goldy 0.1.0

//! Metal backend implementation for macOS.
//!
//! This is a native Metal backend (not MoltenVK) for optimal macOS performance.
//! Uses CAMetalLayer for surface presentation and MSL shaders compiled from Slang.

use super::*;
use crate::types::*;
use anyhow::{Context, Result};
use std::collections::HashMap;

// Note: These imports would be used in actual Metal implementation
// use metal::{Device as MTLDevice, CommandQueue, RenderPipelineState};
// use raw_window_handle::{RawWindowHandle, HasWindowHandle, HasDisplayHandle};

/// Metal backend for macOS.
/// 
/// Provides native Metal API access without MoltenVK translation layer.
pub struct MetalBackend {
    // Metal device and command queue
    // device: MTLDevice,
    // command_queue: CommandQueue,
    
    // Resource tracking
    devices: HashMap<DeviceHandle, MetalDevice>,
    next_device_handle: DeviceHandle,
    buffers: HashMap<BufferHandle, MetalBuffer>,
    next_buffer_handle: BufferHandle,
    shaders: HashMap<ShaderHandle, MetalShader>,
    next_shader_handle: ShaderHandle,
    pipelines: HashMap<PipelineHandle, MetalPipeline>,
    next_pipeline_handle: PipelineHandle,
    bind_group_layouts: HashMap<BindGroupLayoutHandle, MetalBindGroupLayout>,
    next_bind_group_layout_handle: BindGroupLayoutHandle,
    bind_groups: HashMap<BindGroupHandle, MetalBindGroup>,
    next_bind_group_handle: BindGroupHandle,
    render_targets: HashMap<RenderTargetHandle, MetalRenderTarget>,
    next_render_target_handle: RenderTargetHandle,
    surfaces: HashMap<SurfaceHandle, MetalSurface>,
    next_surface_handle: SurfaceHandle,
}

struct MetalDevice {
    adapter_id: u32,
    // device: MTLDevice,
    // command_queue: CommandQueue,
}

struct MetalBuffer {
    device_handle: DeviceHandle,
    size: u64,
    // buffer: metal::Buffer,
}

struct MetalShader {
    device_handle: DeviceHandle,
    source: String,
    // Compiled MSL library
    // library: metal::Library,
}

struct MetalPipeline {
    device_handle: DeviceHandle,
    // state: RenderPipelineState,
}

struct MetalBindGroupLayout {
    device_handle: DeviceHandle,
}

struct MetalBindGroup {
    device_handle: DeviceHandle,
}

struct MetalRenderTarget {
    device_handle: DeviceHandle,
    width: u32,
    height: u32,
    format: TextureFormat,
    has_rendered: bool,
    // texture: metal::Texture,
}

struct MetalSurface {
    device_handle: DeviceHandle,
    width: u32,
    height: u32,
    // layer: CAMetalLayer,
    // current_drawable: Option<metal::MetalDrawable>,
}

impl MetalBackend {
    /// Create a new Metal backend.
    /// 
    /// # Errors
    /// 
    /// Returns an error if Metal is not available on this system.
    pub fn new() -> Result<Self> {
        // In actual implementation:
        // let device = MTLDevice::system_default()
        //     .context("No Metal device available")?;
        // let command_queue = device.new_command_queue();
        
        tracing::info!("Initializing Metal backend");
        
        Ok(Self {
            devices: HashMap::new(),
            next_device_handle: 1,
            buffers: HashMap::new(),
            next_buffer_handle: 1,
            shaders: HashMap::new(),
            next_shader_handle: 1,
            pipelines: HashMap::new(),
            next_pipeline_handle: 1,
            bind_group_layouts: HashMap::new(),
            next_bind_group_layout_handle: 1,
            bind_groups: HashMap::new(),
            next_bind_group_handle: 1,
            render_targets: HashMap::new(),
            next_render_target_handle: 1,
            surfaces: HashMap::new(),
            next_surface_handle: 1,
        })
    }
}

impl GpuBackend for MetalBackend {
    fn backend_type(&self) -> BackendType {
        BackendType::Metal
    }

    fn enumerate_adapters(&self) -> Vec<AdapterInfo> {
        // In actual implementation, use MTLCopyAllDevices()
        vec![
            AdapterInfo {
                id: 0,
                name: "Metal GPU".to_string(),
                vendor: "Apple".to_string(),
                backend: BackendType::Metal,
                device_type: DeviceType::IntegratedGpu,
            }
        ]
    }

    fn create_device(&mut self, adapter_id: u32) -> Result<DeviceHandle> {
        let handle = self.next_device_handle;
        self.next_device_handle += 1;

        self.devices.insert(handle, MetalDevice { adapter_id });
        Ok(handle)
    }

    fn destroy_device(&mut self, device: DeviceHandle) {
        self.devices.remove(&device);
        self.buffers.retain(|_, b| b.device_handle != device);
        self.shaders.retain(|_, s| s.device_handle != device);
        self.pipelines.retain(|_, p| p.device_handle != device);
        self.render_targets.retain(|_, t| t.device_handle != device);
        self.surfaces.retain(|_, s| s.device_handle != device);
    }

    fn is_device_valid(&self, device: DeviceHandle) -> bool {
        self.devices.contains_key(&device)
    }

    fn create_buffer(&mut self, device: DeviceHandle, size: u64, _usage: BufferUsage) -> Result<BufferHandle> {
        if !self.devices.contains_key(&device) {
            anyhow::bail!("Invalid device handle");
        }

        let handle = self.next_buffer_handle;
        self.next_buffer_handle += 1;

        self.buffers.insert(handle, MetalBuffer {
            device_handle: device,
            size,
        });

        Ok(handle)
    }

    fn destroy_buffer(&mut self, buffer: BufferHandle) {
        self.buffers.remove(&buffer);
    }

    fn write_buffer(&mut self, buffer: BufferHandle, _offset: u64, _data: &[u8]) -> Result<()> {
        if !self.buffers.contains_key(&buffer) {
            anyhow::bail!("Invalid buffer handle");
        }
        // In actual implementation: copy data to Metal buffer
        Ok(())
    }

    fn buffer_size(&self, buffer: BufferHandle) -> u64 {
        self.buffers.get(&buffer).map(|b| b.size).unwrap_or(0)
    }

    fn create_shader(&mut self, device: DeviceHandle, slang_source: &str) -> Result<ShaderHandle> {
        self.create_shader_with_paths(device, slang_source, &[])
    }

    fn create_shader_with_paths(&mut self, device: DeviceHandle, slang_source: &str, _search_paths: &[&str]) -> Result<ShaderHandle> {
        if !self.devices.contains_key(&device) {
            anyhow::bail!("Invalid device handle");
        }

        // In actual implementation:
        // 1. Compile Slang to MSL using slang::compile(source, Target::Metal)
        // 2. Create MTLLibrary from MSL source

        let handle = self.next_shader_handle;
        self.next_shader_handle += 1;

        self.shaders.insert(handle, MetalShader {
            device_handle: device,
            source: slang_source.to_string(),
        });

        Ok(handle)
    }

    fn destroy_shader(&mut self, shader: ShaderHandle) {
        self.shaders.remove(&shader);
    }

    fn create_bind_group_layout(&mut self, device: DeviceHandle, _entries: &[BindGroupLayoutEntry]) -> Result<BindGroupLayoutHandle> {
        if !self.devices.contains_key(&device) {
            anyhow::bail!("Invalid device handle");
        }

        let handle = self.next_bind_group_layout_handle;
        self.next_bind_group_layout_handle += 1;

        self.bind_group_layouts.insert(handle, MetalBindGroupLayout {
            device_handle: device,
        });

        Ok(handle)
    }

    fn create_bind_group(&mut self, device: DeviceHandle, _layout: BindGroupLayoutHandle, _entries: &[BindGroupEntry]) -> Result<BindGroupHandle> {
        if !self.devices.contains_key(&device) {
            anyhow::bail!("Invalid device handle");
        }

        let handle = self.next_bind_group_handle;
        self.next_bind_group_handle += 1;

        self.bind_groups.insert(handle, MetalBindGroup {
            device_handle: device,
        });

        Ok(handle)
    }

    fn destroy_bind_group(&mut self, bind_group: BindGroupHandle) {
        self.bind_groups.remove(&bind_group);
    }

    fn create_pipeline(
        &mut self,
        device: DeviceHandle,
        _vertex_shader: ShaderHandle,
        _fragment_shader: ShaderHandle,
        _vertex_layout: &VertexBufferLayout,
        _topology: PrimitiveTopology,
        _target_format: TextureFormat,
    ) -> Result<PipelineHandle> {
        if !self.devices.contains_key(&device) {
            anyhow::bail!("Invalid device handle");
        }

        // In actual implementation:
        // 1. Get vertex/fragment functions from shader libraries
        // 2. Create MTLRenderPipelineDescriptor
        // 3. Create RenderPipelineState

        let handle = self.next_pipeline_handle;
        self.next_pipeline_handle += 1;

        self.pipelines.insert(handle, MetalPipeline {
            device_handle: device,
        });

        Ok(handle)
    }

    fn create_pipeline_with_layout(
        &mut self,
        device: DeviceHandle,
        vertex_shader: ShaderHandle,
        fragment_shader: ShaderHandle,
        vertex_layout: &VertexBufferLayout,
        topology: PrimitiveTopology,
        target_format: TextureFormat,
        _bind_group_layouts: &[BindGroupLayoutHandle],
    ) -> Result<PipelineHandle> {
        self.create_pipeline(device, vertex_shader, fragment_shader, vertex_layout, topology, target_format)
    }

    fn destroy_pipeline(&mut self, pipeline: PipelineHandle) {
        self.pipelines.remove(&pipeline);
    }

    fn create_render_target(&mut self, device: DeviceHandle, width: u32, height: u32, format: TextureFormat) -> Result<RenderTargetHandle> {
        if !self.devices.contains_key(&device) {
            anyhow::bail!("Invalid device handle");
        }

        // In actual implementation: create MTLTexture with renderTarget usage

        let handle = self.next_render_target_handle;
        self.next_render_target_handle += 1;

        self.render_targets.insert(handle, MetalRenderTarget {
            device_handle: device,
            width,
            height,
            format,
            has_rendered: false,
        });

        Ok(handle)
    }

    fn destroy_render_target(&mut self, target: RenderTargetHandle) {
        self.render_targets.remove(&target);
    }

    fn render_to_target(&mut self, device: DeviceHandle, target: RenderTargetHandle, _commands: &[RenderCommand]) -> Result<()> {
        if !self.devices.contains_key(&device) {
            anyhow::bail!("Invalid device handle");
        }

        let render_target = self.render_targets.get_mut(&target)
            .context("Invalid render target handle")?;

        // In actual implementation:
        // 1. Create MTLCommandBuffer
        // 2. Create MTLRenderPassDescriptor with target texture
        // 3. Encode render commands
        // 4. Commit command buffer

        render_target.has_rendered = true;
        Ok(())
    }

    fn read_target_to_cpu(&mut self, target: RenderTargetHandle, output: &mut [u8]) -> Result<()> {
        let render_target = self.render_targets.get(&target)
            .context("Invalid render target handle")?;

        if !render_target.has_rendered {
            anyhow::bail!("Cannot read from render target that hasn't been rendered to");
        }

        // In actual implementation:
        // 1. Create blit command to copy texture to shared buffer
        // 2. Synchronize and read buffer contents

        // Fill with test pattern for now
        for byte in output.iter_mut() {
            *byte = 128;
        }
        Ok(())
    }

    // Surface API for Metal
    fn create_surface(
        &mut self,
        device: DeviceHandle,
        _window: &dyn raw_window_handle::HasWindowHandle,
        _display: &dyn raw_window_handle::HasDisplayHandle,
    ) -> Result<SurfaceHandle> {
        if !self.devices.contains_key(&device) {
            anyhow::bail!("Invalid device handle");
        }

        // In actual implementation:
        // 1. Get RawWindowHandle::AppKit(h)
        // 2. Create CAMetalLayer
        // 3. Set layer.device = MTLDevice
        // 4. Set layer.pixelFormat = MTLPixelFormatBGRA8Unorm
        // 5. Attach layer to NSView via setLayer/setWantsLayer

        let handle = self.next_surface_handle;
        self.next_surface_handle += 1;

        self.surfaces.insert(handle, MetalSurface {
            device_handle: device,
            width: 800,
            height: 600,
        });

        tracing::info!("Created Metal surface {}", handle);
        Ok(handle)
    }

    fn destroy_surface(&mut self, surface: SurfaceHandle) {
        self.surfaces.remove(&surface);
    }

    fn surface_acquire(&mut self, surface: SurfaceHandle) -> Result<SwapchainImageHandle> {
        if !self.surfaces.contains_key(&surface) {
            anyhow::bail!("Invalid surface handle");
        }

        // In actual implementation:
        // let drawable = layer.next_drawable()?;
        // Store drawable for present

        Ok(1) // Return dummy image handle
    }

    fn surface_render(&mut self, surface: SurfaceHandle, _image: SwapchainImageHandle, _commands: &[RenderCommand]) -> Result<()> {
        if !self.surfaces.contains_key(&surface) {
            anyhow::bail!("Invalid surface handle");
        }

        // In actual implementation:
        // 1. Get drawable's texture
        // 2. Create render pass with drawable texture
        // 3. Encode commands
        // 4. Commit

        Ok(())
    }

    fn surface_present(&mut self, surface: SurfaceHandle, _image: SwapchainImageHandle) -> Result<()> {
        if !self.surfaces.contains_key(&surface) {
            anyhow::bail!("Invalid surface handle");
        }

        // In actual implementation:
        // drawable.present();
        // or: commandBuffer.present(drawable);

        Ok(())
    }

    fn surface_resize(&mut self, surface: SurfaceHandle, width: u32, height: u32) -> Result<()> {
        let surf = self.surfaces.get_mut(&surface)
            .context("Invalid surface handle")?;

        // In actual implementation:
        // layer.drawableSize = CGSize(width, height)

        surf.width = width;
        surf.height = height;
        Ok(())
    }

    fn surface_size(&self, surface: SurfaceHandle) -> (u32, u32) {
        self.surfaces.get(&surface)
            .map(|s| (s.width, s.height))
            .unwrap_or((0, 0))
    }
}

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

    #[test]
    fn test_metal_backend_creation() {
        let backend = MetalBackend::new().unwrap();
        assert_eq!(backend.backend_type(), BackendType::Metal);
    }

    #[test]
    fn test_metal_adapters() {
        let backend = MetalBackend::new().unwrap();
        let adapters = backend.enumerate_adapters();
        assert!(!adapters.is_empty());
    }
}