implemented backup file mechanism

* The backup mechanism is supposed to guard against crashes of SciTECO and
  unexpected program terminations (e.g. power cycling, etc.)
* In a given interval (no matter whether busy or idlying on the prompt)
  SciTECO saves all modified buffers with the filename~ (like most other editors).
  As an optimization files are not backed up if they have been backed up
  previously to avoid pointless and possibly slow file system writes.
* While the backup mechanism exists outside of the usual undo-paradigm -
  backup file creating is not bound to character input and it makes no sense
  to restore the exact state of backup files - there are some interesting
  interactions:
  * When a buffer is dirtyfied or saved that was previously backed up, it must always
    be reset to the DIRTY state on rubout, so backups are eventually recreated.
  * When a buffer is dirtyfied first (was clean), the backup file must be
    removed on rubout as well - we don't expect backup files for clean buffers.
* There is currently no automatic way to restore backup files.
  This could potentially be done by opener.tes and session.tes in the future,
  although you couldn't currently always get meaningful user feedback
  (whether he wants to restore the file).
  Perhaps we should at least log a message when detecting backup files that
  are newer than the file that is being opened.

1 files changed, 94 insertions, 12 deletions

diff --git a/src/ring.c b/src/ring.c
index 0dbe911..e42ff14 100644
--- a/src/ring.c
+++ b/src/ring.c
@@ -21,6 +21,7 @@
 
 #include <glib.h>
 #include <glib/gprintf.h>
+#include <glib/gstdio.h>
 
 #include <Scintilla.h>
 
@@ -75,16 +76,21 @@ teco_buffer_undo_edit(teco_buffer_t *ctx)
 }
 
 /** @private @memberof teco_buffer_t */
+static inline gchar *
+teco_buffer_get_backup(teco_buffer_t *ctx)
+{
+	return g_strconcat(ctx->filename, "~", NULL);
+}
+
+/** @private @memberof teco_buffer_t */
 static gboolean
 teco_buffer_load(teco_buffer_t *ctx, const gchar *filename, GError **error)
 {
 	if (!teco_view_load(ctx->view, filename, TRUE, error))
 		return FALSE;
 
-#if 0		/* NOTE: currently buffer cannot be dirty */
-	undo__teco_interface_info_update_buffer(ctx);
-	teco_undo_gboolean(ctx->dirty) = FALSE;
-#endif
+	/* currently buffer cannot be dirty */
+	g_assert(ctx->state == TECO_BUFFER_CLEAN);
 
 	teco_buffer_set_filename(ctx, filename);
 	return TRUE;
@@ -110,7 +116,13 @@ teco_buffer_save(teco_buffer_t *ctx, const gchar *filename, GError **error)
 	 */
 	if (ctx == teco_ring_current && !teco_qreg_current)
 		undo__teco_interface_info_update_buffer(ctx);
-	teco_undo_gboolean(ctx->dirty) = FALSE;
+	if (ctx->state == TECO_BUFFER_DIRTY_BACKEDUP) {
+		g_autofree gchar *filename_backup = teco_buffer_get_backup(ctx);
+		g_unlink(filename_backup);
+		/* on rubout, we do not restore the backup file */
+		ctx->state = TECO_BUFFER_DIRTY;
+	}
+	teco_undo_guint(ctx->state) = TECO_BUFFER_CLEAN;
 
 	/*
 	 * FIXME: necessary also if the filename was not specified but the file
@@ -129,6 +141,11 @@ teco_buffer_save(teco_buffer_t *ctx, const gchar *filename, GError **error)
 static inline void
 teco_buffer_free(teco_buffer_t *ctx)
 {
+	if (ctx->state == TECO_BUFFER_DIRTY_BACKEDUP) {
+		g_autofree gchar *filename_backup = teco_buffer_get_backup(ctx);
+		g_unlink(filename_backup);
+	}
+
 	teco_view_free(ctx->view);
 	g_free(ctx->filename);
 	g_free(ctx);
@@ -222,15 +239,40 @@ teco_ring_find_by_id(teco_int_t id)
 	return NULL;
 }
 
+static void
+teco_ring_undirtify(void)
+{
+	if (teco_ring_current->state == TECO_BUFFER_DIRTY_BACKEDUP) {
+		g_autofree gchar *filename_backup = teco_buffer_get_backup(teco_ring_current);
+		g_unlink(filename_backup);
+	}
+
+	teco_ring_current->state = TECO_BUFFER_CLEAN;
+	teco_interface_info_update(teco_ring_current);
+}
+
+TECO_DEFINE_UNDO_CALL(teco_ring_undirtify);
+
 void
 teco_ring_dirtify(void)
 {
-	if (teco_qreg_current || teco_ring_current->dirty)
+	if (teco_qreg_current)
 		return;
 
-	undo__teco_interface_info_update_buffer(teco_ring_current);
-	teco_undo_gboolean(teco_ring_current->dirty) = TRUE;
-	teco_interface_info_update(teco_ring_current);
+	teco_buffer_state_t old_state = teco_ring_current->state;
+	teco_ring_current->state = TECO_BUFFER_DIRTY;
+	switch (old_state) {
+	case TECO_BUFFER_CLEAN:
+		teco_interface_info_update(teco_ring_current);
+		undo__teco_ring_undirtify();
+		break;
+	case TECO_BUFFER_DIRTY:
+		break;
+	case TECO_BUFFER_DIRTY_BACKEDUP:
+		/* set to TECO_BUFFER_DIRTY on rubout */
+		teco_undo_guint(teco_ring_current->state);
+		break;
+	}
 }
 
 /** Get id of first dirty buffer, or otherwise 0 */
@@ -241,7 +283,7 @@ teco_ring_get_first_dirty(void)
 
 	for (teco_tailq_entry_t *cur = teco_ring_head.first; cur != NULL; cur = cur->next) {
 		teco_buffer_t *buffer = (teco_buffer_t *)cur;
-		if (buffer->dirty)
+		if (buffer->state > TECO_BUFFER_CLEAN)
 			return id;
 		id++;
 	}
@@ -255,13 +297,53 @@ teco_ring_save_all_dirty_buffers(GError **error)
 	for (teco_tailq_entry_t *cur = teco_ring_head.first; cur != NULL; cur = cur->next) {
 		teco_buffer_t *buffer = (teco_buffer_t *)cur;
 		/* NOTE: Will fail for a dirty unnamed file */
-		if (buffer->dirty && !teco_buffer_save(buffer, NULL, error))
+		if (buffer->state > TECO_BUFFER_CLEAN &&
+		    !teco_buffer_save(buffer, NULL, error))
 			return FALSE;
 	}
 
 	return TRUE;
 }
 
+/**
+ * Backup interval in seconds or 0 if disabled.
+ * It's not currently enforced in batch mode.
+ */
+guint teco_ring_backup_interval = 5*60;
+
+/**
+ * Back up all dirty buffers.
+ *
+ * Should be called by the interface every teco_ring_backup_interval seconds.
+ * This does not generate or expect undo tokens, so it can be called
+ * even when idlying.
+ */
+void
+teco_ring_backup(void)
+{
+	g_assert(teco_ring_backup_interval > 0);
+
+	for (teco_tailq_entry_t *cur = teco_ring_head.first; cur != NULL; cur = cur->next) {
+		teco_buffer_t *buffer = (teco_buffer_t *)cur;
+		/*
+		 * Dirty unnamed buffers cannot be backed up.
+		 * Already backed-up buffers don't have to be written again.
+		 * FIXME: Perhaps they should be under ~/UNNAMED~?
+		 */
+		if (buffer->state != TECO_BUFFER_DIRTY || !buffer->filename)
+			continue;
+
+		g_autofree gchar *filename_backup = teco_buffer_get_backup(buffer);
+		/*
+		 * FIXME: Errors are silently ignored.
+		 * Should we log warnings instead?
+		 */
+		teco_view_save(buffer->view, filename_backup, NULL);
+
+		buffer->state = TECO_BUFFER_DIRTY_BACKEDUP;
+	}
+}
+
 gboolean
 teco_ring_edit_by_name(const gchar *filename, GError **error)
 {
@@ -719,7 +801,7 @@ teco_state_ecommand_close(teco_machine_main_t *ctx, GError **error)
 	if (teco_machine_main_eval_colon(ctx) > 0) {
 		if (!teco_buffer_save(buffer, NULL, error))
 			return;
-	} else if (!force && buffer->dirty) {
+	} else if (!force && buffer->state > TECO_BUFFER_CLEAN) {
 		g_set_error(error, TECO_ERROR, TECO_ERROR_FAILED,
 		            "Buffer \"%s\" is dirty",
 			    buffer->filename ? : "(Unnamed)");