lei: Add command for viewing a thread

piem-lei-query presents a message-based overview.  In many cases the
caller will want to use that search result as a seed for finding the
associated thread.  Add a command that construct thread for a given
message.

The threading algorithm is based on public-inbox's.  Some details may
have been lost in translation, but I haven't spotted any differences
yet when doing side-by-side comparisons of output from
piem-lei-query-thread and public-inbox's web interface.  And testing
with a few ~100-message threads, the performance seems to be okay.

The appearance also follows public-inbox's, which I like.

Message-Id: <20210605211402.20304-7-kyle@kyleam.com>

2 files changed, 75 insertions, 0 deletions

diff --git a/tests/piem-lei-tests.el b/tests/piem-lei-tests.el
new file mode 100644
index 0000000..e20c62f
--- /dev/null
+++ b/tests/piem-lei-tests.el
@@ -0,0 +1,74 @@
+;;; piem-lei-tests.el --- tests for piem-lei  -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2021  all contributors <piem@inbox.kyleam.com>
+
+;; Author: Kyle Meyer <kyle@kyleam.com>
+
+;; 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 3 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, see <https://www.gnu.org/licenses/>.
+
+;;; Code:
+
+(require 'ert)
+(require 'piem-lei)
+
+(ert-deftest piem-lei-query--add-child ()
+  (should-error
+   (piem-lei-query--add-child
+    (make-piem-lei-msg :mid "m1")
+    (make-piem-lei-msg :mid "m1")))
+  (let ((m1 (make-piem-lei-msg :mid "m1"))
+        (m2 (make-piem-lei-msg :mid "m2")))
+    (piem-lei-query--add-child m1 m2)
+    (should (equal (piem-lei-msg-parent m2) m1))
+    (should (equal (piem-lei-msg-children m1) (list m2))))
+  (let ((m1 (make-piem-lei-msg :mid "m1"))
+        (m2 (make-piem-lei-msg :mid "m2"))
+        (m3 (make-piem-lei-msg :mid "m3"))
+        (m4 (make-piem-lei-msg :mid "m4")))
+    (piem-lei-query--add-child m1 m2)
+    (piem-lei-query--add-child m1 m4)
+    (piem-lei-query--add-child m3 m2)
+    (should (equal (piem-lei-msg-parent m2) m3))
+    (should (equal (piem-lei-msg-children m1) (list m4)))
+    (should (equal (piem-lei-msg-children m3) (list m2)))))
+
+(ert-deftest piem-lei-query--has-descendant ()
+  (let ((m1 (make-piem-lei-msg :mid "m1"))
+        (m2 (make-piem-lei-msg :mid "m2")))
+    (should-not
+     (piem-lei-query--has-descendant m1 m2))
+    (should-not
+     (piem-lei-query--has-descendant m2 m1)))
+  (let ((m1 (make-piem-lei-msg :mid "m1")))
+    (should (piem-lei-query--has-descendant m1 m1)))
+  (let ((m1 (make-piem-lei-msg :mid "m1"))
+        (m2 (make-piem-lei-msg :mid "m2")))
+    (piem-lei-query--add-child m1 m2)
+    (should (piem-lei-query--has-descendant m1 m2))
+    (should-not
+     (piem-lei-query--has-descendant m2 m1)))
+  (let ((m1 (make-piem-lei-msg :mid "m1"))
+        (m2 (make-piem-lei-msg :mid "m2"))
+        (m3 (make-piem-lei-msg :mid "m3")))
+    (piem-lei-query--add-child m1 m2)
+    (piem-lei-query--add-child m2 m3)
+    (should (piem-lei-query--has-descendant m1 m2))
+    (should (piem-lei-query--has-descendant m1 m3))
+    (should (piem-lei-query--has-descendant m2 m3))
+    (should-not (piem-lei-query--has-descendant m2 m1))
+    (should-not (piem-lei-query--has-descendant m3 m2))
+    (should-not (piem-lei-query--has-descendant m3 m1))))
+
+(provide 'piem-lei-tests)
+;;; piem-lei-tests.el ends here
diff --git a/tests/piem-tests.el b/tests/piem-tests.el
index 5f01a5e..91beb9a 100644
--- a/tests/piem-tests.el
+++ b/tests/piem-tests.el
@@ -21,6 +21,7 @@
 
 (require 'ert)
 (require 'piem)
+(require 'piem-lei-tests)
 (require 'piem-rmail-tests)
 
 (ert-deftest piem-message-link-re ()