Merge: lib/core: Push rope maxlen to 512 instead of 64

[nit.git] / lib / core / text / ropes.nit

# This file is part of NIT (http://www.nitlanguage.org).
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

# Tree-based representation of a String.
#
# Ropes are a data structure introduced in a 1995 paper from
# Hans J. Boehm, Russ Atkinson and Michael Plass.
#
# See:
#
# > Ropes: an Alternative to Strings,
# > *Software - Practice and Experience*,
# > Vol. 25(12), 1315-1330 (December 1995).
#
# The implementation developed here provides an automatic change
# of data structure depending on the length of the leaves.
#
# The length from which a `Rope` is built from a `flat` string
# if defined at top-level (see `maxlen`) and can be redefined by clients
# depending on their needs (e.g. if you need to bench the speed of
# the creation of concat nodes, lower the size of maxlen).
#
# A Rope as defined in the original paper is a Tree made of concatenation
# nodes and containing `Flat` (that is Array-based) strings as Leaves.
#
# Example :
#
# ~~~raw
#                   Concat
#                 /        \
#           Concat          Concat
#          /      \        /      \
#       "My"     " Name"  " is"   " Simon."
# ~~~
#
# Note that the above example is not representative of the actual implementation
# of `Ropes`, since short leaves are merged to keep the rope at an acceptable
# height (hence, this rope here might actually be a `FlatString` !).
module ropes

intrude import flat

# Maxlen is the maximum length of a Leaf node
#
# When concatenating two leaves, if `new_length` > `maxlen`,
# A `Concat` node is created instead
#
# Its purpose is to limit the depth of the `Rope` (this
# improves performance when accessing/iterating).
fun maxlen: Int do return 512

# String using a tree-based representation with leaves as `FlatStrings`
private abstract class Rope
        super Text
end

# Node that represents a concatenation between two `String`
private class Concat
        super Rope
        super String

        redef fun chars do return new RopeChars(self)

        redef fun bytes do return new RopeBytes(self)

        redef var length is noinit

        redef var byte_length is noinit

        redef fun substrings do return new RopeSubstrings.from(self, 0)

        redef fun empty do return ""

        # Cache for the latest accessed FlatString in `self`
        var flat_cache: FlatString is noinit

        # Position of the beginning of `flat_cache` in `self`
        var flat_last_pos_start: Int is noinit

        redef fun to_cstring do
                var len = _byte_length
                var ns = new NativeString(len + 1)
                ns[len] = 0u8
                var off = 0
                for i in substrings do
                        var ilen = i._byte_length
                        i.as(FlatString)._items.copy_to(ns, ilen, i.as(FlatString)._first_byte, off)
                        off += ilen
                end
                return ns
        end

        # Left child of the node
        var left: String
        # Right child of the node
        var right: String

        init do
                var l = _left
                var r = _right
                _length = l.length + r.length
                _byte_length = l.byte_length + r.byte_length
                _flat_last_pos_start = _length
        end

        redef fun is_empty do return _byte_length == 0

        redef fun output do
                _left.output
                _right.output
        end

        redef fun iterator do return new RopeCharIterator.from(self, 0)

        redef fun *(i) do
                var x: String = self
                for j in [1 .. i[ do x += self
                return x
        end

        redef fun [](i) do
                assert i >= 0 and i < _length
                var flps = _flat_last_pos_start
                if i >= flps then
                        var fc = _flat_cache
                        if i < flps + fc._length then return fc.fetch_char_at(i - flps)
                end
                var lf = get_leaf_at(i)
                return lf.fetch_char_at(i - _flat_last_pos_start)
        end

        fun get_leaf_at(pos: Int): FlatString do
                var flps = _flat_last_pos_start
                if pos >= flps then
                        var fc = _flat_cache
                        if pos < flps + fc._length then return fc
                end
                var s: String = self
                var st = pos
                loop
                        if s isa FlatString then break
                        s = s.as(Concat)
                        var lft = s._left
                        var llen = lft.length
                        if pos >= llen then
                                s = s._right
                                pos -= llen
                        else
                                s = lft
                        end
                end
                _flat_last_pos_start = st - pos
                _flat_cache = s
                return s
        end

        redef fun substring(from, count) do
                if from < 0 then
                        count += from
                        if count < 0 then return ""
                        from = 0
                end

                var ln = _length
                if (count + from) > ln then count = ln - from
                if count <= 0 then return ""
                var end_index = from + count - 1

                var flps = _flat_last_pos_start
                if from >= flps then
                        var fc = _flat_cache
                        if end_index < flps + fc._length then
                                return fc.substring_impl(from - flps, count, end_index - flps)
                        end
                end

                var lft = _left
                var llen = lft.length
                if from < llen then
                        if from + count < llen then return lft.substring(from, count)
                        var lsublen = llen - from
                        return lft.substring_from(from) + _right.substring(0, count - lsublen)
                else
                        return _right.substring(from - llen, count)
                end
        end

        redef fun reversed do return new Concat(_right.reversed, _left.reversed)

        redef fun insert_at(s, pos) do
                var lft = _left
                if pos > lft.length then
                        return lft + _right.insert_at(s, pos - lft.length)
                end
                return lft.insert_at(s, pos) + _right
        end

        redef fun to_upper do return new Concat(_left.to_upper, _right.to_upper)

        redef fun to_lower do return new Concat(_left.to_lower, _right.to_lower)

        redef fun +(o) do
                var s = o.to_s
                var slen = s.byte_length
                if s isa Concat then
                        return new Concat(self, s)
                else
                        var r = _right
                        var rlen = r.byte_length
                        if rlen + slen > maxlen then return new Concat(self, s)
                        return new Concat(_left, r + s)
                end
        end

        redef fun copy_to_native(dest, n, src_offset, dest_offset) do
                var l = _left
                if src_offset < l.byte_length then
                        var lcopy = l.byte_length - src_offset
                        lcopy = if lcopy > n then n else lcopy
                        l.copy_to_native(dest, lcopy, src_offset, dest_offset)
                        dest_offset += lcopy
                        n -= lcopy
                        src_offset = 0
                end
                _right.copy_to_native(dest, n, src_offset, dest_offset)
        end

        # Returns a balanced version of `self`
        fun balance: String do
                var children = new Array[String]
                var rnod: String
                var iter: nullable RopeCharIteratorPiece = new RopeCharIteratorPiece(self, false, false, null)
                loop
                        if iter == null then break
                        rnod = iter.node
                        if not rnod isa Concat then
                                children.push rnod
                                iter = iter.prev
                                continue
                        end
                        if not iter.ldone then
                                iter.ldone = true
                                iter = new RopeCharIteratorPiece(rnod._left, false, false, iter)
                        else if not iter.rdone then
                                iter.rdone = true
                                iter = new RopeCharIteratorPiece(rnod._right, false, false, iter)
                        else
                                iter = iter.prev
                        end

                end
                return recurse_balance(children, children.length)
        end

        fun recurse_balance(nodes: Array[String], len: Int): String do
                var finpos = 0
                var stpos = 0
                while stpos < len do
                        if len - stpos > 1 then
                                nodes[finpos] = new Concat(nodes[stpos], nodes[stpos + 1])
                                stpos += 2
                        else
                                nodes[finpos] = nodes[stpos]
                                stpos += 1
                        end
                        finpos += 1
                end
                if finpos == 1 then return nodes[0]
                return recurse_balance(nodes, finpos)
        end
end

# Mutable `Rope`, optimized for concatenation operations
#
# A `RopeBuffer` is an efficient way of building a `String` when
# concatenating small strings.
#
# It does concatenations in an optimized way by having a
# mutable part and an immutable part built by efficiently
# concatenating strings in chain.
#
# Every concatenation operation is done by copying a string to
# the mutable part and flushing it when full.
#
# However, when a long string is appended to the `Buffer`,
# the concatenation is done at it would be in a `Rope`.
class RopeBuffer
        super Rope
        super Buffer

        redef fun chars do return new RopeBufferChars(self)

        redef fun bytes do return new RopeBufferBytes(self)

        # The final string being built on the fly
        private var str: String = ""

        # Current concatenation buffer
        private var ns: NativeString is noinit

        # Next available (e.g. unset) character in the `Buffer`
        private var rpos = 0

        # Length (in chars) of the buffered part
        private var nslen = 0

        # Keeps track of the buffer's currently dumped part
        #
        # This might happen if for instance, a String was being
        # built by concatenating small parts of string and suddenly
        # a long string (length > maxlen) is appended.
        private var dumped: Int is noinit

        # Length of the complete rope in chars (0)
        redef fun length do
                var st = dumped
                var len = str.length
                while st < rpos do
                        st += ns[st].u8len
                        len += 1
                end
                return len
        end

        # Length of the complete rope in bytes
        redef var byte_length = 0

        # Length of the mutable part (in bytes)
        #
        # Is also used as base to compute the size of the next
        # mutable native string (`ns`)
        private var buf_size: Int is noinit

        redef fun substrings do return new RopeBufSubstringIterator.from(self)

        # Builds an empty `RopeBuffer`
        init do
                ns = new NativeString(maxlen)
                buf_size = maxlen
                dumped = 0
        end

        # Builds a new `RopeBuffer` with `str` in it.
        init from(str: String) do
                self.str = str
                ns = new NativeString(maxlen)
                buf_size = maxlen
                _byte_length = str.length
                dumped = 0
        end

        # Resets the informations of the `Buffer`
        #
        # This is called when doing in-place modifications
        # on a previously to_s'd `RopeBuffer`
        private fun reset do
                var nns = new NativeString(buf_size)
                var blen = rpos - dumped
                ns.copy_to(nns, blen, dumped, 0)
                ns = nns
                dumped = 0
                rpos = blen
                written = false
        end

        redef fun [](i) do
                if i < str.length then
                        return str[i]
                else
                        var index = ns.char_to_byte_index_cached(i - str.length, 0, dumped)
                        return ns.char_at(index)
                end
        end

        redef fun []=(i, c) do
                assert i >= 0 and i <= length
                if i == length then add c
                if i < str.length then
                        _byte_length += c.u8char_len - str[i].u8char_len
                        var s = str
                        var l = s.substring(0, i)
                        var r = s.substring_from(i + 1)
                        str = l + c.to_s + r
                else
                        var reali = i - str.length
                        var index = ns.char_to_byte_index_cached(reali, 0, dumped)
                        var st_nxt = ns.char_to_byte_index_cached(reali + 1, reali, index)
                        var loc_c = ns.char_at(index)
                        if loc_c.u8char_len != c.u8char_len then
                                var delta = c.u8char_len - loc_c.u8char_len
                                var remsp = buf_size - rpos
                                if remsp < delta then
                                        buf_size *= 2
                                        var nns = new NativeString(buf_size)
                                        ns.copy_to(nns, index - dumped, dumped, 0)
                                        ns.copy_to(nns, rpos - index - loc_c.u8char_len, index + loc_c.u8char_len, index - dumped + delta)
                                        ns = nns
                                        index = index - dumped
                                else
                                        ns.copy_to(ns, rpos - st_nxt, st_nxt, st_nxt + delta)
                                end
                                _byte_length += delta
                                rpos += delta
                        end
                        ns.set_char_at(index, c)
                end
        end

        redef fun empty do return new RopeBuffer

        redef fun clear do
                str = ""
                _byte_length = 0
                rpos = 0
                dumped = 0
                if written then
                        ns = new NativeString(buf_size)
                        written = false
                end
        end

        redef fun substring(from, count) do
                var strlen = str.length

                if from < 0 then
                        count += from
                        if count < 0 then count = 0
                        from = 0
                end

                if count > length then count = length - from

                if count == 0 then return empty

                if from < strlen then
                        var subpos = strlen - from
                        if count <= subpos then
                                return new RopeBuffer.from(str.substring(from, count))
                        else
                                var l = str.substring_from(from)
                                var rem = count - subpos
                                var nns = new NativeString(rem)
                                ns.copy_to(nns, rem, dumped, 0)
                                return new RopeBuffer.from(l + nns.to_s_unsafe(rem))
                        end
                else
                        var nns = new NativeString(count)
                        ns.copy_to(nns, count, dumped, 0)
                        return new RopeBuffer.from(nns.to_s_unsafe(count))
                end
        end

        redef fun append(s) do
                var slen = s.byte_length
                if slen >= maxlen then
                        persist_buffer
                        str += s.to_s
                        return
                end
                if s isa FlatText then
                        var oits = s._items
                        var from = s.first_byte
                        var remsp = buf_size - rpos
                        if slen <= remsp then
                                oits.copy_to(ns, slen, from, rpos)
                                rpos += slen
                                return
                        end
                        var brk = oits.find_beginning_of_char_at(from + remsp)
                        oits.copy_to(ns, brk, from, rpos)
                        rpos += brk
                        dump_buffer
                        oits.copy_to(ns, slen - remsp, brk, 0)
                        rpos = slen - remsp
                else
                        for i in s.substrings do append i
                end
        end

        redef fun add(c) do
                var rp = rpos
                var remsp = buf_size - rp
                var cln = c.u8char_len
                if cln > remsp then
                        dump_buffer
                        rp = 0
                end
                ns.set_char_at(rp, c)
                rp += cln
                _byte_length += cln
                rpos = rp
        end

        # Converts the Buffer to a FlatString, appends it to
        # the final String and re-allocates a new larger Buffer.
        private fun dump_buffer do
                written = false
                var nstr = new FlatString.with_infos(ns, rpos - dumped, dumped)
                str += nstr
                var bs = buf_size
                bs = bs * 2
                ns = new NativeString(bs)
                buf_size = bs
                dumped = 0
                rpos = 0
        end

        # Similar to dump_buffer, but does not reallocate a new NativeString
        private fun persist_buffer do
                if rpos == dumped then return
                var nstr = new FlatString.with_infos(ns, rpos - dumped, dumped)
                str += nstr
                dumped = rpos
        end

        redef fun output do
                str.output
                new FlatString.with_infos(ns, rpos - dumped, dumped).output
        end

        # Enlarge is useless here since the `Buffer`
        # part is automatically dumped when necessary.
        #
        # Also, since the buffer can not be overused by a
        # single string, there is no need for manual
        # resizing.
        #
        # "You have no power here !"
        redef fun enlarge(i) do end

        redef fun to_s do
                persist_buffer
                written = true
                return str
        end

        redef fun reverse do
                # Flush the buffer in order to only have to reverse `str`.
                if rpos > 0 and dumped != rpos then
                        str += new FlatString.with_infos(ns, rpos - dumped, dumped)
                        dumped = rpos
                end
                str = str.reversed
        end

        redef fun upper do
                if written then reset
                persist_buffer
                str = str.to_upper
        end

        redef fun lower do
                if written then reset
                persist_buffer
                str = str.to_lower
        end
end

redef class FlatString

        redef fun insert_at(s, pos) do
                var l = substring(0, pos)
                var r = substring_from(pos)
                return l + s + r
        end

        redef fun +(o) do
                var s = o.to_s
                var slen = s.byte_length
                var mlen = _byte_length
                if slen == 0 then return self
                if mlen == 0 then return s
                var nlen = slen + mlen
                if s isa FlatString then
                        if nlen > maxlen then return new Concat(self, s)
                        var mits = _items
                        var sifrom = s._first_byte
                        var mifrom = _first_byte
                        var sits = s._items
                        var ns = new NativeString(nlen + 1)
                        mits.copy_to(ns, mlen, mifrom, 0)
                        sits.copy_to(ns, slen, sifrom, mlen)
                        return new FlatString.full(ns, nlen, 0, length + s.length)
                else if s isa Concat then
                        var sl = s._left
                        var sllen = sl.byte_length
                        if sllen + mlen > maxlen then return new Concat(self, s)
                        return new Concat(self + sl, s._right)
                else
                        abort
                end
        end
end

# A simple linked list for use with iterators
private class RopeCharIteratorPiece
        # The encapsulated node of the `Rope`
        var node: String
        # Was its _left child (if any) visited ?
        var ldone: Bool
        # Was its _right child (if any) visited ?
        var rdone: Bool
        # The previous node in the list.
        var prev: nullable RopeCharIteratorPiece
end

# A reverse iterator capable of working with `Rope` objects
private class RopeByteReverseIterator
        super IndexedIterator[Byte]

        # Current NativeString
        var ns: NativeString is noautoinit
        # Current position in NativeString
        var pns: Int is noautoinit
        # Position in the Rope (0-indexed)
        var pos: Int is noautoinit
        # Iterator on the substrings, does the Postfix part of
        # the Rope traversal.
        var subs: IndexedIterator[FlatString] is noautoinit

        init from(root: Concat, pos: Int) do
                self.pos = pos
                subs = new ReverseRopeSubstrings.from(root, pos)
                var s = subs.item
                ns = s._items
                pns = pos - subs.index
        end

        redef fun index do return pos

        redef fun is_ok do return pos >= 0

        redef fun item do return ns[pns]

        redef fun next do
                pns -= 1
                pos -= 1
                if pns >= 0 then return
                if not subs.is_ok then return
                subs.next
                if not subs.is_ok then return
                var s = subs.item
                ns = s._items
                pns = s.last_byte
        end
end

# Forward iterator on the bytes of a `Rope`
private class RopeByteIterator
        super IndexedIterator[Byte]

        # Position in current `String`
        var pns: Int is noautoinit
        # Current `String` being iterated on
        var ns: NativeString is noautoinit
        # Substrings of the Rope
        var subs: IndexedIterator[FlatString] is noautoinit
        # Maximum position to iterate on (e.g. Rope.byte_length)
        var max: Int is noautoinit
        # Position (char) in the Rope (0-indexed)
        var pos: Int is noautoinit

        init from(root: Concat, pos: Int) do
                subs = new RopeSubstrings.from(root, pos)
                pns = pos - subs.index
                self.pos = pos
                ns = subs.item._items
                max = root.byte_length - 1
        end

        redef fun item do return ns[pns]

        redef fun is_ok do return pos <= max

        redef fun index do return pos

        redef fun next do
                pns += 1
                pos += 1
                if pns < subs.item._byte_length then return
                if not subs.is_ok then return
                subs.next
                if not subs.is_ok then return
                ns = subs.item._items
                pns = 0
        end
end


# A reverse iterator capable of working with `Rope` objects
private class RopeCharReverseIterator
        super IndexedIterator[Char]

        # Current NativeString
        var ns: String is noautoinit
        # Current position in NativeString
        var pns: Int is noautoinit
        # Position in the Rope (0-indexed)
        var pos: Int is noautoinit
        # Iterator on the substrings, does the Postfix part of
        # the Rope traversal.
        var subs: IndexedIterator[String] is noautoinit

        init from(root: Concat, pos: Int) do
                self.pos = pos
                subs = new ReverseRopeSubstrings.from(root, pos)
                ns = subs.item
                pns = pos - subs.index
        end

        redef fun index do return pos

        redef fun is_ok do return pos >= 0

        redef fun item do return ns[pns]

        redef fun next do
                pns -= 1
                pos -= 1
                if pns >= 0 then return
                if not subs.is_ok then return
                subs.next
                if not subs.is_ok then return
                ns = subs.item
                pns = ns.length - 1
        end
end

# Forward iterator on the chars of a `Rope`
private class RopeCharIterator
        super IndexedIterator[Char]

        # Position in current `String`
        var pns: Int is noautoinit
        # Current `String` being iterated on
        var str: String is noautoinit
        # Substrings of the Rope
        var subs: IndexedIterator[String] is noautoinit
        # Maximum position to iterate on (e.g. Rope.length)
        var max: Int is noautoinit
        # Position (char) in the Rope (0-indexed)
        var pos: Int is noautoinit

        init from(root: Concat, pos: Int) do
                subs = new RopeSubstrings.from(root, pos)
                pns = pos - subs.index
                self.pos = pos
                str = subs.item
                max = root.length - 1
        end

        redef fun item do return str[pns]

        redef fun is_ok do return pos <= max

        redef fun index do return pos

        redef fun next do
                pns += 1
                pos += 1
                if pns < subs.item.length then return
                if not subs.is_ok then return
                subs.next
                if not subs.is_ok then return
                str = subs.item
                pns = 0
        end
end

# Substrings of a Rope (i.e. Reverse postfix iterator on leaves)
private class ReverseRopeSubstrings
        super IndexedIterator[FlatString]

        # Visit Stack
        var iter: RopeCharIteratorPiece is noinit
        # Position in `Rope`
        var pos: Int is noinit

        # Current leaf
        var str: FlatString is noinit

        init from(root: Concat, pos: Int) do
                var r = new RopeCharIteratorPiece(root, false, true, null)
                var rnod: String = root
                var off = pos
                loop
                        if rnod isa Concat then
                                if off >= rnod._left.length then
                                        off -= rnod._left.length
                                        rnod = rnod._right
                                        r = new RopeCharIteratorPiece(rnod, false, true, r)
                                else
                                        r.ldone = true
                                        rnod = rnod._left
                                        r = new RopeCharIteratorPiece(rnod, false, true, r)
                                end
                        else
                                str = rnod.as(FlatString)
                                r.ldone = true
                                iter = r
                                self.pos = pos - off
                                break
                        end
                end
        end

        redef fun item do return str

        redef fun index do return pos

        redef fun is_ok do return pos >= 0

        redef fun next do
                if pos < 0 then return
                var curr = iter.prev
                var currit = curr.as(not null).node
                while curr != null do
                        currit = curr.node
                        if not currit isa Concat then
                                str = currit.as(FlatString)
                                pos -= str.length
                                iter = curr
                                return
                        end
                        if not curr.rdone then
                                curr.rdone = true
                                curr = new RopeCharIteratorPiece(currit._right, false, false, curr)
                                continue
                        end
                        if not curr.ldone then
                                curr.ldone = true
                                curr = new RopeCharIteratorPiece(currit._left, false, false, curr)
                                continue
                        end
                        curr = curr.prev
                end
                pos = -1
        end
end

private class RopeBufSubstringIterator
        super Iterator[FlatText]

        # Iterator on the substrings of the building string
        var iter: Iterator[FlatText] is noautoinit
        # Makes a String out of the buffered part of the Ropebuffer
        var nsstr: FlatString is noautoinit
        # Did we attain the buffered part ?
        var nsstr_done = false

        init from(str: RopeBuffer) do
                iter = str.str.substrings
                nsstr = new FlatString.with_infos(str.ns, str.rpos - str.dumped, str.dumped)
                if str.length == 0 then nsstr_done = true
        end

        redef fun is_ok do return iter.is_ok or not nsstr_done

        redef fun item do
                assert is_ok
                if iter.is_ok then return iter.item
                return nsstr
        end

        redef fun next do
                if iter.is_ok then
                        iter.next
                        return
                end
                nsstr_done = true
        end
end

# Substrings of a Rope (i.e. Postfix iterator on leaves)
private class RopeSubstrings
        super IndexedIterator[FlatString]

        # Visit Stack
        var iter: RopeCharIteratorPiece is noinit
        # Position in `Rope`
        var pos: Int is noinit
        # Maximum position in `Rope` (i.e. length - 1)
        var max: Int is noinit

        # Current leaf
        var str: FlatString is noinit

        init from(root: Concat, pos: Int) do
                var r = new RopeCharIteratorPiece(root, true, false, null)
                max = root.length - 1
                var rnod: String = root
                var off = pos
                loop
                        if rnod isa Concat then
                                if off >= rnod._left.length then
                                        r.rdone = true
                                        off -= rnod._left.length
                                        rnod = rnod._right
                                        r = new RopeCharIteratorPiece(rnod, true, false, r)
                                else
                                        rnod = rnod._left
                                        r = new RopeCharIteratorPiece(rnod, true, false, r)
                                end
                        else
                                str = rnod.as(FlatString)
                                r.rdone = true
                                iter = r
                                self.pos = pos - off
                                break
                        end
                end
        end

        redef fun item do return str

        redef fun is_ok do return pos <= max

        redef fun index do return pos

        redef fun next do
                pos += str.length
                if pos > max then return
                var it = iter.prev.as(not null)
                var rnod = it.node
                loop
                        if not rnod isa Concat then
                                it.ldone = true
                                it.rdone = true
                                str = rnod.as(FlatString)
                                iter = it
                                break
                        end
                        if not it.ldone then
                                rnod = rnod._left
                                it.ldone = true
                                it = new RopeCharIteratorPiece(rnod, false, false, it)
                        else if not it.rdone then
                                it.rdone = true
                                rnod = rnod._right
                                it = new RopeCharIteratorPiece(rnod, false, false, it)
                        else
                                it = it.prev.as(not null)
                                rnod = it.node
                                continue
                        end
                end
        end
end

# Implementation of a `StringCharView` for `Concat` objects
private class RopeChars
        super StringCharView

        redef type SELFTYPE: Concat

        redef fun [](i) do
                return target[i]
        end

        redef fun iterator_from(i) do return new RopeCharIterator.from(target, i)

        redef fun reverse_iterator_from(i) do return new RopeCharReverseIterator.from(target, i)

end

# Implementation of a `StringCharView` for `Concat` objects
private class RopeBytes
        super StringByteView

        redef type SELFTYPE: Concat

        var cache: FlatString is noinit

        var cache_start: Int = -1

        var cache_end: Int = -1

        redef fun [](i) do
                assert i >= 0 and i < target._byte_length
                var flps = _cache_start
                if i >= flps and i <= _cache_end then
                        return _cache.bytes[i - flps]
                end
                var lf = get_leaf_at(i)
                return lf.bytes[i - _cache_start]
        end

        fun get_leaf_at(pos: Int): FlatString do
                var flps = _cache_start
                if pos >= flps and pos <= _cache_end then
                        return _cache
                end
                var s: String = target
                var st = pos
                loop
                        if s isa FlatString then break
                        s = s.as(Concat)
                        var lft = s._left
                        var llen = lft.byte_length
                        if pos >= llen then
                                s = s._right
                                pos -= llen
                        else
                                s = lft
                        end
                end
                _cache_start = st - pos
                _cache_end = st - pos + s.byte_length - 1
                _cache = s
                return s
        end

        redef fun iterator_from(i) do return new RopeByteIterator.from(target, i)

        redef fun reverse_iterator_from(i) do return new RopeByteReverseIterator.from(target, i)

end

# An Iterator over a RopeBuffer.
class RopeBufferCharIterator
        super IndexedIterator[Char]

        # Subiterator.
        var sit: IndexedIterator[Char] is noautoinit

        redef fun index do return sit.index

        # Init the iterator from a RopeBuffer starting from `pos`.
        init from(t: RopeBuffer, pos: Int) do
                t.persist_buffer
                sit = t.str.chars.iterator_from(pos)
        end

        redef fun is_ok do return sit.is_ok

        redef fun item do
                assert is_ok
                return sit.item
        end

        redef fun next do sit.next
end

# Reverse iterator over a RopeBuffer.
class RopeBufferCharReverseIterator
        super IndexedIterator[Char]

        # Subiterator.
        var sit: IndexedIterator[Char] is noautoinit

        redef fun index do return sit.index

        # Init the iterator from a RopeBuffer starting from `pos`.
        init from(tgt: RopeBuffer, pos: Int) do
                tgt.persist_buffer
                sit = tgt.str.chars.reverse_iterator_from(pos)
        end

        redef fun is_ok do return sit.is_ok

        redef fun item do
                assert is_ok
                return sit.item
        end

        redef fun next do sit.next
end

# View on the chars of a `RopeBuffer`
class RopeBufferChars
        super BufferCharView

        redef type SELFTYPE: RopeBuffer

        redef fun [](i) do return target[i]

        redef fun []=(i,c) do target[i] = c

        redef fun add(c) do target.add c

        redef fun push(c) do target.add c

        redef fun iterator_from(i) do return new RopeBufferCharIterator.from(target, i)

        redef fun reverse_iterator_from(i) do return new RopeBufferCharReverseIterator.from(target, i)
end

# An Iterator over a RopeBuffer.
class RopeBufferByteIterator
        super IndexedIterator[Byte]

        # Subiterator.
        var sit: IndexedIterator[Byte] is noautoinit

        # Native string iterated over.
        var ns: NativeString is noautoinit

        # Current position in `ns`.
        var pns: Int is noautoinit

        # Maximum position iterable.
        var maxpos: Int is noautoinit

        redef var index is noautoinit

        # Init the iterator from a RopeBuffer starting from `pos`.
        init from(t: RopeBuffer, pos: Int) do
                ns = t.ns
                maxpos = t._byte_length
                sit = t.str.bytes.iterator_from(pos)
                pns = pos - t.str.length
                index = pos
        end

        redef fun is_ok do return index < maxpos

        redef fun item do
                if sit.is_ok then return sit.item
                return ns[pns]
        end

        redef fun next do
                index += 1
                if sit.is_ok then
                        sit.next
                else
                        pns += 1
                end
        end
end

# Reverse iterator over a RopeBuffer.
class RopeBufferByteReverseIterator
        super IndexedIterator[Byte]

        # Subiterator.
        var sit: IndexedIterator[Byte] is noautoinit

        # Native string iterated over.
        var ns: NativeString is noautoinit

        # Current position in `ns`.
        var pns: Int is noautoinit

        redef var index is noautoinit

        # Init the iterator from a RopeBuffer starting from `pos`.
        init from(tgt: RopeBuffer, pos: Int) do
                sit = tgt.str.bytes.reverse_iterator_from(pos - (tgt.rpos - tgt.dumped))
                pns = pos - tgt.str.byte_length + tgt.rpos
                index = pos
                ns = tgt.ns
        end

        redef fun is_ok do return index >= 0

        redef fun item do
                if pns >= 0 then return ns[pns]
                return sit.item
        end

        redef fun next do
                index -= 1
                if pns >= 0 then
                        pns -= 1
                else
                        sit.next
                end
        end
end

# View on the chars of a `RopeBuffer`
class RopeBufferBytes
        super BufferByteView

        redef type SELFTYPE: RopeBuffer

        redef fun [](i) do
                if i < target.str.byte_length then
                        return target.str.bytes[i]
                else
                        return target.ns[i - target.str.byte_length]
                end
        end

        redef fun iterator_from(i) do return new RopeBufferByteIterator.from(target, i)

        redef fun reverse_iterator_from(i) do return new RopeBufferByteReverseIterator.from(target, i)
end