shader_type canvas_item;

uniform sampler2D screen_texture : hint_screen_texture;
uniform float damage_amount : hint_range(0.0, 1.0) = 0.0;
uniform float noise_strength : hint_range(0.0, 1.0) = 0.3;
uniform float pulse_strength : hint_range(0.0, 1.0) = 0.2;
uniform float time;

// TODO: uniform vec2 player_uv; // use this to calculate player offset to camera

float random(vec2 uv) {
    return fract(sin(dot(uv.xy ,vec2(12.9898,78.233))) * 43758.5453);
}

void fragment() {
    // Distance from screen center
    vec2 center = vec2(0.5, 0.5);
    float dist = distance(SCREEN_UV, center);
    float edge_factor = smoothstep(0.4, 0.7, dist); // stronger at edges
	float edge_factor_gray = smoothstep(0.0, 1.0-damage_amount, dist);

    // Noise flicker
    float n = random(SCREEN_UV * 200.0 + time * 2.0); 
    float noise = (n - 0.5) * noise_strength;

    // Pulsing intensity
    float pulse = sin(time * 5.0) * pulse_strength;

    // Final intensity
    float final_amount = damage_amount * edge_factor + noise + pulse;
    final_amount = clamp(final_amount, 0.0, 1.0);
	
	vec4 base = texture(screen_texture, SCREEN_UV);
	float gray = dot(base.rgb, vec3(0.299, 0.587, 0.114));
	base.rgb = mix(base.rgb, vec3(gray), edge_factor_gray * damage_amount);
	
    vec4 red_tint = vec4(1.0, 0.0, 0.0, 1.0);
    COLOR = mix(base, red_tint, final_amount);
}