// SPDX-License-Identifier: AGPL-3.0-only

//! Graphics pipeline creation and shader management.

use crate::error::RendererError;
use crate::mesh::Vertex;
use ash::{Device, vk};
use std::io::Cursor;

/// Helper to load SPIR-V bytes and create a Vulkan Shader Module.
///
/// Vulkan expects shader code to be 32-bit aligned; `ash::util::read_spv` is used to correctly interpret the raw bytes as a slice of `u32`.
pub fn create_shader_module(
    device: &Device,
    bytes: &[u8],
) -> Result<vk::ShaderModule, RendererError> {
    let mut cursor = Cursor::new(bytes);

    let code = ash::util::read_spv(&mut cursor)?;

    let create_info = vk::ShaderModuleCreateInfo::default().code(&code);

    let module = unsafe { device.create_shader_module(&create_info, None)? };
    Ok(module)
}

/// Defines the 'interface' of the pipeline (what data we can pass to the shaders).
///
/// This layout defines any push constants or descriptor sets (textures/UBOs) accessed by the shaders during execution.
pub fn create_pipeline_layout(device: &Device) -> Result<vk::PipelineLayout, RendererError> {
    // A single push constant range is defined for the MVP matrix, allowing it to be updated for every draw call with high efficiency.
    #[expect(clippy::expect_used)]
    let push_constant_range = vk::PushConstantRange::default()
        .stage_flags(vk::ShaderStageFlags::VERTEX)
        .offset(0)
        .size(
            u32::try_from(std::mem::size_of::<glam::Mat4>()).expect("Mat4 size exceeds u32 range"),
        );

    let layout_create_info = vk::PipelineLayoutCreateInfo::default()
        .push_constant_ranges(std::slice::from_ref(&push_constant_range));

    let layout = unsafe { device.create_pipeline_layout(&layout_create_info, None)? };
    Ok(layout)
}

/// Creates a Graphics Pipeline for voxel rendering using Vulkan 1.3 Dynamic Rendering.
///
/// The pipeline encapsulates the entire state of the GPU for a specific draw operation, including shader stages, vertex input layout, rasterization settings, and blending.
pub fn create_graphics_pipeline(
    device: &Device,
    layout: vk::PipelineLayout,
    color_format: vk::Format,
) -> Result<vk::Pipeline, RendererError> {
    // 1. Load and compile shader modules
    let (vert_module, frag_module) = load_shader_modules(device)?;
    let entry_point = std::ffi::CString::new("main").map_err(|_| RendererError::InvalidString)?;

    let shader_stages = [
        vk::PipelineShaderStageCreateInfo::default()
            .stage(vk::ShaderStageFlags::VERTEX)
            .module(vert_module)
            .name(&entry_point),
        vk::PipelineShaderStageCreateInfo::default()
            .stage(vk::ShaderStageFlags::FRAGMENT)
            .module(frag_module)
            .name(&entry_point),
    ];

    // 2. Configure Fixed-Function States
    let binding_descriptions = [Vertex::get_binding_description()];
    let attribute_descriptions = Vertex::get_attribute_descriptions();
    let vertex_input_info = vk::PipelineVertexInputStateCreateInfo::default()
        .vertex_binding_descriptions(&binding_descriptions)
        .vertex_attribute_descriptions(&attribute_descriptions);

    let input_assembly = vk::PipelineInputAssemblyStateCreateInfo::default()
        .topology(vk::PrimitiveTopology::TRIANGLE_LIST)
        .primitive_restart_enable(false);

    let viewport_state = vk::PipelineViewportStateCreateInfo::default()
        .viewport_count(1)
        .scissor_count(1);

    let rasterizer = vk::PipelineRasterizationStateCreateInfo::default()
        .depth_clamp_enable(false)
        .rasterizer_discard_enable(false)
        .polygon_mode(vk::PolygonMode::FILL)
        .line_width(1.0)
        .cull_mode(vk::CullModeFlags::BACK)
        .front_face(vk::FrontFace::COUNTER_CLOCKWISE)
        .depth_bias_enable(false);

    let multisampling = vk::PipelineMultisampleStateCreateInfo::default()
        .sample_shading_enable(false)
        .rasterization_samples(vk::SampleCountFlags::TYPE_1);

    let color_blend_attachment = vk::PipelineColorBlendAttachmentState::default()
        .color_write_mask(vk::ColorComponentFlags::RGBA)
        .blend_enable(false);

    let color_blending = vk::PipelineColorBlendStateCreateInfo::default()
        .logic_op_enable(false)
        .attachments(std::slice::from_ref(&color_blend_attachment));

    let dynamic_states = [vk::DynamicState::VIEWPORT, vk::DynamicState::SCISSOR];
    let dynamic_state_info =
        vk::PipelineDynamicStateCreateInfo::default().dynamic_states(&dynamic_states);

    let color_formats = [color_format];
    let mut rendering_info = vk::PipelineRenderingCreateInfo::default()
        .color_attachment_formats(&color_formats)
        .depth_attachment_format(vk::Format::D32_SFLOAT);

    let depth_stencil_state = &vk::PipelineDepthStencilStateCreateInfo::default()
        .depth_test_enable(true)
        .depth_write_enable(true)
        .depth_compare_op(vk::CompareOp::LESS)
        .depth_bounds_test_enable(false)
        .stencil_test_enable(false);

    // 3. Finalize Pipeline Creation
    let pipeline_info = vk::GraphicsPipelineCreateInfo::default()
        .push_next(&mut rendering_info)
        .stages(&shader_stages)
        .vertex_input_state(&vertex_input_info)
        .input_assembly_state(&input_assembly)
        .viewport_state(&viewport_state)
        .rasterization_state(&rasterizer)
        .multisample_state(&multisampling)
        .color_blend_state(&color_blending)
        .dynamic_state(&dynamic_state_info)
        .layout(layout)
        .depth_stencil_state(depth_stencil_state);

    let result = unsafe {
        device.create_graphics_pipelines(vk::PipelineCache::null(), &[pipeline_info], None)
    };

    unsafe {
        device.destroy_shader_module(vert_module, None);
        device.destroy_shader_module(frag_module, None);
    }

    let pipeline = result.map_err(|(_, e)| e)?[0];
    Ok(pipeline)
}

/// Loads the vertex and fragment shader modules from embedded bytes.
fn load_shader_modules(
    device: &Device,
) -> Result<(vk::ShaderModule, vk::ShaderModule), RendererError> {
    let vert_bytes = include_bytes!("../../../assets/shaders/cube.vert.spv");
    let frag_bytes = include_bytes!("../../../assets/shaders/cube.frag.spv");

    let vert_module = create_shader_module(device, vert_bytes)?;
    let frag_module = create_shader_module(device, frag_bytes)?;

    Ok((vert_module, frag_module))
}