const sdf_vs_src = `#version 300 es
    in vec2 a_a; // point from
    in vec2 a_b; // point to

    in int a_stroke_id;
    in vec2 a_pressure;

    uniform vec2 u_scale;
    uniform vec2 u_res;
    uniform vec2 u_translation;
    uniform int u_stroke_count;
    uniform int u_stroke_texture_size;
    uniform highp usampler2D u_stroke_data;
    uniform float u_fixed_pixel_width;
    
    out vec4 v_line;
    out vec2 v_texcoord;
    out vec3 v_color;

    flat out vec2 v_thickness;

    void main() {
        vec2 screen02; 
        float apron = 1.0; // google "futanari inflation rule 34"
        
        int stroke_data_y = a_stroke_id / u_stroke_texture_size;
        int stroke_data_x = a_stroke_id % u_stroke_texture_size;

        vec2 line_dir = normalize(a_b - a_a);
        vec2 up_dir = vec2(line_dir.y, -line_dir.x);
        vec2 pixel = vec2(2.0) / u_res;

        uvec4 stroke_data = texelFetch(u_stroke_data, ivec2(stroke_data_x, stroke_data_y), 0);
        float radius = float(stroke_data.w);

        if (u_fixed_pixel_width > 0.0) {
            radius = u_fixed_pixel_width / u_scale.x;
        }
        
        float rscale = apron / u_scale.x;
        int vertex_index = gl_VertexID % 6;

        vec2 outwards;
        vec2 origin;

        if (vertex_index == 0) {
            // "top left" aka "p1"
            origin = a_a;
            outwards = up_dir - line_dir; 
        } else if (vertex_index == 1 || vertex_index == 5) {
            // "top right" aka "p2"
            origin = a_b;
            outwards = up_dir + line_dir;
        } else if (vertex_index == 2 || vertex_index == 4) {
            // "bottom left" aka "p3"
            origin = a_a;
            outwards = -up_dir - line_dir;
        } else {
            // "bottom right" aka "p4"
            origin = a_b;
            outwards = -up_dir + line_dir;
        }
      
        vec2 pos = origin + normalize(outwards) * radius * 2.0 * max(a_pressure.x, a_pressure.y); // doubling is to account for max possible pressure
        screen02 = (pos.xy * u_scale + u_translation) / u_res * 2.0 + outwards * pixel * apron;
        v_texcoord = pos.xy + outwards * rscale;
        screen02.y = 2.0 - screen02.y;
        v_line = vec4(a_a, a_b);        
        v_thickness = radius * a_pressure; // pressure 0.5 is the "neutral" pressure
        v_color = vec3(stroke_data.xyz) / 255.0;
        if (a_stroke_id >> 31 != 0) {
            screen02 += vec2(100.0); // shift offscreen
        }
        gl_Position = vec4(screen02 - 1.0, (float(a_stroke_id) / float(u_stroke_count)) * 2.0 - 1.0, 1.0);
    }
`;

const sdf_fs_src = `#version 300 es
    precision highp float;

    uniform int u_debug_mode;

    in vec4 v_line;
    in vec2 v_texcoord;
    in vec3 v_color;

    flat in vec2 v_thickness;

    layout(location = 0) out vec4 FragColor;

    void main() {
        if (u_debug_mode == 0) {
            vec2 a = v_line.xy;
            vec2 b = v_line.zw;

            vec2 pa = v_texcoord - a.xy, ba = b.xy - a.xy;
            float h = clamp(dot(pa, ba) / dot(ba, ba), 0.0, 1.0);
            float dist = length(v_texcoord - (a + ba * h)) - mix(v_thickness.x, v_thickness.y, h);

            float fade = 0.5 * length(fwidth(v_texcoord));
            float alpha = 1.0 - smoothstep(-fade, fade, dist);

            //if (alpha > 0.5) alpha = 0.5;

            FragColor = vec4(v_color * alpha, alpha);
        } else {
            FragColor = vec4(0.2, 0.0, 0.0, 0.2);
        }
    }
`;

const tquad_vs_src = `#version 300 es
    in vec2 a_pos;
     
    uniform vec2 u_scale;
    uniform vec2 u_res;
    uniform vec2 u_translation;

    out vec2 v_texcoord;
     
    void main() {
        vec2 screen01 = (a_pos * u_scale + u_translation) / u_res;
        vec2 screen02 = screen01 * 2.0;

        int vertex_index = gl_VertexID % 6;

        if (vertex_index == 0) {
            v_texcoord = vec2(0.0, 0.0);
        } else if (vertex_index == 1 || vertex_index == 5) {
            v_texcoord = vec2(1.0, 0.0);
        } else if (vertex_index == 2 || vertex_index == 4) {
            v_texcoord = vec2(0.0, 1.0);
        } else {
            v_texcoord = vec2(1.0, 1.0);
        }

        screen02.y = 2.0 - screen02.y;
        vec2 screen11 = screen02 - 1.0;

        gl_Position = vec4(screen11, 0, 1);
    }
`;

const tquad_fs_src = `#version 300 es
    precision highp float;
     
    in vec2 v_texcoord;
     
    uniform sampler2D u_texture;
    uniform int u_solid;
    uniform vec4 u_color;

    layout(location = 0) out vec4 FragColor;

    void main() {
        if (u_solid == 0) {
            FragColor = texture(u_texture, v_texcoord);
        } else {
            FragColor = u_color;
        }
    }
`;

const grid_vs_src = `#version 300 es
    in vec2 a_data; // per-instance

    out float v_fadeout;

    uniform vec2 u_scale;
    uniform vec2 u_res;
    uniform vec2 u_translation;
    uniform float u_fadeout;

    void main() {
        vec2 origin;
        vec2 minor_offset;
        vec2 major_offset;

        vec2 pixel = 2.0 / u_res;

        if (a_data.x > 0.0) {
            // Vertical, treat Y as X
            float x = a_data.y;
            origin = vec2(x, 0.0);
            minor_offset = pixel * vec2(1.0, 0.0);
            major_offset = vec2(0.0, 2.0);
        } else {
            // Horizontal, treat Y as Y
            float y = a_data.y;
            origin = vec2(0.0, y);
            minor_offset = pixel * vec2(0.0, 1.0);
            major_offset = vec2(2.0, 0.0);
        }

        vec2 v = (origin * u_scale + u_translation) / u_res * 2.0;
        vec2 pos;

        if (a_data.x > 0.0) {
            v.y = 0.0;
        } else {
            v.x = 0.0;
        }

        if (gl_VertexID % 6 == 0) {
            pos = v; 
        } else if (gl_VertexID % 6 == 1 || gl_VertexID % 6 == 5) {
            pos = v + (a_data.x > 0.0 ? minor_offset : major_offset); 
            //pos = v + minor_offset;
        } else if (gl_VertexID % 6 == 2 || gl_VertexID % 6 == 4) {
            pos = v + (a_data.x > 0.0 ? major_offset : minor_offset); 
            //pos = v + major_offset;
        } else if (gl_VertexID % 6 == 3) {
            pos = v + major_offset + minor_offset; 
            //pos = v + major_offset + minor_offset;
        }

        vec2 screen02 = pos;
        screen02.y = 2.0 - screen02.y;
        v_fadeout = u_fadeout;
        gl_Position = vec4(screen02 - 1.0, 0.0, 1.0);
    }
`;

const dots_vs_src = `#version 300 es
    in vec2 a_center; // per-instance

    out float v_fadeout;

    uniform vec2 u_scale;
    uniform vec2 u_res;
    uniform vec2 u_translation;
    uniform float u_fadeout;

    void main() {
        vec2 v = (a_center * u_scale + u_translation) / u_res * 2.0;
        vec2 pos;
        vec2 pixel = 2.0 / u_res;

        if (gl_VertexID % 6 == 0) {
            pos = v + pixel * vec2(-1.0); 
        } else if (gl_VertexID % 6 == 1) {
            pos = v + pixel * vec2(1.0, -1.0); 
        } else if (gl_VertexID % 6 == 2) {
            pos = v + pixel * vec2(-1.0, 1.0); 
        } else if (gl_VertexID % 6 == 3) {
            pos = v + pixel * vec2(1.0); 
        } else if (gl_VertexID % 6 == 4) {
            pos = v + pixel * vec2(-1.0, 1.0); 
        } else if (gl_VertexID % 6 == 5) {
            pos = v + pixel * vec2(1.0, -1.0); 
        }

        vec2 screen02 = pos;
        screen02.y = 2.0 - screen02.y;
        v_fadeout = u_fadeout;
        gl_Position = vec4(screen02 - 1.0, 0.0, 1.0);
    }
`;

const dots_fs_src = `#version 300 es
    precision highp float;

    in float v_fadeout;

    layout(location = 0) out vec4 FragColor;

    void main() {
        vec3 color = vec3(0.5);
        FragColor = vec4(color * v_fadeout, v_fadeout);
    }
`;


// 
const iquad_vs_src = `#version 300 es
    in vec2 a_topleft;     // per-instance
    in vec2 a_bottomright; // per-instance

    uniform vec2 u_scale;
    uniform vec2 u_res;
    uniform vec2 u_translation;

    out vec3 v_color;

    void main() {
        vec2 pos;

        int vertex_index = gl_VertexID % 6;

        if (vertex_index == 0) {
            // top left
            pos = a_topleft;
        } else if (vertex_index == 1 || vertex_index == 5) {
            // top right
            pos = vec2(a_bottomright.x, a_topleft.y);
        } else if (vertex_index == 2 || vertex_index == 4) {
            // bottom left
            pos = vec2(a_topleft.x, a_bottomright.y);
        } else {
            // bottom right
            pos = a_bottomright;
        }

        v_color = vec3(
            float(int(a_topleft.x) * 908125 % 255) / 255.0, 
            float(int(a_topleft.y) * 257722 % 255) / 255.0, 
            float(int(a_bottomright.y) * 826586 % 255) / 255.0
            );

        vec2 screen01 = (pos * u_scale + u_translation) / u_res;
        vec2 screen02 = screen01 * 2.0;
        screen02.y = 2.0 - screen02.y;
        vec2 screen11 = screen02 - 1.0;
        gl_Position = vec4(screen11, 0.0, 1.0);
    }
`;

const iquad_fs_src = `#version 300 es
    precision highp float;

    layout(location = 0) out vec4 FragColor;

    in vec3 v_color;

    void main() {
        FragColor = vec4(v_color, 0.5);
    }
`;

function init_webgl(state, context) {
    context.canvas = document.querySelector('#c');
    context.gl = context.canvas.getContext('webgl2', {
        'preserveDrawingBuffer': true,
        'desynchronized': true,
        'antialias': false,
    });

    const gl = context.gl;

    gl.enable(gl.BLEND);
    gl.blendFunc(gl.ONE, gl.ONE_MINUS_SRC_ALPHA);
    //gl.blendEquation(gl.MAX);

    //gl.enable(gl.DEPTH_TEST);
    //gl.depthFunc(gl.GEQUAL);

    context.gpu_timer_ext = gl.getExtension('EXT_disjoint_timer_query_webgl2');
    if (context.gpu_timer_ext === null) {
        context.gpu_timer_ext = gl.getExtension('EXT_disjoint_timer_query');
    }
    
    const quad_vs = create_shader(gl, gl.VERTEX_SHADER, tquad_vs_src);
    const quad_fs = create_shader(gl, gl.FRAGMENT_SHADER, tquad_fs_src);

    const sdf_vs = create_shader(gl, gl.VERTEX_SHADER, sdf_vs_src);
    const sdf_fs = create_shader(gl, gl.FRAGMENT_SHADER, sdf_fs_src);

    const dots_vs = create_shader(gl, gl.VERTEX_SHADER, dots_vs_src);
    const dots_fs = create_shader(gl, gl.FRAGMENT_SHADER, dots_fs_src);

    const grid_vs = create_shader(gl, gl.VERTEX_SHADER, grid_vs_src);

    const iquad_vs = create_shader(gl, gl.VERTEX_SHADER, iquad_vs_src);
    const iquad_fs = create_shader(gl, gl.FRAGMENT_SHADER, iquad_fs_src);

    context.programs = {
        'image': create_program(gl, quad_vs, quad_fs),
        'main': create_program(gl, sdf_vs, sdf_fs),
        'dots': create_program(gl, dots_vs, dots_fs),
        'grid': create_program(gl, grid_vs, dots_fs),
        'iquad': create_program(gl, iquad_vs, iquad_fs),
    };

    context.buffers = {
        'b_images': gl.createBuffer(),
        'b_strokes_static': gl.createBuffer(),
        'b_strokes_dynamic': gl.createBuffer(),
        'b_instance_dot': gl.createBuffer(),
        'b_instance_grid': gl.createBuffer(),
        'b_dot':      gl.createBuffer(),
        'b_hud':      gl.createBuffer(),
        'b_iquads':   gl.createBuffer(),
    };

    context.textures = {
        'stroke_data': gl.createTexture(),
        'dynamic_stroke_data': gl.createTexture(),
        'ui': gl.createTexture(),
    };

    gl.bindTexture(gl.TEXTURE_2D, context.textures['stroke_data']);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.NEAREST);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.NEAREST);
    gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA16UI, config.stroke_texture_size, config.stroke_texture_size, 0, gl.RGBA_INTEGER, gl.UNSIGNED_SHORT, new Uint16Array(config.stroke_texture_size * config.stroke_texture_size * 4)); // fill the whole texture once with zeroes to kill a warning about a partial upload

    gl.bindTexture(gl.TEXTURE_2D, context.textures['dynamic_stroke_data']);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.NEAREST);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.NEAREST);
    gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA16UI, config.dynamic_stroke_texture_size, config.dynamic_stroke_texture_size, 0, gl.RGBA_INTEGER, gl.UNSIGNED_SHORT, new Uint16Array(config.dynamic_stroke_texture_size * config.dynamic_stroke_texture_size * 4)); // fill the whole texture once with zeroes to kill a warning about a partial upload

    gl.bindTexture(gl.TEXTURE_2D, context.textures['ui']);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.NEAREST);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.NEAREST);
    gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA16UI, config.ui_texture_size, config.ui_texture_size, 0, gl.RGBA_INTEGER, gl.UNSIGNED_SHORT, new Uint16Array(config.ui_texture_size * config.ui_texture_size * 4)); // fill the whole texture once with zeroes to kill a warning about a partial upload

    const resize_canvas = (entries) => {
        // https://www.khronos.org/webgl/wiki/HandlingHighDPI
        const entry = entries[0];

        let width;
        let height;

        if (entry.devicePixelContentBoxSize) {
            width = entry.devicePixelContentBoxSize[0].inlineSize;
            height = entry.devicePixelContentBoxSize[0].blockSize;
        } else if (entry.contentBoxSize) {
            // fallback for Safari that will not always be correct
            width = Math.round(entry.contentBoxSize[0].inlineSize * devicePixelRatio);
            height = Math.round(entry.contentBoxSize[0].blockSize * devicePixelRatio);
        }

        context.canvas.width = width;
        context.canvas.height = height;

        schedule_draw(state, context);
    }

    const resize_observer = new ResizeObserver(resize_canvas);
    resize_observer.observe(context.canvas);
}

function create_shader(gl, type, source) {
    const shader = gl.createShader(type);

    gl.shaderSource(shader, source);
    gl.compileShader(shader);
    
    if (gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
        return shader;
    }
     
    console.error(type, ':', gl.getShaderInfoLog(shader));

    gl.deleteShader(shader);
}

function create_program(gl, vs, fs) {
    const program = gl.createProgram();

    gl.attachShader(program, vs);
    gl.attachShader(program, fs);
    gl.linkProgram(program);

    if (gl.getProgramParameter(program, gl.LINK_STATUS)) {
        // src: tiny-sdf
        // https://github.com/mapbox/tiny-sdf
        const wrapper = {program};
        const num_attrs = gl.getProgramParameter(program, gl.ACTIVE_ATTRIBUTES);
        const num_uniforms = gl.getProgramParameter(program, gl.ACTIVE_UNIFORMS);

        wrapper.locations = {};

        for (let i = 0; i < num_attrs; i++) {
            const attribute = gl.getActiveAttrib(program, i);
            wrapper.locations[attribute.name] = gl.getAttribLocation(program, attribute.name);
        }

        for (let i = 0; i < num_uniforms; i++) {
            const uniform = gl.getActiveUniform(program, i);
            wrapper.locations[uniform.name] = gl.getUniformLocation(program, uniform.name);
        }

        return wrapper;
    }
    console.error('link:', gl.getProgramInfoLog(program));

    gl.deleteProgram(program);
}