Add $history_remove_dups option to remove dups from history ring.

When set, duplicate entries will be removed from the history ring when
a new entry is added.  The duplicate removal rearranges the history
ring such that created empty slots are right after the "last" position
in the ring, preserving the most history.

Rewrite the next/prev functions to take into account that blank slots can
now be in the middle of the array.

1 files changed, 106 insertions, 15 deletions

diff --git a/history.c b/history.c
index e72e9fb2..054fc54b 100644
--- a/history.c
+++ b/history.c
@@ -23,6 +23,44 @@
 #include "mutt.h"
 #include "history.h"
 
+/* This history ring grows from 0..HistSize, with last marking the
+ * where new entries go:
+ *         0        the oldest entry in the ring
+ *         1        entry
+ *         ...
+ *         x-1      most recently entered text
+ *  last-> x        NULL  (this will be overwritten next)
+ *         x+1      NULL
+ *         ...
+ *         HistSize NULL
+ *
+ * Once the array fills up, it is used as a ring.  last points where a new
+ * entry will go.  Older entries are "up", and wrap around:
+ *         0        entry
+ *         1        entry
+ *         ...
+ *         y-1      most recently entered text
+ *  last-> y        entry (this will be overwritten next)
+ *         y+1      the oldest entry in the ring
+ *         ...
+ *         HistSize entry
+ *
+ * When $history_remove_dups is set, duplicate entries are scanned and removed
+ * each time a new entry is added.  In order to preserve the history ring size,
+ * entries 0..last are compacted up.  Entries last+1..HistSize are
+ * compacted down:
+ *         0        entry
+ *         1        entry
+ *         ...
+ *         z-1      most recently entered text
+ *  last-> z        entry (this will be overwritten next)
+ *         z+1      NULL
+ *         z+2      NULL
+ *         ...
+ *                  the oldest entry in the ring
+ *                  next oldest entry
+ *         HistSize entry
+ */
 struct history
 {
   char **hist;
@@ -206,6 +244,51 @@ static void save_history (history_class_t hclass, const char *s)
   }
 }
 
+/* When removing dups, we want the created "blanks" to be right below the
+ * resulting h->last position.  See the comment section above 'struct history'.
+ */
+static void remove_history_dups (history_class_t hclass, const char *s)
+{
+  int source, dest, old_last;
+  struct history *h = GET_HISTORY(hclass);
+
+  if (!HistSize || !h)
+    return; /* disabled */
+
+  /* Remove dups from 0..last-1 compacting up. */
+  source = dest = 0;
+  while (source < h->last)
+  {
+    if (!mutt_strcmp (h->hist[source], s))
+      FREE (&h->hist[source++]);
+    else
+      h->hist[dest++] = h->hist[source++];
+  }
+
+  /* Move 'last' entry up. */
+  h->hist[dest] = h->hist[source];
+  old_last = h->last;
+  h->last = dest;
+
+  /* Fill in moved entries with NULL */
+  while (source > h->last)
+    h->hist[source--] = NULL;
+
+  /* Remove dups from last+1 .. HistSize compacting down. */
+  source = dest = HistSize;
+  while (source > old_last)
+  {
+    if (!mutt_strcmp (h->hist[source], s))
+      FREE (&h->hist[source--]);
+    else
+      h->hist[dest--] = h->hist[source--];
+  }
+
+  /* Fill in moved entries with NULL */
+  while (dest > old_last)
+    h->hist[dest--] = NULL;
+}
+
 void mutt_init_history(void)
 {
   history_class_t hclass;
@@ -238,6 +321,8 @@ void mutt_history_add (history_class_t hclass, const char *s, int save)
      */
     if (*s != ' ' && (!h->hist[prev] || mutt_strcmp (h->hist[prev], s) != 0))
     {
+      if (option (OPTHISTREMOVEDUPS))
+        remove_history_dups (hclass, s);
       if (save && SaveHist)
         save_history (hclass, s);
       mutt_str_replace (&h->hist[h->last++], s);
@@ -256,13 +341,17 @@ char *mutt_history_next (history_class_t hclass)
   if (!HistSize || !h)
     return (""); /* disabled */
 
-  next = h->cur + 1;
-  if (next > HistSize)
-    next = 0;
-  if (h->hist[next] || (next == h->last))
-    h->cur = next;
-  else
-    h->cur = 0;
+  next = h->cur;
+  do
+  {
+    next++;
+    if (next > HistSize)
+      next = 0;
+    if (next == h->last)
+      break;
+  } while (h->hist[next] == NULL);
+
+  h->cur = next;
   return (h->hist[h->cur] ? h->hist[h->cur] : "");
 }
 
@@ -274,15 +363,17 @@ char *mutt_history_prev (history_class_t hclass)
   if (!HistSize || !h)
     return (""); /* disabled */
 
-  prev = h->cur - 1;
-  if (prev < 0)
+  prev = h->cur;
+  do
   {
-    prev = HistSize;
-    while ((prev > 0) && (prev != h->last) && (h->hist[prev] == NULL))
-      prev--;
-  }
-  if (h->hist[prev] || (prev == h->last))
-    h->cur = prev;
+    prev--;
+    if (prev < 0)
+      prev = HistSize;
+    if (prev == h->last)
+      break;
+  } while (h->hist[prev] == NULL);
+
+  h->cur = prev;
   return (h->hist[h->cur] ? h->hist[h->cur] : "");
 }