test(analytics): add coverage for funding_gap metric

- Add getCampaignAnalytics() function to campaignStore.ts
- Implement funding_gap calculation (target - pledged)
- Add comprehensive unit tests covering:
  - Campaign with partial funding
  - Fully funded campaign (gap = 0)
  - Empty campaign (gap = target)
  - Non-existent campaign (returns undefined)

This is a ~10% contribution toward the larger analytics feature,
implementing the simplest metric that reuses existing campaign data
without additional database queries.

Author: coderolisa

backend/src/services/campaignStore.test.ts

@@ -22,6 +22,7 @@ let getPledges: CampaignStoreModule['getPledges'];
 let getDb: DbModule['getDb'];
 let getCampaignHistory: EventHistoryModule['getCampaignHistory'];
 let addPledge: CampaignStoreModule['addPledge'];
+let getCampaignAnalytics: CampaignStoreModule['getCampaignAnalytics'];
 
 const CREATOR = `G${'A'.repeat(55)}`;
 const CONTRIBUTOR = `G${'B'.repeat(55)}`;
@@ -41,6 +42,7 @@ beforeAll(async () => {
     getCampaign,
     getPledges,
     addPledge,
+    getCampaignAnalytics,
   } = await import('./campaignStore'));
   ({ getDb } = await import('./db'));
   ({ getCampaignHistory } = await import('./eventHistory'));
@@ -208,3 +210,62 @@ describe('campaign pledge pagination', () => {
     expect(page2.pledges[0].amount).toBe(50);
   });
 });
+
+describe('campaign analytics', () => {
+  it('returns correct funding_gap for campaign with pledges', () => {
+    const futureDeadline = Math.floor(Date.now() / 1000) + 86400;
+    const campaign = createCampaign({
+      creator: CREATOR,
+      title: 'Analytics Test Campaign',
+      description: 'Campaign to test analytics metrics',
+      assetCode: 'USDC',
+      targetAmount: 1000,
+      deadline: futureDeadline,
+    });
+
+    addPledge(campaign.id, { contributor: CONTRIBUTOR, amount: 250 });
+
+    const analytics = getCampaignAnalytics(campaign.id);
+    expect(analytics).toBeDefined();
+    expect(analytics?.fundingGap).toBe(750); // 1000 - 250 = 750
+  });
+
+  it('returns zero funding_gap when campaign is fully funded', () => {
+    const futureDeadline = Math.floor(Date.now() / 1000) + 86400;
+    const campaign = createCampaign({
+      creator: CREATOR,
+      title: 'Fully Funded Campaign',
+      description: 'Campaign to test funding_gap when fully funded',
+      assetCode: 'XLM',
+      targetAmount: 500,
+      deadline: futureDeadline,
+    });
+
+    addPledge(campaign.id, { contributor: CONTRIBUTOR, amount: 500 });
+
+    const analytics = getCampaignAnalytics(campaign.id);
+    expect(analytics).toBeDefined();
+    expect(analytics?.fundingGap).toBe(0); // 500 - 500 = 0
+  });
+
+  it('returns funding_gap equal to target for campaign with no pledges', () => {
+    const futureDeadline = Math.floor(Date.now() / 1000) + 86400;
+    const campaign = createCampaign({
+      creator: CREATOR,
+      title: 'Empty Campaign',
+      description: 'Campaign with no pledges to test analytics',
+      assetCode: 'USDC',
+      targetAmount: 2000,
+      deadline: futureDeadline,
+    });
+
+    const analytics = getCampaignAnalytics(campaign.id);
+    expect(analytics).toBeDefined();
+    expect(analytics?.fundingGap).toBe(2000); // 2000 - 0 = 2000
+  });
+
+  it('returns undefined for non-existent campaign', () => {
+    const analytics = getCampaignAnalytics('99999');
+    expect(analytics).toBeUndefined();
+  });
+});

backend/src/services/campaignStore.ts

@@ -1262,3 +1262,26 @@ export function getTopContributors(limit: number = 10): LeaderboardEntry[] {
     averagePledgeAmount: round(row.avg_pledge),
   }));
 }
+
+export interface CampaignAnalytics {
+  fundingGap: number;
+}
+
+/**
+ * Computes basic analytics for a campaign.
+ *
+ * @param campaignId - The unique campaign identifier.
+ * @returns A {@link CampaignAnalytics} object with computed metrics, or undefined if campaign doesn't exist.
+ */
+export function getCampaignAnalytics(campaignId: string): CampaignAnalytics | undefined {
+  const campaign = getCampaign(campaignId);
+  if (!campaign) {
+    return undefined;
+  }
+
+  const fundingGap = round(Math.max(0, campaign.targetAmount - campaign.pledgedAmount));
+
+  return {
+    fundingGap,
+  };
+}