initial

8 files changed, 672 insertions, 0 deletions

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..b338ecb
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,6 @@
+# Copyright (C) 2016 all contributors <msgthr-public@80x24.org>
+# License: GPL-3.0+ <https://www.gnu.org/licenses/gpl-3.0.txt>
+*.gem
+*.gz
+.manifest
+pkg/
diff --git a/COPYING b/COPYING
new file mode 100644
index 0000000..d159169
--- /dev/null
+++ b/COPYING
@@ -0,0 +1,339 @@
+                    GNU GENERAL PUBLIC LICENSE
+                       Version 2, June 1991
+
+ Copyright (C) 1989, 1991 Free Software Foundation, Inc.,
+ 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ Everyone is permitted to copy and distribute verbatim copies
+ of this license document, but changing it is not allowed.
+
+                            Preamble
+
+  The licenses for most software are designed to take away your
+freedom to share and change it.  By contrast, the GNU General Public
+License is intended to guarantee your freedom to share and change free
+software--to make sure the software is free for all its users.  This
+General Public License applies to most of the Free Software
+Foundation's software and to any other program whose authors commit to
+using it.  (Some other Free Software Foundation software is covered by
+the GNU Lesser General Public License instead.)  You can apply it to
+your programs, too.
+
+  When we speak of free software, we are referring to freedom, not
+price.  Our General Public Licenses are designed to make sure that you
+have the freedom to distribute copies of free software (and charge for
+this service if you wish), that you receive source code or can get it
+if you want it, that you can change the software or use pieces of it
+in new free programs; and that you know you can do these things.
+
+  To protect your rights, we need to make restrictions that forbid
+anyone to deny you these rights or to ask you to surrender the rights.
+These restrictions translate to certain responsibilities for you if you
+distribute copies of the software, or if you modify it.
+
+  For example, if you distribute copies of such a program, whether
+gratis or for a fee, you must give the recipients all the rights that
+you have.  You must make sure that they, too, receive or can get the
+source code.  And you must show them these terms so they know their
+rights.
+
+  We protect your rights with two steps: (1) copyright the software, and
+(2) offer you this license which gives you legal permission to copy,
+distribute and/or modify the software.
+
+  Also, for each author's protection and ours, we want to make certain
+that everyone understands that there is no warranty for this free
+software.  If the software is modified by someone else and passed on, we
+want its recipients to know that what they have is not the original, so
+that any problems introduced by others will not reflect on the original
+authors' reputations.
+
+  Finally, any free program is threatened constantly by software
+patents.  We wish to avoid the danger that redistributors of a free
+program will individually obtain patent licenses, in effect making the
+program proprietary.  To prevent this, we have made it clear that any
+patent must be licensed for everyone's free use or not licensed at all.
+
+  The precise terms and conditions for copying, distribution and
+modification follow.
+
+                    GNU GENERAL PUBLIC LICENSE
+   TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
+
+  0. This License applies to any program or other work which contains
+a notice placed by the copyright holder saying it may be distributed
+under the terms of this General Public License.  The "Program", below,
+refers to any such program or work, and a "work based on the Program"
+means either the Program or any derivative work under copyright law:
+that is to say, a work containing the Program or a portion of it,
+either verbatim or with modifications and/or translated into another
+language.  (Hereinafter, translation is included without limitation in
+the term "modification".)  Each licensee is addressed as "you".
+
+Activities other than copying, distribution and modification are not
+covered by this License; they are outside its scope.  The act of
+running the Program is not restricted, and the output from the Program
+is covered only if its contents constitute a work based on the
+Program (independent of having been made by running the Program).
+Whether that is true depends on what the Program does.
+
+  1. You may copy and distribute verbatim copies of the Program's
+source code as you receive it, in any medium, provided that you
+conspicuously and appropriately publish on each copy an appropriate
+copyright notice and disclaimer of warranty; keep intact all the
+notices that refer to this License and to the absence of any warranty;
+and give any other recipients of the Program a copy of this License
+along with the Program.
+
+You may charge a fee for the physical act of transferring a copy, and
+you may at your option offer warranty protection in exchange for a fee.
+
+  2. You may modify your copy or copies of the Program or any portion
+of it, thus forming a work based on the Program, and copy and
+distribute such modifications or work under the terms of Section 1
+above, provided that you also meet all of these conditions:
+
+    a) You must cause the modified files to carry prominent notices
+    stating that you changed the files and the date of any change.
+
+    b) You must cause any work that you distribute or publish, that in
+    whole or in part contains or is derived from the Program or any
+    part thereof, to be licensed as a whole at no charge to all third
+    parties under the terms of this License.
+
+    c) If the modified program normally reads commands interactively
+    when run, you must cause it, when started running for such
+    interactive use in the most ordinary way, to print or display an
+    announcement including an appropriate copyright notice and a
+    notice that there is no warranty (or else, saying that you provide
+    a warranty) and that users may redistribute the program under
+    these conditions, and telling the user how to view a copy of this
+    License.  (Exception: if the Program itself is interactive but
+    does not normally print such an announcement, your work based on
+    the Program is not required to print an announcement.)
+
+These requirements apply to the modified work as a whole.  If
+identifiable sections of that work are not derived from the Program,
+and can be reasonably considered independent and separate works in
+themselves, then this License, and its terms, do not apply to those
+sections when you distribute them as separate works.  But when you
+distribute the same sections as part of a whole which is a work based
+on the Program, the distribution of the whole must be on the terms of
+this License, whose permissions for other licensees extend to the
+entire whole, and thus to each and every part regardless of who wrote it.
+
+Thus, it is not the intent of this section to claim rights or contest
+your rights to work written entirely by you; rather, the intent is to
+exercise the right to control the distribution of derivative or
+collective works based on the Program.
+
+In addition, mere aggregation of another work not based on the Program
+with the Program (or with a work based on the Program) on a volume of
+a storage or distribution medium does not bring the other work under
+the scope of this License.
+
+  3. You may copy and distribute the Program (or a work based on it,
+under Section 2) in object code or executable form under the terms of
+Sections 1 and 2 above provided that you also do one of the following:
+
+    a) Accompany it with the complete corresponding machine-readable
+    source code, which must be distributed under the terms of Sections
+    1 and 2 above on a medium customarily used for software interchange; or,
+
+    b) Accompany it with a written offer, valid for at least three
+    years, to give any third party, for a charge no more than your
+    cost of physically performing source distribution, a complete
+    machine-readable copy of the corresponding source code, to be
+    distributed under the terms of Sections 1 and 2 above on a medium
+    customarily used for software interchange; or,
+
+    c) Accompany it with the information you received as to the offer
+    to distribute corresponding source code.  (This alternative is
+    allowed only for noncommercial distribution and only if you
+    received the program in object code or executable form with such
+    an offer, in accord with Subsection b above.)
+
+The source code for a work means the preferred form of the work for
+making modifications to it.  For an executable work, complete source
+code means all the source code for all modules it contains, plus any
+associated interface definition files, plus the scripts used to
+control compilation and installation of the executable.  However, as a
+special exception, the source code distributed need not include
+anything that is normally distributed (in either source or binary
+form) with the major components (compiler, kernel, and so on) of the
+operating system on which the executable runs, unless that component
+itself accompanies the executable.
+
+If distribution of executable or object code is made by offering
+access to copy from a designated place, then offering equivalent
+access to copy the source code from the same place counts as
+distribution of the source code, even though third parties are not
+compelled to copy the source along with the object code.
+
+  4. You may not copy, modify, sublicense, or distribute the Program
+except as expressly provided under this License.  Any attempt
+otherwise to copy, modify, sublicense or distribute the Program is
+void, and will automatically terminate your rights under this License.
+However, parties who have received copies, or rights, from you under
+this License will not have their licenses terminated so long as such
+parties remain in full compliance.
+
+  5. You are not required to accept this License, since you have not
+signed it.  However, nothing else grants you permission to modify or
+distribute the Program or its derivative works.  These actions are
+prohibited by law if you do not accept this License.  Therefore, by
+modifying or distributing the Program (or any work based on the
+Program), you indicate your acceptance of this License to do so, and
+all its terms and conditions for copying, distributing or modifying
+the Program or works based on it.
+
+  6. Each time you redistribute the Program (or any work based on the
+Program), the recipient automatically receives a license from the
+original licensor to copy, distribute or modify the Program subject to
+these terms and conditions.  You may not impose any further
+restrictions on the recipients' exercise of the rights granted herein.
+You are not responsible for enforcing compliance by third parties to
+this License.
+
+  7. If, as a consequence of a court judgment or allegation of patent
+infringement or for any other reason (not limited to patent issues),
+conditions are imposed on you (whether by court order, agreement or
+otherwise) that contradict the conditions of this License, they do not
+excuse you from the conditions of this License.  If you cannot
+distribute so as to satisfy simultaneously your obligations under this
+License and any other pertinent obligations, then as a consequence you
+may not distribute the Program at all.  For example, if a patent
+license would not permit royalty-free redistribution of the Program by
+all those who receive copies directly or indirectly through you, then
+the only way you could satisfy both it and this License would be to
+refrain entirely from distribution of the Program.
+
+If any portion of this section is held invalid or unenforceable under
+any particular circumstance, the balance of the section is intended to
+apply and the section as a whole is intended to apply in other
+circumstances.
+
+It is not the purpose of this section to induce you to infringe any
+patents or other property right claims or to contest validity of any
+such claims; this section has the sole purpose of protecting the
+integrity of the free software distribution system, which is
+implemented by public license practices.  Many people have made
+generous contributions to the wide range of software distributed
+through that system in reliance on consistent application of that
+system; it is up to the author/donor to decide if he or she is willing
+to distribute software through any other system and a licensee cannot
+impose that choice.
+
+This section is intended to make thoroughly clear what is believed to
+be a consequence of the rest of this License.
+
+  8. If the distribution and/or use of the Program is restricted in
+certain countries either by patents or by copyrighted interfaces, the
+original copyright holder who places the Program under this License
+may add an explicit geographical distribution limitation excluding
+those countries, so that distribution is permitted only in or among
+countries not thus excluded.  In such case, this License incorporates
+the limitation as if written in the body of this License.
+
+  9. The Free Software Foundation may publish revised and/or new versions
+of the General Public License from time to time.  Such new versions will
+be similar in spirit to the present version, but may differ in detail to
+address new problems or concerns.
+
+Each version is given a distinguishing version number.  If the Program
+specifies a version number of this License which applies to it and "any
+later version", you have the option of following the terms and conditions
+either of that version or of any later version published by the Free
+Software Foundation.  If the Program does not specify a version number of
+this License, you may choose any version ever published by the Free Software
+Foundation.
+
+  10. If you wish to incorporate parts of the Program into other free
+programs whose distribution conditions are different, write to the author
+to ask for permission.  For software which is copyrighted by the Free
+Software Foundation, write to the Free Software Foundation; we sometimes
+make exceptions for this.  Our decision will be guided by the two goals
+of preserving the free status of all derivatives of our free software and
+of promoting the sharing and reuse of software generally.
+
+                            NO WARRANTY
+
+  11. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY
+FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW.  EXCEPT WHEN
+OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES
+PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED
+OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.  THE ENTIRE RISK AS
+TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU.  SHOULD THE
+PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING,
+REPAIR OR CORRECTION.
+
+  12. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR
+REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES,
+INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING
+OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED
+TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY
+YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER
+PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE
+POSSIBILITY OF SUCH DAMAGES.
+
+                     END OF TERMS AND CONDITIONS
+
+            How to Apply These Terms to Your New Programs
+
+  If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+  To do so, attach the following notices to the program.  It is safest
+to attach them to the start of each source file to most effectively
+convey the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+    <one line to give the program's name and a brief idea of what it does.>
+    Copyright (C) <year>  <name of author>
+
+    This program is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version.
+
+    This program 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.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License along
+    with this program; if not, write to the Free Software Foundation, Inc.,
+    51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+
+Also add information on how to contact you by electronic and paper mail.
+
+If the program is interactive, make it output a short notice like this
+when it starts in an interactive mode:
+
+    Gnomovision version 69, Copyright (C) year name of author
+    Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+    This is free software, and you are welcome to redistribute it
+    under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License.  Of course, the commands you use may
+be called something other than `show w' and `show c'; they could even be
+mouse-clicks or menu items--whatever suits your program.
+
+You should also get your employer (if you work as a programmer) or your
+school, if any, to sign a "copyright disclaimer" for the program, if
+necessary.  Here is a sample; alter the names:
+
+  Yoyodyne, Inc., hereby disclaims all copyright interest in the program
+  `Gnomovision' (which makes passes at compilers) written by James Hacker.
+
+  <signature of Ty Coon>, 1 April 1989
+  Ty Coon, President of Vice
+
+This General Public License does not permit incorporating your program into
+proprietary programs.  If your program is a subroutine library, you may
+consider it more useful to permit linking proprietary applications with the
+library.  If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.
diff --git a/GNUmakefile b/GNUmakefile
new file mode 100644
index 0000000..49ab677
--- /dev/null
+++ b/GNUmakefile
@@ -0,0 +1,45 @@
+# Copyright (C) 2016 all contributors <msgthr-public@80x24.org>
+# License: GPL-2.0+ <https://www.gnu.org/licenses/gpl-2.0.txt>
+all::
+pkg = msgthr
+RUBY = ruby
+lib := lib
+VERSION := 0.0.0
+
+all:: test
+test_units := $(wildcard test/test_*.rb)
+test: $(test_units)
+$(test_units):
+        $(RUBY) -w -I $(lib) $@ -v
+
+check-warnings:
+        @(for i in $$(git ls-files '*.rb'| grep -v '^setup\.rb$$'); \
+          do $(RUBY) -d -W2 -c $$i; done) | grep -v '^Syntax OK$$' || :
+
+check: test
+
+pkggem := pkg/$(pkg)-$(VERSION).gem
+
+fix-perms:
+        git ls-tree -r HEAD | awk '/^100644 / {print $$NF}' | xargs chmod 644
+
+gem: $(pkggem)
+
+install-gem: $(pkggem)
+        gem install --local $(CURDIR)/$<
+
+$(pkggem): .manifest
+        VERSION=$(VERSION) gem build $(pkg).gemspec
+        mkdir -p pkg
+        mv $(@F) $@
+
+pkg_extra :=
+
+.manifest: fix-perms
+        git ls-files | LC_ALL=C sort >$@+
+        cmp $@+ $@ || mv $@+ $@; rm -f $@+
+
+package: $(pkggem)
+
+.PHONY: all test $(test_units)
+.PHONY: check-warnings fix-perms
diff --git a/README b/README
new file mode 100644
index 0000000..ca7c24c
--- /dev/null
+++ b/README
@@ -0,0 +1,81 @@
+msgthr - non-recursive, container-agnostic message threading
+------------------------------------------------------------
+
+Message threading based on the algorithm described by JWZ in
+<https://www.jwz.org/doc/threading.html> and used in
+countless mail and news readers; but with some features
+removed and improved flexibility:
+
+* No pruning of non-leaf ghosts.  Readers are not shielded
+  from deleted or lost messages.  Equivalent to setting
+  "hide_missing" to "no" in mutt.
+
+* No grouping by subject.  This makes things ideal for short
+  messages such as chat and status updates.  For email, this
+  encourages the use of proper client which set In-Reply-To
+  or References headers.  Equivalent to setting
+  "strict_threads" to "yes" in mutt.
+
+* No recursion; all algorithms are non-recursive to avoid
+  SystemStackError exceptions in deep threads.
+  Memory usage is bound by the number of lightweight containers
+  needed to represent a thread.
+
+* Message format-agnostic, not limited to email or NNTP;
+  but even appropriate for forums, blog comments, IM, etc.
+  For mail and NNTP messages, that means you must extract
+  the Message-ID and parse the References and In-Reply-To
+  headers into an array yourself.
+
+Source code
+-----------
+
+        git clone git://80x24.org/msgthr
+
+Contact
+-------
+
+Feedback is welcome via plain-text mail (no HTML, images, etc).
+Please send comments, user/dev discussion, patches, bug reports,
+and pull requests to the open-to-all mailing list at:
+
+        msgthr-public@80x24.org
+
+No subscription will ever be required to post.  Please Cc: all
+recipients as subscription is not necessary.
+
+Mailing list archives via HTTPS: https://80x24.org/msgthr-public/
+Or NNTP: nntp://news.public-inbox.org/inbox.comp.lang.ruby.msgthr
+
+You may optionally subscribe, but will never be required to:
+
+        msgthr-public+subscribe@80x24.org
+
+This README is our homepage, we would rather be working on cool
+stuff day than worrying about the next browser vulnerability
+because HTML/CSS/JS/images are too complicated for us.
+
+* https://80x24.org/msgthr/README
+
+Copyright
+---------
+
+Copyright 2016, all contributors (see git repo).
+License: GPL-2.0+ <https://www.gnu.org/licenses/gpl-2.0.txt>
+
+msgthr is copyrighted Free Software by all contributors, see logs in
+revision control for names and email addresses of all of them.
+
+msgthr is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as
+published by the Free Software Foundation; either version 2 of
+the License, or (at your option) any later version.
+
+msgthr 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.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public
+License along with this program; if not, see
+https://www.gnu.org/licenses/gpl-2.0.txt
diff --git a/lib/msgthr.rb b/lib/msgthr.rb
new file mode 100644
index 0000000..f8b5896
--- /dev/null
+++ b/lib/msgthr.rb
@@ -0,0 +1,91 @@
+# Copyright (C) 2016 all contributors <msgthr-public@80x24.org>
+# License: GPL-2.0+ <https://www.gnu.org/licenses/gpl-2.0.txt>
+
+# Non-recursive, container-agnostic message threading.
+class Msgthr
+
+  # an Array of root (parent-less) messages, only populated after
+  # calling Msgthr#thread!
+  attr_reader :rootset
+
+  # Initialize a Msgthr object
+  def initialize
+    @id_table = {}
+    @rootset = []
+  end
+
+  # Clear internal data structures to save memory and prepare for reuse
+  def clear
+    @rootset.clear
+    @id_table.clear
+  end
+
+  # Threads the message
+  # This does not sort
+  def thread!
+    ret = @rootset
+    @id_table.each_value { |cont| ret << cont if cont.parent.nil? }.clear
+    ret
+  end
+
+  def order!
+    yield @rootset
+    @rootset.each { |cont| cont.order! { |children| yield(children) } }
+  end
+
+  # non-recursively walk a thread
+  def walk_thread
+    i = -1
+    q = @rootset.map { |cont| [ 0, cont, i += 1 ] }
+    while tmp = q.shift
+      level, cont, idx = tmp
+      yield(level, cont, idx)
+      level += 1
+      i = -1
+      q = cont.children.map { |cld| [ level, cld, i += 1 ] }.concat(q)
+    end
+  end
+
+  # Adds a message to prepare a Msgthr object for threading.
+  #
+  # * +mid+ is a unique identifier for the message in a given thread.
+  #
+  # * +refs+ should be an Array of unique identifiers.  For mail and
+  #   news messages, this is usually the parsed result of the
+  #   "References:" header.  Order should be oldest to newest
+  #   in terms of ancestry, with the last element being the
+  #   immediate parent of the given message.
+  #
+  #   This is +nil+ for messages with no parent.
+  #
+  # * +msg+ is an opaque object which typically contains a
+  #   Mail or Tmail object for handling mail.
+  #
+  # If +mid+ is a String, it is recommended to freeze the string before
+  # calling this method to avoid wasting memory on hash keys.
+  def add(mid, refs, msg)
+    cur = @id_table[mid] ||= Msgthr::Container.new(mid)
+    cur.msg = msg
+    refs or return
+
+    # n.b. centralized messaging systems (e.g. forums) do not need
+    # multiple References:, only decentralized systems need it to
+    # tolerate missing messages
+    prev = nil
+    refs.each do |ref|
+      cont = @id_table[ref] ||= Msgthr::Container.new(ref)
+
+      # link refs together in order implied,
+      # but do not change existing links or loop
+      if prev && !cont.parent && !cont.has_descendent(prev)
+        prev.add_child(cont)
+      end
+      prev = cont
+    end
+
+    # set parent of this message to be the last element in refs
+    prev.add_child(cur) if prev
+  end
+end
+
+require_relative 'msgthr/container'
diff --git a/lib/msgthr/container.rb b/lib/msgthr/container.rb
new file mode 100644
index 0000000..30f6775
--- /dev/null
+++ b/lib/msgthr/container.rb
@@ -0,0 +1,73 @@
+# Copyright (C) 2016 all contributors <msgthr-public@80x24.org>
+# License: GPL-2.0+ <https://www.gnu.org/licenses/gpl-2.0.txt>
+
+# An internal container class, this is exposed for sorting APIs
+# but should not be initialized in your own code.
+class Msgthr::Container
+
+  # Unique message identifier, typically the Message-Id header for mail
+  # and news messages.  This may be any hashable object, Integer values
+  # are allowed and will not be coerced to string values.
+  attr_reader :mid
+
+  # Opaque data pointer, may be used by the user for any purpose.
+  # This may be +nil+ to denote missing (aka "ghost") messages.
+  attr_accessor :msg
+
+  attr_accessor :children # :nodoc:
+  attr_accessor :parent # :nodoc:
+
+  def initialize(mid) # :nodoc:
+    @mid = mid
+    @children = {} # becomes an Array after order!
+    @parent = nil
+    @msg = nil # opaque
+  end
+
+  # returns the topmost message container with an opaque message pointer
+  # in it.  This may be +nil+ if none are available.
+  def topmost
+    q = [ self ]
+    while cont = q.shift
+      return cont if cont.msg
+      q.concat(cont.children.values)
+    end
+    nil
+  end
+
+  def add_child(child) # :nodoc:
+    raise 'cannot become child of self' if child == self
+    cid = child.mid
+
+    # reparenting:
+    parent = child.parent and parent.children.delete(cid)
+
+    @children[cid] = child
+    child.parent = self
+  end
+
+  def has_descendent(child) # :nodoc:
+    seen = Hash.new(0)
+    while child
+      return true if self == child || (seen[child] += 1) != 0
+      child = child.parent
+    end
+    false
+  end
+
+  def order! # :nodoc:
+    seen = { @mid => true }
+    q = [ self ]
+    while cur = q.shift
+      c = []
+      cur.children.each do |cmid, cont|
+        next if seen[cmid]
+        c << cont
+        seen[cmid] = true
+      end.clear
+      yield(c) if c.size > 1
+      cur.children = c
+      q.concat(c)
+    end
+  end
+end
diff --git a/msgthr.gemspec b/msgthr.gemspec
new file mode 100644
index 0000000..0bb591e
--- /dev/null
+++ b/msgthr.gemspec
@@ -0,0 +1,17 @@
+# Copyright (C) 2016 all contributors <msgthr-public@80x24.org>
+# License: GPL-2.0+ <https://www.gnu.org/licenses/gpl-2.0.txt>
+
+Gem::Specification.new do |s|
+  manifest = File.read('.manifest').split(/\n/)
+  s.name = %q{msgthr}
+  s.version = ENV['VERSION'] || '0.0.0'
+  s.authors = ['msgthr hackers']
+  s.summary = 'non-recursive, container-agnostic message threading'
+  s.description = File.read('README').split(/\n\n/)[1].strip
+  s.email = %q{msgthr-public@80x24.org}
+  s.homepage = 'https://80x24.org/msgthr/'
+  s.executables = []
+  s.files = manifest
+  s.licenses = 'GPL-2.0+'
+  s.required_ruby_version = '>= 1.9.3'
+end
diff --git a/test/test_msgthr.rb b/test/test_msgthr.rb
new file mode 100644
index 0000000..2e398c1
--- /dev/null
+++ b/test/test_msgthr.rb
@@ -0,0 +1,20 @@
+# Copyright (C) 2016 all contributors <msgthr-public@80x24.org>
+# License: GPL-2.0+ <https://www.gnu.org/licenses/gpl-2.0.txt>
+require 'test/unit'
+require 'msgthr'
+
+class TestMsgthr < Test::Unit::TestCase
+  def test_msgthr
+    thr = Msgthr.new
+    thr.add('a', %w(c b), 'abc')
+    thr.add('b', %w(c), 'B')
+    thr.add('c', nil, 'c')
+    thr.add('D', nil, 'D')
+    thr.add('d', nil, 'd')
+    thr.thread!
+    rootset = thr.order! { |c| c.sort! { |a, b| a.mid <=> b.mid } }
+    assert_equal %w(D c d), rootset.map(&:mid)
+    assert_equal 'D', rootset[0].msg
+    assert_equal %w(b), rootset[1].children.map(&:mid)
+  end
+end