n32 decode

__tests__/index.ts

@@ -1,17 +1,28 @@
-import n32, { getSymbol } from '../dist';
+import n32, { n32decode, getSymbol, getSymbolValue } from '../dist';
 
 describe('n32', () => {
   it('returns a valid string', () => {
     expect(n32(0)).toBe('0');
     expect(n32(31)).toBe('z');
     expect(n32(32)).toBe('10');
+    expect(n32(1035280)).toBe('zk0g');
     expect(n32(Number.MAX_SAFE_INTEGER)).toBe('7zzzzzzzzzz');
   });
   it('throws an error', () => {
     expect(() => n32(-1)).toThrowError('n32 expects an absolute number.');
   });
 });
 
+describe('n32decode', () => {
+  it('returns a valid number', () => {
+    expect(n32decode('0')).toBe(0);
+    expect(n32decode('z')).toBe(31);
+    expect(n32decode('10')).toBe(32);
+    expect(n32decode('0zk0g')).toBe(1035280);
+    expect(n32decode('7zzzzzzzzzz')).toBe(Number.MAX_SAFE_INTEGER);
+  });
+});
+
 describe('getSymbol', () => {
   it('returns a valid symbol', () => {
     expect(getSymbol(0)).toBe('0');
@@ -25,3 +36,12 @@ describe('getSymbol', () => {
     );
   });
 });
+
+describe('getSymbolValue', () => {
+  it('returns a valid symbol value', () => {
+    expect(getSymbolValue('0')).toBe(0);
+    expect(getSymbolValue('9')).toBe(9);
+    expect(getSymbolValue('a')).toBe(10);
+    expect(getSymbolValue('z')).toBe(31);
+  });
+});

src/index.ts

@@ -6,6 +6,10 @@ export const getSymbol = (index: number): string => {
   return SYMBOLS.charAt(index);
 };
 
+export const getSymbolValue = (symbol: string): number => {
+  return '0123456789abcdefghjkmnpqrstvwxyz'.search(symbol);
+};
+
 const n32 = (number: number): string => {
   if (number < 0) throw new Error('n32 expects an absolute number.');
   if (number < 32) return getSymbol(number);
@@ -22,4 +26,18 @@ const n32 = (number: number): string => {
   return m;
 };
 
+export const n32decode = (n32: string): number => {
+  const BASE = 32;
+  let n = n32.length;
+  let s = 0;
+
+  while (n > 0) {
+    n--;
+    const symbol = n32[n32.length - n - 1];
+    s = getSymbolValue(symbol) * BASE ** n + s;
+  }
+
+  return s;
+};
+
 export default n32;