//! Arena.

#[cfg(not(feature = "std"))]
use alloc::vec::Vec;

#[cfg(not(feature = "std"))]
use core::{
    num::NonZeroUsize,
    ops::{Index, IndexMut},
};

#[cfg(feature = "par_iter")]
use rayon::prelude::*;

#[cfg(feature = "deser")]
use serde::{Deserialize, Serialize};

#[cfg(feature = "std")]
use std::{
    num::NonZeroUsize,
    ops::{Index, IndexMut},
};

use crate::{Node, NodeId};

#[derive(PartialEq, Eq, Clone, Debug)]
#[cfg_attr(feature = "deser", derive(Deserialize, Serialize))]
/// An `Arena` structure containing certain [`Node`]s.
///
/// [`Node`]: struct.Node.html
pub struct Arena<T> {
    nodes: Vec<Node<T>>,
}

impl<T> Arena<T> {
    /// Creates a new empty `Arena`.
    pub fn new() -> Arena<T> {
        Self::default()
    }

    /// Retrieves the `NodeId` correspoding to a `Node` in the `Arena`.
    /// Note that this method can only be used if the datatype of the `Node` implements
    /// the `PartialEq` trait.
    pub fn get_node_id(&self, node: &Node<T>) -> Option<NodeId>
    where
        T: PartialEq,
    {
        if let Some(node_id) = self.nodes.iter().position(|n| n.data == node.data) {
            if let Some(node_id_non_zero) = NonZeroUsize::new(node_id.wrapping_add(1)) {
                Some(NodeId::from_non_zero_usize(node_id_non_zero))
            } else {
                None
            }
        } else {
            None
        }
    }

    /// Creates a new node from its associated data.
    ///
    /// # Panics
    ///
    /// Panics if the arena already has `usize::max_value()` nodes.
    ///
    /// # Examples
    ///
    /// ```
    /// # use indextree::Arena;
    /// let mut arena = Arena::new();
    /// let foo = arena.new_node("foo");
    ///
    /// assert_eq!(*arena[foo].get(), "foo");
    /// ```
    pub fn new_node(&mut self, data: T) -> NodeId {
        let next_index1 = NonZeroUsize::new(self.nodes.len().wrapping_add(1))
            .expect("Too many nodes in the arena");
        self.nodes.push(Node::new(data));
        NodeId::from_non_zero_usize(next_index1)
    }

    /// Counts the number of nodes in arena and returns it.
    ///
    /// # Examples
    ///
    /// ```
    /// # use indextree::Arena;
    /// let mut arena = Arena::new();
    /// let foo = arena.new_node("foo");
    /// let _bar = arena.new_node("bar");
    /// assert_eq!(arena.count(), 2);
    ///
    /// foo.remove(&mut arena);
    /// assert_eq!(arena.count(), 2);
    /// ```
    pub fn count(&self) -> usize {
        self.nodes.len()
    }

    /// Returns `true` if arena has no nodes, `false` otherwise.
    ///
    /// # Examples
    ///
    /// ```
    /// # use indextree::Arena;
    /// let mut arena = Arena::new();
    /// assert!(arena.is_empty());
    ///
    /// let foo = arena.new_node("foo");
    /// assert!(!arena.is_empty());
    ///
    /// foo.remove(&mut arena);
    /// assert!(!arena.is_empty());
    /// ```
    pub fn is_empty(&self) -> bool {
        self.count() == 0
    }

    /// Returns a reference to the node with the given id if in the arena.
    ///
    /// Returns `None` if not available.
    ///
    /// # Examples
    ///
    /// ```
    /// # use indextree::{Arena, NodeId};
    /// let mut arena = Arena::new();
    /// let foo = arena.new_node("foo");
    /// assert_eq!(arena.get(foo).map(|node| *node.get()), Some("foo"));
    /// ```
    ///
    /// Note that this does not check whether the given node ID is created by
    /// the arena.
    ///
    /// ```
    /// # use indextree::Arena;
    /// let mut arena = Arena::new();
    /// let foo = arena.new_node("foo");
    /// let bar = arena.new_node("bar");
    /// assert_eq!(arena.get(foo).map(|node| *node.get()), Some("foo"));
    ///
    /// let mut another_arena = Arena::new();
    /// let _ = another_arena.new_node("Another arena");
    /// assert_eq!(another_arena.get(foo).map(|node| *node.get()), Some("Another arena"));
    /// assert!(another_arena.get(bar).is_none());
    /// ```
    pub fn get(&self, id: NodeId) -> Option<&Node<T>> {
        self.nodes.get(id.index0())
    }

    /// Returns a mutable reference to the node with the given id if in the
    /// arena.
    ///
    /// Returns `None` if not available.
    ///
    /// # Examples
    ///
    /// ```
    /// # use indextree::{Arena, NodeId};
    /// let mut arena = Arena::new();
    /// let foo = arena.new_node("foo");
    /// assert_eq!(arena.get(foo).map(|node| *node.get()), Some("foo"));
    ///
    /// *arena.get_mut(foo).expect("The `foo` node exists").get_mut() = "FOO!";
    /// assert_eq!(arena.get(foo).map(|node| *node.get()), Some("FOO!"));
    /// ```
    pub fn get_mut(&mut self, id: NodeId) -> Option<&mut Node<T>> {
        self.nodes.get_mut(id.index0())
    }

    /// Returns an iterator of all nodes in the arena in storage-order.
    ///
    /// Note that this iterator returns also removed elements, which can be
    /// tested with the [`is_removed()`] method on the node.
    ///
    /// # Examples
    ///
    /// ```
    /// # use indextree::Arena;
    /// let mut arena = Arena::new();
    /// let _foo = arena.new_node("foo");
    /// let _bar = arena.new_node("bar");
    ///
    /// let mut iter = arena.iter();
    /// assert_eq!(iter.next().map(|node| *node.get()), Some("foo"));
    /// assert_eq!(iter.next().map(|node| *node.get()), Some("bar"));
    /// assert_eq!(iter.next().map(|node| *node.get()), None);
    /// ```
    ///
    /// ```
    /// # use indextree::Arena;
    /// let mut arena = Arena::new();
    /// let _foo = arena.new_node("foo");
    /// let bar = arena.new_node("bar");
    /// bar.remove(&mut arena);
    ///
    /// let mut iter = arena.iter();
    /// assert_eq!(iter.next().map(|node| (*node.get(), node.is_removed())), Some(("foo", false)));
    /// assert_eq!(iter.next().map(|node| (*node.get(), node.is_removed())), Some(("bar", true)));
    /// assert_eq!(iter.next().map(|node| (*node.get(), node.is_removed())), None);
    /// ```
    ///
    /// [`is_removed()`]: struct.Node.html#method.is_removed
    pub fn iter(&self) -> impl Iterator<Item = &Node<T>> {
        self.nodes.iter()
    }
}

#[cfg(feature = "par_iter")]
impl<T: Sync> Arena<T> {
    /// Returns an parallel iterator over the whole arena.
    ///
    /// Note that this iterator returns also removed elements, which can be
    /// tested with the [`is_removed()`] method on the node.
    ///
    /// [`is_removed()`]: struct.Node.html#method.is_removed
    pub fn par_iter(&self) -> rayon::slice::Iter<'_, Node<T>> {
        self.nodes.par_iter()
    }
}

impl<T> Default for Arena<T> {
    fn default() -> Self {
        Self { nodes: Vec::new() }
    }
}

impl<T> Index<NodeId> for Arena<T> {
    type Output = Node<T>;

    fn index(&self, node: NodeId) -> &Node<T> {
        &self.nodes[node.index0()]
    }
}

impl<T> IndexMut<NodeId> for Arena<T> {
    fn index_mut(&mut self, node: NodeId) -> &mut Node<T> {
        &mut self.nodes[node.index0()]
    }
}