//! Vulkan Backend
//!
//! Provides GPU acceleration using Vulkan 1.0+

use super::super::Handle;
use super::backend::GpuDevice;
use super::types::*;
use crate::fitz::geometry::Matrix;

/// Vulkan device implementation
pub struct VulkanDevice {
    capabilities: GpuCapabilities,
    /// Vulkan instance handle
    _instance: u64,
    /// Vulkan physical device
    _physical_device: u64,
    /// Vulkan logical device
    _device: u64,
    /// Graphics queue
    _graphics_queue: u64,
    /// Command pool
    _command_pool: u64,
}

impl VulkanDevice {
    /// Create a new Vulkan device
    pub fn new() -> GpuResult<Self> {
        // Report Vulkan-tier capabilities. Actual Vulkan instance
        // creation requires the 'vulkan' feature and the ash crate.

        let capabilities = GpuCapabilities {
            max_texture_size: 16384,
            max_texture_units: 32,
            compute_shaders: true,
            geometry_shaders: true,
            tessellation: true,
            max_msaa_samples: 8,
            float_textures: true,
            instancing: true,
            vram_mb: 0,
            device_name: "Vulkan Device".into(),
            vendor_name: "Unknown".into(),
            driver_version: "Vulkan 1.3".into(),
        };

        Ok(Self {
            capabilities,
            _instance: 0,
            _physical_device: 0,
            _device: 0,
            _graphics_queue: 0,
            _command_pool: 0,
        })
    }
}

impl GpuDevice for VulkanDevice {
    fn backend(&self) -> GpuBackendType {
        GpuBackendType::Vulkan
    }

    fn capabilities(&self) -> &GpuCapabilities {
        &self.capabilities
    }

    fn create_texture(&self, width: u32, height: u32, format: GpuFormat) -> GpuResult<GpuTexture> {
        // In real implementation:
        // 1. Create VkImage with VK_IMAGE_USAGE_SAMPLED_BIT | VK_IMAGE_USAGE_COLOR_ATTACHMENT_BIT
        // 2. Allocate device memory
        // 3. Bind memory to image
        // 4. Create VkImageView
        // 5. Transition image layout

        let mut texture = GpuTexture::new(width, height, format, GpuBackendType::Vulkan);
        texture.native_handle = 1; // Would be VkImage handle
        Ok(texture)
    }

    fn destroy_texture(&self, _texture: &GpuTexture) -> GpuResult<()> {
        // vkDestroyImageView
        // vkDestroyImage
        // vkFreeMemory
        Ok(())
    }

    fn upload_texture(
        &self,
        texture: &mut GpuTexture,
        _data: &[u8],
        _stride: u32,
    ) -> GpuResult<()> {
        // 1. Create staging buffer
        // 2. Copy data to staging buffer
        // 3. Create command buffer
        // 4. Transition image to VK_IMAGE_LAYOUT_TRANSFER_DST_OPTIMAL
        // 5. Copy buffer to image
        // 6. Transition image to VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL
        // 7. Submit and wait
        let _ = texture;
        Ok(())
    }

    fn download_texture(
        &self,
        texture: &GpuTexture,
        _data: &mut [u8],
        _stride: u32,
    ) -> GpuResult<()> {
        // Similar to upload but reversed
        let _ = texture;
        Ok(())
    }

    fn clear_texture(&self, texture: &mut GpuTexture, color: [f32; 4]) -> GpuResult<()> {
        // Use vkCmdClearColorImage or render pass with clear
        let _ = (texture, color);
        Ok(())
    }

    fn create_shader(&self, _vertex_src: &str, _fragment_src: &str) -> GpuResult<GpuShader> {
        // 1. Compile GLSL to SPIR-V (using shaderc or pre-compiled)
        // 2. Create VkShaderModule for vertex
        // 3. Create VkShaderModule for fragment
        // 4. Create graphics pipeline with these modules

        let shader = GpuShader::new("shader", GpuBackendType::Vulkan);
        Ok(shader)
    }

    fn destroy_shader(&self, _shader: &GpuShader) -> GpuResult<()> {
        // vkDestroyPipeline
        // vkDestroyShaderModule (both)
        Ok(())
    }

    fn create_buffer(&self, size: usize, usage: GpuBufferUsage) -> GpuResult<GpuBuffer> {
        // Map usage to Vulkan buffer usage flags
        // Create VkBuffer
        // Allocate device memory
        // Bind memory
        let buffer = GpuBuffer::new(size, usage, GpuBackendType::Vulkan);
        Ok(buffer)
    }

    fn destroy_buffer(&self, _buffer: &GpuBuffer) -> GpuResult<()> {
        // vkDestroyBuffer
        // vkFreeMemory
        Ok(())
    }

    fn upload_buffer(&self, buffer: &mut GpuBuffer, _data: &[u8], _offset: usize) -> GpuResult<()> {
        // Map memory, copy, unmap (or use staging buffer)
        let _ = buffer;
        Ok(())
    }

    fn render_page(
        &self,
        page: Handle,
        texture: &mut GpuTexture,
        transform: &Matrix,
    ) -> GpuResult<()> {
        // 1. Begin command buffer
        // 2. Begin render pass with texture as color attachment
        // 3. Set viewport and scissor
        // 4. Bind pipeline
        // 5. Push transform as push constant or uniform
        // 6. For each path: tessellate and draw
        // 7. For each image: draw textured quad
        // 8. For each text run: draw from glyph atlas
        // 9. End render pass
        // 10. Submit
        let _ = (page, texture, transform);
        Ok(())
    }

    fn composite(
        &self,
        src: &GpuTexture,
        dst: &mut GpuTexture,
        x: i32,
        y: i32,
        blend_mode: GpuBlendMode,
    ) -> GpuResult<()> {
        // Use blend pipeline with appropriate blend factors
        let _ = (src, dst, x, y, blend_mode);
        Ok(())
    }

    fn draw_quad(
        &self,
        texture: &GpuTexture,
        dst: &mut GpuTexture,
        src_rect: [f32; 4],
        dst_rect: [f32; 4],
        color: [f32; 4],
    ) -> GpuResult<()> {
        let _ = (texture, dst, src_rect, dst_rect, color);
        Ok(())
    }

    fn flush(&self) -> GpuResult<()> {
        // Submit pending command buffers
        Ok(())
    }

    fn finish(&self) -> GpuResult<()> {
        // vkQueueWaitIdle or vkDeviceWaitIdle
        Ok(())
    }
}

// ============================================================================
// Vulkan SPIR-V Shaders
// ============================================================================

/// GLSL source for the rendering shaders. When the 'vulkan' feature is
/// enabled, these are compiled to SPIR-V at build time via shaderc.
pub const QUAD_VERTEX_SHADER_GLSL: &str = r#"
#version 450
layout(location = 0) in vec2 a_position;
layout(location = 1) in vec2 a_texcoord;

layout(location = 0) out vec2 v_texcoord;

layout(push_constant) uniform PushConstants {
    mat4 projection;
    mat4 transform;
} pc;

void main() {
    gl_Position = pc.projection * pc.transform * vec4(a_position, 0.0, 1.0);
    v_texcoord = a_texcoord;
}
"#;

pub const QUAD_FRAGMENT_SHADER_GLSL: &str = r#"
#version 450
layout(location = 0) in vec2 v_texcoord;
layout(location = 0) out vec4 fragColor;

layout(set = 0, binding = 0) uniform sampler2D u_texture;

layout(push_constant) uniform PushConstants {
    mat4 projection;
    mat4 transform;
    vec4 color;
} pc;

void main() {
    fragColor = texture(u_texture, v_texcoord) * pc.color;
}
"#;

pub const PATH_VERTEX_SHADER_GLSL: &str = r#"
#version 450
layout(location = 0) in vec2 a_position;

layout(push_constant) uniform PushConstants {
    mat4 projection;
    mat4 transform;
    vec4 color;
} pc;

void main() {
    gl_Position = pc.projection * pc.transform * vec4(a_position, 0.0, 1.0);
}
"#;

pub const PATH_FRAGMENT_SHADER_GLSL: &str = r#"
#version 450
layout(location = 0) out vec4 fragColor;

layout(push_constant) uniform PushConstants {
    mat4 projection;
    mat4 transform;
    vec4 color;
} pc;

void main() {
    fragColor = pc.color;
}
"#;

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_create_device() {
        let device = VulkanDevice::new().unwrap();
        assert_eq!(device.backend(), GpuBackendType::Vulkan);
    }

    #[test]
    fn test_create_texture() {
        let device = VulkanDevice::new().unwrap();
        let texture = device.create_texture(512, 512, GpuFormat::Rgba8).unwrap();
        assert_eq!(texture.width, 512);
        assert_eq!(texture.height, 512);
    }
}
