89 lines
2.6 KiB
TypeScript
89 lines
2.6 KiB
TypeScript
import crypto from "node:crypto"
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// Helper function to calculate the latitude offset
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export function calculateLatWithOffset(
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latitude: number,
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offsetPx: number,
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zoomLevel: number
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): number {
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const earthCircumference = 40075017 // Earth's circumference in meters
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const tileSize = 256 // Height of a tile in pixels (standard in Google Maps)
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// Calculate ground resolution (meters per pixel) at the given latitude and zoom level
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const groundResolution =
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(earthCircumference * Math.cos((latitude * Math.PI) / 180)) /
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(tileSize * Math.pow(2, zoomLevel))
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// Calculate the number of meters for the given offset in pixels
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const metersOffset = groundResolution * offsetPx
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// Convert the meters offset into a latitude offset (1 degree latitude is ~111,320 meters)
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const latOffset = metersOffset / 111320
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// Return the new latitude by subtracting the offset
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return latitude - latOffset
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}
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/**
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* Util functions taken from https://developers.google.com/maps/documentation/maps-static/digital-signature#sample-code-for-url-signing
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* Used to sign the URL for the Google Static Maps API.
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*/
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/**
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* Convert from 'web safe' base64 to true base64.
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*
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* @param {string} safeEncodedString The code you want to translate
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* from a web safe form.
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* @return {string}
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*/
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function removeWebSafe(safeEncodedString: string) {
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return safeEncodedString.replace(/-/g, "+").replace(/_/g, "/")
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}
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/**
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* Convert from true base64 to 'web safe' base64
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*
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* @param {string} encodedString The code you want to translate to a
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* web safe form.
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* @return {string}
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*/
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function makeWebSafe(encodedString: string) {
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return encodedString.replace(/\+/g, "-").replace(/\//g, "_")
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}
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/**
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* Takes a base64 code and decodes it.
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*
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* @param {string} code The encoded data.
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* @return {string}
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*/
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function decodeBase64Hash(code: string) {
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return Buffer.from(code, "base64")
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}
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/**
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* Takes a key and signs the data with it.
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*
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* @param {string} key Your unique secret key.
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* @param {string} data The url to sign.
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* @return {string}
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*/
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function encodeBase64Hash(key: Buffer, data: string) {
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return crypto.createHmac("sha1", key).update(data).digest("base64")
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}
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/**
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* Sign a URL using a secret key.
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*
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* @param {URL} url The url you want to sign.
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* @param {string} secret Your unique secret key.
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* @return {string}
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*/
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export function getUrlWithSignature(url: URL, secret = "") {
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const path = url.pathname + url.search
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const safeSecret = decodeBase64Hash(removeWebSafe(secret))
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const hashedSignature = makeWebSafe(encodeBase64Hash(safeSecret, path))
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return `${url.toString()}&signature=${hashedSignature}`
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}
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