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use super::*;
use std::vec::IntoIter;

pub struct ActionFieldSolver<'a, T> {
    map: &'a HexagonMap<T>,
    open: BTreeMap<AxialPoint, f64>,
    close: BTreeMap<AxialPoint, f64>,
    passable: Box<dyn Fn(&AxialPoint, &T) -> bool>,
    action_cost: Box<dyn Fn(&AxialPoint, &T) -> f64>,
    action_points: f64,
}

impl<T> HexagonMap<T> {
    /// Set the passable function.
    ///
    /// # Arguments
    ///
    /// * `passable`:  A function that returns true if the point is passable.
    ///
    /// returns: PathFinder<T>
    ///
    /// # Examples
    ///
    /// ```
    /// # use hexagon_map::HexagonMap;
    /// ```
    pub fn action_field(&self, start: AxialPoint, action: f64) -> ActionFieldSolver<T> {
        let mut open = BTreeMap::new();
        open.insert(start, 0.0);
        ActionFieldSolver {
            map: self,
            open,
            close: Default::default(),
            action_points: action,
            passable: Box::new(|_, _| true),
            action_cost: Box::new(|_, _| 0.0),
        }
    }
}

impl<'a, T> ActionFieldSolver<'a, T> {
    pub fn with_passable<F>(mut self, passable: F) -> Self
    where
        F: Fn(&AxialPoint, &T) -> bool + 'static,
    {
        self.passable = Box::new(passable);
        self
    }
    pub fn with_cost<F>(mut self, cost: F) -> Self
    where
        F: Fn(&AxialPoint, &T) -> f64 + 'static,
    {
        self.action_cost = Box::new(cost);
        self
    }
}

impl<'a, T> ActionFieldSolver<'a, T> {
    /// Get all passable neighbors from a point
    pub fn neighbors(&self, point: &AxialPoint) -> Vec<(AxialPoint, f64)> {
        let mut neighbors = Vec::with_capacity(6);
        for direction in Direction::all() {
            let key = point.go(direction);
            if let Some(value) = self.map.sparse.get(&key) {
                if !(self.passable)(&key, value) {
                    continue;
                }
                if self.close.contains_key(&key) {
                    continue;
                }
                let cost = (self.action_cost)(point, value);
                neighbors.push((key, cost));
            }
        }
        neighbors
    }
    pub fn solve(mut self) -> impl Iterator<Item = (f64, AxialPoint)> {
        while let Some((point, cost)) = self.open.pop_first() {
            for (neighbor, neighbor_cost) in self.neighbors(&point) {
                let new_cost = cost + neighbor_cost;
                if new_cost > self.action_points {
                    continue;
                }
                else {
                    self.open.insert(neighbor, new_cost);
                }
            }
            self.close.insert(point, cost);
        }
        self.close.iter().map(|(k, v)| (*v, *k)).sorted_unstable_by(|a, b| a.0.partial_cmp(&b.0).unwrap_or(Ordering::Equal))
    }
}

impl<'a, T> IntoIterator for ActionFieldSolver<'a, T> {
    type Item = (f64, AxialPoint);
    type IntoIter = IntoIter<Self::Item>;
    fn into_iter(self) -> Self::IntoIter {
        self.solve().collect_vec().into_iter()
    }
}