Add pre-save and post-save hooks

This adds support for hooks which are executed before/after saving
calcurse data. Hooks can be placed under hooks/pre-save and
hooks/post-save in the data directory and need to be executable.

Potential use cases include:

* Automatically commit any changes to the data files using a VCS.
* Automatically sync with some sever component on data file changes.

Signed-off-by: Lukas Fleischer <lfleischer@calcurse.org>

src/hooks.c

@@ -0,0 +1,63 @@
+/*
+ * Calcurse - text-based organizer
+ *
+ * Copyright (c) 2004-2016 calcurse Development Team <misc@calcurse.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ *      - Redistributions of source code must retain the above
+ *        copyright notice, this list of conditions and the
+ *        following disclaimer.
+ *
+ *      - Redistributions in binary form must reproduce the above
+ *        copyright notice, this list of conditions and the
+ *        following disclaimer in the documentation and/or other
+ *        materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * Send your feedback or comments to : misc@calcurse.org
+ * Calcurse home page : http://calcurse.org
+ *
+ */
+
+#include <stddef.h>
+
+#include "calcurse.h"
+
+int run_hook(const char *name)
+{
+	char *hook_path;
+	char const *arg[2];
+	int pid, ret = -127;
+
+	asprintf(&hook_path, "%s/%s", path_hooks, name);
+	arg[0] = hook_path;
+	arg[1] = NULL;
+
+	if (!io_file_exists(hook_path))
+		return 0;
+
+	wins_prepare_external();
+	if ((pid = shell_exec(NULL, NULL, *arg, arg))) {
+		ret = child_wait(NULL, NULL, pid);
+		if (ret)
+			press_any_key();
+	}
+	wins_unprepare_external();
+
+	return ret;
+}