feat: Implement scheduling functionality for playlist synchronization

- Added a new scheduler module using APScheduler to manage scheduled sync jobs.
- Introduced cron expression validation and job scheduling based on user-defined settings.
- Enhanced frontend to support schedule settings, including cron, daily, and weekly modes.
- Updated API service to handle fetching and saving schedule settings.
- Modified StrategySelector component to include schedule management UI.
- Added new types for schedule settings and modes in the frontend.
- Updated requirements to include APScheduler for scheduling capabilities.

app/utils/scheduler.py

@@ -0,0 +1,123 @@
+from apscheduler.schedulers.background import BackgroundScheduler
+from apscheduler.triggers.cron import CronTrigger
+from app.utils.config import server_config
+from app.utils.logger import logger
+from app.utils.playlist_merge import sync_all_playlists, SyncMode
+import asyncio
+
+scheduler = BackgroundScheduler()
+
+def validate_cron_expression(expression: str) -> bool:
+    try:
+        parts = expression.split()
+        if len(parts) != 5:
+            return False
+        # Try to create a trigger to validate
+        CronTrigger(
+            minute=parts[0],
+            hour=parts[1],
+            day=parts[2],
+            month=parts[3],
+            day_of_week=parts[4]
+        )
+        return True
+    except Exception:
+        return False
+
+def job_function():
+    logger.info("Executing scheduled sync job...")
+    try:
+        # Re-read config to ensure latest values
+        server_config.load()
+        
+        mode_str = server_config.sync_mode
+        regex_rules = server_config.path_rules
+        local_path = server_config.local_path
+        
+        asyncio.run(sync_all_playlists(
+            sync_mode=SyncMode(mode_str),
+            path_rules=regex_rules,
+            local_dir=local_path
+        ))
+        
+        logger.info("Scheduled sync job completed.")
+    except Exception as e:
+        logger.error(f"Scheduled sync job failed: {e}")
+
+def start_scheduler():
+    if not scheduler.running:
+        scheduler.start()
+        logger.info("Scheduler started.")
+    update_scheduler_job()
+
+def update_scheduler_job():
+    scheduler.remove_all_jobs()
+    
+    # Reload config to get latest schedule settings
+    server_config.load()
+    mode = server_config.schedule_mode
+    
+    if mode == "DISABLED":
+        logger.info("Schedule is disabled.")
+        return
+
+    trigger = None
+    
+    if mode == "CRON":
+        cron_exp = server_config.schedule_cron
+        if cron_exp:
+            try:
+                # 5 parts: minute hour day month day_of_week
+                parts = cron_exp.split()
+                if len(parts) == 5:
+                    trigger = CronTrigger(
+                        minute=parts[0],
+                        hour=parts[1],
+                        day=parts[2],
+                        month=parts[3],
+                        day_of_week=parts[4]
+                    )
+            except Exception as e:
+                logger.error(f"Invalid cron expression: {cron_exp}, error: {e}")
+
+    elif mode == "DAILY":
+        time_str = server_config.schedule_daily_time
+        try:
+            hour, minute = map(int, time_str.split(':'))
+            trigger = CronTrigger(hour=hour, minute=minute)
+        except ValueError:
+            logger.error(f"Invalid daily time: {time_str}")
+
+    elif mode == "WEEKLY":
+        days = server_config.schedule_weekly_days # list of ints 0-6 (Sun-Sat)
+        time_str = server_config.schedule_weekly_time
+        
+        # Frontend: 0(Sun), 1(Mon)... 6(Sat)
+        # APScheduler: 0(Mon)... 6(Sun)
+        
+        aps_days = []
+        for d in days:
+            if d == 0: aps_days.append(6)
+            else: aps_days.append(d - 1)
+            
+        days_str = ",".join(map(str, aps_days))
+        
+        try:
+            hour, minute = map(int, time_str.split(':'))
+            trigger = CronTrigger(day_of_week=days_str, hour=hour, minute=minute)
+        except ValueError:
+            logger.error(f"Invalid weekly time: {time_str}")
+
+    if trigger:
+        scheduler.add_job(job_function, trigger)
+        logger.info(f"Added scheduled job with mode {mode} and trigger {trigger}")
+    else:
+        logger.warning(f"Failed to create trigger for mode {mode}")
+
+def get_next_run_time():
+    jobs = scheduler.get_jobs()
+    if not jobs:
+        return None
+    # Assuming only one job
+    job = jobs[0]
+    return job.next_run_time