// based on the WebGL example in the `wasm-bindgen` guide
//
//   https://rustwasm.github.io/wasm-bindgen/examples/webgl.html
//
// and this StackOverflow answer by wangdq
//
//   https://stackoverflow.com/a/39684775
//

extern crate js_sys;
/* use std::f64::consts::PI as PI; */
use sycamore::{prelude::*, rt::{JsCast, JsValue}};
use web_sys::{console, WebGl2RenderingContext, WebGlProgram, WebGlShader};

fn compile_shader(
    context: &WebGl2RenderingContext,
    shader_type: u32,
    source: &str,
) -> WebGlShader {
    let shader = context.create_shader(shader_type).unwrap();
    context.shader_source(&shader, source);
    context.compile_shader(&shader);
    shader
}

// load the given data into the vertex input of the given name
fn bind_vertex_attrib(
    context: &WebGl2RenderingContext,
    program: &WebGlProgram,
    name: &str,
    size: i32,
    data: &[f32]
) {
    // create a data buffer and bind it to ARRAY_BUFFER
    let buffer = context.create_buffer().unwrap();
    context.bind_buffer(WebGl2RenderingContext::ARRAY_BUFFER, Some(&buffer));
    
    // load the given data into the buffer. the function `Float32Array::view`
    // creates a raw view into our module's `WebAssembly.Memory` buffer.
    // allocating more memory will change the buffer, invalidating the view.
    // that means we have to make sure we don't allocate any memory until the
    // view is dropped
    unsafe {
        context.buffer_data_with_array_buffer_view(
            WebGl2RenderingContext::ARRAY_BUFFER,
            &js_sys::Float32Array::view(&data),
            WebGl2RenderingContext::STATIC_DRAW,
        );
    }
    
    // find the target attribute in the program's attribute list
    let attrib_index = context.get_attrib_location(&program, name);
    
    // allow the target attribute to be used
    context.enable_vertex_attrib_array(attrib_index as u32);
    
    // take whatever's bound to ARRAY_BUFFER---here, the data buffer created
    // above---and bind it to the target attribute
    //
    //   https://developer.mozilla.org/en-US/docs/Web/API/WebGLRenderingContext/vertexAttribPointer
    //
    context.vertex_attrib_pointer_with_i32(
        attrib_index as u32,
        size,
        WebGl2RenderingContext::FLOAT,
        false, // don't normalize
        0, // zero stride
        0, // zero offset
    );
}

fn main() {
    // set up a config option that forwards panic messages to `console.error`
    #[cfg(feature = "console_error_panic_hook")]
    console_error_panic_hook::set_once();
    
    sycamore::render(|| {
        let tip = create_signal(0.0);
        let display = create_node_ref();
        
        on_mount(move || {
            // get the display canvas
            let canvas = display
                .get::<DomNode>()
                .unchecked_into::<web_sys::HtmlCanvasElement>();
            let ctx = canvas
                .get_context("webgl2")
                .unwrap()
                .unwrap()
                .dyn_into::<WebGl2RenderingContext>()
                .unwrap();
            
            // compile and attach the vertex and fragment shaders
            let vertex_shader = compile_shader(
                &ctx,
                WebGl2RenderingContext::VERTEX_SHADER,
                r##"#version 300 es
                
                in vec3 position;
                in vec3 color;
                
                out vec4 vertexColor;
                
                const float focal_length = 3.0;
                const float near_clip = 0.1;
                const float far_clip = 20.0;
                const float depth_inv = 1. / (far_clip - near_clip);
                
                void main() {
                    const mat4 world_to_clip = mat4(
                        focal_length, 0.0, 0.0, 0.0,
                        0.0, focal_length, 0.0, 0.0,
                        0.0, 0.0, (near_clip + far_clip) * depth_inv, -1.,
                        0.0, 0.0, 2. * near_clip * far_clip * depth_inv, 0.0
                    );
                    gl_Position = world_to_clip * vec4(position, 1.);
                    vertexColor = vec4(color, 1.);
                }
                "##,
            );
            let fragment_shader = compile_shader(
                &ctx,
                WebGl2RenderingContext::FRAGMENT_SHADER,
                r##"#version 300 es
            
                precision highp float;
                
                in vec4 vertexColor;
                
                out vec4 outColor;
                
                void main() {
                    outColor = vertexColor;
                }
                "##,
            );
            let program = ctx.create_program().unwrap();
            ctx.attach_shader(&program, &vertex_shader);
            ctx.attach_shader(&program, &fragment_shader);
            ctx.link_program(&program);
            let link_status = ctx
                .get_program_parameter(&program, WebGl2RenderingContext::LINK_STATUS)
                .as_bool()
                .unwrap();
            let link_msg = if link_status {
                "Linked successfully"
            } else {
                "Linking failed"
            };
            console::log_1(&JsValue::from(link_msg));
            ctx.use_program(Some(&program));
            
            // create a vertex array and bind it to the graphics context
            let vertex_array = ctx.create_vertex_array().unwrap();
            ctx.bind_vertex_array(Some(&vertex_array));
            
            // set up a repainting routine
            create_effect(move || {
                const VERTEX_CNT: usize = 9;
                
                // set the vertex positions
                let tip_shift = 4.0/3.0 * tip.get() as f32;
                let positions: [f32; 3*VERTEX_CNT] = [
                    // triangle 1
                    1.0 - tip_shift, 1.0 - tip_shift, -5.0 - tip_shift,
                    1.0, -1.0, -7.0,
                    -1.0, 1.0, -7.0,
                    // triangle 2
                    1.0 - tip_shift, 1.0 - tip_shift, -5.0 - tip_shift,
                    -1.0, 1.0, -7.0,
                    -1.0, -1.0, -7.0,
                    // triangle 3
                    1.0 - tip_shift, 1.0 - tip_shift, -5.0 - tip_shift,
                    -1.0, -1.0, -7.0,
                    1.0, -1.0, -7.0
                ];
                bind_vertex_attrib(&ctx, &program, "position", 3, &positions);
                
                // set the vertex colors
                let colors: [f32; 3*VERTEX_CNT] = [
                    // triangle 1
                    1.0, 0.0, 0.5,
                    1.0, 0.0, 0.5,
                    1.0, 0.0, 0.5,
                    // triangle 2
                    0.0, 0.5, 1.0,
                    0.0, 0.5, 1.0,
                    0.0, 0.5, 1.0,
                    // triangle 3
                    0.5, 0.0, 1.0,
                    0.5, 0.0, 1.0,
                    0.5, 0.0, 1.0
                ];
                bind_vertex_attrib(&ctx, &program, "color", 3, &colors);
                
                // clear the screen and draw the scene
                ctx.clear_color(0.0, 0.0, 0.0, 1.0);
                ctx.clear(WebGl2RenderingContext::COLOR_BUFFER_BIT);
                ctx.draw_arrays(WebGl2RenderingContext::TRIANGLES, 0, VERTEX_CNT as i32);
            });
        });
        
        view! {
            div(id="app") {
                canvas(ref=display, width="600", height="600")
                input(
                    type="range",
                    max=1.0,
                    step=0.01,
                    bind:valueAsNumber=tip
                )
            }
        }
    });
}