// Copyright (C) 2020-2025 Jonathan Müller and lexy contributors
// SPDX-License-Identifier: BSL-1.0

#ifndef LEXY_INPUT_ARGV_INPUT_HPP_INCLUDED
#define LEXY_INPUT_ARGV_INPUT_HPP_INCLUDED

#include <lexy/_detail/assert.hpp>
#include <lexy/_detail/iterator.hpp>
#include <lexy/dsl/base.hpp>
#include <lexy/dsl/token.hpp>
#include <lexy/input/base.hpp>
#include <lexy/lexeme.hpp>

namespace lexy
{
class argv_iterator;

/// A sentinel for the command-line arguments.
class argv_sentinel : public _detail::sentinel_base<argv_sentinel, argv_iterator>
{};

/// An iterator over the command-line arguments.
class argv_iterator : public _detail::bidirectional_iterator_base<argv_iterator, const char>
{
public:
    constexpr argv_iterator() noexcept : _arg(nullptr), _c(nullptr) {}

    constexpr const char& deref() const noexcept
    {
        return *_c;
    }

    constexpr void increment() noexcept
    {
        LEXY_PRECONDITION(*this != argv_sentinel{});
        if (*_c == '\0')
        {
            // Go to next argument.
            // We will have one, otherwise the precondition above would have fired.
            ++_arg;
            // Update c to the beginning of next argument.
            _c = *_arg;
        }
        else
            ++_c;
    }
    constexpr void decrement() noexcept
    {
        // Check whether we point to the first character of the argument.
        if (_c == *_arg)
        {
            // Go to end of previous argument.
            --_arg;
            _c = *_arg;
            while (*_c != '\0')
                ++_c;
        }
        else
            --_c;
    }

    constexpr bool equal(argv_iterator rhs) const noexcept
    {
        return _arg == rhs._arg && _c == rhs._c;
    }
    constexpr bool is_end() const noexcept
    {
        // We're at the end if we're at the last character of the last argument,
        // or have an empty argv range.
        return _c == nullptr || (*_c == '\0' && _arg[1] == nullptr);
    }

#ifndef _MSC_VER
private:
    // MSVC is a bad compiler and should feel bad.
    // Or at least fix their friend declarations.
#endif
    constexpr explicit argv_iterator(char** argument, char* c) noexcept : _arg(argument), _c(c) {}

private:
    char** _arg;
    char*  _c;

    friend constexpr argv_iterator argv_begin(int argc, char* argv[]) noexcept;
    friend constexpr argv_iterator argv_end(int argc, char* argv[]) noexcept;
};

/// Returns an iterator to the beginning of the command-line arguments.
constexpr argv_iterator argv_begin(int argc, char* argv[]) noexcept
{
    if (argc <= 1)
        // Create an iterator where *arg_ == nullptr, *c_ == nullptr.
        return argv_iterator(&argv[argc], nullptr);
    else
        return argv_iterator(&argv[1], &argv[1][0]);
}

/// Returns an iterator one past the end of the command-line arguments.
constexpr argv_iterator argv_end(int argc, char* argv[]) noexcept
{
    if (argc <= 1)
        // Create an iterator where *arg_ == nullptr, *c_ == nullptr.
        return argv_iterator(&argv[argc], nullptr);
    else
    {
        // Construct an iterator pointing to the nullptr arg.
        // Then decrement it to get the null terminator of the last argument,
        // which is the actual end.
        argv_iterator one_past_end(&argv[argc], nullptr);
        --one_past_end;
        return one_past_end;
    }
}
} // namespace lexy

namespace lexy
{
template <typename Encoding = default_encoding>
class argv_input
{
public:
    using encoding  = Encoding;
    using char_type = typename encoding::char_type;
    static_assert(std::is_same_v<char_type, char>
                      || Encoding::template is_secondary_char_type<char>(),
                  "invalid encoding for argv");

    //=== constructors ===//
    constexpr argv_input() = default;

    /// Iterate over the range of command-line arguments.
    constexpr argv_input(argv_iterator begin, argv_iterator end) noexcept : _begin(begin), _end(end)
    {}

    /// Iterate over the command-line arguments.
    constexpr argv_input(int argc, char* argv[]) noexcept
    : _begin(argv_begin(argc, argv)), _end(argv_end(argc, argv))
    {}

    //=== reader ===//
    constexpr auto reader() const& noexcept
    {
        return _range_reader<encoding>(_begin, _end);
    }

private:
    argv_iterator _begin, _end;
};

argv_input(int argc, char* argv[]) -> argv_input<>;
} // namespace lexy

namespace lexy
{
template <typename Encoding = default_encoding>
using argv_lexeme = lexeme_for<argv_input<Encoding>>;

template <typename Tag, typename Encoding = default_encoding>
using argv_error = error_for<argv_input<Encoding>, Tag>;

template <typename Encoding = default_encoding>
using argv_error_context = error_context<argv_input<Encoding>>;
} // namespace lexy

namespace lexyd
{
struct _argvsep : token_base<_argvsep>
{
    template <typename Reader>
    struct tp
    {
        typename Reader::marker end;

        constexpr explicit tp(const Reader& reader) : end(reader.current()) {}

        constexpr auto try_parse([[maybe_unused]] Reader reader)
        {
            using encoding = typename Reader::encoding;
            if constexpr (std::is_same_v<Reader, lexy::input_reader<lexy::argv_input<encoding>>>)
            {
                if (reader.peek() != lexy::_detail::transcode_int<encoding>('\0'))
                    return false;

                reader.bump();
                end = reader.current();
                return true;
            }
            else
            {
                return std::false_type{};
            }
        }

        template <typename Context>
        constexpr void report_error(Context& context, const Reader& reader)
        {
            auto err = lexy::error<Reader, lexy::expected_char_class>(reader.position(),
                                                                      "argv-separator");
            context.on(_ev::error{}, err);
        }
    };
};

/// Matches the separator between arguments of an argv_input.
constexpr auto argv_separator = _argvsep{};
} // namespace lexyd

namespace lexy
{
template <>
inline constexpr auto token_kind_of<lexy::dsl::_argvsep> = lexy::literal_token_kind;
} // namespace lexy

#endif // LEXY_INPUT_ARGV_INPUT_HPP_INCLUDED