[elpa] externals/triples b961d0bf1b 2/7: Create `triples-backup' and some surrounding functionality.

[ELPA Syncer]

branch: externals/triples
commit b961d0bf1b32202397ff225353a5866a615c1085
Author: Andrew Hyatt <ahyatt@gmail.com>
Commit: Andrew Hyatt <ahyatt@gmail.com>

    Create `triples-backup' and some surrounding functionality.
    
    Currently this isn't a complete backup solution, more work will need to be 
done
    to make it possible for clients to flexibly use this for their purposes.
---
 CHANGELOG.org   |  1 +
 triples-test.el |  9 +++++++++
 triples.el      | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 56 insertions(+)

diff --git a/CHANGELOG.org b/CHANGELOG.org
index 9b90dbc936..1ad1c559c5 100644
--- a/CHANGELOG.org
+++ b/CHANGELOG.org
@@ -2,6 +2,7 @@ TITLE: Changelog for the triples module for GNU Emacs.
 
 * 0.2
 - Create a default database to encourage a shared triple database.  Add 
information on why this is an interesting idea in the README.
+- Add support for backups of databases via =triples-backup=.
 * 0.1.2
 - Bugfix release to remove backward compatibility with pre-Emacs 29 versions.  
 * 0.1.1
diff --git a/triples-test.el b/triples-test.el
index 44d92ab2da..7bc9587414 100644
--- a/triples-test.el
+++ b/triples-test.el
@@ -345,6 +345,15 @@ easily debug into it.")
                    (sqlite-select db "SELECT COUNT(*) FROM triples WHERE 
subject = ? AND predicate = 'base/type' AND object = 'marker'"
                                   (list (triples-standardize-val "foo")))))))
 
+(ert-deftest triples-backup-strategy-daily ()
+  (cl-letf (((symbol-function 'current-time)
+             (lambda ()
+               (encode-time (iso8601-parse "2023-01-15T12:00Z")))))
+    (should (triples-backup-strategy-daily (encode-time (iso8601-parse 
"2023-01-14T12:00Z"))))
+    (should (triples-backup-strategy-daily (encode-time (iso8601-parse 
"2022-01-01T12:00Z"))))
+    (should-not (triples-backup-strategy-daily (encode-time (iso8601-parse 
"2023-01-15T12:00Z"))))
+    (should-not (triples-backup-strategy-daily (encode-time (iso8601-parse 
"2023-02-01T12:00Z"))))))
+
 (ert-deftest triples-readme ()
   (triples-test-with-temp-db
    (triples-add-schema db 'person
diff --git a/triples.el b/triples.el
index 2e83223295..a91a579dd3 100644
--- a/triples.el
+++ b/triples.el
@@ -46,10 +46,24 @@ available. Builtin is available when the version is Emacs 
29 or
 greater, and emacsql is usable when the `emacsql' package is
 installed.")
 
+(defconst triples-sqlite-executable "sqlite3"
+  "If using emacs 29 builtin sqlite, this specifices the executable.
+It is invoked to make backups.")
+
 (defconst triples-default-database-filename (locate-user-emacs-file 
"triples.db")
   "The default filename triples database. If no database is
 specified, this file is used.")
 
+(defconst triples-backup-files-to-keep 3
+  "How many backups of database to keep.
+Backups are stored in the default location, or the location
+specified in `backup-directory-alist'")
+
+(defconst triples-backup-strategy 'triples-backup-strategy-daily
+  "Function that controls when backups are created.
+Each function is called when a change happens, with no arguments,
+and returns a non-nil value if a backup should be created.")
+
 (defun triples-connect (&optional file)
   "Connect to the database FILE and make sure it is populated.
 If FILE is nil, use `triples-default-database-filename'."
@@ -91,6 +105,38 @@ If FILE is nil, use `triples-default-database-filename'."
     ('builtin (sqlite-close db))
     ('emacsql (emacsql-close db))))
 
+(defun triples-backup (db filename)
+  "Perform a backup of DB, located at path FILENAME.
+This uses the same backup location and names as configured in
+variables such as `backup-directory-alist'. Due to the fact that
+the database is never opened as a buffer, normal backups will not
+work, therefore this function must be called instead.
+
+Th DB argument is currently unused, but may be used in the future
+if emacs's native sqlite gains a backup feature.
+
+This also will clear excess backup files, according to
+`triples-backup-files-to-keep'."
+  (call-process (pcase triples-sqlite-interface
+                  ('builtin triples-sqlite-executable)
+                  ('emacsql emacsql-sqlite-executable))
+                nil nil nil (expand-file-name filename)
+                (format ".backup '%s'" (expand-file-name
+                                        (car (find-backup-file-name
+                                              (expand-file-name filename))))))
+  (let ((backup-files (file-backup-file-names (expand-file-name filename))))
+    (cl-loop for backup-file in (cl-subseq
+                                 backup-files
+                                 (min triples-backup-files-to-keep
+                                      (length backup-files)))
+             do (delete-file backup-file))))
+
+(defun triples-backup-strategy-daily (last-update)
+  "Backup strategy to create a change daily at most.
+LAST-UPDATE is the time of the last update."
+  (>= (/ (time-convert (time-subtract (current-time) last-update) 'integer) 
86400)
+      1))
+
 (defun triples--decolon (sym)
   "Remove colon from SYM."
   (intern (string-replace ":" "" (format "%s" sym))))