# Project State: Itinerary Editor

## Project Reference

**Core Value:** Drag-and-drop that operates on semantic positions (day + sortOrder), not row indices - so user intent is preserved across data reloads.

**Current Focus:** Phase 4 Plan 1 Complete - Modern drag-drop delegates with lift animation and haptics

## Current Position

**Phase:** 4 of 4 (Drag Interaction)
**Plan:** 1 of 2 complete
**Status:** In progress
**Last activity:** 2026-01-18 - Completed 04-01-PLAN.md

```
Progress: [########--] 87.5%
Phase 1:  [##########] 100% (2/2 plans) COMPLETE
Phase 2:  [##########] 100% (2/2 plans) COMPLETE
Phase 3:  [##########] 100% (2/2 plans) COMPLETE
Phase 4:  [#####-----] 50% (1/2 plans)
```

## Performance Metrics

| Metric | Value |
|--------|-------|
| Total Requirements | 23 |
| Completed | 20 |
| Current Phase | 4 (in progress) |
| Plans Executed | 7 |

## Accumulated Context

### Key Decisions

| Decision | Rationale | Phase |
|----------|-----------|-------|
| UITableView over SwiftUI List | SwiftUI drag-drop lacks insertion line precision | Pre-planning |
| (day, sortOrder) position model | Row indices break on reload; semantic position is stable | Pre-planning |
| Insertion lines (not zones) | User wants precise feedback on exact drop location | Pre-planning |
| Invalid drops rejected (snap back) | Cleaner than auto-clamping; user knows what happened | Pre-planning |
| Games get sortOrder from 100 + minutes since midnight | Range 100-1540 leaves room for negative sortOrder items | 01-01 |
| Normalization threshold at 1e-10 | Standard floating-point comparison for precision exhaustion | 01-01 |
| Day 1 = trip.startDate | 1-indexed, games belong to their start date | 01-01 |
| Swift Testing (@Test) over XCTest | Matches existing project test patterns | 01-02 |
| LocalItineraryItem conversion for testing | Avoids #Predicate macro issues with local captures | 01-02 |
| Edge case tests cover all boundaries | Day 0, beyond trip, exact sortOrder, negative/large values | 02-02 |
| Success criteria verification tests | Tests named 'success_*' directly verify ROADMAP criteria | 02-02 |
| Day headers not positioned items | Always first in each day, not part of sortOrder-based ordering | 03-01 |
| Flattener is pure function | No instance state, no side effects for easy testing and determinism | 03-01 |
| gamesByDay dictionary for flattener | Built in reloadData() to pass to flattener | 03-01 |
| success_* test naming convention | Maps tests directly to ROADMAP success criteria | 03-02 |
| Modern drag delegates for custom previews | UITableViewDragDelegate/UITableViewDropDelegate enable lift animation | 04-01 |
| DragContext for session state | Store drag state in session.localContext for access across delegates | 04-01 |
| Lift animation: 1.025x scale, 2-deg tilt | iOS Reminders-style quick/snappy lift per CONTEXT.md | 04-01 |
| Dual haptic generators (light/medium) | Prepare both at drag start for reduced latency | 04-01 |

### Learned

- Previous attempts failed due to row-based thinking instead of semantic positioning
- Travel was incorrectly treated as structural ("travelBefore") instead of positional
- Hard-coded flatten order ignoring sortOrder caused reload issues
- SortOrderProvider provides static methods for all sortOrder calculations
- Trip extension provides instance methods for day number derivation
- 50 midpoint insertions maintain distinct sortOrder values before precision loss
- ItineraryConstraints provides isValidPosition(), validDayRange(), barrierGames() for drag validation
- Travel sortOrder constraints: must be AFTER (not equal to) departure game sortOrder
- ItineraryFlattener.flatten() is the single source of truth for display ordering
- 13 tests now verify deterministic flattening behavior
- Modern drag delegates require holistic implementation (can't separate lift/haptics from delegates)
- CATransform3D with m34 perspective creates convincing 3D lift effect
- Snapshot-based animation avoids modifying actual cell during drag

### TODOs

- [x] Create tests for semantic position persistence (Plan 01-02) - COMPLETE
- [x] Migrate constraint tests to Swift Testing (Plan 02-01) - COMPLETE
- [x] Add edge case tests and API documentation (Plan 02-02) - COMPLETE
- [x] Create ItineraryFlattener utility (Plan 03-01) - COMPLETE
- [x] Add flattening tests (Plan 03-02) - COMPLETE
- [x] Migrate to modern drag-drop delegates (Plan 04-01) - COMPLETE
- [ ] Add insertion line and invalid zone feedback (Plan 04-02) - NEXT

### Blockers

None currently.

## Session Continuity

**Last Session:** 2026-01-18T22:44:26Z
**Stopped at:** Completed 04-01-PLAN.md
**Resume file:** None

### Context for Next Session

Phase 4 Plan 1 complete:
- Migrated to UITableViewDragDelegate/UITableViewDropDelegate
- Implemented lift animation with scale (1.025x), shadow, and tilt (2 degrees)
- Added dual haptic feedback (light grab, medium drop)
- Created DragContext class for drag session state

Requirements completed in 04-01:
- DRAG-01: Lift animation on grab (shadow + slight scale)
- DRAG-06: Haptic feedback on grab (light) and drop (medium)
- DRAG-08: Slight tilt during drag (2-3 degrees)

Ready for 04-02: Themed insertion line, invalid zone feedback, snap-back animation
- DRAG-02: Insertion line showing drop target
- DRAG-03: Items shuffle during drag
- DRAG-04: Magnetic snap on drop
- DRAG-05: Invalid drops with snap-back
- DRAG-07: Auto-scroll at viewport edge

---
*State initialized: 2026-01-18*
*Last updated: 2026-01-18*