PMTiles/js/v2.ts

import {
	Source,
	Header,
	Cache,
	RangeResponse,
	Compression,
	TileType,
} from "./index";
import { decompressSync } from "fflate";

export const shift = (n: number, shift: number) => {
	return n * Math.pow(2, shift);
};

export const unshift = (n: number, shift: number) => {
	return Math.floor(n / Math.pow(2, shift));
};

export const getUint24 = (view: DataView, pos: number) => {
	return shift(view.getUint16(pos + 1, true), 8) + view.getUint8(pos);
};

export const getUint48 = (view: DataView, pos: number) => {
	return shift(view.getUint32(pos + 2, true), 16) + view.getUint16(pos, true);
};

interface Zxy {
	z: number;
	x: number;
	y: number;
}

export interface EntryV2 {
	z: number;
	x: number;
	y: number;
	offset: number;
	length: number;
	is_dir: boolean;
}

const compare = (
	tz: number,
	tx: number,
	ty: number,
	view: DataView,
	i: number
) => {
	if (tz != view.getUint8(i)) return tz - view.getUint8(i);
	const x = getUint24(view, i + 1);
	if (tx != x) return tx - x;
	const y = getUint24(view, i + 4);
	if (ty != y) return ty - y;
	return 0;
};

export const queryLeafdir = (
	view: DataView,
	z: number,
	x: number,
	y: number
): EntryV2 | null => {
	const offset_len = queryView(view, z | 0x80, x, y);
	if (offset_len) {
		return {
			z: z,
			x: x,
			y: y,
			offset: offset_len[0],
			length: offset_len[1],
			is_dir: true,
		};
	}
	return null;
};

export const queryTile = (view: DataView, z: number, x: number, y: number) => {
	const offset_len = queryView(view, z, x, y);
	if (offset_len) {
		return {
			z: z,
			x: x,
			y: y,
			offset: offset_len[0],
			length: offset_len[1],
			is_dir: false,
		};
	}
	return null;
};

const queryView = (
	view: DataView,
	z: number,
	x: number,
	y: number
): [number, number] | null => {
	let m = 0;
	let n = view.byteLength / 17 - 1;
	while (m <= n) {
		const k = (n + m) >> 1;
		const cmp = compare(z, x, y, view, k * 17);
		if (cmp > 0) {
			m = k + 1;
		} else if (cmp < 0) {
			n = k - 1;
		} else {
			return [getUint48(view, k * 17 + 7), view.getUint32(k * 17 + 13, true)];
		}
	}
	return null;
};

const entrySort = (a: EntryV2, b: EntryV2): number => {
	if (a.is_dir && !b.is_dir) {
		return 1;
	}
	if (!a.is_dir && b.is_dir) {
		return -1;
	}
	if (a.z !== b.z) {
		return a.z - b.z;
	}
	if (a.x !== b.x) {
		return a.x - b.x;
	}
	return a.y - b.y;
};

export const parseEntry = (dataview: DataView, i: number): EntryV2 => {
	const z_raw = dataview.getUint8(i * 17);
	const z = z_raw & 127;
	return {
		z: z,
		x: getUint24(dataview, i * 17 + 1),
		y: getUint24(dataview, i * 17 + 4),
		offset: getUint48(dataview, i * 17 + 7),
		length: dataview.getUint32(i * 17 + 13, true),
		is_dir: z_raw >> 7 === 1,
	};
};

export const sortDir = (a: ArrayBuffer): ArrayBuffer => {
	const entries: EntryV2[] = [];
	const view = new DataView(a);
	for (let i = 0; i < view.byteLength / 17; i++) {
		entries.push(parseEntry(view, i));
	}
	return createDirectory(entries);
};

export const createDirectory = (entries: EntryV2[]): ArrayBuffer => {
	entries.sort(entrySort);

	const buffer = new ArrayBuffer(17 * entries.length);
	const arr = new Uint8Array(buffer);
	for (let i = 0; i < entries.length; i++) {
		const entry = entries[i];
		let z = entry.z;
		if (entry.is_dir) z = z | 0x80;
		arr[i * 17] = z;

		arr[i * 17 + 1] = entry.x & 0xff;
		arr[i * 17 + 2] = (entry.x >> 8) & 0xff;
		arr[i * 17 + 3] = (entry.x >> 16) & 0xff;

		arr[i * 17 + 4] = entry.y & 0xff;
		arr[i * 17 + 5] = (entry.y >> 8) & 0xff;
		arr[i * 17 + 6] = (entry.y >> 16) & 0xff;

		arr[i * 17 + 7] = entry.offset & 0xff;
		arr[i * 17 + 8] = unshift(entry.offset, 8) & 0xff;
		arr[i * 17 + 9] = unshift(entry.offset, 16) & 0xff;
		arr[i * 17 + 10] = unshift(entry.offset, 24) & 0xff;
		arr[i * 17 + 11] = unshift(entry.offset, 32) & 0xff;
		arr[i * 17 + 12] = unshift(entry.offset, 48) & 0xff;

		arr[i * 17 + 13] = entry.length & 0xff;
		arr[i * 17 + 14] = (entry.length >> 8) & 0xff;
		arr[i * 17 + 15] = (entry.length >> 16) & 0xff;
		arr[i * 17 + 16] = (entry.length >> 24) & 0xff;
	}
	return buffer;
};

export const deriveLeaf = (view: DataView, tile: Zxy): Zxy | null => {
	if (view.byteLength < 17) return null;
	const numEntries = view.byteLength / 17;
	const entry = parseEntry(view, numEntries - 1);
	if (entry.is_dir) {
		const leaf_level = entry.z;
		const level_diff = tile.z - leaf_level;
		const leaf_x = Math.trunc(tile.x / (1 << level_diff));
		const leaf_y = Math.trunc(tile.y / (1 << level_diff));
		return { z: leaf_level, x: leaf_x, y: leaf_y };
	}
	return null;
};

async function getHeader(source: Source): Promise<Header> {
	const resp = await source.getBytes(0, 512000);

	const dataview = new DataView(resp.data);

	const json_size = dataview.getUint32(4, true);
	const root_entries = dataview.getUint16(8, true);

	const dec = new TextDecoder("utf-8");
	const json_metadata = JSON.parse(
		dec.decode(new DataView(resp.data, 10, json_size))
	);
	let tile_compression = Compression.Unknown;
	if (json_metadata.compression === "gzip") {
		tile_compression = Compression.Gzip;
	}

	let minzoom = 0;
	if ("minzoom" in json_metadata) {
		minzoom = +json_metadata.minzoom;
	}

	let maxzoom = 0;
	if ("maxzoom" in json_metadata) {
		maxzoom = +json_metadata.maxzoom;
	}

	let center_lon = 0;
	let center_lat = 0;
	let center_zoom = 0;
	let min_lon = -180.0;
	let min_lat = -85.0;
	let max_lon = 180.0;
	let max_lat = 85.0;

	if (json_metadata.bounds) {
		const split = json_metadata.bounds.split(",");
		min_lon = +split[0];
		min_lat = +split[1];
		max_lon = +split[2];
		max_lat = +split[3];
	}

	if (json_metadata.center) {
		const split = json_metadata.center.split(",");
		center_lon = +split[0];
		center_lat = +split[1];
		center_zoom = +split[2];
	}

	const header = {
		specVersion: dataview.getUint16(2, true),
		rootDirectoryOffset: 10 + json_size,
		rootDirectoryLength: root_entries * 17,
		jsonMetadataOffset: 10,
		jsonMetadataLength: json_size,
		leafDirectoryOffset: 0,
		leafDirectoryLength: undefined,
		tileDataOffset: 0,
		tileDataLength: undefined,
		numAddressedTiles: 0,
		numTileEntries: 0,
		numTileContents: 0,
		clustered: false,
		internalCompression: Compression.None,
		tileCompression: tile_compression,
		tileType: TileType.Mvt,
		minZoom: minzoom,
		maxZoom: maxzoom,
		minLon: min_lon,
		minLat: min_lat,
		maxLon: max_lon,
		maxLat: max_lat,
		centerZoom: center_zoom,
		centerLon: center_lon,
		centerLat: center_lat,
		etag: resp.etag,
	};
	return header;
}

async function getZxy(
	header: Header,
	source: Source,
	cache: Cache,
	z: number,
	x: number,
	y: number,
	signal?: AbortSignal
): Promise<RangeResponse | undefined> {
	let root_dir = await cache.getArrayBuffer(
		source,
		header.rootDirectoryOffset,
		header.rootDirectoryLength,
		header
	);
	if (header.specVersion === 1) {
		root_dir = sortDir(root_dir);
	}

	const entry = queryTile(new DataView(root_dir), z, x, y);
	if (entry) {
		const resp = await source.getBytes(entry.offset, entry.length, signal);
		let tile_data = resp.data;

		const view = new DataView(tile_data);
		if (view.getUint8(0) == 0x1f && view.getUint8(1) == 0x8b) {
			tile_data = decompressSync(new Uint8Array(tile_data));
		}

		return {
			data: tile_data,
		};
	}
	const leafcoords = deriveLeaf(new DataView(root_dir), { z: z, x: x, y: y });

	if (leafcoords) {
		const leafdir_entry = queryLeafdir(
			new DataView(root_dir),
			leafcoords.z,
			leafcoords.x,
			leafcoords.y
		);
		if (leafdir_entry) {
			let leaf_dir = await cache.getArrayBuffer(
				source,
				leafdir_entry.offset,
				leafdir_entry.length,
				header
			);

			if (header.specVersion === 1) {
				leaf_dir = sortDir(leaf_dir);
			}
			const tile_entry = queryTile(new DataView(leaf_dir), z, x, y);
			if (tile_entry) {
				const resp = await source.getBytes(
					tile_entry.offset,
					tile_entry.length,
					signal
				);
				let tile_data = resp.data;

				const view = new DataView(tile_data);
				if (view.getUint8(0) == 0x1f && view.getUint8(1) == 0x8b) {
					tile_data = decompressSync(new Uint8Array(tile_data));
				}
				return {
					data: tile_data,
				};
			}
		}
	}

	return undefined;
}

export default {
	getHeader: getHeader,
	getZxy: getZxy,
};