#![cfg_attr(feature = "nightly", deny(missing_docs))]
#![cfg_attr(feature = "nightly", feature(external_doc))]
#![cfg_attr(feature = "nightly", doc(include = "../README.md"))]

mod iterator;

pub use iterator::Iterator;

/// Returns the flat-tree of the tree node at the specified depth and offset.
///
/// ## Examples
/// ```rust
/// assert_eq!(flat_tree::index(0, 0), 0);
/// assert_eq!(flat_tree::index(0, 1), 2);
/// assert_eq!(flat_tree::index(0, 2), 4);
/// assert_eq!(flat_tree::index(1, 2), 9);
/// assert_eq!(flat_tree::index(1, 3), 13);
/// assert_eq!(flat_tree::index(2, 1), 11);
/// assert_eq!(flat_tree::index(2, 2), 19);
/// assert_eq!(flat_tree::index(3, 0), 7);
/// assert_eq!(flat_tree::index(3, 1), 23);
/// ```
pub fn index(depth: usize, offset: usize) -> usize {
  (offset << (depth + 1)) | ((1 << depth) - 1)
}

/// Returns the depth of a node.
///
/// ## Examples
/// ```rust
/// assert_eq!(flat_tree::depth(0), 0);
/// assert_eq!(flat_tree::depth(1), 1);
/// assert_eq!(flat_tree::depth(2), 0);
/// assert_eq!(flat_tree::depth(3), 2);
/// assert_eq!(flat_tree::depth(4), 0);
/// ```
pub fn depth(i: usize) -> usize {
  let mut depth = 0;
  let mut i = i;
  while is_odd(i) {
    i >>= 1;
    depth += 1;
  }
  depth
}

/// Returns the offset of a node with a depth.
pub fn offset_with_depth(i: usize, depth: usize) -> usize {
  if is_even(i) {
    i / 2
  } else {
    i >> (depth + 1)
  }
}

/// Returns the offset of a node.
///
/// ## Examples
/// ```rust
/// assert_eq!(flat_tree::offset(0), 0);
/// assert_eq!(flat_tree::offset(1), 0);
/// assert_eq!(flat_tree::offset(2), 1);
/// assert_eq!(flat_tree::offset(3), 0);
/// assert_eq!(flat_tree::offset(4), 2);
/// ```
pub fn offset(i: usize) -> usize {
  offset_with_depth(i, depth(i))
}

/// Returns the parent of a node with a depth.
pub fn parent_with_depth(i: usize, depth: usize) -> usize {
  index(depth + 1, offset_with_depth(i, depth) >> 1)
}

/// Returns the parent of a node.
///
/// ## Examples
/// ```rust
/// assert_eq!(flat_tree::index(1, 0), 1);
/// assert_eq!(flat_tree::index(1, 1), 5);
/// assert_eq!(flat_tree::index(2, 0), 3);
///
/// assert_eq!(flat_tree::parent(0), 1);
/// assert_eq!(flat_tree::parent(2), 1);
/// assert_eq!(flat_tree::parent(1), 3);
/// ```
pub fn parent(i: usize) -> usize {
  parent_with_depth(i, depth(i))
}

/// Returns the sibling of a node with a depth.
pub fn sibling_with_depth(i: usize, depth: usize) -> usize {
  index(depth, offset(i) ^ 1)
}

/// Returns the sibling of a node.
///
/// ## Examples
/// ```rust
/// assert_eq!(flat_tree::sibling(0), 2);
/// assert_eq!(flat_tree::sibling(2), 0);
/// assert_eq!(flat_tree::sibling(1), 5);
/// assert_eq!(flat_tree::sibling(5), 1);
/// ```
pub fn sibling(i: usize) -> usize {
  sibling_with_depth(i, depth(i))
}

/// Returns the parent's sibling, of a node, with a depth.
pub fn uncle_with_depth(i: usize, depth: usize) -> usize {
  sibling_with_depth(parent_with_depth(i, depth), depth + 1)
}

/// Returns the parent's sibling, of a node.
pub fn uncle(i: usize) -> usize {
  uncle_with_depth(i, depth(i))
}

/// Returns both children of a node, with a depth.
pub fn children_with_depth(i: usize, depth: usize) -> Option<(usize, usize)> {
  if is_even(i) {
    None
  } else if depth == 0 {
    Some((i, i))
  } else {
    let offset = offset_with_depth(i, depth) * 2;
    Some((index(depth - 1, offset), index(depth - 1, offset + 1)))
  }
}

/// Returns both children of a node.
///
/// ## Examples
/// ```rust
/// assert_eq!(flat_tree::children(0), None);
/// assert_eq!(flat_tree::children(1), Some((0, 2)));
/// assert_eq!(flat_tree::children(3), Some((1, 5)));
/// assert_eq!(flat_tree::children(9), Some((8, 10)));
/// ```
pub fn children(i: usize) -> Option<(usize, usize)> {
  children_with_depth(i, depth(i))
}

/// Returns only the left child of a node, with a depth
// TODO: handle errors
pub fn left_child_with_depth(i: usize, depth: usize) -> Option<usize> {
  if is_even(i) {
    None
  } else if depth == 0 {
    Some(i)
  } else {
    Some(index(depth - 1, offset_with_depth(i, depth) << 1))
  }
}

/// Returns only the left child of a node.
///
/// ## Examples
/// ```rust
/// assert_eq!(flat_tree::left_child(0), None);
/// assert_eq!(flat_tree::left_child(1), Some(0));
/// assert_eq!(flat_tree::left_child(3), Some(1));
/// ```
pub fn left_child(i: usize) -> Option<usize> {
  left_child_with_depth(i, depth(i))
}

/// Returns only the left child of a node, with a depth.
pub fn right_child_with_depth(i: usize, depth: usize) -> Option<usize> {
  if is_even(i) {
    None
  } else if depth == 0 {
    Some(i)
  } else {
    Some(index(depth - 1, (offset_with_depth(i, depth) << 1) + 1))
  }
}

/// Returns only the left child of a node.
///
/// ## Examples
/// ```rust
/// assert_eq!(flat_tree::right_child(0), None);
/// assert_eq!(flat_tree::right_child(1), Some(2));
/// assert_eq!(flat_tree::right_child(3), Some(5));
/// ```
// TODO: handle errors
pub fn right_child(i: usize) -> Option<usize> {
  right_child_with_depth(i, depth(i))
}

/// Returns the right most node in the tree that the node spans, with a depth.
pub fn right_span_with_depth(i: usize, depth: usize) -> usize {
  if depth == 0 {
    i
  } else {
    (offset_with_depth(i, depth) + 1) * (2 << depth) - 2
  }
}

/// Returns the right most node in the tree that the node spans.
///
/// ## Examples
/// ```rust
/// assert_eq!(flat_tree::right_span(0), 0);
/// assert_eq!(flat_tree::right_span(1), 2);
/// assert_eq!(flat_tree::right_span(3), 6);
/// assert_eq!(flat_tree::right_span(23), 30);
/// assert_eq!(flat_tree::right_span(27), 30);
/// ```
pub fn right_span(i: usize) -> usize {
  right_span_with_depth(i, depth(i))
}

/// Returns the left most node in the tree that the node spans, with a depth.
pub fn left_span_with_depth(i: usize, depth: usize) -> usize {
  if depth == 0 {
    i
  } else {
    offset_with_depth(i, depth) * (2 << depth)
  }
}

/// Returns the left most node in the tree that it spans.
///
/// ## Examples
/// ```rust
/// assert_eq!(flat_tree::left_span(0), 0);
/// assert_eq!(flat_tree::left_span(1), 0);
/// assert_eq!(flat_tree::left_span(3), 0);
/// assert_eq!(flat_tree::left_span(23), 16);
/// assert_eq!(flat_tree::left_span(27), 24);
/// ```
pub fn left_span(i: usize) -> usize {
  left_span_with_depth(i, depth(i))
}

/// Returns the left and right most nodes in the tree that the node spans, with
/// a depth.
pub fn spans_with_depth(i: usize, depth: usize) -> (usize, usize) {
  (
    left_span_with_depth(i, depth),
    right_span_with_depth(i, depth),
  )
}

/// Returns the left and right most nodes in the tree that the node spans.
///
/// ## Examples
/// ```rust
/// assert_eq!(flat_tree::spans(0), (0, 0));
/// assert_eq!(flat_tree::spans(1), (0, 2));
/// assert_eq!(flat_tree::spans(3), (0, 6));
/// assert_eq!(flat_tree::spans(23), (16, 30));
/// assert_eq!(flat_tree::spans(27), (24, 30));
/// ```
pub fn spans(i: usize) -> (usize, usize) {
  spans_with_depth(i, depth(i))
}

/// Returns how many nodes are in the tree that the node spans, with a depth.
pub fn count_with_depth(_: usize, depth: usize) -> usize {
  (2 << depth) - 1
}

/// Returns how many nodes are in the tree that the node spans.
///
/// ## Examples
/// ```rust
/// assert_eq!(flat_tree::count(0), 1);
/// assert_eq!(flat_tree::count(1), 3);
/// assert_eq!(flat_tree::count(3), 7);
/// assert_eq!(flat_tree::count(5), 3);
/// assert_eq!(flat_tree::count(23), 15);
/// assert_eq!(flat_tree::count(27), 7);
/// ```
pub fn count(i: usize) -> usize {
  count_with_depth(i, depth(i))
}

/// Returns a list of all the full roots (subtrees where all nodes have either 2 or 0 children) `<` index.
/// For example `fullRoots(8)` returns `[3]` since the subtree rooted at `3` spans `0 -> 6`,
/// and the tree rooted at `7` has a child located at `9` which is `>= 8`.
///
/// ## Panics
/// If an uneven index is passed.
///
/// ## Examples
/// ```rust
/// use flat_tree::full_roots;
///
/// let mut nodes = Vec::with_capacity(16);
/// full_roots(0, &mut nodes);
/// assert_eq!(nodes, []);
///
/// let mut nodes = Vec::with_capacity(16);
/// full_roots(2, &mut nodes);
/// assert_eq!(nodes, [0]);
///
/// let mut nodes = Vec::with_capacity(16);
/// full_roots(8, &mut nodes);
/// assert_eq!(nodes, [3]);
///
/// let mut nodes = Vec::with_capacity(16);
/// full_roots(20, &mut nodes);
/// assert_eq!(nodes, [7, 17]);
///
/// let mut nodes = Vec::with_capacity(16);
/// full_roots(18, &mut nodes);
/// assert_eq!(nodes, [7, 16]);
///
/// let mut nodes = Vec::with_capacity(16);
/// full_roots(16, &mut nodes);
/// assert_eq!(nodes, [7]);
/// ```
pub fn full_roots(i: usize, nodes: &mut Vec<usize>) {
  assert!(
    is_even(i),
    format!(
      "You can only look up roots for depth 0 blocks, got index {}",
      i
    )
  );
  let mut tmp = i >> 1;
  let mut offset = 0;
  let mut factor = 1;

  loop {
    if tmp == 0 {
      break;
    }
    while factor * 2 <= tmp {
      factor *= 2;
    }
    nodes.push(offset + factor - 1);
    offset += 2 * factor;
    tmp -= factor;
    factor = 1;
  }
}

#[inline]
pub(crate) fn is_even(num: usize) -> bool {
  (num & 1) == 0
}
#[test]
fn test_is_even() {
  assert_eq!(is_even(0), true);
  assert_eq!(is_even(1), false);
  assert_eq!(is_even(2), true);
  assert_eq!(is_even(3), false);
}

#[inline]
pub(crate) fn is_odd(num: usize) -> bool {
  (num & 1) != 0
}
#[test]
fn test_is_odd() {
  assert_eq!(is_odd(0), false);
  assert_eq!(is_odd(1), true);
  assert_eq!(is_odd(2), false);
  assert_eq!(is_odd(3), true);
}

#[test]
fn test_parent_gt_int32() {
  assert_eq!(parent(10_000_000_000), 10_000_000_001);
}

#[test]
fn test_child_to_parent_to_child() {
  let mut child = 0;
  for _ in 0..50 {
    child = parent(child)
  }
  assert_eq!(child, 1_125_899_906_842_623);
  for _ in 0..50 {
    child = left_child(child).expect("no valid number returned");
  }
  assert_eq!(child, 0);
}