// Liquid (lake/river/ocean) shader — a port of the reference's `ocean0_s.bls` path to WGSL.
// RE: docs/knowledge/terrain.md "Liquid" (WoW.exe + ocean0_s.bls + apitrace WoW.17 prog 159).
//
// Ground truth from the live draw (apitrace WoW.17 program 159, ocean0_s.bls) + WoW.exe RE:
//
//   result.rgb = primary*colorTex.rgb + detailTex.rgb + (secondary + 0.25)*detailTex.a
//   result.a   = colorTex.a
//
// where (VERIFIED from the trace's bound textures + uniforms + the binary's depth ramp):
//   * colorTex (unit 0) is the 8×64 depth swatch built by WoW.exe `FUN_0068a830` — a plain **2-endpoint
//     linear lerp** of the zone's dedicated `Light.dbc` water rows, RAW (no ×0.711): `water_shallow.rgb`
//     = IntBand row 16 (river/lake) / 14 (ocean), `water_deep.rgb` = row 17 / 15. Golden-vector-matched
//     to the apitrace swatch ≤1/255 over all 64 rows. (The earlier "reflected sky × 0.711 via
//     `FUN_0068c250`" model fingered the WRONG builder — that fills a separate symmetric grey edge
//     texture, tex 432, never bound on the water unit. Rows 14–17 were right all along.)
//   * detailTex (unit 1) is the animated `lake_a`/`ocean_h` frame: RGB near-black (≈0.014), ALPHA =
//     the ripple. So it adds a faint flat lift + an achromatic shimmer on the crests — NOT the body.
//   * primary = the vertex's lit colour `clamp(ambient + N·L·sun)`. secondary = the specular sheen; P1
//     keeps it + the verified +0.25 constant.
//   * alpha = swatch.a = `mix(water_shallow.w, water_deep.w, V)` over the SAME V as the colour (VERIFIED
//     `WoW.exe FUN_0068a830` α = `127+2·row`, apitrace-confirmed). LightParams endpoints: river 0.5→1.0,
//     ocean 0.75→1.0. Deeper water = more opaque.
//
// A SINGLE swatch row (V) indexes both the colour and the alpha — they track together. V is `clamp(byte/42)`
// for river/lake (VERIFIED `c81768`, saturates ~5 yd → the channel middle hits the deep teal row) and
// byte/255 for ocean (placeholder; ocean uses a non-LUT UV path). (Earlier cuts: ripple-as-colour → black;
// ×8 over-saturated; FLAT colour killed the gradient; sky×0.711 was the wrong builder; `byte/255` was the
// wrong LUT → river middle never went teal. Corrected to rows 14–17 raw lerp + the /42 V, 2026-05-31.)
//
// Two-sided comes from the material (cull off) and is right for EVERY kind: all four reference liquid
// passes force GL_CULL_FACE off at pass entry against a cull-ON device baseline, and `glFrontFace` is
// not even imported (VERIFIED wow-re `liquid-render-state-sided` §6). Blending is per KIND, decided in
// liquid.rs: water/ocean blend with depth-write off; magma/slime are opaque and depth-write. Fog + gamma
// mirror terrain.wgsl (planar eye-Z GL_LINEAR fog in gamma space; raw gamma out — GAMMA LANE, 0161), fog
// applies to every kind — magma and slime included — and WHICH fog block a surface takes is per-surface:
// a WMO interior group's own pool fogs with the interior block, everything else with the scene block
// (see `apply_fog`). Light, fog and both water swatches all come off the ONE shared global-light buffer.

#import bevy_pbr::{
    mesh_functions,
    forward_io::Vertex,
    view_transformations::position_world_to_clip,
    mesh_view_bindings::view,
}

@group(#{MATERIAL_BIND_GROUP}) @binding(100) var frames: texture_2d_array<f32>;
@group(#{MATERIAL_BIND_GROUP}) @binding(101) var frames_samp: sampler;

struct LiquidParams {
    // x = fullbright (magma/slime); y = ocean swatch; z = interior fog; w = sun-sheen shininess.
    kind: vec4<f32>,
    anim: vec4<f32>,          // x = current frame index; y = frame count; zw unused
};
@group(#{MATERIAL_BIND_GROUP}) @binding(102) var<uniform> w: LiquidParams;

// The shared global light (`lighting::global_light`) — the SAME buffer terrain and the models read,
// mirrored here as its canonical row prefix. Liquid used to carry its own copy of every one of these
// values, re-pushed per material by `apply_wow_lighting`; that copy is what left it with only the
// scene fog and no way to see the interior block (decision 0691).
struct WowLight {
    light_ambient: vec4<f32>,      // 0  rgb = ambient; w = Mod2x scale
    light_diffuse: vec4<f32>,      // 1  rgb = sun diffuse; w = clamp flag
    light_sun: vec4<f32>,          // 2  xyz = sun TRAVEL dir (to-light = −xyz)
    light_spec: vec4<f32>,         // 3  rgb = row-9 specular colour; w = TERRAIN shininess (liquid uses w.kind.w)
    fog_color: vec4<f32>,          // 4  rgb = scene fog (block 1, gamma 0..1); w = enable (>0.5)
    fog_params: vec4<f32>,         // 5  x = start yd; y = end yd; w = the farclip wall
    _sh: array<vec4<f32>, 6>,      // 6-11  model SH coeffs — unread here
    _sh_c16: vec4<f32>,            // 12
    water_river: array<vec4<f32>, 2>, // 13-14 shallow/deep river-lake swatch (IntBand 16/17); w = alpha
    water_ocean: array<vec4<f32>, 2>, // 15-16 shallow/deep ocean swatch    (IntBand 14/15); w = alpha
    _grade: vec4<f32>,             // 17
    wmo_fog_color: vec4<f32>,      // 18 rgb = INTERIOR fog (block 2); w = enable
    wmo_fog_params: vec4<f32>,     // 19 x = start yd; y = end yd
};
@group(#{MATERIAL_BIND_GROUP}) @binding(90) var<storage, read> wow_light: WowLight;

struct LiquidVsOut {
    @builtin(position) clip_position: vec4<f32>,
    @location(0) world_position: vec4<f32>,
    @location(1) world_normal: vec3<f32>,
    @location(2) uv: vec2<f32>,
    @location(3) depth: f32,
    // The sun-sheen `secondary` evaluated PER-VERTEX (the faithful 1.12 path: the real client computes
    // the Blinn highlight in its FFP vertex shader and interpolates it across the coarse water mesh).
    // The fragment shader uses this interpolated value directly.
    @location(4) secondary_vtx: vec3<f32>,
}

// Sun sheen (`secondary`): a Blinn highlight of the sun on the flat water surface — the glint that's
// strongest at grazing (sunrise/sunset) sun. `secondary = light_spec.rgb · (N·H)^shininess`. Shared by
// both stages so the per-vertex (faithful) and per-pixel (current) paths run IDENTICAL math — only the
// EVALUATION DOMAIN differs (interpolated vs evaluated per fragment).
fn sun_sheen(world_normal: vec3<f32>, world_pos: vec3<f32>) -> vec3<f32> {
    let n = normalize(world_normal);
    let to_light = -normalize(wow_light.light_sun.xyz);
    let to_view = normalize(view.world_position.xyz - world_pos);
    let half_v = normalize(to_light + to_view);
    let ndoth = max(dot(n, half_v), 0.0);
    // Shininess is WATER's own (`w.kind.w`), not the shared row-3 terrain exponent.
    return wow_light.light_spec.rgb * pow(ndoth, max(w.kind.w, 1.0));
}

// Distance fog — planar eye-Z, GL_LINEAR, gamma space (mirrors terrain.wgsl). Applied to EVERY liquid
// kind, because the reference never disables fog for a liquid batch: the device default for GL_FOG is
// **ON** (`0x593bf0` writes state id `0x0f` = 1) and all 42 fog-enable setters in the binary are
// Push/Pop-scoped, so what a batch inherits at its draw is that default. The ADT lava pass sets only
// cull/lighting/blend (`0x6855ca`/`0x6855d6`/`0x6855e2`) and the WMO magma/slime arm sets only lighting
// (`0x6b6afe`) — neither touches fog — while the WMO *river* arm goes out of its way to re-assert
// `(0x0f, 1)`, which only makes sense in a world where fog-on is liquid's intended state. (VERIFIED
// wow-re `liquid-render-state-sided` §1–§3, §5.)
//
// WHICH fog is a per-surface choice, and it is the reference's own (VERIFIED wow-re `fog-env-state`
// §5, the complete 6-site submit census). The device holds two fog blocks: **block 1** (`+0x70/74/78`)
// is the scene fog, submitted once a frame from `WorldFrame::Render` (`0x66ff20`), and **block 2**
// (`+0x80/84/88`) is block 1 smoothed toward the MFOG/zone target over ~4 s (`0x6cf054`+) — the
// interior haze. Only two call sites in the whole binary re-submit block 2, and they are the WMO
// *geometry* pass (`0x6b51d9`/`0x6b51ea`) and the WMO *liquid* pass (`0x6b6323`–`0x6b6342`), both under
// the same `[0xca7f00]` gate. So an interior room's pool takes the room's fog, in lockstep with the
// walls around it; ADT liquid submits nothing and draws under the scene block. `w.kind.z` is that
// gate, resolved at spawn from the group's `MOGI & 0x48` — the same interior test `wow_model.wgsl`
// uses, which is what keeps the two in step.
fn apply_fog(rgb: vec3<f32>, world_pos: vec3<f32>) -> vec3<f32> {
    var fog_color = wow_light.fog_color;
    var fog_span = wow_light.fog_params.xy;
    if (w.kind.z > 0.5) {
        fog_color = wow_light.wmo_fog_color;
        fog_span = wow_light.wmo_fog_params.xy;
    }
    if (fog_color.w <= 0.5) {
        return rgb;
    }
    let eye_z = -(view.view_from_world * vec4<f32>(world_pos, 1.0)).z;
    let denom = max(fog_span.y - fog_span.x, 0.001);
    let factor = clamp((fog_span.y - eye_z) / denom, 0.0, 1.0);
    return mix(fog_color.xyz, rgb, factor);
}

@vertex
fn vertex(in: Vertex) -> LiquidVsOut {
    var out: LiquidVsOut;
    let world_from_local = mesh_functions::get_world_from_local(in.instance_index);
    out.world_position =
        mesh_functions::mesh_position_local_to_world(world_from_local, vec4<f32>(in.position, 1.0));
    out.clip_position = position_world_to_clip(out.world_position.xyz);
    out.world_normal = mesh_functions::mesh_normal_local_to_world(in.normal, in.instance_index);
    out.uv = in.uv;
    // Per-vertex MCLQ depth (0..1) packed into UV1.x; drives the opacity ramp.
    out.depth = in.uv_b.x;
    // The faithful per-vertex sun sheen — interpolated across the coarse mesh by the fragment stage.
    out.secondary_vtx = sun_sheen(out.world_normal, out.world_position.xyz);
    return out;
}

@fragment
fn fragment(in: LiquidVsOut) -> @location(0) vec4<f32> {
    // HARD FAR-CLIP WALL (same as terrain/models, see terrain.wgsl): discard water beyond the
    // projection far plane so lakes/rivers don't render past the wall. `fog_params.w` = farclip
    // (0 ⇒ disabled).
    if (wow_light.fog_params.w > 0.0) {
        let clip_z = -(view.view_from_world * vec4<f32>(in.world_position.xyz, 1.0)).z;
        if (clip_z > wow_light.fog_params.w) {
            discard;
        }
    }

    // Animated frame. For water/ocean this is the DETAIL ripple (RGB ≈ near-black, ALPHA = ripple);
    // for magma/slime it is the OPAQUE BODY texture.
    let detail = textureSample(frames, frames_samp, in.uv, i32(round(w.anim.x)));

    // Magma / slime (kind.x > 0.5): the animated texture IS the opaque body colour — no depth swatch
    // (the ADT liquid vertex format carries no colour element at all, and the WMO one is a hard
    // `0xffffffff`, so there is nothing to modulate the sheet by) and no N·L (lighting state 0 on both
    // paths). It IS fogged, like every other liquid batch.
    //
    // The earlier "emissive / no-darken / no fog" reading here was WRONG, and wrong twice over: it came
    // from the ADT-lava row of `rf-water-liquid-type-texture-material`, which read GX state `0x37` as an
    // emissive path when `0x37` is the per-stage TEXTURE-MATRIX enable pushing an identity — a texgen
    // *reset*; and that row is the ADT queue, which never dispatches slime at all (Undercity's slime is
    // WMO liquid). Skipping fog is what made a submerged slime surface a flat unshaded sheet at any
    // depth instead of one that recedes into the murk. (VERIFIED wow-re `liquid-render-state-sided`
    // §3/§3.1/§5, which corrects that row.)
    if (w.kind.x > 0.5) {
        return vec4<f32>(apply_fog(detail.rgb, in.world_position.xyz), 1.0);
    }

    // Per-vertex swatch coord V (in `in.depth`, computed CPU-side in wow-formats/liquid.rs): river/lake
    // = `clamp(byte/42)` (VERIFIED WoW.exe `c81768` LUT / `FUN_0068d790`, saturating ~5 yd so the channel
    // middle reaches the deep/teal row), ocean = byte/255 (placeholder, different path). The depth swatch
    // is a plain 2-endpoint lerp (`FUN_0068a830`), so a SINGLE V indexes BOTH the colour and the alpha
    // row: colour `shallow→deep` and opacity `shallow_α→deep_α` track together. (Earlier `×4` colour
    // compression + the gentle `byte/255` V were band-aids for a wrong "V tops at 0.31" belief — removed.)
    let depth = clamp(in.depth, 0.0, 1.0);
    // The kind's swatch endpoints, off the shared light: ocean reads rows 15/16 (IntBand 14/15),
    // river/lake rows 13/14 (IntBand 16/17). Both are packed every frame by `build_light_data`.
    var shallow = wow_light.water_river[0];
    var deep = wow_light.water_river[1];
    if (w.kind.y > 0.5) {
        shallow = wow_light.water_ocean[0];
        deep = wow_light.water_ocean[1];
    }
    let water_tint = mix(shallow.rgb, deep.rgb, depth);

    // Body colour: lit vertex colour × the depth-lerped water-row swatch colour (`primary·colorTex`).
    let n = normalize(in.world_normal);
    let to_light = -normalize(wow_light.light_sun.xyz);
    let ndotl = max(dot(n, to_light), 0.0);
    let primary = clamp(
        wow_light.light_ambient.rgb + wow_light.light_diffuse.rgb * ndotl,
        vec3<f32>(0.0),
        vec3<f32>(1.0),
    );

    // Sun sheen (`secondary`): the `ocean0_s.bls` Blinn highlight, computed PER-VERTEX in `fn vertex`
    // and interpolated across the coarse ~4 yd MCLQ mesh — the faithful 1.12 path (the real client
    // evaluates it in its FFP vertex stage). Per-pixel evaluation of the sharply-peaked `pow(N·H,6)`
    // would fill its broad lobe at full value (a brighter, denser sheen); interpolating from the
    // vertices flattens the peak to match the reference. (A per-pixel/per-vertex A/B toggle proved the
    // two visually identical on our mesh — we keep per-vertex as the faithful mechanism; RE:
    // `docs/knowledge/scratch/liquid-depth/fleck-deep.md`.)
    let secondary = in.secondary_vtx;

    // primary·colorTex.rgb  +  detail.rgb  +  (secondary + 0.25)·detail.a   (the ocean0_s.bls math)
    var rgb = primary * water_tint + detail.rgb + (secondary + vec3<f32>(0.25)) * detail.a;

    // Opacity: depth ramp between the shallow/deep LightParams water alphas, over the SAME V as the
    // colour. Deeper = more opaque, up to α=1.0 where V saturates (river/lake byte 42 ≈ 5 yd), so the
    // channel middle is opaque + teal while the shore stays semi-transparent (V→0, α≈0.5) and the bottom
    // shows through (faithful — the pale edge band). One steep V drives both colour and opacity together.
    let alpha = mix(shallow.w, deep.w, depth);

    // Distance fog (see `apply_fog`) — the water fog colour is also teal, so far water converges on the
    // haze.
    rgb = apply_fog(rgb, in.world_position.xyz);

    // GAMMA LANE (0161): raw gamma out; alpha blends in gamma like the reference's bytes.
    return vec4<f32>(rgb, alpha);
}