---
phase: 01-grundger-st-tippmechanik
plan: 04
subsystem: game
tags: [typing, tdd, adaptive-tempo, keyboard, vitest]

requires:
  - phase: 01-02
    provides: "QWERTZ keyboard rendering with finger colors and highlight/press animations"
  - phase: 01-03
    provides: "Level definitions with key sets and getKeysUpToLevel function"

provides:
  - "Typing exercise engine: generateLetters, createExerciseState, handleKeyPress"
  - "Adaptive tempo logic: 3s start, -200ms/+500ms, bounds 1.5-4s"
  - "Lesson screen UI with falling letters and keyboard integration"
  - "Lesson completion flow: progress update, next level unlock"

affects: [01-05, phase-02, phase-03]

tech-stack:
  added: []
  patterns: ["TDD RED-GREEN for game logic", "State mutation pattern for exercise state", "Cleanup function pattern for screen lifecycle"]

key-files:
  created:
    - src/game/typing.ts
    - src/game/typing.test.ts
  modified:
    - src/ui/screens.ts
    - src/app.ts
    - index.html
    - src/styles/main.css

key-decisions:
  - "Exercise state uses direct mutation pattern (not immutable) for simplicity in game loop"
  - "Streak resets to 0 after speed adjustment to prevent rapid acceleration"

patterns-established:
  - "TDD RED-GREEN: write failing tests first, then implement to pass"
  - "Screen init returns cleanup function for teardown"
  - "onComplete callback pattern for screen-to-app communication"

requirements-completed: [TYPE-01, TYPE-02, TYPE-03, TYPE-04, LEVL-02, LEVL-03]

duration: 2min
completed: 2026-03-29
---

# Phase 01 Plan 04: Typing Exercise Engine Summary

**TDD-tested typing engine with adaptive tempo (3s start, 1.5-4s bounds), lesson screen UI with falling letters and keyboard integration, lesson completion unlocking next level**

## Performance

- **Duration:** 2 min
- **Started:** 2026-03-29T09:09:33Z
- **Completed:** 2026-03-29T09:12:30Z
- **Tasks:** 2
- **Files modified:** 6

## Accomplishments
- Typing exercise engine with 18 passing tests covering letter generation, key press handling, adaptive tempo, and completion detection
- Lesson screen renders falling letter with float animation, keyboard highlights target key, correct press dissolves letter
- Lesson completion updates progress in IndexedDB: adds to completedLevels, advances currentLevel, increments sessions

## Task Commits

Each task was committed atomically:

1. **Task 1: Typing exercise logic (RED-GREEN-REFACTOR)** - `5fe66cb` (feat)
2. **Task 2: Lesson screen UI wiring** - `ba4525d` (feat)

## Files Created/Modified
- `src/game/typing.ts` - Core typing engine: generateLetters, createExerciseState, handleKeyPress, getCurrentLetter, isExerciseComplete
- `src/game/typing.test.ts` - 18 TDD tests covering all exercise behavior
- `src/ui/screens.ts` - Added initLessonScreen with keyboard rendering and keydown handling
- `src/app.ts` - Added startLesson function with progress update on completion
- `index.html` - Lesson screen HTML with letter-area and lesson-keyboard containers
- `src/styles/main.css` - Falling letter styles, float animation, dissolve effect

## Decisions Made
- Exercise state uses direct mutation (not immutable copies) for simplicity in the game loop
- Streak counter resets to 0 after triggering a speed adjustment, preventing rapid acceleration
- db parameter kept in initLessonScreen signature (prefixed with underscore) for future use when lesson analytics are added

## Deviations from Plan

### Auto-fixed Issues

**1. [Rule 1 - Bug] Fixed unused import and parameter TypeScript errors**
- **Found during:** Task 2
- **Issue:** `isExerciseComplete` imported but unused in screens.ts; `db` parameter unused in initLessonScreen
- **Fix:** Removed unused import, prefixed unused param with underscore
- **Files modified:** src/ui/screens.ts
- **Verification:** `npx tsc --noEmit` passes
- **Committed in:** ba4525d (Task 2 commit)

---

**Total deviations:** 1 auto-fixed (1 bug)
**Impact on plan:** Minor TypeScript strictness fix. No scope creep.

## Issues Encountered
None

## User Setup Required
None - no external service configuration required.

## Next Phase Readiness
- Typing engine ready for forest screen integration (Plan 05)
- startLesson exported from app.ts, ready to be called from forest/level map
- All 37 tests passing (levels + db + typing)

---
*Phase: 01-grundger-st-tippmechanik*
*Completed: 2026-03-29*