lib/standard/ropes: Added a forward postfix iterator on Rope.

[nit.git] / lib / standard / ropes.nit

# This file is part of NIT ( http://www.nitlanguage.org ).
#
# This file is free software, which comes along with NIT.  This software is
# distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
# without  even  the implied warranty of  MERCHANTABILITY or  FITNESS FOR A
# PARTICULAR PURPOSE.  You can modify it if you want,  provided this header
# is kept unaltered, and a notification of the changes is added.
# You  are  allowed  to  redistribute it and sell it, alone or as a part of
# another product.

# Nit implementation of the Ropes (see Ropes : An Alternative to Strings,
# SOFTWARE - PRACTICE AND EXPERIENCE, VOL. 25(12), 1315 - 1330 (DECEMBER 1995)
# Hans. J Boehm, Russ Atkinson and Michael Plass)
#
# A rope is a kind of string but instead of being flat, it relies on a binary tree structure to store data.
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
        var length = 0
end

# Node that represents a concatenation between two nodes (of any RopeNode type)
private class Concat
        super RopeNode

        # Left child of the node
        var _left: nullable RopeNode = null
        # Right child of the node
        var _right: nullable RopeNode = null

        fun left: nullable RopeNode do return _left
        fun right: nullable RopeNode do return _right

        fun left=(l: RopeNode)
        do
                _left = l
                length = l.length
                if _right != null then length += _right.length
        end

        fun right=(r: RopeNode)
        do
                _right = r
                length = r.length
                if _left != null then length += _left.length
        end
end

# Leaf of a Rope, contains a FlatString
private class Leaf
        super RopeNode

        # Encapsulated FlatString in the leaf node
        var str: FlatString

        init(val: FlatString) do
                self.str = val
                length = str.length
        end

end

# Basic structure, binary tree with a root node.
#
# Also shared services by subsequent implementations.
abstract class Rope
        super Text

        # Root node, entry point of a Rope.
        private var root: RopeNode

        # Empty Rope
        init do from("")

        # Creates a new Rope with `s` as root
        init from(s: String) do
                if s isa RopeString then root = s.root else root = new Leaf(s.as(FlatString))
        end

        private init from_root(r: RopeNode)
        do
                root = r
        end

        redef fun length do return root.length

        # Iterator on the nodes of the rope, in forward postfix order
        private fun postfix(from: Int): Postfix do return new Postfix.from(self, from)

        # 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
class RopeString
        super Rope
        super String

        redef fun to_s do return self

        # Inserts a String `str` at position `pos`
        fun insert_at(str: String, pos: Int): RopeString
        do
                if str.length == 0 then return self
                if self.length == 0 then return new RopeString.from(str)

                assert pos >= 0 and pos <= length

                if pos == length then return append(str).as(RopeString)

                var path = node_at(pos)

                var last_concat = new Concat

                if path.offset == 0 then
                        last_concat.right = path.leaf
                        if str isa FlatString then last_concat.left = new Leaf(str) else last_concat.left = str.as(RopeString).root
                else if path.offset == path.leaf.length then
                        if str isa FlatString then last_concat.right = new Leaf(str) else last_concat.right = str.as(RopeString).root
                        last_concat.left = path.leaf
                else
                        var s = path.leaf.str
                        var l_half = s.substring(0, s.length - path.offset)
                        var r_half = s.substring_from(s.length - path.offset)
                        var cct = new Concat
                        cct.right = new Leaf(r_half)
                        last_concat.left = new Leaf(l_half)
                        if str isa FlatString then last_concat.right = new Leaf(str) else last_concat.right = str.as(RopeString).root
                        cct.left = last_concat
                        last_concat = cct
                end

                for i in path.stack.reverse_iterator do
                        var nod = new Concat
                        if i.left then
                                nod.right = i.node.right.as(not null)
                                nod.left = last_concat
                        else
                                nod.left = i.node.left.as(not null)
                                nod.right = last_concat
                        end
                        last_concat = nod
                end

                return new RopeString.from_root(last_concat)
        end

        # Adds `s` at the end of self
        fun append(s: String): String
        do
                if self.is_empty then return s
                return new RopeString.from_root(append_to_path(root,s))
        end

        # Builds a new path from root to the rightmost node with s appended
        private fun append_to_path(node: RopeNode, s: String): RopeNode
        do
                var cct = new Concat
                if node isa Leaf then
                        cct.left = node
                        if s isa FlatString then cct.right = new Leaf(s) else cct.right = s.as(RopeString).root
                else if node isa Concat then
                        var right = node.right
                        if node.left != null then cct.left = node.left.as(not null)
                        if right == null then
                                if s isa FlatString then cct.right = new Leaf(s) else cct.right = s.as(RopeString).root
                        else
                                cct.right = append_to_path(right, s)
                        end
                end
                return cct
        end

        # O(log(n))
        #
        #     var rope = new RopeString.from("abcd")
        #     assert rope.substring(1, 2)         ==  "bc"
        #     assert rope.substring(-1, 2)         ==  "a"
        #     assert rope.substring(1, 0)         ==  ""
        #     assert rope.substring(2, 5)         ==  "cd"
        #
        redef fun substring(pos, len)
        do
                if pos < 0 then
                        len += pos
                        pos = 0
                end

                if pos + len > length then len = length - pos

                if len <= 0 then return new RopeString.from("")

                var path = node_at(pos)

                var lf = path.leaf
                var offset = path.offset

                if path.leaf.str.length - offset > len then lf = new Leaf(lf.str.substring(offset,len)) else lf = new Leaf(lf.str.substring_from(offset))

                var nod: RopeNode = lf

                for i in path.stack.reverse_iterator do
                        if i.right then continue
                        var tmp = new Concat
                        tmp.left = nod
                        var r = i.node.right
                        if r != null then tmp.right = r
                        nod = tmp
                end

                var ret = new RopeString
                ret.root = nod

                path = ret.node_at(len-1)

                offset = path.offset
                nod = new Leaf(path.leaf.str.substring(0, offset+1))

                for i in path.stack.reverse_iterator do
                        if i.left then continue
                        var tmp = new Concat
                        tmp.right = nod
                        var l = i.node.left
                        if l != null then tmp.left = l
                        nod = tmp
                end

                ret.root = nod

                return ret
        end
end

# Used to iterate on a Rope
private class IteratorElement

        init(e: RopeNode)
        do
                if e isa Leaf then
                        left = true
                        right = true
                end
                node = e
        end

        # The node being visited
        var node: RopeNode
        # If the node has a left child, was it visited ?
        var left = false
        # If the node has a right child, was it visited ?
        var right = false
        # Was the current node visited ?
        var done = false
end

# Simple Postfix iterator on the nodes of a Rope
private class Postfix
        super IndexedIterator[RopeNode]

        # Target Rope to iterate on
        var target: Rope

        # Current position in Rope
        var pos: Int

        # Visited nodes
        var stack = new List[IteratorElement]

        init from(tgt: Rope, pos: Int)
        do
                self.target = tgt
                self.pos = pos
                if pos < 0 or pos >= tgt.length then return
                var path = tgt.node_at(pos)
                self.pos -= path.offset
                for i in path.stack do
                        var item = new IteratorElement(i.node)
                        item.left = true
                        if i.right then item.right = true
                        stack.push item
                end
                var item = new IteratorElement(path.leaf)
                item.done = true
                stack.push item
        end

        redef fun item
        do
                assert is_ok
                return stack.last.node
        end

        redef fun is_ok do return not stack.is_empty

        redef fun index do return pos

        redef fun next do
                if stack.is_empty then return
                if pos > target.length-1 then
                        stack.clear
                        return
                end
                var lst = stack.last
                if lst.done then
                        if lst.node isa Leaf then
                                pos += lst.node.length
                        end
                        stack.pop
                        next
                        return
                end
                if not lst.left then
                        lst.left = true
                        var nod = lst.node
                        if nod isa Concat and nod.left != null then
                                stack.push(new IteratorElement(nod.left.as(not null)))
                                next
                                return
                        end
                end
                if not lst.right then
                        lst.right = true
                        var nod = lst.node
                        if nod isa Concat and nod.right != null then
                                stack.push(new IteratorElement(nod.right.as(not null)))
                                next
                                return
                        end
                end
                lst.done = true
        end
end