/** Skybox cube for rendering the sky */
export class Skybox {
    private vao: WebGLVertexArrayObject | null = null;
    private vbo: WebGLBuffer | null = null;
    private indexCount: number = 0;

    constructor() {}

    initVAO(gl: WebGL2RenderingContext): void {
        // Cube vertices - positions only
        const vertices = new Float32Array([
            // Front face
            -1, -1,  1,
             1, -1,  1,
             1,  1,  1,
            -1,  1,  1,
            // Back face
            -1, -1, -1,
            -1,  1, -1,
             1,  1, -1,
             1, -1, -1,
            // Top face
            -1,  1, -1,
            -1,  1,  1,
             1,  1,  1,
             1,  1, -1,
            // Bottom face
            -1, -1, -1,
             1, -1, -1,
             1, -1,  1,
            -1, -1,  1,
            // Right face
             1, -1, -1,
             1,  1, -1,
             1,  1,  1,
             1, -1,  1,
            // Left face
            -1, -1, -1,
            -1, -1,  1,
            -1,  1,  1,
            -1,  1, -1,
        ]);

        const indices = new Uint16Array([
            0,  2,  1,    0,  3,  2,   // front
            4,  6,  5,    4,  7,  6,   // back
            8,  10, 9,    8,  11, 10,  // top
            12, 14, 13,   12, 15, 14,  // bottom
            16, 18, 17,   16, 19, 18,  // right
            20, 22, 21,   20, 23, 22,  // left
        ]);

        this.indexCount = indices.length;

        this.vao = gl.createVertexArray();
        gl.bindVertexArray(this.vao);

        this.vbo = gl.createBuffer();
        gl.bindBuffer(gl.ARRAY_BUFFER, this.vbo);
        gl.bufferData(gl.ARRAY_BUFFER, vertices, gl.STATIC_DRAW);

        const ibo = gl.createBuffer();
        gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, ibo);
        gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, indices, gl.STATIC_DRAW);

        // Position attribute
        gl.enableVertexAttribArray(0);
        gl.vertexAttribPointer(0, 3, gl.FLOAT, false, 0, 0);

        gl.bindVertexArray(null);
    }

    draw(gl: WebGL2RenderingContext): void {
        if (!this.vao) return;
        
        gl.bindVertexArray(this.vao);
        gl.drawElements(gl.TRIANGLES, this.indexCount, gl.UNSIGNED_SHORT, 0);
        gl.bindVertexArray(null);
    }
}