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]) -> vk::ShaderModule {
    let mut cursor = Cursor::new(bytes);

    let code = ash::util::read_spv(&mut cursor)
        .expect("Failed to read SPIR-V binary; check if the file is valid");

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

    unsafe {
        device
            .create_shader_module(&create_info, None)
            .expect("Failed to create Vulkan shader 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) -> vk::PipelineLayout {
    // A single push constant range is defined for the Model-View-Projection matrix.
    // This allows the matrix to be updated for every draw call with high efficiency.
    let push_constant_range = vk::PushConstantRange::default()
        .stage_flags(vk::ShaderStageFlags::VERTEX)
        .offset(0)
        .size(std::mem::size_of::<glam::Mat4>() as u32);

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

    unsafe {
        device
            .create_pipeline_layout(&layout_create_info, None)
            .expect("Failed to create pipeline 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,
) -> vk::Pipeline {
    // 1. Load and compile shader modules
    // Using include_bytes! embeds the shaders directly into the engine binary.
    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);

    let entry_point = std::ffi::CString::new("main").unwrap();

    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 Vertex Input
    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);

    // 3. Configure Input Assembly (Drawing mode)
    let input_assembly = vk::PipelineInputAssemblyStateCreateInfo::default()
        .topology(vk::PrimitiveTopology::TRIANGLE_LIST)
        .primitive_restart_enable(false);

    // 4. Viewport and Scissor (Static declarations, dynamic values set at runtime)
    let viewport_state = vk::PipelineViewportStateCreateInfo::default()
        .viewport_count(1)
        .scissor_count(1);

    // 5. Configure Rasterizer (Triangles to Pixels)
    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) // Back-face culling for performance
        .front_face(vk::FrontFace::COUNTER_CLOCKWISE)
        .depth_bias_enable(false);

    // 6. Configure Multisampling (Anti-aliasing)
    let multisampling = vk::PipelineMultisampleStateCreateInfo::default()
        .sample_shading_enable(false)
        .rasterization_samples(vk::SampleCountFlags::TYPE_1);

    // 7. Configure Color Blending
    let color_blend_attachment = vk::PipelineColorBlendAttachmentState::default()
        .color_write_mask(vk::ColorComponentFlags::RGBA)
        .blend_enable(false); // Transparency is not required for the initial implementation

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

    // 8. Define Dynamic States
    // This allows the window to be resized without recreating the entire pipeline.
    let dynamic_states = [vk::DynamicState::VIEWPORT, vk::DynamicState::SCISSOR];
    let dynamic_state_info =
        vk::PipelineDynamicStateCreateInfo::default().dynamic_states(&dynamic_states);

    // 9. Configure Dynamic Rendering (Vulkan 1.3)
    let color_formats = [color_format];
    let mut rendering_info =
        vk::PipelineRenderingCreateInfo::default().color_attachment_formats(&color_formats);

    // 10. 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);

    let pipeline = unsafe {
        device
            .create_graphics_pipelines(vk::PipelineCache::null(), &[pipeline_info], None)
            .expect("Failed to create graphics pipeline")[0]
    };

    // Cleanup temporary shader modules (they are baked into the pipeline now)
    unsafe {
        device.destroy_shader_module(vert_module, None);
        device.destroy_shader_module(frag_module, None);
    }

    pipeline
}