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Fix InstaID precision without using bigint #260

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Merged
merged 3 commits into from
Feb 28, 2022
Merged

Fix InstaID precision without using bigint #260

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c624f1a
Fix InstaID precision without using bigint
Azureit Jan 26, 2022
5cd53a0
use camelCase varaible names and add comments to code
Azureit Jan 28, 2022
a0c04e2
handle private account shortcodes
Azureit Jan 30, 2022
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32 changes: 25 additions & 7 deletions src/ts/functions.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -55,18 +55,36 @@ export const shortcodeToDateString = (shortcode: string): string =>
shortcodeToInstaID(shortcode),
);

export const shortcodeToInstaID = (shortcode: string): number => {
export const shortcodeToInstaID = (shortcode: string): string => {
/* Instagram changed the shortcode generation method at 2012-02-07
2012-02-07T02:01:16.000Z --> o5H__ (old: sequential)
2012-02-07T02:35:23.000Z --> GsBiMipBgr (new: timestamp derived)
2290-05-20T12:17:23.928Z --> ___________ (last possible shortcode with 11 characters)
*/

if (shortcode.length > 28) shortcode = shortcode.slice(0, -28); // handle private account shortcodes

if (shortcode.length < 10 || shortcode.length > 11) return ''; // support new shortcode method only

const alphabet = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_';
let id = 0;
for (const char of shortcode) {
id = (id * 64) + alphabet.indexOf(char);
const cMil = 1000000; // add 6 digits of precision to the Number max limit (safe at least until year 2290)
let idMil = 0; // store numbers above 999999
let idNum = 0; // store numbers below 1000000
for (const char of shortcode) { // base64 to base10
idMil *= 64;
idNum = (idNum * 64) + alphabet.indexOf(char);
if (idNum >= cMil) {
let quot = Math.floor(idNum / cMil);
idMil += quot;
idNum -= quot * cMil;
}
}

return id;
return (idMil.toString() + idNum.toString().padStart(cMil.toString().length - 1, '0')).replace(/^0+/, '');
};

export const instaIDToTimestamp = (id: number) => {
const timestamp = (id / Math.pow(2, 23)) + 1314220021721;
export const instaIDToTimestamp = (id: string) => {
const timestamp = (Number(id) / Math.pow(2, 23)) + 1314220021721;

return new Date(timestamp).toLocaleString();
};