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use anyhow::Result;

use crate::storage::mkvs::{
    cache::Cache,
    tree::{
        Depth, Key, KeyTrait, NodeBox, NodeKind, NodePointer, NodePtrRef, NodeRef, Tree, Value,
    },
};

use super::lookup::FetcherSyncGet;

impl Tree {
    /// Remove entry with given key, returning the value at the key if the key was previously
    /// in the database.
    pub fn remove(&mut self, key: &[u8]) -> Result<Option<Vec<u8>>> {
        let boxed_key = key.to_vec();
        let pending_root = self.cache.borrow().get_pending_root();

        // Remember where the path from root to target node ends (will end).
        self.cache.borrow_mut().mark_position();

        let (new_root, _, old_val) = self._remove(pending_root, 0, &boxed_key)?;
        self.cache.borrow_mut().set_pending_root(new_root);

        Ok(old_val)
    }

    fn _remove(
        &mut self,
        ptr: NodePtrRef,
        bit_depth: Depth,
        key: &Key,
    ) -> Result<(NodePtrRef, bool, Option<Value>)> {
        let node_ref = self
            .cache
            .borrow_mut()
            .deref_node_ptr(ptr.clone(), Some(FetcherSyncGet::new(key, true)))?;

        match classify_noderef!(?node_ref) {
            NodeKind::None => {
                // Remove from nil node.
                Ok((NodePointer::null_ptr(), false, None))
            }
            NodeKind::Internal => {
                // Remove from internal node and recursively collapse the path, if needed.
                let node_ref = node_ref.unwrap();
                let (changed, old_val): (bool, Option<Value>);
                let (remaining_leaf, remaining_left, remaining_right): (
                    Option<NodeRef>,
                    Option<NodeRef>,
                    Option<NodeRef>,
                );
                if let NodeBox::Internal(ref mut n) = *node_ref.borrow_mut() {
                    // Remove from internal node and recursively collapse the branch, if
                    // needed.
                    let bit_length = bit_depth + n.label_bit_length;

                    if key.bit_length() < bit_length {
                        // Lookup key is too short for the current n.Label, so it doesn't exist.
                        return Ok((ptr, false, None));
                    }

                    let (new_child, c, o) = if key.bit_length() == bit_length {
                        self._remove(n.leaf_node.clone(), bit_depth, key)?
                    } else if key.get_bit(bit_length) {
                        self._remove(n.right.clone(), bit_length, key)?
                    } else {
                        self._remove(n.left.clone(), bit_length, key)?
                    };

                    changed = c;
                    old_val = o;

                    if key.bit_length() == bit_length {
                        n.leaf_node = new_child;
                    } else if key.get_bit(bit_length) {
                        n.right = new_child;
                    } else {
                        n.left = new_child;
                    }

                    // Fetch and check the remaining children.
                    // NOTE: The leaf node is always included with the internal node.
                    remaining_leaf = n.leaf_node.borrow().node.clone();
                    remaining_left = self
                        .cache
                        .borrow_mut()
                        .deref_node_ptr(n.left.clone(), Some(FetcherSyncGet::new(key, true)))?;
                    remaining_right = self
                        .cache
                        .borrow_mut()
                        .deref_node_ptr(n.right.clone(), Some(FetcherSyncGet::new(key, true)))?;
                } else {
                    unreachable!("node kind is Internal");
                }

                // If exactly one child including LeafNode remains, collapse it.
                match remaining_leaf {
                    Some(_) => match remaining_left {
                        Some(_) => (),
                        None => match remaining_right {
                            None => {
                                let nd_leaf = noderef_as!(node_ref, Internal).leaf_node.clone();
                                noderef_as_mut!(node_ref, Internal).leaf_node =
                                    NodePointer::null_ptr();
                                self.cache.borrow_mut().remove_node(ptr);
                                return Ok((nd_leaf, true, old_val));
                            }
                            Some(_) => (),
                        },
                    },
                    None => {
                        let mut nd_child: Option<NodeRef> = None;
                        let mut node_ptr: NodePtrRef = NodePointer::null_ptr();
                        let mut both_children = true;
                        match remaining_left {
                            Some(_) => match remaining_right {
                                None => {
                                    node_ptr = noderef_as!(node_ref, Internal).left.clone();
                                    noderef_as_mut!(node_ref, Internal).left =
                                        NodePointer::null_ptr();
                                    nd_child = remaining_left;
                                    both_children = false;
                                }
                                Some(_) => (),
                            },
                            None => match remaining_right {
                                None => (),
                                Some(_) => {
                                    node_ptr = noderef_as!(node_ref, Internal).right.clone();
                                    noderef_as_mut!(node_ref, Internal).right =
                                        NodePointer::null_ptr();
                                    nd_child = remaining_right;
                                    both_children = false;
                                }
                            },
                        }

                        if !both_children {
                            // If child is an internal node, also fix the label.
                            if let Some(nd_child) = nd_child {
                                if let NodeKind::Internal = classify_noderef!(nd_child) {
                                    if let NodeBox::Internal(ref mut inode) = *nd_child.borrow_mut()
                                    {
                                        inode.label = noderef_as!(node_ref, Internal).label.merge(
                                            noderef_as!(node_ref, Internal).label_bit_length,
                                            &inode.label,
                                            inode.label_bit_length,
                                        );
                                        inode.label_bit_length +=
                                            noderef_as!(node_ref, Internal).label_bit_length;
                                        inode.clean = false;
                                        node_ptr.borrow_mut().clean = false;
                                    }
                                }
                            }

                            self.cache.borrow_mut().remove_node(ptr);
                            return Ok((node_ptr, true, old_val));
                        }
                    }
                };

                // Two or more children including leaf_node remain, just mark dirty bit.
                if changed {
                    noderef_as_mut!(node_ref, Internal).clean = false;
                    ptr.borrow_mut().clean = false;
                    // No longer eligible for eviction as it is dirty.
                    self.cache
                        .borrow_mut()
                        .rollback_node(ptr.clone(), NodeKind::Internal);
                }

                Ok((ptr, changed, old_val))
            }
            NodeKind::Leaf => {
                // Remove from leaf node.
                let node_ref = node_ref.unwrap();
                if noderef_as!(node_ref, Leaf).key == *key {
                    let old_val = noderef_as!(node_ref, Leaf).value.clone();
                    self.cache.borrow_mut().remove_node(ptr);
                    return Ok((NodePointer::null_ptr(), true, Some(old_val)));
                }

                Ok((ptr, false, None))
            }
        }
    }
}