use super::*;

/// A schema defining a binary tree over a `TreeHashCache`.
///
/// This structure is used for succinct storage, run-time functionality is gained by converting the
/// schema into a `BTreeOverlay`.
#[derive(Debug, PartialEq, Clone)]
pub struct BTreeSchema {
    /// The depth of a schema defines how far it is nested within other fixed-length items.
    ///
    /// Each time a new variable-length object is created all items within it are assigned a depth
    /// of `depth + 1`.
    ///
    /// When storing the schemas in a list, the depth parameter allows for removing all schemas
    /// belonging to a specific variable-length item without removing schemas related to adjacent
    /// variable-length items.
    pub depth: usize,
    lengths: Vec<usize>,
}

impl BTreeSchema {
    pub fn from_lengths(depth: usize, lengths: Vec<usize>) -> Self {
        Self { depth, lengths }
    }

    pub fn into_overlay(self, offset: usize) -> BTreeOverlay {
        BTreeOverlay::from_schema(self, offset)
    }
}

impl Into<BTreeSchema> for BTreeOverlay {
    fn into(self) -> BTreeSchema {
        BTreeSchema {
            depth: self.depth,
            lengths: self.lengths,
        }
    }
}

/// Provides a status for some leaf-node in binary tree.
#[derive(Debug, PartialEq, Clone)]
pub enum LeafNode {
    /// The leaf node does not exist in this tree.
    DoesNotExist,
    /// The leaf node exists in the tree and has a real value within the given `chunk` range.
    Exists(Range<usize>),
    /// The leaf node exists in the tree only as padding.
    Padding,
}

/// Instantiated from a `BTreeSchema`, allows for interpreting some chunks of a `TreeHashCache` as
/// a perfect binary tree.
///
/// The primary purpose of this struct is to map from binary tree "nodes" to `TreeHashCache`
/// "chunks". Each tree has nodes `0..n` where `n` is the number of nodes and `0` is the root node.
/// Each of these nodes is mapped to a chunk, starting from `self.offset` and increasing in steps
/// of `1` for internal nodes and arbitrary steps for leaf-nodes.
#[derive(Debug, PartialEq, Clone)]
pub struct BTreeOverlay {
    offset: usize,
    /// See `BTreeSchema.depth` for a description.
    pub depth: usize,
    lengths: Vec<usize>,
}

impl BTreeOverlay {
    /// Instantiates a new instance for `item`, where it's first chunk is `inital_offset` and has
    /// the specified `depth`.
    pub fn new<T>(item: &T, initial_offset: usize, depth: usize) -> Self
    where
        T: CachedTreeHash,
    {
        Self::from_schema(item.tree_hash_cache_schema(depth), initial_offset)
    }

    /// Instantiates a new instance from a schema, where it's first chunk is `offset`.
    pub fn from_schema(schema: BTreeSchema, offset: usize) -> Self {
        Self {
            offset,
            depth: schema.depth,
            lengths: schema.lengths,
        }
    }

    /// Returns a `LeafNode` for each of the `n` leaves of the tree.
    ///
    /// `LeafNode::DoesNotExist` is returned for each element `i` in `0..n` where `i >=
    /// self.num_leaf_nodes()`.
    pub fn get_leaf_nodes(&self, n: usize) -> Vec<LeafNode> {
        let mut running_offset = self.offset + self.num_internal_nodes();

        let mut leaf_nodes: Vec<LeafNode> = self
            .lengths
            .iter()
            .map(|length| {
                let range = running_offset..running_offset + length;
                running_offset += length;
                LeafNode::Exists(range)
            })
            .collect();

        leaf_nodes.resize(self.num_leaf_nodes(), LeafNode::Padding);
        leaf_nodes.resize(n, LeafNode::DoesNotExist);

        leaf_nodes
    }

    /// Returns the number of leaf nodes in the tree.
    pub fn num_leaf_nodes(&self) -> usize {
        self.lengths.len().next_power_of_two()
    }

    /// Returns the number of leafs in the tree which are padding.
    pub fn num_padding_leaves(&self) -> usize {
        self.num_leaf_nodes() - self.lengths.len()
    }

    /// Returns the number of nodes in the tree.
    ///
    /// Note: this is distinct from `num_chunks`, which returns the total number of chunks in
    /// this tree.
    pub fn num_nodes(&self) -> usize {
        2 * self.num_leaf_nodes() - 1
    }

    /// Returns the number of internal (non-leaf) nodes in the tree.
    pub fn num_internal_nodes(&self) -> usize {
        self.num_leaf_nodes() - 1
    }

    /// Returns the chunk of the first node of the tree.
    fn first_node(&self) -> usize {
        self.offset
    }

    /// Returns the root chunk of the tree (the zero-th node)
    pub fn root(&self) -> usize {
        self.first_node()
    }

    /// Returns the first chunk outside of the boundary of this tree. It is the root node chunk
    /// plus the total number of chunks in the tree.
    pub fn next_node(&self) -> usize {
        self.first_node() + self.num_internal_nodes() + self.num_leaf_nodes() - self.lengths.len()
            + self.lengths.iter().sum::<usize>()
    }

    /// Returns the height of the tree where a tree with a single node has a height of 1.
    pub fn height(&self) -> usize {
        self.num_leaf_nodes().trailing_zeros() as usize
    }

    /// Returns the range of chunks that belong to the internal nodes of the tree.
    pub fn internal_chunk_range(&self) -> Range<usize> {
        self.offset..self.offset + self.num_internal_nodes()
    }

    /// Returns all of the chunks that are encompassed by the tree.
    pub fn chunk_range(&self) -> Range<usize> {
        self.first_node()..self.next_node()
    }

    /// Returns the number of chunks inside this tree (including subtrees).
    ///
    /// Note: this is distinct from `num_nodes` which returns the number of nodes in the binary
    /// tree.
    pub fn num_chunks(&self) -> usize {
        self.next_node() - self.first_node()
    }

    /// Returns the first chunk of the first leaf node in the tree.
    pub fn first_leaf_node(&self) -> usize {
        self.offset + self.num_internal_nodes()
    }

    /// Returns the chunks for some given parent node.
    ///
    /// Note: it is a parent _node_ not a parent _chunk_.
    pub fn child_chunks(&self, parent: usize) -> (usize, usize) {
        let children = children(parent);

        if children.1 < self.num_internal_nodes() {
            (children.0 + self.offset, children.1 + self.offset)
        } else {
            let chunks = self.n_leaf_node_chunks(children.1);
            (chunks[chunks.len() - 2], chunks[chunks.len() - 1])
        }
    }

    /// Returns a vec of (parent_chunk, (left_child_chunk, right_child_chunk)).
    pub fn internal_parents_and_children(&self) -> Vec<(usize, (usize, usize))> {
        let mut chunks = Vec::with_capacity(self.num_nodes());
        chunks.append(&mut self.internal_node_chunks());
        chunks.append(&mut self.leaf_node_chunks());

        (0..self.num_internal_nodes())
            .map(|parent| {
                let children = children(parent);
                (chunks[parent], (chunks[children.0], chunks[children.1]))
            })
            .collect()
    }

    /// Returns a vec of chunk indices for each internal node of the tree.
    pub fn internal_node_chunks(&self) -> Vec<usize> {
        (self.offset..self.offset + self.num_internal_nodes()).collect()
    }

    /// Returns a vec of the first chunk for each leaf node of the tree.
    pub fn leaf_node_chunks(&self) -> Vec<usize> {
        self.n_leaf_node_chunks(self.num_leaf_nodes())
    }

    /// Returns a vec of the first chunk index for the first `n` leaf nodes of the tree.
    fn n_leaf_node_chunks(&self, n: usize) -> Vec<usize> {
        let mut chunks = Vec::with_capacity(n);

        let mut chunk = self.offset + self.num_internal_nodes();
        for i in 0..n {
            chunks.push(chunk);

            match self.lengths.get(i) {
                Some(len) => {
                    chunk += len;
                }
                None => chunk += 1,
            }
        }

        chunks
    }
}

fn children(parent: usize) -> (usize, usize) {
    ((2 * parent + 1), (2 * parent + 2))
}

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

    fn get_tree_a(n: usize) -> BTreeOverlay {
        BTreeSchema::from_lengths(0, vec![1; n]).into_overlay(0)
    }

    #[test]
    fn leaf_node_chunks() {
        let tree = get_tree_a(4);

        assert_eq!(tree.leaf_node_chunks(), vec![3, 4, 5, 6])
    }

    #[test]
    fn internal_node_chunks() {
        let tree = get_tree_a(4);

        assert_eq!(tree.internal_node_chunks(), vec![0, 1, 2])
    }

    #[test]
    fn internal_parents_and_children() {
        let tree = get_tree_a(4);

        assert_eq!(
            tree.internal_parents_and_children(),
            vec![(0, (1, 2)), (1, (3, 4)), (2, (5, 6))]
        )
    }

    #[test]
    fn chunk_range() {
        let tree = get_tree_a(4);
        assert_eq!(tree.chunk_range(), 0..7);

        let tree = get_tree_a(1);
        assert_eq!(tree.chunk_range(), 0..1);

        let tree = get_tree_a(2);
        assert_eq!(tree.chunk_range(), 0..3);

        let tree = BTreeSchema::from_lengths(0, vec![1, 1]).into_overlay(11);
        assert_eq!(tree.chunk_range(), 11..14);

        let tree = BTreeSchema::from_lengths(0, vec![7, 7, 7]).into_overlay(0);
        assert_eq!(tree.chunk_range(), 0..25);
    }

    #[test]
    fn get_leaf_node() {
        let tree = get_tree_a(4);
        let leaves = tree.get_leaf_nodes(5);

        assert_eq!(leaves[0], LeafNode::Exists(3..4));
        assert_eq!(leaves[1], LeafNode::Exists(4..5));
        assert_eq!(leaves[2], LeafNode::Exists(5..6));
        assert_eq!(leaves[3], LeafNode::Exists(6..7));
        assert_eq!(leaves[4], LeafNode::DoesNotExist);

        let tree = get_tree_a(3);
        let leaves = tree.get_leaf_nodes(5);

        assert_eq!(leaves[0], LeafNode::Exists(3..4));
        assert_eq!(leaves[1], LeafNode::Exists(4..5));
        assert_eq!(leaves[2], LeafNode::Exists(5..6));
        assert_eq!(leaves[3], LeafNode::Padding);
        assert_eq!(leaves[4], LeafNode::DoesNotExist);

        let tree = get_tree_a(0);
        let leaves = tree.get_leaf_nodes(2);

        assert_eq!(leaves[0], LeafNode::Padding);
        assert_eq!(leaves[1], LeafNode::DoesNotExist);

        let tree = BTreeSchema::from_lengths(0, vec![3]).into_overlay(0);
        let leaves = tree.get_leaf_nodes(2);
        assert_eq!(leaves[0], LeafNode::Exists(0..3));
        assert_eq!(leaves[1], LeafNode::DoesNotExist);

        let tree = BTreeSchema::from_lengths(0, vec![3]).into_overlay(10);
        let leaves = tree.get_leaf_nodes(2);
        assert_eq!(leaves[0], LeafNode::Exists(10..13));
        assert_eq!(leaves[1], LeafNode::DoesNotExist);
    }

    #[test]
    fn root_of_one_node() {
        let tree = get_tree_a(1);

        assert_eq!(tree.root(), 0);
        assert_eq!(tree.num_internal_nodes(), 0);
        assert_eq!(tree.num_leaf_nodes(), 1);
    }

    #[test]
    fn child_chunks() {
        let tree = get_tree_a(4);

        assert_eq!(tree.child_chunks(0), (1, 2))
    }
}