#include <psemek/audio/echo.hpp>
#include <psemek/audio/engine.hpp>
#include <psemek/audio/utils.hpp>

#include <cmath>
#include <vector>

namespace psemek::audio
{

	namespace
	{

		struct echo_impl
			: audio::effect
		{
			echo_impl(float delay, float volume)
				: delay_(delay)
				, volume_(volume)
			{}

			void init(int frequency, int channels) override
			{
				int sample_count = std::round(delay_ * frequency) * channels;
				samples_.reserve(sample_count);
			}

			std::string_view name() const override
			{
				return "echo";
			}

			void operator()(std::int16_t * data, std::size_t size) override
			{
				if (samples_.size() < samples_.capacity())
				{
					auto count = std::min(samples_.capacity() - samples_.size(), size);
					std::copy(data, data + count, std::back_inserter(samples_));
					pos_ += count;
					data += count;
					size -= count;

					if (pos_ == samples_.capacity())
						pos_ = 0;
				}

				for (; size > 0; ++data, --size)
				{
					float s = clamp((*data) + samples_[pos_] * volume_);
					samples_[pos_] = *data;
					*data = s;

					++pos_;
					if (pos_ == samples_.capacity())
						pos_ = 0;
				}
			}

		private:
			std::vector<std::int16_t> samples_;
			std::size_t pos_ = 0;
			float delay_;
			float volume_;
		};

	}

	std::shared_ptr<effect> echo(float delay, float volume)
	{
		return std::make_shared<echo_impl>(delay, volume);
	}

}