<?php

namespace App\Service;

use JumPHP\Kernel\Engine;

/**
 * The glow of the whole picture: a post-processing shader (OpenGL on the desktop, WebGL in the browser) that makes
 * what is bright bleed light around it (flames, halos, the exit, lava), with a soft colour grade. Option "bloom", off by default: it also makes texts and buttons bleed.
 * Without a GL context (headless tests) nothing happens: the game looks the same, without the bloom.
 */
final class Effects
{
    private const BLOOM = <<<'GLSL'
        vec3 glow(vec2 uv) {
            vec3 c = texture2D(u_frame, uv).rgb;
            float l = max(c.r, max(c.g, c.b));
            return c * smoothstep(0.55, 1.0, l);
        }
        void main() {
            vec2 px = 1.0 / u_resolution;
            float s = max(1.0, u_viewport.z / max(1.0, u_view.x));
            vec3 c = texture2D(u_frame, v_uv).rgb;
            vec3 b = vec3(0.0);
            for (int i = 0; i < 8; i++) {
                float a = 0.7854 * float(i);
                vec2 d = vec2(cos(a), sin(a)) * px * s;
                b += glow(v_uv + d * 1.6) * 0.9 + glow(v_uv + d * 3.6) * 0.6 + glow(v_uv + d * 6.5) * 0.35;
            }
            c += b * 0.055;
            c = mix(c, c * c * (3.0 - 2.0 * c), 0.25);
            gl_FragColor = vec4(c, 1.0);
        }
        GLSL;

    private ?bool $on = null;

    public function isOn(Engine $engine): bool
    {
        return (bool)$engine->options->get('bloom', false);
    }

    public function available(Engine $engine): bool
    {
        return $engine->gl()->isAvailable();
    }

    /** Puts the shader on or off as the option says (call from enter()). */
    public function apply(Engine $engine): void
    {
        $want = $this->isOn($engine) && $this->available($engine);
        if ($this->on === $want) {
            return;
        }
        $this->on = $want;
        $engine->gl()->setPostShader($want ? self::BLOOM : null);
    }

    public function toggle(Engine $engine): void
    {
        $engine->options->set('bloom', !$this->isOn($engine));
        $this->apply($engine);
    }
}