use std::sync::atomic::{AtomicBool, Ordering};

use crate::{
    config::{ToxicPair, UserConfig},
    errors::SearchError,
    resident::ResidentId,
    schedule::MonthlySchedule,
    slot::Slot,
    timer::Timer,
    workload::{WorkloadBounds, WorkloadTracker},
};

use rand::{rngs::SmallRng, seq::SliceRandom, SeedableRng};
use rayon::{
    current_thread_index,
    iter::{IntoParallelRefIterator, ParallelIterator},
};

pub struct Scheduler {
    pub config: UserConfig,
    pub bounds: WorkloadBounds,
    pub timer: Timer,
}

impl Scheduler {
    pub fn new(config: UserConfig, bounds: WorkloadBounds) -> Self {
        Self {
            config,
            bounds,
            timer: Timer::default(),
        }
    }

    pub fn new_with_config(config: UserConfig) -> Self {
        let bounds = WorkloadBounds::new_with_config(&config);

        Self {
            config,
            bounds,
            timer: Timer::default(),
        }
    }

    pub fn run(
        &self,
        schedule: &mut MonthlySchedule,
        tracker: &mut WorkloadTracker,
    ) -> Result<bool, SearchError> {
        schedule.prefill(&self.config);
        for (slot, res_id) in schedule.0.iter() {
            tracker.insert(*res_id, &self.config, *slot);
        }

        //TODO: add validation

        // find first non-manually-filled slot
        let slot = (0..=self.config.total_slots)
            .find(|&slot_idx| !schedule.0.contains_key(&Slot::from(slot_idx)))
            .map(Slot::from)
            .ok_or(SearchError::ScheduleFull)?;

        let resident_ids = self.valid_residents(slot, schedule, tracker);
        let solved_in_thread = AtomicBool::new(false);

        let sovled_state = resident_ids.par_iter().find_map_any(|&id| {
            let mut local_schedule = schedule.clone();
            let mut local_tracker = tracker.clone();

            local_schedule.insert(slot, id);
            local_tracker.insert(id, &self.config, slot);

            let solved = self.search(
                &mut local_schedule,
                &mut local_tracker,
                slot.next(),
                &solved_in_thread,
            );

            match solved {
                Ok(true) => Some((local_schedule, local_tracker)),
                Ok(false) => None,
                Err(e) => {
                    let thread_id = current_thread_index().unwrap();
                    log::log!(e.log_level(), "Thread Id: [{}] {}", thread_id, e);
                    None
                }
            }
        });

        if let Some((solved_schedule, solved_tracker)) = sovled_state {
            *schedule = solved_schedule;
            *tracker = solved_tracker;
            return Ok(true);
        }

        Ok(false)
    }

    /// DFS where maximum depth is calculated by total_days_of_month + odd_days_of_month each node is called a slot
    /// Starts with schedule partially completed from the user interface
    /// Ends with a full schedule following restrictions and fairness
    pub fn search(
        &self,
        schedule: &mut MonthlySchedule,
        tracker: &mut WorkloadTracker,
        slot: Slot,
        solved_in_thread: &AtomicBool,
    ) -> Result<bool, SearchError> {
        if solved_in_thread.load(Ordering::Relaxed) {
            return Err(SearchError::SolutionFound);
        }

        if self.timer.limit_exceeded() {
            return Err(SearchError::Timeout);
        }

        if schedule.has_resident_in_consecutive_days(&slot.previous()) {
            return Ok(false);
        }

        if self.found_solution(slot) {
            solved_in_thread.store(true, Ordering::Relaxed);
            return Ok(true);
        }

        if schedule.is_slot_manually_assigned(&slot) {
            return self.search(schedule, tracker, slot.next(), solved_in_thread);
        }

        let mut rng = SmallRng::from_rng(&mut rand::rng());
        let mut valid_resident_ids = self.valid_residents(slot, schedule, tracker);
        valid_resident_ids.shuffle(&mut rng);
        valid_resident_ids.sort_by_key(|res_id| {
            let type_count = tracker.current_shift_type_workload(res_id, slot.shift_type());
            let workload = tracker.current_workload(res_id);
            (type_count, workload)
        });

        for id in valid_resident_ids {
            schedule.insert(slot, id);
            tracker.insert(id, &self.config, slot);

            if self.search(schedule, tracker, slot.next(), solved_in_thread)? {
                return Ok(true);
            }

            schedule.remove(slot);
            tracker.remove(id, &self.config, slot);
        }

        Ok(false)
    }

    pub fn found_solution(&self, slot: Slot) -> bool {
        slot.greater_than(self.config.total_days)
    }

    /// Return all valid residents for the current slot
    pub fn valid_residents(
        &self,
        slot: Slot,
        schedule: &MonthlySchedule,
        tracker: &WorkloadTracker,
    ) -> Vec<ResidentId> {
        let is_holiday_slot = self.config.is_holiday_or_weekend_slot(slot);
        let other_resident_id = slot
            .other_position()
            .and_then(|partner_slot| schedule.get_resident_id(&partner_slot));

        self.config
            .residents
            .iter()
            .filter(|r| {
                if let Some(other_id) = other_resident_id {
                    if &r.id == other_id {
                        return false;
                    }

                    if self
                        .config
                        .toxic_pairs
                        .iter()
                        .any(|tp| tp.matches(&ToxicPair::from((r.id, *other_id))))
                    {
                        return false;
                    }
                }

                !r.negative_shifts.contains(&slot.day)
                    && r.allowed_types.contains(&slot.shift_type())
                    && !tracker.reached_workload_limit(&self.bounds, &r.id)
                    && (!is_holiday_slot || !tracker.reached_holiday_limit(&self.bounds, &r.id))
                    && !tracker.reached_shift_type_limit(&self.bounds, &r.id, slot.shift_type())
            })
            .map(|r| r.id)
            .collect()
    }
}