document.addEventListener('DOMContentLoaded', main);

function draw(state, context) {
    const gl = context.gl;
    const locations = context.locations;
    const buffers = context.buffers;
    const width = window.innerWidth;
    const height = window.innerHeight;

    gl.viewport(0, 0, context.canvas.width, context.canvas.height);
    gl.clearColor(context.bgcolor.r, context.bgcolor.g, context.bgcolor.b, 1);
    gl.clear(gl.COLOR_BUFFER_BIT);
    gl.useProgram(context.program);
    
    gl.enableVertexAttribArray(locations['a_pos']);
    gl.enableVertexAttribArray(locations['a_color']);

    gl.uniform2f(locations['u_res'], context.canvas.width, context.canvas.height);
    gl.uniform2f(locations['u_scale'], state.canvas.zoom, state.canvas.zoom);
    gl.uniform2f(locations['u_translation'], state.canvas.offset.x, state.canvas.offset.y);
    gl.uniform1i(locations['u_layer'], 0);

    const total_pos_size = context.static_positions_f32.byteLength + context.dynamic_positions_f32.byteLength;
    const total_color_size = context.static_colors_u8.byteLength + context.dynamic_colors_u8.byteLength; 
    const total_point_count = (context.static_positions.length + context.dynamic_positions.length) / 2;

    gl.bindBuffer(gl.ARRAY_BUFFER, buffers['b_pos']);
    gl.vertexAttribPointer(locations['a_pos'], 2, gl.FLOAT, false, 0, 0);
    gl.bufferData(gl.ARRAY_BUFFER, total_pos_size, gl.DYNAMIC_DRAW);
    gl.bufferSubData(gl.ARRAY_BUFFER, 0, context.static_positions_f32);
    gl.bufferSubData(gl.ARRAY_BUFFER, context.static_positions_f32.byteLength, context.dynamic_positions_f32);

    gl.bindBuffer(gl.ARRAY_BUFFER, buffers['b_color']);
    gl.vertexAttribPointer(locations['a_color'], 3, gl.UNSIGNED_BYTE, true, 0, 0);
    gl.bufferData(gl.ARRAY_BUFFER, total_color_size, gl.DYNAMIC_DRAW);
    gl.bufferSubData(gl.ARRAY_BUFFER, 0, context.static_colors_u8);
    gl.bufferSubData(gl.ARRAY_BUFFER, context.static_colors_u8.byteLength, context.dynamic_colors_u8);    

    gl.drawArrays(gl.TRIANGLES, 0, total_point_count);
}

function main() {
    const state = {
        'canvas': {
            'offset': { 'x': 0, 'y': 0 },
            'zoom': 1.0,
        },

        'cursor': {
            'x': 0,
            'y': 0,
        },

        'moving': false,
        'drawing': false,
        'spacedown': false,
        
        'stroke_width': 8,

        'current_stroke': {
            'color': 0,
            'points': [],
        },

        'strokes': [],
    };

    const context = {
        'canvas': null,
        'gl': null,
        'program': null,
        'buffers': {},
        'locations': {},
        'static_positions': [],
        'dynamic_positions': [],
        'static_colors': [],
        'dynamic_colors': [],
        'static_positions_f32': new Float32Array(0),
        'dynamic_positions_f32': new Float32Array(0),
        'static_colors_u8': new Uint8Array(0),
        'dynamic_colors_u8': new Uint8Array(0),
        'bgcolor': {'r': 0, 'g': 0, 'b': 0},
    };

    init_webgl(state, context);
    init_listeners(state, context);

    window.requestAnimationFrame(() => draw(state, context));
}