center_alignment_generate.hpp

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//  Copyright (c) 2001-2008 Hartmut Kaiser
// 
//  Distributed under the Boost Software License, Version 1.0. (See accompanying 
//  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)

#if !defined(BOOST_SPIRIT_KARMA_CENTER_ALIGNMENT_GENERATE_FEB_27_2007_1216PM)
#define BOOST_SPIRIT_KARMA_CENTER_ALIGNMENT_GENERATE_FEB_27_2007_1216PM

#if defined(_MSC_VER) && (_MSC_VER >= 1020)
#pragma once      // MS compatible compilers support #pragma once
#endif

#include <boost/spirit/home/support/component.hpp>
#include <boost/spirit/home/support/unused.hpp>
#include <boost/mpl/assert.hpp>

namespace boost { namespace spirit { namespace karma { namespace detail 
{
    ///////////////////////////////////////////////////////////////////////////
    //  The center_generate template function is used for all the different
    //  flavors of the center[] directive. 
    ///////////////////////////////////////////////////////////////////////////
    template <typename OutputIterator, typename Context, typename Delimiter, 
        typename Parameter, typename Embedded, typename Padding>
    inline static bool 
    center_generate(OutputIterator& sink, Context& ctx, 
        Delimiter const& d, Parameter const& param, Embedded const& e, 
        unsigned int const width, Padding const& p) 
    {
        // make sure all generator parameters are valid
        BOOST_MPL_ASSERT_MSG(
            (spirit::traits::is_component<karma::domain, Embedded>::value), 
            embedded_is_not_convertible_to_a_generator, (Context, Embedded));

        BOOST_MPL_ASSERT_MSG(
            (spirit::traits::is_component<karma::domain, Padding>::value), 
            padding_is_not_convertible_to_a_generator, (Context, Padding));

        typedef 
            typename result_of::as_component<karma::domain, Embedded>::type 
        embedded;
        typedef 
            typename result_of::as_component<karma::domain, Padding>::type 
        padding;

        // wrap the given output iterator to allow left padding
        detail::enable_buffering<OutputIterator> buffering(sink, width);

        // first generate the embedded output 
        embedded ec = spirit::as_component(karma::domain(), e);
        typedef typename embedded::director director;
        bool r = director::generate(ec, sink, ctx, d, param);

        buffering.disable();    // do not perform buffering any more
        
        // generate the left padding
        detail::enable_counting<OutputIterator> 
            counting(sink, (sink.buffer_size() + width) / 2);

        padding pc = spirit::as_component(karma::domain(), p);
        typedef typename padding::director padding_director;
        while (r && sink.count() < width) 
            r = padding_director::generate(pc, sink, ctx, unused, unused);

        if (r) {
            // copy the embedded output to the target output iterator
            sink.buffer_copy();
        
            // generate the right padding
            std::size_t const max_count = width + (width - sink.buffer_size()) / 2;
            while (r && sink.count() < max_count) 
                r = padding_director::generate(pc, sink, ctx, unused, unused);
        }
        return r;
    }

}}}}   // namespace boost::spirit::karma::detail

#endif