#![deny(clippy::all, clippy::pedantic)]

use std::collections::BTreeMap;
use std::time::{Duration, Instant};

use glfw::window::KeyState;
use glfw::{Window, WindowBuilder};

use crate::camera::Camera;
use crate::object::{Id as ObjectId, Object};
use crate::vector::Vec2;

mod matrix;
mod opengl;
mod projection;
mod renderer;
mod transform;

pub mod camera;
pub mod color;
pub mod object;
pub mod vector;
pub mod vertex;

pub use glfw::window::Key;
pub use glfw::WindowSize;

#[derive(Debug)]
pub struct Engine
{
    /// Objects have to be dropped before window. Otherwise, UB.
    objects: BTreeMap<ObjectId, Object>,
    window: Window,
    camera: Camera,
    delta_time: Duration,
}

impl Engine
{
    /// Creates and initializes a new engine.
    ///
    /// # Errors
    /// Will return `Err` if window creation or window configuration fails.
    pub fn new(window_size: &WindowSize, window_title: &str) -> Result<Self, Error>
    {
        let window_builder = WindowBuilder::new();

        #[cfg(feature = "debug")]
        let window_builder =
            window_builder.hint(glfw::window::Hint::OpenGLDebugContext, 1);

        let window = window_builder
            .create(window_size, window_title)
            .map_err(Error::CreateWindowFailed)?;

        window
            .make_context_current()
            .map_err(Error::ConfigureWindowFailed)?;

        window.set_framebuffer_size_callback(move |new_window_size| {
            crate::renderer::set_viewport(&Vec2::ZERO, &new_window_size);
        });

        crate::renderer::initialize(&window).map_err(Error::InitializeRendererFailed)?;

        Ok(Self {
            window,
            objects: BTreeMap::new(),
            camera: Camera::new(),
            delta_time: Duration::ZERO,
        })
    }

    pub fn add_object(&mut self, object: Object)
    {
        self.objects.insert(object.id(), object);
    }

    pub fn set_objecs(&mut self, objects: impl IntoIterator<Item = Object>)
    {
        self.objects
            .extend(objects.into_iter().map(|object| (object.id(), object)));
    }

    #[must_use]
    pub fn get_object_by_id(&self, id: ObjectId) -> Option<&Object>
    {
        self.objects.get(&id)
    }

    #[must_use]
    pub fn get_object_by_id_mut(&mut self, id: ObjectId) -> Option<&mut Object>
    {
        self.objects.get_mut(&id)
    }

    /// Starts the engine.
    ///
    /// # Errors
    /// Will return `Err` if updating the window fails.
    pub fn start(&mut self, mut func: impl FnMut(&mut Self)) -> Result<(), Error>
    {
        let mut prev_frame_start: Option<Instant> = None;

        while !self.window.should_close() {
            self.update_delta_time(&mut prev_frame_start);

            func(self);

            let window_size = self.window.size().map_err(Error::GetWindowSizeFailed)?;

            crate::renderer::render(self.objects.values(), &window_size, &self.camera);

            self.window
                .swap_buffers()
                .map_err(Error::UpdateWindowFailed)?;

            self.window
                .poll_events()
                .map_err(Error::UpdateWindowFailed)?;
        }

        Ok(())
    }

    pub fn camera(&mut self) -> &mut Camera
    {
        &mut self.camera
    }

    /// Returns the current delta time. Will be 0 if not called from the function
    /// passed to [`start`].
    #[must_use]
    pub fn delta_time(&self) -> &Duration
    {
        &self.delta_time
    }

    /// Returns whether or not a keyboard key is currently pressed.
    ///
    /// # Errors
    /// Will return `Err` if getting the key state fails.
    pub fn is_key_pressed(&self, key: Key) -> Result<bool, Error>
    {
        self.window
            .get_key(key)
            .map(|key_state| matches!(key_state, KeyState::Pressed))
            .map_err(Error::GetKeyStateFailed)
    }

    fn update_delta_time(&mut self, prev_frame_start: &mut Option<Instant>)
    {
        let frame_start_time = Instant::now();

        if let Some(last_frame_start) = prev_frame_start {
            self.delta_time = frame_start_time.duration_since(*last_frame_start);
        }

        *prev_frame_start = Some(frame_start_time);
    }
}

/// Engine Error
#[derive(Debug, thiserror::Error)]
pub enum Error
{
    #[error("Failed to create window")]
    CreateWindowFailed(#[source] glfw::Error),

    #[error("Failed to configure window")]
    ConfigureWindowFailed(#[source] glfw::Error),

    #[error("Failed to initialize renderer")]
    InitializeRendererFailed(#[source] renderer::Error),

    #[error("Failed to update window")]
    UpdateWindowFailed(#[source] glfw::Error),

    #[error("Failed to get window size")]
    GetWindowSizeFailed(#[source] glfw::Error),

    #[error("Failed to get key state")]
    GetKeyStateFailed(#[source] glfw::Error),
}