types: narrow EntropyFunction to discriminated union

Author: dingosky

src/lib/bits.ts

@@ -88,14 +88,14 @@ const fillEntropy = (entropyOffset: number, entropyBuffer: ArrayBuffer, entropyF
   const nEntropyBytes = entropyBytes.length
   const nEntropyBits = 8 * nEntropyBytes
 
-  const [byValues, entropySource] = entropyFunction
+  const { byValues, source } = entropyFunction
 
   if (entropyOffset === nEntropyBits) {
     // No carry
     if (byValues) {
-      entropyByValues(0, entropyBuffer, entropySource as EntropyByValues)
+      entropyByValues(0, entropyBuffer, source)
     } else {
-      entropyByBytes(0, entropyBuffer, entropySource as EntropyByBytes)
+      entropyByBytes(0, entropyBuffer, source)
     }
   } else {
     // Handle carry
@@ -110,9 +110,9 @@ const fillEntropy = (entropyOffset: number, entropyBuffer: ArrayBuffer, entropyF
 
     // Fill right bytes with new random values
     if (byValues) {
-      entropyByValues(nUnusedBytes, entropyBuffer, entropySource as EntropyByValues)
+      entropyByValues(nUnusedBytes, entropyBuffer, source)
     } else {
-      entropyByBytes(nUnusedBytes, entropyBuffer, entropySource as EntropyByBytes)
+      entropyByBytes(nUnusedBytes, entropyBuffer, source)
     }
   }
 

src/lib/puid.ts

@@ -1,6 +1,6 @@
 import { randomBytes } from 'node:crypto'
 
-import { EntropyByBytes, EntropyByValues, EntropyFunction, Puid, PuidConfig, PuidResult } from '../types/puid'
+import { EntropyFunction, Puid, PuidConfig, PuidResult } from '../types/puid'
 
 import muncher from './bits'
 import { Chars, charsName, validChars } from './chars'
@@ -12,17 +12,17 @@ const round2 = (f: number): number => round(f * 100) / 100
 const { ceil, round } = Math
 
 const selectEntropyFunction = (puidConfig: PuidConfig): EntropyFunction => {
-  if (puidConfig.entropyValues) return [true, puidConfig.entropyValues as EntropyByValues]
-  if (puidConfig.entropyBytes) return [false, puidConfig.entropyBytes as EntropyByBytes]
+  if (puidConfig.entropyValues) return { byValues: true, source: puidConfig.entropyValues }
+  if (puidConfig.entropyBytes) return { byValues: false, source: puidConfig.entropyBytes }
 
   // Prefer Web Crypto in environments where it's available
   type CryptoLike = { getRandomValues?: (b: Uint8Array) => void }
   const cryptoObj = (globalThis as { crypto?: CryptoLike }).crypto
   const gv = cryptoObj?.getRandomValues?.bind(cryptoObj) as ((b: Uint8Array) => void) | undefined
-  if (gv) return [true, gv]
+  if (gv) return { byValues: true, source: gv }
 
   // Fallback to Node's randomBytes
-  return [false, randomBytes]
+  return { byValues: false, source: randomBytes }
 }
 
 /**

src/lib/puid.web.ts

@@ -1,4 +1,4 @@
-import { EntropyByBytes, EntropyByValues, EntropyFunction, Puid, PuidConfig, PuidResult } from '../types/puid'
+import { EntropyFunction, Puid, PuidConfig, PuidResult } from '../types/puid'
 
 import muncher from './bits'
 import { Chars, charsName, validChars } from './chars'
@@ -10,13 +10,13 @@ const round2 = (f: number): number => round(f * 100) / 100
 const { ceil, round } = Math
 
 const selectEntropyFunction = (puidConfig: PuidConfig): EntropyFunction => {
-  if (puidConfig.entropyValues) return [true, puidConfig.entropyValues as EntropyByValues]
-  if (puidConfig.entropyBytes) return [false, puidConfig.entropyBytes as EntropyByBytes]
+  if (puidConfig.entropyValues) return { byValues: true, source: puidConfig.entropyValues }
+  if (puidConfig.entropyBytes) return { byValues: false, source: puidConfig.entropyBytes }
 
   type CryptoLike = { getRandomValues?: (b: Uint8Array) => void }
   const cryptoObj = (globalThis as { crypto?: CryptoLike }).crypto
   const gv = cryptoObj?.getRandomValues?.bind(cryptoObj) as ((b: Uint8Array) => void) | undefined
-  if (gv) return [true, gv]
+  if (gv) return { byValues: true, source: gv }
 
   // No Node randomBytes fallback in web entry
   throw new Error('No entropy source available: provide entropyValues or ensure Web Crypto is available')

src/types/puid.ts

@@ -25,7 +25,9 @@ export type PuidBitsSlicer = (puidBits: PuidBits) => number[]
 export type PuidEncoder = (n: number) => number
 
 export type EntropySource = EntropyByBytes | EntropyByValues
-export type EntropyFunction = [byValues: boolean, source: EntropySource]
+export type EntropyFunction =
+  | { byValues: true; source: EntropyByValues }
+  | { byValues: false; source: EntropyByBytes }
 
 export type PuidInfo = {
   readonly bits: number