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:

// 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:

// 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)

trigger_ref: core.intervaltimer
parameters:
  unit: seconds
  interval: 30

Cron Timer (Weekdays at 9 AM)

trigger_ref: core.crontimer
parameters:
  expression: "0 0 9 * * 1-5"
  timezone: "UTC"

DateTime Timer (New Year's Eve)

trigger_ref: core.datetimetimer
parameters:
  fire_at: "2024-12-31T23:59:59Z"
  timezone: "UTC"

Testing Evidence

$ 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.