attune/work-summary/2026-02-04-timer-sensor-complete-implementation.md

# Timer Sensor Complete Implementation

**Date**: 2026-02-04
**Component**: Timer Sensor (`attune-core-timer-sensor`)
**Status**: ✅ Complete

## Summary

Implemented full support for all three timer trigger types in the timer sensor using `tokio-cron-scheduler` for efficient asynchronous scheduling. The timer sensor now handles interval timers, cron timers, and one-shot datetime timers seamlessly.

## Changes Made

### 1. Dependencies
- **Added**: `tokio-cron-scheduler = "0.15"` to `crates/sensor-timer/Cargo.toml`
- Provides robust, async-first cron scheduling with support for:
  - Repeated jobs (intervals)
  - Cron expression-based scheduling
  - One-shot jobs (datetime)

### 2. Timer Manager Refactoring (`timer_manager.rs`)

**Architecture Changes**:
- Replaced individual `JoinHandle<()>` per timer with shared `JobScheduler` instance
- Added job UUID tracking: `HashMap<rule_id, job_uuid>` 
- Wrapped scheduler in `Mutex` for safe shutdown access
- Made constructor async to initialize and start scheduler

**Key Methods Updated**:
- `new()` → async, creates and starts JobScheduler
- `start_timer()` → Uses scheduler to add jobs, tracks UUIDs
- `stop_timer()` → Removes jobs from scheduler by UUID
- `stop_all()` → Removes all tracked jobs
- `shutdown()` → NEW: Gracefully shuts down the scheduler

**Job Creation Methods**:
```rust
// Interval timers
async fn create_interval_job(...) -> Result<Job>
  - Uses Job::new_repeated_async()
  - Converts time units to seconds
  - Creates "core.intervaltimer" events

// Cron timers  
async fn create_cron_job(...) -> Result<Job>
  - Uses Job::new_async() with cron expression
  - Queries next fire time from scheduler
  - Creates "core.crontimer" events

// DateTime timers
async fn create_datetime_job(...) -> Result<Job>
  - Uses Job::new_one_shot_async()
  - Calculates duration until fire time
  - Validates fire time is in future
  - Creates "core.datetimetimer" events
```

**Event Payloads**:
Each timer type now generates events with correct trigger ref and payload schema:

| Timer Type | Trigger Ref | Key Fields |
|------------|-------------|------------|
| Interval | `core.intervaltimer` | `interval_seconds`, `execution_count` |
| Cron | `core.crontimer` | `expression`, `next_fire_at`, `execution_count` |
| DateTime | `core.datetimetimer` | `fire_at`, `fired_at`, `delay_ms` |

### 3. Main Service (`main.rs`)

Updated to handle async timer manager:
```rust
// Create timer manager (now async)
let timer_manager = TimerManager::new(api_client.clone())
    .await
    .context("Failed to initialize timer manager")?;

// Shutdown handling
timer_manager.shutdown().await?;
```

### 4. Sensor Configuration (`packs/core/sensors/interval_timer_sensor.yaml`)

Updated to reflect support for all three timer types:
- Changed description from "interval timer" to "timer" sensor
- Added trigger types: `core.crontimer`, `core.datetimetimer`
- Updated documentation with examples for all three types
- Clarified that tokio-cron-scheduler is used

### 5. Comprehensive Testing

Added 4 new integration tests:
1. `test_all_timer_types_comprehensive` - Tests all three types concurrently
2. `test_cron_various_expressions` - Validates multiple cron patterns
3. `test_datetime_timer_future_validation` - Tests various future times
4. `test_mixed_timer_replacement` - Tests switching timer types for same rule

**Test Results**: ✅ 34 tests passing (30 existing + 4 new)

### 6. Documentation

Created comprehensive documentation:

**`docs/sensors/timer-sensor-implementation.md`** (6.7K):
- Overview of all three timer types
- Use cases for each type
- Configuration examples
- Event payload schemas
- Implementation details
- Architecture explanation
- Testing guide

**`docs/QUICKREF-timer-types.md`** (2.6K):
- Quick reference for all timer types
- Common examples
- Cron format guide
- Decision matrix for choosing timer type
- Event payload summaries

## Technical Highlights

### Efficient Scheduling
- Single shared `JobScheduler` for all timers across all rules
- Async-first design with tokio integration
- Low overhead job management with UUID tracking
- Clean job lifecycle: creation → tracking → removal → cleanup

### Cron Expression Support
Uses `croner` crate (via tokio-cron-scheduler) for cron parsing:
- Standard 6-field format: `second minute hour day month weekday`
- Supports special characters: `*`, `,`, `-`, `/`
- Built-in validation of expressions
- Query next execution time

### One-Shot Timer Handling
DateTime timers:
- Validate fire time is in future (reject past times)
- Calculate duration until fire time using chrono
- Fire exactly once, then automatically cleaned up
- Track delay between scheduled and actual fire time

### Graceful Shutdown
- Stops all active timers
- Properly shuts down scheduler
- Prevents job execution after shutdown signal
- Clean resource cleanup

## Example Usage

### Interval Timer (Every 30 seconds)
```yaml
trigger_ref: core.intervaltimer
parameters:
  unit: seconds
  interval: 30
```

### Cron Timer (Weekdays at 9 AM)
```yaml
trigger_ref: core.crontimer
parameters:
  expression: "0 0 9 * * 1-5"
  timezone: "UTC"
```

### DateTime Timer (New Year's Eve)
```yaml
trigger_ref: core.datetimetimer
parameters:
  fire_at: "2024-12-31T23:59:59Z"
  timezone: "UTC"
```

## Testing Evidence

```bash
$ cargo test -p attune-core-timer-sensor
running 34 tests
test result: ok. 34 passed; 0 failed; 0 ignored

$ cargo check -p attune-core-timer-sensor --all-targets
Finished `dev` profile [unoptimized + debuginfo]
# Zero warnings ✅
```

## Benefits

1. **Complete Feature Parity**: All three timer types now fully functional
2. **Robust Scheduling**: Production-ready cron scheduler library
3. **Efficient Resource Usage**: Single scheduler for all timers
4. **Clean Architecture**: Clear separation of timer types
5. **Comprehensive Testing**: All timer types and edge cases covered
6. **Well Documented**: Implementation guide and quick reference

## Future Enhancements

Potential improvements identified in documentation:
- Full timezone support for cron expressions (currently UTC only)
- Persistence for job recovery after restart
- Job execution history and statistics
- Advanced scheduling (chaining, dependencies, priorities)
- Performance metrics and monitoring

## Files Modified

- `crates/sensor-timer/Cargo.toml` - Added tokio-cron-scheduler dependency
- `crates/sensor-timer/src/timer_manager.rs` - Complete refactor for all timer types
- `crates/sensor-timer/src/main.rs` - Updated for async constructor and shutdown
- `packs/core/sensors/interval_timer_sensor.yaml` - Updated sensor metadata

## Files Created

- `docs/sensors/timer-sensor-implementation.md` - Complete implementation guide
- `docs/QUICKREF-timer-types.md` - Quick reference for timer types
- `work-summary/2026-02-04-timer-sensor-complete-implementation.md` - This file

## Compatibility

- ✅ Backward compatible with existing interval timers
- ✅ Adds new functionality (cron and datetime)
- ✅ No breaking changes to API or configuration
- ✅ Existing rules continue to work unchanged

## Conclusion

The timer sensor is now feature-complete with support for all three timer types. The implementation uses industry-standard scheduling patterns, comprehensive testing, and clear documentation. The sensor is production-ready for handling diverse timing requirements in Attune workflows.