Add a garbage collector for note files

Now that we use hashes to identify notes, a garbage collector comes in
handy. We search for note files that aren't referenced anywhere. Such
files might come up if a note, that isn't connected with any other item,
is edited.

Huge parts of this code are very hackish due to our data structure
layout and the way our hash table implementation works.

Signed-off-by: Lukas Fleischer <calcurse@cryptocrack.de>

src/note.c

@@ -35,10 +35,17 @@
  */
 
 #include <unistd.h>
+#include <dirent.h>
 
 #include "calcurse.h"
 #include "sha1.h"
 
+struct note_gc_hash {
+  char *hash;
+  char buf[MAX_NOTESIZ + 1];
+  HTABLE_ENTRY (note_gc_hash);
+};
+
 /* Edit a note with an external editor. */
 void
 edit_note (char **note, char *editor)
@@ -120,3 +127,109 @@ note_read (char *buffer, FILE *fp)
   while (getc (fp) != ' ');
   buffer[MAX_NOTESIZ] = '\0';
 }
+
+static void
+note_gc_extract_key (struct note_gc_hash *data, char **key, int *len)
+{
+  *key = data->hash;
+  *len = strlen (data->hash);
+}
+
+static int
+note_gc_cmp (struct note_gc_hash *a, struct note_gc_hash *b)
+{
+  return strcmp (a->hash, b->hash);
+}
+
+/* Spot and unlink unused note files. */
+void
+note_gc (void)
+{
+  HTABLE_HEAD (htp, NOTE_GC_HSIZE, note_gc_hash) gc_htable =
+      HTABLE_INITIALIZER (&gc_htable);
+  struct note_gc_hash *hp;
+  DIR *dirp;
+  struct dirent *dp;
+  llist_item_t *i;
+  struct note_gc_hash tmph;
+  char notepath[BUFSIZ];
+
+  if (!(dirp = opendir (path_notes)))
+    return;
+
+  /* Insert all note file names into a hash table. */
+  HTABLE_GENERATE (htp, note_gc_hash, note_gc_extract_key, note_gc_cmp);
+  do
+    {
+      if ((dp = readdir (dirp)) && *(dp->d_name) != '.')
+        {
+          hp = mem_malloc (sizeof (struct note_gc_hash));
+
+          strncpy (hp->buf, dp->d_name, MAX_NOTESIZ + 1);
+          hp->hash = hp->buf;
+
+          HTABLE_INSERT (htp, &gc_htable, hp);
+        }
+    }
+  while (dp);
+
+  closedir (dirp);
+
+  /* Remove hashes that are actually in use. */
+  LLIST_TS_FOREACH (&alist_p, i)
+    {
+      struct apoint *apt = LLIST_GET_DATA (i);
+      if (apt->note)
+        {
+          tmph.hash = apt->note;
+          free (HTABLE_REMOVE (htp, &gc_htable, &tmph));
+        }
+    }
+
+  LLIST_FOREACH (&eventlist, i)
+    {
+      struct event *ev = LLIST_GET_DATA (i);
+      if (ev->note)
+        {
+          tmph.hash = ev->note;
+          free (HTABLE_REMOVE (htp, &gc_htable, &tmph));
+        }
+    }
+
+  LLIST_TS_FOREACH (&recur_alist_p, i)
+    {
+      struct recur_apoint *rapt = LLIST_GET_DATA (i);
+      if (rapt->note)
+        {
+          tmph.hash = rapt->note;
+          free (HTABLE_REMOVE (htp, &gc_htable, &tmph));
+        }
+    }
+
+  LLIST_FOREACH (&recur_elist, i)
+    {
+      struct recur_event *rev = LLIST_GET_DATA (i);
+      if (rev->note)
+        {
+          tmph.hash = rev->note;
+          free (HTABLE_REMOVE (htp, &gc_htable, &tmph));
+        }
+    }
+
+  LLIST_FOREACH (&todolist, i)
+    {
+      struct todo *todo = LLIST_GET_DATA (i);
+      if (todo->note)
+        {
+          tmph.hash = todo->note;
+          free (HTABLE_REMOVE (htp, &gc_htable, &tmph));
+        }
+    }
+
+  /* Unlink unused note files. */
+  HTABLE_FOREACH (hp, htp, &gc_htable)
+    {
+      snprintf (notepath, BUFSIZ, "%s%s", path_notes, hp->hash);
+      unlink (notepath);
+    }
+}