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use crate::{error::Error, Node};

use std::collections::{HashMap, HashSet};
use std::fmt;
use std::hash::Hash;
use std::sync::{Arc, RwLock};

pub type InnerDependencyMap<I> = HashMap<I, HashSet<I>>;
pub type DependencyMap<I> = Arc<RwLock<InnerDependencyMap<I>>>;

/// Dependency graph
pub struct DepGraph<I>
where
    I: Clone + fmt::Debug + Eq + Hash + PartialEq + Send + Sync + 'static,
{
    pub ready_nodes: Vec<I>,
    pub deps: DependencyMap<I>,
    pub rdeps: DependencyMap<I>,
}

impl<I> DepGraph<I>
where
    I: Clone + fmt::Debug + Eq + Hash + PartialEq + Send + Sync + 'static,
{
    /// Create a new DepGraph based on a vector of edges.
    pub fn new(nodes: &[Node<I>]) -> Self {
        let (deps, rdeps, ready_nodes) = DepGraph::parse_nodes(nodes);

        DepGraph {
            ready_nodes,
            deps,
            rdeps,
        }
    }

    fn parse_nodes(nodes: &[Node<I>]) -> (DependencyMap<I>, DependencyMap<I>, Vec<I>) {
        let mut deps = InnerDependencyMap::<I>::default();
        let mut rdeps = InnerDependencyMap::<I>::default();
        let mut ready_nodes = Vec::<I>::default();

        for node in nodes {
            deps.insert(node.id().clone(), node.deps().clone());

            if node.deps().is_empty() {
                ready_nodes.push(node.id().clone());
            }

            for node_dep in node.deps() {
                if !rdeps.contains_key(node_dep) {
                    let mut dep_rdeps = HashSet::new();
                    dep_rdeps.insert(node.id().clone());
                    rdeps.insert(node_dep.clone(), dep_rdeps.clone());
                } else {
                    let dep_rdeps = rdeps.get_mut(node_dep).unwrap();
                    dep_rdeps.insert(node.id().clone());
                }
            }
        }

        (
            Arc::new(RwLock::new(deps)),
            Arc::new(RwLock::new(rdeps)),
            ready_nodes,
        )
    }
}

impl<I> IntoIterator for DepGraph<I>
where
    I: Clone + fmt::Debug + Eq + Hash + PartialEq + Send + Sync + 'static,
{
    type Item = I;
    type IntoIter = DepGraphIter<I>;

    fn into_iter(self) -> Self::IntoIter {
        DepGraphIter::<I>::new(self.ready_nodes.clone(), self.deps.clone(), self.rdeps)
    }
}

#[derive(Clone)]
pub struct DepGraphIter<I>
where
    I: Clone + fmt::Debug + Eq + Hash + PartialEq + Send + Sync + 'static,
{
    ready_nodes: Vec<I>,
    deps: DependencyMap<I>,
    rdeps: DependencyMap<I>,
}

impl<I> DepGraphIter<I>
where
    I: Clone + fmt::Debug + Eq + Hash + PartialEq + Send + Sync + 'static,
{
    pub fn new(ready_nodes: Vec<I>, deps: DependencyMap<I>, rdeps: DependencyMap<I>) -> Self {
        Self {
            ready_nodes,
            deps,
            rdeps,
        }
    }
}

impl<I> Iterator for DepGraphIter<I>
where
    I: Clone + fmt::Debug + Eq + Hash + PartialEq + Send + Sync + 'static,
{
    type Item = I;

    fn next(&mut self) -> Option<Self::Item> {
        if let Some(id) = self.ready_nodes.pop() {
            // Remove dependencies and retrieve next available nodes, if any.
            let next_nodes = remove_node_id::<I>(id.clone(), &self.deps, &self.rdeps).unwrap();

            // Push ready nodes
            self.ready_nodes.extend_from_slice(&next_nodes);

            // Return the node ID
            Some(id)
        } else {
            // No available node
            None
        }
    }
}

/// Remove all references to the node ID in the dependencies.
///
pub fn remove_node_id<I>(
    id: I,
    deps: &DependencyMap<I>,
    rdeps: &DependencyMap<I>,
) -> Result<Vec<I>, Error>
where
    I: Clone + fmt::Debug + Eq + Hash + PartialEq + Send + Sync + 'static,
{
    let rdep_ids = {
        match rdeps.read().unwrap().get(&id) {
            Some(node) => node.clone(),
            // If no node depends on a node, it will not appear
            // in rdeps.
            None => Default::default(),
        }
    };

    let mut deps = deps.write().unwrap();
    let next_nodes = rdep_ids
        .iter()
        .filter_map(|rdep_id| {
            let rdep = match deps.get_mut(&rdep_id) {
                Some(rdep) => rdep,
                None => return None,
            };

            rdep.remove(&id);

            if rdep.is_empty() {
                Some(rdep_id.clone())
            } else {
                None
            }
        })
        .collect();

    // Remove the current node from the list of dependencies.
    deps.remove(&id);

    Ok(next_nodes)
}