feat: splitFund() to split fixed amount

RELEASE.md

@@ -1,5 +1,9 @@
 # Releases
 
+## 0.1.7
+
+- FEATURE: new feature splitFund(amount) can return an array of parameter's fraction based on established fundme pointer pool.
+
 ## 0.1.6
 
 - Bump dependencies

src/fund/errors.ts

@@ -60,6 +60,9 @@ export const invalidWeight = (address: string, weight: string | number | undefin
   return `weight for payment pointer ${address}#${weight} is invalid.`;
 };
 
+// split fund
+export const splitFundError = `must set web monetization pointer address with fund() before split.`;
+
 /*****************************
  *                           *
  *  Server-side fund()       *

src/fund/mod.ts

@@ -1,2 +1,3 @@
 export { fund } from "./fund";
+export { splitFund } from "./split";
 export { setDefaultAddress, getCurrentPointerPool, getCurrentPointerAddress } from "./utils";

src/fund/split.ts

@@ -0,0 +1,31 @@
+import { FundmeError, splitFundError } from "./errors";
+import { getCurrentPointerPool, getPoolWeightSum } from "./utils";
+import { calculateRelativeWeight } from "./relative-weight";
+import { createPool } from "./set-pointer-multiple";
+
+interface splittedFund {
+  address: string;
+  amount: number;
+  weight: string | number;
+}
+
+export function splitFund(amount: number): splittedFund[] {
+  let pool: WMPointer[] = createPool(getCurrentPointerPool());
+  let sum = 0;
+  if (!pool.length) {
+    throw FundmeError(splitFundError);
+  } else {
+    // process pointer pool
+    pool = calculateRelativeWeight(pool);
+    sum = getPoolWeightSum(pool);
+  }
+
+  return pool.map((pointer: WMPointer) => {
+    const fraction = (pointer.weight as number) / sum;
+    return {
+      address: pointer.address,
+      amount: amount * fraction,
+      weight: pointer.weight!,
+    };
+  });
+}

tests/fund/client-side/split-fund.spec.ts

@@ -0,0 +1,37 @@
+import { FundmeError, splitFundError } from "../../../src/fund/errors";
+import { fund } from "../../../src/fund/fund";
+import { splitFund } from "../../../src/fund/split";
+import { setCurrentPointer } from "../../../src/fund/utils";
+
+describe("split fund works as expected", () => {
+  test("it split correct amount", () => {
+    fund([
+      "$wallet.example/test-1#10",
+      "$wallet.example/test-2#20",
+      "$wallet.example/platform#30%",
+    ]);
+    const amount = 60;
+    expect(splitFund(amount)).toEqual([
+      {
+        address: "$wallet.example/test-1",
+        amount: 14,
+        weight: 7,
+      },
+      {
+        address: "$wallet.example/test-2",
+        amount: 28,
+        weight: 14,
+      },
+      {
+        address: "$wallet.example/platform",
+        amount: 18,
+        weight: 9,
+      },
+    ]);
+  });
+
+  test("it throw an error if pointers haven't yet initiated", () => {
+    setCurrentPointer([]);
+    expect(() => splitFund(1)).toThrowError(FundmeError(splitFundError));
+  });
+});