From: Lucas Bajolet <r4pass@hotmail.com>
Date: Wed, 4 Jun 2014 20:41:48 +0000 (-0400)
Subject: lib/standard/ropes: Search method and classes added.
X-Git-Tag: v0.6.6~43^2~24
X-Git-Url: http://nitlanguage.org

lib/standard/ropes: Search method and classes added.

Signed-off-by: Lucas Bajolet <r4pass@hotmail.com>
---

diff --git a/lib/standard/ropes.nit b/lib/standard/ropes.nit
index eef9360..30966ee 100644
--- a/lib/standard/ropes.nit
+++ b/lib/standard/ropes.nit
@@ -17,6 +17,29 @@ module ropes
 
 intrude import string
 
+# Used when searching for a particular node
+# Returns the path to the node from the root of the rope
+# Also, the node and the offset for seeked position in the rope
+private class Path
+	# Leaf found
+	var leaf: Leaf
+	# Offset in leaf
+	var offset: Int
+	# Stack of the nodes traversed, and the path used
+	var stack: List[PathElement]
+end
+
+# An element for a Path, has the concat node and whether or not
+# left or right child was visited.
+private class PathElement
+	# Visited node
+	var node: Concat
+	# Was the left child visited ?
+	var left = false
+	# Was the right child visited ?
+	var right = false
+end
+
 # A node for a Rope
 private abstract class RopeNode
 	# Length of the node
@@ -87,6 +110,38 @@ abstract class Rope
 	end
 
 	redef fun length do return root.length
+
+	# Path to the Leaf for `position`
+	private fun node_at(position: Int): Path
+	do
+		assert position >= 0 and position < length
+		return get_node_from(root.as(not null), 0, position, new List[PathElement])
+	end
+
+	# Builds the path to Leaf at position `seek_pos`
+	private fun get_node_from(node: RopeNode, curr_pos: Int, seek_pos: Int, stack: List[PathElement]): Path
+	do
+		assert curr_pos >= 0
+		if node isa Leaf then return new Path(node, seek_pos - curr_pos, stack)
+		node = node.as(Concat)
+
+		if node.left != null then
+			var next_pos = curr_pos + node.left.length
+			stack.add(new PathElement(node))
+			if next_pos > seek_pos then
+				stack.last.left = true
+				return get_node_from(node.left.as(not null), curr_pos, seek_pos, stack)
+			end
+			stack.last.right = true
+			return get_node_from(node.right.as(not null), next_pos, seek_pos, stack)
+		else
+			var vis = new PathElement(node)
+			vis.right = true
+			stack.add(vis)
+			return get_node_from(node.right.as(not null), curr_pos, seek_pos, stack)
+		end
+	end
+
 end
 
 # Rope that cannot be modified