// Copyright (c) 2016 The vulkano developers
// Licensed under the Apache License, Version 2.0
// <LICENSE-APACHE or
// https://www.apache.org/licenses/LICENSE-2.0> or the MIT
// license <LICENSE-MIT or https://opensource.org/licenses/MIT>,
// at your option. All files in the project carrying such
// notice may not be copied, modified, or distributed except
// according to those terms.

// Welcome to the triangle example!
//
// This is the only example that is entirely detailed. All the other examples avoid code
// duplication by using helper functions.
//
// This example assumes that you are already more or less familiar with graphics programming
// and that you want to learn Vulkan. This means that for example it won't go into details about
// what a vertex or a shader is.

use vulkano::buffer::{BufferUsage, CpuAccessibleBuffer};
use vulkano::command_buffer::{AutoCommandBufferBuilder, DynamicState, SubpassContents};
use vulkano::device::{Device, DeviceExtensions};
use vulkano::framebuffer::{Framebuffer, FramebufferAbstract, RenderPassAbstract, Subpass};
use vulkano::image::view::ImageView;
use vulkano::image::{ImageUsage, SwapchainImage};
use vulkano::instance::{Instance, PhysicalDevice};
use vulkano::pipeline::viewport::Viewport;
use vulkano::pipeline::GraphicsPipeline;
use vulkano::swapchain;
use vulkano::swapchain::{
    AcquireError, ColorSpace, FullscreenExclusive, PresentMode, SurfaceTransform, Swapchain,
    SwapchainCreationError,
};
use vulkano::sync;
use vulkano::sync::{FlushError, GpuFuture};

use vulkano_win::VkSurfaceBuild;
use winit::event::{Event, WindowEvent};
use winit::event_loop::{ControlFlow, EventLoop};
use winit::window::{Window, WindowBuilder};

use std::sync::Arc;

fn main() {
    // The first step of any Vulkan program is to create an instance.
    //
    // When we create an instance, we have to pass a list of extensions that we want to enable.
    //
    // All the window-drawing functionalities are part of non-core extensions that we need
    // to enable manually. To do so, we ask the `vulkano_win` crate for the list of extensions
    // required to draw to a window.
    let required_extensions = vulkano_win::required_extensions();

    // Now creating the instance.
    let instance = Instance::new(None, &required_extensions, None).unwrap();

    // We then choose which physical device to use.
    //
    // In a real application, there are three things to take into consideration:
    //
    // - Some devices may not support some of the optional features that may be required by your
    //   application. You should filter out the devices that don't support your app.
    //
    // - Not all devices can draw to a certain surface. Once you create your window, you have to
    //   choose a device that is capable of drawing to it.
    //
    // - You probably want to leave the choice between the remaining devices to the user.
    //
    // For the sake of the example we are just going to use the first device, which should work
    // most of the time.
    let physical = PhysicalDevice::enumerate(&instance).next().unwrap();

    // Some little debug infos.
    println!(
        "Using device: {} (type: {:?})",
        physical.name(),
        physical.ty()
    );

    // The objective of this example is to draw a triangle on a window. To do so, we first need to
    // create the window.
    //
    // This is done by creating a `WindowBuilder` from the `winit` crate, then calling the
    // `build_vk_surface` method provided by the `VkSurfaceBuild` trait from `vulkano_win`. If you
    // ever get an error about `build_vk_surface` being undefined in one of your projects, this
    // probably means that you forgot to import this trait.
    //
    // This returns a `vulkano::swapchain::Surface` object that contains both a cross-platform winit
    // window and a cross-platform Vulkan surface that represents the surface of the window.
    let event_loop = EventLoop::new();
    let surface = WindowBuilder::new()
        .build_vk_surface(&event_loop, instance.clone())
        .unwrap();

    // The next step is to choose which GPU queue will execute our draw commands.
    //
    // Devices can provide multiple queues to run commands in parallel (for example a draw queue
    // and a compute queue), similar to CPU threads. This is something you have to have to manage
    // manually in Vulkan.
    //
    // In a real-life application, we would probably use at least a graphics queue and a transfers
    // queue to handle data transfers in parallel. In this example we only use one queue.
    //
    // We have to choose which queues to use early on, because we will need this info very soon.
    let queue_family = physical
        .queue_families()
        .find(|&q| {
            // We take the first queue that supports drawing to our window.
            q.supports_graphics() && surface.is_supported(q).unwrap_or(false)
        })
        .unwrap();

    // Now initializing the device. This is probably the most important object of Vulkan.
    //
    // We have to pass five parameters when creating a device:
    //
    // - Which physical device to connect to.
    //
    // - A list of optional features and extensions that our program needs to work correctly.
    //   Some parts of the Vulkan specs are optional and must be enabled manually at device
    //   creation. In this example the only thing we are going to need is the `khr_swapchain`
    //   extension that allows us to draw to a window.
    //
    // - A list of layers to enable. This is very niche, and you will usually pass `None`.
    //
    // - The list of queues that we are going to use. The exact parameter is an iterator whose
    //   items are `(Queue, f32)` where the floating-point represents the priority of the queue
    //   between 0.0 and 1.0. The priority of the queue is a hint to the implementation about how
    //   much it should prioritize queues between one another.
    //
    // The list of created queues is returned by the function alongside with the device.
    let device_ext = DeviceExtensions {
        khr_swapchain: true,
        ..DeviceExtensions::none()
    };
    let (device, mut queues) = Device::new(
        physical,
        physical.supported_features(),
        &device_ext,
        [(queue_family, 0.5)].iter().cloned(),
    )
    .unwrap();

    // Since we can request multiple queues, the `queues` variable is in fact an iterator. In this
    // example we use only one queue, so we just retrieve the first and only element of the
    // iterator and throw it away.
    let queue = queues.next().unwrap();

    // Before we can draw on the surface, we have to create what is called a swapchain. Creating
    // a swapchain allocates the color buffers that will contain the image that will ultimately
    // be visible on the screen. These images are returned alongside with the swapchain.
    let (mut swapchain, images) = {
        // Querying the capabilities of the surface. When we create the swapchain we can only
        // pass values that are allowed by the capabilities.
        let caps = surface.capabilities(physical).unwrap();

        // The alpha mode indicates how the alpha value of the final image will behave. For example
        // you can choose whether the window will be opaque or transparent.
        let alpha = caps.supported_composite_alpha.iter().next().unwrap();

        // Choosing the internal format that the images will have.
        let format = caps.supported_formats[0].0;

        // The dimensions of the window, only used to initially setup the swapchain.
        // NOTE:
        // On some drivers the swapchain dimensions are specified by `caps.current_extent` and the
        // swapchain size must use these dimensions.
        // These dimensions are always the same as the window dimensions
        //
        // However other drivers dont specify a value i.e. `caps.current_extent` is `None`
        // These drivers will allow anything but the only sensible value is the window dimensions.
        //
        // Because for both of these cases, the swapchain needs to be the window dimensions, we just use that.
        let dimensions: [u32; 2] = surface.window().inner_size().into();

        // Please take a look at the docs for the meaning of the parameters we didn't mention.
        Swapchain::new(
            device.clone(),
            surface.clone(),
            caps.min_image_count,
            format,
            dimensions,
            1,
            ImageUsage::color_attachment(),
            &queue,
            SurfaceTransform::Identity,
            alpha,
            PresentMode::Fifo,
            FullscreenExclusive::Default,
            true,
            ColorSpace::SrgbNonLinear,
        )
        .unwrap()
    };

    // We now create a buffer that will store the shape of our triangle.
    let vertex_buffer = {
        #[derive(Default, Debug, Clone)]
        struct Vertex {
            position: [f32; 2],
        }
        vulkano::impl_vertex!(Vertex, position);

        CpuAccessibleBuffer::from_iter(
            device.clone(),
            BufferUsage::all(),
            false,
            [
                Vertex {
                    position: [-0.5, -0.25],
                },
                Vertex {
                    position: [0.0, 0.5],
                },
                Vertex {
                    position: [0.25, -0.1],
                },
            ]
            .iter()
            .cloned(),
        )
        .unwrap()
    };

    // The next step is to create the shaders.
    //
    // The raw shader creation API provided by the vulkano library is unsafe, for various reasons.
    //
    // An overview of what the `vulkano_shaders::shader!` macro generates can be found in the
    // `vulkano-shaders` crate docs. You can view them at https://docs.rs/vulkano-shaders/
    //
    // TODO: explain this in details
    mod vs {
        vulkano_shaders::shader! {
            ty: "vertex",
            src: "
				#version 450

				layout(location = 0) in vec2 position;

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

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

				layout(location = 0) out vec4 f_color;

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

    let vs = vs::Shader::load(device.clone()).unwrap();
    let fs = fs::Shader::load(device.clone()).unwrap();

    // At this point, OpenGL initialization would be finished. However in Vulkan it is not. OpenGL
    // implicitly does a lot of computation whenever you draw. In Vulkan, you have to do all this
    // manually.

    // The next step is to create a *render pass*, which is an object that describes where the
    // output of the graphics pipeline will go. It describes the layout of the images
    // where the colors, depth and/or stencil information will be written.
    let render_pass = Arc::new(
        vulkano::single_pass_renderpass!(
            device.clone(),
            attachments: {
                // `color` is a custom name we give to the first and only attachment.
                color: {
                    // `load: Clear` means that we ask the GPU to clear the content of this
                    // attachment at the start of the drawing.
                    load: Clear,
                    // `store: Store` means that we ask the GPU to store the output of the draw
                    // in the actual image. We could also ask it to discard the result.
                    store: Store,
                    // `format: <ty>` indicates the type of the format of the image. This has to
                    // be one of the types of the `vulkano::format` module (or alternatively one
                    // of your structs that implements the `FormatDesc` trait). Here we use the
                    // same format as the swapchain.
                    format: swapchain.format(),
                    // TODO:
                    samples: 1,
                }
            },
            pass: {
                // We use the attachment named `color` as the one and only color attachment.
                color: [color],
                // No depth-stencil attachment is indicated with empty brackets.
                depth_stencil: {}
            }
        )
        .unwrap(),
    );

    // Before we draw we have to create what is called a pipeline. This is similar to an OpenGL
    // program, but much more specific.
    let pipeline = Arc::new(
        GraphicsPipeline::start()
            // We need to indicate the layout of the vertices.
            // The type `SingleBufferDefinition` actually contains a template parameter corresponding
            // to the type of each vertex. But in this code it is automatically inferred.
            .vertex_input_single_buffer()
            // A Vulkan shader can in theory contain multiple entry points, so we have to specify
            // which one. The `main` word of `main_entry_point` actually corresponds to the name of
            // the entry point.
            .vertex_shader(vs.main_entry_point(), ())
            // The content of the vertex buffer describes a list of triangles.
            .triangle_list()
            // Use a resizable viewport set to draw over the entire window
            .viewports_dynamic_scissors_irrelevant(1)
            // See `vertex_shader`.
            .fragment_shader(fs.main_entry_point(), ())
            // We have to indicate which subpass of which render pass this pipeline is going to be used
            // in. The pipeline will only be usable from this particular subpass.
            .render_pass(Subpass::from(render_pass.clone(), 0).unwrap())
            // Now that our builder is filled, we call `build()` to obtain an actual pipeline.
            .build(device.clone())
            .unwrap(),
    );

    // Dynamic viewports allow us to recreate just the viewport when the window is resized
    // Otherwise we would have to recreate the whole pipeline.
    let mut dynamic_state = DynamicState {
        line_width: None,
        viewports: None,
        scissors: None,
        compare_mask: None,
        write_mask: None,
        reference: None,
    };

    // The render pass we created above only describes the layout of our framebuffers. Before we
    // can draw we also need to create the actual framebuffers.
    //
    // Since we need to draw to multiple images, we are going to create a different framebuffer for
    // each image.
    let mut framebuffers =
        window_size_dependent_setup(&images, render_pass.clone(), &mut dynamic_state);

    // Initialization is finally finished!

    // In some situations, the swapchain will become invalid by itself. This includes for example
    // when the window is resized (as the images of the swapchain will no longer match the
    // window's) or, on Android, when the application went to the background and goes back to the
    // foreground.
    //
    // In this situation, acquiring a swapchain image or presenting it will return an error.
    // Rendering to an image of that swapchain will not produce any error, but may or may not work.
    // To continue rendering, we need to recreate the swapchain by creating a new swapchain.
    // Here, we remember that we need to do this for the next loop iteration.
    let mut recreate_swapchain = false;

    // In the loop below we are going to submit commands to the GPU. Submitting a command produces
    // an object that implements the `GpuFuture` trait, which holds the resources for as long as
    // they are in use by the GPU.
    //
    // Destroying the `GpuFuture` blocks until the GPU is finished executing it. In order to avoid
    // that, we store the submission of the previous frame here.
    let mut previous_frame_end = Some(sync::now(device.clone()).boxed());

    event_loop.run(move |event, _, control_flow| {
        match event {
            Event::WindowEvent {
                event: WindowEvent::CloseRequested,
                ..
            } => {
                *control_flow = ControlFlow::Exit;
            }
            Event::WindowEvent {
                event: WindowEvent::Resized(_),
                ..
            } => {
                recreate_swapchain = true;
            }
            Event::RedrawEventsCleared => {
                // It is important to call this function from time to time, otherwise resources will keep
                // accumulating and you will eventually reach an out of memory error.
                // Calling this function polls various fences in order to determine what the GPU has
                // already processed, and frees the resources that are no longer needed.
                previous_frame_end.as_mut().unwrap().cleanup_finished();

                // Whenever the window resizes we need to recreate everything dependent on the window size.
                // In this example that includes the swapchain, the framebuffers and the dynamic state viewport.
                if recreate_swapchain {
                    // Get the new dimensions of the window.
                    let dimensions: [u32; 2] = surface.window().inner_size().into();
                    let (new_swapchain, new_images) =
                        match swapchain.recreate_with_dimensions(dimensions) {
                            Ok(r) => r,
                            // This error tends to happen when the user is manually resizing the window.
                            // Simply restarting the loop is the easiest way to fix this issue.
                            Err(SwapchainCreationError::UnsupportedDimensions) => return,
                            Err(e) => panic!("Failed to recreate swapchain: {:?}", e),
                        };

                    swapchain = new_swapchain;
                    // Because framebuffers contains an Arc on the old swapchain, we need to
                    // recreate framebuffers as well.
                    framebuffers = window_size_dependent_setup(
                        &new_images,
                        render_pass.clone(),
                        &mut dynamic_state,
                    );
                    recreate_swapchain = false;
                }

                // Before we can draw on the output, we have to *acquire* an image from the swapchain. If
                // no image is available (which happens if you submit draw commands too quickly), then the
                // function will block.
                // This operation returns the index of the image that we are allowed to draw upon.
                //
                // This function can block if no image is available. The parameter is an optional timeout
                // after which the function call will return an error.
                let (image_num, suboptimal, acquire_future) =
                    match swapchain::acquire_next_image(swapchain.clone(), None) {
                        Ok(r) => r,
                        Err(AcquireError::OutOfDate) => {
                            recreate_swapchain = true;
                            return;
                        }
                        Err(e) => panic!("Failed to acquire next image: {:?}", e),
                    };

                // acquire_next_image can be successful, but suboptimal. This means that the swapchain image
                // will still work, but it may not display correctly. With some drivers this can be when
                // the window resizes, but it may not cause the swapchain to become out of date.
                if suboptimal {
                    recreate_swapchain = true;
                }

                // Specify the color to clear the framebuffer with i.e. blue
                let clear_values = vec![[0.0, 0.0, 1.0, 1.0].into()];

                // In order to draw, we have to build a *command buffer*. The command buffer object holds
                // the list of commands that are going to be executed.
                //
                // Building a command buffer is an expensive operation (usually a few hundred
                // microseconds), but it is known to be a hot path in the driver and is expected to be
                // optimized.
                //
                // Note that we have to pass a queue family when we create the command buffer. The command
                // buffer will only be executable on that given queue family.
                let mut builder = AutoCommandBufferBuilder::primary_one_time_submit(
                    device.clone(),
                    queue.family(),
                )
                .unwrap();

                builder
                    // Before we can draw, we have to *enter a render pass*. There are two methods to do
                    // this: `draw_inline` and `draw_secondary`. The latter is a bit more advanced and is
                    // not covered here.
                    //
                    // The third parameter builds the list of values to clear the attachments with. The API
                    // is similar to the list of attachments when building the framebuffers, except that
                    // only the attachments that use `load: Clear` appear in the list.
                    .begin_render_pass(
                        framebuffers[image_num].clone(),
                        SubpassContents::Inline,
                        clear_values,
                    )
                    .unwrap()
                    // We are now inside the first subpass of the render pass. We add a draw command.
                    //
                    // The last two parameters contain the list of resources to pass to the shaders.
                    // Since we used an `EmptyPipeline` object, the objects have to be `()`.
                    .draw(
                        pipeline.clone(),
                        &dynamic_state,
                        vertex_buffer.clone(),
                        (),
                        (),
                        vec![],
                    )
                    .unwrap()
                    // We leave the render pass by calling `draw_end`. Note that if we had multiple
                    // subpasses we could have called `next_inline` (or `next_secondary`) to jump to the
                    // next subpass.
                    .end_render_pass()
                    .unwrap();

                // Finish building the command buffer by calling `build`.
                let command_buffer = builder.build().unwrap();

                let future = previous_frame_end
                    .take()
                    .unwrap()
                    .join(acquire_future)
                    .then_execute(queue.clone(), command_buffer)
                    .unwrap()
                    // The color output is now expected to contain our triangle. But in order to show it on
                    // the screen, we have to *present* the image by calling `present`.
                    //
                    // This function does not actually present the image immediately. Instead it submits a
                    // present command at the end of the queue. This means that it will only be presented once
                    // the GPU has finished executing the command buffer that draws the triangle.
                    .then_swapchain_present(queue.clone(), swapchain.clone(), image_num)
                    .then_signal_fence_and_flush();

                match future {
                    Ok(future) => {
                        previous_frame_end = Some(future.boxed());
                    }
                    Err(FlushError::OutOfDate) => {
                        recreate_swapchain = true;
                        previous_frame_end = Some(sync::now(device.clone()).boxed());
                    }
                    Err(e) => {
                        println!("Failed to flush future: {:?}", e);
                        previous_frame_end = Some(sync::now(device.clone()).boxed());
                    }
                }
            }
            _ => (),
        }
    });
}

/// This method is called once during initialization, then again whenever the window is resized
fn window_size_dependent_setup(
    images: &[Arc<SwapchainImage<Window>>],
    render_pass: Arc<dyn RenderPassAbstract + Send + Sync>,
    dynamic_state: &mut DynamicState,
) -> Vec<Arc<dyn FramebufferAbstract + Send + Sync>> {
    let dimensions = images[0].dimensions();

    let viewport = Viewport {
        origin: [0.0, 0.0],
        dimensions: [dimensions[0] as f32, dimensions[1] as f32],
        depth_range: 0.0..1.0,
    };
    dynamic_state.viewports = Some(vec![viewport]);

    images
        .iter()
        .map(|image| {
            let view = ImageView::new(image.clone()).unwrap();
            Arc::new(
                Framebuffer::start(render_pass.clone())
                    .add(view)
                    .unwrap()
                    .build()
                    .unwrap(),
            ) as Arc<dyn FramebufferAbstract + Send + Sync>
        })
        .collect::<Vec<_>>()
}