# 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

	# Transforms the current node to a Leaf.
	# This might be costly to invoke since this produces a FlatString concatenation.
	# Can be used internally to limit the growth of the Rope when working with small leaves.
	fun to_leaf: Leaf is abstract
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
	# Right child of the node
	var right: nullable RopeNode

	init(l: nullable RopeNode, r: nullable RopeNode)
	do
		left = l
		right = r
		if l != null then length += l.length
		if r != null then length += r.length
	end

	redef fun to_leaf
	do
		if left == null then
			if right == null then return new StringLeaf("".as(FlatString))
			return right.to_leaf
		end
		if right == null then return left.as(not null).to_leaf
		return new StringLeaf((left.to_leaf.str.as(FlatString) + right.to_leaf.str.as(FlatString)).as(FlatString))
	end
end

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

	# Encapsulated FlatString in the leaf node
	var str: FlatText

end

private class StringLeaf
	super Leaf

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

	redef fun to_leaf do return self
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

	# Cached version of self as a flat String
	private var str_representation: nullable NativeString = null

	# 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 StringLeaf(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)

	# Iterator on the leaves of the rope, forward order
	private fun leaves(from: Int): LeavesIterator do return new LeavesIterator(self, from)

	# Iterator on the substrings from 0, in forward order
	redef fun substrings do return new SubstringsIterator(self, 0)

	# Iterator on the substrings, starting at position `from`, in forward order
	fun substrings_from(from: Int): IndexedIterator[Text] do return new SubstringsIterator(self, from)

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

	# Iterator on the leaves of the rope, backwards order
	private fun reverse_leaves(from: Int): ReverseLeavesIterator do return new ReverseLeavesIterator(self,from)

	# Iterator on the substrings, in reverse order
	fun reverse_substrings: IndexedIterator[Text] do return new ReverseSubstringsIterator(self, length-1)

	# Iterator on the substrings, in reverse order, starting iteration at position `from`
	fun reverse_substrings_from(from: Int): IndexedIterator[Text] do return new ReverseSubstringsIterator(self, from)

	redef fun output
	do
		for i in substrings do
			i.output
		end
	end

	redef fun to_cstring
	do
		if str_representation != null then return str_representation.as(not null)

		var native_final_str = calloc_string(length + 1)

		native_final_str[length] = '\0'

		if self.length == 0 then
			str_representation = native_final_str
			return native_final_str
		end

		var offset = 0

		for i in substrings do
			var str = i.flatten
			if str isa FlatString then str.items.copy_to(native_final_str, str.length, str.index_from, offset)
			offset += i.length
		end

		str_representation = native_final_str

		return native_final_str
	end

	# 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

	redef fun ==(o)
	do
		if not o isa Text then return false
		if o.length != self.length then return false
		var oit = o.chars.iterator
		for i in self.chars.iterator do
			if i != oit.item then return false
			oit.next
		end
		return true
	end
end

# Rope that cannot be modified
class RopeString
	super Rope
	super String

	redef fun to_s do return self

	redef fun empty do return once new RopeString.from("")

	redef var chars: SequenceRead[Char] = new RopeStringChars(self)

	redef fun reversed
	do
		var ret = empty.as(RopeString)
		for i in substrings do
			ret = ret.prepend(i.reversed.to_s).as(RopeString)
		end
		return ret
	end

	redef fun to_upper
	do
		var ret = empty
		for i in substrings do
			ret += i.to_upper
		end
		return ret
	end

	redef fun to_lower
	do
		var ret = empty
		for i in substrings do
			ret += i.to_lower
		end
		return ret
	end

	redef fun +(o) do return insert_at(o.to_s, length)

	redef fun *(n)
	do
		var ret = new RopeString.from("")
		for i in [0..n[ do
			ret = (ret + self).as(RopeString)
		end
		return ret
	end

	# Inserts a String `str` at position `pos`
	redef fun insert_at(str, pos)
	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: Concat

		if path.offset == 0 then
			if str isa FlatString then
				last_concat = new Concat(new StringLeaf(str), path.leaf)
			else
				last_concat = new Concat(str.as(RopeString).root, path.leaf)
			end
		else if path.offset == path.leaf.length then
			if str isa FlatString then
				last_concat = new Concat(path.leaf, new StringLeaf(str))
			else
				last_concat = new Concat(path.leaf, str.as(RopeString).root)
			end
		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: Concat
			var ll = new StringLeaf(l_half.as(FlatString))
			if str isa FlatString then
				cct = new Concat(ll, new StringLeaf(str))
			else
				cct = new Concat(ll, str.as(RopeString).root)
			end
			last_concat = new Concat(cct, new StringLeaf(r_half.as(FlatString)))
		end

		for i in path.stack.reverse_iterator do
			if i.left then
				last_concat = new Concat(last_concat, i.node.right)
			else
				last_concat = new Concat(i.node.left, last_concat)
			end
		end

		return new RopeString.from_root(last_concat)
	end

	# Adds `s` at the beginning of self
	redef fun prepend(s) do return insert_at(s, 0)

	# Adds `s` at the end of self
	redef fun append(s)
	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: Concat
		if node isa Leaf then
			if s isa FlatString then
				cct = new Concat(node, new StringLeaf(s))
			else
				cct = new Concat(node, s.as(RopeString).root)
			end
		else
			var n = node.as(Concat)
			var right = n.right
			var lft = n.left.as(not null)
			if right == null then
				if s isa FlatString then
					cct = new Concat(lft, new StringLeaf(s))
				else
					cct = new Concat(lft, s.as(RopeString).root)
				end
			else
				cct = new Concat(lft, 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 StringLeaf(lf.str.substring(offset,len).as(FlatString)) else lf = new StringLeaf(lf.str.substring_from(offset).as(FlatString))

		var nod: RopeNode = lf

		for i in path.stack.reverse_iterator do
			if i.right then continue
			nod = new Concat(nod, i.node.right)
		end

		var ret = new RopeString
		ret.root = nod

		path = ret.node_at(len-1)

		offset = path.offset
		nod = new StringLeaf(path.leaf.str.substring(0, offset+1).as(FlatString))

		for i in path.stack.reverse_iterator do
			if i.left then continue
			nod = new Concat(i.node.left, nod)
		end

		ret.root = nod

		return ret
	end
end

redef class FlatString

	redef fun append(s) do return (new RopeString.from(self)) + s

	redef fun prepend(s) do return (new RopeString.from(self)).prepend(s)

	redef fun insert_at(s, pos)
	do
		if pos == 0 then return prepend(s)
		if pos == length then return append(s)

		var l = substring(0,pos)
		var r = substring_from(pos)
		var ret: String = new RopeString.from(l)
		ret += s
		return ret + r
	end

end

private class RopeStringChars
	super SequenceRead[Char]

	var tgt: Rope

	redef fun [](pos)
	do
		assert pos < tgt.length
		var path = tgt.node_at(pos)
		return path.leaf.str.chars[path.offset]
	end

	redef fun iterator do return iterator_from(0)

	redef fun iterator_from(pos) do return new RopeCharIterator(tgt, pos)

	redef fun reverse_iterator do return reverse_iterator_from(tgt.length-1)

	redef fun reverse_iterator_from(pos) do return new ReverseRopeCharIterator(tgt, pos)
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

# Iterates on the leaves (substrings) of the Rope
class LeavesIterator
	super IndexedIterator[Leaf]

	private var nodes: Postfix

	init(tgt: Rope, pos: Int)
	do
		nodes = tgt.postfix(pos)
	end

	redef fun is_ok do return nodes.is_ok

	redef fun item
	do
		assert is_ok
		return nodes.item.as(Leaf)
	end

	redef fun index do return nodes.index

	redef fun next
	do
		while nodes.is_ok do
			nodes.next
			if nodes.is_ok and nodes.item isa Leaf then break
		end
	end
end

# Uses the leaves and calculates a new substring on each iteration
class SubstringsIterator
	super IndexedIterator[Text]

	private var nodes: IndexedIterator[Leaf]

	# Current position in Rope
	var pos: Int

	# Current substring, computed from the current Leaf and indexes
	var substring: Text

	init(tgt: Rope, pos: Int)
	do
		nodes = tgt.leaves(pos)
		self.pos = pos
		if pos < 0 or pos >= tgt.length then return
		make_substring
	end

	# Compute the bounds of the current substring and makes the substring
	private fun make_substring
	do
		substring = nodes.item.str
		var min = 0
		var length = substring.length
		if nodes.index < pos then
			min = pos - nodes.index
		end
		substring = substring.substring(min, length)
	end

	redef fun is_ok do return nodes.is_ok

	redef fun item
	do
		assert is_ok
		return substring
	end

	redef fun index do return pos

	redef fun next
	do
		pos += substring.length
		nodes.next
		if nodes.is_ok then make_substring
	end

end

class RopeCharIterator
	super IndexedIterator[Char]

	var substrings: IndexedIterator[Text]

	var pos: Int

	var max: Int

	var substr_iter: IndexedIterator[Char]

	init(tgt: Rope, from: Int)
	do
		substrings = tgt.substrings_from(from)
		max = tgt.length - 1
		if not substrings.is_ok then
			pos = tgt.length
			return
		end
		pos = from
		substr_iter = substrings.item.chars.iterator
	end

	redef fun item do return substr_iter.item

	redef fun is_ok do return pos <= max

	redef fun index do return pos

	redef fun next
	do
		pos += 1
		if substr_iter.is_ok then
			substr_iter.next
		end
		if not substr_iter.is_ok then
			substrings.next
			if substrings.is_ok then
				substr_iter = substrings.item.chars.iterator
			end
		end
	end
end

private class ReversePostfix
	super IndexedIterator[RopeNode]

	var target: Rope

	var pos: Int

	var min = 0

	var stack = new List[IteratorElement]

	init from(tgt: Rope, pos: Int)
	do
		self.pos = pos
		target = tgt
		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 elemt = new IteratorElement(i.node)
			elemt.right = true
			if i.left then
				elemt.left = true
			end
			stack.push elemt
		end
		stack.push(new IteratorElement(path.leaf))
		stack.last.done = true
	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 < min then
			stack.clear
			return
		end
		var lst = stack.last
		if lst.done then
			stack.pop
			next
			return
		end
		if not lst.right then
			var nod = lst.node.as(Concat)
			var rgt = nod.right
			lst.right = true
			if rgt != null then
				stack.push(new IteratorElement(rgt))
				next
				return
			end
		end
		if not lst.left then
			var nod = lst.node.as(Concat)
			var lft = nod.left
			lst.left = true
			if lft != null then
				stack.push(new IteratorElement(lft))
				next
				return
			end
		end
		if lst.node isa Leaf then pos -= lst.node.length
		lst.done = true
	end
end

private class ReverseLeavesIterator
	super IndexedIterator[Leaf]

	var nodes: ReversePostfix

	init(tgt: Rope, from: Int)
	do
		nodes = tgt.reverse_postfix(from)
	end

	redef fun is_ok do return nodes.is_ok

	redef fun item do
		assert is_ok
		return nodes.item.as(Leaf)
	end

	redef fun next do
		while nodes.is_ok do
			nodes.next
			if nodes.is_ok then if nodes.item isa Leaf then break
		end
	end

	redef fun index do return nodes.index

end

private class ReverseSubstringsIterator
	super IndexedIterator[Text]

	var leaves: ReverseLeavesIterator

	var pos: Int

	var str: Text

	init(tgt: Rope, from: Int)
	do
		leaves = tgt.reverse_leaves(from)
		pos = from
		if not leaves.is_ok then return
		str = leaves.item.str
		make_substring
	end

	fun make_substring
	do
		if pos >= (leaves.index + str.length - 1) then return
		str = str.substring(0, (pos - leaves.index + 1))
	end

	redef fun is_ok do return leaves.is_ok

	redef fun item do
		assert is_ok
		return str
	end

	redef fun index do return pos

	redef fun next do
		pos -= str.length
		leaves.next
		if not leaves.is_ok then return
		str = leaves.item.str
		make_substring
	end
end

private class ReverseRopeCharIterator
	super IndexedIterator[Char]

	var substrs: IndexedIterator[Text]

	var pos: Int

	var subiter: IndexedIterator[Char]

	init(tgt: Rope, from: Int)
	do
		substrs = tgt.reverse_substrings_from(from)
		if not substrs.is_ok then
			pos = -1
			return
		end
		subiter = substrs.item.chars.reverse_iterator
		pos = from
	end

	redef fun is_ok do return pos >= 0

	redef fun item do
		assert is_ok
		return subiter.item
	end

	redef fun index do return pos

	redef fun next do
		pos -= 1
		if subiter.is_ok then subiter.next
		if not subiter.is_ok then
			if substrs.is_ok then substrs.next
			if substrs.is_ok then subiter = substrs.item.chars.reverse_iterator
		end
	end
end