned char c){ return std::tolower(c); });

    return { scheme_string, uri::Error::None, uri.substr(pos + 1) };
}

std::tuple<uri::Authority, uri::Error, uri::string_view_type> parse_authority(uri::string_arg_type uri) {
    uri::Authority authority;

    bool has_authority = uri.length() >= 2 && uri[0] == '/' && uri[1] == '/';
    if (!has_authority) {
        return { authority, uri::Error::None, uri };
    }

    auto pos = uri.substr(2).find('/');
    auto auth_string = uri.substr(2, pos);
    auto rem = uri.substr(pos + 2);
    authority.authority = auth_string;

    pos = auth_string.find('@');
    if (pos != uri::npos) {
        authority.userinfo = std::string(auth_string.substr(0, pos));
        auth_string = auth_string.substr(pos + 1);
    }

    char* end_ptr = nullptr;
    if (!auth_string.empty() && auth_string[0] != '[') {
        pos = auth_string.find(':');
        if (pos != uri::npos) {
            authority.port = std::strtol(&auth_string[pos + 1], &end_ptr, 10);
            if (end_ptr != &*auth_string.end()) {
                return { authority, uri::Error::InvalidPort, auth_string };
            }
        }
    }

    authority.host = auth_string.substr(0, pos);

    return { authority, uri::Error::None, rem };
}

std::tuple<std::string, uri::Error, uri::string_view_type> parse_path(uri::string_arg_type uri) {
    auto pos = uri.find_first_of("#?");
    if (pos == uri::npos) {
        auto path = std::string(uri);
        return { path, uri::Error::None, "" };
    } else {
        auto path = std::string(uri.substr(0, pos));
        return { path, uri::Error::None, uri.substr(pos + 1) };
    }
}

std::tuple<uri::query_type, std::string, uri::Error, uri::string_view_type> parse_query(uri::string_arg_type uri) {
    auto hash_pos = uri.find('#');
    auto query_substring = uri.substr(0, hash_pos);
    auto query_string = std::string(query_substring);
    uri::query_type query;
    while (!query_substring.empty()) {
        auto delim_pos = query_substring.find_first_of("&;?", 0);
        auto arg = query_substring.substr(0, delim_pos);
        auto equals_pos = arg.find('=');
        if (equals_pos == uri::npos) {
            query[std::string(arg)] = "";
        } else {
            query[std::string(arg.substr(0, equals_pos))] = arg.substr(equals_pos + 1);
        }
        if (delim_pos == uri::npos) {
            query_substring = "";
        } else {
            query_substring = query_substring.substr(delim_pos + 1);
        }
    }

    return {query, query_string, uri::Error::None, uri.substr(hash_pos + 1) };
}

std::tuple<std::string, uri::Error, uri::string_view_type> parse_fragment(uri::string_arg_type uri) {
    return { std::string(uri), uri::Error::None, uri };
}

} // anon namespace

namespace uri {

inline Uri parse_uri(uri::string_arg_type uri_in) {
    uri::Error error;

    string_view_type uri;
    std::string scheme;
    std::tie(scheme, error, uri) = ::parse_scheme(uri_in);
    if (error != Error::None) {
        return Uri(error);
    }

    Authority authority;
    std::tie(authority, error, uri) = ::parse_authority(uri);
    if (error != Error::None) {
        return Uri(error);
    }

    std::string path;
    std::tie(path, error, uri) = ::parse_path(uri);
    if (error != Error::None) {
        return Uri(error);
    }

    query_type query;
    std::string query_string;
    std::tie(query, query_string, error, uri) = ::parse_query(uri);
    if (error != Error::None) {
        return Uri(error);
    }

    std::string fragment;
    std::tie(fragment, error, uri) = ::parse_fragment(uri);
    if (error != Error::None) {
        return Uri(error);
    }

    return Uri(scheme, authority, path, query, query_string, fragment);
}

} // namespace uri

#endif // SIMPLE_URI_PARSER_LIBRARY_H