URI.hpp

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// Copyright Take Vos 2022.
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE_1_0.txt or copy at https://www.boost.org/LICENSE_1_0.txt)
 
#pragma once
 
#include "../cast.hpp"
#include "../exception.hpp"
#include "../ranges.hpp"
#include "../hash.hpp"
#include "../strings.hpp"
#include "../concepts.hpp"
#include "../charconv.hpp"
#include <string>
#include <optional>
#include <ranges>
 
namespace hi { inline namespace v1 {
 
#define HI_SUB_DELIM '!', '$', '&', '\'', '(', ')', '*', '+', ',', ';', '='
#define HI_PCHAR HI_SUB_DELIM, ':', '@'
 
class URI {
private:
    using const_iterator = std::string_view::const_iterator;
 
public:
    class authority_type {
    public:
        constexpr authority_type() noexcept = default;
        constexpr authority_type(authority_type const&) noexcept = default;
        constexpr authority_type(authority_type&&) noexcept = default;
        constexpr authority_type& operator=(authority_type const&) noexcept = default;
        constexpr authority_type& operator=(authority_type&&) noexcept = default;
 
        constexpr authority_type(std::string_view const& rhs) noexcept
        {
            parse(rhs);
        }
 
        // constexpr void normalize(std::optional<std::string> const& scheme) noexcept
        //{
        //     hi_not_implemented();
        // }
 
        [[nodiscard]] constexpr std::optional<std::string> const& userinfo() const noexcept
        {
            return _userinfo;
        }
 
        constexpr authority_type& set_userinfo(std::optional<std::string> const& rhs) noexcept
        {
            _userinfo = rhs;
            return *this;
        }
 
        [[nodiscard]] constexpr std::string const& host() const noexcept
        {
            return _host;
        }
 
        constexpr authority_type& set_host(std::string const& rhs)
        {
            validate_host(rhs);
            _host = to_lower(rhs);
            return *this;
        }
 
        [[nodiscard]] constexpr std::optional<std::string> const& port() const noexcept
        {
            return _port;
        }
 
        constexpr authority_type& set_port(std::optional<std::string> const& rhs)
        {
            if (rhs) {
                validate_port(*rhs);
                _port = *rhs;
            } else {
                _port = {};
            }
            return *this;
        }
 
        [[nodiscard]] constexpr friend bool operator==(authority_type const&, authority_type const&) noexcept = default;
        [[nodiscard]] constexpr friend auto operator<=>(authority_type const&, authority_type const&) noexcept = default;
 
        [[nodiscard]] constexpr friend size_t to_string_size(authority_type const& rhs) noexcept
        {
            auto size = 0_uz;
            if (rhs._userinfo) {
                size += rhs._userinfo->size() + 1;
            }
            size += rhs._host.size();
            if (rhs._port) {
                size += rhs._port->size() + 1;
            }
            return size;
        }
 
        [[nodiscard]] constexpr friend std::string to_string(authority_type const& rhs) noexcept
        {
            auto r = std::string{};
 
            if (rhs._userinfo) {
                r += URI::encode<HI_SUB_DELIM, ':'>(*rhs._userinfo);
                r += '@';
            }
 
            if (rhs._host.empty() or rhs._host.front() != '[') {
                r += URI::encode<HI_SUB_DELIM>(rhs._host);
            } else {
                r += URI::encode<HI_SUB_DELIM, '[', ']', ':'>(rhs._host);
            }
 
            if (rhs._port) {
                r += ':';
                r += *rhs._port;
            }
 
            return r;
        }
 
    private:
        std::optional<std::string> _userinfo = {};
        std::string _host = {};
        std::optional<std::string> _port = {};
 
        [[nodiscard]] constexpr static void validate_host(std::string_view str)
        {
            if (str.starts_with('[') and not str.ends_with(']')) {
                throw uri_error("The host-component starts with '[' has missing ']' at end");
            } else if (str.ends_with(']') and str.starts_with('[')) {
                throw uri_error("The host-component ends with ']' has missing '[' at start");
            }
        }
 
        [[nodiscard]] constexpr static void validate_port(std::string_view str)
        {
            for (auto c : str) {
                if (not(c >= '0' and c <= '9')) {
                    throw uri_error("The port-component contains a non-digit.");
                }
            }
        }
 
        [[nodiscard]] constexpr const_iterator parse_userinfo(const_iterator first, const_iterator last) noexcept
        {
            for (auto it = first; it != last; ++it) {
                if (hilet c = *it; c == '@') {
                    set_userinfo(URI::decode(first, it));
                    return it + 1; // Skip over '@'.
                }
            }
 
            // Reached at end of URI, this is not a userinfo.
            return first;
        }
 
        [[nodiscard]] constexpr const_iterator parse_host(const_iterator first, const_iterator last) noexcept
        {
            if (first == last) {
                return first;
            }
 
            auto it = first;
            if (*it == '[') {
                while (it != last) {
                    if (*it == ']') {
                        set_host(URI::decode(first, it + 1));
                        return it + 1; // Skip over ']'.
                    }
                }
                // End of URI mean this is not a host, interpret as path instead.
                return first;
 
            } else {
                for (; it != last; ++it) {
                    if (hilet c = *it; c == ':') {
                        // End of host.
                        set_host(URI::decode(first, it));
                        return it;
                    }
                }
 
                // End of URI means that the host is the last part of the URI
                set_host(URI::decode(first, last));
                return last;
            }
        }
 
        [[nodiscard]] constexpr const_iterator parse_port(const_iterator first, const_iterator last) noexcept
        {
            set_port(std::string{first, last});
            return last;
        }
 
        constexpr void parse(std::string_view rhs) noexcept
        {
            auto first = rhs.cbegin();
            auto last = rhs.cend();
            auto it = parse_userinfo(first, last);
            it = parse_host(it, last);
 
            if (it != last and *it == ':') {
                it = parse_port(++it, last);
            }
        }
    };
 
    class path_type : public std::vector<std::string> {
    public:
        constexpr path_type() noexcept = default;
        constexpr path_type(path_type const&) noexcept = default;
        constexpr path_type(path_type&&) noexcept = default;
        constexpr path_type& operator=(path_type const&) noexcept = default;
        constexpr path_type& operator=(path_type&&) noexcept = default;
 
        [[nodiscard]] constexpr static std::vector<std::string> parse(std::string_view str)
        {
            auto r = make_vector<std::string>(std::views::transform(std::views::split(str, std::string_view{"/"}), [](auto&& x) {
                return URI::decode(std::string_view{std::ranges::begin(x), std::ranges::end(x)});
            }));
 
            if (r.size() == 1 and r.front().empty()) {
                // An empty string will evaluate to a single segment.
                r.clear();
            }
            if (not r.empty() and (r.back() == "." or r.back() == ".." or r.back() == "**")) {
                // ".", ".." and "**" are directories always terminate with a slash.
                r.emplace_back();
            }
 
            return r;
        }
 
        constexpr path_type(std::string_view str) noexcept : std::vector<std::string>(parse(str))
        {
            hi_axiom(holds_invariant());
        }
 
        [[nodiscard]] constexpr bool absolute() const noexcept
        {
            return size() >= 2 and front().empty();
        }
 
        [[nodiscard]] constexpr bool double_absolute() const noexcept
        {
            return size() >= 3 and (*this)[0].empty() and (*this)[1].empty();
        }
 
        [[nodiscard]] constexpr bool is_root() const noexcept
        {
            return size() == 2 and (*this)[0].empty() and (*this)[1].empty();
        }
 
        [[nodiscard]] constexpr std::optional<std::string> filename() const noexcept
        {
            if (empty() or back().empty()) {
                return {};
            } else {
                return back();
            }
        }
 
        constexpr path_type& remove_filename() noexcept
        {
            switch (size()) {
            case 0: // Don't remove a filename from an empty path.
                break;
            case 1: // relative filename, make the path empty.
                clear();
                break;
            default: // relative or absolute directory with optional filename. Just empty the last path segment.
                back().clear();
            }
            hi_axiom(holds_invariant());
            return *this;
        }
 
        [[nodiscard]] constexpr friend path_type merge(path_type base, path_type const& ref, bool base_has_authority) noexcept
        {
            if (base_has_authority and base.empty()) {
                // A URL with an authority and empty path is implicitly the root path.
                base.emplace_back();
                base.emplace_back();
            }
 
            if (not base.empty()) {
                // Remove the (possibly empty) filename from the base.
                base.pop_back();
            }
            base.insert(base.cend(), ref.cbegin(), ref.cend());
 
            if (base.size() == 1 and base.front().empty()) {
                // Empty ref-path added to root base-path, fix by appending an empty filename.
                base.emplace_back();
            }
 
            hi_axiom(base.holds_invariant());
            return base;
        }
 
        [[nodiscard]] constexpr friend path_type remove_dot_segments(path_type path) noexcept
        {
            for (auto it = path.cbegin(); it != path.cend();) {
                if (*it == ".") {
                    //  Remove any "." from the path.
                    it = path.erase(it);
 
                } else if (*it == "..") {
                    if (it == path.cbegin()) {
                        // Remove the ".." at the start of a relative path.
                        it = path.erase(it);
 
                    } else if (it - 1 == path.cbegin() and (it - 1)->empty()) {
                        // Remove just the ".." at the start of an absolute path.
                        it = path.erase(it);
 
                    } else {
                        // Remove ".." and the segment in front of it.
                        it = path.erase(it - 1, it + 1);
                    }
                } else {
                    // Ignore other segments.
                    ++it;
                }
            }
 
            if (path.size() == 1 and path.front().empty()) {
                // After removing the ".." at the start of the path we are left with an empty segment.
                path.clear();
            }
 
            hi_axiom(path.holds_invariant());
            return path;
        }
 
        [[nodiscard]] constexpr bool holds_invariant() const noexcept
        {
            if (empty()) {
                return true;
            }
 
            if (back() == "." or back() == ".." or back() == "**") {
                // ".", ".." and "**" are always directories and may not be the last segment.
                return false;
            }
            return true;
        }
 
        [[nodiscard]] constexpr friend size_t to_string_size(path_type const& rhs) noexcept
        {
            size_t r = 0_uz;
            for (hilet& segment : rhs) {
                r += segment.size();
            }
            r += rhs.size() + 1;
            return r;
        }
 
        [[nodiscard]] constexpr friend std::string to_string(path_type const& rhs, bool has_scheme = false) noexcept
        {
            auto r = std::string{};
            r.reserve(to_string_size(rhs));
 
            auto segment_is_empty = false;
            for (auto it = rhs.cbegin(); it != rhs.cend(); ++it) {
                segment_is_empty = it->empty();
 
                if (it == rhs.cbegin() and not has_scheme) {
                    r += URI::encode<HI_SUB_DELIM, '@'>(*it);
                } else {
                    r += URI::encode<HI_PCHAR>(*it);
                }
                r += '/';
            }
 
            if (not r.empty() and not segment_is_empty) {
                // The last path-component was a filename, remove the trailing slash '/'.
                r.pop_back();
            }
            return r;
        }
    };
 
    constexpr URI() noexcept = default;
    constexpr URI(URI const&) noexcept = default;
    constexpr URI(URI&&) noexcept = default;
    constexpr URI& operator=(URI const&) noexcept = default;
    constexpr URI& operator=(URI&&) noexcept = default;
 
    constexpr explicit URI(std::string_view str)
    {
        parse(str);
    }
 
    constexpr explicit URI(std::string const& str) : URI(std::string_view{str}) {}
 
    constexpr explicit URI(const char *str) : URI(std::string_view{str}) {}
 
    [[nodiscard]] constexpr bool empty() const noexcept
    {
        return not _scheme and not _authority and _path.empty() and not _query and not _fragment;
    }
 
    constexpr operator bool() const noexcept
    {
        return not empty();
    }
 
    [[nodiscard]] constexpr std::optional<std::string> const& scheme() const noexcept
    {
        return _scheme;
    }
 
    constexpr URI& set_scheme(std::optional<std::string> const& rhs)
    {
        if (rhs) {
            validate_scheme(*rhs);
            _scheme = *rhs;
        } else {
            _scheme = {};
        }
        return *this;
    }
 
    [[nodiscard]] constexpr std::optional<authority_type> const& authority() const noexcept
    {
        return _authority;
    }
 
    constexpr URI& set_authority(std::optional<authority_type> const& rhs) noexcept
    {
        _authority = rhs;
        return *this;
    }
 
    [[nodiscard]] constexpr path_type const& path() const noexcept
    {
        return _path;
    }
 
    constexpr URI& set_path(path_type const& rhs)
    {
        validate_path(rhs, to_bool(_authority));
        _path = rhs;
        return *this;
    }
 
    [[nodiscard]] constexpr std::optional<std::string> filename() const noexcept
    {
        return _path.filename();
    }
 
    constexpr URI& remove_filename() noexcept
    {
        _path.remove_filename();
        return *this;
    }
 
    [[nodiscard]] constexpr std::optional<std::string> const& query() const noexcept
    {
        return _query;
    }
 
    constexpr URI& set_query(std::optional<std::string> const& rhs) noexcept
    {
        _query = rhs;
        return *this;
    }
 
    [[nodiscard]] constexpr std::optional<std::string> const& fragment() const noexcept
    {
        return _fragment;
    }
 
    constexpr URI& set_fragment(std::optional<std::string> const& rhs) noexcept
    {
        _fragment = rhs;
        return *this;
    }
 
    [[nodiscard]] constexpr friend std::string to_string(URI const& rhs) noexcept
    {
        auto r = std::string{};
        r.reserve(to_string_size(rhs));
 
        if (rhs._scheme) {
            r += *rhs._scheme;
            r += ':';
        }
 
        if (rhs._authority) {
            r += '/';
            r += '/';
            r += to_string(*rhs._authority);
        }
 
        r += to_string(rhs._path, to_bool(rhs._scheme));
 
        if (rhs._query) {
            r += '?';
            r += URI::encode<HI_PCHAR, '/', '?'>(*rhs._query);
        }
 
        if (rhs._fragment) {
            r += '#';
            r += URI::encode<HI_PCHAR, '/', '?'>(*rhs._fragment);
        }
 
        return r;
    }
 
    friend std::ostream& operator<<(std::ostream& lhs, URI const& rhs) noexcept
    {
        return lhs << to_string(rhs);
    }
 
    [[nodiscard]] constexpr friend bool operator==(URI const& lhs, URI const& rhs) noexcept = default;
    [[nodiscard]] constexpr friend auto operator<=>(URI const& lhs, URI const& rhs) noexcept = default;
 
    [[nodiscard]] constexpr friend URI operator/(URI const& base, URI const& ref) noexcept
    {
        auto target = URI{};
 
        if (ref._scheme) {
            target._scheme = ref._scheme;
            target._authority = ref._authority;
            target._path = remove_dot_segments(ref._path);
            target._query = ref._query;
        } else {
            if (ref._authority) {
                target._authority = ref._authority;
                target._path = remove_dot_segments(ref._path);
                target._query = ref._query;
 
            } else {
                if (ref._path.empty()) {
                    target._path = base._path;
                    if (ref._query) {
                        target._query = ref._query;
                    } else {
                        target._query = base._query;
                    }
                } else {
                    if (ref._path.absolute()) {
                        target._path = remove_dot_segments(ref._path);
                    } else {
                        target._path = remove_dot_segments(merge(base._path, ref._path, to_bool(base._authority)));
                    }
                    target._query = ref._query;
                }
                target._authority = base._authority;
            }
            target._scheme = base._scheme;
        }
 
        target._fragment = ref._fragment;
 
        return target;
    }
 
    [[nodiscard]] constexpr friend bool operator==(URI const& lhs, std::string_view rhs) noexcept
    {
        return lhs == URI(rhs);
    }
 
    [[nodiscard]] constexpr friend auto operator<=>(URI const& lhs, std::string_view rhs) noexcept
    {
        return lhs == URI(rhs);
    }
 
    [[nodiscard]] constexpr friend URI operator/(URI const& base, std::string_view ref) noexcept
    {
        return base / URI(ref);
    }
 
    [[nodiscard]] constexpr static std::string decode(std::string_view rhs)
    {
        auto r = std::string{rhs};
 
        for (auto i = r.find('%'); i != std::string::npos; i = r.find('%', i)) {
            // This may throw a parse_error, if not hexadecimal
            auto c = from_string<uint8_t>(r.substr(i + 1, 2), 16);
 
            // Replace the % encoded character.
            r.replace(i, 3, 1, char_cast<char>(c));
 
            // Skip over encoded-character.
            ++i;
        }
 
        return r;
    }
 
    [[nodiscard]] constexpr static std::string decode(const_iterator first, const_iterator last)
    {
        return decode(std::string_view{first, last});
    }
 
    template<char... Extras, typename It, typename ItEnd>
    [[nodiscard]] constexpr static std::string encode(It first, ItEnd last) noexcept
    {
        auto r = std::string{};
        if constexpr (requires { std::distance(first, last); }) {
            r.reserve(std::distance(first, last));
        }
 
        for (auto it = first; it != last; ++it) {
            hilet c = *it;
            // clang-format off
            if (((
                    (c >= 'a' and c <= 'z') or
                    (c >= 'A' and c <= 'Z') or
                    (c >= '0' and c <= '9') or
                    c == '-' or c == '.' or c == '_' or c == '~'
                ) or ... or (c == Extras))) {
                r += c;
 
            } else {
                r += '%';
                auto uc = char_cast<uint8_t>(c);
                if (auto nibble = narrow_cast<char>(uc >> 4); nibble <= 9) {
                    r += '0' + nibble;
                } else {
                    r += 'A' + nibble - 10;
                }
                if (auto nibble = narrow_cast<char>(uc & 0xf); nibble <= 9) {
                    r += '0' + nibble;
                } else {
                    r += 'A' + nibble - 10;
                }
            }
            // clang-format on
        }
 
        return r;
    }
 
    template<char... Extras, typename Range>
    [[nodiscard]] constexpr static std::string encode(Range&& range) noexcept
    {
        return encode<Extras...>(std::ranges::begin(range), std::ranges::end(range));
    }
 
private:
    std::optional<std::string> _scheme;
    std::optional<authority_type> _authority;
    path_type _path;
    std::optional<std::string> _query;
    std::optional<std::string> _fragment;
 
    [[nodiscard]] constexpr friend size_t to_string_size(URI const& rhs) noexcept
    {
        auto size = 0_uz;
        if (rhs._scheme) {
            size += rhs._scheme->size() + 1;
        }
        if (rhs._authority) {
            size += to_string_size(*rhs._authority) + 2;
        }
        size += to_string_size(rhs._path);
 
        if (rhs._query) {
            size += rhs._query->size() + 1;
        }
        if (rhs._fragment) {
            size += rhs._fragment->size() + 1;
        }
 
        return size;
    }
 
    [[nodiscard]] constexpr static bool is_scheme_start(char c) noexcept
    {
        return (c >= 'a' and c <= 'z') or (c >= 'A' and c <= 'Z');
    }
 
    [[nodiscard]] constexpr static bool is_scheme(char c) noexcept
    {
        return is_scheme_start(c) or (c >= '0' and c <= '9') or c == '+' or c == '-' or c == '.';
    }
 
    [[nodiscard]] constexpr static void validate_scheme(std::string_view str)
    {
        if (str.empty()) {
            throw uri_error("The scheme-component is not allowed to be empty (it is allowed to not exist).");
        }
        if (not is_scheme_start(str.front())) {
            throw uri_error("The scheme-component does not start with [a-zA-Z].");
        }
        for (auto c : str) {
            if (not is_scheme(c)) {
                throw uri_error("The scheme-component contains a character outside [a-zA-Z0-9.+-].");
            }
        }
    }
 
    [[nodiscard]] constexpr static void validate_path(path_type const& path, bool has_authority)
    {
        if (has_authority) {
            if (not(path.empty() or path.absolute())) {
                throw uri_error("A path-component in a URI with an authority-component must be empty or absolute.");
            }
        } else if (path.double_absolute()) {
            throw uri_error("A path-component in a URI without an authority-component may not start with a double slash '//'.");
        }
    }
 
    [[nodiscard]] constexpr const_iterator parse_scheme(const_iterator first, const_iterator last)
    {
        for (auto it = first; it != last; ++it) {
            if (hilet c = *it; c == ':') {
                set_scheme(std::string{first, it});
                return it + 1; // Skip over ':'.
 
            } else if (c == '/' or c == '?' or c == '#') {
                // Invalid character, this is not a scheme.
                return first;
            }
        }
 
        // Reached at end of URI, this is not a scheme.
        return first;
    }
 
    [[nodiscard]] constexpr const_iterator parse_authority(const_iterator first, const_iterator last)
    {
        for (auto it = first; it != last; it++) {
            if (hilet c = *it; c == '/' or c == '?' or c == '#') {
                set_authority(authority_type{std::string_view{first, it}});
                return it;
            }
        }
 
        set_authority(authority_type{std::string_view{first, last}});
        return last;
    }
 
    [[nodiscard]] constexpr const_iterator parse_path(const_iterator first, const_iterator last)
    {
        for (auto it = first; it != last; it++) {
            if (hilet c = *it; c == '?' or c == '#') {
                set_path(path_type{std::string_view{first, it}});
                return it;
            }
        }
 
        set_path(path_type{std::string_view{first, last}});
        return last;
    }
 
    [[nodiscard]] constexpr const_iterator parse_query(const_iterator first, const_iterator last)
    {
        for (auto it = first; it != last; it++) {
            if (hilet c = *it; c == '#') {
                set_query(URI::decode(first, it));
                return it;
            }
        }
 
        set_query(URI::decode(first, last));
        return last;
    }
 
    [[nodiscard]] constexpr const_iterator parse_fragment(const_iterator first, const_iterator last)
    {
        set_fragment(URI::decode(first, last));
        return last;
    }
 
    constexpr void parse(std::string_view str)
    {
        auto first = str.cbegin();
        auto last = str.cend();
        auto it = parse_scheme(first, last);
 
        if (std::distance(it, last) >= 2 and it[0] == '/' and it[1] == '/') {
            it += 2;
            it = parse_authority(it, last);
        }
 
        it = parse_path(it, last);
 
        if (it != last and *it == '?') {
            it = parse_query(++it, last);
        }
 
        if (it != last and *it == '#') {
            it = parse_fragment(++it, last);
        }
    }
 
    friend struct std::hash<URI>;
};
 
#undef HI_PCHAR
#undef HI_SUB_DELIM
 
}} // namespace hi::v1
 
template<>
struct std::hash<hi::URI> {
    [[nodiscard]] size_t operator()(hi::URI const& rhs) const noexcept
    {
        return std::hash<std::string>{}(to_string(rhs));
    }
};
 
template<typename CharT>
struct std::formatter<hi::URI, CharT> : std::formatter<std::string, CharT> {
    auto format(hi::URI const& t, auto& fc)
    {
        return std::formatter<std::string, CharT>::format(to_string(t), fc);
    }
};