/**
 * The scenery loader's decoding, without three.js so it can be tested with node: the server's converted models
 * (NifFile::Encode) and the client's DDS textures (DXT1/3/5 and uncompressed), which the browser decodes itself.
 */

/**
 * A model from /api/scenery/:zone/mesh/:asset: {header, meshes: [{...header entry, positions, normals, uvs, colors,
 * indices}]} with typed arrays viewing the response (normals int8 x3, colors uint8 RGBA, indices uint16).
 */
export function parseModel(buffer) {
	const view = new DataView(buffer);
	const length = view.getUint32(0, true);
	const header = JSON.parse(new TextDecoder().decode(new Uint8Array(buffer, 4, length)));
	const base = 4 + length;
	const meshes = header.meshes.map((entry) => {
		let offset = base + entry.offset;
		const n = entry.vertices;
		const mesh = { ...entry };
		mesh.positions = new Float32Array(buffer, offset, n * 3);
		offset += n * 12;
		if (entry.normals) {
			mesh.normals = new Int8Array(buffer, offset, n * 3);
			offset += (n * 3 + 3) & ~3;
		}
		if (entry.uv) {
			mesh.uvs = new Float32Array(buffer, offset, n * 2);
			offset += n * 8;
		}
		if (entry.uv2) {
			mesh.uvs2 = new Float32Array(buffer, offset, n * 2);
			offset += n * 8;
		}
		if (entry.colors) {
			mesh.colors = new Uint8Array(buffer, offset, n * 4);
			offset += n * 4;
		}
		mesh.indices = new Uint16Array(buffer, offset, entry.indices);
		return mesh;
	});
	return { header, meshes };
}

/**
 * The shader (mapShaders.gameValue) the game draws a mesh of a model with, or null when the manifest doesn't say
 * (-1 is fixed function). A multishader model's parts name theirs in their node names (mesh.shaderTag, a mapShaders
 * id); a tag the client can't use falls back to the LEGO shader.
 */
export function shaderOf(manifest, asset, mesh) {
	if (!manifest || !manifest.shaders) return null;
	const shader = manifest.shaders[asset];
	if (shader === undefined || shader === null) return null;
	if (shader !== manifest.multishader) return shader;
	const tagged = mesh && mesh.shaderTag >= 0 && manifest.shaderTags ? manifest.shaderTags[mesh.shaderTag] : undefined;
	return tagged !== undefined && tagged >= 3 && tagged <= 108 ? tagged : manifest.defaultShader;
}

// NifFile::eShaderLook bits
export const SHADER_LOOK = { UNLIT: 1, NO_TEXTURE: 2, NO_VERTEX_COLORS: 4, MATERIAL_COLOR: 8, TWO_LAYERS_BLENDED: 16, TWO_LAYERS_ADDED: 32, REFLECTIVE: 64, BRUSHED: 128, EMISSIVE: 256,
	GLITTER: 512, SPARKLE: 1024 };

/**
 * The UGC server's glitter (UgcGlitter) for a three.js material, drawn in the shader from hashes of cells:
 *
 * Flecks ({flecks}): flat flakes over the color before the light, as the game's LEGO-AnimUV shader lays its fleck
 * texture over the vertex color: `flecks` a tile, `fleckSize` model units across (0.7 to 1.3 of it), each as bright as
 * its facet catches the light (0.3 to 1 of `fleckOpacity` percent, mostly dim). On `coordinates` 'uv' (the mesh's
 * 'glitterUv' attribute, in tiles) or 'position' (a box projection of the object's position, `tile` units a tile).
 *
 * Sparkles ({sparkles}): what the game's Distortion Directional shader does with the sparkle texture: two layers of
 * sparkles (`sparkleAmount` percent covered, `sparkleSize` across) sliding at the client's rates (a tile in 24 s at
 * three quarters the scale, and in 48 s), drawn only where both have one (the alpha test), in `sparkleColor`. On
 * 'glitterSparkleUv' (in sparkle tiles) or the projected position (`sparkleTile` units a tile). With `sparklesOnly`
 * the rest of the surface is discarded and the sparkles keep the material's color (the made model's sparkle shapes,
 * whose vertex colors are the sparkles').
 *
 * Returns {update(seconds)} to move the sparkles.
 */
export function addGlitter(material, { coordinates = 'uv', tile = 1.6, flecks = 80, fleckSize = 0.05, fleckOpacity = 80, sparkles = false,
	sparkleTile = 7.5, sparkleSize = 0.1, sparkleAmount = 5, sparkleColor = [1, 1, 1], sparklesOnly = false } = {}) {
	const fleckCells = Math.max(1, Math.sqrt(flecks));
	// A sparkle's radius in sparkle tiles, and cells of one sparkle each covering `sparkleAmount` percent
	const sparkleRadius = sparkleSize / Math.max(sparkleTile, 1e-3) / 2;
	const sparkleShare = Math.min(Math.max(sparkleAmount / 100, 0), 0.5);
	const sparkleCells = sparkleShare > 0 ? Math.sqrt(sparkleShare / (Math.PI * sparkleRadius * sparkleRadius)) : 1;
	const uniforms = {
		glitterTime: { value: 0 }, glitterTile: { value: tile }, glitterCells: { value: fleckCells },
		glitterFleckRadius: { value: fleckSize / Math.max(tile, 1e-3) / 2 * fleckCells }, glitterOpacity: { value: Math.min(Math.max(fleckOpacity / 100, 0), 1) },
		glitterFlecksOn: { value: sparklesOnly ? 0 : 1 },
		sparkleOn: { value: sparkles && sparkleShare > 0 ? 1 : 0 }, sparkleTileSize: { value: sparkleTile }, sparkleCells: { value: sparkleCells },
		sparkleCellRadius: { value: sparkleRadius * sparkleCells }, sparkleColor: { value: new Float32Array(sparkleColor) }, sparklesOnly: { value: sparklesOnly ? 1 : 0 }
	};
	material.onBeforeCompile = (shader) => {
		Object.assign(shader.uniforms, uniforms);
		const byPosition = coordinates === 'position';
		shader.vertexShader = 'varying vec3 vGlitterPosition;\nvarying vec3 vGlitterNormal;\n' +
			(byPosition ? '' : 'attribute vec2 glitterUv;\nvarying vec2 vGlitterUv;\nattribute vec2 glitterSparkleUv;\nvarying vec2 vGlitterSparkleUv;\n') +
			shader.vertexShader.replace('#include <begin_vertex>', '#include <begin_vertex>\n' +
				(byPosition ? `vec4 glitterAt = vec4(transformed, 1.0);
vec3 glitterNormal = objectNormal;
#ifdef USE_INSTANCING
glitterAt = instanceMatrix * glitterAt;
glitterNormal = mat3(instanceMatrix) * glitterNormal;
#endif
vGlitterPosition = glitterAt.xyz;
vGlitterNormal = glitterNormal;
` : 'vGlitterUv = glitterUv;\nvGlitterSparkleUv = glitterSparkleUv;\n'));
		shader.fragmentShader = `uniform float glitterTime;
uniform float glitterTile;
uniform float glitterCells;
uniform float glitterFleckRadius;
uniform float glitterOpacity;
uniform float glitterFlecksOn;
uniform float sparkleOn;
uniform float sparkleTileSize;
uniform float sparkleCells;
uniform float sparkleCellRadius;
uniform vec3 sparkleColor;
uniform float sparklesOnly;
varying vec3 vGlitterPosition;
varying vec3 vGlitterNormal;
` + (byPosition ? '' : 'varying vec2 vGlitterUv;\nvarying vec2 vGlitterSparkleUv;\n') + `
float glitterHash(vec2 p) { return fract(sin(dot(p, vec2(127.1, 311.7))) * 43758.5453); }
// A flat disc of radius r (in cells) at a random place in each cell, its edge a pixel wide
float glitterDisc(vec2 uv, float cells, float r, float salt) {
	vec2 at = uv * cells;
	vec2 cell = floor(at);
	vec2 centre = r + (1.0 - 2.0 * r) * vec2(glitterHash(cell + salt), glitterHash(cell + salt + 17.0));
	float d = length(fract(at) - centre);
	float edge = max(fwidth(d), 1e-4);
	return clamp((r - d) / edge + 0.5, 0.0, 1.0);
}
float glitterFleck(vec2 uv) {
	vec2 cell = floor(uv * glitterCells);
	float size = 0.7 + 0.6 * glitterHash(cell + 29.0);
	float facet = glitterHash(cell + 41.0);
	return glitterOpacity * (0.3 + 0.7 * facet * facet) * glitterDisc(uv, glitterCells, min(glitterFleckRadius * size, 0.45), 0.0);
}
// Two layers sliding as Distortion Directional's (2-layer technique): uv * 0.75 + a tile in 24 s, uv - 0.3 + a tile in 48 s
float glitterSparkle(vec2 uv) {
	float r = min(sparkleCellRadius, 0.45);
	float a = glitterDisc(uv * 0.75 + vec2(glitterTime / 24.0, 0.0), sparkleCells, r, 3.0);
	float b = glitterDisc(uv - 0.3 + vec2(glitterTime / 48.0, 0.0), sparkleCells, r, 7.0);
	return step(0.996, a + b);
}
` + shader.fragmentShader.replace('#include <color_fragment>', '#include <color_fragment>\n' + (byPosition ? `
	vec3 glitterN = abs(vGlitterNormal);
	vec2 glitterPlane = glitterN.x >= glitterN.y && glitterN.x >= glitterN.z ? vGlitterPosition.zy : glitterN.y >= glitterN.z ? vGlitterPosition.xz : vGlitterPosition.xy;
	vec2 glitterUv = glitterPlane / glitterTile;
	vec2 glitterSparkleUv = glitterPlane / sparkleTileSize;
` : 'vec2 glitterUv = vGlitterUv;\nvec2 glitterSparkleUv = vGlitterSparkleUv;\n') + `
	if (glitterFlecksOn > 0.5) diffuseColor.rgb = mix(diffuseColor.rgb, vec3(1.0), glitterFleck(glitterUv));
	if (sparkleOn > 0.5) {
		float glitterSparkles = glitterSparkle(glitterSparkleUv);
		if (sparklesOnly > 0.5 && glitterSparkles < 0.5) discard;
		if (sparklesOnly < 0.5) diffuseColor = mix(diffuseColor, vec4(sparkleColor, 1.0), glitterSparkles);
	}
`);
	};
	material.customProgramCacheKey = () => 'glitter-' + coordinates;
	material.needsUpdate = true;
	return { update(seconds) { uniforms.glitterTime.value = seconds; } };
}

// The UGC server's glitter settings for addGlitter (window.LDD_GLITTER), its defaults without them
export function glitterSettings() {
	const g = window.LDD_GLITTER || {};
	const speed = g.speed > 0 ? g.speed : 1, sparkleSize = g.sparkleSize > 0 ? g.sparkleSize : 0.1;
	return {
		tile: g.tile || 1.6, flecks: g.flecks ?? 80, fleckSize: g.fleckSize || 0.05, fleckOpacity: g.fleckOpacity ?? 80,
		sparkles: !!g.sparkles, sparkleSize, sparkleAmount: g.sparkleAmount ?? 5, sparkleTile: 75 * sparkleSize * speed,
		sparkleTint: g.sparkleTint ?? 30, sparkleBrightness: g.sparkleBrightness ?? 100
	};
}

// NifFile::eTechniqueFlag bits (what a technique does besides its family and eShaderLook bits)
export const TECHNIQUE = {
	UV_ANIM: 1, DOUBLE_SIDED: 2, BLEND: 4, ALPHA_TEST: 8, ADDITIVE: 16, NO_AMBIENT: 32, GLOW: 64, IGNORE_VERTEX_ALPHA: 128,
	SUPER_EMISSIVE: 256, GRAYSCALE: 512, SHINY_GLINT: 1024, SPECULAR: 2048, NON_DECAL: 4096, OCEAN_FX: 8192, RIM_LIGHT: 16384,
	DIFFUSE_ONLY: 32768, ANIM_ALPHA: 65536, BASIC_EMISSIVE: 131072, NO_FOG: 262144, NOT_DRAWN: 524288, NO_BLEND: 1048576
};

/**
 * The conversion format (Scenery.cpp FORMAT_VERSION) these views are written for. Manifest URLs carry it, so a
 * browser never draws with a manifest it kept from an older server (they are cached for up to a day).
 */
export const SCENERY_FORMAT = 6;

/** A manifest URL asking for SCENERY_FORMAT's manifest (the server ignores the parameter; browsers cache by it). */
export function manifestUrl(url) {
	return url + (url.includes('?') ? '&' : '?') + 'format=' + SCENERY_FORMAT;
}

/**
 * Whether a manifest's models are drawn with the game's shaders: it has the zone's lighting and says which technique
 * each shader is (format 4 on). Older manifests have neither all shaders' techniques nor the looks the shaders need,
 * so they are drawn with the viewer's own lights rather than every shader guessed as LEGO.
 */
export function gameShaded(manifest) {
	return !!(manifest && manifest.lighting && (manifest.techniques || manifest.technique));
}

// A technique the manifest doesn't name: the LEGO shader's, as the client falls back to it
const LEGO_TECHNIQUE = { family: 'lego', look: 0, alpha: 'decal', flags: 0 };
const FIXED_TECHNIQUE = { family: 'fixed', look: 0, alpha: 'opacity', flags: 0 };

/**
 * The technique (NifFile::TechniqueFor, the manifest's "techniques" by gameValue) a mesh of a model is drawn with:
 * {shader, family, look, alpha, flags}. A manifest-wide "technique" (the flairs') is every mesh's; without a shader the
 * mesh is fixed function; a shader the table lacks is drawn as LEGO.
 */
export function techniqueOf(manifest, asset, mesh) {
	if (manifest && manifest.technique) return { shader: null, ...manifest.technique };
	const shader = shaderOf(manifest, asset, mesh);
	if (shader === null || shader < 0) return { shader, ...FIXED_TECHNIQUE };
	const known = manifest.techniques && manifest.techniques[shader];
	return { shader, ...(known || LEGO_TECHNIQUE) };
}

/**
 * What a texture's alpha does in the game (the technique's, NifFile::eTextureAlpha): 'opacity' see-through where the
 * alpha is; 'decal' the texture is laid over the vertex colors by its alpha (LEGO shaders); 'ignored' it does nothing.
 */
export function textureAlphaMode(manifest, asset, mesh) {
	if (!manifest || (!manifest.techniques && !manifest.technique)) {
		// A manifest from before the techniques (format 3 and older) names only the shaders whose alpha isn't opacity
		const shader = shaderOf(manifest, asset, mesh);
		return (shader !== null && manifest && manifest.textureAlpha && manifest.textureAlpha[shader]) || 'opacity';
	}
	return techniqueOf(manifest, asset, mesh).alpha || 'opacity';
}

/**
 * How a mesh is drawn under the game's shaders, when the manifest has the zone's lighting: {family (game-shaders.js),
 * lit, texture, vertexColors, material, layers, metal, emissive, textureAlpha, uvAnim, flags, blend, doubleSided,
 * hidden} — whether the scene's sun and ambient light it, its texture and vertex colors are used, whether its
 * NiMaterialProperty colors are (only fixed function and the "Material" shaders use them), how a two layer shader puts
 * its dark texture with the base one ('blended', 'added' or null), whether it is metal ('polished', 'brushed' or null),
 * whether it glows (LEGO-Emissive: the vertex alpha is then no opacity), whether its texture moves as the .nif's
 * texture transform says, its blending ('nif': as NiAlphaProperty says; 'blend': see-through without depth writes;
 * 'test': cut out; 'additive'; 'opaque') and whether the game draws it in the world at all (hidden: post-processing
 * and shadow shaders). Null without lighting or techniques in the manifest (older servers, gameShaded), for the
 * viewer's own lights.
 */
export function gameLook(manifest, asset, mesh) {
	if (!gameShaded(manifest)) return null;
	const technique = techniqueOf(manifest, asset, mesh);
	const fixedFunction = technique.family === 'fixed';
	const bits = technique.look || 0;
	const flags = technique.flags || 0;
	return {
		family: technique.family,
		lit: !(bits & SHADER_LOOK.UNLIT),
		texture: !(bits & SHADER_LOOK.NO_TEXTURE),
		// Fixed function reads them as NiVertexColorProperty says; the shaders always do, unless they have none
		vertexColors: !!(mesh.colors && !(bits & SHADER_LOOK.NO_VERTEX_COLORS) && (!fixedFunction || mesh.vertexColors !== 0)),
		material: fixedFunction || !!(bits & SHADER_LOOK.MATERIAL_COLOR),
		layers: bits & SHADER_LOOK.TWO_LAYERS_BLENDED ? 'blended' : bits & SHADER_LOOK.TWO_LAYERS_ADDED ? 'added' : null,
		metal: metalOf(bits),
		emissive: !!(bits & SHADER_LOOK.EMISSIVE),
		textureAlpha: technique.alpha || 'opacity',
		uvAnim: !!(flags & TECHNIQUE.UV_ANIM),
		flags,
		blend: flags & TECHNIQUE.ADDITIVE ? 'additive' : flags & TECHNIQUE.BLEND ? 'blend' : flags & TECHNIQUE.ALPHA_TEST ? 'test' : flags & TECHNIQUE.NO_BLEND ? 'opaque' : 'nif',
		doubleSided: !!(flags & TECHNIQUE.DOUBLE_SIDED),
		hidden: !!(flags & TECHNIQUE.NOT_DRAWN)
	};
}

/**
 * How a mesh drawn with `look` is blended: {transparent, depthWrite, additive, alphaCutoff, doubleSided}. Most of the
 * game's files have alpha blending switched on; it only shows where something is see-through (`seeThrough`: the
 * material, a vertex or the texture's alpha as opacity). Blended meshes still write depth, as Gamebryo's default does,
 * unless the technique turns that off.
 */
export function blendingOf(look, mesh, seeThrough) {
	const cutoff = mesh.test >= 0 ? Math.max(mesh.test / 255, 0.01) : 0;
	const doubleSided = !!mesh.doubleSided || !!(look && look.doubleSided);
	switch (look ? look.blend : 'nif') {
		case 'additive': return { transparent: true, depthWrite: false, additive: true, alphaCutoff: 0, doubleSided };
		case 'blend': return { transparent: true, depthWrite: false, additive: false, alphaCutoff: cutoff, doubleSided };
		case 'test': return { transparent: false, depthWrite: true, additive: false, alphaCutoff: cutoff || 0.5, doubleSided };
		case 'opaque': return { transparent: false, depthWrite: true, additive: false, alphaCutoff: 0, doubleSided };
		default: return { transparent: !!(mesh.blend && seeThrough), depthWrite: true, additive: false, alphaCutoff: cutoff, doubleSided };
	}
}

// A shader's metal from its eShaderLook bits: 'polished', 'brushed' or null
export function metalOf(bits) {
	if (!(bits & SHADER_LOOK.REFLECTIVE)) return null;
	return bits & SHADER_LOOK.BRUSHED ? 'brushed' : 'polished';
}

/**
 * Meshes of a model that look the same (texture, colors, blending, sides, attributes) joined into one, so a model
 * made of many pieces (the zones' "glom" files have over a hundred) costs a few draw calls instead of one per piece.
 * Order is kept otherwise; indices become 32-bit when a joined mesh passes 65535 vertices.
 */
export function mergeMeshes(meshes) {
	const groups = new Map();
	for (const mesh of meshes) {
		if (!mesh.vertices || !mesh.indices.length) continue;
		const key = JSON.stringify([mesh.texture, mesh.diffuse, mesh.emissive, mesh.alpha, mesh.blend, mesh.test, mesh.doubleSided,
			mesh.vertexColors, mesh.clampU, mesh.clampV, !!mesh.normals, !!mesh.uvs, !!mesh.colors, mesh.shaderTag, mesh.darkTexture, !!mesh.uvs2, mesh.look, mesh.uvScroll]);
		if (!groups.has(key)) groups.set(key, []);
		groups.get(key).push(mesh);
	}
	return [...groups.values()].map((list) => {
		if (list.length === 1) return list[0];
		const first = list[0];
		const vertices = list.reduce((sum, m) => sum + m.vertices, 0);
		const indexCount = list.reduce((sum, m) => sum + m.indices.length, 0);
		const out = { ...first, vertices, positions: new Float32Array(vertices * 3) };
		if (first.normals) out.normals = new Int8Array(vertices * 3);
		if (first.uvs) out.uvs = new Float32Array(vertices * 2);
		if (first.uvs2) out.uvs2 = new Float32Array(vertices * 2);
		if (first.colors) out.colors = new Uint8Array(vertices * 4);
		out.indices = vertices > 65535 ? new Uint32Array(indexCount) : new Uint16Array(indexCount);
		let v = 0, i = 0;
		for (const m of list) {
			out.positions.set(m.positions, v * 3);
			if (out.normals) out.normals.set(m.normals, v * 3);
			if (out.uvs) out.uvs.set(m.uvs, v * 2);
			if (out.uvs2) out.uvs2.set(m.uvs2, v * 2);
			if (out.colors) out.colors.set(m.colors, v * 4);
			for (let k = 0; k < m.indices.length; k++) out.indices[i + k] = m.indices[k] + v;
			v += m.vertices;
			i += m.indices.length;
		}
		return out;
	});
}

// sRGB byte -> linear byte, for vertex colors (three.js takes vertex colors as linear)
const SRGB_TO_LINEAR = new Uint8Array(256);
for (let i = 0; i < 256; i++) {
	const c = i / 255;
	SRGB_TO_LINEAR[i] = Math.round((c <= 0.04045 ? c / 12.92 : Math.pow((c + 0.055) / 1.055, 2.4)) * 255);
}
export function linearColors(srgb) {
	const out = new Uint8Array(srgb.length);
	for (let i = 0; i < srgb.length; i += 4) {
		out[i] = SRGB_TO_LINEAR[srgb[i]];
		out[i + 1] = SRGB_TO_LINEAR[srgb[i + 1]];
		out[i + 2] = SRGB_TO_LINEAR[srgb[i + 2]];
		out[i + 3] = srgb[i + 3];
	}
	return out;
}

const FOURCC = { 0x31545844: 'DXT1', 0x33545844: 'DXT3', 0x35545844: 'DXT5' };

/**
 * A DDS file's header and mipmap levels: {format: 'DXT1'|'DXT3'|'DXT5'|'RGBA', width, height, levels: [{width,
 * height, data}]}, starting at the first level no larger than maxSize (so big textures cost less), or null when the
 * file isn't a DDS this reads. Uncompressed files (24 or 32 bits with masks) come back as RGBA, one level.
 */
export function parseDds(buffer, maxSize = 4096) {
	if (buffer.byteLength < 128) return null;
	const view = new DataView(buffer);
	if (view.getUint32(0, true) !== 0x20534444) return null; // "DDS "
	const height = view.getUint32(12, true), width = view.getUint32(16, true);
	const mipCount = Math.max(1, view.getUint32(28, true));
	const pfFlags = view.getUint32(80, true);
	const fourCC = view.getUint32(84, true);
	if (!width || !height || width > 8192 || height > 8192) return null;
	let offset = 128;
	if (pfFlags & 0x4) {
		const format = FOURCC[fourCC];
		if (!format) return null;
		const blockBytes = format === 'DXT1' ? 8 : 16;
		const levels = [];
		let w = width, h = height;
		for (let i = 0; i < mipCount; i++) {
			const size = Math.max(1, (w + 3) >> 2) * Math.max(1, (h + 3) >> 2) * blockBytes;
			if (offset + size > buffer.byteLength) break;
			levels.push({ width: w, height: h, data: new Uint8Array(buffer, offset, size) });
			offset += size;
			w = Math.max(1, w >> 1);
			h = Math.max(1, h >> 1);
		}
		let first = 0;
		while (first < levels.length - 1 && (levels[first].width > maxSize || levels[first].height > maxSize)) first++;
		const chosen = levels.slice(first);
		if (!chosen.length) return null;
		return { format, width: chosen[0].width, height: chosen[0].height, levels: chosen };
	}
	if (!(pfFlags & 0x40)) return null;
	const bits = view.getUint32(88, true);
	if (bits !== 32 && bits !== 24) return null;
	const masks = [92, 96, 100, 104].map((at) => view.getUint32(at, true));
	const hasAlpha = (pfFlags & 0x1) && masks[3];
	const bytes = bits / 8;
	if (offset + width * height * bytes > buffer.byteLength) return null;
	const shift = (mask) => (mask ? 31 - Math.clz32(mask & -mask) : 0);
	const shifts = masks.map(shift);
	const rgba = new Uint8Array(width * height * 4);
	const src = new Uint8Array(buffer, offset, width * height * bytes);
	for (let i = 0, s = 0; i < width * height; i++, s += bytes) {
		const pixel = bytes === 4 ? (src[s] | (src[s + 1] << 8) | (src[s + 2] << 16) | (src[s + 3] << 24)) >>> 0 : src[s] | (src[s + 1] << 8) | (src[s + 2] << 16);
		rgba[i * 4] = (pixel & masks[0]) >>> shifts[0];
		rgba[i * 4 + 1] = (pixel & masks[1]) >>> shifts[1];
		rgba[i * 4 + 2] = (pixel & masks[2]) >>> shifts[2];
		rgba[i * 4 + 3] = hasAlpha ? (pixel & masks[3]) >>> shifts[3] : 255;
	}
	const image = downscale({ format: 'RGBA', width, height, levels: [{ width, height, data: rgba }] }, maxSize);
	image.alpha = !!hasAlpha;
	return image;
}

/**
 * A DDS cube map (the client's environment cubes, textures/env and textures/metal) as six RGBA faces no larger than
 * maxSize: {faces: [{format: 'RGBA', width, height, data}]} in the file's order (+X, -X, +Y, -Y, +Z, -Z, as WebGL
 * takes them). With `plain`, a DDS that isn't a cube comes back as its one face instead; null otherwise.
 */
export function parseDdsCube(buffer, maxSize = 256, plain = false) {
	if (buffer.byteLength < 128) return null;
	const view = new DataView(buffer);
	if (view.getUint32(0, true) !== 0x20534444) return null;
	const isCube = (view.getUint32(112, true) & 0x200) !== 0;
	if (isCube === plain) return null;
	const height = view.getUint32(12, true), width = view.getUint32(16, true);
	const mipCount = Math.max(1, view.getUint32(28, true));
	const pfFlags = view.getUint32(80, true);
	const format = FOURCC[view.getUint32(84, true)];
	if (!(pfFlags & 0x4) || !format || !width || !height || width > 4096 || height > 4096) return null;
	const blockBytes = format === 'DXT1' ? 8 : 16;
	const levelBytes = (w, h) => Math.max(1, (w + 3) >> 2) * Math.max(1, (h + 3) >> 2) * blockBytes;
	let faceBytes = 0;
	for (let i = 0, w = width, h = height; i < mipCount; i++, w = Math.max(1, w >> 1), h = Math.max(1, h >> 1)) faceBytes += levelBytes(w, h);
	const count = isCube ? 6 : 1;
	if (128 + faceBytes * count > buffer.byteLength) return null;
	const faces = [];
	for (let f = 0; f < count; f++) {
		const data = new Uint8Array(buffer, 128 + f * faceBytes, levelBytes(width, height));
		const rgba = decodeDxt(format, width, height, data);
		faces.push(downscale({ format: 'RGBA', width, height, levels: [{ width, height, data: rgba }] }, maxSize).levels[0]);
	}
	return plain ? { format: 'RGBA', ...faces[0] } : { faces: faces.map((face) => ({ format: 'RGBA', ...face })) };
}

// Halve an RGBA image (box filter) until it fits maxSize
function downscale(image, maxSize) {
	let { width, height, data } = image.levels[0];
	while (width > maxSize || height > maxSize) {
		const w = Math.max(1, width >> 1), h = Math.max(1, height >> 1);
		const out = new Uint8Array(w * h * 4);
		for (let y = 0; y < h; y++) {
			for (let x = 0; x < w; x++) {
				for (let c = 0; c < 4; c++) {
					const at = (dx, dy) => data[((Math.min(y * 2 + dy, height - 1)) * width + Math.min(x * 2 + dx, width - 1)) * 4 + c];
					out[(y * w + x) * 4 + c] = (at(0, 0) + at(1, 0) + at(0, 1) + at(1, 1) + 2) >> 2;
				}
			}
		}
		width = w; height = h; data = out;
	}
	return { format: 'RGBA', width, height, levels: [{ width, height, data }] };
}

function color565(value, out, at) {
	out[at] = ((value >> 11) & 31) * 255 / 31 | 0;
	out[at + 1] = ((value >> 5) & 63) * 255 / 63 | 0;
	out[at + 2] = (value & 31) * 255 / 31 | 0;
}

/**
 * One DXT level as RGBA bytes (for GPUs without S3TC support, e.g. most phones). DXT1 blocks whose first color is
 * not greater than the second have a transparent fourth color.
 */
export function decodeDxt(format, width, height, data) {
	const out = new Uint8Array(width * height * 4);
	const blockBytes = format === 'DXT1' ? 8 : 16;
	const bw = Math.max(1, (width + 3) >> 2), bh = Math.max(1, (height + 3) >> 2);
	const palette = new Uint8Array(16);
	const alphas = new Uint8Array(16);
	for (let by = 0; by < bh; by++) {
		for (let bx = 0; bx < bw; bx++) {
			const block = (by * bw + bx) * blockBytes;
			const colorAt = format === 'DXT1' ? block : block + 8;
			const c0 = data[colorAt] | (data[colorAt + 1] << 8), c1 = data[colorAt + 2] | (data[colorAt + 3] << 8);
			color565(c0, palette, 0);
			color565(c1, palette, 4);
			palette[3] = palette[7] = palette[11] = palette[15] = 255;
			if (c0 > c1 || format !== 'DXT1') {
				for (let c = 0; c < 3; c++) {
					palette[8 + c] = (2 * palette[c] + palette[4 + c]) / 3 | 0;
					palette[12 + c] = (palette[c] + 2 * palette[4 + c]) / 3 | 0;
				}
			} else {
				for (let c = 0; c < 3; c++) palette[8 + c] = (palette[c] + palette[4 + c]) >> 1;
				palette[12] = palette[13] = palette[14] = palette[15] = 0;
			}
			if (format === 'DXT3') {
				for (let i = 0; i < 16; i++) alphas[i] = ((data[block + (i >> 1)] >> ((i & 1) * 4)) & 15) * 17;
			} else if (format === 'DXT5') {
				const a0 = data[block], a1 = data[block + 1];
				const table = [a0, a1];
				if (a0 > a1) for (let i = 1; i < 7; i++) table.push(((7 - i) * a0 + i * a1) / 7 | 0);
				else { for (let i = 1; i < 5; i++) table.push(((5 - i) * a0 + i * a1) / 5 | 0); table.push(0, 255); }
				// 48 bits of 3-bit indices
				let bits = 0, count = 0, byte = block + 2;
				for (let i = 0; i < 16; i++) {
					if (count < 3) { bits |= data[byte++] << count; count += 8; }
					alphas[i] = table[bits & 7];
					bits >>= 3; count -= 3;
				}
			}
			const indices = data[colorAt + 4] | (data[colorAt + 5] << 8) | (data[colorAt + 6] << 16) | (data[colorAt + 7] << 24);
			for (let i = 0; i < 16; i++) {
				const x = bx * 4 + (i & 3), y = by * 4 + (i >> 2);
				if (x >= width || y >= height) continue;
				const p = ((indices >>> (i * 2)) & 3) * 4;
				const at = (y * width + x) * 4;
				out[at] = palette[p];
				out[at + 1] = palette[p + 1];
				out[at + 2] = palette[p + 2];
				out[at + 3] = format === 'DXT1' ? palette[p + 3] : alphas[i];
			}
		}
	}
	return out;
}

/** A level chain is complete (usable for mipmapping) when it runs down to 1x1. */
export function completeChain(levels) {
	const last = levels[levels.length - 1];
	return levels.length > 0 && last.width === 1 && last.height === 1;
}

/**
 * Objects of a manifest grouped by model: Map asset -> [{index, x, y, z, qx, qy, qz, qw, scale}].
 */
export function groupObjects(objects) {
	const byAsset = new Map();
	for (let i = 0; i < objects.asset.length; i++) {
		const asset = objects.asset[i];
		if (!byAsset.has(asset)) byAsset.set(asset, []);
		byAsset.get(asset).push({
			index: i, x: objects.pos[i * 3], y: objects.pos[i * 3 + 1], z: objects.pos[i * 3 + 2],
			qx: objects.rot[i * 4], qy: objects.rot[i * 4 + 1], qz: objects.rot[i * 4 + 2], qw: objects.rot[i * 4 + 3], scale: objects.scale[i],
			// A tint per object ([r, g, b, ...]), for the flairs
			color: objects.color ? [objects.color[i * 3], objects.color[i * 3 + 1], objects.color[i * 3 + 2]] : null,
			// The game doesn't draw it (a trigger or blocking volume): only shown on request
			hidden: !!(objects.hidden && objects.hidden[i]),
			// The zone scene it was placed in (null: the manifest has none), for scenes like the game
			scene: objects.scene ? objects.scene[i] : null
		});
	}
	return byAsset;
}

/** Split instances into square cells `size` wide (by x and z): Map "cx,cz" -> instances. */
export function cellsOf(instances, size) {
	const cells = new Map();
	for (const instance of instances) {
		const key = Math.floor(instance.x / size) + ',' + Math.floor(instance.z / size);
		if (!cells.has(key)) cells.set(key, []);
		cells.get(key).push(instance);
	}
	return cells;
}

// ---- Scenes, as the game client streams them (ZoneScenes on the server) ----

export const GLOBAL_SCENE = 0;
const NO_SCENE = 255;

/**
 * The manifest's terrain scene map (sceneMap: {chunks: [{x, z, maxX, maxZ, size, runs (base64)}]}) ready for
 * sceneAt, or null without one.
 */
export function decodeSceneMap(json) {
	if (!json || !json.chunks || !json.chunks.length) return null;
	const chunks = json.chunks.map((c) => {
		// Runs of [length, scene] (ZoneScenes::RunLengths)
		const bytes = typeof atob === 'function' ? atob(c.runs) : Buffer.from(c.runs, 'base64').toString('binary');
		const cells = new Uint8Array(c.size * c.size).fill(NO_SCENE);
		for (let i = 0, at = 0; i + 1 < bytes.length && at < cells.length; i += 2) {
			const length = bytes.charCodeAt(i);
			cells.fill(bytes.charCodeAt(i + 1), at, Math.min(at + length, cells.length));
			at += length;
		}
		// Cells per unit as the client works it out, in 32-bit floats
		const perX = Math.fround(c.size / Math.fround(c.maxX - c.x)), perZ = Math.fround(c.size / Math.fround(c.maxZ - c.z));
		return { ...c, cells, perX, perZ };
	});
	return {
		chunks,
		minX: Math.min(...chunks.map((c) => c.x)), minZ: Math.min(...chunks.map((c) => c.z)),
		maxX: Math.max(...chunks.map((c) => c.maxX)), maxZ: Math.max(...chunks.map((c) => c.maxZ))
	};
}

/**
 * The scene at (x, z) as the client's TerrainManager::GetSceneAtPos finds it (ZoneScenes::SceneMap::SceneAt): the
 * nearest cell of the chunk under the point, the point clamped to the terrain; the global scene where there's none.
 */
export function sceneAt(map, x, z) {
	if (!map || !Number.isFinite(x) || !Number.isFinite(z)) return GLOBAL_SCENE;
	const EDGE = 0.001;
	x = Math.min(Math.max(x, map.minX), map.maxX);
	z = Math.min(Math.max(z, map.minZ), map.maxZ);
	for (const c of map.chunks) {
		const px = Math.min(x, map.maxX - 1 / c.perX), pz = Math.min(z, map.maxZ - 1 / c.perZ);
		if (px < c.x - EDGE || px >= c.maxX - EDGE || pz < c.z - EDGE || pz >= c.maxZ - EDGE) continue;
		const cx = Math.min(Math.max(Math.floor(c.perX * (px - c.x) + 0.5), 0), c.size - 1);
		const cz = Math.min(Math.max(Math.floor(c.perZ * (pz - c.z) + 0.5), 0), c.size - 1);
		const scene = c.cells[cx * c.size + cz];
		return scene === NO_SCENE ? GLOBAL_SCENE : scene;
	}
	return GLOBAL_SCENE;
}

/** The scenes the client keeps loaded with the player in `scene` (manifest.scenes): the global scene, it and its neighbours. */
export function loadedScenes(scenes, scene) {
	const loaded = new Set([GLOBAL_SCENE]);
	if (scene === GLOBAL_SCENE) return loaded;
	loaded.add(scene);
	const entry = (scenes || []).find((s) => s.id === scene);
	if (entry) for (const n of entry.neighbours) loaded.add(n);
	return loaded;
}

/**
 * The camera's near plane for a view `distance` from what it looks at. A depth buffer's precision goes with
 * near / distance², so a fixed small near plane (0.5) makes coplanar pieces fight (ground overlays, floor rings, road
 * pieces) once the camera is far out; the game's own camera stays close to the player. A four hundredth
 * of the distance keeps close-ups working and far views steady.
 */
export function nearPlaneFor(distance) {
	return Math.min(20, Math.max(0.5, distance / 400));
}