//! Scheduler service for automatic trigger execution
//!
//! Periodically scans scheduled triggers and fires them at the appropriate time.

use std::sync::Arc;
use std::sync::atomic::{AtomicBool, Ordering};
use chrono::{Datelike, Timelike};
use tokio::sync::Mutex;
use tokio::time::{self, Duration};
use zclaw_types::Result;
use crate::Kernel;

/// Scheduler service that runs in the background and executes scheduled triggers
pub struct SchedulerService {
    kernel: Arc<Mutex<Option<Kernel>>>,
    running: Arc<AtomicBool>,
    check_interval: Duration,
}

impl SchedulerService {
    /// Create a new scheduler service
    pub fn new(kernel: Arc<Mutex<Option<Kernel>>>, check_interval_secs: u64) -> Self {
        Self {
            kernel,
            running: Arc::new(AtomicBool::new(false)),
            check_interval: Duration::from_secs(check_interval_secs),
        }
    }

    /// Start the scheduler loop in the background
    pub fn start(&self) {
        if self.running.compare_exchange(false, true, Ordering::SeqCst, Ordering::SeqCst).is_err() {
            tracing::warn!("[Scheduler] Already running, ignoring start request");
            return;
        }

        let kernel = self.kernel.clone();
        let running = self.running.clone();
        let interval = self.check_interval;

        tokio::spawn(async move {
            tracing::info!("[Scheduler] Starting scheduler loop with {}s interval", interval.as_secs());

            let mut ticker = time::interval(interval);
            // First tick fires immediately — skip it
            ticker.tick().await;

            while running.load(Ordering::Relaxed) {
                ticker.tick().await;

                if !running.load(Ordering::Relaxed) {
                    break;
                }

                if let Err(e) = Self::check_and_fire_scheduled_triggers(&kernel).await {
                    tracing::error!("[Scheduler] Error checking triggers: {}", e);
                }
            }

            tracing::info!("[Scheduler] Scheduler loop stopped");
        });
    }

    /// Stop the scheduler loop
    pub fn stop(&self) {
        self.running.store(false, Ordering::Relaxed);
        tracing::info!("[Scheduler] Stop requested");
    }

    /// Check if the scheduler is running
    pub fn is_running(&self) -> bool {
        self.running.load(Ordering::Relaxed)
    }

    /// Check all scheduled triggers and fire those that are due
    async fn check_and_fire_scheduled_triggers(
        kernel_lock: &Arc<Mutex<Option<Kernel>>>,
    ) -> Result<()> {
        // Collect due triggers under lock
        let to_execute: Vec<(String, String, String)> = {
            let kernel_guard = kernel_lock.lock().await;
            let kernel = match kernel_guard.as_ref() {
                Some(k) => k,
                None => return Ok(()),
            };

            let triggers = kernel.list_triggers().await;
            let now = chrono::Utc::now();

            let scheduled: Vec<_> = triggers.iter()
                .filter(|t| {
                    t.config.enabled && matches!(t.config.trigger_type, zclaw_hands::TriggerType::Schedule { .. })
                })
                .collect();

            if scheduled.is_empty() {
                return Ok(());
            }

            tracing::debug!("[Scheduler] Checking {} scheduled triggers", scheduled.len());

            scheduled.iter()
                .filter_map(|t| {
                    if let zclaw_hands::TriggerType::Schedule { ref cron } = t.config.trigger_type {
                        if Self::should_fire_cron(cron, &now) {
                            Some((t.config.id.clone(), t.config.hand_id.clone(), cron.clone()))
                        } else {
                            None
                        }
                    } else {
                        None
                    }
                })
                .collect()
        }; // Lock dropped here

        // Execute due triggers (acquire lock per execution)
        // DESIGN NOTE: Triggers execute sequentially within each check cycle. This is intentional:
        // 1. Prevents concurrent hand runs from competing for shared resources
        // 2. Maintains deterministic ordering for trigger execution
        // 3. A long-running hand will delay subsequent triggers in the same cycle
        //    but will NOT skip them — they are processed on the next tick.
        // If parallel execution is needed, spawn each execute_hand in a separate task
        // and collect results via JoinSet.
        let now = chrono::Utc::now();
        for (trigger_id, hand_id, cron_expr) in to_execute {
            tracing::info!(
                "[Scheduler] Firing scheduled trigger '{}' → hand '{}' (cron: {})",
                trigger_id, hand_id, cron_expr
            );

            let kernel_guard = kernel_lock.lock().await;
            if let Some(kernel) = kernel_guard.as_ref() {
                let trigger_source = zclaw_types::TriggerSource::Scheduled {
                    trigger_id: trigger_id.clone(),
                };

                let input = serde_json::json!({
                    "trigger_id": trigger_id,
                    "trigger_type": "schedule",
                    "cron": cron_expr,
                    "fired_at": now.to_rfc3339(),
                });

                match kernel.execute_hand_with_source(&hand_id, input, trigger_source).await {
                    Ok((_result, run_id)) => {
                        tracing::info!(
                            "[Scheduler] Successfully fired trigger '{}' → run {}",
                            trigger_id, run_id
                        );
                    }
                    Err(e) => {
                        tracing::error!(
                            "[Scheduler] Failed to execute trigger '{}': {}",
                            trigger_id, e
                        );
                    }
                }
            }
        }

        Ok(())
    }

    /// Simple cron expression matcher
    ///
    /// Supports basic cron format: `minute hour day month weekday`
    /// Also supports interval shorthand: `every:Ns`, `every:Nm`, `every:Nh`
    fn should_fire_cron(cron: &str, now: &chrono::DateTime<chrono::Utc>) -> bool {
        let cron = cron.trim();

        // Handle interval shorthand: "every:30s", "every:5m", "every:1h"
        if let Some(interval_str) = cron.strip_prefix("every:") {
            return Self::check_interval_shorthand(interval_str, now);
        }

        // Handle ISO timestamp for one-shot: "2026-03-29T10:00:00Z"
        if cron.contains('T') && cron.contains('-') {
            if let Ok(target) = chrono::DateTime::parse_from_rfc3339(cron) {
                let target_utc = target.with_timezone(&chrono::Utc);
                // Fire if within the check window (± check_interval/2, approx 30s)
                let diff = (*now - target_utc).num_seconds().abs();
                return diff <= 30;
            }
        }

        // Standard 5-field cron: minute hour day_of_month month day_of_week
        let parts: Vec<&str> = cron.split_whitespace().collect();
        if parts.len() != 5 {
            tracing::warn!("[Scheduler] Invalid cron expression (expected 5 fields): '{}'", cron);
            return false;
        }

        let minute = now.minute() as i32;
        let hour = now.hour() as i32;
        let day = now.day() as i32;
        let month = now.month() as i32;
        let weekday = now.weekday().num_days_from_monday() as i32; // Mon=0..Sun=6

        Self::cron_field_matches(parts[0], minute)
            && Self::cron_field_matches(parts[1], hour)
            && Self::cron_field_matches(parts[2], day)
            && Self::cron_field_matches(parts[3], month)
            && Self::cron_field_matches(parts[4], weekday)
    }

    /// Check if a single cron field matches the current value
    fn cron_field_matches(field: &str, value: i32) -> bool {
        if field == "*" || field == "?" {
            return true;
        }

        // Handle step: */N
        if let Some(step_str) = field.strip_prefix("*/") {
            if let Ok(step) = step_str.parse::<i32>() {
                if step > 0 {
                    return value % step == 0;
                }
            }
            return false;
        }

        // Handle range: N-M
        if field.contains('-') {
            let range_parts: Vec<&str> = field.split('-').collect();
            if range_parts.len() == 2 {
                if let (Ok(start), Ok(end)) = (range_parts[0].parse::<i32>(), range_parts[1].parse::<i32>()) {
                    return value >= start && value <= end;
                }
            }
            return false;
        }

        // Handle list: N,M,O
        if field.contains(',') {
            return field.split(',').any(|part| {
                part.trim().parse::<i32>().map(|p| p == value).unwrap_or(false)
            });
        }

        // Simple value
        field.parse::<i32>().map(|p| p == value).unwrap_or(false)
    }

    /// Check interval shorthand expressions
    fn check_interval_shorthand(interval: &str, now: &chrono::DateTime<chrono::Utc>) -> bool {
        let (num_str, unit) = if interval.ends_with('s') {
            (&interval[..interval.len()-1], 's')
        } else if interval.ends_with('m') {
            (&interval[..interval.len()-1], 'm')
        } else if interval.ends_with('h') {
            (&interval[..interval.len()-1], 'h')
        } else {
            return false;
        };

        let num: i64 = match num_str.parse() {
            Ok(n) => n,
            Err(_) => return false,
        };

        if num <= 0 {
            return false;
        }

        let interval_secs = match unit {
            's' => num,
            'm' => num * 60,
            'h' => num * 3600,
            _ => return false,
        };

        // Check if current timestamp is within the scheduler check window of an interval boundary.
        // The scheduler checks every `check_interval` seconds (default 60s), so we use ±30s window.
        let timestamp = now.timestamp();
        let remainder = timestamp % interval_secs;
        // Fire if we're within ±30 seconds of an interval boundary
        remainder <= 30 || remainder >= (interval_secs - 30)
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use chrono::Timelike;

    #[test]
    fn test_cron_field_wildcard() {
        assert!(SchedulerService::cron_field_matches("*", 5));
        assert!(SchedulerService::cron_field_matches("?", 5));
    }

    #[test]
    fn test_cron_field_exact() {
        assert!(SchedulerService::cron_field_matches("5", 5));
        assert!(!SchedulerService::cron_field_matches("5", 6));
    }

    #[test]
    fn test_cron_field_step() {
        assert!(SchedulerService::cron_field_matches("*/5", 0));
        assert!(SchedulerService::cron_field_matches("*/5", 5));
        assert!(SchedulerService::cron_field_matches("*/5", 10));
        assert!(!SchedulerService::cron_field_matches("*/5", 3));
    }

    #[test]
    fn test_cron_field_range() {
        assert!(SchedulerService::cron_field_matches("1-5", 1));
        assert!(SchedulerService::cron_field_matches("1-5", 3));
        assert!(SchedulerService::cron_field_matches("1-5", 5));
        assert!(!SchedulerService::cron_field_matches("1-5", 0));
        assert!(!SchedulerService::cron_field_matches("1-5", 6));
    }

    #[test]
    fn test_cron_field_list() {
        assert!(SchedulerService::cron_field_matches("1,3,5", 1));
        assert!(SchedulerService::cron_field_matches("1,3,5", 3));
        assert!(SchedulerService::cron_field_matches("1,3,5", 5));
        assert!(!SchedulerService::cron_field_matches("1,3,5", 2));
    }

    #[test]
    fn test_should_fire_every_minute() {
        let now = chrono::Utc::now();
        assert!(SchedulerService::should_fire_cron("every:1m", &now));
    }

    #[test]
    fn test_should_fire_cron_wildcard() {
        let now = chrono::Utc::now();
        // Every minute match
        assert!(SchedulerService::should_fire_cron(
            &format!("{} * * * *", now.minute()),
            &now,
        ));
    }

    #[test]
    fn test_should_not_fire_cron() {
        let now = chrono::Utc::now();
        let wrong_minute = if now.minute() < 59 { now.minute() + 1 } else { 0 };
        assert!(!SchedulerService::should_fire_cron(
            &format!("{} * * * *", wrong_minute),
            &now,
        ));
    }
}