From 22ec6381b83fd5465410568c29c43a54c39ac711 Mon Sep 17 00:00:00 2001
From: Chris Parsons <chrisparsons1127@gmail.com>
Date: Thu, 9 Apr 2026 01:59:46 +0000
Subject: [PATCH] feat: add calculateReplacementLevel and calculateVORP to
 ev-calculator

---
 app/services/__tests__/ev-calculator.test.ts | 47 ++++++++++++++++++++
 app/services/ev-calculator.ts                | 35 +++++++++++++++
 2 files changed, 82 insertions(+)

diff --git a/app/services/__tests__/ev-calculator.test.ts b/app/services/__tests__/ev-calculator.test.ts
index 0436257..8425665 100644
--- a/app/services/__tests__/ev-calculator.test.ts
+++ b/app/services/__tests__/ev-calculator.test.ts
@@ -4,6 +4,8 @@ import {
   validateProbabilities,
   normalizeProbabilities,
   calculateProjectedTotal,
+  calculateReplacementLevel,
+  calculateVORP,
   type ScoringRules,
   type ProbabilityDistribution,
 } from "../ev-calculator";
@@ -359,3 +361,48 @@ describe("calculateProjectedTotal", () => {
     expect(result.projectedPoints).toBe(156.37); // Rounded
   });
 });
+
+describe("calculateReplacementLevel", () => {
+  it("returns average EV of 12th-14th players (indices 11-13) when 14+ players exist", () => {
+    const evs = Array.from({ length: 16 }, (_, i) => 100 - i * 10);
+    // evs = [100, 90, 80, 70, 60, 50, 40, 30, 20, 10, 0, -10, -20, -30, -40, -50]
+    // indices 11-13 = -10, -20, -30 → avg = -20
+    expect(calculateReplacementLevel(evs)).toBeCloseTo(-20);
+  });
+
+  it("returns average EV of 12th-14th when exactly 14 players", () => {
+    const evs = Array.from({ length: 14 }, (_, i) => 100 - i * 5);
+    // evs[11] = 45, evs[12] = 40, evs[13] = 35 → avg = 40
+    expect(calculateReplacementLevel(evs)).toBeCloseTo(40);
+  });
+
+  it("uses available players starting at index 11 when fewer than 14", () => {
+    const evs = [50, 40, 30, 20, 15, 12, 10, 8, 6, 4, 2, 1]; // 12 players
+    // Only index 11: evs[11] = 1 → avg = 1
+    expect(calculateReplacementLevel(evs)).toBeCloseTo(1);
+  });
+
+  it("uses last player when fewer than 12 players", () => {
+    const evs = [50, 40, 30, 20, 10]; // 5 players
+    // Use last player: evs[4] = 10
+    expect(calculateReplacementLevel(evs)).toBeCloseTo(10);
+  });
+
+  it("returns 0 for empty array", () => {
+    expect(calculateReplacementLevel([])).toBe(0);
+  });
+});
+
+describe("calculateVORP", () => {
+  it("returns ev minus replacement level", () => {
+    expect(calculateVORP(75, 40)).toBeCloseTo(35);
+  });
+
+  it("returns negative value when ev is below replacement level", () => {
+    expect(calculateVORP(20, 40)).toBeCloseTo(-20);
+  });
+
+  it("returns 0 when ev equals replacement level", () => {
+    expect(calculateVORP(40, 40)).toBe(0);
+  });
+});
diff --git a/app/services/ev-calculator.ts b/app/services/ev-calculator.ts
index 1f0aafe..781ae07 100644
--- a/app/services/ev-calculator.ts
+++ b/app/services/ev-calculator.ts
@@ -168,3 +168,38 @@ export function calculateProjectedTotal(
     participantsRemaining: remainingParticipantEVs.length,
   };
 }
+
+/**
+ * Calculate the replacement level EV for a sport's season.
+ *
+ * Replacement level = average EV of players ranked 12th–14th (1-indexed).
+ * These are the last picks in a standard 12-team draft, representing the
+ * baseline any manager could pick up off the waiver wire.
+ *
+ * @param sortedEvs - All participant EVs for a sport season, sorted descending
+ * @returns Replacement level EV
+ */
+export function calculateReplacementLevel(sortedEvs: number[]): number {
+  if (sortedEvs.length === 0) return 0;
+
+  // Target: average EVs at 1-indexed positions 12-14 (0-indexed: 11-13)
+  const startIdx = Math.min(11, sortedEvs.length - 1);
+  const endIdx = Math.min(13, sortedEvs.length - 1);
+  const slice = sortedEvs.slice(startIdx, endIdx + 1);
+  const avg = slice.reduce((sum, ev) => sum + ev, 0) / slice.length;
+  return avg;
+}
+
+/**
+ * Calculate Value Over Replacement Player (VORP).
+ *
+ * VORP = participant EV − replacement level EV
+ * Positive = better than replacement; negative = worse than replacement.
+ *
+ * @param ev - Participant's expected value
+ * @param replacementLevel - Replacement level EV from calculateReplacementLevel
+ * @returns VORP value
+ */
+export function calculateVORP(ev: number, replacementLevel: number): number {
+  return ev - replacementLevel;
+}