ropes: Fix the behavior of `RopeBuffer.clear` when used with `to_s`.

[nit.git] / lib / standard / 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 :
#
# `            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 string

# 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 64

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

private abstract class RopeString
        super Rope
        super String

        redef fun chars is cached do return new RopeChars(self)
end

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

        redef var length: Int

        redef fun substrings do return new RopeSubstrings(self)

        redef fun empty do return ""

        redef fun to_cstring is cached do
                var len = length
                var ns = new NativeString(len + 1)
                ns[len] = '\0'
                var off = 0
                for i in substrings do
                        var ilen = i.length
                        i.as(FlatString).items.copy_to(ns, ilen, i.as(FlatString).index_from, off)
                        off += ilen
                end
                return ns
        end

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

        init(l: String, r: String) is old_style_init do
                left = l
                right = r
                length = l.length + r.length
        end

        redef fun output do
                left.output
                right.output
        end

        redef fun iterator do return new RopeIter(self)

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

        redef fun [](i) do
                var llen = left.length
                if i >= llen then return right[i - llen]
                return left[i]
        end

        redef fun substring(from, len) do
                var llen = left.length
                if from < llen then
                        if from + len < llen then return left.substring(from,len)
                        var lsublen = llen - from
                        return left.substring_from(from) + right.substring(0, len - lsublen)
                else
                        return right.substring(from - llen, len)
                end
        end

        redef fun reversed do return new Concat(right.reversed, left.reversed)

        redef fun insert_at(s, pos) do
                if pos > left.length then
                        return left + right.insert_at(s, pos - left.length)
                end
                return left.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.length
                if s isa Concat then
                        return new Concat(self, s)
                else
                        var r = right
                        var rlen = r.length
                        if rlen + slen > maxlen then return new Concat(left, new Concat(r, s))
                        return new Concat(left, r + s)
                end
        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: Sequence[Char] is cached do return new RopeBufferChars(self)

        # The final string being built on the fly
        private var str: String is noinit

        # Current concatenation buffer
        private var ns: NativeString is noinit

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

        # Length of the mutable part
        #
        # 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: Iterator[String] do return new RopeBufSubstringIterator(self)

        # Builds an empty `RopeBuffer`
        init do
                str = ""
                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
                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)
                dumped = 0
                rpos = blen
                written = false
        end

        redef fun empty do return new RopeBuffer

        redef fun clear do
                str = ""
                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_with_length(rem))
                        end
                else
                        var nns = new NativeString(count)
                        ns.copy_to(nns, count, dumped, 0)
                        return new RopeBuffer.from(nns.to_s_with_length(count))
                end
        end

        redef fun append(s) do
                var slen = s.length
                length += slen
                var rp = rpos
                if s isa Rope or slen > maxlen then
                        if rp > 0 and dumped != rp then
                                str += new FlatString.with_infos(ns, rp - dumped, dumped, rp - 1)
                                dumped = rp
                        end
                        str = str + s
                        return
                end
                var remsp = buf_size - rp
                var sits: NativeString
                var begin: Int
                if s isa FlatString then
                        begin = s.index_from
                        sits = s.items
                else if s isa FlatBuffer then
                        begin = 0
                        sits = s.items
                else
                        if slen <= remsp then
                                for i in s.chars do
                                        ns[rpos] = i
                                        rpos += 1
                                end
                        else
                                var spos = 0
                                for i in [0..remsp[ do
                                        ns[rpos] = s[spos]
                                        rpos += 1
                                        spos += 1
                                end
                                dump_buffer
                                while spos < slen do
                                        ns[rpos] = s[spos]
                                        spos += 1
                                        rpos += 1
                                end
                        end
                        return
                end
                if slen <= remsp then
                        if remsp <= 0 then
                                dump_buffer
                                rpos = 0
                        else
                                sits.copy_to(ns, slen, begin, rp)
                                rpos += slen
                        end
                else
                        sits.copy_to(ns, remsp, begin, rp)
                        rpos = buf_size
                        dump_buffer
                        var nlen = slen - remsp
                        sits.copy_to(ns, nlen, begin + remsp, 0)
                        rpos = nlen
                end
        end

        redef fun add(c) do
                var rp = rpos
                if rp >= buf_size then
                        dump_buffer
                        rp = 0
                end
                ns[rp] = c
                rp += 1
                length += 1
                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, rpos - 1)
                str += nstr
                var bs = buf_size
                bs = bs * 2
                ns = new NativeString(bs)
                buf_size = bs
                dumped = 0
        end

        redef fun output do
                str.output
                new FlatString.with_infos(ns, rpos - dumped, dumped, rpos - 1).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
                written = true
                var nnslen = rpos - dumped
                if nnslen == 0 then return str
                return str + new FlatString.with_infos(ns, rpos - dumped, dumped, rpos - 1)
        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, rpos - 1)
                        dumped = rpos
                end
                str = str.reversed
        end

        redef fun upper do
                if written then reset
                str = str.to_upper
                var mits = ns
                for i in [0 .. rpos[ do
                        mits[i] = mits[i].to_upper
                end
        end

        redef fun lower do
                if written then reset
                str = str.to_lower
                var mits = ns
                for i in [0 .. rpos[ do
                        mits[i] = mits[i].to_lower
                end
        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.length
                var mlen = 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.index_from
                        var mifrom = index_from
                        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 ns.to_s_with_length(nlen)
                else if s isa Concat then
                        var sl = s.left
                        var sllen = sl.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 RopeIterPiece
        # 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 RopeIterPiece
end

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

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

        init(root: RopeString) is old_style_init do
                pos = root.length - 1
                subs = new ReverseRopeSubstrings(root)
                ns = subs.item
                pns = ns.length - 1
        end

        init from(root: RopeString, 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 RopeIter
        super IndexedIterator[Char]

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

        init(root: RopeString) is old_style_init do
                subs = new RopeSubstrings(root)
                pns = 0
                str = subs.item
                max = root.length - 1
                pos = 0
        end

        init from(root: RopeString, 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[String]

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

        # Current leaf
        var str: String is noinit

        init(root: RopeString) is old_style_init do
                var r = new RopeIterPiece(root, false, true, null)
                pos = root.length - 1
                var lnod: String = root
                loop
                        if lnod isa Concat then
                                lnod = lnod.right
                                r = new RopeIterPiece(lnod, false, true, r)
                        else
                                str = lnod
                                iter = r
                                break
                        end
                end
        end

        init from(root: RopeString, pos: Int) do
                var r = new RopeIterPiece(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 RopeIterPiece(rnod, false, true, r)
                                else
                                        r.ldone = true
                                        rnod = rnod.left
                                        r = new RopeIterPiece(rnod, false, true, r)
                                end
                        else
                                str = rnod
                                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.node
                while curr != null do
                        currit = curr.node
                        if not currit isa Concat then
                                str = currit
                                pos -= str.length
                                iter = curr
                                return
                        end
                        if not curr.rdone then
                                curr.rdone = true
                                curr = new RopeIterPiece(currit.right, false, false, curr)
                                continue
                        end
                        if not curr.ldone then
                                curr.ldone = true
                                curr = new RopeIterPiece(currit.left, false, false, curr)
                                continue
                        end
                        curr = curr.prev
                end
                pos = -1
        end
end

private class RopeBufSubstringIterator
        super Iterator[String]

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

        init(str: RopeBuffer) is old_style_init do
                iter = str.str.substrings
                nsstr = new FlatString.with_infos(str.ns, str.rpos - str.dumped, str.dumped, str.rpos - 1)
                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[String]

        # Visit Stack
        var iter: RopeIterPiece 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: String is noinit

        init(root: RopeString) is old_style_init do
                var r = new RopeIterPiece(root, true, false, null)
                pos = 0
                max = root.length - 1
                var rnod: String = root
                loop
                        if rnod isa Concat then
                                rnod = rnod.left
                                r = new RopeIterPiece(rnod, true, false, r)
                        else
                                str = rnod
                                r.rdone = true
                                iter = r
                                break
                        end
                end
        end

        init from(root: RopeString, pos: Int) do
                var r = new RopeIterPiece(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 RopeIterPiece(rnod, true, false, r)
                                else
                                        rnod = rnod.left
                                        r = new RopeIterPiece(rnod, true, false, r)
                                end
                        else
                                str = rnod
                                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
                var rnod = it.node
                loop
                        if not rnod isa Concat then
                                it.ldone = true
                                it.rdone = true
                                str = rnod
                                iter = it.as(not null)
                                break
                        end
                        if not it.ldone then
                                rnod = rnod.left
                                it.ldone = true
                                it = new RopeIterPiece(rnod, false, false, it)
                        else if not it.rdone then
                                it.rdone = true
                                rnod = rnod.right
                                it = new RopeIterPiece(rnod, false, false, it)
                        else
                                it = it.prev
                                rnod = it.node
                                continue
                        end
                end
        end
end

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

        var tgt: RopeString

        init(s: RopeString) is old_style_init do tgt = s

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

        redef fun iterator_from(i) do return new RopeIter.from(tgt, i)

        redef fun reverse_iterator_from(i) do return new RopeReviter.from(tgt, i)

end

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

        # Subiterator.
        var sit: IndexedIterator[Char]

        # Native string iterated over.
        var ns: NativeString

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

        # Maximum position iterable.
        var maxpos: Int

        redef var index: Int

        # Init the iterator from a RopeBuffer.
        init(t: RopeBuffer) is old_style_init do
                ns = t.ns
                maxpos = t.rpos
                sit = t.str.chars.iterator
                pns = t.dumped
                index = 0
        end

        # Init the iterator from a RopeBuffer starting from `pos`.
        init from(t: RopeBuffer, pos: Int) do
                ns = t.ns
                maxpos = t.length
                sit = t.str.chars.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 RopeBufferReviter
        super IndexedIterator[Char]

        # Subiterator.
        var sit: IndexedIterator[Char]

        # Native string iterated over.
        var ns: NativeString

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

        redef var index: Int

        # Init the iterator from a RopeBuffer.
        init(tgt: RopeBuffer) is old_style_init do
                sit = tgt.str.chars.reverse_iterator
                pns = tgt.rpos - 1
                index = tgt.length - 1
                ns = tgt.ns
        end

        # Init the iterator from a RopeBuffer starting from `pos`.
        init from(tgt: RopeBuffer, pos: Int) do
                sit = tgt.str.chars.reverse_iterator_from(pos - tgt.rpos - tgt.dumped)
                pns = pos - tgt.str.length
                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 RopeBufferChars
        super BufferCharView

        redef type SELFTYPE: RopeBuffer

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

        redef fun []=(i,c) do
                if i == target.length then target.add c
                if i < target.str.length then
                        var s = target.str
                        var l = s.substring(0, i)
                        var r = s.substring_from(i + 1)
                        target.str = l + c.to_s + r
                else
                        target.ns[i - target.str.length] = c
                end
        end

        redef fun add(c) do target.add c

        redef fun push(c) do target.add c

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

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