feat: add award winner resolver with tiebreak logic and tests

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/server/services/award-winner-resolver.ts

@@ -0,0 +1,37 @@
+/**
+ * Resolve the winner of a PICK_WINNER award given all votes and the chair's userId.
+ * Logic: count votes per project. If one project has the most, it wins.
+ * If tied, the chair's pick wins among the tied projects.
+ */
+export function resolveAwardWinner(
+  votes: Array<{ userId: string; projectId: string }>,
+  chairUserId: string
+): string {
+  if (votes.length === 0) {
+    throw new Error('Cannot resolve winner with no votes')
+  }
+
+  // Tally votes per project
+  const tally = new Map<string, number>()
+  for (const v of votes) {
+    tally.set(v.projectId, (tally.get(v.projectId) || 0) + 1)
+  }
+
+  const maxVotes = Math.max(...tally.values())
+  const topProjects = [...tally.entries()]
+    .filter(([, count]) => count === maxVotes)
+    .map(([pid]) => pid)
+
+  if (topProjects.length === 1) {
+    return topProjects[0]
+  }
+
+  // Tie: chair's pick wins if among tied projects
+  const chairVote = votes.find((v) => v.userId === chairUserId)
+  if (chairVote && topProjects.includes(chairVote.projectId)) {
+    return chairVote.projectId
+  }
+
+  // Chair voted for a non-tied project — pick alphabetically for stability
+  return topProjects.sort()[0]
+}

tests/unit/award-master.test.ts

@@ -0,0 +1,47 @@
+import { describe, it, expect } from 'vitest'
+import { resolveAwardWinner } from '@/server/services/award-winner-resolver'
+
+describe('resolveAwardWinner', () => {
+  it('returns the sole voted project when all agree', () => {
+    const votes = [
+      { userId: 'u1', projectId: 'p1' },
+      { userId: 'u2', projectId: 'p1' },
+    ]
+    expect(resolveAwardWinner(votes, 'u1')).toBe('p1')
+  })
+
+  it('returns the majority winner when no tie', () => {
+    const votes = [
+      { userId: 'u1', projectId: 'p1' },
+      { userId: 'u2', projectId: 'p2' },
+      { userId: 'u3', projectId: 'p1' },
+    ]
+    expect(resolveAwardWinner(votes, 'u1')).toBe('p1')
+  })
+
+  it('uses chair vote as tiebreaker', () => {
+    const votes = [
+      { userId: 'chair', projectId: 'p2' },
+      { userId: 'u2', projectId: 'p1' },
+    ]
+    expect(resolveAwardWinner(votes, 'chair')).toBe('p2')
+  })
+
+  it('returns chair pick when tied and chair voted for one of the tied projects', () => {
+    const votes = [
+      { userId: 'chair', projectId: 'p3' },
+      { userId: 'u2', projectId: 'p1' },
+      { userId: 'u3', projectId: 'p2' },
+    ]
+    expect(resolveAwardWinner(votes, 'chair')).toBe('p3')
+  })
+
+  it('returns sole vote for solo sponsor', () => {
+    const votes = [{ userId: 'sponsor', projectId: 'p1' }]
+    expect(resolveAwardWinner(votes, 'sponsor')).toBe('p1')
+  })
+
+  it('throws if no votes', () => {
+    expect(() => resolveAwardWinner([], 'chair')).toThrow()
+  })
+})