// Some relevant documentation:
//
// - Tessellation overview           https://www.khronos.org/opengl/wiki/Tessellation
// - Tessellation Control Shader     https://www.khronos.org/opengl/wiki/Tessellation_Control_Shader
// - Tessellation Evaluation Shader  https://www.khronos.org/opengl/wiki/Tessellation_Evaluation_Shader
// - Tessellation real-world usage 1 http://ogldev.atspace.co.uk/www/tutorial30/tutorial30.html
// - Tessellation real-world usage 2 https://prideout.net/blog/?p=48

// Notable elements of this example:
//
// - Usage of a tessellation control shader and a tessellation evaluation shader.
// - `tessellation_shaders` and `tessellation_state` are called on the pipeline builder.
// - The use of `PrimitiveTopology::PatchList`.

use std::{error::Error, sync::Arc};
use vulkano::{
    buffer::{Buffer, BufferContents, BufferCreateInfo, BufferUsage, Subbuffer},
    command_buffer::{
        allocator::StandardCommandBufferAllocator, AutoCommandBufferBuilder, CommandBufferUsage,
        RenderPassBeginInfo,
    },
    device::{
        physical::PhysicalDeviceType, Device, DeviceCreateInfo, DeviceExtensions, DeviceFeatures,
        Queue, QueueCreateInfo, QueueFlags,
    },
    image::{view::ImageView, Image, ImageUsage},
    instance::{Instance, InstanceCreateFlags, InstanceCreateInfo},
    memory::allocator::{AllocationCreateInfo, MemoryTypeFilter, StandardMemoryAllocator},
    pipeline::{
        graphics::{
            color_blend::{ColorBlendAttachmentState, ColorBlendState},
            input_assembly::{InputAssemblyState, PrimitiveTopology},
            multisample::MultisampleState,
            rasterization::{PolygonMode, RasterizationState},
            tessellation::TessellationState,
            vertex_input::{Vertex, VertexDefinition},
            viewport::{Viewport, ViewportState},
            GraphicsPipelineCreateInfo,
        },
        layout::PipelineDescriptorSetLayoutCreateInfo,
        DynamicState, GraphicsPipeline, PipelineLayout, PipelineShaderStageCreateInfo,
    },
    render_pass::{Framebuffer, FramebufferCreateInfo, RenderPass, Subpass},
    swapchain::{
        acquire_next_image, Surface, Swapchain, SwapchainCreateInfo, SwapchainPresentInfo,
    },
    sync::{self, GpuFuture},
    Validated, VulkanError, VulkanLibrary,
};
use winit::{
    application::ApplicationHandler,
    event::WindowEvent,
    event_loop::{ActiveEventLoop, EventLoop},
    window::{Window, WindowId},
};

fn main() -> Result<(), impl Error> {
    let event_loop = EventLoop::new().unwrap();
    let mut app = App::new(&event_loop);

    event_loop.run_app(&mut app)
}

struct App {
    instance: Arc<Instance>,
    device: Arc<Device>,
    queue: Arc<Queue>,
    command_buffer_allocator: Arc<StandardCommandBufferAllocator>,
    vertex_buffer: Subbuffer<[MyVertex]>,
    rcx: Option<RenderContext>,
}

struct RenderContext {
    window: Arc<Window>,
    swapchain: Arc<Swapchain>,
    render_pass: Arc<RenderPass>,
    framebuffers: Vec<Arc<Framebuffer>>,
    pipeline: Arc<GraphicsPipeline>,
    viewport: Viewport,
    recreate_swapchain: bool,
    previous_frame_end: Option<Box<dyn GpuFuture>>,
}

impl App {
    fn new(event_loop: &EventLoop<()>) -> Self {
        let library = VulkanLibrary::new().unwrap();
        let required_extensions = Surface::required_extensions(event_loop).unwrap();
        let instance = Instance::new(
            library,
            InstanceCreateInfo {
                flags: InstanceCreateFlags::ENUMERATE_PORTABILITY,
                enabled_extensions: required_extensions,
                ..Default::default()
            },
        )
        .unwrap();

        let device_extensions = DeviceExtensions {
            khr_swapchain: true,
            ..DeviceExtensions::empty()
        };
        let device_features = DeviceFeatures {
            tessellation_shader: true,
            fill_mode_non_solid: true,
            ..DeviceFeatures::empty()
        };
        let (physical_device, queue_family_index) = instance
            .enumerate_physical_devices()
            .unwrap()
            .filter(|p| p.supported_extensions().contains(&device_extensions))
            .filter(|p| p.supported_features().contains(&device_features))
            .filter_map(|p| {
                p.queue_family_properties()
                    .iter()
                    .enumerate()
                    .position(|(i, q)| {
                        q.queue_flags.intersects(QueueFlags::GRAPHICS)
                            && p.presentation_support(i as u32, event_loop).unwrap()
                    })
                    .map(|i| (p, i as u32))
            })
            .min_by_key(|(p, _)| match p.properties().device_type {
                PhysicalDeviceType::DiscreteGpu => 0,
                PhysicalDeviceType::IntegratedGpu => 1,
                PhysicalDeviceType::VirtualGpu => 2,
                PhysicalDeviceType::Cpu => 3,
                PhysicalDeviceType::Other => 4,
                _ => 5,
            })
            .unwrap();

        println!(
            "Using device: {} (type: {:?})",
            physical_device.properties().device_name,
            physical_device.properties().device_type,
        );

        let (device, mut queues) = Device::new(
            physical_device,
            DeviceCreateInfo {
                queue_create_infos: vec![QueueCreateInfo {
                    queue_family_index,
                    ..Default::default()
                }],
                enabled_extensions: device_extensions,
                enabled_features: device_features,
                ..Default::default()
            },
        )
        .unwrap();

        let queue = queues.next().unwrap();

        let memory_allocator = Arc::new(StandardMemoryAllocator::new_default(device.clone()));
        let command_buffer_allocator = Arc::new(StandardCommandBufferAllocator::new(
            device.clone(),
            Default::default(),
        ));

        let vertices = [
            MyVertex {
                position: [-0.5, -0.25],
            },
            MyVertex {
                position: [0.0, 0.5],
            },
            MyVertex {
                position: [0.25, -0.1],
            },
            MyVertex {
                position: [0.9, 0.9],
            },
            MyVertex {
                position: [0.9, 0.8],
            },
            MyVertex {
                position: [0.8, 0.8],
            },
            MyVertex {
                position: [-0.9, 0.9],
            },
            MyVertex {
                position: [-0.7, 0.6],
            },
            MyVertex {
                position: [-0.5, 0.9],
            },
        ];
        let vertex_buffer = Buffer::from_iter(
            memory_allocator,
            BufferCreateInfo {
                usage: BufferUsage::VERTEX_BUFFER,
                ..Default::default()
            },
            AllocationCreateInfo {
                memory_type_filter: MemoryTypeFilter::PREFER_DEVICE
                    | MemoryTypeFilter::HOST_SEQUENTIAL_WRITE,
                ..Default::default()
            },
            vertices,
        )
        .unwrap();

        App {
            instance,
            device,
            queue,
            command_buffer_allocator,
            vertex_buffer,
            rcx: None,
        }
    }
}

impl ApplicationHandler for App {
    fn resumed(&mut self, event_loop: &ActiveEventLoop) {
        let window = Arc::new(
            event_loop
                .create_window(Window::default_attributes())
                .unwrap(),
        );
        let surface = Surface::from_window(self.instance.clone(), window.clone()).unwrap();
        let window_size = window.inner_size();

        let (swapchain, images) = {
            let surface_capabilities = self
                .device
                .physical_device()
                .surface_capabilities(&surface, Default::default())
                .unwrap();
            let (image_format, _) = self
                .device
                .physical_device()
                .surface_formats(&surface, Default::default())
                .unwrap()[0];

            Swapchain::new(
                self.device.clone(),
                surface,
                SwapchainCreateInfo {
                    min_image_count: surface_capabilities.min_image_count.max(2),
                    image_format,
                    image_extent: window.inner_size().into(),
                    image_usage: ImageUsage::COLOR_ATTACHMENT,
                    composite_alpha: surface_capabilities
                        .supported_composite_alpha
                        .into_iter()
                        .next()
                        .unwrap(),
                    ..Default::default()
                },
            )
            .unwrap()
        };

        let render_pass = vulkano::single_pass_renderpass!(
            self.device.clone(),
            attachments: {
                color: {
                    format: swapchain.image_format(),
                    samples: 1,
                    load_op: Clear,
                    store_op: Store,
                },
            },
            pass: {
                color: [color],
                depth_stencil: {},
            },
        )
        .unwrap();

        let framebuffers = window_size_dependent_setup(&images, &render_pass);

        let pipeline = {
            let vs = vs::load(self.device.clone())
                .unwrap()
                .entry_point("main")
                .unwrap();
            let tcs = tcs::load(self.device.clone())
                .unwrap()
                .entry_point("main")
                .unwrap();
            let tes = tes::load(self.device.clone())
                .unwrap()
                .entry_point("main")
                .unwrap();
            let fs = fs::load(self.device.clone())
                .unwrap()
                .entry_point("main")
                .unwrap();
            let vertex_input_state = MyVertex::per_vertex().definition(&vs).unwrap();
            let stages = [
                PipelineShaderStageCreateInfo::new(vs),
                PipelineShaderStageCreateInfo::new(tcs),
                PipelineShaderStageCreateInfo::new(tes),
                PipelineShaderStageCreateInfo::new(fs),
            ];
            let layout = PipelineLayout::new(
                self.device.clone(),
                PipelineDescriptorSetLayoutCreateInfo::from_stages(&stages)
                    .into_pipeline_layout_create_info(self.device.clone())
                    .unwrap(),
            )
            .unwrap();
            let subpass = Subpass::from(render_pass.clone(), 0).unwrap();

            GraphicsPipeline::new(
                self.device.clone(),
                None,
                GraphicsPipelineCreateInfo {
                    stages: stages.into_iter().collect(),
                    vertex_input_state: Some(vertex_input_state),
                    input_assembly_state: Some(InputAssemblyState {
                        topology: PrimitiveTopology::PatchList,
                        ..Default::default()
                    }),
                    tessellation_state: Some(TessellationState {
                        // Use a patch_control_points of 3, because we want to convert one
                        // *triangle* into lots of little ones. A value of 4 would convert a
                        // *rectangle* into lots of little triangles.
                        patch_control_points: 3,
                        ..Default::default()
                    }),
                    viewport_state: Some(ViewportState::default()),
                    rasterization_state: Some(RasterizationState {
                        polygon_mode: PolygonMode::Line,
                        ..Default::default()
                    }),
                    multisample_state: Some(MultisampleState::default()),
                    color_blend_state: Some(ColorBlendState::with_attachment_states(
                        subpass.num_color_attachments(),
                        ColorBlendAttachmentState::default(),
                    )),
                    dynamic_state: [DynamicState::Viewport].into_iter().collect(),
                    subpass: Some(subpass.into()),
                    ..GraphicsPipelineCreateInfo::layout(layout)
                },
            )
            .unwrap()
        };

        let viewport = Viewport {
            offset: [0.0, 0.0],
            extent: window_size.into(),
            depth_range: 0.0..=1.0,
        };

        let previous_frame_end = Some(sync::now(self.device.clone()).boxed());

        self.rcx = Some(RenderContext {
            window,
            swapchain,
            render_pass,
            framebuffers,
            pipeline,
            viewport,
            recreate_swapchain: false,
            previous_frame_end,
        });
    }

    fn window_event(
        &mut self,
        event_loop: &ActiveEventLoop,
        _window_id: WindowId,
        event: WindowEvent,
    ) {
        let rcx = self.rcx.as_mut().unwrap();

        match event {
            WindowEvent::CloseRequested => {
                event_loop.exit();
            }
            WindowEvent::Resized(_) => {
                rcx.recreate_swapchain = true;
            }
            WindowEvent::RedrawRequested => {
                let window_size = rcx.window.inner_size();

                if window_size.width == 0 || window_size.height == 0 {
                    return;
                }

                rcx.previous_frame_end.as_mut().unwrap().cleanup_finished();

                if rcx.recreate_swapchain {
                    let (new_swapchain, new_images) = rcx
                        .swapchain
                        .recreate(SwapchainCreateInfo {
                            image_extent: window_size.into(),
                            ..rcx.swapchain.create_info()
                        })
                        .expect("failed to recreate swapchain");

                    rcx.swapchain = new_swapchain;
                    rcx.framebuffers = window_size_dependent_setup(&new_images, &rcx.render_pass);
                    rcx.viewport.extent = window_size.into();
                    rcx.recreate_swapchain = false;
                }

                let (image_index, suboptimal, acquire_future) = match acquire_next_image(
                    rcx.swapchain.clone(),
                    None,
                )
                .map_err(Validated::unwrap)
                {
                    Ok(r) => r,
                    Err(VulkanError::OutOfDate) => {
                        rcx.recreate_swapchain = true;
                        return;
                    }
                    Err(e) => panic!("failed to acquire next image: {e}"),
                };

                if suboptimal {
                    rcx.recreate_swapchain = true;
                }

                let mut builder = AutoCommandBufferBuilder::primary(
                    self.command_buffer_allocator.clone(),
                    self.queue.queue_family_index(),
                    CommandBufferUsage::OneTimeSubmit,
                )
                .unwrap();

                builder
                    .begin_render_pass(
                        RenderPassBeginInfo {
                            clear_values: vec![Some([0.0, 0.0, 0.0, 1.0].into())],
                            ..RenderPassBeginInfo::framebuffer(
                                rcx.framebuffers[image_index as usize].clone(),
                            )
                        },
                        Default::default(),
                    )
                    .unwrap()
                    .set_viewport(0, [rcx.viewport.clone()].into_iter().collect())
                    .unwrap()
                    .bind_pipeline_graphics(rcx.pipeline.clone())
                    .unwrap()
                    .bind_vertex_buffers(0, self.vertex_buffer.clone())
                    .unwrap();
                unsafe { builder.draw(self.vertex_buffer.len() as u32, 1, 0, 0) }.unwrap();

                builder.end_render_pass(Default::default()).unwrap();

                let command_buffer = builder.build().unwrap();
                let future = rcx
                    .previous_frame_end
                    .take()
                    .unwrap()
                    .join(acquire_future)
                    .then_execute(self.queue.clone(), command_buffer)
                    .unwrap()
                    .then_swapchain_present(
                        self.queue.clone(),
                        SwapchainPresentInfo::swapchain_image_index(
                            rcx.swapchain.clone(),
                            image_index,
                        ),
                    )
                    .then_signal_fence_and_flush();

                match future.map_err(Validated::unwrap) {
                    Ok(future) => {
                        rcx.previous_frame_end = Some(future.boxed());
                    }
                    Err(VulkanError::OutOfDate) => {
                        rcx.recreate_swapchain = true;
                        rcx.previous_frame_end = Some(sync::now(self.device.clone()).boxed());
                    }
                    Err(e) => {
                        println!("failed to flush future: {e}");
                        rcx.previous_frame_end = Some(sync::now(self.device.clone()).boxed());
                    }
                }
            }
            _ => {}
        }
    }

    fn about_to_wait(&mut self, _event_loop: &ActiveEventLoop) {
        let rcx = self.rcx.as_mut().unwrap();
        rcx.window.request_redraw();
    }
}

#[derive(BufferContents, Vertex)]
#[repr(C)]
struct MyVertex {
    #[format(R32G32_SFLOAT)]
    position: [f32; 2],
}

/// This function is called once during initialization, then again whenever the window is resized.
fn window_size_dependent_setup(
    images: &[Arc<Image>],
    render_pass: &Arc<RenderPass>,
) -> Vec<Arc<Framebuffer>> {
    images
        .iter()
        .map(|image| {
            let view = ImageView::new_default(image.clone()).unwrap();

            Framebuffer::new(
                render_pass.clone(),
                FramebufferCreateInfo {
                    attachments: vec![view],
                    ..Default::default()
                },
            )
            .unwrap()
        })
        .collect::<Vec<_>>()
}

mod vs {
    vulkano_shaders::shader! {
        ty: "vertex",
        src: r"
            #version 450

            layout(location = 0) in vec2 position;

            void main() {
                gl_Position = vec4(position, 0.0, 1.0);
            }
        ",
    }
}

mod tcs {
    vulkano_shaders::shader! {
        ty: "tess_ctrl",
        src: r"
            #version 450

            // A value of 3 means a patch consists of a single triangle.
            layout(vertices = 3) out;

            void main(void) {
                // Save the position of the patch, so the TES can access it. We could define our
                // own output variables for this, but `gl_out` is handily provided.
                gl_out[gl_InvocationID].gl_Position = gl_in[gl_InvocationID].gl_Position;

                // Many triangles are generated in the center.
                gl_TessLevelInner[0] = 10;
                // No triangles are generated for this edge.
                gl_TessLevelOuter[0] = 1;
                // Many triangles are generated for this edge.
                gl_TessLevelOuter[1] = 10;
                // Many triangles are generated for this edge.
                gl_TessLevelOuter[2] = 10;

                // These are only used when TES uses `layout(quads)`.
                // gl_TessLevelInner[1] = ...;
                // gl_TessLevelOuter[3] = ...;
            }
        ",
    }
}

// There is a stage in between TCS and TES called Primitive Generation (PG). Shaders cannot be
// defined for it. It takes `gl_TessLevelInner` and `gl_TessLevelOuter` and uses them to generate
// positions within the patch and pass them to TES via `gl_TessCoord`.
//
// When TES uses `layout(triangles)` then `gl_TessCoord` is in Barycentric coordinates. If
// `layout(quads)` is used then `gl_TessCoord` is in Cartesian coordinates. Barycentric coordinates
// are of the form (x, y, z) where x + y + z = 1 and the values x, y and z represent the distance
// from a vertex of the triangle.
// https://mathworld.wolfram.com/BarycentricCoordinates.html

mod tes {
    vulkano_shaders::shader! {
        ty: "tess_eval",
        src: r"
            #version 450

            layout(triangles, equal_spacing, cw) in;

            void main(void) {
                // Retrieve the vertex positions set by the TCS.
                vec4 v1 = gl_in[0].gl_Position;
                vec4 v2 = gl_in[1].gl_Position;
                vec4 v3 = gl_in[2].gl_Position;

                // Convert `gl_TessCoord` from Barycentric coordinates to Cartesian coordinates.
                gl_Position = vec4(
                    gl_TessCoord.x * v1.x + gl_TessCoord.y * v2.x + gl_TessCoord.z * v3.x,
                    gl_TessCoord.x * v1.y + gl_TessCoord.y * v2.y + gl_TessCoord.z * v3.y,
                    gl_TessCoord.x * v1.z + gl_TessCoord.y * v2.z + gl_TessCoord.z * v3.z,
                    1.0
                );
            }
        ",
    }
}

mod fs {
    vulkano_shaders::shader! {
        ty: "fragment",
        src: r"
            #version 450

            layout(location = 0) out vec4 f_color;

            void main() {
                f_color = vec4(1.0, 1.0, 1.0, 1.0);
            }
        ",
    }
}