use glam::{Mat4, Quat, Vec2, Vec3};
use std::time::Instant;
use winit::event::{ElementState, VirtualKeyCode};

pub trait Camera {
    fn get_eye(&self) -> [f32; 4];
    fn get_vp(&self) -> [[f32; 4]; 4];
}

pub struct Flycam {
    // input
    is_up_pressed: bool,
    is_down_pressed: bool,
    is_forward_pressed: bool,
    is_backward_pressed: bool,
    is_left_pressed: bool,
    is_right_pressed: bool,
    mouse_dx: f32,
    mouse_dy: f32,
    // state
    last_update: Instant,
    pan: f32,
    tilt: f32,
    position: Vec3,
    // constants
    speed: f32,
    turn_speed: f32,
    aspect: f32,
    fovy: f32,
    znear: f32,
    zfar: f32,
}

impl Flycam {
    pub fn new(speed: f32, turn_speed: f32) -> Self {
        Self {
            is_up_pressed: false,
            is_down_pressed: false,
            is_forward_pressed: false,
            is_backward_pressed: false,
            is_left_pressed: false,
            is_right_pressed: false,
            mouse_dx: 0.0,
            mouse_dy: 0.0,
            last_update: Instant::now(),
            pan: 0.0,
            tilt: 0.0,
            position: Vec3::new(0.0, 0.5, 1.0),
            speed,
            turn_speed,
            aspect: 1.0, // TODO compute from size
            fovy: std::f32::consts::FRAC_PI_2,
            znear: 0.01,
            zfar: 100.0,
        }
    }
}

impl Flycam {
    pub fn process_keyboard(&mut self, key: VirtualKeyCode, state: ElementState) {
        let is_pressed = state == ElementState::Pressed;
        match key {
            VirtualKeyCode::Space => {
                self.is_up_pressed = is_pressed;
            }
            VirtualKeyCode::LShift => {
                self.is_down_pressed = is_pressed;
            }
            VirtualKeyCode::W | VirtualKeyCode::Up => {
                self.is_forward_pressed = is_pressed;
            }
            VirtualKeyCode::A | VirtualKeyCode::Left => {
                self.is_left_pressed = is_pressed;
            }
            VirtualKeyCode::S | VirtualKeyCode::Down => {
                self.is_backward_pressed = is_pressed;
            }
            VirtualKeyCode::D | VirtualKeyCode::Right => {
                self.is_right_pressed = is_pressed;
            }
            _ => {}
        }
    }

    pub fn process_mouse(&mut self, mouse_dx: f64, mouse_dy: f64) {
        self.mouse_dx += mouse_dx as f32;
        self.mouse_dy += mouse_dy as f32;
    }

    pub fn resize(&mut self, width: u32, height: u32) {
        self.aspect = (width as f32) / (height as f32);
    }

    pub fn update(&mut self) {
        let dt = self.last_update.elapsed();
        self.last_update = Instant::now();
        let dt = dt.as_micros() as f32 / 1_000_000.0;

        let t = self.turn_speed;
        self.pan += t * self.mouse_dx;
        self.tilt += t * self.mouse_dy;
        self.mouse_dx = 0.0;
        self.mouse_dy = 0.0;

        let tilt_limit = std::f32::consts::FRAC_PI_2;
        if self.tilt < -tilt_limit {
            self.tilt = -tilt_limit;
        } else if self.tilt > tilt_limit {
            self.tilt = tilt_limit;
        }

        let s = dt * self.speed;
        let axis = Self::key_axis;
        let truck = s * axis(self.is_backward_pressed, self.is_forward_pressed);
        let dolly = s * axis(self.is_right_pressed, self.is_left_pressed);
        let boom = s * axis(self.is_down_pressed, self.is_up_pressed);
        self.move_position(truck, dolly, boom);
    }

    fn key_axis(negative: bool, positive: bool) -> f32 {
        if negative {
            if positive {
                0.0
            } else {
                -1.0
            }
        } else {
            if positive {
                1.0
            } else {
                0.0
            }
        }
    }

    fn move_position(&mut self, truck: f32, dolly: f32, boom: f32) {
        // truck direction from straight down
        let h = Vec2::new(self.pan.sin(), -self.pan.cos());
        // truck direction from the side
        let v = Vec2::new(self.tilt.cos(), -self.tilt.sin());
        // composite to get forward direction
        let truck_to = Vec3::new(h.x * v.x, v.y, h.y * v.x);

        let dolly_to = Vec3::new(-self.pan.cos(), 0.0, -self.pan.sin());

        self.position += (truck_to * truck) + (dolly_to * dolly);
        self.position.y += boom;
    }
}

impl Camera for Flycam {
    fn get_eye(&self) -> [f32; 4] {
        self.position.extend(0.0).to_array()
    }

    fn get_vp(&self) -> [[f32; 4]; 4] {
        let orientation = Quat::from_euler(glam::EulerRot::XYZ, self.tilt, self.pan, 0.0);
        let rotation = Mat4::from_quat(orientation);
        let view = rotation * Mat4::from_translation(-self.position);
        let proj = Mat4::perspective_rh_gl(self.fovy, self.aspect, self.znear, self.zfar);
        let vp = proj * view;
        vp.to_cols_array_2d()
    }
}