Arafatk/DataViz

package btree

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
    entry    *Entry
    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 already at end, go to end
    if iterator.position == end {
        goto end
    }
    // If at beginning, get the left-most entry in the tree
    if iterator.position == begin {
        left := iterator.tree.Left()
        if left == nil {
            goto end
        }
        iterator.node = left
        iterator.entry = left.Entries[0]
        goto between
    }
    {
        // Find current entry position in current node
        e, _ := iterator.tree.search(iterator.node, iterator.entry.Key)
        // Try to go down to the child right of the current entry
        if e+1 < len(iterator.node.Children) {
            iterator.node = iterator.node.Children[e+1]
            // Try to go down to the child left of the current node
            for len(iterator.node.Children) > 0 {
                iterator.node = iterator.node.Children[0]
            }
            // Return the left-most entry
            iterator.entry = iterator.node.Entries[0]
            goto between
        }
        // Above assures that we have reached a leaf node, so return the next entry in current node (if any)
        if e+1 < len(iterator.node.Entries) {
            iterator.entry = iterator.node.Entries[e+1]
            goto between
        }
    }
    // Reached leaf node and there are no entries to the right of the current entry, so go up to the parent
    for iterator.node.Parent != nil {
        iterator.node = iterator.node.Parent
        // Find next entry position in current node (note: search returns the first equal or bigger than entry)
        e, _ := iterator.tree.search(iterator.node, iterator.entry.Key)
        // Check that there is a next entry position in current node
        if e < len(iterator.node.Entries) {
            iterator.entry = iterator.node.Entries[e]
            goto between
        }
    }

end:
    iterator.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 already at beginning, go to begin
    if iterator.position == begin {
        goto begin
    }
    // If at end, get the right-most entry in the tree
    if iterator.position == end {
        right := iterator.tree.Right()
        if right == nil {
            goto begin
        }
        iterator.node = right
        iterator.entry = right.Entries[len(right.Entries)-1]
        goto between
    }
    {
        // Find current entry position in current node
        e, _ := iterator.tree.search(iterator.node, iterator.entry.Key)
        // Try to go down to the child left of the current entry
        if e < len(iterator.node.Children) {
            iterator.node = iterator.node.Children[e]
            // Try to go down to the child right of the current node
            for len(iterator.node.Children) > 0 {
                iterator.node = iterator.node.Children[len(iterator.node.Children)-1]
            }
            // Return the right-most entry
            iterator.entry = iterator.node.Entries[len(iterator.node.Entries)-1]
            goto between
        }
        // Above assures that we have reached a leaf node, so return the previous entry in current node (if any)
        if e-1 >= 0 {
            iterator.entry = iterator.node.Entries[e-1]
            goto between
        }
    }
    // Reached leaf node and there are no entries to the left of the current entry, so go up to the parent
    for iterator.node.Parent != nil {
        iterator.node = iterator.node.Parent
        // Find previous entry position in current node (note: search returns the first equal or bigger than entry)
        e, _ := iterator.tree.search(iterator.node, iterator.entry.Key)
        // Check that there is a previous entry position in current node
        if e-1 >= 0 {
            iterator.entry = iterator.node.Entries[e-1]
            goto between
        }
    }

begin:
    iterator.Begin()
    return false

between:
    iterator.position = between
    return true
}

// CurrentNode returns the current node of the iterator
func (iterator *Iterator) CurrentNode() *Node {
    return iterator.node
}

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

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

// 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
    iterator.entry = nil
}

// 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
    iterator.entry = nil
}

// 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()
}