//! Drawing a sky with WebGL2 (docs/backgrounds.md §6): every mark in one

//! instanced draw, every link in one line buffer. Shaders are here as

//! string literals; marks are drawn as signed-distance shapes, so they

//! stay crisp at any device pixel ratio.

use wasm_bindgen::prelude::*;

use web_sys::{WebGl2RenderingContext as Gl, WebGlBuffer, WebGlProgram, WebGlShader, WebGlUniformLocation, WebGlVertexArrayObject};

const MARK_VS: &str = r#"#version 300 es

layout(location = 0) in vec2 corner;

layout(location = 1) in vec2 center;

layout(location = 2) in float size;

layout(location = 3) in float shape;

layout(location = 4) in vec4 colour;

uniform vec2 view;

out vec2 uv;

out float vshape;

out vec4 vcolour;

out float px;

void main() {

    float r = size + 1.5;

    vec2 p = center + corner * r;

    uv = corner * r / size;

    vshape = shape;

    vcolour = colour;

    px = 1.0 / size;

    gl_Position = vec4(p.x / view.x * 2.0 - 1.0, 1.0 - p.y / view.y * 2.0, 0.0, 1.0);

}

"#;

const MARK_FS: &str = r#"#version 300 es

precision mediump float;

in vec2 uv;

in float vshape;

in vec4 vcolour;

in float px;

out vec4 frag;

void main() {

    vec2 a = abs(uv);

    float d;

    if (vshape < 0.5) {

        d = length(uv) - 1.0;                       // a push: a dot

    } else if (vshape < 1.5) {

        d = (a.x + a.y) * 0.85 - 1.0;               // a proposal: a diamond

    } else if (vshape < 2.5) {

        d = abs(length(uv) - 0.72) - 0.28;          // an issue: a ring

    } else if (vshape < 3.5) {

        d = min(a.x + 3.5 * a.y, 3.5 * a.x + a.y) * 0.5 - 0.5;  // a release: a star

    } else {

        d = abs(length(uv) - 0.85) - 0.12;          // a repository: a thin ring

    }

    float cover = 1.0 - smoothstep(-px, px, d);

    frag = vcolour * cover;

}

"#;

const LINE_VS: &str = r#"#version 300 es

layout(location = 0) in vec2 pos;

layout(location = 1) in vec4 colour;

uniform vec2 view;

out vec4 vcolour;

void main() {

    vcolour = colour;

    gl_Position = vec4(pos.x / view.x * 2.0 - 1.0, 1.0 - pos.y / view.y * 2.0, 0.0, 1.0);

}

"#;

const LINE_FS: &str = r#"#version 300 es

precision mediump float;

in vec4 vcolour;

out vec4 frag;

void main() { frag = vcolour; }

"#;

/// Floats per mark instance and per line vertex (sky::Sky's layouts).

const MARK_FLOATS: i32 = 8;

const LINE_FLOATS: i32 = 6;

pub struct Renderer {

    gl: Gl,

    marks: WebGlProgram,

    lines: WebGlProgram,

    mark_view: Option<WebGlUniformLocation>,

    line_view: Option<WebGlUniformLocation>,

    mark_vao: WebGlVertexArrayObject,

    line_vao: WebGlVertexArrayObject,

    instances: WebGlBuffer,

    line_buf: WebGlBuffer,

}

fn shader(gl: &Gl, kind: u32, src: &str) -> Result<WebGlShader, JsValue> {

    let s = gl.create_shader(kind).ok_or("no shader")?;

    gl.shader_source(&s, src);

    gl.compile_shader(&s);

    if gl.get_shader_parameter(&s, Gl::COMPILE_STATUS).as_bool() == Some(true) {

        Ok(s)

    } else {

        Err(gl.get_shader_info_log(&s).unwrap_or_default().into())

    }

}

fn program(gl: &Gl, vs: &str, fs: &str) -> Result<WebGlProgram, JsValue> {

    let p = gl.create_program().ok_or("no program")?;

    gl.attach_shader(&p, &shader(gl, Gl::VERTEX_SHADER, vs)?);

    gl.attach_shader(&p, &shader(gl, Gl::FRAGMENT_SHADER, fs)?);

    gl.link_program(&p);

    if gl.get_program_parameter(&p, Gl::LINK_STATUS).as_bool() == Some(true) {

        Ok(p)

    } else {

        Err(gl.get_program_info_log(&p).unwrap_or_default().into())

    }

}

fn float_attrib(gl: &Gl, loc: u32, size: i32, stride: i32, offset: i32, divisor: u32) {

    gl.enable_vertex_attrib_array(loc);

    gl.vertex_attrib_pointer_with_i32(loc, size, Gl::FLOAT, false, stride * 4, offset * 4);

    gl.vertex_attrib_divisor(loc, divisor);

}

impl Renderer {

    pub fn new(gl: Gl) -> Result<Renderer, JsValue> {

        let marks = program(&gl, MARK_VS, MARK_FS)?;

        let lines = program(&gl, LINE_VS, LINE_FS)?;

        let mark_view = gl.get_uniform_location(&marks, "view");

        let line_view = gl.get_uniform_location(&lines, "view");

        // Marks: one shared quad, and one instance per mark.

        let mark_vao = gl.create_vertex_array().ok_or("no vertex array")?;

        gl.bind_vertex_array(Some(&mark_vao));

        let quad = gl.create_buffer().ok_or("no buffer")?;

        gl.bind_buffer(Gl::ARRAY_BUFFER, Some(&quad));

        let corners: [f32; 8] = [-1.0, -1.0, 1.0, -1.0, -1.0, 1.0, 1.0, 1.0];

        // Safety: the view is used at once, before anything can allocate.

        unsafe {

            let view = js_sys::Float32Array::view(&corners);

            gl.buffer_data_with_array_buffer_view(Gl::ARRAY_BUFFER, &view, Gl::STATIC_DRAW);

        }

        float_attrib(&gl, 0, 2, 2, 0, 0);

        let instances = gl.create_buffer().ok_or("no buffer")?;

        gl.bind_buffer(Gl::ARRAY_BUFFER, Some(&instances));

        float_attrib(&gl, 1, 2, MARK_FLOATS, 0, 1);

        float_attrib(&gl, 2, 1, MARK_FLOATS, 2, 1);

        float_attrib(&gl, 3, 1, MARK_FLOATS, 3, 1);

        float_attrib(&gl, 4, 4, MARK_FLOATS, 4, 1);

        // Links: plain lines, two vertices each.

        let line_vao = gl.create_vertex_array().ok_or("no vertex array")?;

        gl.bind_vertex_array(Some(&line_vao));

        let line_buf = gl.create_buffer().ok_or("no buffer")?;

        gl.bind_buffer(Gl::ARRAY_BUFFER, Some(&line_buf));

        float_attrib(&gl, 0, 2, LINE_FLOATS, 0, 0);

        float_attrib(&gl, 1, 4, LINE_FLOATS, 2, 0);

        gl.bind_vertex_array(None);

        gl.enable(Gl::BLEND);

        // Colours are premultiplied.

        gl.blend_func(Gl::ONE, Gl::ONE_MINUS_SRC_ALPHA);

        Ok(Renderer { gl, marks, lines, mark_view, line_view, mark_vao, line_vao, instances, line_buf })

    }

    /// Draw one frame: `instances` and `lines` as sky::Sky lays them out,

    /// in a view of `w` by `h` CSS pixels on a canvas of `pw` by `ph`.

    pub fn draw(&self, w: f32, h: f32, pw: i32, ph: i32, instances: &[f32], lines: &[f32]) {

        let gl = &self.gl;

        gl.viewport(0, 0, pw, ph);

        gl.clear_color(0.0, 0.0, 0.0, 0.0);

        gl.clear(Gl::COLOR_BUFFER_BIT);

        if !lines.is_empty() {

            gl.use_program(Some(&self.lines));

            gl.uniform2f(self.line_view.as_ref(), w, h);

            gl.bind_vertex_array(Some(&self.line_vao));

            gl.bind_buffer(Gl::ARRAY_BUFFER, Some(&self.line_buf));

            // Safety: as above, the view does not outlive this call.

            unsafe {

                let view = js_sys::Float32Array::view(lines);

                gl.buffer_data_with_array_buffer_view(Gl::ARRAY_BUFFER, &view, Gl::STREAM_DRAW);

            }

            gl.draw_arrays(Gl::LINES, 0, lines.len() as i32 / LINE_FLOATS);

        }

        if !instances.is_empty() {

            gl.use_program(Some(&self.marks));

            gl.uniform2f(self.mark_view.as_ref(), w, h);

            gl.bind_vertex_array(Some(&self.mark_vao));

            gl.bind_buffer(Gl::ARRAY_BUFFER, Some(&self.instances));

            unsafe {

                let view = js_sys::Float32Array::view(instances);

                gl.buffer_data_with_array_buffer_view(Gl::ARRAY_BUFFER, &view, Gl::STREAM_DRAW);

            }

            gl.draw_arrays_instanced(Gl::TRIANGLE_STRIP, 0, 4, instances.len() as i32 / MARK_FLOATS);

        }

        gl.bind_vertex_array(None);

    }

}