//! # Fog Example (Étape 25)
//!
//! Demonstrates distance fog: objects fade into the fog color as they recede,
//! creating the illusion of an infinite world (Skyrim/GTA pattern).
//!
//! The scene has a row of cubes receding into the distance and scattered spheres,
//! all sitting on a large ground plane. Switch fog modes with number keys to
//! compare the three attenuation curves.
//!
//! ## Pipeline
//! Fog is applied in the main pass fragment shader (after lighting, before tone
//! mapping). It uses the fragment's world-space distance to the camera and
//! blends the final color toward `fog_color`.
//!
//! ## Controls
//! | Key | Action |
//! |-----|--------|
//! | Drag (LMB) | Orbit camera |
//! | Wheel | Zoom |
//! | `1` | Linear fog (near=5, far=30) |
//! | `2` | Exponential fog (density=0.04) |
//! | `3` | Exponential² fog (density=0.06) — best for masking |
//! | `4` | Fog OFF |
//! | `R` | Reset camera |
//!
//! ## Build & Run
//! ```sh
//! cargo run -p wsg-lib --example fog --features "all-prims"
//! ```

use glam::Vec3;
use winit::event::MouseButton;
use winit::keyboard::KeyCode;
use wsg_lib::app::AppBuilder;
use wsg_lib::camera::CameraController;
use wsg_lib::core::{FogConfig, ToneMapper, Transform};
use wsg_lib::mesh::{cube, icosphere, plane};
use wsg_lib::AppHandler;
use wsg_lib::utils::WsgError;

struct FogDemo {
    camera: CameraController,
}

impl AppHandler for FogDemo {
    fn setup(&mut self, app: &mut wsg_lib::App) {
        app.scene
            .register_shader("standard", wsg_lib::utils::STANDARD_SHADER_PATH)
            .unwrap();

        // Large ground plane — will fade into fog at distance.
        app.scene
            .create_mesh("ground_mesh", plane(80.0, 80.0, 1, 1), None)
            .unwrap();
        app.scene.add_entity("ground", "ground_mesh").unwrap();

        // Row of cubes receding into the distance.
        app.scene
            .create_mesh("cube_mesh", cube(1.0), None)
            .unwrap();
        for i in 0..15 {
            let z = -2.0 - i as f32 * 2.5;
            let mut tf = Transform::identity();
            tf.translation = Vec3::new(0.0, 0.5, z);
            app.scene
                .add_entity_with_transform(&format!("cube_{i}"), "cube_mesh", tf)
                .unwrap();
        }

        // Scattered spheres at various distances.
        app.scene
            .create_mesh("sphere_mesh", icosphere(0.8, 3), None)
            .unwrap();
        let positions = [
            Vec3::new(3.0, 0.8, -5.0),
            Vec3::new(-4.0, 0.8, -10.0),
            Vec3::new(5.0, 0.8, -15.0),
            Vec3::new(-3.0, 0.8, -20.0),
            Vec3::new(0.0, 0.8, -30.0),
        ];
        for (i, pos) in positions.iter().enumerate() {
            let mut tf = Transform::identity();
            tf.translation = *pos;
            app.scene
                .add_entity_with_transform(&format!("sphere_{i}"), "sphere_mesh", tf)
                .unwrap();
        }

        // Directional light.
        let light_dir = Vec3::new(-0.5, -1.0, -0.3).normalize();
        app.scene
            .add_directional_light(light_dir, [1.0, 0.95, 0.85], 1.2)
            .unwrap();
        app.scene.set_ambient([0.08, 0.08, 0.1]);

        // Camera — positioned to look down the row of cubes.
        self.camera.yaw = 0.0;
        self.camera.pitch = 0.15;
        self.camera.distance = 8.0;
        self.camera.target = Vec3::new(0.0, 0.5, -8.0);
        self.camera.apply_to(app.scene.camera_mut());

        // Print initial fog status.
        eprintln!("[Fog] Initial: Exponential² (density=0.06)");
        eprintln!("[Fog] Keys: 1=linear 2=exp 3=exp² 4=off R=reset");
    }

    fn update(&mut self, app: &mut wsg_lib::App) {
        // Orbit camera.
        let (dx, dy) = app.input.mouse_delta();
        if app.input.mouse_button_held(MouseButton::Left) {
            self.camera.orbit(dx, dy);
        }
        let (_, sy) = app.input.scroll_delta();
        self.camera.zoom(sy);

        // Fog mode switching.
        if app.input.key_pressed(KeyCode::Digit1) {
            app.renderer_mut()
                .set_fog(Some(FogConfig::linear([0.7, 0.75, 0.85], 5.0, 30.0)));
            eprintln!("[Fog] → Linear (near=5, far=30)");
        }
        if app.input.key_pressed(KeyCode::Digit2) {
            app.renderer_mut()
                .set_fog(Some(FogConfig::exponential([0.7, 0.75, 0.85], 0.04)));
            eprintln!("[Fog] → Exponential (density=0.04)");
        }
        if app.input.key_pressed(KeyCode::Digit3) {
            app.renderer_mut()
                .set_fog(Some(FogConfig::exponential2([0.7, 0.75, 0.85], 0.06)));
            eprintln!("[Fog] → Exponential² (density=0.06)");
        }
        if app.input.key_pressed(KeyCode::Digit4) {
            app.renderer_mut().set_fog(None);
            eprintln!("[Fog] → OFF");
        }
        if app.input.key_pressed(KeyCode::KeyR) {
            self.camera.yaw = 0.0;
            self.camera.pitch = 0.15;
            self.camera.distance = 8.0;
        }

        self.camera.apply_to(app.scene.camera_mut());
    }

    fn render(&mut self, app: &mut wsg_lib::App, frame: &wsg_lib::core::Frame) {
        app.render_scene(frame.view());
    }
}

#[pollster::main]
async fn main() -> Result<(), WsgError> {
    let app = AppBuilder::new()
        .title("WSG — Fog (3 modes)")
        .size(1024, 640)
        .with_fog(FogConfig::exponential2([0.7, 0.75, 0.85], 0.06))
        .with_hdr(ToneMapper::Aces)
        .build()
        .await?;
    app.run(FogDemo {
        camera: CameraController::default(),
    })
}