Lapsed donor logic

[pujitakalinadhabhotla]

Description

Implements Lapsed Donor Logic in the backend to identify donors whose most recent successful donation occurred more than a specified number of months ago (default: 6 months), and who do not have an active recurring donation.

Changes Made

• Backend changes
• Test additions/changes

Repository

• Added findLapsedDonors(numMonths: number)
• Filters to SUCCEEDED donations only
• Groups by email
• Applies HAVING MAX(createdAt) cutoff logic
• Excludes donors with recurring donations via NOT EXISTS subquery

Service

• Added getLapsedDonors(numMonths = 6)
• Validates numMonths is a positive number
• Delegates to repository
• Returns { emails: string[] }

Controller

• Added getLapsedDonors endpoint
• Accepts optional numMonths
• Defaults to 6 when not provided

Testing & Verification

• Unit tests pass
• Manual testing completed
• No breaking changes

Verification Steps:

donations.repository.spec.ts

• Filters only SUCCEEDED donations
• Applies HAVING MAX(createdAt) cutoff
• Ensures recurring donors are excluded
• Normalizes and deduplicates emails
• Validates positive numMonths

donations.service.spec.ts

• Verifies delegation to repository
• Validates default of 6 months
• Ensures error thrown for non-positive values

donations.controller.spec.ts

• Verifies service called with provided value
• Verifies default behavior when undefined

Related Issues

Closes #69

[aaronashby]

LGTM! Good stuff, Pujita 👍🏾