pub mod error;

use std::ffi::{CStr, c_char};
use ash::{Entry, Instance, ext, vk, Device};
use tracing::{debug, error, info, warn};

pub use error::RendererError;

/// The core renderer structure holding the Vulkan instance and debug resources.
pub struct Renderer {
    /// The entry point to the Vulkan library.
    _entry: Entry,
    /// The Vulkan instance handle.
    instance: Instance,
    /// The debug utils instance, if enabled (debug builds only).
    debug_utils: Option<ext::debug_utils::Instance>,
    /// The debug messenger handle, if enabled (debug builds only).
    debug_messenger: vk::DebugUtilsMessengerEXT,
    /// The selected physical device (GPU).
    physical_device: vk::PhysicalDevice,
    /// The logical device handle.
    device: Device,
    /// The handle to the graphics queue.
    graphics_queue: vk::Queue,
    /// The index of the graphics queue family.
    graphics_queue_index: u32,
}

impl Renderer {
    /// Initializes the Vulkan renderer.
    ///
    /// This function loads the Vulkan library, creates an instance, selects a GPU,
    /// and initializes a logical device with a graphics queue.
    ///
    /// `required_extensions` are raw C-strings (pointers) provided by the windowing system.
    pub fn new(required_extensions: &[*const c_char]) -> Result<Self, RendererError> {
        let entry = unsafe { Entry::load() }?;

        // Prepare extensions and layers
        let mut extensions: Vec<*const c_char> = required_extensions.to_vec();
        let mut layers: Vec<*const c_char> = Vec::new();

        // Enable debug extensions and validation layers in debug builds
        #[cfg(debug_assertions)]
        {
            extensions.push(ext::debug_utils::NAME.as_ptr());
            layers.push(c"VK_LAYER_KHRONOS_validation".as_ptr());
        }

        let app_info = vk::ApplicationInfo::default()
            .api_version(vk::API_VERSION_1_3);

        let create_info = vk::InstanceCreateInfo::default()
            .application_info(&app_info)
            .enabled_extension_names(&extensions)
            .enabled_layer_names(&layers);

        // Create the Vulkan instance
        let instance = unsafe { entry.create_instance(&create_info, None)? };

        // Setup debug messenger for validation layer feedback
        #[cfg(debug_assertions)]
        let (debug_utils, debug_messenger) = {
            let debug_info = vk::DebugUtilsMessengerCreateInfoEXT::default()
                .message_severity(
                    vk::DebugUtilsMessageSeverityFlagsEXT::WARNING |
                    vk::DebugUtilsMessageSeverityFlagsEXT::ERROR
                )
                .message_type(
                    vk::DebugUtilsMessageTypeFlagsEXT::GENERAL |
                    vk::DebugUtilsMessageTypeFlagsEXT::VALIDATION |
                    vk::DebugUtilsMessageTypeFlagsEXT::PERFORMANCE
                )
                .pfn_user_callback(Some(vulkan_debug_callback));

            let utils = ext::debug_utils::Instance::new(&entry, &instance);
            let messenger = unsafe { utils.create_debug_utils_messenger(&debug_info, None)? };

            (Some(utils), messenger)
        };

        #[cfg(not(debug_assertions))]
        let (debug_utils, debug_messenger) = (None, vk::DebugUtilsMessengerEXT::null());

        let physical_device = Self::pick_physical_device(&instance)?;

        // Find the graphics queue and create the logical device
        let graphics_queue_index = Self::find_graphics_queue_family(&instance, physical_device)?;
        let (device, graphics_queue) = Self::create_logical_device(&instance, physical_device, graphics_queue_index)?;

        Ok(Self {
            _entry: entry,
            instance,
            debug_utils,
            debug_messenger,
            physical_device,
            device,
            graphics_queue,
            graphics_queue_index,
        })
    }

    /// Selects the best physical device (GPU) available on the system.
    ///
    /// This function filters for devices supporting graphics operations and scores
    /// them based on their type, preferring discrete GPUs.
    fn pick_physical_device(instance: &Instance) -> Result<vk::PhysicalDevice, RendererError> {
        let devices = unsafe { instance.enumerate_physical_devices()? };

        let selected = devices.into_iter()
            .filter(|&device| {
                // Check if the device has a queue family that supports graphics
                let props = unsafe { instance.get_physical_device_queue_family_properties(device) };
                props.iter().any(|p| p.queue_flags.contains(vk::QueueFlags::GRAPHICS))
            })
            .max_by_key(|&device| {
                // Score the device based on its type
                let props = unsafe { instance.get_physical_device_properties(device) };
                match props.device_type {
                    vk::PhysicalDeviceType::DISCRETE_GPU => 1000,
                    vk::PhysicalDeviceType::INTEGRATED_GPU => 100,
                    _ => 1,
                }
            })
            .ok_or(RendererError::NoSuitableGpu)?;

        let props = unsafe { instance.get_physical_device_properties(selected) };
        info!("Selected GPU: {:?}", unsafe { CStr::from_ptr(props.device_name.as_ptr()).to_string_lossy() });

        Ok(selected)
    }

    /// Finds the index of the first queue family that supports graphics operations.
    fn find_graphics_queue_family(
        instance: &Instance,
        physical_device: vk::PhysicalDevice,
    ) -> Result<u32, RendererError> {
        let props = unsafe { instance.get_physical_device_queue_family_properties(physical_device) };

        props.iter().enumerate()
            .find(|(_, p)| p.queue_flags.contains(vk::QueueFlags::GRAPHICS))
            .map(|(i, _)| i as u32)
            .ok_or(RendererError::NoSuitableGpu)
    }

    /// Creates a logical device and retrieves the handle to its graphics queue.
    fn create_logical_device(
        instance: &Instance,
        physical_device: vk::PhysicalDevice,
        queue_index: u32,
    ) -> Result<(Device, vk::Queue), RendererError> {
        // Request a single queue from the graphics family
        let queue_priorities = [1.0];
        let queue_info = vk::DeviceQueueCreateInfo::default()
            .queue_family_index(queue_index)
            .queue_priorities(&queue_priorities);

        // Enable modern Vulkan 1.3 features
        let mut features_13 = vk::PhysicalDeviceVulkan13Features::default()
            .dynamic_rendering(true) // Removes the need for RenderPasses/Framebuffers
            .synchronization2(true);  // Cleaner memory barriers and synchronization

        // We need the swapchain extension to present images to the window
        let device_extensions = [ash::khr::swapchain::NAME.as_ptr()];

        let create_info = vk::DeviceCreateInfo::default()
            .queue_create_infos(std::slice::from_ref(&queue_info))
            .enabled_extension_names(&device_extensions)
            .push_next(&mut features_13);

        let device = unsafe { instance.create_device(physical_device, &create_info, None)? };
        let graphics_queue = unsafe { device.get_device_queue(queue_index, 0) };
        
        Ok((device, graphics_queue))
    }
}

/// Ensures all Vulkan resources are destroyed in the correct order.
impl Drop for Renderer {
    fn drop(&mut self) {
        unsafe {
            self.device.destroy_device(None);

            if let Some(utils) = &self.debug_utils {
                utils.destroy_debug_utils_messenger(self.debug_messenger, None);
            }

            self.instance.destroy_instance(None);
        }   
    }
}

/// The callback function invoked by Vulkan's validation layers.
///
/// This function translates Vulkan debug messages into `tracing` events.
unsafe extern "system" fn vulkan_debug_callback(
    message_severity: vk::DebugUtilsMessageSeverityFlagsEXT,
    _message_type: vk::DebugUtilsMessageTypeFlagsEXT,
    p_callback_data: *const vk::DebugUtilsMessengerCallbackDataEXT<'_>,
    _user_data: *mut std::ffi::c_void,
) -> vk::Bool32 {
    // Safety: p_callback_data is guaranteed to be valid by the Vulkan spec
    let callback_data = unsafe { *p_callback_data };
    
    // Convert raw C string to Rust string for logging
    let message = if callback_data.p_message.is_null() {
        "".into()
    } else {
        unsafe { CStr::from_ptr(callback_data.p_message).to_string_lossy() }
    };

    // Route severity to matching tracing macro
    match message_severity {
        vk::DebugUtilsMessageSeverityFlagsEXT::VERBOSE => debug!("{message}"),
        vk::DebugUtilsMessageSeverityFlagsEXT::INFO => info!("{message}"),
        vk::DebugUtilsMessageSeverityFlagsEXT::WARNING => warn!("{message}"),
        vk::DebugUtilsMessageSeverityFlagsEXT::ERROR => error!("{message}"),
        _ => info!("{message}"),
    }

    // TRUE aborts the Vulkan call that triggered the warning
    vk::FALSE
}