shader_type spatial;
render_mode blend_mix, depth_draw_never, cull_disabled;

// Snow globals
global uniform float global_snow_start_time;
global uniform float global_snow_accumulation_speed;
global uniform float global_snow_melt_time;
global uniform float global_snow_melt_speed;
global uniform vec4  global_snow_color;

// Rain globals
global uniform float global_rain_intensity;

// Snow parameters
uniform float snow_edge_softness : hint_range(0.01, 0.5) = 0.15;
uniform float snow_color_variation : hint_range(0.0, 0.15) = 0.05;

// Rain wetness parameters
uniform float wetness_darkening : hint_range(0.0, 0.5) = 0.25;
uniform float wet_roughness : hint_range(0.0, 0.3) = 0.05;

void fragment() {
    // Snow accumulation
    float snow_amount = 0.0;
    if (global_snow_start_time >= 0.0) {
        snow_amount = clamp((TIME - global_snow_start_time) * global_snow_accumulation_speed, 0.0, 1.0);
    }
    if (global_snow_melt_time >= 0.0) {
        float melt = clamp((TIME - global_snow_melt_time) * global_snow_melt_speed, 0.0, 1.0);
        snow_amount *= (1.0 - melt);
    }

    // UV-based snow mask: accumulates from the top of the quad
    float top_mask = 1.0 - UV.y;
    float snow_mask = smoothstep(1.0 - snow_amount, 1.0 - snow_amount + snow_edge_softness, top_mask);
    snow_mask *= step(0.01, snow_amount);

    // Snow color with slight variation
    float shade = fract(sin(dot(UV, vec2(12.9898, 78.233))) * 43758.5453);
    shade = mix(-snow_color_variation, snow_color_variation, shade);
    vec3 snow_albedo = clamp(global_snow_color.rgb + vec3(shade), 0.0, 1.0);

    // Rain wetness
    float rain_int = clamp(global_rain_intensity, 0.0, 1.0);
    float rain_factor = wetness_darkening * rain_int;

    // Combine: snow takes priority over rain
    if (snow_mask > rain_factor) {
        ALBEDO = snow_albedo;
        ROUGHNESS = 0.15;
        METALLIC = 0.0;
        ALPHA = snow_mask;
    } else if (rain_int > 0.01) {
        ALBEDO = vec3(0.0);
        ROUGHNESS = wet_roughness;
        METALLIC = 0.0;
        ALPHA = rain_factor;
    } else {
        ALPHA = 0.0;
    }
}