#include "common_uniforms"

@group(0) @binding(0) var sky_tex: texture_2d<f32>;
@group(0) @binding(1) var sky_sampler: sampler;
@group(0) @binding(2) var<uniform> globals: GlobalUniforms;

struct VertexOutput {
    @builtin(position) position: vec4<f32>,
    @location(0) uv: vec2<f32>,
};

@vertex
fn vs_main(@builtin(vertex_index) vertex_index: u32) -> VertexOutput {
    var pos = array<vec2<f32>, 3>(
        vec2<f32>(-1.0, -1.0),
        vec2<f32>( 3.0, -1.0),
        vec2<f32>(-1.0,  3.0)
    );
    
    var out: VertexOutput;
    out.position = vec4<f32>(pos[vertex_index], 0.0, 1.0);
    out.uv = vec2<f32>(pos[vertex_index].x * 0.5 + 0.5, 1.0 - (pos[vertex_index].y * 0.5 + 0.5));
    return out;
}

@fragment
fn fs_main(in: VertexOutput) -> @location(0) vec4<f32> {
    // Convert UV to NDC
    let ndc_x = in.uv.x * 2.0 - 1.0;
    let ndc_y = (1.0 - in.uv.y) * 2.0 - 1.0; // Un-flip Y for NDC (Y-up)
    
    // Unproject to find world direction
    // We want the direction from camera to the far plane at this pixel
    let clip_pos = vec4<f32>(ndc_x, ndc_y, 1.0, 1.0);
    let world_pos_h = globals.inv_view_proj * clip_pos;
    let world_pos = world_pos_h.xyz / world_pos_h.w;
    
    let ray_dir = normalize(world_pos - globals.camera_pos_time.xyz);
    
    // Spherical Mapping
    let u = atan2(ray_dir.z, ray_dir.x) / 6.28318 + 0.5;
    let v = asin(clamp(ray_dir.y, -1.0, 1.0)) / 3.14159 + 0.5;
    
    return textureSample(sky_tex, sky_sampler, vec2<f32>(u, v));
}