Arafatk/DataViz

package redblacktree

import "github.com/Arafatk/Dataviz/containers"

func assertIteratorImplementation() {
    var _ containers.ReverseIteratorWithKey = (*Iterator)(nil)
}

// Iterator holding the iterator's state
type Iterator struct {
    tree     *Tree
    node     *Node
    position position
}

type position byte

const (
    begin, between, end position = 0, 1, 2
)

// Iterator returns a stateful iterator whose elements are key/value pairs.
func (tree *Tree) Iterator() Iterator {
    return Iterator{tree: tree, node: nil, position: begin}
}

// Next moves the iterator to the next element and returns true if there was a next element in the container.
// If Next() returns true, then next element's key and value can be retrieved by Key() and Value().
// If Next() was called for the first time, then it will point the iterator to the first element if it exists.
// Modifies the state of the iterator.
func (iterator *Iterator) Next() bool {
    if iterator.position == end {
        goto end
    }
    if iterator.position == begin {
        left := iterator.tree.Left()
        if left == nil {
            goto end
        }
        iterator.node = left
        goto between
    }
    if iterator.node.Right != nil {
        iterator.node = iterator.node.Right
        for iterator.node.Left != nil {
            iterator.node = iterator.node.Left
        }
        goto between
    }
    if iterator.node.Parent != nil {
        node := iterator.node
        for iterator.node.Parent != nil {
            iterator.node = iterator.node.Parent
            if iterator.tree.Comparator(node.Key, iterator.node.Key) <= 0 {
                goto between
            }
        }
    }

end:
    iterator.node = nil
    iterator.position = end
    return false

between:
    iterator.position = between
    return true
}

// Prev moves the iterator to the previous element and returns true if there was a previous element in the container.
// If Prev() returns true, then previous element's key and value can be retrieved by Key() and Value().
// Modifies the state of the iterator.
func (iterator *Iterator) Prev() bool {
    if iterator.position == begin {
        goto begin
    }
    if iterator.position == end {
        right := iterator.tree.Right()
        if right == nil {
            goto begin
        }
        iterator.node = right
        goto between
    }
    if iterator.node.Left != nil {
        iterator.node = iterator.node.Left
        for iterator.node.Right != nil {
            iterator.node = iterator.node.Right
        }
        goto between
    }
    if iterator.node.Parent != nil {
        node := iterator.node
        for iterator.node.Parent != nil {
            iterator.node = iterator.node.Parent
            if iterator.tree.Comparator(node.Key, iterator.node.Key) >= 0 {
                goto between
            }
        }
    }

begin:
    iterator.node = nil
    iterator.position = begin
    return false

between:
    iterator.position = between
    return true
}

// Value returns the current element's value.
// Does not modify the state of the iterator.
func (iterator *Iterator) Value() interface{} {
    return iterator.node.Value
}

// Key returns the current element's key.
// Does not modify the state of the iterator.
func (iterator *Iterator) Key() interface{} {
    return iterator.node.Key
}

// NodeColor returns the current element's node color
// Does not modify the state of the iterator.
func (iterator *Iterator) NodeColor() color {
    return iterator.node.color
}

// Begin resets the iterator to its initial state (one-before-first)
// Call Next() to fetch the first element if any.
func (iterator *Iterator) Begin() {
    iterator.node = nil
    iterator.position = begin
}

// End moves the iterator past the last element (one-past-the-end).
// Call Prev() to fetch the last element if any.
func (iterator *Iterator) End() {
    iterator.node = nil
    iterator.position = end
}

// First moves the iterator to the first element and returns true if there was a first element in the container.
// If First() returns true, then first element's key and value can be retrieved by Key() and Value().
// Modifies the state of the iterator
func (iterator *Iterator) First() bool {
    iterator.Begin()
    return iterator.Next()
}

// Last moves the iterator to the last element and returns true if there was a last element in the container.
// If Last() returns true, then last element's key and value can be retrieved by Key() and Value().
// Modifies the state of the iterator.
func (iterator *Iterator) Last() bool {
    iterator.End()
    return iterator.Prev()
}