/*
 * Copyright (C) 2023  Christopher J. Howard
 *
 * This file is part of Antkeeper source code.
 *
 * Antkeeper source code is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * Antkeeper source code is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Antkeeper source code.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <engine/gl/vertex-buffer.hpp>
#include <stdexcept>
#include <glad/gl.h>
#include <utility>

namespace gl {

namespace
{
	static constexpr GLenum buffer_usage_lut[] =
	{
		GL_STREAM_DRAW,
		GL_STREAM_READ,
		GL_STREAM_COPY,
		GL_STATIC_DRAW,
		GL_STATIC_READ,
		GL_STATIC_COPY,
		GL_DYNAMIC_DRAW,
		GL_DYNAMIC_READ,
		GL_DYNAMIC_COPY
	};
}

vertex_buffer::vertex_buffer(buffer_usage usage, std::size_t size, std::span<const std::byte> data):
	m_usage{usage},
	m_size{size}
{
	if (!data.empty())
	{
		// Bounds check
		if (data.size() < size)
		{
			throw std::out_of_range("Vertex buffer construct operation exceeded data bounds.");
		}
	}
	
	const GLenum gl_usage = buffer_usage_lut[std::to_underlying(m_usage)];
	glCreateBuffers(1, &m_gl_named_buffer);
	glNamedBufferData(m_gl_named_buffer, static_cast<GLsizeiptr>(m_size), data.empty() ? nullptr : data.data(), gl_usage);
}

vertex_buffer::vertex_buffer(const vertex_buffer& buffer):
	vertex_buffer(buffer.m_usage, buffer.m_size)
{
	copy(buffer, m_size);
}

vertex_buffer::vertex_buffer(vertex_buffer&& buffer):
	m_gl_named_buffer{std::exchange(buffer.m_gl_named_buffer, 0)},
	m_usage{std::move(buffer.m_usage)},
	m_size{std::exchange(buffer.m_size, 0)}
{}

vertex_buffer::~vertex_buffer()
{
	if (m_gl_named_buffer)
	{
		glDeleteBuffers(1, &m_gl_named_buffer);
	}
}

vertex_buffer& vertex_buffer::operator=(const vertex_buffer& buffer)
{
	repurpose(buffer.m_usage, buffer.m_size);
	copy(buffer, m_size);
	
	return *this;
}

vertex_buffer& vertex_buffer::operator=(vertex_buffer&& buffer)
{
	if (m_gl_named_buffer)
	{
		glDeleteBuffers(1, &m_gl_named_buffer);
	}
	
	m_gl_named_buffer = std::exchange(buffer.m_gl_named_buffer, 0);
	m_usage = std::move(buffer.m_usage);
	m_size = std::exchange(buffer.m_size, 0);
	
	return *this;
}

void vertex_buffer::repurpose(buffer_usage usage, std::size_t size, std::span<const std::byte> data)
{
	if (!data.empty())
	{
		// Bounds check
		if (data.size() < size)
		{
			throw std::out_of_range("Vertex buffer resize operation exceeded data bounds.");
		}
	}
	
	m_usage = usage;
	m_size = size;
	
	const auto gl_usage = buffer_usage_lut[std::to_underlying(m_usage)];
	glNamedBufferData(m_gl_named_buffer, static_cast<GLsizeiptr>(m_size), data.empty() ? nullptr : data.data(), gl_usage);
}

void vertex_buffer::write(std::size_t offset, std::span<const std::byte> data)
{
	// Ignore empty write operations
	if (data.empty())
	{
		return;
	}
	
	// Bounds check
	if (offset + data.size() > m_size)
	{
		throw std::out_of_range("Vertex buffer write operation exceeded buffer bounds.");
	}
	
	glNamedBufferSubData(m_gl_named_buffer, static_cast<GLintptr>(offset), static_cast<GLsizeiptr>(data.size()), data.data());
}

void vertex_buffer::read(std::size_t offset, std::span<std::byte> data) const
{
	// Ignore empty read operations
	if (data.empty())
	{
		return;
	}
	
	// Bounds check
	if (offset + data.size() > m_size)
	{
		throw std::out_of_range("Vertex buffer read operation exceeded buffer bounds.");
	}
	
	glGetNamedBufferSubData(m_gl_named_buffer, static_cast<GLintptr>(offset), static_cast<GLsizeiptr>(data.size()), data.data());
}

void vertex_buffer::copy(const vertex_buffer& read_buffer, std::size_t copy_size, std::size_t read_offset, std::size_t write_offset)
{
	// Bounds check
	if (read_offset + copy_size > read_buffer.m_size)
	{
		throw std::out_of_range("Vertex buffer copy operation exceeded read buffer bounds.");
	}
	if (write_offset + copy_size > m_size)
	{
		throw std::out_of_range("Vertex buffer copy operation exceeded write buffer bounds.");
	}
	
	glCopyNamedBufferSubData(read_buffer.m_gl_named_buffer, m_gl_named_buffer, static_cast<GLintptr>(read_offset), static_cast<GLintptr>(write_offset), static_cast<GLsizeiptr>(copy_size));
}

} // namespace gl