# Tasks: Copy-Paste Detection Quality Gate

**Input**: Design documents from `/specs/015-add-jscpd-gate/`
**Prerequisites**: plan.md (required), spec.md (required for user stories), research.md, data-model.md, quickstart.md

**Tests**: Not explicitly requested in the spec. Test tasks are omitted.

**Organization**: Tasks are grouped by user story to enable independent implementation and testing of each story.

## Format: `[ID] [P?] [Story] Description`

- **[P]**: Can run in parallel (different files, no dependencies)
- **[Story]**: Which user story this task belongs to (e.g., US1, US2, US3)
- Include exact file paths in descriptions

---

## Phase 1: Setup

**Purpose**: Install jscpd and create its configuration file

- [x] T001 Install jscpd as a dev dependency by adding it to `package.json` devDependencies and running `pnpm install`
- [x] T002 Create jscpd configuration file at `.jscpd.json` with threshold (5%), minLines (5), minTokens (50), pattern for TypeScript/TSX files, ignore list for `node_modules`, `dist`, `build`, `coverage`, `.specify`, `specs`, and add a standalone `"jscpd": "jscpd"` script to `package.json`

**Checkpoint**: jscpd is installed and `pnpm jscpd` runs successfully, scanning TypeScript/TSX files and producing a report

---

## Phase 2: User Story 1 - Automated Copy-Paste Detection on Commit (Priority: P1) 🎯 MVP

**Goal**: Pre-commit hook blocks commits when code duplication exceeds the configured threshold

**Independent Test**: Introduce a duplicated code block across two files, attempt to commit, and verify the commit is blocked with a clear duplication report. Remove the duplication and verify the commit succeeds.

### Implementation for User Story 1

- [x] T003 [US1] Add `jscpd` to the `"check"` script chain in `package.json` so it runs as part of the merge gate (e.g., `"check": "knip && biome check . && tsc --build && vitest run && jscpd"`)

**Checkpoint**: Running `pnpm check` now includes jscpd. Since Lefthook runs `pnpm check` as the pre-commit hook, commits are automatically gated by copy-paste detection. A commit with duplicated code above threshold is blocked.

---

## Phase 3: User Story 2 - On-Demand Duplication Scanning (Priority: P2)

**Goal**: Developers can run duplication scanning independently via a standalone command

**Independent Test**: Run `pnpm jscpd` on the codebase and verify it produces a duplication report with file paths and line numbers for any detected duplicates, or exits cleanly if none found.

### Implementation for User Story 2

No additional tasks — `pnpm jscpd` was already configured in T002. This story is satisfied by the setup phase.

**Checkpoint**: `pnpm jscpd` runs independently and produces a readable duplication report

---

## Phase 4: User Story 3 - Integration with Existing Quality Gate (Priority: P3)

**Goal**: Copy-paste detection runs as part of the unified `pnpm check` command alongside all other checks

**Independent Test**: Run `pnpm check` and verify jscpd output appears in the results alongside knip, biome, tsc, and vitest output.

### Implementation for User Story 3

No additional tasks — integration into `pnpm check` was completed in T003. This story is satisfied by the US1 implementation.

**Checkpoint**: `pnpm check` includes jscpd and the full gate passes on a clean codebase

---

## Phase 5: Polish & Cross-Cutting Concerns

**Purpose**: Validate the full workflow end-to-end

- [x] T004 Verify `pnpm check` passes on the current codebase (no existing duplication above threshold), confirm scan completes within 10 seconds (SC-002), verify no false positives on import statements or type declarations (SC-003), and adjust threshold or ignore patterns in `.jscpd.json` if needed
- [x] T005 Verify Knip does not flag jscpd as an unused dependency by running `pnpm knip`

---

## Dependencies & Execution Order

### Phase Dependencies

- **Setup (Phase 1)**: No dependencies — T001 then T002
- **US1 (Phase 2)**: Depends on T002
- **US2 (Phase 3)**: Satisfied by T002 (no additional work)
- **US3 (Phase 4)**: Satisfied by T003 (no additional work)
- **Polish (Phase 5)**: Depends on T003

### Execution Order

```
T001 → T002 → T003 → T004, T005 (parallel)
```

### Parallel Opportunities

- T004 and T005 can run in parallel (independent validations)
- This is a small, linear feature — limited parallelism needed

---

## Implementation Strategy

### MVP First (User Story 1 Only)

1. Complete Phase 1: Install jscpd + configure (T001, T002)
2. Complete Phase 2: Add to check script (T003)
3. **STOP and VALIDATE**: Attempt a commit with duplicated code — verify it's blocked
4. All three user stories are satisfied at this point

### Incremental Delivery

This feature is small enough that all stories are delivered in a single pass:
1. T001-T002: Setup → `pnpm jscpd` works (US2 done)
2. T003: Add to check → pre-commit gate works (US1 done), quality gate works (US3 done)
3. T004-T005: Polish → verify everything integrates cleanly

---

## Notes

- This is a tooling/configuration feature — no domain, application, or adapter code changes
- All changes are at the workspace root (`package.json`, `.jscpd.json`)
- Lefthook config (`lefthook.yml`) does NOT need changes — it already runs `pnpm check`
- US2 and US3 are naturally satisfied by the setup and US1 implementation with no additional tasks