shader_type canvas_item;

uniform float fill : hint_range(0.0, 1.0) = 0.0;

uniform vec4 liquid_color : source_color = vec4(0.2, 0.5, 0.8, 1.0);
uniform vec4 bg_color : source_color = vec4(0.08, 0.08, 0.12, 1.0);
uniform vec4 border_color : source_color = vec4(0.2, 0.2, 0.28, 1.0);

uniform float corner_radius : hint_range(0.0, 0.5) = 0.06;
uniform float border_width : hint_range(0.0, 0.1) = 0.008;

uniform float wave_amp : hint_range(0.0, 0.05) = 0.012;
uniform float wave_freq : hint_range(0.0, 15.0) = 4.0;


float rr_sdf(vec2 p, vec2 half_size, float r) {
	vec2 d = abs(p) - half_size + r;
	return min(max(d.x, d.y), 0.0) + length(max(d, 0.0)) - r;
}


void fragment() {
	vec2 half_size = vec2(0.5, 0.5);
	vec2 uv_centered = UV - half_size;

	float max_r = min(corner_radius, half_size.x);

	// Outer rounded rect
	float outer_d = rr_sdf(uv_centered, half_size, max_r);
	float outer = 1.0 - smoothstep(0.0, max(0.001, fwidth(outer_d)), max(outer_d, 0.0));

	// Inner (inset by border_width)
	float inner_r = max(0.0, max_r - border_width);
	float inner_hw = max(0.0, half_size.x - border_width);
	float inner_hh = max(0.0, half_size.y - border_width);
	float inner_d = rr_sdf(uv_centered, vec2(inner_hw, inner_hh), inner_r);
	float inner = 1.0 - smoothstep(0.0, max(0.001, fwidth(inner_d)), max(inner_d, 0.0));

	// Liquid fill with a gentle animated wave at the surface.
	// UV.y = 0 is top, UV.y = 1 is bottom. fill = 0 → empty, fill = 1 → full.
	float wave = sin(UV.x * wave_freq * 6.283 + TIME * 1.5) * wave_amp;
	float fill_line = 1.0 - fill + wave;
	float liquid = smoothstep(fill_line - 0.001, fill_line + 0.001, UV.y);
	liquid *= inner;

	// Base background
	vec3 col = bg_color.rgb;

	// Liquid with subtle depth gradient
	vec3 liq = mix(liquid_color.rgb, liquid_color.rgb * 1.35, 1.0 - UV.y);
	col = mix(col, liq, liquid);

	// Surface highlight line at the top of the liquid column
	float surface = smoothstep(fill_line - 0.008, fill_line, UV.y) - smoothstep(fill_line, fill_line + 0.002, UV.y);
	col += surface * vec3(0.3, 0.4, 0.5) * liquid;

	// Border
	col = mix(col, border_color.rgb, outer - inner);

	COLOR = vec4(col, outer);
}