# Investigation Plan: Bedtime Graph Issue

## Objective
Investigate why the "Bedtime" graph shows unexpected times when a specific `bedtime_ref` is set.

## Current Understanding
- The `BedtimePlot.tsx` component displays a graph where the Y-axis (or values) are formatted using `formatMinutesAfter(value, bedtime_ref)`.
- The data comes from the `/api/stats/wake-sleep-times` endpoint.
- The backend calculates `bedtime_minutes` based on sessions that started on or before the `bedtime_ref`.

## Investigation Steps

### Step 1: Analyze Backend Logic
- [ ] Examine `get_wake_sleep_times` in `backend/app/routers/stats.py` to understand how `bedtime_minutes` is calculated.
- [ ] Verify if the logic correctly identifies "bedtime" for various sleep session scenarios (e.g., sessions crossing midnight).
- [ ] Identify potential edge cases where the `s.start_time.time() <= b_ref_time` condition might be problematic.

### Step 2: Analyze Frontend Logic
- [ ] Examine `BedtimePlot.tsx` and `useStats.ts` to see how the data is consumed and formatted.
- [ ] Understand how `formatMinutesAfter` interacts with the values returned by the backend.

### Step 3: Data Simulation & Verification
- [ ] Create a set of test cases (mocked data) representing different sleep scenarios.
- [ ] Manually calculate the expected `bedtime_minutes` for these scenarios using the current logic.
- [ ] Compare with what the user reported to confirm the bug's nature.

### Step 4: Propose and Implement Fixes
- [ ] Refine the backend logic to better represent "bedtime" if current logic is insufficient.
- [ ] Ensure the frontend correctly displays the intended time.
- [ ] Verify that changes do not break other parts of the stats page (e.g., Wakeup times).

## Future Tasks
- [ ] Run tests to ensure correctness after implementation.
- [ ] Finalize documentation/explanation of the fix.